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    "title": "A Treatise on Civil Engineering,  by D.H. Mahan, 1873",
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    "ocrText": "Google\nThis is a digital copy of a book that was preserved for generations on library shelves before it was carefully scanned by Google as part of a project\nto make the world's books discoverable online.\nIt has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject\nto copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books\nare our gateways to the past, representing a wealth of history, culture and knowledge that's often difficult to discover.\nMarks, notations and other marginalia present in the original volume will appear in this file - a reminder of this book's long journey from the\npublisher to a library and finally to you.\nUsage guidelines\nGoogle is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the\npublic and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing this resource, we have taken steps to\nprevent abuse by commercial parties, including placing technical restrictions on automated querying.\nWe also ask that you:\n+ Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for\npersonal, non-commercial purposes.\n+ Refrain from automated querying Do not send automated queries of any sort to Google's system: If you are conducting research on machine\ntranslation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the\nuse of public domain materials for these purposes and may be able to help.\n+ Maintain attribution The Google \"watermark\" you see on each file is essential for informing people about this project and helping them find\nadditional materials through Google Book Search. Please do not remove it.\n+ Keep it legal Whatever your use, remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just\nbecause we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other\ncountries. Whether a book is still in copyright varies from country to country, and we can't offer guidance on whether any specific use of\nany specific book is allowed. Please do not assume that a book's appearance in Google Book Search means it can be used in any manner\nanywhere in the world. Copyright infringement liability can be quite severe.\nAbout Google Book Search\nGoogle's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers\ndiscover the world's books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web\nathttp://books.google.com/\nGODFREY LOWELL CABOT SCIENCE LIBRARY\nof the Harvard College Library\nThis book is\nFRAGILE\nand circulates only with permission.\nPlease handle with care\nand consult a staff member\nbefore photocopying.\nThanks for your help in preserving\nHarvard's library collections.\nDigitized by Goog\nDigitized by Google\nDigitized by Google\nbbh\nint\nDigitized by Google\nDigitized by Google\nDigitized by Google\nDigitized by Google\nEAST RIVER BRIDGE.See page 379.\nDigitized by Google\nDigitized by Google\nA TREATISE\nON\nCIVIL ENGINEERING.\nBY\nD. H. MAHAN, LL.D.,\nLATE PROFESSOR OF CIVIL ENGINEERING AT WEST POINT, M. Y.\nREVISED AND EDITED, WITH ADDITIONS AND NEW PLATES,\nBy DE VOLSON WOOD,\nPROFESSOR OF MATHEMATICS AND MECHANICS IN STEVENS' INSTITUTE OF TECHNOLOGY\n(FORMERLY PROFESSOR OF CIVIL ENGINEERING IN THE UNIVERSITY OF MICHI-\nGAN); AUTHOR OF A TREATISE ON THE RESISTANCE OF MATERIALS;\nTREATISE ON BRIDGES AND ROOFS, ETC.\nNEW YORK:\nJOHN WILEY & SON,\n15 ASTOR PLACE,\n1873.\nDigitized by Google\nEng. 455. \"3.3\nJUN 20 1917\nTRANSFERRED TO\nПАПУАЛЬ COLLEGE LILRARY\n3.10\nENTERED, according to Act of Congress, in the year 1878, by\nJOHN WILEY,\nIn the Office of the Librarian of Congress, at Washington, D. C.\nPOOLE & MACLAUCHLAN,\nPRINTERS AND BOOKBINDERS,\n805-213 East 12th St.,\nNEW YORK.\nDigitized by Google\nPREFACE.\nTHE works of the late Professor Mahan are too well and\ntoo favorably known to need special comment from the\npresent Editor.\nThe first edition of his work on Civil Engineering ap-\npeared when engineering as a learned profession was scarcely\nrecognized in this country, and when but a very limited\namount of instruction upon the science which pertains to it\nwas given in our schools. Descriptions of processes and of\nworks executed were the essential means of giving the infor-\nmation which was needed by the engineer. This determined\nthe essential characteristic of his work, which is descriptive.\nMore recently, numerous schools have been established,\nwhich are intended to give thorough instruction in the science\nof engineering, and in which the courses of instruction are\nlargely filled with mathematical analysis. But analysis\nalone, however important, can never take the place of descrip-\ntive matter. Every successful structure serves as a guide in\nthe construction of all future similar works. Thus the expe-\nrience of one may become the wisdom of many.\nBefore his untimely death, Professor Mahan had prepared\nDigitized by Google\niv\nPREFACE.\na thorough revision of this work, and about one-third of it\nhad passed through the press when the present Editor took\ncharge of it.\nI have endeavored to do full justice to the original author\nby preserving the essential character of the work, and retain-\ning nearly all the matter which he had prepared; still, I have\nomitted a few paragraphs which were deemed non-essential,\nand condensed others. I have also added considerable new\nmatter, which is scattered throughout that portion of the\nwork which I have had in charge. I trust that my labors\nhave added to the value of the work.\nDE V. W.\nHOBOKEN, Aug., 1873.\nDigitized by Google\nCONTENTS.\nCHAPTER I.\nGENERAL PROPERTIES OF BUILDING MATERIALS.\nARTICLE.\nPAGE.\n1-2. Introductory Remark\n3\nI. STONE.\nB-16. Silicious Stones\n4\n17-20. Argillaceous Stones\n8\n21-29. Calcareous Stones\n9\n30-36. Gypsum-Durability of Stone\n13\n37-38. Effects of Heat-Hardness of Stone\n15\nII. LIME.\n38-41. Classification\n18\n42-49. Hydraulic Limes and Cements\n19\n50-55. Physical Characteristics of Hydraulic Limestones\n23\n56-60. Calcination of Limestone\n25\nIII. LIME-KILNS.\n61-76. Descriptions of Lime-kilns\n27\n77. Calcination of the Stone\n36\n78-95. Reducing Calcined Stone to Powder\n37\n96-103. Artificial Hydraulic Limes and Cements\n41\n104-114. Puzzolanas\n43\nIV. MORTAR.\n115-120. Classification-Qualities\n46\n121-127. Sand, Properties of\n47\n128-134. Hydraulic Mortar\n48\n135-138. Mortars exposed to Weather\n50\n139-142. Manipulations of Mortar-Machines for\n51\n143-150. Setting and Durability of Mortars\n57\n151-152. Theory of the Hardening of Mortars\n58\nV. CONCRETE BETON.\n153-157. Concrete-Manufacture and Uses.\n59\n158-166. Béton-Manufacture and Uses\n60\nDigitized by Google\n1.\nCONTENTS.\nARTICLE.\nPAGE.\n167. Ransome's Artificial Stone\n63\n168-182. Béton Aggloméré\n64\n183-186. Adherence of Mortar.\n73\nVI. MASTICS.\n187-198. Composition of-Bituminous Mastic.\n74\nVII. BRICKS.\n199-211. Common Brick-Fire-Brick-Tile\n77\nVIII. WOOD.\n212-214. Timber-Parts of the Trunk of a Tree\n79\n215-217. Felling Trees-Time and Treatment\n80\n218-225. Methods of Seasoning Timber\n81\n226. Wet and Dry Rot\n83\n227-239. Preservation of Timber\n83\n240-242. Durability of Timber\n86\n243-248. Forest Trees of the United States which are used for Timber. 86\nIX. METALS.\n249-263. Cast Iron, Qualities of\n89\n264-277. Wrought Iron, Qualities of\n92\n278-289. Durability of Iron\n94\n290-298. Preservatives of Iron\n95\n299. Corrugated Iron\n97\n300. Steel\n98\n301. Copper\n98\n302. Zinc\n99\n303. Tin\n99\n304. Lead\n99\nX. PAINT AND VARNISHES.\n805-308. Composition and Uses of Paints\n100\n809-313. Composition and Uses of Varnishes\n100\n314. Zoöfagous Paint\n103\n315. Methods of Preserving Exposed Surfaces of Stone\n103\nCHAPTER II.\nEXPERIMENTAL RESEARCHES ON THE STRENGTH OF MATERIALS.\n316-326. Physical Properties of Bodies\n106\n327-335. Strength of Stone\n109\n336-342. Strength of Mortars and Cements\n115\n343-347. Strength of Timber\n119\n348-365. Strength of Cast Iron\n131\n366-367. Effect of Impact upon Cast-Iron Bars\n144\n368-374. Strength of Wrought Iron\n147\nDigitized by\nGoogle\nCONTENTS.\nvii\nARTICLE,\nPAGE.\n375. Strength of Steel\n163\n376. Strength of Copper\n166\n377. Effects of Temperature on the Tensile Strength\n167\n378. Strength of Cast Tin, of Cast Lead, hard Gun-metal\n167\n879. Coefficients of Linear Expansion due to Heat.\n167\n380. Adhesion of Iron Spikes to Timber\n170\nCHAPTER III.\nMASONRY.\nI. Classification Masonry\n174\nII. Cut-stone Masonry\n174\nIII. Rubble-stone Masonry\n183\nIV. Brick Masonry\n183\nV. FOUNDATIONS OF STRUCTURES ON LAND.\n417-418. Definition-Importance.\n190\n420. Classification of Soils\n190\n421-423. Foundations on Rock\n191\n424-425. Foundations on Sand\n192\n426-430. Foundations on Compressible Soils\n192\n431-440. Foundations on Piles\n196\n441-443. Sand for Bed of Foundation\n203\nVI. FOUNDATIONS OF STRUCTURES IN WATER.\n444-449. Coffer-Work-Caisson\n208\n452-455. Foundations on Heavy Blocks of Loose Stone\n217\n456. Pneumatic Processes\n220\n457-458. Pneumatic Piles\n220\n459. Pneumatic Caissons. ST. LOUIS BRIDGE\n229\nEAST RIVER BRIDGE.\n234\nVII. CONSTRUCTION OF MASONRY.\n461-466. Foundation Courses-Construction of\n236\n467. Classification of Structures of Masonry\n238\n4d8. Walls of Enclosures\n238\n469. Walls for Vertical Supports\n239\n470. Areas.\n239\n471-479. Retaining Walls. FORM AND DIMENSIONS\n239\n480-490. Modes of Strengthening Retaining Walls-Counterforts-Re-\nlieving Arches\n244\n491-493. Lintel-Plate-Bande.\n247\n493-503. Arches-Definitions-Annular Arches-Dome\n248\n504-513. Details of the Masonry of Arches\n252\n514-516. Angle of Rupture\n257\n517-519. Remarks upon the Strengthening of Abutments\n258\n520. Precautions against Settling\n258\n521-523. Pointing of Masonry\n259\n524-526. Repairs of Masonry\n260\n527. Effects of Temperature on Masonry\n261\nDigitized by\nGoogle\nviii\nCONTENTS.\nARTICLE.\nPAGE\nCHAPTER IV.\nFRAMING.\n528-539. General Principles\n263\n540. Solid-built Beams\n265\n541-547. Joints of Different Kinds\n267\n548. Open-built Beams\n271\n549-550. Framing for Intermediate Supports\n272\n551. Experiments on the Strength of Frames\n274\n552-553. Wooden Arches\n277\nCHAPTER V.\nBRIDGES.\n554. Classification of Bridges\n279\nII. STONE BRIDGES.\n555-556. Location of Stone Bridges\n279\n557-561. Survey-Management of the Water-way\n280\n562. Number of Bays\n282\n563-567. Classification of Arches-Definitions\n282\n568. Oblique Arches\n285\n569. Arched Bridges\n289\n570-576. Centring for Arches\n289\n577. Style of Architecture\n294\n578-587. Construction of the Foundations\n294\n588-590. Superstructure\n302\n591-592. Approaches-Water-wings\n305\n593-594. Enlargement of the Water-way-General Remarks\n306\n595-596. Table of Bridges,\n308\nIII. WOODEN BRIDGES.\n597-604. Timber Foundations\n310\n605-606. Definitions of Terms\n314\n607. Long's Truss\n315\n608. Town's Truss\n316\n609. Howe's Truss.\n317\n610. Schuylkill Bridge\n317\n611. Burr's Truss\n318\n612. Pratt's Truss\n320\n613. McCallum's Truss\n320\n614. Canal Bridge\n820\n615. Wooden Arches\n321\n616-621. General Remarks\n322\n622. Architecture of Wooden Bridges\n324\n623. Table of Wooden Bridges\n324\nIV. CAST-IRON BRIDGES.\n624-627. General Remarks\n325\n628-630. Cast-iron Arches\n827\nDigitized by\nGoogle\nCONTENTS.\nix\nARTICLE.\nPAGE.\n631. Open Cast-iron Beams\n831\n632. Effects of Temperature on Stone and Cast-iron Bridges\n331\nV. IRON TRUSSED BRIDGES.\n633. Whipple's Trapezoidal Truss\n332\n634. Modification of Whipple's Truss\n334\n635. Linville's Bridge.\n334\n636. Whipple's Arched Truss\n337\n637. Bollman's Truss\n337\n638. Fink's Truss.\n338\n639. Post's Truss\n339\n640. Alleghany River Bridge\n344\n641. St. Louis and Illinois Bridge\n344\n642. Kuilenberg Bridge\n347\nVI. TUBULAR BRIDGES.\n643. Tubular Frames of Wrought Iron\n347\n644. Experiments with a Model Tube\n349\n645. Britannia Tubular Bridge\n350\n646. Formula for Computing the Strength of Wrought-iron Tubes 354\n647. Victoria Bridge\n354\nVII. SUSPENSION BRIDGES.\n648-653. General Remarks\n857\n654-655. Anchorage\n359\n656-658. Position and Construction of the Cables\n360\n659. Vertical Suspension Bars\n361\n660-662. Construction of Wire Cables\n361\n663-664. Construction of the Piers and Abutments\n362\n665. Main Chains, &c\n363\n666. Attachment of Suspending Chains\n364\n667. Roadway\n364\n668. Vibrations\n365\n669. Means of Preserving the Chains\n366\n670. Proofs of Suspension Bridges\n366\n671. Durability\n367\n672. Suspension Bridge near Berwick, England\n868\n673. Menai Bridge\n368\n674. Fribourg Bridge\n370\n675. Hungerford and Lambeth Bridge\n371\n676. Monongahela Wire Bridge\n373\n677. Niagara Railroad Suspension Bridge\n374\n678. East River Suspension Bridge.\n379\nVIII. MOVABLE BRIDGES.\n679. Definitions\n880\n680. Draw Bridges\n881\n681. Turning Bridges\n384\n682. Swing Bridge at Providence, Rhode Island\n885\n683. Rolling Bridges\n391\n684. Boat Bridges\n391\nDigitized by Google\nCONTENTS.\nARTICLE.\nPAGE.\nIX. AQUEDUCT BRIDGES.\n685. General Principles\n391\n686. Canal Aqueducts\n392\n687. Trunk of Cast Iron or Timber\n392\nCHAPTER VI.\nROOFS.\n688. Definition\n893\n689. Remark\n393\n690. General Data\n393\n691. Weight of Snow\n394\n692. The Force of Wind\n394\n693. Ordinary Roof Truss.\n394\n695. An Iron Roof Truss\n396\n696. Roof of a Gas-House\n397\n697. An Example of Trussing\n398\n698. Depot Roof Truss\n399\n699. Roof of a Rolling Mill\n400\n700. Truss of the State Capitol, Vermont\n400\n701. Example of Roof at the University of Michigan\n402\nCHAPTER VII.\nROADS.\n702. Establishing a Common Road\n403\n703. Reconnaissance\n403\n704-708. Surveying and Locating Common Roads\n405\n709. Gradients\n407\n710-718. Final Location\n408\n714-720. Earthwork-Excavations and Embankments\n411\n721. Drainage\n416\n722. Road-coverings\n419\n723. Pavements-Wood and Stone\n420\n724. McAdam and Telford Roads\n423\n726. Gravel Roads\n425\n728. Asphaltic Roads\n427\n729. Repairing Common Roads\n428\n780. Cross Dimensions of Common Roads\n429\n731. Plank Roads\n430\nII. RAILWAYS.\n732. Definition\n430\n788-736. Rails\n430\n787. Supports\n433\n738. Ballast\n434\n739. Temporary Railways\n434\n740. Gauge\n435\n742. Curves\n436\n743. Sidings, etc\n436\n746-747. Gradients\n438\n748-753. Tunnels\n439\nDigitized by\nGoogle\nCONTENTS.\nxi\nARTICLE.\nPAGE.\n754-768. Experiments of Baron Von Weber on the Stability of the\nPermanent Way\n442\n755. Stability of Rails to Lateral Pressure\n42\n756. Stability of the Permanent Way\n43\n757. Stability of the Permanent Way to Resist Horizontal Dis-\nP acement\n444\n759. Stability of the Rails on the Sleepers\n448\n762-763. Experiments on the Resisting Power of Railway Spikes\n451\n764. Experiments on the Effect of Bed-plates.\n454\n765. Force Required to Draw Spikes\n456\n766. Total Resistance due to Spikes and Friction\n458\n768. Weber's Deductions from Tabulated Results.\n461\n769. Sleepers\n462\n770. Rail Joints\n464\n771-776. Steel Rails\n464\nCHAPTER VIII.\nCANALS.\n777-780. General Remarks\n467\n781. Cross Section\n470.\n782-783. Supply of Water\n471\n784-786. Locks-Use of, eto\n472\n787-793. Feeders and Reservoirs\n474\n794. Lifts of Locks\n479\n795. Levels\n480\n796-815. Locks-Principles of Construction\n482\n816-817. Accessory Works-Culverts\n488\n818-819. Aqueducts-Canal Bridges\n489\n820-822. Waste-weir-Guard Lock\n490\n823. General Dimensions of Canals\n491\n824. Locomotion on Canals\n493\nCHAPTER IX.\nRIVERS.\n825-829. Natural Features of Rivers\n494\n830-831. River Improvements\n495.\n832-833. Means of Protecting the Banks-Innndations\n496\n834-841. Elbows-Bars\n497\n842-849. Slack-water Navigation\n501\nCHAPTER X.\nSEA-COAST IMPROVEMENTS.\n850-854. Classification-Action of Tides.\n504\n855-856. Roadsteads\n506\n857-863. Harbors\n508\n864-866. Quays\n511\n867. Dikes.\n512\n868. Groins\n513\n869. Sea-walls\n513\nDigitized by\nGoogle\nDigitized by Google\nELEMENTARY COURSE\nOF\nCIVIL ENGINEERING.\nCHAPTER I.\nBUILDING MATERIALS.\nL STONE. II. LIME. III. LIMEKILNS. IV. MORTARS.\nV. CONCRETES AND BETONS. VI. MASTICS. VII. BRICK.\nVIII. WooD. IX. METALS. X. PAINTS, VARNISHES,\nETC.\nSUMMARY.\nBUILDING-MATERIALS, their properties, application, and classification\n(Arts. 1-2).\nI.\nSTONE.\nSILICIOUS STONES-Sienite, Porphyry, Green-Stone, Granite and Gneiss,\nMica Slate, Buhr or Mill Stone, Horn-Stone, Steatite or Soap-Stone,\nTalcose Slate, and Sand-Stone (Arts. 3-16).\nARGILLACEOUS STONEa-Roofing-Slate, Graywacke Slate, and Hornblende\nSlate (Arta. 17-20).\nCALCAREOUS STONES -Common Limestone. MARBLES-Statuary Marble,\nConglomerate Marble. Birdseye Marble, Lumachella Marble, Verd\nAntique Marble, Veined, Golden, Italian, Irish, etc., Marbles. Localities\nwhere the Limestones and Marbles are found and quarried for use (Arts.\n21-29), Gypsum (Art. 30).\nDurability of Stone (Arts. 31-36).\nEffects of heat on Stone (Art. 87).\nHardness of Stone (Art. 38).\nDigitized by Google\n2\nCIVIL ENGINEERING.\nII.\nLIME.\nCLASSIFICATION OF LIME-Common lime, Hydraulic lime, Hydraulic\ncement, Limestones that yield Hydraulic limes and Hydraulic ce-\nments, Analyses of these stones (Arts. 39-49). Physical characters and\ntests of Hydraulic Limestones (Arts. 50-55). Calcination of Lime-\nstones (Arts. 56-60).\nIII.\nLIMEKILNS.\nCLASSIFICATION AND KINDS OF (Arts. 61-77). Methods of reducing cal-\ncined stone to powder; by slaking by grinding (Arts. 78-95). Arti-\nficial hydraulic limes and cements (Arts. (96-103). Puzzolana, etc.\n(Arts. 104-114).\nIV.\nMORTAR.\nCLASSIFICATION OF (Arts. 115-116). Uses of (Art. 117). Qualities of,\non what dependent (Arts. 117-120). Classification of Sand (Arts. 121-\n127). Composition of Hydraulic mortar (Arts. 128-134). Mortar ex-\nposed to weather (Arts. 135-138). Manipulation of Mortar and Concrete\n(Arts. 139-142). Setting and durability of Mortar (Arts. 143-150).\nTheory of Mortars (151-152).\nV.\nCONCRETES AND BETONS.\nCONCRETE OF COMMON LIME, MANUFACTURE AND USES (Arts. 154-157).\nBeton, its composition, manufacture and uses (Arts. 158-161). Beton\nCoignet (Arts. 162-166). Ransome's artificial stone (Art. 167). Beton\naggloméré (Arta 168-182). Adhesion of Mortar to other materials\n(Arts. 183-186).\nVI.\nMASTICS.\nMASTICS, COMPOSITION OF (Art. 187). Bituminous Mastic, Composition\nand Manufacture of (Arts. 188-198).\nVII.\nBRICK.\nPROPERTIES, USES AND MANUFACTURE OF (Arts. 199-209). Fire-Brick\n(Art. 210). Tiles (Art. 211).\nDigitized by Google\nBUILDING MATERIALS.\n3\nVIII.\nWOOD.\nTIMBER, KINDS OF (Art. 212). Parts and properties of the trunks of\nTrees (Arts. 213-214). Felling of Trees (Arts. 215-216). Girdling and\nbarking trunks of Trees (Art. 217). Methods of seasoning Timber\n(Arts. 224-225). Wet and dry rot (Art. 226). Preservation of Timber\n(Arta. 227-242). Forest Trees of the United States (Arta. 243-248).\nIX.\nMETALS.\nCAST IRON, VARIETIES OF (Arts. 249-263). Wrought Iron, Varieties of\n(Arts. 264-277). Durability of Iron (Arts. 278-289). Preservatives of\nIron (Arts. 290-298). Corrugated Iron (Art. 299). Steel (Art. 300).\nCOPPER and its alloys (Art 301).\nZINC and its alloys (Art. 302).\nTIN (Art. 303).\nLEAD (Art. 304).\nX.\nPAINTS AND VARNISHES.\nPAINTS, COMPOSITION, USES AND DURABILITY OF (Arts. 305-308). Var-\nnishes, Composition and Uses of (Arts. 309-311). Varnish for Zincked\nIron (Arts. 312-313). Zoofagous Paint (Art 314). Methods of preserv-\ning exposed surfaces of Stone (Art. 315).\n1. A KNOWLEDGE of the properties of building materials\nis one of the most important branches of Civil Engineering.\nAn engineer, to be enabled to make a judicious selection\nof materials, and to apply them so that the ends of sound\neconomy and skilful workmanship shall be equally sub-\nserved, must know :-\n1st. Their ordinary durability under the various circum-\nstances in which they are employed, and the means of in-\ncreasing it when desirable.\n2d. Their capacity to sustain, without injury to their\nphysical qualities, permanent strains, whether exerted to\ncrush them, tear them asunder, or to break them trans-\nversely.\nDigitized by Google\n4\nCIVIL ENGINEERING.\n3d. Their resistance to rupture and wear, from percussion\nand attrition.\n4th. Finally, the time and expense necessary to convert\nthem to the uses for which they may be required.\n2. The materials in general use for civil constructions\nmay be arranged under the three following heads:-\n1st. Those which constitute the more solid components of\nstructures, as Stone, Brick, Wood, and the Metals.\n2d. The cements in general, as Mortar, Mastics, Glue,\netc., which are used to unite the more solid parts.\n3d. The various mixtures and chemical preparations, as\nsolutions of Salts, Paints, Bituminous Substances, etc.,\nemployed to coat the more solid parts, and protect them\nfrom the chemical and mechanical action of atmospheric\nchanges, and other causes of destructibility.\nI.\nSTONE.\n3. The term Stone, or Rock, is applied to any aggregation\nof several mineral substances.\nStones, for the convenience of description, may be arranged\nunder three general heads-the silicious, the argillaceous,\nand the calcareous.\n4. SILICIOUS STONES. The stones arranged under\nthis head receive their appellation from silex, the principal\nconstituent of the minerals which compose them. They are\nalso frequently designated, either according to the mineral\nfound most abundantly in them, or from the appearance of\nthe stone, as feldspathic, quartzose, arenaceous, etc.\n5. The silicious stones generally do not effervesce with\nacids, and emit sparks when struck with a steel. They pos-\nsess, in a high degree, the properties of strength, hardness,\nand durability; and, although presenting great diversity in\nthe degree of these properties, as well as in their structure,\nthey furnish an extensive variety of the best stone for the\nvarious purposes of the engineer and architect.\n6. Sienite, Porphyry, and Green-stone, from the abun-\nDigitized by Google\nBUILDING MATERIALS.\nБ\ndance of feldspar which they contain, are often designated\nas feldspathic rocks. For durability, strength, and hard-\nness, they may be placed in the first rank of silicious\nstones.\n7. Sienite consists of a granular aggregation of feldspar,\nhornblende, and quartz. It furnishes one of the most valua-\nble building stones, particularly for structures which require\ngreat strength, or are exposed to any very active causes of\ndestructibility, as sea walls, lighthouses, and fortifications.\nSienite occurs in extensive beds, and may be obtained, from\nthe localities where it is quarried, in blocks of any requisite\nsize. It does not yield easily to the chisel, owing to its great\nhardness, and when coarse-grained it cannot be wrought to a\nsmooth surface. Like all stones in which feldspar is found,\nthe durability of sienite depends essentially upon the com-\nposition of this mineral, which, owing to the potash it con-\ntains, sometimes decomposes very rapidly when exposed to\nthe weather. The durability of feldspathic rocks, however,\nis very variable, even where their composition is the same;\nno pains should therefore be spared to ascertain this prop-\nerty in stone taken from new quarries, before using it for\nimportant public works.\n8. Porphyry. This stone is usually composed of com-\npact feldspar, having crystals of the same, and sometimes\nthose of other minerals, scattered through the mass. Por-\nphyry furnishes stones of various colors and texture; the\nusual color being reddish, approaching to purple, from which\nthe stone takes its name. One of the most beautiful varie-\nties is a brecciated porphyry, consisting of angular fragments\nof the stone united by a cement of compact feldspar.\nPorphyry, from its rareness and extreme hardness, is seldom\napplied to any other than ornamental purposes. The best\nknown localities of sienite and porphyry in the United\nStates are in the neighborhood of Boston.\n9. Green-stone. This stone is a mixture of hornblende\nwith common and compact feldspar, presenting sometimes a\ngranular though usually a compact texture. Its ordinary\ncolor, when dry, is some shade of brown; but, when wet, it\nbecomes greenish, from which it takes its name. Green-\nstone is very hard, and one of the most durable rocks; but,\noccurring in small and irregular blocks, its uses as a build-\ning stone are very restricted. When walls of this stone are\nbuilt with very white mortar, they present a picturesque ap-\npearance, and it is on that account well adapted to rural\narchitecture. Green-stone might also be used as a material\nDigitized by\nGoogle\n6\nCIVIL ENGINEERING.\nfor road-making; large quantities of it are annually taken\nfrom the principal locality of this rock in the United\nStates, SO well known as the Palisades, on the Hudson, for\nconstructing wharves, as it is found to withstand well the\naction of salt water.\n10. Granite and Gneiss. The constituents of these two\nstones are the saine, being a granular aggregation of quartz,\nfeldspar, and mica, in variable proportions. They differ only\nin their structure-gneiss being a stratified rock, the ingre-\ndients of which occur frequently in a more or less laminated\nstate. Gneiss, although less valuable than granite, owing to\nthe effect of its structure on the size of the blocks which it\nyields, and from its not splitting as smoothly as granite\nacross its beds of stratification, furnishes a building stone\nsuitable for most architectural purposes. It is also a good\nflagging material, when it can be obtained in thin slabs.\nGranite varies greatly in quality according to its texture\nand the relative proportion of its constituents. When the\nquartz is in excess, it renders the stone hard and brittle, and\nvery difficult to be worked with the chisel. An excess of\nmica usually makes the stone friable. An excess of feldspar\ngives the stone a white hue, and makes it freer under the\nchisel. The best granites are those with a fine grain, in\nwhich the constituents seem uniformly disseminated through\nthe mass. The color of granite is usually some shade of\ngray; when it varies from this, it is owing to the color of the\nfeldspar. One of its varieties, known as Oriental granite,\nhas a fine reddish hue, and is chiefly used for ornamental\npurposes. Granite is sometimes mistaken for sienite, when\nit contains but little mica.\nThe quality of granite is affected by the foreign minerals\nwhich it may contain; hornblende is said to render it tough,\nand schorl makes it quite brittle. The protoxide and sul-\nphurets of iron are the most injurious in their effects on\ngranite; the former by conversion into a peroxide, and the\nlatter, by decomposing, destroying the structure of the stone,\nand causing it to break up and disintegrate.\nGranite, gneiss, and sienite, differ so little in their essen-\ntial qualities, as a building material, that they may be used\nindifferently for all structures of a solid and durable charac-\nter. Thev are extensively quarried in most of the New\nEngland States, in New York, and in some of the other\nStates intersected by the great range of primitive rocks,\nwhere the quarries lie contiguous to tidewater.\n11, Mica Slate. The constituents of this stone are quartz\nDigitized by\nGoogle\nBUILDING MATERIALS.\n7\nand mica, the latter predominating. It is principally used\nas a Aagging stone, and as a fire stone, or lining for fur-\nnaces.\n12. Buhr or Mill stone. This is a very hard, durable\nstone, presenting a peculiar, honeycomb appearance. It\nmakes a good building material for common purposes, and\nis also suitable for road coverings.\n13. Horn-stone. This is a highly silicious and very hard\nstone. It resembles flint in its structure, and takes its name\nfrom its translucent, horn-like appearance. It furnishes a\nvery good road material.\n14. Steatite, or Soap-stone. This stone is a partially\nindurated talc. It is a very soft stone, not suitable for ordi-\nnary building purposes. It furnishes a good fire-stone, and\nis used for the lining of fireplaces.\n15. Talcose Slate. This stone resembles mica slate, be-\ning an aggregation of quartz and talc. It is applied to the\nsame purposes as mica slate.\n16. Sand-stone. This stone consists of grains of silicious\nsand, arising from the disintegration of silicious rocks,\nwhich are united by some natural cement, generally of an\nargillaceous or a silicious character.\nThe strength, hardness, and durability of sand-stone vary\nbetween very wide limits. Some varieties being little in-\nferior to good granite, as a building stone, others being very\nsoft, friable, and disintegrating rapidly when exposed to the\nweather. The least durable sand-stones are those which con-\ntain the most argillaceous matter; those of a feldspathic char-\nacter are also found not to withstand well the action of the\nweather.\nSand-stone is used very extensively as a building stone, for\nflagging, for road materials, and some of its varieties furnish\nan excellent fire-stone. Most of the varieties of sand-stone\nyield readily under the chisel and saw, and split evenly, and,\nfrom these properties, have received from workmen the name\nof free-stone. The colors of sand-stone present also a variety\nof shades, principally of gray, brown, and red.\nThe formations of sand-stone in the United States are very\nextensive, and a number of quarries are worked. in New\nEngland, New York, and the Middle States. These forma-\ntions, and the character of the stone obtained from them, are\nminutely described in the Geological Reports of these\nStates, which have been published within the last few\nyears.\nMost of the stone used for the public buildings in Wash-\nDigitized by\nGoogle\n8\nCIVIL ENGINEERING.\nington is a sand-stone obtained from quarries on Acquia\nCreek and the Rappahannock. Much of this stone is felds-\npathic, possesses but little strength, and disintegrates rapidly.\nThe red sand-stones which are used in our large cities are\neither from quarries in a formation extending from the\nHudson to North Carolina, or from a separate deposit in the\nValley of the Connecticut. The most durable and hard\nportions of these formations occur in the neighborhood of\ntrap dikes. The fine flagging-stone used in our cities is\nmostly obtained either from the Connecticut quarries, or\nfrom others near the Hudson, in the Catskill group of\nmountains. Many quarries, which yield an excellent build-\ning stone, are worked in the extensive formations along the\nAppalachian range, which extends through the interior,\nthrough New York and Virginia, and the intermediate\nStates.\n17. Argillaceous Stones. The stones arranged under\nthis head are mostly composed of clay, in a more or less\nindurated state, and presenting a laminated structure. They\nvary greatly in strength, and are generally not durable,\ndecomposing in some cases very rapidly, from changes in\nthe metallic sulphurets and salts found in most of them.\nThe uses of this class of stones are restricted to roofing and\nflagging.\n18. Roofing Slate. This well-known stone is obtained\nfrom a hard, indurated clay, the surfaces of the lamina\nhaving a natural polish. The best kinds split into thin,\nuniform, light slabs; are free from sulphurets of iron\ngive a clear ringing sound when struck; and absorb but\nlittle water. Much of the roofing slate quarried in the\nUnited States is of a very inferior quality, and becomes\nrotten, or decomposes, after a few years' exposure. The\ndurability of the best European slate is about one hundred\nyears; and it is stated that the material obtained from some\nof the quarries worked in the United States is not apparently\ninferior to the best foreign slate brought into our markets.\nSeveral quarries of roofing slate are worked in the New\nEngland States, New York and Pennsylvania.\n19. Graywacke Slate. The composition of this stone\nis mostly indurated clay. It has a more earthy appearabce\nthan argillaceous slate, and is generally distinctly arenace-\nous. Its colors are usually dark gray, or red. It is quarried\nprincipally for flagging-stone.\n20. Hornblende Slate. This stone, known also as green\nstone slate, properly belongs to the silicious class. It con-\nDigitized by Google\nBUILDING MATERIALS.\n9\nsists mostly of hornblende having a laminated structure. It\nis chiefly quarried for flagging-stone.\n21. Calcareous Stones. Lime is the principal constitu-\nent of this class, the carbonates of which, known as lime-\nstone and marble, furnish a large amount of ordinary build-\ning stone, most of the ornamental stones, and the chief in-\ngredient in the composition of the cements and mortars used\nin stone and brick work. Limestone effervesces copiously\nwith acids; its texture is destroyed by a strong heat, which\nalso drives off its carbonic acid and water, converting it into\nquick lime. By absorbing water, quick-lime is converted into\na hydrate, or what is known as slaked lime; considerable\nheat is evolved during this chemical change, and the stone\nincreases in bulk, and gradually crumbles down into a fine\npowder.\nThe limestones present great diversity in their physical\nproperties. Some of them seem as durable as the best sili-\ncious stones, and are but little inferior to them in strength\nand hardness; others decompose rapidly on exposure to the\nweather; and some kinds-are so soft, that when first quarried,\nthey can be scratched with the nail, and broken between the\nfingers.\nThe limestones are generally impure carbonates; and\nwe are indebted to these impurities for some of the\nmost beautiful, as well as the most valuable materials used\nfor constructions. Those which are colored by metallic\noxides, or by the presence of other minerals, furnish the\nlarge number of colored and variegated marbles; while those\nwhich contain a certain proportion of clay, or of magnesia,\nyield, on calcination, those cements which, from their posses-\nsing the property of hardening under water, have received the\nvarious appellations of hydraulic lime, water lime, Roman\ncement, etc.\nLimestone is divided into two principal classes, granular\nlimestone and compact limestone. Each of these furnishes\nboth the marbles and ordinary building stone. The varieties\nnot susceptible of receiving a polish are sometimes called\ncommon limestone.\nThe granular limestones are generally superior to the\ncompact for building purposes. Those which have the\nfinest grain are the best, both for marbles and ordinary\nbuilding stone. The coarse-grained varieties are frequently\nfriable, and disintegrate rapidly when exposed to the weather.\nAll the varieties, both of the compact and granular, work\nfreely under the chisel and grit-saw, and may be obtained\nDigitized by Google\n10\nCIVIL ENGINEERING.\nin blocks of any suitable dimensions for the heaviest struc-\ntures.\nThe durability of limestone is very materially affected\nby the foreign minerals it may contain; the presence of\nclay injures the stone, particularly when, as sometimes hap-\npens, it runs through the będ in very minute veins blocks\nof stone having this imperfection soon separate along these\nveins on exposure to moisture. The protoxide, the proto-car-\nbonate, and the sulphuret of iron, are also very destructive in\ntheir effects; frequently causing, by their chemical changes,\nrapid disintegration.\nAmong the varieties of impure carbonates of lime, the\nmagnesian limestones, called dolomites, merit to be particu-\nlarly noticed. They are regarded in Europe as a superior\nbuilding material ; those being considered the best which\nare most crystalline, and are composed of nearly equal pro-\nportions of the carbonates of lime and magnesia. Some of\nthe quarries of this stone, which have been opened in New\nYork and Massachusetts, have given a different result; the\nstone obtained from them being, in some cases, extremely\nfriable.\n22. Marbles.-The term marble is now applied exclu-\nsively to any limestones which will receive a polish. Owing\nto the cost of preparing marble, it is mostly restricted in its\nuses to ornamental purposes. The marbles present great\nvariety, both in color and appearance, and have generally\nreceived some appropriate name descriptive of these acci-\ndents.\n23. Statuary Marble is of the purest white, finest grain,\nand free from all foreign minerals. It receives that delicate\npolish, without glare, which admirably adapts it to the pur-\nposes of the sculptor, for whose use it is mostly reserved.\n24. Conglomerate Marble. This consists of two varie-\nties; the one termed pudding stone, which is composed of\nrounded pebbles embedded in compact limestone; the other\ntermed breccia, consisting of angular fragments united in a\nsimilar manner. The colors of these marbles are generally\nvariegated, forming a very handsome ornamental material.\n25. Bird's-eye Marble. The name of this stone is de-\nscriptive of its appearance, which arises from the cross sec-\ntions of a peculiar fossil (fucoides demissus) contained in\nthe mass, made in sawing or splitting it.\n26. Lumachella Marble. This is obtained from a lime-\nstone having shells embedded in it, and takes its name from\nthis circumstance.\nDigitized by Google\nBUILDING MATERIALS.\n11\n27. Verd Antique. This is a rare and costly variety, of\na beautiful green color, caused by veins and blotches of ser-\npentine diffused through the limestone.\n28. The terms veined, golden, Italian, Irish, etc., given to\nthe marbles found in our markets are significant of their ap-\npearance, or of the localities from which they are procured.\n29. Limestone is 80 extensively diffused throughout the\nUnited States, and quarried, either for building stone or\nto furnish lime, in so many localities, that it would be im-\npracticable to enumerate all within any moderate compass.\nOne of the most remarkable formations of this stone extends,\nin an uninterrupted bed, from Canada, through the States of\nVermont, Mass., Conn., New York, New Jersey, Penn., and\nVirg., and in all probability much farther south.\nMarbles are quarried in various localities in the United\nStates. Among the most noted are the quarries in Berk-\nshire Co., Mass., which furnish both pure and variegated\nmarbles; those on the Potomac, from which the columns of\nconglomerate marbles were obtained that are seen in the\ninterior of the Capitol at Washington; several in New York,\nwhich furnish white, the bird's-eye, and other variegated\nkinds; and some in Conn., which, among other varieties,\nfurnish a verd antique of handsome quality.\nLinestone is burned, either for building or agricultural\npurposes, in almost every locality where deposits of the\nstone occur. Thomaston, in Maine, has supplied for some\nyears most of the markets on the sea-board with a material\nwhich is considered as a superior article for ordinary build-\ning purposes. One of the greatest additions to the building\nresources of our country was made in the discovery of the\nhydraulic or water limestones of New York. The prepara-\ntion of this material, so indispensable for all hydraulic works\nand heavy structures of stone, is carried on extensively at\nRondout, on the Delaware and Hudson canal, in Madison Co.,\nand is sent to every part of the United States, being in\ngreat demand for all the public works carried on under the\nsuperintendence of our civil and military engineers. A not\nless valuable addition to our building materials has been\nmade by Prof. W. B. Rogers, who, a few years since, direct-\ned the attention of engineers to the dolomites, for their good\nhydraulic properties. From experiments made by Vicat,\nin France, who first there observed the saine properties in\nthe dolomite, and from those in our country, it appears highly\nprobable that the magnesian limestones, containing a cer-\ntain proportion of magnesia, will be found fully equal to\nDigitized by Google\n12\nCIVIL ENGINEERING.\nthe argillaceous, from which hydraulic lime has hitherto\nbeen solely obtained.\nBoth of these limestones belong to very extensive forma-\ntions. The hydraulic limestones of New York occur in a\ndeposit called the Water-lime Group, in the Geological Survey\nof New York corresponding to formation VI. of Prof. H.\nB. Rogers' arrangement of the rocks of Penn. This forma-\ntion is co-extensive with the Helderberg Range as it crosses\nNew York; it is exposed in many of the valleys of Penn.\nand Vir., west of the Great Valley. It may be sought for\njust below or not far beneath the Oriskany sand-stones of\nthe New York Survey, which correspond to formation VII.\nof Rogers. This sand-stone is easily recognized, being of a\nyellowish white color, granular texture, with large cavities\nleft by decayed shells. The limestone is usually an earthy\ndrab-colored rock, sometimes a greenish blue, which does not\nslake after being burned.\nThe hydraulic magnesian limestones belong to the for-\nmations II. and VI. of Rogers; the first of these is the same\nas the Black River or Mohawk limestone of the New York\nSurvey. It is the oldest fossiliferous limestone in the United\nStates, and occurs throughout the whole bed, associated with\nthe slates which occupy formation III. of Rogers, and are\ncalled the Hudson River Group in the New York Survey.\nThis extensive bed lies in the great Appalachian Valley,\nknown as the Valley of Lake Champlain, Valley of the Hud-\nson, as far as the Highlands, Cumberland Valley, Valley of\nVirginia, and Valley of East Tennessee. The same stone is\nfound in the deposits of some of the western valleys of the\nmountain region of Penn. and Virginia.\nThus far no deposits of hydraulic limestones have been\nfound on the Pacific Coast.\nThe importance of hydraulic lime to the security of struc-\ntures exposed to constant moisture renders a knowledge of\nthe geological positions of those limestones from which it\ncan be obtained an object of great interest. From the results\nof the various geological surveys made in the United States\nand in Europe, limestone, possessing hydraulic properties\nwhen calcined, may be looked for among those beds which\nare found in connection with the shales, or other argillaceous\ndeposits. The celebrated Roman or Parker's cement, of\nEngland, which, from its prompt induration in water, has\nbecome an important article of commerce, is manufactured\nfrom nodules of a concretionary argillaceous limestone, called\nseptaria, from being traversed by veins of sparry carbonate\nDigitized by Google\nBUILDING MATERIALS.\n13\nof lime. Nodules of this character are found in Mass., and\nin some other States; and it is probable they would yield, if\nsuitably calcined and ground, an article in nowise inferior to\nthat imported.\n30. GYPSUM, or PLASTER of PARIS. This stone is\na sulphate of lime, and has received its name from the exten-\nsive use made of it at Paris, and in its neighborhood, where\nit is quarried and sent to all parts of the world; being of a\nsuperior quality, owing, it is stated, to a certain portion of\ncarbonate of lime which the stone contains. Gypsum is a\nvery soft stone, and is not used as a building stone. Its chief\nutility is in furnishing a beautiful material for the ornamental\ncasts and mouldings in the interior of edifices. For this pur-\npose it is prepared by calcining, or, as the workmen term it,\nboiling the stone, until it is deprived of its water of crystal-\nlization. In this state it is made into a thin paste, and poured\ninto moulds to form the cast, in which it hardens very\npromptly. Calcined plaster of Paris is also used as a cement\nfor stone; but it is eminently unfit for this purpose for\nwhen exposed, in any situation, to moisture, it absorbs it with\navidity, swells, cracks, and exfoliates rapidly.\nGypsum is found in various localities in the United States.\nLarge quantities of it are quarried in New York, both for\nbuilding and agricultural purposes.\n31. DURABILITY OF STONE. The most important\nproperties of stone, as a building material, are its durability\nunder the ordinary circumstances of exposure to weather ;\nits capacity to sustain, without change, high degrees of tem-\nperature ; and its resistance to the destructive action of fresh\nand salt water.\nThe wear of stone from ordinary exposure is very variable,\ndepending, not only upon the texture and constituent elements\nof the stone, but also upon the locality and position it may OC-\ncupy in a structure, with respect to the prevailing driving\nrains. The chemist and geologist have not, thus far, laid down\nany infallible rules to guide the engineer in the selection of a\nmaterial that may be pronounced durable for the ordinary\nperiod allotted to the works of man. In truth the subject ad-\nmits of only general indications ; for stones having the same\ntexture and chemical composition, from causes not fully as-\ncertained, are found to possess very different degrees of dura-\ntion. This has been particularly noted in feldspathic rocks.\nAs a general rule, those stones which are fine-grained, absorb\nDigitized by Google\n14\nCIVIL ENGINEERING.\nleast water, and are of greatest specific gravity, are also most\ndurable under ordinary exposures. The weight of a stone,\nhowever, may arise from a large proportion of iron in thestate\nof a protoxide, a circumstance generally unfavorable to its\ndurability. Besides the various chemical combinations of iron,\npotash and clay, when found in considerable quantities, both\nin the primary and sedimentary silicious rocks, greatly affect\ntheir durability. The potash contained in feldspar dissolves,\nand, carrying off a considerable proportion of the silica, leaves\nnothing but aluminous matter behind. The clay, on the other\nhand, absorbs water, becomes soft, and causes the stone to\ncrumble to pieces. Iron in the form of protoxide, in some cases\nonly, discolors the stone by its conversion into a peroxide.-\nThis discoloration, while it greatly diminishes the value of\nsome stones, as in white marble, in others is not disagreeable\nto the eye, producing often a mottled appearance in buildings\nwhich adds to the picturesque effect.\n32. Frost, or rather the alternate actions of freezing and\nthawing, is the most destructive agent of Nature with which\nthe engineer has to contend. Its effects vary with the texture\nof stones ; those of a fissile nature usually splitting, while the\nmore porous kinds disintegrate, or exfoliate at the surface.-\nWhen stone from a new quarry is to be tried, the best indication\nof its resistance to frost may be obtained from an examination\nof any rocks of the same kind, within its vicinity, which are\nknown to have been exposed for a long period. Submitting\nthe stone fresh from the quarry to the direct action of freez-\ning would seem to be the most certain test, were the stone\ndestroyed by the expansive action of the frost ; but\nbesides the uncertainty of this test, it is known that some\nstones, which, when first quarried, are much affected by frost,\nsplitting under its action, become impervious to it after they\nhave lost the moisture of the quarry, as they do not re-absorb\nnear so large an amount as they bring from the quarry.\n33. M. Brard, a French chemist, has given a process for\nascertaining the effects of frost on stone, which has met with\nthe approval of many French architects and engineers of\nstanding, as it corresponds with their experience. M. Brard\ndirects that a small cubical block, about two inches on the\nedge, shall be carefully sawed from the stone to be tested. A\ncold saturated solution of sulphate of soda is prepared, placed\nover a fire, and brought to the boiling point. The stone, sus-\npended from a string, is immersed in the boiling liquid, and\nkept there during thirty minutes; it is then carefully with-\ndrawn; the liquid is decanted free from sediment into a flat\nDigitized by Google\nBUILDING MATERIALS.\n15\nvessel, and the stone is suspended over it in a cool cellar. An\nefflorescence of the salt soon makes its appearance on the\nstone, when it must be again dipped into the liquid. This\nshould be done once or more frequently during the day, and\nthe process be continued in this way for about a week. The\nearthy sediment, found at the end of this period in the vessel,\nis weighed, and its quantity will give an indication of the like\neffect of frost. This process, with the official statement of a\ncommission of engineers and architects, by whom it was test-\ned, is minutely detailed in vol. 38, Annales de Chimie et de\nPhysique, and the results are such as to commend it to the\nattention of engineers in submitting new stones to trial.\n34. From more recent experiments by Dr. Owen it was\nfound that the results obtained by exposing the more porous\nstones to the alternate action of freezing and thawing during\na portion of a winter were very different from those resulting\nfrom Brard's method, owing to the action of the salts being\nchemical as well as mechanical.\n35. By the absorption of water, stones become softer and\nmore friable. The materials for road coverings should be\nselected from those stones which absorb least water, and are\nalso hard and not brittle. Granite, and its varieties, lime-\nstone, and common sand-stone, do not make good road mate-\nrials of broken stone. All the hornblende rocks, porphyry,\ncompact feldspar, and the quartzose rock associated with\ngraywacke, furnish good, durable road coverings. The fine-\ngrained granites which contain but a small proportion of mica,\nthe fine-grained silicious sand-stones which are free from clay,\nand carbonate of lime, form a durable material when used in\nblocks for paving. Mica slate, talcose slate, hornblende slate,\nsome varieties of gneiss, some varieties of sand-stone of a\nslaty structure, and graywacke slate, yield excellent materials\nfor flag-stone.\n36. The influence of locality on the durability of stone is\nvery marked. Stone is observed to wear more rapidly in\ncities than in the country and the stone in those parts of edi-\nfices exposed to the prevailing rains and winds, soonest exhib-\nits signs of decay. The disintegration of the stratified stones\nplaced in a wall is mainly effected by the position which the\nstrata or quarry bed receives, with respect to the exposed sur-\nface; proceeding faster when the faces of the strata are ex-\nposed, than in the contrary position.\n37. EFFECTS OF HEAT.-Stones which resist a high\ndegree of heat without fusing are used for lining furnaces,\nDigitized by Google\n16\nCIVIL ENGINEERING.\nand are termed fire-stones. A good fire-stone should not only\nbe infusible, but also not liable to crack or exfoliate from\nheat. Stones that contain lime, or magnesia, except in the\nform of silicates, are usually unsuitable for fire-stones. Some\nporous silicious limestones, as well as some gypsous silicious\nrocks, resist moderate degrees of heat. Stones that contain\nmuch potash are very fusible under high temperatures, run-\nning into a glassy substance. Quartz and mica, in various\ncombinations, furnish a good fire-stone; as, for example, finely\ngranular quartz with thin layers of mica, mica slate of the\nsame structure, and some kinds of gneiss which contain a\nlarge proportion of arenaceous quartz. Several varieties of\nsand-stone make a good lining for furnaces. They are usual-\nly those varieties which are free from feldspar, somewhat\nporous, and are uncrystallized in the mass. Talcose slate like-\nwise furnishes a good fire-stone.\n38. RESISTANCE TO ATTRITION.-Hardness is an\nessential quality in stone exposed to wear from the attrition\nof hard bodies. Stones selected for paving, flagging, and\nsteps for stairs, should be hard, and of a grain sufficiently\ncoarse not to admit of becoming very smooth under the action\nto which they are submitted. As great hardness adds to the\ndifficulty of working stone with the chisel, and to the cost of\nthe prepared material, builders prefer the softer or free-stones,\nsuch as the limestones and sand-stones, for most building pur-\nposes. The following are some of the results, on this point,\nobtained from experiment:\nTable showing the result of experiments made under the di-\nrection of Mr. Walker, on the wear of different stones in\nthe tramway on the Commercial Road, London, from\n27th March, 1830, to 24th August, 1831, being a period of\nseventeen months. Transactions of Civil Engineers, vol. 1.\nName of stone.\nSup. area\nLoss of\nin feet.\nOriginal weight.\nweight by\nLoss per\nRelative\nsup. foot.\nlosses.\nwear.\ncwt.\nqra.\nlbs.\nGuernsey\n4.734\n7\n1\n12.75\n4.50\n0.951\n1.000\nHerme\n5.250\n7\n3 24.25\n5.50\n1.048\n1.102\nBudle\n6.336\n9\n0 15.75\n7.75\n1.223\n1,286\nPeterhead (blue)\n3.484\n4\n1\n7.50\n6.25\n1.795\n1.887\nHeytor\n4.813\n6\n0 15.25\n8.25\n1.915\n2.014\nAberdeen (red)\n5.375\n7\n2 11.50\n11.50\n2.139\n2.249\nDartmoor\n4.500\n6\n2 25.00\n12.50\n2.778\n2.921\nAberdeen (blue)\n4.823\n6\n2 16.00\n14.75\n3.058\n3.216\nDigitized by Google\nBUILDING MATERIALS.\n17\nThe Commercial Road stoneway consists of two parallel lines\nof rectangular tramstones, 18 inches wide by 12 inches deep,\nand jointed to each other endwise, for the wheels to travel on,\nwith a common street pavement between for the horses.\nThe following table gives the résults of some experiments\non the wear of a fine-grained sand-stone pavement, by M.\nCoriolis, during eight years, upon the paved road from Paris\nto Toulouse, the carriage over which is about 500 tons daily,\npublished in the Annales des Ponts et Chausées, for March\nand April, 1834:\nVolume of water absorbed by the\nWeight of a\ndry stone after one day's im-\nMean annual\ncubic foot\nmersion, compared with that of\nwear.\nthe stone.\n158lbs.\nNeglected as insensible.\n0.1023 inch.\n154 \"\n\"\n0.1063 \"\n156 \"\n\"\n0.1299 \"\n150 \"\n1 in volume.\n0.2126 \"\n148 \"\nA\n\"\n0.2677 \"\nM. Coriolis remarks, that the weight of water absorbed af-\nfords one of the best indications of the durability of the fine-\ngrained sand-stones used in France for pavements. An\nequally good test of the relative durability of stones of the\nsame kind, M. Coriolis states, is the more or less clearness of\nsound given out by striking the stone with a hammer.\nThe following results are taken from an article by Mr.\nJames Frost, Cw. Engineer, inserted in the Journal of the\nFranklin Institute for Oct. 1835, on the resistance of various\nsubstances to abrasion. The substances were abraded against\na piece of white statuary marble, which was taken as a stand-\nard, represented by 100, by means of fine emery and sand.\nThe relative resistance was calculated from the weight lost by\neach substance during the operation.\nComparative Resistance to Abrasion.\nAberdeen granite\n980\nHard Yorkshire paving stone\n827\nItalian black marble\n260\nKilkenny black marble\n110\nStatuary Marble\n100\nOld Portland stone\n79\nRoman Cement stone\n69\nFine-grained Newcastle grindstone\n53\nStock brick\n84\nCoarse-grained Newcastle grindstone\n14\nBath stone\n12\n2\nDigitized by Google\n18\nCIVIL ENGINEERING.\nII.\nLIME.\n38. CLASSIFICATION OF LIME.-Considered as a\nbuilding material, lime is now usually divided into three prin-\ncipal classes: Common or Air lime, Hydraulic lime, and Hy-\ndraulic, or Water cement.\n39. Common, or air lime, is so called because the paste\nmade from it with water will harden only in the air.\n40. Hydraulic lime and hydraulic cement both take their\nname from hardening under water. The former differs from\nthe latter in two essential points. It slakes thoroughly, like\ncommon lime, when deprived of its carbonic acid, and it does\nnot harden promptly under water. Hydraulic cement, on the\ncontrary, does not slake, and usually hardens very soon.\n4L Our nomenclature, with regard to these substances, is\nstill quite defective for scientific arrangement. For the lime-\nstones which yield hydraulic lime when completely calcined,\nalso give an hydraulic cement when deprived of a portion only\nof their carbonic acid; and other limestones yield, on calci-\nnation, a result which can neither be termed lime nor hydraulic\ncement, owing to its slaking very imperfectly, and not retain-\ning the hardness which it quickly takes when first placed un-\nder water.\nM. Vicat, whose able researches into the properties of lime\nand mortars are so well known, has proposed to apply the term\ncement limestones (calcaires à ciment) to those stones which,\nwhen completely calcined, yield hydraulic cement, and which\nunder no degree of calcination will give hydraulic lime. For\nthe limestones which yield hydraulic lime when completely\ncalcined, and which, when subjected to a degree of heat insuf-\nficient to drive off all their carbonic acid, yield hydraulic ce-\nment, he proposes to retain the name hydraulic limestones;\nand to call the cement obtained from their incomplete calci-\nnation under-burnt hydraulic cement (ciments d'incuits), to\ndistinguish it from that obtained from the cement stone. With\nrespect to those limestones which, by calcination, give a result\nthat partakes partly of the properties both of limes and ce-\nments, he proposes for them the name of dividing limes (chaux\nlimites.)\nThe terms fat and meager are also applied to limes; owing\nto the difference in the quality of the paste obtained from\nthem with the same quantity of water. The fat limes give a\nDigitized by Google\nLIMES.\n19\npaste which is unctuous both to the sight and touch. The meager\nlimes yield a thin paste. These names were of some impor-\ntance when first introduced, as they served to distinguish com-\nmon from hydraulic lime, the former being always fat, the\nlatter meager; but, later experience having shown that all\nmeager limes are not hydraulic, the terms are no longer of\nuse, except to designate qualities of the paste of limes.\n42. Hydraulic Limes and Cements. The limestones\nwhich yield these substances are either argillaceous, or mag-\nnesian, or argillo-magnesian. The products of their calcina-\ntion vary considerably in their hydraulic properties. Some\nof the hydraulic limes harden, or set very slowly under water,\nwhile others set rapidly. The hydraulic cements set in a very\nshort time. This diversity in the hydraulic energy of the ar-\ngillaceous limestones arises from the variable proportions in\nwhich the lime and clay enter into their composition.\n43. M. Petot, a civil engineer in the French service, in an\nable work entitled Recherches sur la Chauffournerie, gives\nthe following table, exhibiting these combinations, and the\nresults obtained from their calcination.\nLime.\nClay.\nResulting products.\nDistinctive characters of the products.\n100\n0\nVery fat lime.\nIncapable of hardening in water.\n90\n10\nLime a little hydraulic.\nSlakes like pure lime, when\n80\n20\ndo. quite hydraulic.\nproperly calcined, and hard-\n70\n30\ndo.\ndo.\nens under water.\n60\n40\nPlastic, or hydraulie cement.\nDoes not slake under any cir-\n50\n50\ndo.\ncumstances, and hardens un-\n40\n60\ndo.\nder water with rapidity.\n30\n70\nCalcareous puzzolano (brick).\nDoes not slake nor harden un-\n20\n80\ndo.\ndo.\nder water, unless mixed with\n10\n90\ndo.\ndo.\na fat or an hydraulic lime.\n0\n100\nPuzzolano of pure clay do.\nSame as the preceding.\n44. The most celebrated European hydraulic cements are\nobtained from argillaceous limestones, which vary but slightly\nin their constituent elements and properties. The following\ntable gives the results of analyses to determine the relative\nproportions of lime and clay in these cements.\nDigitized by Google\n20\nCIVIL ENGINEERING.\nTable of Foreign Hydraulic Cements, showing the relative\nproportions of Clay and Lime contained in them.\nLOCALITY.\nLime.\nClay.\nEnglish, (commonly known as Parker's, or Roman coment)\n55.40\n44.60\nFrench, (made from Boulogne pebbles)\n54.00\n46.00\nDo.\n(Poully)\n42.86\n57.14\nDo.\ndo.\n36.37\n63.68\nDo.\n(Baye)\n21.62 78.38\nRussian\n62.00.38.00\nThe hydraulic cements used in England are obtained from\nvarious localities, and differ but little in the relative propor-\ntions of lime and clay found in them. Parker's cement, so\ncalled from the name of the person who first introduced it, is\nobtained by calcining nodules of septaria. The composition\nof these nodules is the same as that of the Boulogne pebbles\nfound on the opposite coast of France. The stones which\nfurnish the English and French hydraulic cements contain\nbut a very small amount of magnesia.\n45. A hydraulic cement known as natural Portland cement\nis manufactured in France, at Boulogne, where the stone,\nwhich is very soft, is found underlying the strata which fur-\nnish the Boulogne pebbles.\n46. The best known hydraulic cements of the United States\nare manufactured in the State of New York. The following\nanalyses of some of the hydraulic limestones, from the most\nnoted localities, published in the Geological Report of the\nState of New York, 1839, are given by Dr. Beck.\nAnalysis of the Manlius Hydraulic Limestone.\nCarbonic acid\n39.80\nLime\n26.24\nMagnesia.\n18.80\nSilica and alumina\n13.50\nOxide of iron\n1.25\nMoisture and loss\n1.41\n100.00\nThis stone belongs to the same bed which yields the hy-\ndraulic cement obtained near Kingston, in Upper Canada.\nDigitized by\nGoogle\nLIMES.\n21\nAnalysis of the Chittenango Hydraulic Limestone, before\nand after calcination.\nUnburnt.\nBurnt.\nCarbonic acid\n39.33\nCarbonic acid and moisture.\n10.90\nLime\n25.00\nLime\n39.50\nMagnesia\n17.83\nMagnesia\n22.27\nSilica\n11.76\nSilica\n16.56\nAlumina\n2.73\nAlumina and oxide of iron\n10.77\nPeroxide of iron\n1.50\nMoisture\n1.50\n100.00\n100.00\nAnalysis of the Hydraulic Limestone from Ulster Co.,\nalong the line of the Delaware and Hudson Canal, before\nand after burning.\nUnburnt.\nBurnt.\nCarbonic acid\n34.20\n5\nLime\n25.50\n37.60\nMagnesia\n12.85\n16.65\nSilica.\n15.37\n22.75\nAlumina\n9.18\n13.40\nOxide of Iron\n2.25\n3.30\nBituminous matter, moisture, and loss\n1.20\n1.30\n100.00\n100.00\nThe hydraulic cement from this last locality has become\ngenerally well known, having been successfully used for most\nof the military and civil public works on the sea-board.\nFrom the results of the analyses of all the above lime-\nstones, it appears that the proportions of lime and clay\ncontained in them place them under the head of hydraulic\ncements, according to the classification of M. Petot. They\ndo not slake, and they all set rapidly under water.\n47. The discovery of the hydraulic properties of certain\nmagnesian limestones is of recent date, and is due to M.\nVicat, who first drew attention to the subject. M. Vicat\ninclines to the opinion that magnesia alone, without the\npresence of some clay, will yield only a feeble hydraulic\nlime. He states, that he has never been able to obtain any\nother, from proceeding synthetically with common lime and\nmagnesia; and that he knows of no well-anthenticated in-\nstance in which any of the dolomites, either of the primitive\nor transition formations, have yielded a good hydraulic lime.\nThe stones from these formations, he states, are devoid of\nDigitized by\nGoogle\n22\nCIVIL ENGINEERING.\nclay; being very pure crystalline carbonates, or else contain\nsilex only in the state of fine sand. From M. Vicat's experi-\nments it is rendered certain that carbonate of magnesia in\ncombination with carbonate of lime, in proportion of 40 parts\nof the latter to from 30 to 40 of the former, will produce a\nfeebly hydraulic lime, which does not appear to increase in\nhardness after it has once set; but that, with the same pro-\nportions, some hundredths of clay are requisite to give\nhydraulic energy to the compound. This proportion of clay\nM. Vicat supposes may cause the formation of triple hydro-\nsilicates of lime, alumina, and magnesia, having all the\ncharacteristic properties of good hydraulic lime.\n48. The hydraulic properties of the magnesian limestones\nof the United States were noticed by Professor W. B. Rogers,\nwho, in his Report of the Geological Survey of Virginia,\n1838, has given the following analyses of some of the stones\nfrom different localities.\nNo. 1.\nNo. 2.\nNo. 3.\nNo. 4\nCarbonate of lime\n55.80\n53.23\n48.20\n55.03\nCarbonate of magnesia\n39.20\n41.00\n35.76\n24.16\nAlumina and oxide of iron\n1.50\n0.80\n1.20\n2.60\nSilicia and insoluble matter\n2.50\n2.80\n12.10\n15.30\nWater\n0.40\n0.40\n2.73\n1.20\nLoss\n0.60\n1.77\n0.01\n1.71\n100.00\n100.00\n100.00\n100.00\nThe limestone No. 1 of the above table is from Sheppards-\ntown on the Potomac, in Virginia; it is extensively manu-\nfactured for hydraulic cement. No. 2 is from the Natural\nBridge, and banks of Cedar Creek, Virginia; it makes a good\nhydraulic cement. No. 3 is from New Y ork, and is extensively\nburnt for cement. No. 4 is from Louisville, Kentucky; said\nto make a good cement.\n49. M. Vicat states, that a magnesian limestone of France,\ncontaining the following constituents, lime 40 parts, magnesia\n21, and silicia 21, yields a good hydraulic cement; and he\ngives the following analysis of a stone which gives a good\nhydraulic lime.\nCarbonate of lime\n50.60\nCarbonate of magnesia\n42.00\nSilicia\n5.00\nAlumina\n2.00\nOxide of iron\n0.40\n100.00\nDigitized by\nGoogle\nLIMES.\n23\nBy comparing the constituents of these last two stones with\nthe analyses of the cement-stones of New York, and the mag-\nnesian hydraulic limestones of Prof. Rogers, it will be seen\nthat they consist, respectively, of nearly the same combina-\ntions of lime, magnesia, and silica.\nAlthough not brought out in the analysis of the preceding\nstones, there is probably none in which the alkaline salts do\nnot occur, and, in some, of sufficient amount to injure mortar\nmade from them, by their efflorescence.\n50. PHYSICAL CHARACTERS AND TESTS OF HY-\nDRAULIC LIMESTONES. The simple external characters\nof a limestone, as color, texture, fracture, and taste, are in-\nsufficient to enable a person to decide whether it belongs to\nthe hydraulic class; although they assist conjecture, particu-\nlarly if the rock, from which the specimen is taken, is found\nin connection with the clay deposits, or if it belong to a\nstratum whose general level and characteristics are the same\nas the argillo-magnesian rocks. These rocks are generally\nsome shade of drab, or of gray, or of a dark grayish-blue;\nhave a compact texture; fracture even or conchoidal; with a\nclayey or earthy smell and taste. Although the hydraulic\nlimestones are usually colored, still it may happen that the\nstone may be of a pure white, arising from the combination\nof lime with a pure clay.\nThe difficulty of pronouncing upon the class to which a\nlimestone belongs, from its physical properties alone, renders\nit necessary to resort to a chemical analysis, and even to direct\nexperiment to decide the question.\n51. A prejudice exists among lime manufacturers and\nbuilders in favor of the dark-colored products of calcined\nhydraulic limestones, but without any foundation, so far as\nexperiment goes, as some of the most celebrated cements are\nlight colored. As a general rule, a dark-colored material is\nan unfavorable sign, as showing the presence of some foreign\ningredient.\n52. In making a complete chemical analysis of a lime-\nstone, more skill in chemical manipulations is requisite than\nengineers usually possess; but a person who has the ordinary\nelementary knowledge of chemistry can readily ascertain the\nquantity of clay or of magnesia contained in a limestone, and\nfrom these two elements can pronounce, with tolerable cer-\ntainty, upon its hydraulic properties. To arrive at this con-\nclusion, a small portion of the stone to be tested-about five\ndrachms-is taken and reduced to a powder; this is placed\nDigitized by Google\n24\nCIVIL ENGINEERING.\nin a capsule, or an ordinary watch crystal, and slightly diluted\nmuriatic acid is poured over it until it ceases to effervesce.\nThe capsule is then gently heated, and the liquor evaporated,\nuntil the residue in the capsule has acquired the consistence\nof thin paste. This paste is thrown into a pint of pure water\nand well shaken up, and the mixture is then filtered. The\nresidue left on the filtering paper is thoroughly dried, by\nbringing it to a red heat; this being weighed will give the\nclay, or insoluble matter, contained in the stone. It is import-\nant to ascertain the state of mechanical division of the in-\nsoluble matter thus obtained ; for if it be wholly granular, the\nstone will not yield hydraulic lime. The granular portion\nmust therefore be carefully separated from the other before\nthe latter is dried and weighed.\n53. If the sample tested contains magnesia, an indication\nof this will be given by the slowness with which the acid acts;\nif the quantity of magnesia be but little, the solution will at\nfirst proceed rapidly and then become more sluggish. To\nascertain the quantity of magnesia, clear lime-water must be\nadded to the filtered solution as long as any precipitate is\nformed, and this precipitate must be quickly gathered on fil-\ntering paper, and then be washed with pure water. The resi-\ndue from this washing is the magnesia. It must be thoroughly\ndried before being weighed, to ascertain its proportion to the\nclay.\n54. Having ascertained, by the preceding analysis, the\nprobable hydraulic energy of the stone, a sample of it should\nalso be submitted to direct experiment. This may be likewise\ndone on a small scale. A sample of the stone must be re-\nduced to fragments about the size of a walnut. A crucible,\nperforated with holes for the free admission of air, is filled with\nthese fragments, and placed over a fire sufficiently powerful\nto drive off the carbonic acid of the stone. The time for\neffecting this will depend on the intensity of the heat. When\nthe heat has been applied for three or four hours, a small por-\ntion of the calcined stone may be tried with an acid, and the\ndegree of the calcination may be judged of by the more or\nless copiousness of the effervescence that ensues. If no\neffervescence takes place, the operation may be considered\ncompleted. The calcined stone should be tried soon after it\nhas become cold otherwise, it should be kept in a glass jar\nmade as air tight as practicable until used.\n55. When the calcined stone is to be tried, it is first slaked\nby placing it in a small basket, which is immersed for five or\nsix seconds in pure water. The stone is emptied from the\nDigitized by\nGoogle\nLIMES.\n25\nbasket so soon as the water has drained off, and is allowed to\nstand until the slaking is terminated. This process will pro-\nceed more or less rapidly, according to the quality of the stone,\nand the degree of its calcination. In some cases, it will be\ncompleted in a few minutes; in others, portions only of the\nstone will fall to powder, the rest crumbling into lumps which\nslake very sluggishly; while other varieties, as the true cement\nstones, give no evidence of slaking. If the stone slakes either\ncompletely or partially, it must be converted into a paste of\nthe consistence of soft putty, being ground up thoroughly, if\nnecessary, in an iron mortar. The paste is made into a cake,\nand placed on the bottom of an ordinary tumbler, care being\ntaken to make the diameter of the cake the same as that of\nthe tumbler. The vessel is filled with water, and the time of\nimmersion noted. If the lime is only moderately hydraulic,\nit will have become hard enough at the end of fifteen or twen-\nty days, to resist the pressure of the finger, and will continue\nto harden slowly, more particularly from the sixth or eighth\nmonth after immersion; and at the end of a year it will have\nacquired the consistency of hard soap, and will dissolve slowly\nin pure water. A. fair hydraulic lime will have hardened so\nas to resist the pressure of the finger, in about six or eight days\nafter immersion, and will continue to grow harder until from\nsix to twelve months after immersion; it will then have ac-\nquired the hardness of the softest calcareous stones, and will\nbe no longer soluble in pure water. When the stone is emi-\nnently hydraulic, it will have become hard in from two to four\ndays after immersion, and in one month it will be quite hard\nand insoluble in pure water; after six months, its hardness\nwill be about equal to the more absorbent calcareous stones\nand it will splinter from a blow, presenting a slaty fracture.\nAs the hydraulic cements do not slake perceptibly, the burnt\nstone must first be reduced to a fine powder before it is made\ninto a paste. The paste, when kneaded between the fingers,\nbecomes warm, and will generally set in a few minutes, either\nin the open air or in water. Hydraulic cements are far more\nsparingly soluble in pure water than the hydraulic lime; and\nthe action of pure water upon them ceases, apparently, after\na few weeks' immersion in it.\n56. Calcination of Limestone. The effect of heat on\nlime-stones varies with the constituent elements of the stone.\nThe pure limestones will stand a high degree of temperature\nwithout fusing, losing only their carbonic acid and water.\nThe impure stones containing silica fuse completely under a\ngreat heat, and become more or less vitrified when the tem-\nDigitized by Google\n26\nCIVIL ENGINEERING.\nperature much exceeds a red heat. The action of heat on the\nimpure limestones, besides driving off their carbonic acid and\nwater, modifies the relations of their other chemical constitu-\nents. The argillaceous stones, for example, yield an insoluble\nprecipitate when acted on by an acid before calcination, but\nare perfectly soluble afterwards, unless the silex they contain\nhappens to be in the form of grains.\n57. The calcination of the hydraulic limestones, from their\nfusible nature, requires to be conducted with great care for,\nif not pushed far enough, the under-burnt portions will not\nslake; and, if carried too far, the stone becomes dead or\nsluggish; slakes very slowly and imperfectly at first; and, if\nused in this state for masonry, may do injury by the swelling\nwhich accompanies the after-slaking.\n58. The more or less facility with which the impure lime-\nstones can be burned depends upon several causes; as the\ncompactness of the stone, the size of the fragments submit-\nted to heat, and the presence of a current of air, or of aque-\nous vapor. The more compact stones yield their carbonic\nacid less readily than those of an opposite texture. Stones\nwhich, when broken into very small lumps, can be calcined\nunder the red heat of an ordinary fire in a few hours, will re-\nquire a far greater degree of temperature, and for a much\nlonger period, when broken into fragments of six or eight\ninches in diameter. This is particularly the case with the im-\npure limestones, which, when in large lumps, vitrify at. the\nsurface before the interior is thoroughly burnt.\n59. If a current of vapor is passed over the stone after it has\ncommenced to give off its carbonic acid, the remaining por-\ntion of the gas which, under ordinary circumstances, is expelled\nwith great difficulty, particularly near the end of the process\nof calcination, will be carried off much sooner. The influence\nof an aqueous current is attributed, by M. Gay-Lussac, purely\nto a mechanical action, by removing the gas as it is evolved,\nand his experiments go to show that a like effect is produced\nby an atmospheric current. In burning the impure lime-\nstones, however, an aqueous current produces the farther\nbeneficial effect of preventing the vitrification of the stone\nwhen the temperature has become too elevated; but as the\nvapor, on coming in contact with the heated stone, carries off\na large portion of the heat, this, together with the latent heat\ncontained in it, may render its use in some cases far from\neconomical.\n60. Wood, charcoal, peat, the bituminous and the anthra-\ncite coals are used for fuel in lime-burning. M. Vicat states,\nDigitized by Google\nLIME-KILNS.\n27\nthat wood is the best fuel for burning hydraulic limestones\nthat charcoal is inferior to bituminous coal ; and that the re-\nsults from this last are very uncertain. When wood is used,\nit should be dry and split up, to burn quickly and give a clear\nblaze. The common opinion among lime-burners, that the\ngreener the fuel the better, and that the limestone should be\nwatered before it is placed in the kiln, is wrong; as a large\nportion of the heat is consumed in converting the water in both\ncases into vapor. Coal is a more economical fuel than wood,\nand is therefore generally preferred to it; but it requires\nparticular care in ascertaining the proper quantity for use.\nIII.\nLIME KILNS.\nLIME KILNS. Great diversity is met with in the forms and\nproportions of lime-kilns. Wherever attention has been paid\nto economy in fuel, the cylindrical, ovoidal, or the inverted\nconical form has been adopted. The two first being preferred\nfor wood and the last for coal.\n61 The whole of the burnt lime is either drawn from the\nkiln at once, or else the burning is SO regulated, that fresh\nstone and fuel are added as the calcined portions are with-\ndrawn. The latter method is usually followed when the fuel\nused is coal. The stone and coal, broken into proper sizes\n(Fig. 1), and in proportions determined by experiment, are\nFig. 1 represents a vertical section through the axis and centre lines of\nthe entrances communicating with the interior of a kiln for burning\nC\nlime with coal.\nA, solid masonry of the kiln, which is built up on the exterior like a\nsquare tower, with two arched entrances at B, B on opposite sides.\nC. interior of the kiln, lined with fire-brick or stone.\nD, ash-pit.\nc, a openings between B, B and the interior through which the burnt\nlime is drawn.\nB\nB\nD\nplaced in the kiln in alternate layers; the coal is ignited at\nthe bottom of the kiln, and fresh strata are added at the top,\nas the burnt mass settles down and is partially withdrawn at the\nDigitized by Google\n28\nCIVIL ENGINEERING.\nbottom. Kilns used in this way are called perpetual kilns ;\nthey are more economical in the consumption of fuel than\nthose in which the burning is intermitted, and which are, on\nthis account, termed intermittent kilns. Wood may also be\nused as fuel in perpetual kilns; but not with such economy\nas coal; it moreover presents many inconveniences, in sup-\nplying the kiln with fresh stone, and in regulating its dis-\ncharge. The inverted conical-shaped kiln is generally adopted\nfor coal, and the ovoidal-shaped for wood.\n62. Some care is requisite in filling the the kiln with stone\nwhen a wood fire is used. A dome (Fig. 2) is formed of the\nFig. 2 represents a vertical section through the axis and\ncentre line of the entrance of a lime-kiln for wood.\nA, solid masonry of the kiln.\nD\nB, arched entrance.\nC, doorway for drawing kiln and supplying fuel.\nD, interior of kiln.\nE, dome of broken stone, shown by the dotted line.\nE\nC\nB\nlargest blocks of the broken stone, which either rests on the\nbottom of the kiln or on the ash-grate. The lower diameter\nof the dome is a few feet less than that of the kiln; and its\ninterior is made sufficiently capacious to receive the fuel which,\ncut into short lengths, is placed up endwise around the dome.\nThe stone is placed over and around the courses which form\nthe dome, the largest blocks in the centre of the kiln. The\nmanagement of the fire is a matter of experiment. For the\nfirst eight or ten hours it should be carefully regulated, in or-\nder to bring the stone gradually to a red heat. By applying\na high heat at first, or by any sudden increase of it until the\nmass has reached a nearly uniform temperature, the stone is\napt to shiver, and choke the kiln, by stopping the voids be-\ntween the courses of stone which form the dome. After the\nstone is brought to a red heat, the supply of fuel should be\nuniform until the end of the calcination. The practice some-\ntimes adopted, of abating the fire towards the end, is bad, as\nthe last portions of carbonic acid retained by the stone, require\na high degree of heat for their expulsion. The indications of\ncomplete calcination are generally manifested by the diminu-\ntion which gradually takes place in the mass, and which, at\nthis stage, is about one sixth of the primitive volume; by the\nbroken appearance of the stone which forms the dome, the\nDigitized by\nGoogle\nLIME-KILNS.\n29\ninterstices between which being also choked up by fragments\nof the burnt stone; and by the ease with which an iron bar\nmay be forced down through the burn stone in the kiln. When\nthese indications of complete calcination are observed, the\nkiln should be closed for ten or twelve hours, to confine the\nheat and finish the burning of the upper strata.\n63. The form and relative dimensions of a kiln for wood can\nbe determined only by careful experiment. If too great\nheight be given to the mass, the lower portions may be over-\nburned before the upper are burned enough. The propor-\ntions between the height and mean horizontal section, will\ndepend upon the texture of the stone; the size of the frag-\nments into which it is broken for burning; and the more or\nless facility with which it vitrifies. In the memoir of M.\nPetot, already cited, it is stated as the result of experiments\nmade at Brest, that large-sized kilns are more economical, both\nin the consumption of fuel and in the cost of attendance, than\nsmall ones; but that there is no notable economy in fuel when\nthe mean horizontal section of the kiln exceeds sixty square\nfeet.\n64. The circular seems the most suitable form for the hori-\nzontal sections of a kiln, both for strength and economizing\nthe heat. Were the section the same throughout, or the form\nof the interior of the kiln cylindrical, the strata of stone,\nabove a certain point, would be very imperfectly burned when\nthe lower were enough so, owing to the rapidity with which\nthe inflamed gases, arising from the combustion, are cooled by\ncoming into contact with the stone. To procure, therefore, a\ntemperature throughout the heated mass which shall be nearly\nuniform, the horizontal sections of the kiln should gradually\ndecrease from the point where the flame rises, which is near\nthe top of the dome of broken stone, to the top of the kiln.\nThis contraction of the horizontal section, from the bottom\nupward, should not be made too rapidly, as the draft would\nbe injured, and the capacity of the kiln too much diminished;\nand in no case should the area of the top opening be less than\nabout one fourth the area of the section taken near the top of\nthe dome. The best manner of arranging the sides of the kiln,\nin the plane of the longitudinal section, is to connect the top\nopening with the horizontal section through the top of the\ndome, by an arc of a circle whose tangent at the lower point\nshall be vertical.\n65. Lime-kilns are constructed either of brick or of some\nof the more refractory stones. The walls of the kiln should\nbe sufficiently thick to confine the heat, and, when the locality\nDigitized by Google\n30\nCIVIL ENGINEERING.\nadmits of it they are built into a side hill; otherwise, it may\nbe necessary to use iron hoops, and vertical bars of iron, to\nstrengthen the brick-work. The interior of the kiln should\nbe faced either with good fire-brick or with fire-stone.\n66. M. Petot prefers kilns arranged with fire-grates, and an\nash-pit under the dome of broken stone, for the reason that\nthey give the means of better regulating the heat, and of\nthrowing the flame more in the axis of the kiln than can be\ndone in kilns without them. The action of the flame is thus\nmore uniformly felt through the mass of stone above the top\nof the dome, while that of the radiated heat upon the stone\naround the dome is also more uniform.\n67. M. Petot states, that the height of the mass of stone\nabove the top of the dome should not be greater than from\nten to thirteen feet, depending on the more or less compact\ntexture of the stone, and the more or less ease with which it\nvitrifies. He proposes to use kilns with two stories (Fig. 3),\nE\nFig. 8 represents a vertical section\nthrough the axis and centre line of\nthe entrance of a lime-kiln with two\nstories for wood.\nD\nA, solid masonry of the kiln.\nB, dome shown by the dotted line.\nC, interior of lower story.\nD, dome of upper story.\nE, interior of upper story.\na, arched entrance to kiln.\n0\nb, receptacle for water to furnish a cur-\nrent of aqueous vapor.\nc, doorway for drawing kiln, etc., closed\nby a fire-proof door.\nd, ash-pit under fire-grate.\nB\ne, upper doorway for drawing kiln, etc.\nc\na\nb\nfor the purpose of economizing the fuel, by using the heat\nwhich passes off from the top of the lower story, and would\notherwise be lost, to heat the stone in the upper story; this\nstory being arranged with a side-door, to introduce fuel under\nits dome of broken stone, and complete the calcination when\nthat of the stone in the lower story is finished.\nM. Petot gives the following general directions for regulat-\ning the relative dimensions of the parts of the kiln. The\ngreatest horizontal section of the kiln is placed rather below\nthe top of broken stone; the diameter of this section being\n1.82, the diameter of the grate. The height of the dome\nDigitized by Google\nLIME-KILNS.\n31\nabove the grate is from 3 to 6 feet, according to the quantity\nof fuel to be consumed hourly. The bottom of the kiln, on\nwhich the piers of the dome rest, is from 4 to 6 inches above\nthe top of the grate; the diameter of the kiln at this point\nbeing about 2 feet 9 inches greater than that of the grate.\nThe diameter of the horizontal section at top is 0.63 the di-\nameter of the greatest horizontal section. The horizontal sec-\ntions of the kiln diminish from the section near the top of the\ndome to the top and bottom of the kiln; the sides of the kiln\nreceiving the form shown in Fig. 3: the object of contracting\nthe kiln towards the bottom being to allow the stone near the\nbottom to be thoroughly burned by the radiated heat. The grate\nis formed of cast-iron bars of the usual form, the area of the\nspaces betwen the bars being one fourth the total area of the\ngrate. The bottom of the ash-pit, which may be on the same\nlevel as the exterior ground, is placed 18 inches below the\ngrate; and at the entrance of the ash-pit is placed a reservoir\nfor water, about 18 inches in depth, to furnish an aqueous\ncurrent. The draft through the grate is regulated by a lateral\nair channel to the ash-pit, which can be totally or partially\nshut by a valve; the area of the cross section of this channel\nis one tenth the total area of the grate. A square opening,\n16 inches wide, the bottom of which is on a level with\nthe bottom of kiln, leads to the dome for the supply of the\nfuel. This opening is closed with a fire-proof and air-tight\ndoor.\nIn arranging a kiln with two stories, M. Petot states, that\nthe grates of the upper story are so soon destroyed by the\nheat, that it is better to suppress them, and to place the fuel\nfor completing the calcination of the stone of this story on\nthe top of the burnt stone of the lower story.\n68. Lime burning has become a special branch of industry\nin the United States, in which a large amount of capital is\nembarked, so that the engineer has now no other concern in\nthe manufacture of this material than to be able to test and\nselect from the samples offered him to suit the application he\nintends making of his material.\n69. There are two principal classes of lime-kilns employed\nby the manufacturers of lime in the United States. These\nvary but little from each other in form and dimensions in the\nlocalities in which they are used throughout the country.\n70. The first class belongs to the perpetual kilns, the\nstone and fuel, which is usually bituminous or anthracite coal,\nbeing placed in the kiln in alternate layers, in proportions\npointed out by experience, which is fed in like manner at the\nDigitized\nby\nGoogle\n32\nCIVIL ENGINEERING.\ntop as the calcined stone is gradually drawn out at the bottom.\nIn some cases the chamber of these kilns is simply an invert-\ned frustum of a cone in form.\nb\nd\nFig. 4 represents a section through the axis of the\nperpetual lime-kilns in ordinary use in the United\nA\nStates for coal as the fuel.\nE\nA, body of the kiln.\nF\nB, thimble, or lower frustum.\na\nc\nC, D, draw pit.\nF, body of the masonry.\nab, c d, sides of conical-shaped kiln.\nB\nC\nD\n71. In others (Fig. 4) the body or upper portion of the chamber\nis cylindrical, whilst the lower portion is an inverted conical\nfrustum, the two surfaces being united by an annular one\ntangent to each.\n72. The second class is the flume or furnace kiln. In this\nthe stone placed in the chamber of the kiln is calcined by the\ncombustion of the fuel, either wood or coal, placed in furnaces\nnear the bottom of the chamber. This class may be used\neither as intermittent or perpetual kilns.\n73. In both classes the stone for burning is broken into\nlumps, none of which should be over eight inches in size in\nany direction. In the selection of the lumps great care and\nexperience are required on the part of the kiln attendants, in\norder to obtain a product of uniform quality, as admixtures\nof stones varying in any important degree in their constituent\nelements, particularly in those of hydraulic limestones, may\nso vitiate the results as to render them useless for hydraulic\nstructures.\n74. In others they are formed of the frusta of two conical\nsurfaces, as shown by the dotted lines a b, c d, united at\ntheir larger bases (Fig. 4).\nThe diameter a c of the thimble varies from eight to ten feet ;\nthe diameter at the bottom from eighteen inches to three\nfeet ; the height of the thimble from seven to ten feet. The\nupper diameter of the body of the kiln, if conical, is about a\nDigitized by Google\nLIMI-KILNS.\n33\nFig. 7.\nFig. 6.\nC\nC\nC\nC\nH\nH\nM\nM\nC\nC\nK\na\na\nC\ng g\nL\nN\nFig. 5.\nC\nK\na\nH\nH\nK\nK\nK\n(I\nC\nFig. 5 is a horizontal section taken at CO, Fign. 6, 7; Fig. 6 is a vertical section taken at\nKK, Fig. 5, through the main furnace; and Fig. 7 a vertical section through\nA A of the water flame kiln for coal.\nG, body of the masonry.\nH, H is the cupola or body of the kiln.\nI, wall dividing the cupola, and rising from bottom of kiln to a level with the side-fiues.\nJ, wooden crib on top.\nK, furnace arches.\nL, ash pit.\nM, water-pipes for supplying water-pans 0 and ash pans f.\nN, curved iron lining at bottom serving as a slide.\na, a, concaves in interior of cupola.\nb, b, grates.\na c, hot-water coal-pans.\n& & sight-holes for examining burning of body of lime and punching it downwards.\na, g, side fines,\n3\nDigitized by Google\n34\nCIVIL ENGINEERING.\nfoot less than the lower ; if cylindrical, the same as the lower.\nThe height of the body from twelve to twenty feet. The\ndraw door from eighteen inches to three feet. The height of\nthe draw pit nine feet.\nThe body A of the masonry is sometimes rectangular and\nsometimes circular in plan, and about six feet in thickness.\nIt is secured on the outside either by strips of wood let into\nthe masonry, or by iron curbs. The lining of the kiln is of the\nbest fire-brick.\nThe kiln, for burning, is filled with alternate layers of coal\nand stone, those of the latter not exceeding six inches in thick-\nness. The fire is started from beneath, with dry wood. The\ndrawing of the kiln is done two or three times every twenty-\nfour hours.\n75. The perpetual draw water-flame kilns, for both coal and\nwood, patented by Mr. C. D. Page, of Rochester, New York,\nhave met with very general favor in our large lime burning\nlocalities.\nThe cupola which contains the burning lime, it will be seen,\nis chiefly cylindrical, being terminated at top and bottom by\nconical frusta.\nThe cupola space issix by eight feet between the main walls\nAA. The main walls from out to out are eighteen by twenty\nfeet at the base of the kiln fifteen by sixteen feet at the top\nand forty feet high. The main walls are strengthened as usual\nwith timber curbs. The wooden crib at top, which is strong-\nly boarded to the height of four feet, serves as a reservoir for\nthe raw stone.\nThis kiln receives its name from the coal being first placed\nin pans of hot water, the steam from which being decomposed\nfacilitates the process of burning by the decomposition of the\nsteam.\n76. Hoffman Kiln. General Q. A. Gillmore, of the Uni-\nted States Corps of Engineers, to whom the profession is\nalready SO much indebted for his researches on the limes and\ncements in the United States, has given in his recent pam-\nphlet, No. 19, Professional Papers, Corps of Engineers, U.S.\nArmy, an account of what is known as the Hoffman Kiln,\nof which the following is a brief description :-\nThis kiln (Figs. 8, 9, 10, 11) consists of an annular arch, A,\nA', the plan of which may be a circle, an oval, or as in Fig.\n8. The height of the arch being from eight to nine feet, and\nspan from ten to twelve feet; the middle line of the chamber\nA measuring one hundred and fifty feet. This void space is\ntermed the burning chamber.\nDigitized\nby\nGoogle\nLIME-KILNS.\n35\nThe chimney C, C' (Figs. 10, 11) may stand in the central\nspace B, B', or exterior to the kiln. In the latter case a smoke\nflue leads to it under the burning chamber. Fourteen radial\nflues lead from the burning chambers to the smoke chamber,\nFig. 8.\na\nD\n9\n10\n8\nFig. 11.\n\"\nC\n7\nb\nc\n12\n6\nD\nA\n13\nS\nA\n14\n*\nFig. 10.\nVI\n2\nA\nc'\nc\nd\nFig. 9.\nE\n50\nB.\nB\nA\nA\nD\nFig. 8. Horizontal section of kiln on A B, Fig. 9.\nFig. 9. Vertical section on CD, Fig. 8.\nFig. 10. Elevation of chimney.\nFig. 11. Section of chimney at A B, Fig. 10.\nA, A', Burning chamber.\nB. B', Smoke chamber.\nC, C, Chimney.\nD. Doorways.\na, b, Lime-stone in process of burning.\n0, c,\ndo.\ndo.\nof cooling.\nc,d,\ndo.\ndo.\nof drawing.\nd,e,\ndo.\ndo.\nof setting up.\nas,\ndo.\ndo.\nof drying.\nf.a,\ndo.\ndo.\nof taking up waste heat.\neach having a bell-shaped damper, which can be opened or\nclosed at pleasure. There are fourteen arched doors, D, D,\nthrough the outer wall, each five feet high, and four feet wide.\nThe arched top of the burning chamber is pierced, at inter-\nvals of three or four feet, with holes, five inches in diameter,\ntermed feed-holes, through which fuel is supplied to the fires.\nDigitized by Google\n36\nCIVIL ENGINEERING.\nThey are in number about three hundred, each closed with\na bell-shaped cover fitting over a rim or curb, and dipping\ninto sand.\nThe entire structure is of solid stone or brick masonry, and\ncovered with a roof.\nThe burning chamber is lined with fire-brick for burning\nhydraulic cement.\n77. Calcination of the stone.-When the kiln is in opera-\ntion all the doorways (Fig. 8) numbered from 1 to 14, from\nleft to right are kept closed with temporary brickwork, ex-\ncept two or three. Let the open ones be 1 and 2. The\nburnt lime is drawn from No. 2, and raw stone taken in\nat No. 1 and piled up in the burning chamber, leaving\nvertical openings under the feed holes, and horizontal ones\nunder the mass for the circulation of air around the periphery\nof the burning chamber.\nWhen the kiln is going, all the compartments but two,\nbetween each two consecutive doorways, are filled with stone,\nin all stages, from the raw to thoroughly calcined.\nSuppose compartments 1 and 2 empty, and all the others\nfilled. No. 3 contains cement from stone put in 12 days ago;\nNo. 4 that from stone put in 11 days ago; and so on around\nto compartment 14, which was filled yesterday. Separating\nNo. 14 from No. 1 is a sheet iron partition, as nearly as pos-\nsible air-tight. This partition, called the cut-off, is movable.\nYesterday it was between 13 and 14; to-morrow it will be\nbetween 1 and 2, and so on, being moved on one compart-\nment each day. All the dampers are closed to-day except\nNo. 14; yesterday all were closed except No. 13; to-morrow\nonly No. 1 will be open. To-day men are removing burnt\ncement from compartment No. 2, and others are setting raw\nstone in compartment No. 1. Yesterday they were setting\nstone in No. 14, and removing cement from No. 1. To-\nmorrow they will be removing cement from No. 3, and filling\nNo. 2 with raw stone; 80 that every day the setting, drawing,\ncut-off, and open damper advance one compartment. The\nfires are in the centre of the mass, from the burnt cement end\nround to the raw stone end ; say in compartments 7 and 8\nto-day, 6 and 7 yesterday, 8 and 9 to-morrow, advancing one\ncompartment per day, like the drawing and setting.\n\" The compartment that was in fire yesterday, say No. 6, is\nstill very hot to-day, No. 5 less hot, No. 4 cooler, and so on to\nNo. 2, where the cement is cool enough to be handled, and\nmen are removing it from the kiln, wheelbarrows, or trucks\non portable railway tracks, being used for the purpose.\nDigitized by\nGoogle\nLIME-KILNS.\n37\nThe compartments not yet fired are heated by the hot\ngases passing through them to the chimney, the stone in the\ncompartment next the fire being at a full red heat, while\nthat farthest off, which was put in yesterday, is only warm.\n\" The draught of the chimney is sufficient to draw air in at\nthe open doorways, through the entire mass of cement and\nraw stone, to the open flue, which is the one by the cut-off.\n\" In passing through the burnt cement the air takes up the\nresidue of heat and becomes hotter and hotter, till, after pas-\nsing through the cement burned yesterday, the hot current\nignites at once the dust coal as it falls from the feed pipes,\nand the gases thus formed being carried on, mixed with air,\nit is probable the stone is burned considerably in advance of\nwhere the coal is supplied.\n\" As the hot gases of combustion pass on, they give up their\nheat to the limestone, till, on arriving at the chimney, there\nis only heat enough remaining to cause a draught in a well-\nconstructed chimney 140 to 150 feet in height. It is plain\nthat all the heat of combustion is utilized, except such as may\nescape through the walls of the kiln, and as the masonry is\nvery massive, the loss from this cause is very slight.\n\" One peculiar feature of these kilns is, that although less\nlikely to get out of order than other kilns, from the fact that\nthere is no movement in the burning mass, repairs may be\neasily made without letting the fire go down.\n\" There are Hoffman kilns in which the fires have not been\nextinguished for five years.\"\n78. Methods of reducing the calcined stone to pow-\nder.-The calcined stone may be reduced to powder, either\nby a chemical or mechanical process. By the first, water\ncombines with the lime, forming a hydrate of lime, which\nprocess is termed slaking. By the second the calcined\nstone is first broken into small lumps; these are then ground\nin a mill to the requisite degree of fineness, ascertained by\nthe sieves through which the ground product must pass.\n79. Slaking--This may be done in three ways:\nBy pouring sufficient water on the burnt stone to convert\nthe slaked lime into a thin paste, which is termed drowning\nthe lime.\nBy placing the burnt stone in a basket, and immersing it\nfor a few seconds in water, during which time it will imbibe\nenough water to cause it to fall, by slaking, into a dry pow-\nder; or by sprinkling the burnt stone with a sufficient quan-\ntity of water to produce the same effect.\nBy allowing the stone to slake spontaneously, from the\nDigitized by Google\n38\nCIVIL ENGINEERING.\nmoisture it imbibes from the atmosphere, which is termed\nair-slaking.\n80. Opinion seems to be settled among engineers, that\ndrowning is the worst method of slaking lime which is to be\nused for mortars. When properly done, however, it produces\na finer paste than either of the other methods; and it may\ntherefore be resorted to whenever a paste of this character, or\na whitewash is wanted. Some care, however, is requisite to\nproduce this result. The stone should be fresh from the kiln,\notherwise it is apt to slake into lumps or fine grit. All the\nwater used should be poured over the stone at once, which\nshould be arranged in a basin or vessel, so that the water sur-\nrounding it may be gradually imbibed as the slaking proceeds.\nIf fresh water be added during the slaking, it checks the\nprocess, and. causes a gritty paste to form.\n81. In slaking by immersion, or by sprinkling with water,\nthe stone should be reduced to small-sized fragments, other-\nwise the slaking will not proceed uniformly. The fat limes\nshould be in lumps, about the size of a walnut, for immersion\nand, when withdrawn from the water, should be placed im-\nmediately in bins, or be covered with sand, to confine the\nheat and vapour. If left exposed to the air, the lime becomes\nchilled and separates into a coarse grit, which takes some time\nto slake thoroughly when more water is added. Sprinkling\nthe lime is a more convenient process than immersion, and is\nequally good. To effect the slaking in this way, the stone\nshould be broken into fragments of a suitable size, which ex-\nperiment will determine, and be placed in small heaps, sur-\nrounded by sufficient sand to cover them up when the slaking\nis nearly completed. The stone is then sprinkled with about\none fourth its bulk of water, poured through the rose of a\nwatering-pot, those lumps which seem to slake most sluggishly\nreceiving the most water; when the process seems completed,\nthe heap is carefully covered over with the sand, and allowed\nto remain a day or two before it is used.\n82. Slaking either by immersion or by sprinkling is con-\nsidered the best. The quantity of water imbibed by lime\nwhen slaked by immersion, varies with the nature of the lime\n100 parts of fat lime will take up only 18 parts of water; and\nthe same quantity of ineager lime will imbibe from 20 to 35\nparts. One volume, in powder, of the burnt stone of rich lime\nyields from 1.50 to 1.70 in volume of powder of slaked lime\nwhile one volume of meager lime, under like circumstances,\nwill yield from 1.80 to 2.18 in volume of slaked lime.\n83. Quick lime, when exposed to the free action of the air\nDigitized by\nGoogle\nLIME.\n39\nin a dry locality, slakes slowly, by imbibing moisture from\nthe atmosphere, with a slight disengagement of heat. Opinion\nseems to be divided with regard to the effect of this method\nof slaking on fat limes. Some assert, that the mortar made\nfrom them is better than that obtained from any other process,\nand attribute this result to the re-conversion of a portion of\nthe slaked lime into a carbonate ; others state the reverse to\nobtain, and assign the same cause for it. With regard to\nhydraulic limes, all agree that they are greatly injured by air-\nslaking.\n84. When the slaking is imperfect and is owing as in\nmost cases to the stone having been unequally burned, the\nlime should be reduced to a paste in a mortar mill that will\ngrind fine all the lumps. This is particularly necessary in\nhydraulic limes, which are also improved in energy by this\nreduction of the underburned lumps.\n85. Air-slaked fat limes increase two-fifths in weight, and\nfor one volume of quick lime yield 3.52 volumes of slaked\nlime. The meager limes increase one-eighth in weight, and\nfor one volume of quick lime yield from 1.75 to 2.25 volumes\nof slaked lime.\n86. The dry hydrates of lime, when exposed to the at-\nmosphere, gradually absorb carbonic acid and water. This\nprocess proceeds very slowly, and the slaked lime never re-\ngains all the carbonic acid which is driven off by the calcina-\ntion of the lime-stone. When converted into a thick paste,\nand exposed to the air, the hydrates gradually absorb carbonic\nacid; this action first takes place on the surface, and proceeds\nmore slowly from year to year towards the interior of the ex-\nposed mass. The absorption of gas proceeds more rapidly in\nthe meager than in the fat limes. Those hydrates which are\nmost thoroughly slaked become hardest. The hydrates of the\npure fat limes become in time very hard, while those of the\nhydraulic limes become. only moderately hard.\n87. The fat limes, when slaked by drowning, may be pre-\nserved for a long period in the state of paste, if placed in a\ndamp situation and kept from contact with the air. They\nmay also be preserved for a long time without change, when\nslaked by immersion to a dry powder, if placed in covered\nvessels. Hydraulic limes, under similar circumstances, will\nharden if kept in the state of paste, and will deteriorate when\nin powder, unless kept in perfectly air-tight vessels.\n88. The hydrates of fat lime, from air-slaking or immersion,\nrequire a smaller quantity of water to reduce them to the state\nof paste than the others; but, when immersed in water, they\nDigitized by\nGoogle\n40\nCIVIL ENGINEERING.\ngradually imbibe their full dose of water, the paste becom-\ning thicker, but remaining unchanged in volume. Exposed\nin this way, the water will in time dissolve out all the lime of\nthe hydrate which has not been reconverted into a sub-carbo-\nnate, by the absorption of carbonic acid before immersion ;\nand if the water contain carbonic acid, it will also dissolve the\ncarbonated portions.\n89. The hydrates of hydraulic lime, when immersed in\nwater in the state of thin pastes, reject a portion of the water\nfrom the paste, and become hard in time; if the paste be\nvery stiff, they imbibe more water, set quickly, and acquire\ngreater hardness in time than the soft pastes. The pastes of\nthe hydrates of hydraulic lime, which have hardened in the\nair, will retain their hardness when placed in water.\n90. All limes seem to have their hydraulic energy affected\nby the degree of their calcination; but only in their first\nstages of immersion. This is observed even in underburned\ncommon lime which, when suitably reduced, is found to be\nslightly hydraulic.\n91. The pastes of the fat limes shrink very unequally in\ndrying, and the shrinkage increases with the purity of the\nlime; on this account it is difficult to apply them alone to any\nbuilding purposes, except in very thin layers. The pastes of\nthe hydraulic limes can only be used with advantage under\nwater, or where they are constantly exposed to humidity; and\nin these situations they are never used alone, as they are\nfound to succeed as well, and to present more economy, when\nmixed with a portion of sand.\n92. Manner of reducing hydraulic cement.-As the\ncement stones will not slake, they must be reduced to a fine\npowder by some mechanical process, before they can be con\nverted into a hydrate. They methods usually employed for\nthis purpose consist in first breaking the burnt stone into small\nfragments, either under iron cylinders, or in conical-shaped\nmills suitably formed for this purpose. The product is next\nground between a pair of stones, or else crushed by an iron\nroller. The coarser particles are separated from the fine\npowder by the ordinary processes with sieves. The powder\nis then carefully packed in air-tight casks, and kept for use.\n93. Hydraulic cement, like hydraulic lime, deteriorates by\nexposure to the air, and may in time lose all its hydraulic\nproperties. On this account it should be used when fresh\nfrom the kiln; for, however carefully packed, it cannot be\nwell preserved when transported to any distance.\n94. The déterioration of hydraulic cements, from exposure\nDigitized by Google\nLIME.\n41\nto the air, arises, probably, from a chemical disunion between\nthe constituent elements of the burnt stone, occasioned by\nthe absorption of water and carbonic acid. When injured,\ntheir energy can be restored by submitting them to a much\nslighter degree of heat than that which is requisite to calcine\nthe stone suitably in the first instance. From the experi-\nments of M. Petot, it appears that a red heat, kept up for\na short period, is sufficient to restore damaged hydraulic\ncements.\n95. \" As a rule, all hydraulic cements produced at a low\nheat, whether derived from argillaceous or argillo-magnesian\nlime-stones, are light in weight and quick-setting, and never\nattain, when made into mortar or béton, more than 30 to 33\nper cent. of the strength and hardness of Portland cement\nplaced in similar circumstances. They are also greatly in-\nferior to good hydraulic lime. This is true of all cements\nmade at a low heat, including even those derived from lime-\nstones, that might, with proper burning, have yielded Portland\ncement. The celebrated Roman cement, the twice-kilned\nartificial cements, the quick-setting French cement, like that\nof Vassy, and all the hydraulic cements manufactured at the\npresent day in the United States, belong to this category.\"\n96. ARTIFICIAL HYDRAULIC LIMES AND CE-\nMENTS. The discovery of the argillaceous character of the\nstones which yield hydraulic limes and cements, connected\nwith the fact that brick reduced to a fine powder, as well as\nseveral substances of volcanic origin having nearly the same\nconstituent elements as. ordinary brick, when mixed in suita-\nble proportions with common lime, will yield a paste that\nhardens under water, has led, within a recent period, to arti-\nficial methods of producing compounds possessing the proper-\nties of natural hydraulic limestones.\n97. M. Vicat was the first to point out the method of form-\ning an artificial hydraulic lime, by mixing common lime and\nunburnt clay, in suitable proportions, and then calcining\nthem. The experiments of M. Vicat have been repeated by\nseveral eminent engineers with complete success, and among\nothers by General Pasley, who, in a recent work by him,\nObservations on Limes, Calcareous Cements, etc., has given,\nwith minute detail, the results of his experiments; from which\nit appears that an hydraulic cement, fully equal in quality to\nthat obtained from natural stones, can be made by mixing\ncommon lime, either in the state of a carbonate or of a hy-\ndrate, with clay, and subjecting the mixture to a suitable de-\nDigitized by Google\n42\nCIVIL ENGINEERING.\ngree of heat. In some parts of France, where chalk is found\nabundantly, the preparation of artificial hydraulic lime has\nbecome a branch of manufacture.\n98. Different methods have been pursued in preparing this\nmaterial, the main object being to secure the finest mechan-\nical division of the two ingredients, and their thorough mix-\nture. For this purpose the lime-stone, if soft, like chalk or\ntufa, may be reduced in a wash-mill, or a rolling-mill, to the\nstate of a soft pulp; it is then incorporated with the clay, by\npassing them through a pug-mill. The mixture is next\nmoulded into small blocks, or made up into balls between 2\nand 3 inches diameter, by hand, and well dried. The balls\nare placed in a kiln,-suitably calcined, and are finally slaked,\nor ground down fine for use.\n99. If the lime-stone be hard, it must be calcined and\nslaked in the usual manner, before it can be mixed with the\nclay. The process for mixing the ingredients, their calcina-\ntion, and further preparation for use, are the same as in the\npreceding case.\n100. The artificial hydraulic cement manufactured in\nFrance, at Boulogne, and possessing the same qualities as the\nartificial Portland cement, is composed of 79.5 per cent. of\ncarbonate of lime in powder, and 20.5 of clay, which, after\nbeing thoroughly mixed, are subjected to a very high degree\nof temperature.\n101. What is known, in commerce and among engineers,\nas artificial Portland cement, is a mixture of the blue clay of\nthe London basin and chalk, formed by grinding the materials\ntogether in water. The semi-fluid mixture is run off into\nvats, and, after settling and attaining sufficient consistency, is\ndried by artificial heat and then calcined, at a high tempera-\nture, to the verge of vitrification. It is then reduced for use\nto a very fine powder. It is said not to deteriorate from ex-\nposure to the air, provided it be kept from moisture.\n102. Artificial hydraulic lime, prepared from the hard\nlimestones, is more expensive than that made from the soft;\nbut it is stated to be superior in quality to the latter.\n103. As clays are seldom free from carbonate of lime, and\nas the limestones which yield common or fat lime may con-\ntain some portion of clay, the proper proportions of the two\ningredients, to produce either an hydraulic lime or a cement,\nmust be determined by experiment in each case, guided by a\nprevious analysis of the two ingredients to be tried.\nIf the lime be pure, and the clay be free from lime, then\nthe combinations in the proportions given in the table of M.\nDigitized by\nGoogle\nLIME.\n43\nPetot will give, by calcination, like results with the same\nproportions when found naturally combined.\n104. Puzzolana, etc. The practice of using brick or tile-\ndust, or a volcanic substance known by the name of puzzo-\nlana, mixed with common lime, to form an hydraulic lime,\nwas known to the Romans, by whom mortars composed of these\nmaterials were extensively used in their hydraulic constructions.\nThis practice has been more or less followed by modern engi-\nneers, who, until within a few years, either used the puzzolana\nof Italy, where it is obtained near Mount Vesuvius, in a pul-\nverulent state, or a material termed Trass, manufactured in\nHolland, by grinding to a fine powder a volcanic stone obtained\nnear Andernach, on the Rhine.\nExperiments by several eminent chemists have extended\nthe list of natural substances which, when properly burnt and\nreduced to powder, have the same properties as puzzolana.\nThey mostly belong to the feldspathic and schistose rocks,\nand are either fine sand, or clays more or less indurated.\nThe following Table gives the results of analyses of Puzzo-\nlana, Trass, a Basalt, and a Schistus, which, when burnt\nand powdered, were found to possess the properties of\npuzzolana.\nPuzzolana.\nTrass.\nBasalt.\nSchistus.\nSilica\n0.445\n0.570\n44.50\n46.00\nAlumina\n0.150\n0.120\n16.75\n26.00\nLime\n0.088\n0.026\n9.50\n4.00\nMagnesia\n0.047\n0.010\n-\n-\nOxide of iron\n0.120\n0.050\n20.00\n14.00\nOxide of manganese\n-\n-\n2.37\n8.00\nPotassa\n0.014\n0.070\nr\n-\nSoda\n0.030\n0.010\n2.60\n-\nWater and loss\n0.106\n0.144\n4.28\n2.00\n1.000\n1.000\n100.00\n100.00\n105. Whether natural puzzolanas occur in the United\nStates, is not known. The great abundance of natural hy-\ndraulic cements would probably cause no demand for them,\nnor for artificial puzzolanas for building purposes.\n106. All of these substances, when prepared artificially,\nare now generally known by the name of artificial puzzolanas,\nin contradistinction to those which occur naturally.\n107. General Treussart, of the French Corps of Military\nEngineers, first attempted a systematic investigation of the\nDigitized by\nGoogle\n44\nCIVIL ENGINEERING.\nproperties of artificial puzzolanas made from ordinary clay,\nand of the best manner of preparing them on a large scale.\nIt appears from the results of his experiments, that the plas-\ntic clays used for tiles, or pottery, which are unctuous to the\ntouch, the alumina in them being in the proportion of one\nfifth to one third of the silica, furnish the best artificial puzzo-\nlanas when suitably burned. The clays which are more mea-\nger, and harsher to the touch, yield an inferior article, but are\nin some cases preferable, from the greater ease with which\nthey can be reduced to a powder.\n108. As the clays mostly contain lime, magnesia, some of\nthe metallic oxides, and alkaline salts, General Treussart en-\ndeavored to ascertain the influence of these substances upon\nthe qualities of the artificial puzzolanas from clays in which\nthey are found. He states, that the carbonate of potash and\nthe muriate of soda seem to act beneficially; that magnesia\nseems to be passive, as well as the oxide of iron, except when\nthe latter is found in a large proportion, when it acts hurtful-\nly and that the lime has a material influence on the degree\nof heat required to convert the clay into a good artificial puz-\nzolana.\n109. The management of the heat, in the preparation of\nthis material, seems of the first consequence; and General\nTreussart recommends that direct experiment be resorted to,\nas the most certain means of ascertaining the proper point.\nFor this purpose, specimens of the clay to be tried may be\nkneaded into balls as large as an egg, and the balls when dry,\nbe submitted to different degrees of heat in a kiln, or furnace,\nthrough which a current of air must pass over the balls, as\nthis last circumstance is essential to secure a material possess-\ning the best hydraulic qualities. Some of the balls are with-\ndrawn as soon as their color indicates that they are under-\nburnt; others when they have the appearance of well-burnt\nbrick; and others when their color shows that they are over-\nburnt, but before they become vitrified. The burnt balls are\nreduced to an impalpable powder, and this is mixed with a\nhydrate of fat lime, in the proportion of two parts of the pow-\nder to one of lime in paste. Water is added, if necessary, to\nbring the different mixtures to the consistence of a thick pulp;\nand they are separately placed in glass vessels, covered with\nwater, and allowed to remain until they harden. The com-\npound which hardens most promptly will indicate the most\nsuitable degree of heat to be applied.\n110. As the carbonates of lime, of potash, and of soda, act\nas fluxes on silica, the presence of either one of them will\nDigitized by Google\nLIME.\n45\nmodify the degree of heat necessary to convert the clay into\na good natural puzzolana. Clay, containing about one tenth\nof lime, should be brought to about the state of slightly-burnt\nbrick. The ochreous clays require a higher degree of heat to\nconvert them into a good material, and should be burnt until\nthey assuine the appearance of well-burnt brick. The more\nrefractory clays will bear a still higher degree of heat; but\nthe calcination should in no case be carried to the point of\nincipient vitrification.\n111. The quantity of lime contained in the clay can be read-\nily ascertained beforehand, by treating a small portion of the\nclay, diffused in water, with enough muriatic acid to dissolve\nout the lime; and this last might serve as a guide in the pre-\nliminary stages of the experiments.\n112. General Treussart states, as the results of his experi-\nments, that the mixture of artificial puzzolana and fat lime\nforms an hydraulic paste superior in quality to that obtained\nby M. Vicat's process for making artificial hydraulic lime.\nM. Curtois, a French civil engineer, in a memoir on these ar-\ntificial compounds, published in the Annales des Ponts et\nChaussées, 1834, and General Pasley, more recently, adopt\nthe conclusion of General Treussart. M. Vicat's process ap-\npears best adapted when chalk, or any very soft lime-stone,\nwhich can be readily converted to a soft pulp, is used, as\noffering more economy, and affording an hydraulic lime which\nis sufficiently strong for most building purposes. By it Gen-\neral Pasley has succeeded in obtaining an artificial hydraulic\ncement which is but little, if at all, inferior to the best natu-\nral varieties; a result which has not been obtained from any\ncombination of fat lime with puzzolana, whether natural or\nartificial.\n113. All the puzzolanas possess the important property of\nnot deteriorating by exposure to the air, which is not the case\nwith any of the hydraulic limes or cements. This property\nmay render them very serviceable in many localities, where\nonly common or feebly hydraulic lime can be obtained.\n114. The well-known artificial Portland cement, manufac-\ntured in England, is composed of an intimate mixture of chalk\nand clay, in the state of paste, which is then dried and burned\nin kilns or ovens; the product of the calcination being flinty,\nor like vitrified brick. This degree of calcination is essential\nto the excellence of the material, of which its weight, or spe-\ncific gravity, is one of the best tests.\nAnother more recent method of giving a certain degree of\nhydraulicity to common limes, and of improving that of hy-\nDigitized by Google\n46\nCIVIL ENGINEERING.\ndraulic limes, is to place the calcined stone, after it has been\ndrawn from the kiln, in arched ovens which can be made air-\ntight, in which it can be subjected to the action of a fire, from\na grate beneath; so that the heat can be equally diffused\nthroughout the mass, which is brought only to a slight glow,\nas seen by the eye. When in this condition, iron pots contain-\ning sulphur are placed underneath, and the sulphur, converted\ninto vapour, allowed to permeate the mass of lime; the escape\nof the vapour from the oven having been previously provided\nagainst. After the sulphur has been consumed the mass is\nallowed to cool, and is then ground fine like other cements.\nThis product is known in commerce as Scott's cement, from\nthe name of the inventor, an officer of the Royal Engineers.\nSee Professional Papers of the Corps of Royal Engineers.\nVol. X. New Series.\nIV.\nMORTAR.\n115. Mortar is any mixture of lime in paste with sand. It\nmay be divided into two principal classes; Hydraulic mor-\ntar, which is made of hydraulic lime, and Common mortar,\nmade of common lime.\n116. The term Grout is applied to any mortar in a thin or\nfluid state; and the terms Concrete and Beton, to mortars in-\ncorporated with gravel and small fragments of stone or brick.\n117. Mortar is used for various purposes in building. It\nserves as a cement to unite blocks of stone, or brick. In con-\ncrete and beton, which may be regarded as artificial conglom-\nerate stones, it forms the matrix by which the gravel and\nbroken stone are held together; and it is the principal mate-\nrial with which the exterior surfaces of walls and the interior\nof edifices are coated.\n118. The quality of mortars, whether used for structures\nexposed to the weather, or for those immersed in water, will\ndepend upon the nature of the materials used ; their propor-\ntions; the manner in which the lime has been converted in-\nto a paste to receive the sand ; and the mode employed to\nmix the ingredients. Upon all of these points experiment\nDigitized by Google\nMORTAR.\n47\nis the only unerring guide for the engineer ; for the\ngreat diversity in the constituent elements of limestones, as\nwell as in the other ingredients of mortars, must necessarily\nalone give rise to diversities in results ; and when, to these\ncauses of variation, are superadded those resulting from dif-\nferent processes pursued in the manipulations of slaking the\nlime and mixing the ingredients, no surprise should be felt at\nthe seemingly opposite conclusions at which writers, who have\npursued the subject experimentally, have arrived. From the\ngreat mass of facts, however, presented on this subject within\na few years, some general rules may be laid down, which the\nengineer may safely follow, in the absence of the means of\nmaking direct experiments.\n119. As to the action of salt water on artificial hydraulic\nlimes made by mixing common lime with a natural or artifi-\ncial puzzolana, opinion among European engineers seems di-\nvided. Some state that they withstand well the action of salt\nwater ; others that they only resist this action after the expos-\ned surface becomes coated with barnacles, oysters, etc.\n120. The view now generally taken of mortar is, that being\nan artificial sandstone, the nearer its constituents approach\nthose of the natural sandstones, the better will be the result\nobtained; and that therefore the best proportions for its in-\ngredients are those in which each grain of sand is enveloped\nwith just sufficient lime, in a barely moist state, to cause the\nwhole mass to cohere and set quickly. Too much lime causes\nshrinkage and cracks and when too much water is added\nthe mass in drying is found to be porous.\n121. Sand. This inaterial, which forms one of the ingre-\ndients of mortar, is the granular product arising from the dis-\nintegration of rocks. It may, therefore, like the rocks from\nwhich it is derived, be divided into three principal varieties\n-the silicious, the calcareous, and the argillaceous.\nSand is also named from the locality where it is obtained,\nas pit sand, which is procured from excavations in alluvial, or\nother deposits of disintegrated rock; river sand, and sea sand,\nwhich are taken from the shores of the sea, or rivers.\nBuilders again classify sand according to the size of the\ngrain. The term coarse sand is applied when the grain va-\nries between ]th and 11ᵗʰ of an inch in diameter the term fine\nsand, when the grain is between 16th and 14th of an inch in\ndiameter; and the term mixed sand is used for any mixture\nof the two preceding kinds.\n122. The silicious sands, arising from the quartzose rocks,\nare the most abundant, and are usually preferred by builders.\nDigitized by\nGoogle\n48\nCIVIL ENGINEERING.\nThe calcareous sands, from hard calcareous rocks, are more\nrare, but form a good ingredient for mortar. Some of the\nargillaceous sands possess the properties of the less energetic\npuzzolanas, and are therefore very valuable, as forming with\ncommon lime an artificial hydraulic lime.\n123. The property which some argillaceous sands possess,\nof forming with common, or slightly hydraulic lime a com-\npound which will harden under water, has been long known\nin France, where these sands are termed arènes. The sands\nof this nature are usually found in hillocks along river valleys.\nThese hillocks sometimes rest on calcareous rocks, or argil-\nlaceous tufas, and are frequently formed of alternate beds of\nthe sand and pebbles. The sand is of various colors, such as\nyellow, red, and green, and seems to have been formed from\nthe disintegration of clay in a more or less indurated state.\nThe arènes are not as energetic as either natural or artificial\npuzzolanas; still they form, with common lime, an excellent\nmortar for masonry exposed either to the open air, or to\nhumid localities, as the foundations of edifices.\n124. Pit-sand has a rougher and more angular grain than\nriver or sea sand ; and, on this account, is generally prefer-\nred by builders for mortars used for brick, or stone-work.\nWhether it forms a stronger mortar than the other two is not\npositively settled, although some experiments would lead to\nthe conclusion that it does.\n125. River and sea sand are by some preferred for plaster-\ning, because they are whiter, and have a finer and more uni-\nform grain than pit sand ; but as the sands from the shores of\ntidal waters contain salts, they should not be used, owing to\ntheir hygrometric properties, before the salts are dissolved out\nin fresh water by careful washing.\n126. Pit sand is seldom obtained free from a mixture of\ndirt, or clay ; and these, when found in any notable quantity\nin it, give a weak and bad mortar. Earthy sands should,\ntherefore, be cleansed from dirt before using them for mor-\ntar ; this may be effected by washing the sand in shallow vats,\nand allowing the turbid water, in which the clay, dust and\nother like impurities are held in suspension, to run off.\n127. Sand, when pure or well cleansed, may be known by\nnot soiling the fingers when rubbed between them.\n128. Hydraulic mortar. This material may be made\nfrom the natural hydraulic limes ; from those which are pre-\npared by M. Vicat's process ; or from a mixture of common\nor feebly hydraulic lime with a natural or artificial puzzolana.\nAll writers, however, agree that it is better to use a natural\nDigitized by Google\nMORTAR.\n49\nthan an artificial hydraulic lime, when the former can be\nreadily procured.\n129. When the lime used is strongly hydraulic, M. Vicat is\nof opinion that sand alone should be used with it, to form\na good hydraulic mortar. General Treussart has drawn the\nconclusion, from his experiments, that the mortar of all hy-\ndraulic limes is improved by an addition of a natural or arti-\nficial puzzolana. The quantity of sand used may vary from\n11 to 2 parts of the lime in bulk, when reduced to a thick\npulp.\n130. The practice of the United States Corps of Engineers,\nin the construction of heavy masonry, has been to add from\n2.5 to 3.5, in bulk, of compact sand to one of lime of a thick\npaste in the composition of their hydraulic mortars ; and it\nhas been found that an equal bulk of common lime in paste\ncan be mixed with hydraulic cement paste without occasion-\ning any material diminution in the strength of the resulting\nmortar.\n131. For hydraulic mortars, made of common, feeble, or or-\ndinary hydraulic limes, and artificial puzzolana, M. Vicat\nstates that the puzzolana should be the weaker as the lime is\nmore strongly hydraulic; using, for example, a very ener-\ngetic puzzolana with a fat or a feebly hydraulic lime. The\nproportion of sand which can be incorporated with these in-\ngredients, to form an hydraulic mortar, is stated by General\nTreussart to be one volume to one of puzzolana, and one of\nlime in paste.\n132. In proportioning the ingredients, the object to which\nthe mortar is to be applied should be regarded. When it is\nto serve to unite stone, or brick work, it is better that the hy-\ndraulic lime should be rather in excess: when it is used as a\nmatrix for beton, no more lime should be used than is strictly\nrequired. No harm will arise from an excess of good hydrau-\nlic lime, in any case; but an excess of common lime is injuri-\nous to the quality of the mortar.\n133. Common and ordinary hydraulic limes, when made\ninto mortar with arènes, give a good material for hydraulic\npurposes. The proportions in which these have been found\nto succeed well, are one of lime to three of arènes.\n134. Hydraulic cement, from the promptitude with which\nit hardens, both in the air and under water, is an invalu-\nable material where this property is essential. Any dose of\nsand injures its properties as a cement. But hydraulic ce-\nment may be added with decided advantage to a mortar of\ncommon, or of feebly hydraulic lime and sand. It is in this\n4\nDigitized by\nGoogle\n50\nCIVIL ENGINEERING.\nway that it is generally used in our public works. The French\nengineers give the preference to a good hydraulic mortar over\nhydraulic cement, both for uniting stone, or brick work, and\nfor plastering. They find, from their practice, that when\nused as a stucco, it does not withstand well the effects of\nweather; that it swells and cracks in time; and, when laid on\nin successive coats, that they become detached from each\nother.\nGeneral Pasley, who has paid great attention to the pro-\nperties of natural and artificial hydraulic cements, does not\nagree with the French engineers in his conclusions. He states\nthat, when skilfully applied, hydraulic cement is superior to\nany hydraulic mortar for masonry, but that it must be used\nonly in thin joints, and when applied as a stucco, that it\nshould be laid on in but one coat; or, if it be laid on in two,\nthe second must be added long before the first has set, so that,\nin fact, the two make but one coat. By attending to these\nprecautions, General Pasley states that a stucco of hydraulic\ncement and sand will withstand perfectly the effects of frost.\n135. Mortars exposed to weather.-The French engi-\nneers, who have paid great attention to the subject of mortars,\ncoincide in the opinion, that a mortar cannot be made of fat\nlime and any inert sands, like those of the silicious, or calca-\nreous kinds, which will withstand the ordinary exposure of\nweather; and that, to obtain a good mortar for this purpose,\neither the hydraulic limes mixed with sand must be employed,\nor else common lime mixed either with arènes, or with a puz-\nzolana and sand.\n136. Any pure sand, mixed in proper proportions with hy-\ndraulic lime, will give a good mortar for the open air; but\nthe hardness of the mortar will be affected by the size of the\ngrain, particularly when hydraulic lime is used. Fine sand\nyields the best mortar with good hydraulic lime; mixed sand\nwith the feebly hydraulic limes; and coarse sand with fat\nlime.\n137. For mortar to be used for filling the exterior of the\njoints, or as it is termed, for pointing, the amount of lime paste\nin bulk should be but slightly greater than that of the void\nspaces of grains of sand. The bulk of sand for this purpose\nshould be from 2.5 to 2.75 that of the lime paste.\n138. The proportion which the lime should bear to the\nsand seems to depend, in some measure, on the manner in\nwhich the lime is slaked. M. Vicat states, that the strength\nof mortar made of a stiff paste of fat lime, slaked in the ordi-\nnary way, increases from 0.50 to 2.40 to one of the paste in\nDigitized by Google\nMORTAR.\n51\nvolume; and that, when the lime is slaked by immersion, one\nvolume of the like paste will give a mortar that increases in\nstrength from 0.50 to 2.20 parts of sand.\nFor one volume of a paste of hydraulic lime, slaked in the\nordinary way, the strength of the mortar increases from 0 to\n1.80 parts of sand; and, when slaked by immersion, the mor-\ntar of a like paste increases in strength from 0 to 1.70 parts\nof sand. In every case, when the dose of sand was increased\nbeyond these proportions, the strength of the resulting mortar\nwas found to decrease.\n139. Manipulations of mortar.-The quality of hydrau-\nlic mortar, which is to be immersed in water, is more affected\nby the manner in which the lime is slaked, and the ingredients\nmixed, than that of mortar which is to be exposed to the\nweather; although in both cases the increase of strength, by\nthe best manipulations, is sufficient to make a study of them\na matter of some consequence.\n140. The results obtained from the ordinary method of\nslaking, by sprinkling, or by immersion, in the case of good\nhydraulic limes, are nearly the same. Spontaneous, or air-\nslaking, gives invariably the worst results. For common and\nslightly hydraulic lime, M. Vicat states that air-slaking yields\nthe best results, and ordinary slaking the worst.\n141. The ingredients of mortar are incorporated either by\nmanual labor, or by machinery: the latter method gives results\nsuperior to the former. The machines commonly used for mix-\ning mortar are either the ordinary pug-mill (Fig. 12) employed\nby brickmakers for tempering clay, or a grinding-mill (Fig. 13).\nThe grinding-mill is the best machine, because it not only re-\nduces the lumps, which are found in the most carefully burnt\nstone, after the slaking is apparently complete, but it brings the\nlime to the state of a uniform stiff paste, which it should re-\nceive before the sand is incorporated with it. The same\nshould be done with respect to the addition of cement, or of\nan alkaline silicate to the lime paste, the former in powder,\nand the latter in solution, being uniformly sprinkled over the\nsurface and then thoroughly incorporated with the other ma-\nterials by the action of the mill. Care should be taken not\nto add too much water, particularly when the mortar is to be\nimmersed in water. The mortar-mill, on this account, should\nbe sheltered from rain; and the quantity of water with which\nit is supplied may vary with the state of the weather. Noth-\ning seems to be gained by carrying the process of mixing be-\nyond obtaining a uniform mass of the consistence of plastic\nclay. Mortars of hydraulic lime are injured by long expo-\nDigitized by Google\n52\nCIVIL ENGINEERING.\nsure to the air, and frequent turnings and mixings with a\nshovel or spade; those of common lime, under like circum-\nD\nF\nFig. 18 represents a vertical section through\nthe axis of a pug-mill, for mixing or tem-\npering mortar. This mill consists of a\nhooped vessel, of the form of a conical\nfrustum, which receives the ingredients,\nand a vertical shaft, to which arms with\nteeth, resembling an ordinary rake, are\nC\nattached, for the purpose of mixing the\ningredients.\nB\nA, A, section of sides of the vessel.\nA\nB, vertical shaft to which the arms o are of-\nfixed.\nD, horisontal bar for giving a circular mo-\nC\ntion to the shaft B.\nE, sills of timber supporting the mill.\nC\nB, wrought-iron support through which the\nupper part of the shaft passes.\nE\nE\nstances seem to be improved. Mortar which has been set\naside for a day or two, will become sensibly firmer; if not\nFig. 18 represents a part of a mill for crushing the lime\nA\nand tempering the mortar.\nA, heavy wheel of timber, or cast iron.\nB\nB, horizontal bar passing through the wheel, which at\none extremity is fixed to a vertical shaft, and is ar-\nranged at the other (C) with the proper gearing for\nC\na horse.\nD, a circular trough, with a trapezoidal cross section\nD\nwhich receives the ingredients to be mixed. The\ntrough may be from 20 to 80 feet in diameter; about\n18 inches wide at top, and 12 inches deep; and be\nbuilt of hard brick, stone, or timber laid on a firm\nfoundation.\nallowed to stand too long, it may be again reduced to its\nclayey consistence, by simply pounding it with a beetle, with-\nout any fresh addition of water.\nFort Warren Mortar Mill.-This mill (Fig. 14) which\nwas used by Col. Thayer in the construction of Fort Warren,\nBoston Harbor, consists of a circular trough, built of brick,\nwhich was fifteen feet in diameter, measured between the\ncentre line of the trough, the cross section of which (A) was\nthirty-three inches in width at the top, thirteen inches at the\nDigitized by Google\nMORTAR.\n53\nbottom, and twenty-four inches deep. The brick side-walls\n(A) twelve inches thick at top, and built vertically on the in-\nterior and outside, rested on an annular trench of concrete,\nD\nE\nF\nC\nC\nC\nA\nA\nB\nFig. 14. Section through the axis of the Fort Warren Mortar MIN.\nA, Annular trough for mixing the mortar.\nA, Brick sides of trough.\nB, Central brick cylinder.\nC, Annular space for holding lime in paste.\nD, Wheel of mill.\nE, Shaft worked by horse power.\nF, Wooden trough for conveying lime paste to C.\nG, Horse track.\none foot thick, which was laid on an annular bed of broken\nstone, two feet thick, for drainage.\nIn the centre of the circle enclosed by the trough, a verti-\ncal post, surrounded with broken stone, encased by a brick\ncylinder (B) has a gudgeon at top, around which the horizon-\ntal shaft (E) turns, that gives motion to the wheel (D) for\nmixing the mortar.\nThe wheel (D) is made of wood on the sides and periphery,\nand has an iron tire twelve inches broad and half an inch\nthick; the interior being filled with sand to give it sufficient\nweight to grind any lumps in the lime to a paste. The diam-\neter of the wheel is eight feet, and thickness eight inches.\nThe radius of the horse track for working the wheel is\ntwenty feet.\nThe annular space between the trough and the brick cylin-\nder in the centre is floored with concrete, resting on a bed of\nbroken stone.\nLieut. W. H. Wright, in his Treatise on Mortars, thus de-\nscribes the use made of this annular ring: \"The space be-\ntween the cylinder and trough is used as a reservoir for the\nslaked lime. It is conveniently divided by means of movable\nradial partitions into sixteen equal parts,\" each containing the\nsixteenth part of a cask of lime in paste.\nA wooden trough (F) leads from the reservoir where the\nDigitized by Google .\n54\nCIVIL ENGINEERING.\nlime is slaked and converted into a creamy consistence, to the\nannular ring (C), where it is allowed to stand as long as pos-\nsible before being thrown, with the requisite quantity of\n[sand, into the mill.\nThe malaxator.-Many advantages are claimed for a mill\ndesigned by M. Coignet, recently introduced in France, and\nemployed in mixing béton aggloméré for the works in and\nabout Paris. It is called a malaxator, and consists of twin\nscrews, having their helices interlocked, and turning and ex-\nerting their force in the same direction. This machine may\nbe described as follows :\nFig. 15.\nB\nm\nA\nD\nA\n9\nK\n0\nF\nD\nR\nS\nT\n5\nt\nR'\nH\nA is the frame of the machine, having at the upper end the\ncross-pieces B, upon which are mounted the gearings, and at\nthe lower part the cross-piece cc', upon which are fixed the\nrests or steps for the lower part of the helices to run in.\nD are the cores of the helices, upon which are fastened\neither continuous or interrupted blades S S S, forming the\nthread of the helix. Continuous blades are more generally\nused.\nK are wagon-wheels, mounted on an axle, which enable the\nmachine to be transported thereon, and which, when the ma-\nchine is in use, serve to maintain the malaxator at its proper\nDigitized by Google\nMORTAR.\n55\ninclination (about twenty-five degrees). The brace J is used\nto steady the malaxator.\nM N m N', gearings of any kind for giving motion to the\nhelices, either by steam, horse-power, or hand-power q, coni-\ncal sleeves or stoppers, adjustable upon the shafts D, for re-\ngulating the exodus of the artificial stone paste, and by re-\ntarding the same, increasing the pressure and malaxation of\nthe paste in the part Q' of the machine.\nQ, body of the malaxator, corresponding in shape and size\nto the helices.\nP, receiving chamber, where the materials enter the mal-\naxator.\nT, sand hopper, with its adjustable register or gate t, and,\nwhen required, a sifting apparatus; q', sliding gate, to allow\nof the drainage of the machine.\nS' S', feeding screws, working in the lower part of the two\nhoppers R' R', the one for lime, the other for sand, or any\nother material or substance to be introduced into the artificial\nstone paste, and feeding the same to the chamber P;\nr r' r\" r\", pulleys, for chains or belts g, for transmitting the\nmovement to the feeding screws S' S'; t' t\", spur-wheel\nand pinion (changeable for others of different relative speed),\nfor regulating the exact amount of the two substances in the\nhoppers R' R', to be delivered, in so many turns of the\nhelices, into the receiving chamber P.\nZ is a pipe for supplying the water, for which there is an\noverflow at W. The sand being drowned or fully saturated\nin a given proportion, by varying the overflow W, gives the\nproper amount of water for each turn of the helices.\nH are movable wooden shafts, which are placed in proper\nstraps in the machine, and serve to hitch or harness a horse to\nthe same when it has to be taken from one place to another,\nmaking it a perfect wagon.\nThe advantages claimed for the malaxator are the following:\nFirst. The apparatus, having the receiving chamber P upon\nthe ground, is fed easily, with little labor and the part Q',\nor delivery, being elevated, allows of a wheelbarrow or basket\nbeing placed under to receive the artificial stone paste. This\ninclination also causes a more powerful malaxation, by retard-\ning the progress of the matter, owing to the specific gravity.\nSecond. The gearings are out of the way, away from sand,\nwater, dust, etc.\nThird. The helices having their blades interlaid, their\naction upon the materials is of quite a different character than\nwhen said helices are not thus conjugated.\nDigitized by Google\n56\nCIVIL ENGINEERING.\nFourth. The sand is gauged by a register. The lime and\nthe hydraulic cement, the coloring matter, texture giver, or\nany other material used, may be also fed automically, and the\nmachine once set by the inspector, the product is invariably\nthe same, besides saving the labor of a hand whose trustwor-\nthiness is required to obtain good results. The continuous in-\ntroduction by small and regular quantities of the different\nD\nQ\nc\nd\nE\nE\nd\nb\nG\ne\nH\ng\nH\nN\nP\nP\nF\nc\nFig. 16 represents a vertical section of the\nA, A. vertical guides for movable band.\nmixing cylinder for beton coignet.\nE, E, short stationary arms.\na, side of cylinder.\nG, G, movable band.\nb, cast iron base.\nH, H, handles for lifting band.\nc, vertical shaft.\nI, supply trough.\nd, d, curved arms.\nL, scraper.\n6, e, helicoidal blades.\nN, revolving horizontal plate.\nJ.J. cycloidal arms.\nP, immovable bottom plate.\ng, horizontal opening at the base.\nsubstances, and the constant amount of the water supplied to\nthe sand, place the materials in the best circumstances for\nproducing, by proper action of the helices, an excellent result,\nDigitized by Google\nMORTAR.\n57\ndifficult to obtain if the component ingredients had been\nthrown in by shovel or basketfuls at a time. (See Profes-\nsional Papers, Corps of Engineers, No. 19).\nAnother form of mill, which is shown in Fig. 16, has been\nmade use of in France for mixing certain kinds of beton. It\nconsists of a vertical cylinder a resting on a cylindrical base\nof cast iron b. A vertical shaft c passes through the cylinder,\nhaving attached to it curved arins d, which, by revolving\nhorizontally, serve to mix the sand and lime. The distributor\nQ revolves horizontally, receives the sand and lime which come\nfrom the conducting trough I, and distributes them equally\naround for mixing. Short stationary arms E E are attached\nto the side of the cylinder, and form, with the movable arms,\nbreaks for dashing and mixing the sand and lime. Three\nhelicoidal blades e e, attached to the lower part of the shaft,\nforce the mixture downwards and outwards. Cycloidal arms\nff, revolving horizontally near the floor of the cylinder, expel\nthe mixture at the side opening around the bottom. A mova-\nble band of iron G G, by being moved up or down, enlarges\nor diminishes the opening around the bottom. h h, vertical\nguiding shafts for movable band. H H, handles by which\nthe band G G is moved. A plate N is attached to c and re-\nvolves horizontally, receiving the mixture from the cylinder.\nA curved plate of iron L, fixed to immovable bottom-plate P,\nscrapes mixture from N as it revolves.\n143. Setting and durability of mortars. Mortar of\ncommon lime, without any addition of puzzolana, will not setin\nhumid situations, like the foundations of edifices, until after a\nvery long lapse of time. They set very soon when exposed\nto the air, or to an atmosphere of carbonic acid gas. If, after\nhaving become hard in the open air, they are placed under\nwater, they in time lose their cohesion and fall to pieces.\n144. Common mortars, which have had time to harden,\nresist the action of severe frosts very well, if they are made\nrather poor, or with an excess of sand. The sand should be\nover 2.40 parts, in bulk, to one volume of the lime in paste\nand coarse sand is found to give better results than fine sand.\n145. Good hydraulic mortars set equally well in damp\nsituations, and in the open air; and those which have hard-\nened in the air will retain their hardness when immersed in\nwater. They also resist well the action of frost, if they have\nhad time to set before exposure to it; but, like common mortars,\nthey require to be made with an excess of sand, to withstand\nwell atmospheric changes.\n146. The surface of a mass of hydraulic mortar, whether\nDigitized by Google\n58\nCIVIL ENGINEERING.\nmade of a natural hydraulic lime or otherwise, when im-\nmersed in water, becomes more or less degraded by the action\nof the water upon the lime, particularly in a current. When\nthe water is stagnant, a very thin crust of carbonate of lime\nforms on the surface of the mass, owing to the absorption by\nthe lime of the carbonic acid gas in the water. This crust,\nif the water be not agitated, will preserve the soft mortar\nbeneath it from the farther action of the water, until it has\nhad time to become hard, when the water will no longer act\nupon the lime in any perceptible degree.\n147. Hydraulic mortars set with more or less promptness,\naccording to the character of the hydraulic lime, or of the\npuzzolana which enters into their composition. Artificial hy-\ndraulic mortars, with an excess of lime, set more slowly than\nwhen the lime is in a just proportion to the other ingredients.\n148. The quick-setting hydraulic limes are said to furnish\na mortar which, in time, acquires neither as much strength\nnor hardness as that from the slower-setting hydraulic limes.\nArtificial hydraulic mortars, on the contrary, which set quick-\nly gain, in time, more strength and hardness than those which\nset slowly.\n149. The time in which hydraulic mortars, immersed in\nwater, attain their greatest hardness, is not well ascertained.\nMortars made of strong hydraulic limes do not show any\nappreciable increase of hardness after the second year of\ntheir immersion; while the best artificial hydraulic mortars\ncontinue to harden, in a sensible degree, during the third year\nafter their immersion.\n150. It is found from experience that those mortars which\nattain the highest degree of hardness on the surface, absorb\nthe least amount of water and are less liable to injury from\nfrost and weather.\n151. Theory of Mortars. The paste of a hydrate, either\nof common or of hydraulic lime, when exposed to the air, ab-\nsorbs carbonic acid gas from it; passes to the state of sub-\ncarbonate of lime; without, however, rejecting the water of\nthe hydrate, and gradually hardens. The time required for\nthe complete saturation of the mass exposed, will depend on\nits bulk. The absorption of the gas commences at the surface\nand proceeds more slowly towards the centre. The harden-\ning of mortars exposed to the atmosphere is generally attrib-\nuted to this absorption of the gas, as no chemical action of\nlime upon quartzose sand, which is the usual kind employed\nfor mortars, has hitherto been detected by the most careful\nexperiments.\nDigitized by Google.\nCONCRETE.\n59\nThe depth to which the absorption of carbonic acid ex-\ntends in hydraulic lime, and also in some degree the hardening,\ndecreases as the hydraulic energy caused by the silica that\nenters into their composition is the greater.\n152. With regard to hydraulic mortars, it is difficult to ac-\ncount for their hardening, except upon the effect which the\nsilicate of lime may have upon the excess of simple hydrate\nof uncombined lime contained in the mass. M. Petot sup-\nposes, that the particles of silicate of lime form so many\ncentres, around which the uncombined hydrates group them-\nselves in a crystalline form; becoming thus sufficiently hard\nto resist the solvent action of water. With respect to the\naction of quartzose sand in hydraulic mortars, M. Petot\nthinks that the grains produce the same mechanical effect as\nthe particles of the silicate of lime, in inducing the aggrega-\ntion of the uncombined hydrate.\nV.\nCONCRETE. BETON.\n153. This term is applied, by English architects and engi-\nneers, to a mortar of finely-pulverized quick-lime, sand, and\ngravel. These materials are first thoroughly mixed in a dry\nstate, sufficient water is added to bring the mass to the ordi-\nnary consistence of mortar, and it is then rapidly worked up\nby a shovel, or else passed through a pug-mill. The concrete\nis used immediately after the materials are well incorporated,\nand while the mass is hot.\n154. The materials for concrete are compounded in various\nproportions. The most approved are those in which the lime\nand sand are in the proper proportions to form a good mortar,\nand the gravel is twice the bulk of the sand. The gravel\nused should be clean, and any pebbles contained in it larger\nthan an egg, should be broken up before the materials are\nincorporated.\n155. Hot water has in some cases been used in making\nconcrete. It causes the mass to set more rapidly, but is not\notherwise of any advantage.\nDigitized by Google\n60\nCIVIL ENGINEERING.\n156. The bulk of a mass of concrete, when first made, is\nfound to be about one-fifth less than the total bulk of the dry\nmaterials. But, as the lime slakes, the mass of concrete is\nfound to expand about three eighths of an inch in height, for\nevery foot of the mass in depth.\n157. The use of concrete is at present mostly restricted to\nforming a solid bed, in bad soils, for the foundations of edi-\nfices. It has also been used to form blocks of artificial stone,\nfor the walls of buildings and other like purposes; but ex-\nperience has shown that it possesses neither the durability\nnor strength requisite for structures of a permanent character,\nwhen exposed to the action of water, or of the weather.\n158. BETON. The term béton is applied, by French\nengineers, to any mixture of hydraulic mortar with fragments\nof brick, stone, or gravel; and it is now also used by English\nengineers in the same sense.\n159. The proportions of the ingredients used for béton are\nvariously stated by different authors. The sole object for\nwhich the gravel, or the broken stone is used, being to obtain\na more economical material than a like mass of hydraulic\nmortar alone would yield, the quantity of broken stone should\nbe as great as can be thoroughly united by the mortar. The\nsmallest amount of mortar, therefore, that can be used for\nthis purpose, will be that which will be just equal in volume\nto the void spaces in any given bulk of the broken stone, or\ngravel. The proportion which the volume occupied by the\nvoid spaces bears to any bulk of a loose material, like broken\nstone, or gravel, may be readily ascertained by filling a vessel\nof known capacity with the loose material, and pouring in as\nmuch water as the vessel will contain. The volume of water\nthus found, will be the same as that of the void spaces.\nBéton made of mortar and broken stone, in which the pro-\nportions of the ingredients were ascertained by the process\njust detailed, has been found to give satisfactory results; but,\nin order to obviate any defect arising from imperfect manip-\nulation, it is usual to add an excess of mortar above that of\nthe void spaces.\n160. In a large amount of concrete used for the foundation\nbed and backing of the sea walls built for the protection of\nthe islands in Boston Harbor, which was composed of hydrau-\nlic mortar made with salt water and the common shingle of\nthe shores, which varied in size from that of a pea to pebbles\nof six inches in diameter, the proportions used for the foun-\ndation bed was about one part in volume of stiff mortar to three\nDigitized\nby\nGoogle\nCONCRETE.\n61\nparts in volume of shingle for the foundation bed, and two\nand seven-tenths parts for the backing of the walls. The\nsmall and large pebbles of the shingle were so proportioned\nas to give the least amount of void space to be filled by the\nmortar; this void space being from twenty to twenty-five per\ncent. of the volume of shingle.\nThe materials were mixed by hand ; the shingle first being\nspread out upon a platform of rough boards to the depth of\nfrom eight to twelve inches, the larger pebbles on top the\nmortar was spread in a layer of uniform thickness over this,\nand the whole worked up with shovels and hoes until\nthoroughly incorporated.-(Papers on Practical Engineering,\nNo. 2. Report of Col. S. Thayer, U.S. Corps of Engineers.)\nIn the hydraulic concrete used upon some others of our\npublic works, the broken fragments of granite were in bulk\nabout 14 that of the hydraulic mortar. Besides this, other\nfragments, from a quarter to three-quarters of a cubic foot each,\nand forming about one-twelfth of the volume of the concrete,\nwere worked into the layer as they were carried up. This\npractice is a very usual one for foundation beds, as it effects a\nsaving of cost.\nThe best and most economical béton is made of a mixture\nof broken stone, or brick, in fragments not larger than a\nhen's egg, and of coarse and fine gravel mixed in suitable\nproportions.\nIn making béton, the mortar is first prepared, and then in-\ncorporated with the finer gravel; the resulting mixture is\nspread out into a cake, 4 or 6 inches in thickness, over which\nthe coarser gravel and broken stone are uniformly strewed\nand pressed down, the whole mass being finally brought to a\nhomogeneous state with the hoe and shovel.\nBéton is used for the same purposes as concrete, to which\nit is superior in every respect, but particularly so for foun-\ndations laid under water, or in humid localities.\n161. Béton made of small fragments of stone or pebbles\nhas within recent years been applied to the construction of the\nwalls of houses. For this purpose, the concrete is laid up in\nlayers and rammed within a plank boxing having an interior\nwidth equal to the thickness of wall. The sides of the boxing\nare confined by vertical posts which can be suitably adjusted\nto the required thickness of the wall ; the whole being sup-\nported by a suitable scaffolding. In the case of hollow walls,\na slip of board of the thickness of the required hollow, or\nvoid, and slightly wedge-shaped to admit of its being easily\nremoved, is laid horizontally within the box, and the layer of\nDigitized by\nGoogle\n62\nCIVIL ENGINEERING.\nconcrete rammed well in around it; ordinary brick being in-\nserted as ties to connect the interior and exterior portions of\nthe wall.\nIn the sewers and many public and private edifices recently\nconstructed in Paris of concrete, the proportions used were\none part in volume of lime, one fourth of one volume of\nhydraulic cement, to five volumes of sand. It is stated that in\nsix or eight hours after beginning a given length of sewer the\ncentres can be safely removed and that, in four or five days\nafter a section has been completed, it can be opened for use.\nFor the construction of arches, the volume of cement used is\ndoubled.\nSome of the buildings above referred to were constructed\nwith groined or cylindrical arched fire-proof floors, of spans\nfrom nine to twenty-eight feet, the rise in each case being one\ntenth of the span; the thickness of the arches, at the crown,\nvarying from five and a half to fourteen inches.\nThe crushing weight of this concrete is nearly fifty-four\nhundred pounds to the square inch the tenacity about five\nhundred pounds.\n162. An artificial sandstone, termed Béton-Coignet from\nthe inventor, is very extensively manufactured and used in\nFrance for all building purposes, as foundations, walls, light\narches, etc. It sets and hardens in a comparatively short time.\nIts constituents are clean river sand from four to five parts in\nvolume; common or hydraulic lime one part in volume\nhydraulic or artificial Portland cement from one-quarter to\nthree-quarters of one part in volume; water variable, but only\nenough to moisten the other materials and cause them to\ncohere. Coarse sand from one-twentieth to three-twentieths\nof an inch in diameter is said to give the best results; the\nfiner sands requiring more care in the preparation of the\nconcrete and in packing it when laid to secure greater so-\nlidity.\n163. In preparing the concrete the lime and sand are made\ninto heaps of about one cubic yard in volume in alternate\nlayers of the two ingredients. Each heap is then worked up\ndry with the shovel. In this state it is delivered by suitable\nmachinery, like that for raising grain, into the top of a pug-\nmill of a cylindrical body formed of boiler iron. The revolv-\ning vertical shaft of the mill, which is driven by steam or\nanimal power, has curved arms affixed horizontally to it, the\ntwo lower arms being of suitable forms to press the mixed\nmaterial downwards, and expel it through an aperture, where\nit is received into boxes, or hand barrows, and conveyed to\nDigitized by\nGoogle\nCONCRETE.\n63\nwhere it is to be laid or moulded. The water for the mixing\nis either thrown in as needed, by hand into the top of the\nmill, or else supplied by a circular trough perforated with\nholes, which is placed around the inside of the mill at top.\nWhen cement is one of the ingredients, it is first made into a\nsuitable paste with water, and then added to the others, from\na vessel over the top of the mill, from which it is poured in a\nuniform manner, and in the requisite amount.\n164. For all ordinary work, one passage through the pug-\nmill is sufficient, but where greater thoroughness in the mix-\nture is a requisite, the concrete may be passed through the\nmill a second time.\n165. The concrete when laid or moulded is put in in suc-\ncessive layers, from one to three inches in thickness, and\npacked moderately by hand with pestles weighing from fif-\nteen to thirty pounds.\n166. To increase the rapidity of the setting, when necessary,\nthe materials may be heated, in process of mixing, by a spi-\nral tube or worm, through which heated air, steam, or hot\nwater is caused to circulate.\n167. Among other artificial conglomerates, that known as\nRansome's artificial stone, from the name of the inventor, is\nnow coming into use in England. This material consists of\nclean river sand the grains of which are cemented with the\nsilicate of lime. To effect this union a silicate of soda is\nformed, by digesting common flints in a solution of caustic\nsoda, in iron air-tight cylindrical vessels, by means of steam,\nunder a pressure of seventy pounds, which circulates through\na coil of iron pipes. The sand, after being thoroughly dried,\nis mixed with a sufficient volume of finely ground carbonate\nof lime to fill the voids between the grains. To each bushel\nof this mixture a gallon of the silicate is added, and the\nwhole thoroughly mixed in a loam mill. The mixture is then\nmoulded, and immediately after the solution of the chloride\nof calcium is thrown over it with ladles; the moulded blocks\nare then immersed in the solution, in open tanks, which is\nkept boiling, by steam passed through it in pipes, for several\nhours, according to the size of the blocks. This process ex-\npels any air that may have been retained in the blocks and\nfacilitates the forming of the silicate of calcium. The block\nis then taken out and the chloride of sodium, that has been\nformed, thoroughly washed out with fresh water poured over\nthe block.\nThis artificial stone is found to be very hard, and some\nspecimens to have offered as great a resistance to rupture, by\nDigitized by\nGoogle\n64\nCIVIL ENGINEERING.\ncompression and extension, as the best sandstones and mar-\nbles.\n168. General Gillmore in his Report, Professional Papers,\nCorps of Engineers, No. 19, gives the following account of\nbéton-Coignet or aggloméré.\nBeton Agglomere. This name is given to a béton of\nvery superior quality, or, more properly speaking, an artificial\nstone of great strength and hardness, which has resulted from\nthe experiments and researches, extending through many\nyears, of M. François Coignet, of Paris.\nThe essential conditions which must be carefully observed\nin making this béton are as follows:\nFirst. Only materials of the first excellence of their kind,\nwhether common or hydraulic lime, or hydraulic cement, can\nbe used for the matrix.\nSecond. The quantity of water must not exceed what is\nbarely sufficient to convert the matrix into a stiff, viscous paste.\nThird. The matrix must be incorporated with the solid\ningredients by a thorough and prolonged mixing or trituration,\nproducing an artificial stone paste, decidedly incoherent in\ncharacter until compacted by pressure, in which every grain\nof sand and gravel is completely coated with a thin film of\nthe paste. There must be no excess of paste when the matrix\nis common lime alone. With hydraulic lime this precaution\nis less important, and with good cement it is unnecessary.\nFourth. The béton or artificial stone is formed by thorough-\nly ramming the stone paste, in thin, successive layers, with\niron-shod rammers.\n169. The materials employed in making his béton are\nsand, common lime, hydraulic lime, and Portland cement.\nThe sand should be as clean as that ordinarily required for\nmortar, for stone or brick masonry of good quality. Sand\ncontaining 5 or 6 per cent. of clay may be used without\nwashing, for common work, by proportionally increasing the\namount of matrix. Either fine or coarse sand will answer,\nor, preferably, a mixture of both, containing gravel as large\nas a small pea, and even a small proportion of pebbles as\nlarge as a hazel nut. There is an advantage in mixing\nseveral sizes together, in such proportion as shall reduce the\nvolume of voids to a minimum. Coarse sand makes a harder\nand stronger béton than fine sand. The extremes to be\navoided are a too minute subdivision and weakening of the\nmatrix, by the use of fine sand only, on the one hand, and an\nundue enlargement of the volume of voids, by the exclusive\nuse of coarse sand, on the other.\nDigitized by\nGoogle\nCONCRETE.\n65\nThe silicions sands are considered the best, though all\nkinds are employed. When special results are desired in the\nway of strength, texture, or color, the sand should be selected\naccordingly.\n170. The common lime should be air-slaked, or, better\nstill, it may be slaked by aspersion with the minimum\nquantity of water that will reduce it to an impalpable pow-\nder. It should be passed through a fine wire screen to\nexclude all lumps, and used within a day or two after\nslaking, or else kept in boxes or barrels protected from 'the\natmosphere.\nIt is scarcely practicable, under ordinary circumstances,\nto employ fat lime alone as the matrix of béton aggloméré,\nparticularly in monolithic constructions, in consequence of its\ntardy induration. Even when used in combination with\nhydraulic lime or cement it acts as a diluent.\n171. Attempts to make béton of even average quality,\nwithout good hydraulic ingredients, have failed in the United\nStates; and it is extremely doubtful whether any character-\nistic excellence can be attained, after the lapse of weeks or\neven months, by a mixture of this character.\n172. The most suitable hydraulic limes are those derived\nfrom the argillaceons limestones, in contradistinction to the\nmagnesian or argillo-magnesian varieties. These limestones\ncontain before burning from 15 to 25 per cent.-generally\nless than 20 per cent.-of clay. After burning, the lime is\nslaked to powder by aspersion with water, and sifted to\nexclude unslaked lumps.\nHydraulic lime cannot be considered an essential ingre-\ndient of béton aggloméré, except in comparison with common\nlime. It may be altogether replaced by good hydraulic\ncement, or it may be used alone, or mixed with common lime,\nto the entire exclusion of cement. A stiff paste of this lime\nshould set in the air in from ten to fifteen hours, and\nsustain a wire point one-twenty-fourth of an inch in diameter,\nloaded with one pound, in eighteen to twenty-four hours.\nIts energy, and therefore its value, varies directly with the\namount of clay which it contains, which generally will not\nexceed 20 per cent. before burning, although it may reach 25\nper cent. Beyond this point the burnt stone can seldom be\nreduced by slaking and becomes a cement.\nNo hydraulic lime of this variety has ever been manufac-\ntured in the United States. It is not known that stone suit-\nable for it exists here.\n173. The heavy slow-setting Portland cements, natural or\n5\nDigitized by Google\n66\nCIVIL ENGINEERING.\nartificial, are the only ones suitable for béton aggloméré.\nThey are manufactured extensively throughout Europe.\nThis cement is produced by burning, with a heat of great\nintensity and duration, argillaceous limestones, containing\nfrom 20 to 22 per cent. of clay, or an artificial mixture of\ncarbonate of lime and clay in similar proportions, and then\nreducing the product to fine powder between millstones. In\nthis condition its weight should not fall short of 101 pounds\nand will seldom exceed 128 pounds to the bushel, poured in\nloosely and struck, without being shaken down or compacted.\nBetween these limits additional weight may always be con-\nferred in the burning, by augmenting the intensity and\nduration of the heat; and both the tensile strength, and the\ntime required to set, increase directly with the weight. For\nexample, a Portland cement weighing 100 pounds to the\nUnited States bushel, that will set in half an hour, and sus-\ntain when seven days old a tensile strain of 200 pounds on a\nsectional area of one square inch, would have its time for\nsetting increased to four or five hours, and its tensile strength\nto about 400 pounds, if burnt to weigh 124 pounds to the\nbushel. An increase in weight of 24 pounds to the bushel\nnearly doubles the ultimate tensile strength of Portland\ncement.\nWhen the matrix of béton aggloméré is Portland cement\nalone, it is customary to prolong the process of trituration, in\norder to retard the set; or, if more convenient, the mixture\nmay be passed through the mill twice or even three times,\nwith an interval of an hour or more between each mixing.\nThis course is specially desirable when the cement weighs\nless than 100 hundred pounds to the bushel, and is correspond-\ningly quick-setting.\n174. English engineers generally require that the cement\nshall be ground so fine that at least 90 per cent. of it shall\npass a No. 30 wire sieve, of 36 wires to the lineal inch, and\nshall weigh not less than 106 pounds to the struck bushel,\nwhen loosely poured into the measure. When made into a\nstiff paste without sand, it should be capable of sustaining\nwithout rupture a tensile strain of 400 pounds on a sectional\narea 11 inch square, or 21 square inches (equal to 178\npounds to the sectional square inch), seven days after being\nmoulded the sample being immersed six of these days in\nfresh water.\n175. Experience has repeatedly demonstrated, and they\nhave become well recognized facts, that in order to obtain\nuniformly good béton or artificial stone, with sand, and\nDigitized by Google\nCONCRETE.\n67\neither hydraulic lime or Portland cement, or both, it is neces-\nsary-\nFirst. To regulate, in a systematic manner, the amount of\nwater employed in the manufacture thereof.\nSecond. To obtain, with a minimum quantity of water, the\ncementing material or matrix in a state of plastic or viscous\npaste.\nThird. To cause each grain of sand or gravel to be entire-\nly lubricated with a thin film or coating of this paste; and\nFourth. To bring each and every grain into close and inti-\nmate contact with those which surround it.\nIt is also equally true, that the best results possible to be\nproduced from any given materials will be attained when the\nabove-named conditions are enforced.\n176. It is impossible to produce a cementing material, of\nsuitable quality for béton aggloméré, by the ordinary meth-\nods and machinery used for making mortars; for if we take\nthe powder of hydraulic lime or Portland cement, and add\nthe quantity of water necessary to convert it into a paste by\nthe usual treatment, it will usually contain so much moisture,\neven after being incorporated with the sand, that it cannot be\ncompacted by ramming, but will yield under the repeated\nblows of the rammer like jelly. If the quantity of water be\nreduced to that point which would render the mixture, with\nthe usual treatment, susceptible of being thoroughly compact-\ned by rammers, much of the cementing substance will re-\nmain more or less inert, and will perform but indifferently\nwell the functions of a matrix.\n177. To prepare the matrix, there is taken of the hydrau-\nlic lime or cement powder, say one hundred parts, by meas-\nure, and of water from thirty to thirty-five or forty parts,\nwhich should be the smallest amount that will accomplish\nthe object in view. These are introduced together into a\nsuitable mill, acting upon the materials by both compression\nand friction, and are subjected to a thorough and prolonged\ntrituration, until the result is a plastic, viscous, and sticky\npaste, of a peculiar character, in both its physical appearance\nand the manner in which it comports itself under the subse-\nquent treatment with rammers. There would appear to be\nno mystery in this part of the process, yet the excellence of\nthe béton aggloméré is greatly dependent on its proper\nexecution.\nIf too much water be used, the mixture cannot be suitably\nrammed if too little, it will be deficient in strength.\n178. The sand should be deprived of surplus moisture,\nDigitized by\nGoogle\n68\nCIVIL ENGINEERING.\nalthough it is not necessary that it be absolutely dry. A uni-\nform state of moisture or dryness should be aimed at, in\norder that the proper quantity of water may be added with\ncertainty.\n179. The matrix in paste, and the sand, having been mix-\ned together in the desired proportions (given hereafter), are\nthen introduced into a powerful mill, and subjected to a\nthorough and energetic trituration until, without the addition\nof more water, the paste presents the desired degree of homo-\ngeneity and plasticity.\nWhen, for any special purpose, it is desired to introduce\ninto the mixture a quantity of Portland cement, in order to\nincrease the hardness or the rapidity of induration, it had\nbetter be added during the process of trituration, mixed with the\nrequisite increment of water, SO that after proper mixing the\nwhole material will present the appearance of a short paste,\nor pasty powder, which is quite characteristic of this process\nof manipulation.\nIn ordinary practice, when sand and hydraulic lime only\nare employed, it will be found to answer very well to mix\nthe two together dry, with shovels, and then spread them out\non the floor and sprinkle them with the requisite minimum\namount of water. The dampened mixture is then shoveled\ninto the mill and triturated, as already described.\nWhen a portion of Portland cement is used, it may also be\nincorporated with the other ingredients before the water is\nadded, or introduced into the mixture in the mill, as may be\npreferred.\nWhen Portland alone is used for the matrix, the process is\nthe same as when lime alone is used, except that the tritura-\ntion should be more prolonged, especially if the cement be\nrather light and quick-setting.\nHaving both equally at command, the following propor-\ntions are employed for divers purposes, according to circum-\nstances and the quality of the materials:\nSand. by volume\n6\n5\n4\n5\n5\n4\n4\n5\n5\n5\nHydraulic lime in powder, by\nvolume\n1\n1\n1\n1\n1\n1\n1\n1\n1\n1\nPortland cement in powder, by\nvolume\n0\n0\n0\nt\n1\nt\n+\n1\n1t\n11\nIt will rarely occur that the proportions given in the two\ncolumns on the right of the above table need be used. They\nDigitized by Google\nCONCRETE.\n69\nare suitable for ornamented blocks, requiring removal and\nhandling a day or two after being made.\nIt may sometimes happen that too much water has been\nintroduced in the preparation of the paste. A proper correct-\nive, in such case, is the introduction into the mill of a suitable\nquantity of each of the ingredients, mixed together dry in the\nrequired proportions.\nBy employing none but white sand and the lighter-colored\nvarieties of lime and cement, a stone closely imitating white\nmarble may be made, while, by the introduction of coloring\nmatter into the paste, such as ochres, oxides, carbonates, etc.,\nor fragments of natural stones, any variations in shade or tex-\nture may be produced, from the most delicate buff and drab,\nto the darkest grays and browns.\nIn some cases it may be found more convenient to measure\nthe ingredients directly into the mill, alternating with the\ndifferent materials, in regular order, using for the purpose\nmeasures of various sizes, corresponding with the required\nproportions.\nWhen it is specially desirable to obtain stone of the maxi-\nmum degree of strength and hardness, the paste may be re-\nturned a second or even a third time to the mill, but in all\ncases the mass must be brought to the characteristic state of\nincoherent pasty powder, or short paste.\n180. The materials, after being mixed to a state of pasty\npowder, have to be agglomerated in moulds, in order to become\nbéton or artificial stone. In other words, the grains of sand\nand gravel, each coated all over with a thin film of the matrix\n-entirely exhausting the matrix thereby-have to be brought\ninto close and intimate contact with each other. This is ac-\ncomplished by ramming the paste in thin, successive layers,\nin a mould of the form and dimensions required for the stone,\nand made so as to be capable of sustaining heavy pressure\nfrom within, and of being taken apart at pleasure.\nInto this mould, supposing it to be for a detached building\nblock, and not for monolithic masonry, a quantity of the stone\npaste is thrown with a shovel, and spread out in a layer from\n11 to 2 inches thick. It is then thoroughly compacted by the\nrepeated and systematic blows of an iron-shod rammer, until\nthe stratum of material is reduced to about one-third its origi-\nnal thickness. When this is done, its surface is scratched or\nroughened up with an iron rake, in order to secure a perfect\nbond with the succeeding stratum, and more of the material is\nadded and packed in the same manner. This process is con-\ntinued until the mould is full. The upper surface is then\nDigitized by\nGoogle\n70\nCIVIL ENGINEERING.\nstruck with a straight-edge, and smoothed off with a trowel,\nafter which the full mould may at once be turned over on a\nbed of sand, and the bottom, side, and end pieces removed.\nThe block is then finished. If small, such as one man\ncan handle, it may be safely removed after one day. Larger\npieces, like sills, lintels, steps, platforms, etc., should be allowed\na longer time to harden, in consequence of their greater\nweight.\nIn case of monolithic masonry, the moulds usually consist\nof a series of planks placed one above the other horizontally,\nand supported against exterior uprights, so arranged as to give\nthe required form to the work under construction. These\nplanks are raised up as the wall progresses, so that each day's\nwork shall unite intimately with that of the previous day, pro-\nducing a smooth and even surface, without joints, ridges, or\nmarks of any kind.\nA characteristic property of this stone paste, when prop-\nerly mixed, is that it does not assume a jelly-like motion when\nrammed.\nIts degree of moisture must be precisely such that the effect\nof each blow of the rammer shall be distinct, local, and per-\nmanent, without disturbing the contiguous material compacted\nby previous blows. If it be too moist, the mass will shake\nlike wet clay, and if it be too dry, it will break up around the\nrammer like sand. In either case the materials cannot be\ncompacted and agglomerated in that manner and to that\ndegree which is characteristic of, and peculiar to, béton agglo-\nméré.\nIn monolithic buildings of this béton, it is customary to\nconstruct all the flues, pipes, and other openings for heating\nand ventilating, and for conveying water, gas, and smoke, in\nthe thickness of the wall, by using movable cores of the re-\nquired size and form, around which the material is packed.\nAs the work progresses the cores are moved up.\nOrnamental work of simple design may be placed upon the\nexterior of the building, by attaching the moulds to the plank-\ning which gives form to the wall.\nMore elaborate designs, especially if they are of bold relief,\nlike cornices, and hoods for windows and doors, had better be\nmoulded in detached pieces some days in advance, and hoisted\ninto position when required.\n181. All kinds of masonry in thin walls, whether of brick,\nstone, common concrete, or béton aggloméré, are liable to\ncrack from unequal settlement, or from the expansion and\ncontraction due to ordinary changes of temperature. In\nDigitized\nby\nGoogle\nCONCEETE.\n71\nhouses, such cracks are more to be apprehended at the re-en-\ntering angles of the exterior walls, and at the junctions of the\nexterior and partition walls, than elsewhere. In concrete or\nbéton masonry such cracks may be prevented in a great\nmeasure, without inconvenience and at a nominal cost, by em-\nbedding and incorporating in the work as it progresses,\nat the angles and junctions referred to, pieces of old scrap-\niron of irregular shape, such as bolts, rings, hooks, clamps,\nwire, etc.\nAny masonry of fair quality, constructed in large masses\nwith special reference to inertia, whether to resist the thrusts\nof earthen embankments, the statical pressure of water, the\nforce of the current in running streams, or for any other pur-\npose, possesses a degree of ultimate strength much greater\nthan the usual factor of safety would require, and largely in\nexcess of any strain that it would ever have to sustain. This\nexcess of strength, or rather the material which confers it, may\nbe readily saved in works built of béton aggloméré, by leaving\nlarge hollows or voids in the heart of the wall, and filling them\nup with sand or heavy earth.\nEven if the voids remain unfilled, a hollow wall is more\nstable than a solid one containing the same quantity of ma-\nterial, for the reason that the moments of the forces which\nconfer stability are greater in the former than in the latter.\n182. Durability. The densest mortars that can be pro-\nduced from given materials are the best, and the use of a\nlarge amount of water is incompatible with the condition of\ndensity.\nThe best pointing mortar, indeed, is a béton aggloméré, an-\nswering fully to the description of that material, being pre-\npared with a small proportion of water, and applied by caulk-\ning it into the joints. In northern climates it has to sustain\nthe severest tests to which masonry of any description can be\nexposed; to alternations of cold and heat, moisture and dry-\nness, freezing and thawing.\nBéton aggloméré, when the volume of matrix is so adjsuted\nthat the voids in the sand are completely filled-say in the\nproportion generally of one of the matrix to two and a\nhalf or three of sand-becomes in process of time as imper-\nvious to water as many of the compact natural stones, while\nits matured strength exceeds that of the best qualities of\nsandstone, some of the granites, and many of the limestones\nand marbles.\nChemical tests have shown this béton to be practically im-\npervious to water.\nDigitized\nby\nGoogle\n72\nCIVIL ENGINEERING.\nThis material, therefore, possesses all the characteristic\nproperties of durability, being dense, hard, strong, and homo-\ngeneous; and there would appear to be no reason for suppos-\ning that it may not, with entire safety, be applied to out-door\nconstructions, even in the most northerly portions of the\nUnited States.\nIt is injured by freezing before it has had time to set. Im-\nportant works should not, therefore, be executed during the\nwinter in cold climates.\nThe effect of freezing on newly made béton is to detach a\nthin scale from the exposed surface, producing a rough and\nunsightly appearance; but the injury does not extend into the\nmass of the material, unless the frost be very intense.\nIn monolithic constructions, the plank coffre affords suffi-\ncient protection to the face surfaces of the work against mod-\nerate frost, and, when the temperature ranges generally not\nmuch lower than the freezing point during the day, work\nmay be safely carried on, if care be taken to cover over the\nnew material at night. After it has once set, and has had a\nfew hours to harden, neither severe frost, nor alternate freez-\ning and thawing, has any perceptible effect upon it, and,\nunder any and all circumstances, it is much less liable to\ninjury from these causes, and requires fewer precautions\nfor its protection against them, than common hydraulic con-\ncrete.\nMonolithic constructions in béton aggloméré may advan-\ntageously be carried on whenever it is not too cold to lay first-\nclass brick masonry.\nIn Paris and vicinity operations are not generally suspended\nduring the winter, unless the cold be unusually severe for that\nclimate.\nPieces of statuary, and other specimens ornamented with\ndelicate tracery, have been exposed for five consecutive winters\nto the weather in New York City, without undergoing the\nslightest perceptible change.\nThe power possessed by béton aggloméré of resisting the\nsolvent action of salts (principally the sulphates of magnesia\nand soda) and certain gases contained in sea water, rests upon\nanalogy rather than upon proof based upon adequate experi-\nence and observation.\nEminent European engineers do not hesitate to use Portland\ncement concrete, mixed with a comparatively large dose of\nwater, for very important submarine constructions. The\nmatrix of this concrete possesses less density and strength\nthan that of béton aggloméré, and if the lime be excluded\nDigitized by Google\nCONCRETE.\n73\nfrom the latter, the induration in the two cases would be due\nto precisely the same chemical action. The materials are\nindeed identical in composition under this condition, with the\nexception that there is an excess of water, and consequently\nan element of weakness, in the English concrete, which does\nnot attach to the béton. The durability of the latter in sea\nwater, without being much discussed, has been very generally\nconceded.\nMonolithic constructions under water cannot be executed\nin béton aggloméré, for the reason that the prescribed ram-\nming in thin layers would necessarily have to be omitted, and\nsome other mode of compacting the mixture followed. This\nmaterial, however, when laid green through water, loses its\ndistinct name and character, as well as its superior strength\nand hardness, and becomes common béton or concrete, with\nthe coarser ballast omitted. Its use in this form certainly\noffers no advantages with regard to strength, while in point\nof economy the usual proportions of matrix, sand and shingle,\nor broken stone, is preferable.\n183. Adherence of Mortar. The force with which mor-\ntars in general adhere to other materials, depends on the\nnature of the material, its texture, and the state of the sur-\nface to which the mortar is applied.\n184. Mortar adheres most strongly to brick; and more\nfeebly to wood than to any other material. Among stones,\nits adhesion to limestone is generally greatest; and to basalt\nand sandstones, least. Among stones of the same class, it\nadheres generally better to the porous and coarse-grained,\nthan to the compact and fine-grained. Among surfaces, it\nadheres more strongly to the rough than to the smooth.\n185. The adhesion of common mortar to brick and stone,\nfor the first few years, is greater than the cohesion of its own\nparticles. The force with which hydraulic cement adheres\nto the same materials, is less than that of the cohesion be-\ntween its own particles; and, from some recent experiments\nof Colonel Pasley, on this subject, it would seem that hy-\ndraulic cement adheres with nearly the same force to polished\nsurfaces of stone as to rough surfaces.\n186. From experiments made by Rondelet, on the adhesion\nof common mortar to stone, it appears that it required a force\nvarying from 15 to 30 pounds on the square inch, applied\nperpendicular to the plane of the joint, to separate the mortar\nand stone after six months union whereas only 5 pounds to\nthe square inch was required to separate the same surfaces,\nwhen applied parallel to the plane of the joint.\nDigitized by Google\n74\nCIVIL ENGINEERING.\nFrom experiments made by Colonel Pasley, he concludes\nthat the adhesive force of hydraulic cement to stone, may be\ntaken as high as 125 pounds on the square inch, when the\njoint has had time to harden throughout; but, he remarks,\nthat as in large joints the exterior part of the joint may have\nhardened while the interior still remains soft, it is not safe to\nestimate the adhesive force, in such cases, higher than from\n30 to 40 pounds on the square inch.\nVI.\nMASTICS.\n187. The term Mastic is generally applied to artificial or\nnatural combinations of bituminous or resinous substances\nwith other ingredients. They are converted to various uses\nin constructions, either as cements for other materials, or as\ncoatings, to render them impervious to water.\n188. Bituminous Mastic. The knowledge of this ma-\nterial dates back to an early period; but it is only within,\ncomparatively speaking, a few years that it has come into\ncommon use in Europe and this country. The most usual\nform in which it is now employed, is a combination of min-\neral tar and powdered bituminous limestone.\n189. The localities of each of these substances are very\nnumerous; but they are chiefly brought into the market from\nseveral places in Switzerland and France, where these min-\nerals are found in great abundance ; the most noted being\nVal-de-Travers in Switzerland, and Seyssel in France.\n190. The mineral tar is usually obtained by boiling in\nwater a soft sandstone, called by the French molasse, which\nis strongly impregnated with the tar. In this process, the tar\nis disengaged and rises to the surface of the water, or adheres\nto the sides of the vessel, and the earthy matter remains at\nthe bottom. An analysis of a rich specimen of the Seyssel\nbituminous sandstone gave the following results :-\nBituminous oil\n086\nCarbon\n}\nBitumen\n106\n020\nQuartzy grains\n690\nCalcareous grains\n204\n1.000\nDigitized by\nGoogle\nMASTIOS.\n75\n191. The bituminous limestone which, when reduced to a\npowdered state, is mixed with the mineral tar, is known at the\nlocalities mentioned by the name of asphaltum, an appellation\nwhich is now usually given to the mastic. This limestone oc-\ncurs in the secondary formations, and is found to contain\nvarious proportions of bitumen, varying mostly from 3 to 15\nper cent., with the other ordinary minerals, as argile, etc.,\nwhich are met with in this formation.\n192. The clay contained in asphaltic rock, as it is not im-\npregnated, like the carbonate of lime, with the bitumen, is\nhurtful, causing, at times, the cracks seen in asphaltic pave-\nments.\nSome rocks contain an oily element, like petroleum, which,\nrendering the mastic made from them too fat, must first be\ndistilled out.\n193. The bituminous mastic is prepared from these two\nmaterials by heating the mineral tar in cast-iron or sheet-iron\nboilers, and stirring in the proper proportion of the powdered\nlimestone. This operation, although very simple in its kind,\nrequires great attention and skill on the part of the workmen\nin managing the fire, as the mastic may be injured by too low,\nor too high a degree of heat. The best plan appears to be, to\napply a brisk fire until the boiling liquid commences to give\nout a thin whitish vapor. The fire is then moderated and\nkept at a uniform state, and the powdered stone is gradually\nadded, and mixed in with the tar by stirring the two well to-\ngether. When the temperature has been raised too high, the\nheated mass gives out a yellowish or brownish vapor. In this\nstate it should be stirred rapidly, and be removed at once from\nthe fire.\n194. The asphaltic stone may be reduced to powder, either\nby roasting it in vessels over a fire, or by grinding it down in\nthe ordinary mortar-mill. For roasting, the stone is first re-\nduced to fragments the size of an egg. These fragments are\nput into an iron vessel; heat is applied, and the stone is re-\nduced to powder by stirring it and breaking it up with an\niron instrument. This process is not only less economical than\ngrinding, but the material loses a portion of its tar from\nevaporation, besides being liable to injury from too great a\ndegree of heat. For grinding, the stone is first broken as for\nroasting. Care should be taken, during the process, to stir the\nmass frequently, otherwise it may form into a cake. Cold dry\nweather is the best season for this operation; the stone, how-\never, should not be exposed to the weather.\n195. Owing to the variable quantity of mineral tar in\nDigitized by\nGoogle\n76\nCIVIL ENGINEERING.\nbituminous limestone, the best proportions of the tar and\npowdered stone for bituminous mastic cannot be assigned be-\nforehand. Three or four per cent. too much of tar is said to\nimpair both the durability and tenacity of the mastic; while\ntoo small a quantity is equally prejudicial. Generally, from\neight to ten per cent. of the tar, by weight, has been found to\nyield a favorable result.\n196. Mastics have been formed by mixing vegetable tar,\npitch, and other resinous substances, with litharge, powdered\nbrick, powdered limestone, etc. ; but the results obtained have\ngenerally been inferior to those from bituminous mastic.\n197. Mineral tar is more durable than vegetable tar, and on\nthis account it has been used alone as a coating for other\nmaterials, but not with the same success as mastic. Employed\nin this way the tar in time becomes dry and peels off ; where-\nas, in the form of mastic, the hard matter with which it is\nmixed prevents the evaporation of the oily portion of the tar,\nand thus promotes its durability.\n198. The uses to which bituminous mastic is applied are\ndaily increasing. It has been used for paving in a variety of\nforms either as a cement for large blocks of stone, or as the\nmatrix of a concrete formed of small fragments of stone or\ngravel; as a pointing, it is found to be more serviceable, for\nsome purposes, than hydraulic cement; it forms one of the best\nwater-tight coatings for cisterns, cellars, the cappings of arches,\nterraces, and other similar roofings now in use and is a good\npreservative agent for wood-work exposed to wet or damp.\nVII.\nBRICK.\n199. This material is properly an artificial stone, formed by\nsubmitting common clay, which has undergone suitable pre-\nparation, to a temperature sufficient to convert it into a semi-\nvitrified state.\nBrick may be used for nearly all the purposes to which\nstone is applicable; for when carefully made, its strength, hard-\nness, and durability, are but little inferior to the more ordinary\nkinds of building stone. It remains unchanged under the ex-\ntremes of temperature; resists the action of water; sets firmly\nDigitized by Google\nBRICKS.\n77\nand promptly with mortar; and being both cheaper and\nlighter than stone, is preferable to it for many kinds of struc-\ntures, as arches, the walls of houses, &c.\n200. The art of brick-making is a distinct branch of the\nuseful arts, and does not properly belong to that of the en-\ngineer. But as the engineer may at times be obliged to pre-\npare this material himself, the following outline of the process\nmay prove of service.\n201. The best brick earth is composed of a mixture of pure\nclay and sand, deprived of pebbles of every kind, but par-\nticularly of those which contain lime, and pyritous or other\nmetallic substances; as these substances, when in large\nquantities, and in the form of pebbles, act as fluxes, and de-\nstroy the shape of the brick, and weaken it by causing cavities\nand cracks; but in small quantities, and equally diffused\nthroughout the earth, they assist the vitrification, and give it\na more uniform character.\n202. Good brick earth is frequently found in a natural\nstate, and requires no other preparation for the purposes of\nthe brick-maker. When he is, obliged to prepare the earth by\nmixing the pure clay and sand, direct experiments should in\nall cases be made, to ascertain the proper proportions of the\ntwo. If the clay is in excess, the temperature required to\nsemi-vitrify it will cause it to warp, shrink, and crack; and\nif there is an excess of sand, complete vitrification will ensue,\nunder similar circumstances.\n203. The quality of the brick depends as much on the\ncare bestowed on its manufacture, as on the quality of the\nearth. The first stage of the process is to free the earth from\npebbles, which is most effectually done by digging it out early\nin the autumn, and exposing it in small heaps to the weather\nduring the winter. In the spring the heaps are carefully\nriddled, if necessary, and the earth is then in a proper state\nto be kneaded or tempered. The quantity of water required\nin tempering will depend on the quality of the earth no\nmore should be used than will be sufficient to make the earth\nSO plastic as to admit of its being easily moulded by the\nworkman. About half a cubic foot of water to one of the\nearth is, in most cases, a good proportion. If too much water\nbe used, the brick will not only be very slow in drying, but\nit will, in most cases, crack, owing to the surface becoming\ncompletely dry before the moisture of the interior has had\ntime to escape; the consequence of which will be, that the\nbrick, when burnt, will be either entirely unfit for use, or very\nweak.\nDigitized by Google\n78\nCIVIL ENGINEERING.\n204. Machinery is now coming into very general use in\nmoulding brick: it is superior to manual labor, not only\nfrom the labor saved, but from its yielding a better quality\nof brick, by giving it great density, which adds to its\nstrength.\n205. Great attention is requisite in drying the brick before\nit is burned. It should be placed, for this purpose, in a dry\nexposure, and be sheltered from the direct action of the wind\nand sun, in order that the moisture may be carried off slowly\nand uniformly from the entire surface. When this precau-\ntion is not taken, the brick will generally crack from the un-\nequal shrinking, arising from one part drying more rapidly\nthan the rest.\n206. The burning and cooling should be done with equal\ncare. A very moderate fire should be applied under the arches\nof the kiln for about twenty-four hours, to expel any remain-\ning moisture from the raw brick: this is known to be com-\npletely effected when the smoke from the kiln is no longer\nblack. The fire is then increased until the bricks of the\narches attain a white heat; it is then allowed to abate in\nsome degree, in order to prevent complete vitrification; and\nit is alternately raised and lowered in this way until the\nburning is complete, which may be ascertained by examining\nthe bricks at the top of the kiln. The cooling should be\nslowly effected; otherwise the bricks will not withstand the\neffects of the weather. It is done by closing the mouths of\nthe arches, and the top and sides of the kiln, in the most ef-\nfectual manner with moist clay and burnt brick, and allow-\ning the kiln to remain in this state until the warmth has sub-\nsided.\n207. Brick of a good quality exhibits a fine, compact, uni-\nform texture, when broken across; gives a clear, ringing\nsound, when struck; and is of a cherry red, or brownish\ncolor. Three varieties are found in the kiln : those which\nform the arches, denominated arch brick, are always vitrified\nin part, and present a grayish glassy appearance at one end\nthey are very hard, but brittle, of inferior strength, and set\nbadly with mortar; those from the interior of the kiln,\nusually denominated body, hard, or cherry brick, are of the\nbest quality; those from near the top and sides are generally\nunderburnt, and are denominated soft, pale, or sammel\nbrick; they have neither sufficient strength nor durability for\nheavy masonry, nor the outside courses of walls which are\nexposed to the weather.\n208. The quality of good brick may be improved by soak-\nDigitized by Google\nTIMBER.\n79\ning it for some days in water, and re-burning it. This pro-\ncess increases both the strength and durability, and renders\nthe brick more suitable for hydraulic constructions, as it is\nfound not to imbibe water SO readily after having under-\ngone it.\n209. The size and form of bricks present but trifling varia-\ntions. They are generally rectangular parallelopipeds, from\neight to nine inches long, from four to four and a half wide,\nand from two to two and a quarter thick. Thin brick is\ngenerally of a better quality than thick, because it can be\ndried and burned more uniformly.\n210. Fire-brick. This material is used for the facing of\nfurnaces, fireplaces, &c., where a high degree of temperature\nis to be sustained. It is made of a very refractory kind of\npure clay, that remains unchanged by a degree of heat which\nwould vitrify and completely destroy ordinary brick. A\nvery remarkable brick of this character has been made of\nagaric mineral; it remains unchanged under the highest\ntemperature, is one of the worst conductors of heat, and so\nlight that it will float on water.\n211. Tiles. As a roof-covering, tiles are in many respects\nsuperior to slate, or metallic coverings. They are strong and\ndurable, and are very suitable for the covering of arches, as\ntheir great weight is not so objectionable here as in the case\nof roofs formed of frames of timber.\nTiles should be made of the best potter's clay, and be\nmoulded with great care, to give them the greatest density\nand strength. They are of very variable form and size ; the\nworst being the flat square form, as, from the liability of the\nclay to warp in burning, they do not make a perfectly water-\ntight covering.\nVIII.\nWOOD.\n212. This material holds the next rank to stone, owing to\nits durability and strength, and the very general use made of\nit in constructions. To suit it to the purposes of the en-\ngineer, the tree is felled after having attained its mature\ngrowth, and the trunk, the larger branches that spring from\nthe trunk, and the main parts of the root, are cut into suita-\nDigitized by\nGoogle\n80\nCIVIL ENGINEERING.\nble dimensions and seasoned, in which state the term tim-\nber is applied to it. The crooked, or compass timber of the\nbranches and roots is mostly applied to the purposes of ship-\nbuilding-for the knees and other parts of the frame-work of\nvessels requiring crooked timber. The trunk furnishes all\nthe straight timber.\n213. Trunk. The trunk of a full-grown tree presents\nthree distinct parts: the bark, which forms the exterior coat-\ning; the sap-wood, which is next to the bark; the heart, or\ninner part, which is easily distinguishable from the sap-wood\nby its greater firmness and darker color.\n214. The heart forms the essential part of the trunk, as a\nbuilding material. The sap-wood possesses but little strength\nand is subject to rapid decay, owing to the great quantity of\nfermentable matter contained in it; and the bark is not only\nwithout strength, but, if suffered to remain on the tree after\nit is felled, it hastens the decay of the sap-wood and heart.\n215. Felling. Trees should not be felled for timber until\nthey have attained their mature growth, nor after they exhibit\nsymptoms of decline; otherwise, the timber will be less\nstrong, and far less durable. Most forest trees arrive at ma-\nturity between fifty and one hundred years, and commence\nto decline after one hundred and fifty or two hundred years.\nThe age of the tree can, in most cases, be ascertained either\nby its external appearances, or by cutting into the centre of\nthe trunk, and counting the rings, or layers, of the sap and\nheart, as a new ring is formed each year in the process of\nvegetation. When the tree commences to decline, the ex-\ntremities of the old branches, and particularly the top, exhibit\nsigns of decay.\n216. Trees should not be felled while the sap is in circula-\ntion; for this substance is of a peculiarly fermentable nature,\nand therefore very productive of destruction to the wood.\nThe winter months, and July, are the seasons in which trees\nare felled for timber, as the sap is generally considered as\ndormant during these months. This practice, however, is in\npart condemned by some writers; and the recent experiments\nof M. Boucherie, in France, support this opinion, and indicate\nmidsummer and autumn as the seasons in which the sap is\nleast active, and therefore as most favorable for felling.\n217. Girdling and Barking. As the sap-wood, in most\ntrees, forms a large portion of the trunk, experiments have\nbeen made for the purpose of improving its strength and\ndurability. These experiments have been mostly directed\ntowards the manner of preparing the tree before felling it.\nDigitized by\nGoogle\nTIMBER.\n81\nOne method consists in girdling, or making an incision with\nan axe around the trunk, completely through the sap-wood,\nand suffering the tree to stand in this state until it is dead\nthe other consists in barking, or stripping the entire trunk of\nits bark, without wounding the sap-wood, early in the spring,\nand allowing the tree to stand until the new leaves have put\nforth and fallen before it is felled. The sap-wood of trees,\ntreated by both of these methods, was found very much\nimproved in hardness, strength, and durability; the results\nfrom girdling were, however, inferior to those from barking.\n218. Methods of Seasoning. The seasoning of timber is\nof the greatest importance, not only to its durability, but to\nthe solidity of the structure for which it may be used; as a\nvery slight shrinking of soine of the pieces, arising from the\nseasoning of the wood, might, in many cases, cause material\ninjury, if not complete destruction to the structure. Timber\nis considered as sufficiently seasoned, for the purposes of frame-\nwork, when it has lost about one-fifth of the weight which it\nhas in a green state. Several methods are in use for season-\ning timber: they consist either in an exposure to the air for a\ncertain period in a sheltered position, which is termed natu-\nral seasoning; in immersion in water, termed water season-\ning; or in boiling, or steaming.\n219. For natural seasoning, it is usually recommended to\nstrip the trunk of its branches and bark immediately upon\nfelling, and to remove it to some dry position, until it can be:\nsawed into suitable scantling. From the experiments of M.\nBoucherie, just cited, it would seem that better results would\nensue from allowing the branches and bark to remain on the-\ntrunk for some days after felling. In this state, the vital ac-\ntion of the tree continuing in operation, the sap-vessels will be\ngradually exhausted of sap and filled with air, and the trunk\nthus better prepared for the process of seasoning. To com-\nplete the seasoning, the sawed timber should be piled under\ndrying-sheds, where it will be freely exposed to the circula-\ntion of the air, but sheltered from the direct action of the wind,\nrain, and sun. By taking these precautions, an equable eva-\nporation of the moisture will take place over the entire sur-\nface, which will prevent either warping or splitting, which\nnecessarily ensues when one part dries more rapidly than an-\nother. It is further recommended, instead of piling the\npieces on each other in a horizontal position, that they be laid.\non cast-iron supports properly prepared, and with a sufficient\ninclination to facilitate the dripping of the sap from one end ;-\nand that heavy round timber be bored through the centre, to.\n6\nDigitized by Google\n82\nCIVIL ENGINEERING.\nexpose a greater surface to the air, as it has been found that\nit cracks more in seasoning than square timber.\nNatural seasoning is preferable to any other, as timber sea-\nsoned in this way is both stronger and more durable than when\nprepared by any artificial process. Most timber will require,\non an average, about two years to become fully seasoned in\nthe natural way.\n220. The process of seasoning by immersion in water is\nslow and imperfect, as it takes years to saturate heavy timber\nand the soluble matter is discharged very slowly, and chiefly\nfrom the exterior layers of the immersed wood. The practice\nof keeping timber in water, with a view to facilitate its sea-\nsoning, has been condemned as of doubtful utility ; particu-\nlarly immersion in salt water, where the timber is liable to the\ninroads of those two very destructive inhabitants of our waters,\nthe Limnoria Terebrans and Teredo Navalis; the former\nof which rapidly destroys the heaviest logs, by gradually eat-\ning in between the annual rings; and the latter, the well-\nknown ship-worm, by converting timber into a perfect honey-\ncomb state by its numerous perforations.\n221. Steaming is mostly in use for ship-building, where it\nis necessary to soften the fibres, for the purpose of bending\nlarge pieces of timber. This is effected by placing the timber\nin strong steam-tight cylinders, where it is subjected to the\naction of steam long enough for the object in view; the\nperiod usually allowed is one hour to each inch in thickness.\nSteaming slightly impairs the strength of timber, but renders\nit less subject to decay, and less liable to warp and crack.\n222. When timber is used for posts partly embedded in the\nground, it is usual to char the part embedded, to preserve it\nfrom decay. This method is only serviceable when the timber\nhas been previously well seasoned but for green timber it is\nhighly injurious, as by closing the pores it prevents the evap-\noration from the surface, and thus causes fermentation and\nrapid decay within.\n223. The most durable timber is procured from trees of a\nclose, compact texture, which, on analysis, yield the largest\nquantity of carbon. And those which grow in moist and\nshady localities furnish timber which is weaker and less dur-\nable than that from trees growing in a dry, open exposure.\n224. Defects of Timber. Timber is subject to defects,\narising either from some peculiarity in the growth of the tree,\nor from the effects of the weather. Straight-grained timber,\nfree from knots, is superior in strength and quality as a build-\ning material to that which is the reverse.\nDigitized by\nGoogle\nTIMBER.\n83\n225. The action of high winds, or of severe frosts, injures\nthe tree while standing: the former separating the layers from\neach other, forming what is denominated rolled timber ; the\nlatter cracking the timber in several places, from the surface\nto the centre. These defects, as well as those arising from\nworms, or age, are easily seen by examining a cross section of\nthe trunk.\n226. Wet and Dry Rot. The wet and dry rot are the\nmost serious causes of the decay of timber; as all the remedies\nthus far proposed to prevent them are too expensive to admit\nof a very general application. Both of these causes have the\nsaine origin: fermentation, and consequent putrefaction. The\nwet rot takes place in wood exposed, alternately, to moisture\nand dryness and the dry rot is occasioned by want of a free\ncireulation of air, as in confined warm localities, like cellars\nand the more confined parts of vessels.\nTrees of rapid growth, which contain a large portion of\nsap-wood, and timber of every description, when used green,\nwhere there is a want of a free circulation of air, decay very\nrapidly with the rot.\n227. Preservation of Timber. Numberless experiments\nhave been made on the preservation of timber, and many\nprocesses for this purpose have been patented, both in Europe\nand this country. Several of these processes have yielded\nthe most satisfactory results; and nearly all have proved\nmore or less efficacious. The means mostly resorted to have\nbeen the saturation of the timber in the solution of some salt\nwith a metallic or earthy base, thus forming an insoluble\ncompound with the soluble matter of the timber. The salts\nwhich have been most generally tried are, the sulphate of\niron or copper, and the chloride of mercury, zinc, or calcium.\nThe results obtained from the chlorides have been more satis-\nfactory than those from the sulphates the latter class of salts\nwith metallic bases possess undoubted antiseptic properties\nbut it is stated that the freed sulphuric acid, arising from\nthe chemical action of the salt on the wood, impairs the\nwoody fibre, and changes it into a substance resembling\ncarbon.\n228. The processes which have come into most general use\nare those of Mr. Kyan and of Sir W. Burnett, called after\nthe patentees kyanizing and burnetizing. Kyan's process is\nto saturate the timber. with a solution of chloride of mercury\nusing for the solution one pound of the salt to five gallons of\nwater. Burnett uses a solution of chloride of zinc, in the pro-\nportion of one pound of the salt to ten gallous of water, for\nDigitized by\nGoogle\n84\nCIVIL ENGINEERING.\ncommon purposes; and a more highly concentrated solution\nwhen the object is also to render the wood incombustible.\n229. As timber under the ordinary circumstances of im-\nmersion imbibes the solutions very slowly, a more expeditious,\nas well as more perfect means of saturation has been used of\nlate, which consists in placing the wood to be prepared in\nstrong wrought-iron cylinders, lined with felt and boards, to\nprotect the iron from the action of the solution, where, first\nby exhausting the cylinders of air, and then applying a strong\npressure by means of a force-pump, the liquid is forced into\nthe sap and air vessels, and penetrates to the very centre of\nthe timber.\n230. Among the patented processes in our country, that of\nMr. Earle has received most notice. This consists in boiling\nthe timber in a solution of the sulphates of copper and iron.\nOpinion seems to be divided as to the efficacy of this method.\nIt has been tried for the preservation of timber for artillery\ncarriages, but not with satisfactory results.\n231. M. Boucherie, to whose able researches on this subject\nreference has been made, noticing the slowness with which\naqueous solutions were imbibed by wood, when simply im-\nmersed in them, conceived the ingenious idea of rendering\nthe vital action of the sap-vessels subservient to a thorough\nimpregnation of every part of the trunk where there was this\nvitality. To effect this, he first immersed the butt-end of a\nfreshly-felled tree in a liquid, and found that it was diffused\nthroughout all parts of the tree in a few days, by the action\nin question. But, finding it difficult to manage trees of some\nsize when felled, M. Boucherie next attempted to saturate\nthem before felling; for which purpose he bored an auger-\nhole through the trunk, and made a saw-cut from the auger-\nhole outwards, on each side, to within a few inches of the\nexterior, leaving enough of the fibres untouched to support\nthe tree. One end of the auger-hole was then stopped, as\nwell as all of the saw-cut on the exterior, and the liquid was\nintroduced by a tube inserted into the open end of the auger-\nhole. This method was found equally efficacious with the\nfirst, and more convenient.\n232. After examining the action of the various neutral\nsalts on the soluble matter contained in wood, M. Boucherie\nwas led to try the impure pyrolignite of iron, both from its\nchemical composition and its cheapness. The results of this\nexperiment were perfectly satisfactory. The pyrolignite of\niron, in the proportion of one-fiftieth in weight of the green\nDigitized by Google\nTIMBER.\n85\nwood, was found not only to preserve the wood from decay,\nbut to harden it to a very high degree.\n233. Observing that the pliability and elasticity of wood\ndepended, in a great measure, on the moisture contained in it,\nM. Boucherie next directed his attention to the means of\nimproving these properties. For this purpose he tried solu-\ntions of various deliquescent salts, which were found to an-\nswer the end proposed. Among these solutions he gives the\npreference to that of chloride of calcium, which also, when\nconcentrated, renders the wood incombustible. He also re-\ncommends for like purposes the mother-water of salt-marshes,\nas cheaper than the solution of the chloride of calcium.\nTimber prepared in this way is not only improved in elasticity\nand pliability, but is prevented from warping and cracking ;\nthe timber, however, is subject to greater variations weight\nthan when seasoned naturally.\n234. M. Boucherie is of opinion that the earthy chlorides\nwill also act as preservatives, but to insure this he recom\nmends that they be mixed with one-fifth of pyrolignite of\niron.\n235. From other experiments of M. Boucherie, it appears\nthat the sap may be expelled from any freshly-felled timber\nby the pressure of a liquid, and the timber be impregnated\nas thoroughly as by the preceding processes. To effect this,\nthe piece to be saturated is placed in an upright position, so\nthat the sap may flow readily from the lower end; a water-\ntight bag, containing the liquid, is affixed to the upper ex-\ntremity, which is surmounted by the liquid, the pressure from\nwhich expels the sap, and fills the sap-vessels with the liquid.\nThe process is complete when the liquid is found to issue in a\npure state from the lower end of the stick.\n237. Either of the above processes may be applied in im-\npregnating timber with coloring matter for ornamental pur-\nposes. The plan recommended by M. Boucherie consists in\nintroducing separately the solutions by the chemical union of\nwhich the color is to be formed.\n238. The rapid decay of railroad sleepers has led to more\nrecent experiments in Europe, where timber is scarce and\ndear. Opinion now is in favor of impregnating them with\ncreosote, as the best preservative from wet rot.\n239. The effect of time on the durability of timber, pre-\npared by any of the various chemical processes which have\njust beeu detailed, remains to be seen; although results of\nthe most satisfactory nature may be looked for, considering\nthe severe tests to which most of them have been submitted,\nDigitized by Google\n86\nCIVIL ENGINEERING.\nby exposure in situations peculiarly favorable to the destruc-\ntion of ligneous substances.\n240. Durability of Timber. The durability of timber,\nwhen not prepared by any of the above-mentioned processes,\nvaries greatly under different circumstances of exposure. If\nplaced in a sheltered position, and exposed to a free circula-\ntion of air, timber will last for centuries, without showing any\nsensible changes in its physical properties. An equal, if not\nsuperior, durability is observed when it is immersed in fresh\nwater, or embedded in thick walls, or underground, so as to\nbe beyond the influence of atmospheric changes.\n241. In salt water, however, particularly in warm climates,\ntimber is rapidly destroyed by the two animals already\nnoticed: the one, the limnoria terebrans, attacking, it is said,\nonly stationary wood, while the attacks of the other, the\nteredo navalis, are general. Various means have been tried\nto guard against the ravages of these destructive agents; that\nof sheathing exposed timber with copper, or with a coating\nof hydraulic ceinent, affixed to the wood by studding it thick-\nly over with broad-headed nails to give a hold to the cement,\nhas met with full success; but the oxidation of the metal,\nand the liability to accident of the cement, limit their effica-\ncy to cases where they can be renewed. The chemical pro-\ncesses for preserving timber from decay do not appear to\nguard them in salt water. A process, however, of preserving\ntimber by impregnating it with coal tar, patented in this\ncountry by Professor Renwick, appears, from careful experi-\nments, also to be efficacious against the attack of the ship-\nworm. A coating of Jeffery's marine glue, when impregnated\nwith some of the insoluble mineral poisons destructive to\nanimal life, is said to subserve the same end.\n242. The best seasoned timber will not withstand the effects\nof exposure to the weather for a much greater period than\ntwenty-five years, unless it is protected by a coating of paint\nor pitch, or of oil laid on hot, when the timber is partly\ncharred over a light blaze. These substances themselves, be-\ning of a perishable nature, require to be renewed from time to\ntime, and will, therefore, be serviceable only in situations\nwhich admit of their renewal. They are, moreover, more\nhurtful than serviceable to unseasoned timber, as by closing\nthe pores of the exterior surface they prevent the moisture\nfrom escaping from within, and therefore promote one of the\nchief causes of decay.\n243. Forest Trees of the United States. The forests of\nour own country produce a great variety of the best timber for\nDigitized by Google\nTIMBER.\n87\nevery purpose, and supply abundantly both our own and for-\neign markets. The following genera are in most common\nuse.\n244. Oak. About forty-four species of this tree are enu-\nmerated by botanists, as found in our forests and those of\nMexico. The most of them afford a good building material,\nexcept the varieties of red oak, the timber of which is weak\nand decays rapidly.\nThe White Oak (Querous Alba), so named from the color\nof its bark, is among the most valuable of the species, and is\nin very general use, but is mostly reserved for naval construc-\ntions; its trunk, which is large, serving for heavy fraine-work,\nand the roots and larger branches affording the best compass\ntimber. The wood is strong and durable, and of a slightly\nreddish tinge; it is not suitable for boards, as it shrinks about\n3'2 in seasoning, and is very subject to warp and crack.\nThis tree is found most abundantly in the Middle States.\nIt is seldom seen, in comparison with other forest trees, in the\nEastern and Southern States, or in the rich valleys of the\nWestern States.\nPost Oak (Quercus Obtusiloba). This tree seldom attains\na greater diameter than about fifteen inches, and on this ac-\ncount is mostly used for posts, from which use it takes its\nname. The wood has a yellowish hue, and close grain ; is said\nto exceed white oak in strength and durability; and is there-\nfore an excellent building material for the lighter kinds of\nframe-work. This tree is found most abundantly in the\nforests of Maryland and Virginia, and is there frequently\ncalled Box White Oak, and Iron Oak. It also grows in the\nforests of the Southern and Western States, but is rarely seen\nfarther north than the mouth of the Hudson River.\nChestnut White Oak (Quercus Prinus Palustris). The\ntimber of this tree is strong and durable, but inferior to the\ntwo preceding species. The tree is abundant from North\nCarolina to Florida.\nRock Chestnut Oak, (Quercus Prinus Monticola.) The tim-\nber of this tree is mostly in use for naval constructions, for\nwhich it is esteemed inferior only to the white oak. The\ntree is found in the Middle States, and as far north as Ver-\nmont.\nLive Oak (Quercus Virens). The wood of this tree is\nof a yellowish tinge; it is heavy, compact, and of a fine\ngrain; it is stronger and more durable than any other species,\nand on this account it is considered invaluable for the pur-\nposes of ship-building, for which it is exclusively reserved.\nDigitized by\nGoogle\n88\nCIVIL ENGINEERING.\nThe live oak is not found farther north than the neighbor-\nhood of Norfolk, Virginia, nor farther inland than from fif-\nteen to twenty miles from the seacoast. It is found in abun-\ndance along the coast south, and in the adjacent islands as far\nas the mouth of the Mississippi.\n245. Pine. This very interesting genus is considered in-\nferior only to the oak, from the excellent timber afforded by\nnearly all of its species. It is regarded as a most valuable\nbuilding material, owing to its strength and durability, the\nstraightness of its fibre, the ease with which it is wrought,\nand its applicability to all the purposes of constructions in\nwood.\nYellow Pine (Pinus Mitis). The heart-wood of this tree\nis fine-grained, moderately resinous, strong and durable; but\nthe sap-wood is very inferior, decaying rapidly on exposure to\nthe weather. The timber is in very general use for frame-\nwork, &c.\nThis tree is found throughout our country, but in the great-\nest abundance in the Middle States. In the Southern States\nit is known as Spruce Pine and Short-leaved Pine.\nLong-leaved Pine, or Southern Pine (Pinus Australis).\nThis tree has but little sap-wood, and the resinous matter is\nuniformly distributed throughout the heart-wood, which pre-\nsents a fine compact grain, having more hardness, strength,\nand durability than any other species of the pine, owing to\nwhich qualities the timber is in very great demand.\nThe tree is first met with near Norfolk, Virginia, and from\nthis point south it is abundantly found.\nWhite Pine, or Northern Pine (Pinus Strobus). This tree\ntakes its name from the color of its wood, which is white, soft,\nlight, straight-grained, and durable. It is inferior in strength\nto the species just described, and has, moreover, the defect of\nswelling in damp weather. Its timber is, however, in great\ndemand as a good building material, being almost the only\nkind in use in the Eastern and Northern States for the frame-\nwork and joinery of houses, &c.\nThe finest specimens of this tree grow in the forests of\nMaine. It is found in great abundance between the 43d and\n47th parallels, N. L.\n246. Among the forest trees in less general use than the oak\nand pine, the Locust, the Chestnut, the Red Cedar, and the\nLarch hold the first place for hardness, strength, and\ndurability. They are chiefly used for the frame-work of ves-\nsels. The chestnut, the locust, and the cedar are preferred to\nall other trees for posts.\nDigitized by\nGoogle\nMETALS.\n89\n247. The Black or Double Spruce (Abies Nigra) also af-\nfords an excellent material, its timber being strong, durable,\nand light.\n248. The Juniper or White Cedar, and the Cypress are\nvery celebrated for affording a material which is very light,\nand of great durability when exposed to the weather; owing\nto these qualities, it is almost exclusively used for shingles\nand other exterior coverings. These two trees are found in\ngreat abundance in the swamps of the Southern States.\nIX.\nMETALS.\nThe metals in most common use in constructions are Iron,\nCopper, Zinc, Tin, and Lead.\n249. IRON. This metal is very extensively used for the\npurposes of the engineer and architect, both in the state of\nCast Iron and Wrought Iron.\n250. Cast Iron is one of the most valuable building materi-\nals, owing to its great strength, hardness, and durability, and\nthe ease with which it can be cast, or moulded, into the best\nforms, for the purposes to which it is to be applied.\n251. Cast iron is divided into two principal varieties the\nGray cast iron, and White cast iron. There exists a very\nmarked difference between the properties of these two\nvarieties. There are, besides, many intermediate varieties,\nwhich partake more or less of the properties of these two, às\nthey approach, in their external appearances, nearer to the one\nor the other.\n252. Gray cast iron, when of a good quality, is slightly\nmalleable in a cold state, and will yield readily to the action\nof the file, when the hard outside coating is removed. This\nvariety is also sometimes termed soft gray cast iron; it is\nsofter and tougher than the white iron. When broken, the sur-\nface of the fracture presents a granular structure; the color\nis gray; and the lustre is what is termed metallic, resembling\nsmall brilliant particles of lead strewed over the surface.\n253. White cast iron is very hard and brittle; when re-\ncently broken, the surface of the fracture presents a distinctly-\nDigitized by\nGoogle\n90\nCIVIL ENGINEERING.\nmarked crystalline structure; the color is white; and lustre\nvitreous, or bearing a resemblance to the reflected light from\nan aggregation of small crystals.\n254. Mr. Mallet, in a very able Report made to the British\nAssociation for the Advancement of Science, remarking on\nthe great want of uniformity, among manufacturers of iron, in\nthe terms used to describe its different varieties, proposes the\nfollowing nomenclature, as comprising every variety, with\ntheir distinctive characters.\nSilvery. Least fusible; thickens rapidly when fluid by a\nspontaneous puddling; crystals vesicular, often crystalline;\nincapable of being cut by chisel or file; ultimate cohesion a\nmaximum; elastic range a minimum.\nMicaceous. Very soft; greasy feel; peculiar micaceous\nappearance, generally owing to excess of manganese; soils\nthe fingers strongly; crystals large; runs very fluid; con-\ntraction large.\nMottled. Tough and hard filed or cut with difficulty\ncrystals large and small mixed ; sometimes runs thick; con-\ntraction in cooling a maximum.\nBright Gray. Toughness and hardness most suitable for\nworking; ultimate cohesion and elastic range generally are\nbalanced most advantageously; crystals uniform, very mi-\nnute.\nDull Gray. Less tough than the preceding; other char-\nacters alike ; contraction in cooling a minimum.\nDark Gray. Most fusible; remains long fluid; exudes\ngraphite in cooling; soils the fingers; crystals large and\nlamella; ultimate cohesion a minimum, and elastic range a\nmaximum.\n255. The gray iron is most suitable where strength is re-\nquired; and the white, where hardness is the principal re-\nquisite.\n256. The color and lustre, presented by the surface of a re-\ncent fracture, are the best indications of the quality of iron.\nA uniform dark gray color, and high metallic lustre, are in-\ndications of the best and strongest. With the same color, but\nless lustre, the iron will be found to be softer and weaker, and\nto crumble readily. Iron without lustre, of a dark and mot-\ntled color, is the sofest and weakest of the gray varieties.\nIron of a light gray color and high metallic lustre is usual-\nly very hard and tenacious. As the color approaches to\nwhite, and the metallic lustre changes to vitreous, hardness\nand brittleness become more marked, until the extremes of a\ndull, or grayish white color, and a very high vitreous lustre,\nDigitized\nby\nGoogle\nMETALS.\n91\nare attained, which are the indications of the hardest and\nmost brittle of the white variety.\n257. The quality of cast iron may also be tested, by strik-\ning a smart stroke with a hammer on the edge of a casting.\nIf the blow produces a slight indentation, without any appear-\nance of fracture, it shows that the iron is slightly. malleable,\nand, therefore, of a good quality; if, on the contrary, the\nedge is broken, it indicates brittleness in the material, and a\nconsequent want of strength.\n258. The strength of cast iron varies with its density; and\nthis element depends upon the temperature of the metal when\ndrawn from the furnace; the rate of cooling; the head of\nmetal under which the casting is made ; and the bulk of the\ncasting.\n259. The density of iron cast in vertical moulds increases,\naccording to Mr. Mallet's experiments, very rapidly from the\ntop downward, to a depth of about four feet below the top ;\nfrom this point to the bottom, the rate of increase is very\nnearly uniform. All other circumstances remaining the\nname, the density decreases with the bulk of the casting\nhence large are proportionally weaker than small castings.\n260. From all of these causes, by which the strength of\niron may be influenced, it is very difficult to judge of the\nquality of a casting by its external characters; in general,\nhowever, if the exterior presents a uniform appearance, de-\nvoid of marked inequalities of surface, it will be an indica-\ntion of uniform strength.\n261. The economy in the manufacture of cast iron, arising\nfrom the use of the hot blast, has naturally directed attention\nto the comparative merits between iron produced by this pro-\ncess and that from the cold blast. This subject has been\nably investigated by Messrs. Fairbairn and Hodgkinson, and\ntheir results published in the Seventh Report of the British\nAssociation.\nMr. Hodgkinson remarks on this subject, in reference to the\nresults of his experiments: \"It is rendered exceedingly\nprobable that the introduction of a heated blast into the\nmanufacture of cast iron, has injured the softer irons, while\nit has frequently mollified and improved those of a harder\nnature; and considering the small deterioration that some\n\" irons have sustained, and the apparent benefit to those of\nothers, \"together with the great saving effected by the heated\nblast, there seems good reason for the process becoming as\ngeneral as it has done.\"\n262. From a number of specific gravities given in these\nDigitized by\nGoogle\n92\nCIVIL ENGINEERING.\nReports, the mean specific gravity of cold blast iron is nearly\n7.091, that of hot blast, 7.021.\n263. Mr. Fairbairn concludes his Report with these obser-\nvations, as the results of the investigations of himself and\nMr. Hodgkinson \" The ultimatum of our inquiries, made in\nthis way, stands, therefore, in the ratio of strength, 1000 for\nthe cold blast, to 1024.8 for the hot blast; leaving the small\nfractional difference of 24.8 in favor of the hot blast.\"\n\"The relative powers to sustain impact, are likewise in\nfavor of the hot blast, being in the ratio of 1000 to 1226.3.\"\n264. Wrought Iron. The color, lustre, and texture of a\nrecent fracture, present, also, the most certain indications of\nthe quality of wrought iron. The fracture submitted to ex-\namination, should be of bars at least one inch square ; or, if\nof flat bars, they should be at least half an inch thick; other-\nwise, the texture will be so greatly changed, arising from the\ngreater elongation of the fibres, in bars of smaller dimensions,\nas to present none of those distinctive differences observable\nin the fracture of large bars.\n265. The surface of a recent fracture of good iron, presents\na clear gray color, and high metallic lustre the texture is\ngranular, and the grains have an elongated shape, and are\npointed and slightly crooked at their ends, giving the idea of\na powerful force having been employed to produce the frac-\nture. When a bar, presenting these appearances, is ham-\nmered, or drawn out into small bars, the surface of fracture\nof these hars will have a very marked fibrous appearance, the\nfilaments being of a white color and very elongated.\n266. When the texture is either laminated, or crystalline, it\nis an indication of some defect in the metal, arising either\nfrom the mixture of foreign ingredients, or else from some\nneglect in the process of forging.\n267. Burnt iron is of a clear gray color, with a slight\nshade of blue, and of a slaty texture. It is soft and brittle.\n268. Cold short iron, or iron that cannot be hammered\nwhen cold without breaking, presents nearly the same appear-\nance as burnt iron, but its color inclines to white. It is very\nhard and brittle.\n269. Hot short iron, or that which breaks under the ham-\nmer when heated, is of a dark color without lustre. This de-\nfect is usually indicated in the bar by numerous cracks on the\nedges.\n270. The fibrous texture, which is developed only in small\nbars by hammering, is an inherent quality of good iron ;\nthose varieties which are not susceptible of receiving this pe-\nDigitized by Google\nMETALS.\n93\nculiar texture, are of an inferior quality, and should never be\nused for purposes requiring great strength : the filaments of\nbad varieties are short, and the fracture is of a deep color, be-\ntween lead gray and dark gray.\n271. The best wrought iron presents two varieties; the\nHard and Soft. The hard variety is very strong and ductile.\nIt preserves its granular texture a long time under the action\nof the hammer, and only develops the fibrous texture when\nbeaten, or drawn out into small rods : its filaments then pre-\nsent a silver-white appearance.\n272. The soft variety is weaker than the hard ; it yields\neasily to the hammer; and it commences to exhibit, under its\naction, the fibrous texture in tolerably large bars. The color\nof the fibres is between a silver white and light gray.\n273. Iron may be naturally of a good quality, and still,\nfrom being badly refined, not present the appearances which\nare regarded as sure indications of its excellence. Among\nthe defects arising from this cause are blisters, flaws, and\ncinder-holes. Generally, however, if the surface of fracture\npresents a texture partly crystalline and partly fibrous, or a\nfine granular texture, in which some of the grains seem\npointed and crooked at the points, together with a light gray\ncolor without lustre, it will indicate natural good qualities,\nwhich require only careful refining to be fully developed.\n274. The strength of wrought iron is very variable, as it\ndepends not only on the natural qualities of the metal, but\nalso upon the care bestowed in forging, and the greater or less\ncompression of its fibres, when drawn or hammered into bars\nof different sizes.\n275. In the Report made by the sub-committee, Messrs.\nJohnson and Reeves, on the strength of Boiler Iron (Journal\nof Franklin Institute, vol. 20, New Series), it is stated that\nthe following order of superiority obtains among the different\nkinds of pig metal, with respect to the malleable iron which\nthey furnish :-1 Lively gray ; 2 White, 3 Mottled gray. ;\n4 Dead gray, 5 Mixed metals.\nThe Report states, So far as these experiments may be\nconsidered decisive of the question, they favor the lighter\ncomplexion of the cast metal, in preference to the darker and\nmottled varieties; and they place the mixture of different\nsorts among the worst modifications of the material to be\nused, where the object is mere tenacity.\"\n276. These experiments also show that piling iron of dif-\nferent degrees of fineness in the same plate is injurious to its\nquality, owing to the consequent inequality of the welding.\nDigitized by\nGoogle\n94\nCIVIL ENGINEERING.\n277. From these experiments, the mean specific gravity of\nboiler iron is 7.7344, and of bar iron, 7.7254.\n278. Durability of Iron. The durability of iron, under\nthe different circumstances of exposure to which it may be\nsubmitted, depends on the manner in which the casting may\nhave been made ; the bulk of the piece employed; the more\nor less homogeneousness of the mass ; its density and hard-\nness.\n279. Among the most recent and able researches upon the\naction of the ordinary corrosive agents on iron, and the pre-\nservative means to be employed against them, those of Mr.\nMallet, given in the Report alreadv mentioned, hold the first\nrank. A brief recapitulation of the most prominent conclu-\nsions at which he has arrived, is all that can be attempted in\nthis place.\n280. When iron is only partly immersed in water, or\nwholly immersed in water composed of strata of different\ndensities, like that of tidal rivers, a voltaic pile of one solid\nand two fluid bodies is formed, which causes a more rapid\ncorrosion than when the liquid is of uniform density.\n281. The corrosive action of the foul sea water of docks and\nharbors is far more powerful than that of clear sea or fresh\nwater, owing to the action of the hydro-sulphuric acid which,\nbeing disengaged from the mud, impregnates the water, and\nacts on the iron.\n282. In clear fresh river water, the corrosive action is less\nthan under any other circumstances of immersion owing to\nthe absence of corrosive agents, and the firm adherence of the\noxide formed, which presents a hard coat that is not washed\noff as in sea water.\n283. In clear sea water, the rate of corrosion of iron bars,\none inch thick, is from 3 to 4 tenths of an inch for cast iron\nin a century, and about 6 tenths of an inch for wrought\niron.\n284. Wrought iron corrodes more rapidly in hot sea water\nthan under any other circumstances of immersion.\n285. The same iron when chill cast corrodes more rapidly\nthan when cast in green sand ; this arises from the chilled\nsurface being less uniform, and therefore forming voltaic\ncouples of iron of different densities, by which the rapidity\nof corrosion is increased.\n286. Castings made in dry sand and loam are more durable\nunder water than those made in green sand.\n287. Thin bars of iron corrode more rapidly than those of\nmore bulk. This difference in the rate of corrosion is more\nDigitized by\nGoogle\nMETALS.\n95\nstriking in the soft, or graphitic specimens of cast iron, than\nin the hard and silvery. It is caused by the more rapid rate\nof cooling in thin than in thick bars, by which the density of\nthe surface of the former becomes less uniform. These\ncauses of destructibility may, in some degree, be obviated in\ncastings composed of ribbed pieces, by making the ribs of\nequal thickness with the main pieces, and causing them to be\ncooled in the sand, before stripping the moulds.\n288. ,The hard crust of cast iron promotes its durability;\nwhen this is removed to the depth of one-fourth of an inch,\nthe iron corrodes more rapidly in both air and water.\n289. Corrosion takes place the less rapidly in any variety\nof iron, in proportion as it is more homogeneous, denser,\nharder, and closer grained, and the less graphitic.\n290. Preservatives of Iron-The more ordinary means\nused to protect iron against the action of corrosive agents, con-\nsist of paints and varnishes. These, under the usual circum-\nstances of atmospheric exposure are of but slight efficacy, and\nrequire to be frequently renewed. In water, they are all\nrapidly destroyed, with the exception of boiled coal-tar, which\nwhen laid on hot iron, leaves a bright and solid varnish of\nconsiderable durability and protective power.\n291. The rapidly increasing purposes to which iron has\nbeen applied, within the last few years, has led to researches\nupon the agency of electro-chemical action, as a means of\nprotecting it from corrosion, both in air and water. Among\nthe processes resorted to for this purpose, that of zinking, or\nas it is more commonly known, galvanizing iron has been\nmost generally introduced. The experiments of Mr. Mallet,\non this process, are decidedly against zinc as a permanent\nelectro-chemical protector. Mr. Mallet states, as the result of\nhis observations, that zinc applied in fusion, in the ordinary\nmanner, over the whole surface of iron, will not preserve it\nlonger than about two years; and that, so soon as oxidation\ncommences at any point of the iron, the protective power of\nthe zinc becomes considerably diminished, or even entirely\nnull. Mr. Mallet concludes: \" On the whole, it may be\naffirmed that, under all circumstances, zinc has not yet been\nso applied to iron, as to rank as an electro-chemical protector\ntowards it in the strict sense; hitherto it has not become\na preventive, but merely a more or less effective palliative to\ndestruction.\"\n292. In extending his researches on this subject, with\nalloys of copper and zinc, and copper and tin, Mr. Mallet\nfound that the alloys of the last metals accelerate the corro-\nDigitized by\nGoogle\n96\nCIVIL ENGINEERING.\nsion of iron, when voltaically associated with it in sea water\nand that an alloy of the two first, represented by 23Zn+\n8Cu, in contact with iron, protects it as fully as zinc alone,\nand suffers but little loss from the electro-chemical action ;\nthus presenting a protective energy more permanent and in-\nvariable than that of zinc, and giving a nearer approxima-\ntion to the solution of the problem, \" to obtain a mode of\nelectro-chemical protection such, that while the iron shall be\npreserved the protector shall not be acted on, and whose pro-\ntection shall be invariable.\"\n293. In the course of his experiments, Mr. Mallet ascer-\ntained that the softest gray cast iron bears such a voltaic\nrelation to hard bright cast iron, when immersed in sea water\nand voltaically associated with it, that although oxidation\nwill not be prevented on either, it will still be greatly retard-\ned on the hard, at the expense of the soft iron.\n294. In concluding the details of his important researches\non this subject, Mr. Mallet makes the following judicious\nremarks: The engineer of observant habit will soon have\nperceived, that in exposed works in iron, equality of section\nor scantling, in all parts sustaining equal strain, is far from\ninsuring equal passive power of permanent resistance, unless,\nin addition to a general allowance for loss of substance by\ncorrosion, this latter element be so provided for, that it shall\nbe equally balanced over the whole structure; or, if not,\nshall be compelled to confine itself to portions of the general\nstructure, which may lose substance with injuring its sta-\nbility.\"\nThe principles we have already established sufficiently\nguide us in the modes of effecting this regard must not only\nbe had to the contact of dissimilar metals, or of the same in\ndissimilar fluids, but to the scantling of the casting and of its\nparts, and to the contact of cast iron with wrought iron or\nsteel, or of one sort of cast iron with another. Thus, in a sus-\npension bridge, if the links of the chains be hammered, and\nthe pins rolled, the latter, where equally exposed, will be eat-\nen away long before the former. In marine steam-boilers, the\nrivets are hardened by hammering until cold; the plates,\ntherefore, are corroded through round the rivets before these\nhave suffered sensibly ; and in the air-pumps and condensers\nof engines working with sea water, or in pit work, and pumps\nlifting mineralized or 'bad' water from mines, the cast iron\nperishes first round the holes through which wrought iron\nbolts, &c., are inserted. And abundant other instances might\nbe given, showing that the effects here spoken of are in prac-\nDigitized by\nGoogle\nMETALS.\n97\ntical operation to an extent that should press the means of\ncounteracting them on the attention of the engineer.\"\n295. Since Mr. Mallet's Report to the British Association,\nhe has invented two processes for the protection of iron from\nthe action of the atmosphere and of water the one by means\nof a coating formed of a triple alloy of zinc, mercury, and\nsodium, or potassium ; the other by an amalgam of palladium\nand mercury.\n296. The first process consists of forming an alloy of the\nmetals used, in the following manner. To 1,292 parts of zinc\nby weight, in a state of fusion, 202 parts of mercury are add-\ned, and the metals are well mixed, by stirring with a rod of\ndry wood, or one of iron coated with clay; sodium, or potas-\nsium is next added, in small quantities at a time, in the pro-\nportion of one pound to every ton by weight of the other two\nmetals. The iron to be coated with this alloy is first cleared\nof all adhering oxide, by immersing it in a warm dilute so-\nlution of sulphuric, or of hydrochloric acid, washing it in\nclear cold water, and detaching all scales, by striking it with\na hammer; it is then scoured clean by the hand with sand, or\nemery, under a small stream of water, until a bright metallic\nlustre is obtained while still wet, it is immersed in a bath\nformed of equal parts of the cold saturated solutions of chlo-\nride of zine and sal-ammoniac, to which as much more solid sal\nammoniac is added as the solution will take up. The iron is\nallowed to remain in this bath until it is covered by minute\nbubbles of gas; it is then taken out, allowed to drain a few\nseconds, and plunged into the fused alloy, from which it is\nwithdrawn so soon as it has acquired the same temperature.\nWhen taken from the metallic bath, the iron should be plung-\ned in cold water and well washed.\n297. Care must be taken that the iron be not kept too long\nin the metallic bath, otherwise it may be fused, owing to the\ngreat affinity of the alloy for iron. At the proper fusing\ntemperature of the alloy, about 680° Fahr., it will dissolve\nplates of iron one-eighth of an inch thick in a few seconds;\non this account, whenever small articles of iron have to be pro-\ntected, the affinity of the alloy for iron should be satisfied, by\nfusing some iron in it before immersing that to be coated.\n298. The other process, which has been termed. palladiumis-\ning, consists in coating the iron, prepared as in the first pro-\ncess for the reception of the metallic coat, with an amalgam\nof palladium and mercury.\n299. Corrugated Iron.-This term is applied to sheet iron\nprepared by being moulded, and having the plane surface\n7\nDigitized by Google\n98\nCIVIL ENGINEERING.\nbroken by longitudinal or sectional ridges, for the purpose of\ngiving the sheet great stiffness and strength. Corrugated iron\nis used principally for roofing, and sometimes in place of brick\nfor forming the arches between the iron beams in fire-proof\nstructures.\n300. Steel.-The name steel is given to a compound of iron\nand carbon, in which the amount of iron is usually not less\nthan 97 per cent. Where the amount of carbon is less than\n.0065, the compound is termed steely iron; when more than\n1.8 the compound is cast iron.\nSteel, like iron, is seldom pure, containing other substances,\nof which sulphur and silicon are the most common.\nThe different kinds of steel are named either from the\nmodes of manufacture, or their appearance, or from some con-\nstituent, or from some inventor's process. Thus we have\nnatural steels obtained directly from the ores and bearing\nmostly local names; blistered, shear, tilted and crucible or\ncast steel; Woolz or Damask steel; Bessemer's and Martin's\nsteel tungstein, chromium, and titanium steel.\nThese varieties are obtained by various processes. Thus\nwe have the puddling process by which the varieties of natural\nsteel are made; the cementative process; the Martin-Siemems\nprocess; the Bessemer process; &c.\nThe average specific gravity of natural steels is 7.5; of\ntilted steel 7.9; cast steel 7.8; Bessemer steel from 7.79 to\n7.87; chromium steel from 7.81 to 7.85.\nThe chromium steel is said to possess the greatest tensile\nstrength; and among those more abundantly manufactured\nthe Bessemer still ranks highest in this respect.\nCOPPER.\n301. The most ordinary and useful application of this\nmetal in constructions, is that of sheet copper, which is used\nfor roof coverings, and like purposes. Its durability under\nthe ordinary changes of atmosphere is very great. Sheet cop-\nper, when quite thin, is apt to be defective, from cracks ari-\nsing from the process of drawing it out. These may be\nremedied, when sheet copper is to be used for a water-tight\nsheathing, by tinning the sheets on oneside. Sheets prepared\nin this way have been found to be very durable.\nThe alloys of copper and zinc, known under the name of\nbrass, and those of copper and tin, known as bronze, gun-metal,\nand bell-metal, are, in some cases, substituted for iron, owing\nDigitized by Google\nMETALS.\n99\nto their superior hardness to copper, and being less readily\noxidized than iron.\nZINO.\n302. This metal is used mostly in the form of sheets; and\nfor water-tight sheathings it has nearly displaced every other\nkind of sheet metal. The pure metallic surface of zinc soon\nbecomes covered with a very thin, hard, transparent oxide,\nwhich is unchangeable both in air and water, and preserves\nthe metal beneath it from farther oxidation. It is this prop-\nerty of the oxide of zinc, which renders this metal so valua-\nble for sheathing purposes; but its durability is dependent\nupon its not being brought into contact with iron in the pres-\nence of moisture, as the galvanic action which would then\nensue, would soon destroy the zinc. On the same account\nzinc should be perfectly free from the presence of iron, as a\nvery small quantity of the oxide of this last metal, when con-\ntained in zinc, is found to occasion its rapid destruction.\nBesides the alloys of zinc already mentioned, this metal\nalloyed with copper forms one of the most useful solders; and\nits alloy with lead has been proposed as a cramping metal for\nuniting the parts of iron work together, or iron work to other\nmaterials, in the place of lead, which is usually employed for\nthis purpose, but which accelerates the destruction of iron in\ncontact with it.\nTIN.\n303. The most useful application of tin is as a coating for\nsheet iron, or sheet copper: the alloy which it forms, in this\nway, upon the surfaces of the metals in question, preserves\nthem for some time from oxidation. Alloyed with lead it\nforms one of the most useful solders.\nLEAD.\n304. Lead in sheets forms a very good and durable roof\ncovering, but it is inferior to both copper and zinc in tenacity\nand durability; and is very apt to tear asunder on inclined\nsurfaces, particularly if covered with other materials, as in\nthe case of the capping of water-tight arches.\nDigitized by\nGoogle\n100\nCIVIL ENGINEERING.\nX.\nPAINTS AND VARNISHES.\n305. Paints are mixtures of certain fixed and volatile oils,\nchiefly those of linseed and turpentine, with several of the\nmetallic salts and oxides, and other substances which are used\neither as pigments, or to give what is termed a body to the\npaint, and also to improve its drying properties.\n306. Paints are mainly used as protective agents to secure\nwood and metals from the destructive action of air and water.\nThis they but imperfectly effect, owing to the unstable nature\nof the oils that enter into their composition, which are not\nonly destroyed by the very agents against which they are used\nas protectors, but by the chemical changes which result from\nthe action of the elements of the oil upon the metallic salts\nand oxides.\n307. Paints are more durable in air than in water. In the\nlatter element, whether fresh or salt, particularly if foul,\npaints are soon destroyed by the chemical changes which take\nplace, both from the action of the water upon the oils, and\nthat of the hydrosulphuric acid contained in foul water upon\nthe metallic salts and oxides.\n308. However carefully made or applied, paints soon be-\ncome permeable to water, owing to the very minute pores\nwhich arise from the chemical changes in their constituents.\nThese changes will have but little influence upon the preser-\nvative action of paints upon wood exposed to the effects of\nthe atmosphere, provided the wood be well seasoned before\nthe paint is applied, and that the latter be renewed at suitable\nintervals of time. On metals these changes have a very im-\nportant bearing. The permeability of the paint to moisture\ncauses the surface of the metal under it to rust, and this cause\nof destruction is, in most cases, promoted by the chemical\nchanges which the paint undergoes.\n309. Varnishes are solutions of various resinous substances\nin solvents which possess the property of drying rapidly.\nThey are used for the same purposes as paints, and have gen-\nerally the same defects.\n310. The following are some of the more usual composi-\ntions of paints and varnishes.\nDigitized by\nGoogle\nPAINTS AND VARNISH.\n101\nWhite Paint (for exposed wood).\nWhite lead, ground in oil\n80\nBoiled oil\n9\nRaw oil\n9\nSpirits turpentine\n4\nThe white lead to be ground in the oil, and the spirits of\nturpentine added.\nBlack Paint.\nLamp-black\n28\nLitharge\n1\nJapan varnish\n1\nLinseed oil, boiled\n73\nSpirite turpentine\n1\nLead Color.\nWhite lead, ground in oil\n75\nLamp-black\n1\nBoiled linseed oil\n23\nLitharge\n0.5\nJapan varnish\n0.5\nSpirite turpentine\n2.5\nGray, or Stone Color (for buildings).\nWhite lead ground in oil\n78\nBoiled oil.\n9.5\nRaw oil\n9.5\nSpirits of turpentine.\n8\nTurkey umber.\n0.5\nLamp-black\n0.25\nLackers for Cast Iron.\n1. - Black lead, pulverized\n12\nRed lead\n12\nLitharge\n5\nLamp-black\n5\nLinseed oil\n66\n2.- Anti-corrosion\n40 lbs.\nGrant's black, ground in oil\n4 \"\nRed lead, as a dryer\n8 \"\nLinseed oil\n4 gals.\nSpirits turpentine\n1 pint.\nCopal Varnish.\nGum copal (in clean lumps)\n26.5\nBoiled linseed oil\n42.5\nSpirits turpentine\n81\nJapan Varnish.\nLitharge\n4\nBoiled oil\n87\nSpirite turpentine\n2\nRed lead.\nB\nUmber\n1\nGum shellac\n8\nSugar of lead\n2\nWhite vitriol\n1\nDigitized by Google\n102\nCIVIL ENGINEERING.\nThe proportions of the above compositions are given in 100\nparts, by weight, with the exception of lacker 2.\nThe beautiful black polish on the Berlin castings for orna-\nmental purposes, is said to be produced by laying the follow-\ning composition on the hot iron, and then baking it.\nBitumen of India\n0.5\nResin\n0.5\nDrying oil\n1.0\nCopal, or amber varnish\n1.0\nEnough oil of turpentine is to be added to this mixture to\nmake it spread.\n311. From experiments made by Mr. Mallet, on the pre-\nservative properties of paints and varnishes for iron immersed\nin water, it appears that caoutchouc varnish is the best for\niron in hot water, and asphaltum varnish under all other\ncircumstances; but that boiled coal-tar, laid on hot iron,\nforms a superior coating to either of the foregoing.\n312. Varnish for Zincked Iron. Mr. Mallet recommends\nthe following compositions for a paint, termed by him zoofa-\ngous paint, and a varnish to be used to preserve zincked iron\nboth from corrosion and from fouling in sea water.\nTo 50 lbs. of foreign asphaltum, melted and boiled in an\niron vessel for three or four hours, add 16 lbs. of red lead\nand litharge ground to a fine powder, in equal proportions,\nwith 10 gals. of drying linseed oil, and bring the whole to a\nnearly boiling temperature. Melt, in a second vessel, 8 lbs.\nof gum-anime; to which add 2 gals. of drying linseed oil at\na boiling heat, with 12 lbs. of caoutchouc partially dissolved\nin coal-tar naphtha. Pour the contents of the second vessel\ninto the first, and boil the whole gently, until the varnish,\nwhen taken up between two spatulas, is found to be tough\nand ropy. This composition, when quite cold, is to be thinned\ndown for use with from 30 to 35 gals. of spirits of turpentine,\nor of coal naphtha.\n313. It is recommended that the iron should be heated be-\nfore receiving this varnish, and that it should be applied with\na spatula, or a flexible slip of horn, instead of the ordinary\nbrush.\nWhen dry and hard, it is stated that this varnish is not\nacted upon by any moderately diluted acid or alkali; and,\nby long immersion in water, it does not form a partially sol-\nuble hydrate, as is the case with purely resinous varnishes\nand oil paints. It can with difficulty be removed by a sharp-\npointed tool; and is so elastic, that a plate of iron covered\nDigitized by\nGoogle\n7\nPAINTS AND VARNISH.\n103\nwith it may be bent several times before it will become de-\ntached.\n314. Zoofagous Paint. To 100 lbs. of a mixture of dry-\ning linseed oil, red lead, sulphate of barytes, and a little\nspirits of turpentine, add 20 lbs. of the oxychloride of copper,\nand 3 lbs. of yellow soap and common rosin, in equal propor-\ntions, with a little water.\nWhen zincked iron is exposed to the atmosphere alone, the\nvarnish is a sufficient protection for it ; but when it is im-\nmersed in sea water, and it is desirable, as in iron ships, to\nprevent it from fouling, by marine plants and animals attach-\ning themselves to it, the paint should be used, on account of\nits poisonous qualities. The paint is applied over the varnish,\nand is allowed to harden three or four days before immer-\nsion.\n315. Methods of Preserving Exposed Surfaces of Stone.\nPaints and similar means of preservation from the action of\nthe weather have been used on the exposed surfaces of ma-\nsonry composed of materials that were found not to with-\nstand well this action ; besides these, preparations of the alka-\nline silicates, known as soluble glass, have of late been\nrecommended as of a more durable character for this purpose.\nThese solutions are applied either by syringes or by a brush\nto the surface of the stone, it having been previously cleansed\nof all extraneous matter. Three applications on three succes-\nsive days are said to be sufficient to harden and preserve any\nstone.\nAnother mode of effecting the same object has been pro-\nposed, which is to use two solutions of mineral substances\nwhich, successively applied to the surface of the stone, shall\nform an insoluble chemical compound. One method propos-\ned is to saturate the stone at the surface with a weak solution\nof silicate of potash or soda, on which a solution of chloride of\ncalcium or barium is applied. From this an insoluble silicate\nof lime or barium will be formed in the pores of the stone,\nwhich will render it weather-proof.\nLike processes have been used for dyeing or coloring stone\nfor certain architectural effects. For this purpose some of\nthe soluble sulphates are used in various combinations, accord-\ning to the color to be obtained.\nDigitized by\nGoogle\nCHAPTER IL\n316. WHATEVER may be the physical structure of materials,\nwhether fibrous or granular, experiment has shown that they\nall possess certain general properties, among the most impor-\ntant of which to the engineer are those of contraction, elon-\ngation, deflection, torsion, lateral adhesion, and shearing, and\nthe resistance which these offer to the forces by which they\nare called into action.\nEXPERIMENTAL RESEARCHES ON THE STRENGTH OF MATERIALS.\nI. GENERAL DEDUCTIONS FROM EXPERIMENTS. II. STRENGTH\nOF STONE. III. STRENGTH OF MORTARS AND CONCRETES.\nIV. STRENGTH OF TIMBER. V. STRENGTH OF CAST IRON.\nVI. STRENGTH OF WROUGHT IRON. VII. STRENGTH OF\nSTEEL. VIII. STRENGTH OF COPPER. IX. STRENGTH OF\nOTHER MATERIALS. X. LINEAR CONTRACTION AND EXPAN-\nSION OF METALS AND OTHER MATERIALS FROM TEMPERATURE.\nXI. ADHESION OF IRON SPIKES TO TIMBER.\nSUMMARY.\nI.\nGENERAL DEDUCTIONS FROM EXPERIMENTS.\nPhysical properties of solid bodies and the various experiments to test them\n(Arts. 316-326).\nII.\nSTRENGTH OF STONE.\nResistance of stone to crushing and transverse strains (Arts. 327-333).\nPractical deductions (Art. 334).\nExpansion of stone from increase of temperature (Art. 835).\nIII.\nSTRENGTH OF MORTARS AND CONCRETES.\nStrength of mortars (Arts. 386-340).\nStrength and other properties of Portland cement (Art. 341).\nStrength of concrete and béton (Art. 342).\nDigitized by Google\nSTRENGTH OF MATERIALS.\n105\nIV.\nSTRENGTH OF TIMBER.\nResistance to tensile strain (Art. 848).\nResistance to compressive strain (Art. 344).\nResistance of square pillars (Art. 345).\nResistance to transverse strains (Art. 346).\nResistance to detrusion (Art. 847).\nV.\nSTRENGTH OF CAST IRON.\nResistance to tensile strain (Art. 848).\nResistance to compressive strain (Art. 349-354).\nResistance to transverse strain (Art. 355-361).\nInfluence of form upon the strength of cast-iron beams (Art. 362-364).\nFormulas for determining the ultimate strength of cast-iron beams of the\nabove form (Art. 365).\nEffect of horizontal impact upon cast-iron bars (Art. 366-367).\nVI.\nSTRENGTH OF WEOUGHT IRON.\nResistance to tensile strain (Art. 868).\nResistance to compressive strain (Art. 369-372).\nResistance of iron wire to impact (Art. 873.)\nResistance to torsion (Art. 874).\nVII.\nSTRENGTH OF STEEL.\nStrength and other properties of steel (Art. 375).\nVIII.\nSTRENGTH OF COPPER.\nResistance to tensile and compressive strains (Art. 376-377).\nIX.\nSTRENGTH OF OTHER METALS.\nStrength of cast tin, cast lead, gun-metal, and brass (Art. 378).\nX.\nLINEAR CONTRACTION AND EXPANSION OF METALS AND OTHER\nMATERIALS FROM TEMPERATURE.\nXI.\nADHESION OF IRON SPIKES TO TIMBER.\nDigitized by Google\n106\nCIVIL ENGINEERING.\n317. All solid bodies, when submitted to strains by which\nany of these properties are developed, have, within certain\nlimits, termed the limits of elasticity, the property of wholly\nor partially resuming their original state, when the strain is\ntaken off.\n318. To what extent bodies possess the property of total re-\ncovery of form, when relieved from a strain, is still a matter\nof doubt. It has been generally assumed, that the elasticity\nof a material does not undergo permanent injury by any strain\nless than about one-third of that which would entirely destroy\nits force of cohesion, thereby causing rupture. But from the\nmore recent experiments on this point made by Mr. Hodgkin-\nson and others on cast iron, it appears that the restoring power\nof this material is destroyed by very slight strains; and it is\nrendered probable that this and most other materials receive\na permanent change of form, or set, under any strain, how-\never small.\n319. The extension, or contraction of a solid, may be effect-\ned either by a force acting in the direction in which the con-\ntraction or elongation takes place, or by one acting trans-\nversely, so as to bend the body. Experiments have been made\nto ascertain, directly, the proportion between the amount of\ncontraction or elongation, and the forces by which they are\nproduced. From these experiments, it results, that the con-\ntractions or elongations are, within certain limits, proportional\nto the forces, but that an equal amount of contraction, or elon-\ngation is not produced by the same amount of force. From\nthe experiments of Mr. Hodgkinson and M. Duleau, it ap-\npears that in cast and malleable iron the contraction or elon-\ngation caused by the same amount of pressure or tension is\nnearly equal; while in timber, according to Mr. Hodgkinson,\nthe amount of contraction is about four-fifths of the elonga-\ntion for the same force.\n320. When a solid of any of the materials used in construc-\ntions is acted upon by a force SO as to produce deflection, ex-\nperiment has shown that the fibres towards the concave side'\nof the bent solid are contracted, while those towards the con-\nvex side are elongated; and that, between the fibres which\nare contracted and those which are elongated, others are found\nwhich have not undergone any change of length. The part\nof the solid occupied by these last fibres has received the name\nof the neutral line or neutral axis.\n321. The hypothesis usually adopted, with respect to the\ncircumstances attending this kind of strain, is that the con-\nDigitized\nby\nGoogle\nSTRENGTH OF MATERIALS.\n107\ntractions and elongations of the fibres on each side of the neu-\ntral axis are proportional to their distances from this line and\nthat, for slight deflections, the neutral axis passes through the\ncentre of gravity of the sectional area. From experiments,\nhowever, by Mr. Hodgkinson and Mr. Barlow, on bars having\na rectangular cross-section, it appears that the neutral axis, in\nforged iron and cast iron, lies nearer to the concave than to\nthe convex surface of the bent solid, and, probably, shifts its\nposition when the degree of deflection is 80 great as to cause\nrupture. In timber, according to Mr. Barlow, the neutral\naxis lies nearest to the convex surface; and, from his experi-\nments on solids of forged iron and timber with a rectangular\nsectional figure, he places the neutral axis at about three-\neighths of the depth of the section from the convex side in\ntimber, and between one-third and one-fifth of the depth of\nthe section from the concave side in forged iron.\n322. When the strain to which a solid is subjected is suf-\nficiently great to destroy the cohesion between its particles\nand cause rupture, experiment has shown that the force pro-\nducing this effect, whether it act by tension, 40 as to draw the\nfibres asunder, or by compression, to crush them, is propor-\ntional to the sectional area of the solid.\n323. From experiments made to ascertain the circumstan-\nces of rupture by a tensile force, it appears that the solid torn\napart exhibits a surface of fracture more or less even, accord-\ning to the nature of the material.\n324. Most of the experiments on the resistance to rupture\nby compression, have been made on small cubical blocks, and\nhave given a measure of this resistance greater than can be\ndepended upon in practical applications, when the height of\nthe solid exceeds three times the radius of its base. This\npoint has been very fully elucidated in the experiments of\nMr. Hodgkinson upon the rupture by compression of solids\nwith circular and rectangular bases. These experiments go\nto prove that the circumstances of rupture, and the resistance\noffered by the solid, vary in a constant manner with its height,\nthe base remaining the same. In columns of cast iron, with\ncircular sectional areas, it was found that the resistance re-\nmained constant for a height less than three times the radius\nof the base ; that, from this height to one equal to six times\nthe radius of the base, the resistance still remained constant,\nbut was less than in the former case; and that, for any height\ngreater than six times the radius of the base, the resistance\ndecreased with the height. In the two first cases the solids\nwere found to yield either by the upper portion sliding off\nDigitized by Google\n108\nCIVIL ENGINEERING.\nupon the lower, in the direction of a plane making a constant\nangle with the axis of the solid ; or else by separating into\nconical or wedge-shaped blocks, having the upper and lower\nsurfaces of the solid as their bases, the angle at the apex be-\ning double that made by the plane and axis of the solid.\nWith regard to the resistance, it was found that they varied in\nthe ratio of the area of the bases of the solids. Where the\nheight of the solid was greater than six times the radius of\nthe base, rupture generally took place by bending.\n325. From experiments by Mr. Hodgkinson, on wood and\nother substances, it would appear that like circumstances ac-\ncompany the rupture of all materials by compression ; that is,\nwithin certain limits, they all yield by an oblique surface of\nfracture, the angle of which with the axis of the solid is con-\nstant for the same material ; and that the resistance offered\nwithin these limits are proportional to the areas of the\nbases.\n326. Among the most interesting deductions drawn by Mr.\nHodgkinson, from the wide range of his experiments upon the\nstrength of materials, is the one which points to the existence\nof a constant relation between the resistances offered by ma-\nterials of the same kind to rupture from compression, tension,\nand a transverse strain. The following Table gives these re-\nlations, assuming the measure of the crushing force at 1000.\nMean transverse force\nDESCRIPTION OF MATERIAL\nCrushing force par\nMean tensile force\nsquare inch.\nper square inch.\nof a bar 1 inch square\nand 1 foot long.\nTimber\n1000\n1900\n85.1\nCast iron\n1000\n158\n19.8\nStone\n1000\n100\n9.8\nGlass (plate and crown).\n1000\n123\n10\nDigitized by\nGoogle\nSTRENGTH OF STONE.\n109\nII.\nSTRENGTH OF STONE.\n327. The marked difference in the structure and in the\nproportions of the component elements frequently observed in\nstone from the same quarry would lead to the conclusion\nthat corresponding variations would be found in the strength\nof stones belonging to the same class, a conclusion which ex-\nperiment has confirmed. The experiments made by different\nindividuals on this subject, from not having been conducted\nin the same manner, and from the omission in most cases of\ndetails respecting the structure and component elements of\nthe material tried, have, in some instances, led to contradic-\ntory results. A few facts, however, of a general character,\nhave been ascertained, which may serve as guides in ordinary\ncases ; but in important structures, where heavy pressures are\nto be sustained, direct experiment is the only safe course for\nthe engineer to follow, in selecting a material from untried\nquarries.\n328. Owing to the ease with which stones generally break\nunder a percussive force, and from the comparatively slight\nresistance they offer to a tensile force and to a transverse\nstrain, they are seldom submitted in structures to any other\nstrain than one of compression; and cases but rarely occur\nwhere this strain is not greatly beneath that which the better\nclass of building stones can sustain permanently, without un-\ndergoing any change in their physical properties. Where the\ndurability of the stone, therefore, is well ascertained, it may\nbe safely used without a resort to any specific experiment\nupon its strength, whenever, in its structure and general ap-\npearance, it resembles a material of the same class known to\nbe good.\n329. The following table exhibits the principal results of\nexperiments made by Mr. G. Rennie, and published in the\nPhilosophical Transactions of 1818. The stones tried were\nin small cubes, measuring one and a half inches on the edge.\nThe table gives the pressure, in tons, borne by each superficial\ninch of the stone at the moment of crushing.\nDigitized by\nGoogle\n110\nCIVIL ENGINEERING.\nDESCRIPTION OF STONE.\nSpec. gravity.\nCrushing w'ght.\nGranites.\nAberdeen, (blue)\n2.625\n4.88\nPeterhead\n-\n3.70\nCornwall\n2.662\n2.83\nSandstones.\nDundee\n2.580\n2.96\nDo\n2.506\n2.70\nDerby (red and friable)\n2.316\n1.40\nLimestones.\nMarble (white-veined Italian)\n2.726\n4.32\nDo. (white Brabant)\n2.697\n4.11\nLimerick (black compact)\n2.598\n3.95\nDevonshire (red marble)\n-\n3.31\nPortland stone (Ane-grained oolite)\n2.428\n2.04\nThe following resultsare taken from a series of experiments\nmade under the direction of Messrs. Bramah & Sons, and\npublished in Vol. 1, Transactions of the Institution of\nCivil Engineers. The first column of numbers gives the\nweights, in tons, borne by each superficial inch when the\nstones commenced to fracture; the second column gives the\ncrushing weight, in tons, on the same surface.\nDESCRIPTION OF STONE.\nAver. weight pro-\nAverage crushing\nducing fractures.\nweight.\nGranites.\nHerme\n4.77\n6.64\nAberdeen (blue)\n4.13\n4.64\nHeytor\n8.94\n6.19\nDartmoor\n3.52\n5.48\nPeterhead (red)\n2.88\n4.88\nPeterhead (blue gray)\n2.86\n4.86\nSandstones.\nYorkshire\n2.87\n3.94\nCraigleith\n1.89\n2.97\nHumbic\n1.69\n2.06\nWhitby\n1.00\n1.06\nThe following table is taken from one published in Vol.\nDigitized by Google\nSTRENGTH OF STONE.\n111\n2, Civil Engineer and Architect's Journal, which forms a\npart of the Report on the subject of selecting stone for the\nNew Houses of Parliament. The specimens submitted to ex-\nperiment were cubical blocks measuring two inches on an\nedge.\nSpecific gravity.\nWeight produ-\nDESCRIPTION OF STONE.\ncing fracture.\nCrushing wght.\nSandstones.\nCraigleith\n2.232\n1.89\n3.5\nDarley Dale\n2.628\n2.75\n8.1\nHeddon\n2.229\n0.82\n1.75\nKenton\n2.247\n1.51\n2.21\nMansfield\n2.338\n0.88\n1.64\nMagnesian Limestones.\nBolsover\n2.816\n2.21\n3.75\nHuddlestone\n2.147\n1.03\n1.92\nRoach Abbey\n2.134\n0.75\n1.78\nPark Nook\n2.138\n0.32\n1.92\nOolites.\nAncaster\n2.182\n0.75\n1.04\nBath Box\n1.839\n0.56\n0.66\nPortland\n2.145\n0.95\n1.75\nKetton\n2.045\n0.69\n1.18\nLimestones.\nBarnack\n2.090\n0.50\n0.79\nChilmark (silicious)\n2.481\n1.32\n3.19\nHamhill\n2.260\n0.69\n1.80\nThe numbers of the first column give the specific gravities\nthose in the second column the weight in tons on a square\ninch, when the stone commenced to fracture; and those in the\nthird the crushing weight on a square inch.\nThe following table exhibits the results of experiments on\nthe resistance of stone to a transverse strain, made by Colonel\nPasley, on prisms 4 inches long, the cross section being a\nsquare of 2 inches on a side; the distance between the points\nof support 3 inches.\n330. The conductors of the experiments on the stone for\nthe New Houses of Parliament, Messrs. Daniell and Wheat-\nstone, who also made a chemical analysis of the stones, and\napplied to them Brard's process for testing their resistance to\nDigitized by Google\n112\nCIVIL ENGINEERING.\nWeight of stone\nDESCRIPTION OF STONE.\nper cubic foot\nAverage breaking\nin lbs.\nweight in lbs.\n1. Kentish Rag\n165.69\n4581\n2. Yorkshire Landing\n147.67\n2887\n3. Cornish granite\n172.24\n2808\n4. Portland\n148.08\n2682\n5. Craigleith\n144.47\n1896\n6. Bath\n122.58\n666\n7. Well-burned bricks\n91.71\n752\n8. Inferior bricks\n-\n329\nfrost, have appended the following conclusions from their\nexperiments :- If the stones be divided into classes, accor-\nding to their chemical composition, it will be found that in\nall stones of the same class there exists generally a close rela-\ntion between their various physical qualities. Thus it will be\nobserved that the specimen which has the greatest specific\ngravity possesses the greatest cohesive strength, absorbs the\nleast quantity of water, and disintegrates the least by the pro-\ncess which imitates the effects of weather. A comparison of\nall the experiments shows this to be the general rule, though\nit is liable to individual exceptions.\"\n\" But this will not enable us to compare stones of different\nclasses together. The sandstones absorb the least quantity of\nwater, but they disintegrate more than the magnesian lime-\nstones, which, considering their compactness, absorb a great\ndeal.\"\n331. Like conclusions to the preceding were reached by a\ncommission for testing the properties of some of the stones\nand marbles used in the construction of the Capitol at Wash-\nington.\nBut few experiments have been made upon the strength\nand other properties of the building stones of the United\nStates, and those of a local character. From the reports of a\npublic commission, and of Professor R. Johnson, on the mar-\nbles and micaceous stratified stones used in the walls and\nfoundations of the Capitol at Washington, the same general\nconclusions were arrived at as in the report of Messrs. Daniell\nand Wheatstone above cited. The strength of the marbles\nsubmitted to experiment varied from about seven thousand\nto twenty-four thousand pounds to the square inch ; the mica-\nceous stones used in the foundations averaged about fifteen\nthousand pounds to the square inch ; some specimens of sand-\nstone gave about five thousand pounds to the square inch ; and\nDigitized by Google\nSTRENGTH OF STONE.\n113\none of sienite about twenty-nine thousand pounds to the square\ninch.-Report of the Architect of Public Buildings, Dec. 1,\n1852.\n332. Rondelet, from a numerous series of experiments on\nthe same subject, published in his work, Art de Bâtir, has\narrived at like conclusions with regard to the relations between\nthe specific gravity and strength of stones belonging to the\nsame class.\nAmong the results of the more recent experiments on this\nsubject, those obtained by Mr. Hodgkinson, showing the\nrelation between the crushing, the tensile, and the transverse\nstrength of stone, have already been given.\nM. Vicat, in a memoir on the same subject, published in\nthe Annales des Ponts et Chaussées, 1833, has arrived at an'\nopposite conclusion from Mr. Hodgkinson, stating as the re-\nsults of his experiments, that no constant relation exists be-\ntween the crushing and tensile strength of stone in general,\nand that there is no other means of determining these two\nforces but by direct experiment in each case.\n333. The influence of form on the strength of stone, and\nthe circumstances attending the rupture of hard and soft\nstones, have been made the subject of particular experiments\nby Rondelet and Vicat. Their experiments agree in estab-\nlishing the points that the crushing weight is in proportion to\nthe area of the base. Vicat states, more generally, that the\npermanent weights borne by similar solids of stone, under like\ncircumstances, will be as the squares of their homologous\nsides. These two authors agree on the point that the circular\nform of the base is the most favorable to strength. They\ndiffer on most other points, and particularly on the manner in\nwhich the different kinds of stone yield by rupture.\n334. Practical Deductions. Were stones placed under\nthe same circumstances in structures as in the experiments\nmade to ascertain their strength, there would be no difficulty in.\nassigning the fractional part of the weight termed the work-\ning strain or working loud which, in the comparatively short\nperiod usually given to an experiment, will crush them, could:\nbe borne by them permanently with safety. But, indepen-\ndently of the accidental causes of destruction to which struc-\ntures are exposed, imperfections in the material itself, as well\nas careless workmanship, from which it is often placed in the\nmost unfavorable circumstances of resistance, require to be\nguarded against. M. Vicat, in the memoir before mentioned,\nstates that a permanent strain of 1300 of the crushing force of\nexperiment may be borne by stone without danger of impair-\n8\nDigitized by Google\n114\nCIVIL ENGINEERING.\ning its cohesive strength, provided it be placed under the\nmost favorable circumstances of resistance. This fraction of\nthe crushing weight of experiment is greater than ordinary\ncircumstances would justify, and it is recommended in prac-\ntice not to submit any stone to a greater permanent strain\nthan one-tenth of the crushing weight of experiments made\non small cubes measuring about two inches on an edge.\nOther authorities state that cut stone in cases like the vous-\nsoirs of arches and stone pillars should not be subjected to a\nworking strain greater than 10ᵗʰ of the crushing weight of\nexperiment.\nThe following table shows the permanent strain, and\ncrushing weight, for a square foot of the stones in some of\nthe most remarkable structures in Europe.\nPermanent\nCrushing\nstrain.\nweight.\nPillars of the dome of St. Peter's (Rome)\n33330\n536000\nDo.\nSt. Paul's (London)\n39450\n537000\nDo.\nSt. Geneviève (Paris)\n60000\n456000\nDo.\nChurch of Toussaint (Angers)\n90000\n900000\nLower courses of the piers of the Bridge of Neuilly\n3600\n570000\nThe stone employed in all the structures enumerated in the\nTable, is some variety of limestone.\n335. Expansion of Stone from Increase of Tempera-\nture. Experiments have been made in this country by Prof.\nBartlett, and in England by Mr. Adie, to ascertain the expan-\nsion of stone for every degree of Fahrenheit. The experi-\nments of Prof. Bartlett give the following results:\nGranite expands for every degree\n000004825\nMarble\n.000005668\nSandstone\n000009532\nDigitized by\nGoogle\nSTRENGTH OF MORTARS.\n115\nTable of the Expansion of Stone, etc., from the Experiments\nof Alexander J. Adie, Civil Engineer, Edinburgh.\nDecimal of\nDecimal of\nDecimal of\nan inch on\nDESCRIPTION OF STONE.\n28 inches\nlength for\nlength for\nRemarks.\n180° F.\nfor 180° F.\n1° F.\n1. Roman cement\n.0830048\n.0014849\n.00000750\n2. Sicilian white marble\n.0325892\n.0014147\n.00000780\nOne experiment (moist).\n.0258946\n.00110411\n.00000618\nMean of three (dry).\n8. Carrara marble\n.0274844\n.0011928\n.00000662\nOne experiment (moist).\n.0150-405\n.0006539\n.00000868\nMean of two (dry).\n4. Sand-stone (Craigleith)\n.0270098\n.0011748\n.00000658\nMean of four experiments.\n5. Slate (Weich)\n.0238659\n.0010376\n.00000576\nMean of three\ndo.\n.0220416\n.0009588\n6. Red granite (Peterhead).\n.00000582\nOne experiment (moist).\n.0206266\n.0006968\n.00000498\nMean of two (dry).\n7. Arbroath pavement\n0206652\n.0008985\n.00000499\nMean of four experiments.\n8. Caithness pavement\n.0205788\n.0008947\n.00000497\nMean of three\ndo.\n9. Green-stone (Ratho)\n.0186048\n.0008069\n.00000449\nMean of three\ndo.\n10. Gray granite (Abordeen)\n.01815695\n.00078943\n.00000488\nMean of two\ndo.\n11. Best stock brick\n.0126542\n.0005502\n.00000806\nMean of two\ndo.\n12. Fire brick\n.0113384\n.0004928\n.00000274\nMean of two\ndo.\n18. Black marble (Galway)\n.0102894\n.00044519\n.00000247\nMean of three\ndo.\nIII.\nSTRENGTH OF MORTARS AND CONGRETES.\n336. Strength of Mortars. A very wide range of experi-\nments has been made, within a few years back, by engineers\nboth at home and abroad, upon the resistance offered by mor-\ntars to a transversal strain, with a view to compare their qual-\nities, both as regards their constituent elements and the\nprocesses followed in their manipulation. As might naturally\nhave been anticipated, these experiments have presented very\ndiversified, and in many instances, contradictory results. The\ngeneral conclusions, however, drawn from them, have been\nnearly the same in the majority of cases; and they furnish\nthe engineer with the most reliable guides in this important\nbranch of his art.\n337. The usual method of conducting these experiments has\nbeen to subject small rectangular prisms of mortas, resting on\npoints of support at their extremities, to a transversal strain\napplied at the centre point between the bearings. This, per-\nhaps, is as unexceptionable and convenient a method as can\nbe followed for testing the comparative strength of mortars.\nDigitized by\nGoogle\n116\nCIVIL ENGINEERING.\n338. M. Vicat, in the work already cited, gives the follow-\ning as the average resistances on the square inch offered by\nmortars to a force of traction ; the deductions being drawn\nfrom experiments on the resistance to a transversal strain.\nMortars of very strong hydraulic lime\n170 pounds.\n\"\nordinary\ndo.\n140\n\"\n\"\nmedium\ndo.\n100\n\"\n\"\ncommon lime\ndo.\n40\n\"\n\"\ndo.\n(bad quality)\n10\n\"\nThese experiments were made upon prisms a year old,\nwhich had been exposed to the ordinary changes of\nweather. With regard to the best hydraulic mortars of the\nsame age which had been, during that same period, either\nimmersed in water, or buried in a damp position, M. Vicat\nstates that their average tenacity may be estimated at 140\npounds on the square inch.\n339. General Trenssart, in his work on hydraulic and com-\nmon mortars, has given in detail a large number of experi-\nments on the transversal strength of artifical hydraulic mor-\ntars, made by submitting small rectangular parallelopipeds\nof mortar, six inches in length and two inches square, to a\ntransversal strain applied at the centre point between the\nbearings, which were four inches apart. From these experi-\nments he deduces the following practical conclusions.\nThat when the parallelopipeds sustain a transversal strain\nvarying between 220 and 330 pounds, the corresponding mor-\ntar will be suitable for common gross masonry ; but that for\nimportant hydraulic works the parallelopipeds should sustain,\nbefore yielding, from 330 to 440 pounds.\n340. The only published experiments on this subject made\nin this country are those of Colonel Totten, appended to his\ntranslation of General Treussart's work. The results of these\nexperiments are of peculiar value to the American engineer,\nas they were made upon materials in very general use on the\npublic works throughout the country.\nFrom these experiments Colonel Totten deduces the follow-\ning general results :\n1st. That mortar of hydraulic cement and sand is the strong-\ner and harder as the quality of sand is less.\n2d. That common mortar is the stronger and harder as the\nquantity of sand is less.\n3d. That any addition of common lime to a mortar of\nhydraulic cement and sand weakens the mortar, but that a\nlittle lime may be added without any considerable diminution\nof the strength of the mortar, and with a saving of expense.\nDigitized by\nGoogle\nSTRENGTH OF MORTARS.\n117\n4th. The strength of common mortars is considerably\nimproved by the addition of an artificial puzzolana, but more\nso by the addition of an hydraulic cement.\n5th. Fine sand generally gives a stronger mortar than\ncoarse sand.\n6th. Lime slaked by sprinkling gave better results than\nlime slaked by drowning. A few experiments made on air-\nslaked lime were unfavorable to that mode of slaking.\n7th. Both hydraulic and common mortar vielded better\nresults when made with a small quantity of water than when\nmade thin.\n8th. Mortar made in the mortar-mill was found to be su-\nperior to that mixed in the usual way with a hoe.\n9th. Fresh water gave better results than salt water.\n341. Strength and Other Properties of Portland Cement.\nFrom experiments made in England by Mr. Grant on the re-\nsistance to crushing of blocks of Portland cement, and of\nPortland cement mortars, the following results are deduced.\n1st. The strength of the blocks in both cases increased with\ntime. The blocks. of pure cement bearing respectively nearly\n4,000 lbs. on the square inch after three months; over 5,000\nlbs. at six months; and nearly 6,000 lbs. at nine months.\n2d. The strength of the blocks of mortar also increased\nwith time; but decreased as the volume of sand used was\nincreased. The blocks made with one volume of sand to one\nof cement bore about 2,500 lbs, on the square inch, and those\nmade of six volumes of sand to one of cement 959 lbs. at\nthe end of three months; whilst those made of one volume\nof sand to one of cement bore 4,561 lbs. on the square inch\nat the end of nine months, and those made of six volumes of\nsand to one of cement bore 1,678 lbs. on the square inch at\nthe end of the same period.\nFrom numerous experiments made by Mr. Grant in England,\non Portland cement, he draws the following conclusions :-\n1st. Portland cement, if it be preserved from moisture,\ndoes not, like Roman cement, lose its strength by being kept\nin casks or sacks, but rather improves by age.\n2d. The longer it is in setting, the more its strength in-\ncreases.\n3d. Very strong Portland cement is heavy, of a blue-gray\ncolor, and sets slowly. Quick setting cement has, generally,\ntoo large a portion of clay in its composition, is brownish in\ncolor, and turns out weak if not useless.\n4th. The less the amount of water in working the cement\nup the better.\nDigitized by Google\n118\nCIVIL ENGINEERING.\n5th. It is of the greatest importance that the stones or\nbricks, with which Portland cement is used, should be thor-\noughly soaked with water. If under water, in a quiescent\nstate, the cement will be stronger than out of water.\n6th. Blocks of brickwork, or of concrete, made with Port-\nland cement, if kept under water until required for use,\nwould be much stronger than if kept dry.\n7th. Salt water is as good for mixing with Portland cement\nas fresh water.\n8th. Roman cement is very ill adapted for being mixed\nwith sand.\n9th. The resistance of a block of pure Portland cement to\nextension after an immersion of one year was about 480 lbs.\non the square inch ; whilst the resistances of blocks made of\nsand and cement, after the same period of immersion, decreased\nwith the quantity of sand added. Blocks of one volume of\ncement in paste to one of sand giving three-fourths the re-\nsistance of those of pure ceinent; and those of one volume\nof cement to five of sand giving only one-sixth of the resist-\nance of blocks of pure cement.\n10th. Roman cement is only one-third the strength of\nPortland cement.-Procedings of the Institution of Civil\nEngineers, Vol. XXV., p. 66.\n342. Concrete and Beton. From experiments made on\nconcrete, prepared according to the most approved process in\nEngland, by Colonel Pasley, it appears that this material is\nvery inferior in strength to good brick, and the weaker kinds\nof natural stones.\nFrom experiments made by Colonel Totten on béton, the\nfollowing conclusions are drawn:\nThat béton made of a mortar composed of hydraulic\ncement, common lime, and sand, or of a mortar of hydraulic\ncement and sand, without lime, was the stronger as the quan-\ntity of sand was the smaller. But there may be 0.50 of sand,\nand 0.25 of common lime, without sensible deterioration\nand as much as 1.00 of sand, and 0.25 of lime, without great\nloss of strength.\nBéton made with just sufficient mortar to fill the void spaces\nbetween the fragments of stone was found to be less strong\nthan that made with double this bulk of mortar. But Colonel\nTotten remarks, that this result is perhaps attributable to the\ndifficulty of causing SO small a quantity of mortar to penetrate\nthe voids, and unite all the fragments perfectly, in experi-\nments made on a small scale.\nThe strongest béton was obtained by using quite small\nDigitized by Google\nSTRENGTH OF TIMBER.\n119\nfragments of brick, and the weakest from small, rounded,\nstone gravel.\nA béton formed by pouring grout among fragments of\nstone, or brick, was inferior in strength to that made in the\nusual way with mortar.\nComparing the strength of the bétons on which the experi-\nments were made, which were eight months old when tried,\nwith that of a sample of sound red sandstone of good qual-\nity, it appears that the strongest prisms of béton were only\nhalf as strong as the sandstone.\nThe working strain on masses of concrete, brick, and rubble\nmasonry seldom exceeds in structures that of one-sixth of the\ncrushing weight of blocks of these materials.\nIV.\nSTRENGTH OF TIMBER.\nA wide range of experiments has been made on the resist-\nance of timber to compression, extension, and a transverse\nstrain, presenting very variable results. Among the most\nrecent, and which command the greatest confidence from the\nability of their authors, are those of Professor Barlow and\nMr. Hodgkinson: the former on the resistance to extension\nand a transverse strain; the latter on that to compression.\nDigitized by Google\n120\nCIVIL ENGINEERING.\nThe following Table, taken from Vol. V. Professional\nPapers of the English Royal Engineers. No. V. Re-\nmarks and Experiments on various Woods, give some\nvaluable results on American timber subjected to a strain\nparallel to the fibre. The column marked C gives the co-\nhesive strength.\nMean\nC.\nExtreme\nTransverse\npractical\nNo. of piece and\naverage specific\nNo. of experiment.\nDimen-\nsions.\nMean area of Trans-\nlimit of C.\ngravity.\nB.\nverse Section.\nD.\nBreaking weight.\nComputed break-\ning weight per\nsquare inch.\nApproximate\nproportion.\nRemarks.\nin.\nin.\nin.\nlbs.\nlbs.\nlbs.\n9\n.6\n.607\n.8642\n8088\n8478\n10\n.605\n.613\n.8708\n4051\n10925\n5-9\nMr. Barlow's English ash, sp.\ngr. 760 C=17887.\nASH, AMERICAN.\n11\n.608\n.615\n.8789\n4142\n11077\n4-7\nMr. Emerson's do., C=6070.\n12\n.585\n.575\n.8368\n2528\n7517\n7-9\nNo. 9\n18\n.615\n.615\n.3782\n2528\n6684\n4800\n636\n14\n.598\n.61\n.8617\n2675\n7395\n8-9\n15\n.588\n.61\n.3586\n2387\n6656\n8-4\n16\n.597\n.6\n.8582\n2580\n7202\n5-6\n17\n.62\n.62\n.8844\n3478\n9085\n8380\n18\n.588\n.598\n.3516\n2958\n8819\n19\nCrushed.\n20\n.61\n.61\n.8721\n8755\n10091\nMr. Barlow's English Beech,\nsp. gr. 696 C=9912.\n21\n.607\n.608\n.866\n8687\n10078\n8000\nBEECH, AMERICAN.\nMr. Tredgold's do., sp. gr. 696,\nC=2860.\nif there be\nno crush-\ning force.\n22\nCrushed.\n28\n.68\n.612\n.3855\n3687\n9564\n24\n.598.\n.612\nCrushed.\n9512\n25\n.608\n.575\n.8467\n2567\n7404\n5-6\nBIRCH, BLACK\nNo. 17\n26\n.612\n.59\n.361\n2086\n5778\n9-10\nMr. Emerson's Birch, 4290.\nAMERICAN.\n645\n27\n.628\n.56\n.8516\n2460\n6996\n5-8\n28\n.627\n.597\n.3748\n2823\n7512\n11-14\n4250\n29\n.601\n597\n.3623\n1904\n5255\n8-4\n80\n.595\n.597\n.3552\n1848\n8809\n6959\n45\n.598\n.582\n.3451\n3528\n10223\nNo. 29\n46\n.58\n.597\n.3846\n4734\n14148\n685\n47\n.587\nELM, CANADA.\n.58\n.8404\n4500\n13219\n48\n.605\n.578\n.8496\n4263\n12193\nRecords lost.\n8000\nNo. 26\n49\n.597\n.575\n.8482\n4399\n12817\n703\n50\n.6\n.578\n.3468\n4852\n18990\n12765\nDigitized by Google\nSTRENGTH OF TIMBER.\n121\nMean\nC.\nExtreme\nTransverse\npractical\nNo. of piece and\naverage specific\nNo. of experiment.\nDimen-\nsions.\nMean area of Trans-\nlimit of C.\ngravity.\nB.\nverse Section.\nD.\nBreaking weight.\nComputed break-\ning weight per\nsquare inch.\nApproximate\nproportion.\nRemarks.\nin.\nin.\nin.\nlbs.\nlbs.\nlbs.\n51\n.588\n618\n.3602\n8518\n9766\n11-13\n52\n.588\n.61\n.8556\n4185\n11628\n4-5\nHICKORY, AMER-\nNo. 88\n58\n.566\n.59\n.8339\n8859\n11557\n10-13\n856\n54\n.598\n.575\n.8409\n4022\n11798\n8-4\n8000\nICAN.\n55\n.595\n.595\n.854\n8648\n10305\n5-6\n56\n.595\n.588\n.3498\n3893\n11192\n10-13\nNo. 30\n57\n.68\n.608\n.383\n4372\n11420\n854\n11095\nNo. 45\n80\n.59\n.595\n.851\n4414\n12547\n9-10\n716\n81\n.598\n.595\n.856\n4890\n18786\n6-7\nMr. Barlow's Canadian Oak,\nOAK, WHITE AMERI-\nsp. gr. 872, C=11428.\n82\n.587\n.597\n.3504\n3201\n9107\n88\n.598\n.542\n.3241\n2958\n9126\n4-5\n6000\nCAN.\nNo. 49\n84\n.59\n.505\n.3451\n2958\n8578-\n4-5\n600\n85\n.597\n.598\n.857\n8088\n8646\n4-5\n86\n.588\n.607\n.3569\n2755\n7719\n7-8\nNo. 45\n716\n87\n.608\n.627\n.3812\n3523\n9241\n9750\n88\n.582\n.566\n.8994\n8528\n10710\n6-7\nNo. 51\n89\n.607\n.573\n.8478\n3716\n10684\n7-9\nOAK. BASKET,\n987\n90\n.628\n.588\n.8661\nAMERICAN.\n8853\n9158\n91\n.542\n.61\n.8806\n8557\n10759\n5-6\n6000\n92\n.585\n.697\n.4077\n8365\n8258\n1-11\n98\n.608\n.547\n.8325\n2769\n8297\n7-9\n94\n.602\n.608\n.363\n4129\n11374\n9891\n120\n.605\n.605\n.866\n3876\n9224\n8-4\n\" River and green,\" beats\nNo. 62\n121\n.595\n.605\n.8599\n2815\n6482\n7-10\nsawn and seasoned,\" with\nOAK, ENGLISH, SAWN\n881\n122\n.605\n.605\n.866\n2725\n7445\nreference to both S and C.\nAND SEASONED.\n123\n.593\n.6\n.3558\n2815\n6506\n5500\nThe uninjured state of the\ngrain has, Iapprehend, more\n124\n.598\n.61\n.3647\n3213\n8809\n7-11\nto do with the strength than\nNo. 68\n125\n.6\n.605\n.868\n2963\n8162\n7-11\nthe condition as to the dry-\n886\n126\n.6\n.59\n.884\n2408\n6802\n5-6\nness.\n127\n.585\n.6\n.351\n2408\n6860\nTredgold's English Oak sp. gr.\n830, C=8960.\n7530\nNo. 65\n1230\n128\n.598\n.6\n.8588\n3528\n9832\nOAK, HOLM, AMERI-\nNo. 67\n129\n.603\n.6\n.3618\n2688\n7429\n1141\n180\n.59\n.608\n.3587\n4118\n11466\nRecords lost.\n4000\nCAN.\nNo. 68\n181\n.57\n.608\n.8487\n8111\n9051\n1140\n132\n.627\n.577\n.3617\n2128\n5888\n188\n.597\n.578\n.8420\n2128\n6222\n8814\nDigitized by Google\n122\nCIVIL ENGINEERING.\nC.\nExtreme\nMean\npractical\nNo. of piece and\naverage specific\nTransverse\ngravity.\nNo. of experiment.\nMean area of Trans-\nlimit of C.\nDimen-\nsions.\nverse Section.\nB.\nD.\nBreaking weight.\nComputed break-\ning weight per-\nsquare inch.\nApproximate\nproportion.\nRemarks.\nin.\nin.\nin.\nlbs.\nlbs.\nlbs.\n184\n.585\n.607\n.855\n1528\n4304\n2-3\nMr. Barlow's New England\nNo. 76\nFir, sp. gr. 558, C=9947.\nPINE, RED AMERI-\n568\n185\n.587\n.6\n.3522\n1925\n5467\n2-3\n186\n.582\n.592\n.3445\n1868\n5422\n3-5\nCAN.\n187\n.587\n.59\n.8468\n1748\n5047\n3-5\n8000\nMr. Tredgold's Yellow Ameri-\nNo. 78\ncan, sp. gr. 460, C=8900.\n689\n138\n.587\n.59\n.3463\n1975\n5708\n23\n189\n.588\n.64\n.8763\n2449\n6508\n5408\n140\n.62\n.625\n.3875\n1424\n8674\n5-7\n141\n.607\n.602\n.8654\n1204\n8295\n2-3\nPINE. WHITE\nAMERICAN.\nNo. 71\n142\n.68\n.627\n.895\n1555\n3936\n5-6\n450\n148\n.685\n.635\n.8968\n1897\n8520\n5-7\n2200\n144\n.607\n.625\n.8798\n1295\n3418\n10-13\n145\n.627\n.617\n.8868\n1408\n3640\n8580\n343. Resistance to Tensile Strain. The following table\nexhibits the specific gravity, and the mean resistance per\nsquare inch of various kinds of timber, from the experiments\nof Prof. Barlow.\nThe working strain on beams subjected to extension should\nnot exceed 1½ of the rupturing strain in permanent structures,\nbut for temporary purposes, like scaffolding, &c., it may be\nplaced at 1th the rupturing strain with safety.\nBut few direct experiments have been made upon the\nelongations of timber from a strain in the direction of the\nfibres. From some made in France by MM. Minard and\nDesormes, it would appear that bars of oak having a sectional\narea of one square inch will be elongated .001176 of their\nlength by a strain of one ton.\n344. Resistance to Compressive Strains. The follow-\ning Table exhibits the results obtained by Mr. Hodgkinson\nfrom experiments on short cylinders of timber with flat ends.\nThe diameter of each cylinder was one inch, and its height two\ninches. The results, in the first column, are a mean from\nabout three experiments on timber moderately dry, being\nsuch as is used for making models for castings; those in the\nsecond column were obtained in a like manner, from similar\nDigitized by\nGoogle\nSTRENGTH OF TIMBER.\n123\nMean strength of\nDESCRIPTION OF TIMBER.\nSpec. grav.\ncohesion per\nsquare inch.\nAsh (English)\n0.760\n17000\nBeech, do.\n0.700\n11500\nBox\n1.000\n20000\nDeal (Christiania)\n0.680\n11000\nDo. (Memel)\n0.590\n11000\nElm\n0.540\n5780\nFir (New England)\n0.550\n12000\nDo. (Riga)\n0.750\n12600\nDo. (Mar Forest)\n0.700\n12000\nLarch (Scotch)\n0.540\n7000\nLocust\n0.950\n20580\nMahogany\n0.637\n8000\nNorway spars\n0.580\n12000\nOak (English)\nS from\n0.700\n9000\nto\n0.900\n15000\nDo. (African)\n0.980\n14400\nDo. (Adriatic)\n0.990\n14000\nDo. (Canadian)\n0.872\n12000\nDo. (Dantzic)\n0.760\n14500\nPear\n0.646\n9800\nPoon\n0.600\n14000\nPine (pitch)\n0.660\n10500\nDo. (red)\n0.660\n10000\nTeak\n0.750\n15000\nspecimens, which were turned and kept dry in a warm place\ntwo months longer. A comparison of the results in the two\ncolumns shows the effect of drying on the strength of tim-\nber; wet timber not having half the strength of the same\nwhen dry. The circumstances of rupture were the same as\nalready stated in the general observations under this head ;\nthe height of the wedge which would slide off in timber\nbeing about half the diameter or thickness of the specimen\ncrushed.\n345. Resistance of Square Pillars. Mr. Hodgkinson has\nmade a number of invaluable experiments on the strength of\npillars of timber, and of columns of iron and steel, and from\nthem has deduced formulse for calculating the pressure\nwhich they will support before breaking. The experiments\non timber were made on pillars with flat ends. The follow-\ning are the formulæ from which their strength may be esti-\nmated.\nCalling the breaking weight in lbs., W.\n\"\nthe side of the square base in inches, d.\n\"\nthe length of the pillar in feet, l.\nDigitized by\nGoogle\n124\nCIVIL ENGINEERING.\nStrength per square inch\nDESCRIPTION OF WOOD.\nin lbs.\nAlder\n6831\n6960\nAsh\n8688\n9363\nBaywood\n7518\n7518\nBeech\n7788\n19363\nBirch (American)\n3297\n11663\nDo. (English)\n3297\n6402\nCedar\n5674\n5863\nCrab\n6499\n7148\nRed deal\n5748\n6586\nWhite deal\n6781\n7293\nElder\n7451\n9973\nElm\n-\n10331\nFir (spruce)\n6499\n6819\nHornbeam\n4588\n7289\nMahogany\n8198\n8198\nOak (Quebec)\n4231\n5982\nDo. (English)\n6484\n10058\nDo. (Dantzio, very dry)\n-\n7731\nPine (pitch)\n6790\n6790\nDo. (yellous, full of turpentine)\n5375\n5445\nDo. (red)\n5395\n7518\nPoplar\n3107\n5124\nPlum (wet)\n3654\n-\nDo. (dry)\n8241\nto 1049\nSycamore\n7082\n-\nTeak\n-\n12101\nLarch (fallen two months)\n3201\n5568\nWalnut\n6063\n7227\nWillow\n2898\n6128\nThen for long columns of oak, in which the side of the\nsquare base is less than 8¹₀th the height of the column;\nW = 24542\nand for red deal,\nW = 17511\nFor shorter pillars, where the ratio between their thickness\nand height is such that they still yield by bending, the\nstrength is estimated by the following formula:\nCalling the weight calculated from either of the preceding\nformulæ, W.\nCalling the crushing weight, as estimated from the pro-\nceeding table, W'.\nCalling the breaking weight in lbs., W\".\nThen the formula for the strength is\nW\" = W+&W' WW'\nDigitized by Google\nSTRENGTH OF TIMBER.\n125\nIn each of the preceding formulæ d must be taken in\ninches, and l in feet.\nThe same rule is followed in proportioning the rupturing\nto the working strain in timber subjected to compression as in\ntimber subjected to extension.\n346. Resistance to Transverse Strains. As. timber,\nfrom the purposes to which it is applied, is for the most part\nexposed to a transverse strain, the far greater number of ex-\nperiments have been made to ascertain the relations between\nthe strain, the deflection caused by it, and the linear dimen-\nsions of the piece subjected to the strain. These relations have\nbeen made the subject of mathematical investigations, found-\ned upon data derived from experiment, which will be given\nin the APPENDIX. The following table exhibits the results of\nexperiments made upon beams having a rectangular sectional\narea, which were laid horizontally upon supports at their ends,\nand subjected to a strain applied at the middle point between\nthe supports, in a vertical direction.\nFor a more convenient application of the formulse to the\nresults of the experiments, the notation adopted in the pre-\nceding Art. will be here given.\nCall the transverse force necessary to break the beam in\nlbs., W.\nCall the distance between the supports in inches, l.\n\" the horizontal breadth of the sectional area in\ninches, b.\nCall the vertical depth of the sectional area in inches, d.\n\" the deflection arising from a weight w in inches, f.\nTable of Experiments with the foregoing Notation.\nValues\nValues\nValue\nValue\nValue\nValue\nDESCRIPTION OF WOOD.\nSpecific\nof\nof\nof\nof\nof\nof\nAuthors of\ngrav.\n1.\nb.\nd.\nf.\nto.\nW.\nexperiments.\nInches.\nInches.\nInches.\nInches.\nlbs.\nlbs.\nOak (English)\n.934\n84\n2\n2\n1.280\n200\n687\nProf. Barlow.\nDo. (Canadian)\n.872\n84\n2\n2\n1.080\n225\n678\n\"\nPine (American)\n-\n84\n2\n2\n0.981\n150\n\"\n-\nOak (English)\n-\n30\n1\n1\n0.5\n187\n-\nTredgold.\nWhite spruce (Cana\ndian)\n.465\n24\n1\n1\n0.5\n180\n285\n\"\nWhite pine (American)\n.455\n85.2\n2.75\n5.55\n0.177\n777\n5189\nLieut. Brown.\nBlack spruce,\ndo.\n.490\n85.2\n2.75\n5.55\n0.177\n892\n5646\n\"\nSouthern pine, do.\n.872\n85.2\n2.75\n5.54\n0.177\n1175\n9287\n\"\nDigitized\nby\nGoogle\n126\nCIVIL ENGINEERING.\nThe following Table, taken from Vol. V. Professional\nPapers of the English Royal Engineers. No. V. Re-\nmarks and Experiments on various Woods, gives the value\nof S, in the formula S = 4ad Wl for transverse strains, in\nwhich l, the length of the pieces subjected to experiment,\nwas from five to six feet; the distance between the points\nof support four feet; the ends of the pieces not confined.\nTransverse\ndimensions.\nNo. of experiment.\nSpecific gravity.\nMean depth.\nMean breadth.\nBreaking weight.\nUltimate deflection.\nWeight giving a deflection =\n1-100 length.\nWeight at which the deflections\nceased to be at all uniform.\nCorresponding deflections.\nValue of S from formula\nIM\n.6pet\nS=\nNo. of weights applied succes-\nsively.\nDetail Remarks.\nin.\nin.\nlbs.\nin.\nlbs.\nlbs.\nin.\n7\n618\n1.98\n1.98\n1101\n2.0\n390\n642\n.8\n1702\n21\nGood specimen gave\nwarning at 1017 1bs.,\nASH, AMERICAN.\nthen fell rapidly and\nbroke at 1101 lbs.\n8\n580\n2.0\n1.85\n808\n1.8\n298\n478\n.8\n1300\n16\nTolerable specimen;\ngave warning grad-\nually at 751 lbs.\n9\n696\n2.0\n1.85\n1017\n8.0\n271\n584\n.925\n1649\n19\nDo. as No. 8.\n611\n1550\n10\n782\n2.05\n1.98\n1241\n2.7\n428\n697\n.85\n1790\n24\nTolerable specimen\ngave warning at 603\nBEECH, AMERI-\nlbs.\n11\n788\n2.0\n2.0\n1078\n1.9\n416\n642\n.775\n1609\n20\nCAN.\nGood specimen gave\nwarning at 1017 lbs.\n12\n765\n1.98\n20\n1157\n2.6\n428\n534\n.625\n1770\n24\nDo. broke well and\ngradually.\n778\n1728\n18\n764\n2.0\n2.0\n1521\n1.7\n540\n1241\n1.275\n2282\n30\nVery good specimen;\nwarning at 1270 lbs.,\nbroke suddenly at\nBIRCH, BLACK AMERI-\n1521.\n14\n646\n2.0\n1.98\n1297\n2.8\n390\n697\n.875\n1965\n26\nGood specimen; broke\nsuddenly at 1297 lbs.\nCAN.\n15\n720\n2.0\n2.0\n1017\n2.7\n487\n642\n1.1\n1525\n24\nDo., broke with a long\nscarf and gradually.\n16\n684\n2.0\n2.0\n1129\n2.5\n536\n808\n1.17\n1698\n25\nDo., broke well, but with\nlittle warning.\n17\n645\n2.0\n2.0\n1185\n8.8\n470\n642\n1.1\n1777\n25\nDo. Do. Do.\n682\n1848\nAll taken from the same\npiece.\n26\n703\n2.046\n2.008\n1877\n8.1\n280\n761\n0.9\n1966\n88\nELM, CAN-\n27\n700\n2.05\n2.037\n1265\n2.5\n486\n649\n1.5\n1799\n35\nThe great uniformity of\nADA.\n28\n712\n2.087\n2.03\n1321\n3.5\n488\n678\n0.8\n1891\n86\ntexture in this wood\n29\n685\n2.08\n2.025\n1265\n8.5\n451\n621\n0.74\n1819\n35\npresented no irregu-\nlarities for comment\n700\n1869\nduring straining.\nDigitized by Google\nSTRENGTH OF TIMBER.\n127\nTransverse\ndimensions.\nNo. of experiment.\nSpecific gravity\nMean depth.\nMean breadth.\nBreaking weight.\nUltimate deflection.\nWeight giving a deflection =\n1-100 length.\nWeight at which the deflections\nceased to be at all uniform.\nCorresponding deflections.\nValue of 8 from formula\nW1\n,SPW\nNo. of weights applied succes-\nsively.\nDetail Remarks.\nS=\nin.\nin.\nlbs.\nin.\nlbs.\nlbs.\nin.\n80\n854\n2.0\n2.0\n1380\n8.0\n390\n857\n1.75\n1995\n27\nGood piece, but with\na small knot 12 inches\nfrom centre; gave\nwarning at 1129 lbs.,\nHICKORY, AMERICAN.\nbroke at 1880 equally\nat the knot and cen-\ntre.\n31\n888\n1.98\n1.97\n857\n1.2\n390\n590\n.7\n1882\n16\nIndifferent specimen,\ntwo-fifths sap.\n32\n866\n2.08\n2.0\n1270\n1.9\n481\n910\n.975\n1607\n29\nGood specimen, warn-\ning at 642 lbs.\n83\n856\n2.0\n1.98\n1157\n8.0\n405\n590\n.7\n1753\n28\nDo. warning at 1129\nlbs., broke well and\ngradually.\n871\n1672\n45\n716\n1.98\n1.92\n1800\n2.0\n870\n751\n1.025\n2181\n80\nGood specimen, warn-\ning at 1240 lbs.\n46\n1.95\n1.92\n968\n2.0\n331\n478\n.75\n1582\n18\nBroke soon at a knot;\nno specific gravity\nmentioned, 46 and 47\nhaving been at first\nsupposed to be too\nOAK, WHITE AMERICAN.\nunsatisfactory; they\nwere, however, re-\ncorded, as No. 50 did\nnot give a very much\nbetter result.\n47\n1.98\n1.98\n803\n2.0\n426\n642\n.775\n1842\n15\n48\n666\n2.05\n2.08\n1120\n1.9\n286\n590\n1.0\n1580\n22\nGood-looking specimen.\nbut slightly tainted\nwith dry-rot; broke\nwith little warning.\n49\n600\n2.00\n2.08\n1297\n20\n849\n478\n.65\n1916\n26\nDo. Do. broke with a\nlong scarf.\n50\n600\n2.17\n0.86\n584\n1.8\n211\n366\n.9\n1582\n10\nA slab specimen from\n48.\n645\n1699\n51\n987\n1.88\n1.69\n910\n8.5\n244\n478\n1.15\n1929\n17\nFair specimen; warn-\ning at about 400 lbs. ;\nbroke with a long\nOAK, BASKET, AMERI-\nscarf.\n52\n947\n1.81\n1.68\n697\n8.6\n207\n810\n1.6\n1889\n18\nBroke at a large worm-\nhole, to which this\nCAN.\nwood seems to be sub-\nject.\n58\n987\n1.8\n1.6\n808\n8.0\n478\n1.8\n1859\n15\nDo. These three speci-\nmens were all from\nthe same log.\n940\n1709\nDigitized by Google\n128\nCIVIL ENGINEERING.\nTransverse\ndimensions.\nNo. of experiment.\nSpecific gravity.\nMean depth.\nMean breadth.\nBreaking weight.\nUltimate deflection.\nWeight giving a deflection =\n1-100 length.\nWeight at which the deflections\nceased to be at all uniform.\nCorresponding deflections.\nValue of S from formula\nWI\n4ads\"\nNo. of weights applied succes-\nsively.\nDetail Remarks.\nin.\nin.\nlbs.\nin.\nlbs.\nlbs.\nin.\n64\n1120\n2.029\n2.004\n1041\n1.8\n388\n813\n.86\n1518\n28\n65\n1230\n2.025\n2.015\n1433\n2.4\n424\n565\n.67\n2080\n85\nOAK. AMERICAN,\nHOLM OR LIVE OAK.\n66\n1121\n2.046\n2.039\n1265\n2.8\n893\n818\n.74\n1780\n32\n67\n1141\n2.029\n1.99\n1489\n3.8\n429\n318\n.7\n2181\n86\n68\n1140\n2.042\n2.028\n878\n1.8\n347\n257\n.62\n24\nEvidently a bad speci-\nmen, though it looked\nwell.\n69\n1209\n2.025\n2.017\n1209\n2.2\n868\n458\n.58\n1756\n81\n1160\n1862\n70\n422\n2.01\n2.0\n910\n1.8\n316\n584\n.75\n1851\n16\nGood clean specimen\nbroke short without\nPINE, WHITE AMER-\nwarning.\n71\n450\n2.0\n2.0\n910\n1.7\n348\n590\n.8\n1865\n16\nDo. Do.\nICAN.\n72\n432\n2.0\n20\n910\n1.8\n857\n590\n.85\n1865\n16\nDo. All from the same\nlog.\n78\n480\n2.008\n1.99\n1041\n1557\n28\nDo.\nNo remarks made\n74\n480\n1.98\n1.97\n985\n1531\n27\nDo.\nat the time of\n75\n458\n2.0\n1.99\n1041\n1509\n28\nDo.\nexperiment.\n458\n1456\n76\n568\n2.0\n1.98\n1157\n2.1\n369\n642\n.8\n1753\n23\nSnapped at the centre\nthough there was a\nPINE. RED AM-\nknot 8 inches from it.\nERICAN.\n77\n656\n2.0\n2.0\n1420\n2.5\n459\n590\n.6\n2130\n82\nGood clean specimen.\n78\n689\n2.0\n2.0\n1800\n2.1\n459\n968\n1.125\n1950\n28\nDo., but broke remark-\nably short, and with-\nout warning.\n621\n1944\nDeflection of Wooden Beams. Professor W. A. Norton,\nof the Scientific School of Yale College, made a careful series\nof experiments, to test the practical accuracy of the formula\nderived from the generally-received theory of the deflection\nof beams of a rectangular cross-section, arising from a weight\nacting at the middle point of the beam resting on two sup-\nports, its axis being horizontal.\nPr\nThis formula is : f=mEbd ; in which\nP is the applied pressure ; f, the deflection due to P; E, the\nmodulus of elasticity of the material ; b, the breadth; d, the\nDigitized by Google\nSTRENGTH OF TIMBER.\n129\ndepth; and i, the distance between the points of support of\nthe beam; and m, a constant to be derived from experiment.\nFrom this formula, if accurate, the amount of deflection\nshould vary directly as the pressure and cube of the length,\nand inversely as the breadth and cube of the depth; but from\nProf. Norton's experiments it appears:-\n1. That the deflection varies approximately as the pressures,\nbut rather increasing according to a less rapid law.\n2. That, although the deflections are not uniformly in-\nversely as the breadth, still the variation from this law is but\nslight.\n3. That, except in beams whose length bore a high propor-\ntion to their depth,\" the law indicated, that the deflections are\ninversely proportional to the cubes, is far from being accurate.\nIn other cases it \" decreases according to a less rapid law than\nthe inverse cube of the depth.\"\n4. The experiments also show, that the law, that the defloc-\ntion is directly proportional to the cube of the length, also\nfails.\nFrom these experiments Prof. Norton says:-\n\" We may conclude, from these results, that the deflection\nincreases according to a less rapid law than the cube of the\nlength of the stick. We have already seen that it decreases\nin a less rapid proportion than the inverse cube of the depth.\nIt follows, therefore, that the true formula for the deflection\nprobably contains at least one additional term, which varies\nless rapidly than as the cube of the length directly and the\ncube of the depth inversely; or in other words, contains l in\nthe numerator, and d in the denominator, each raised to a\nlower power than the cube.\"\n\" Further, it would seem, then, that the true theory of de-\nflection conducts to the following formula, in the special case\nof a beam resting on two supports and loaded in the middle.\nThe following table gives the values of E for white pine,\nand the calculated values of the constant C.\n\" The general formula applicable to white pine sticks of the\ngeneral quality used in these experiments will be obtained by\ntaking the mean of the several values of E and C given in the\nabove table. To test the theoretical formula we have obtained\nwe will take the mean values of E and C, for the second set\nof sticks, given at the bottom of the fourth and fifth columns,\nviz. : E=1,427,965 pounds, and C=0.0000094. We thus\nhave\n9\nDigitized by\nGoogle\n130\nCIVIL ENGINEERING.\nor, taking P=100 lbs.,\nThe general formula for the deflection may also take the\nfollowing form:\nTABLE\nSticks.\nDiff. of Extreme Pressures.\nDiff. of Intermediate\nPressures.\nBet No. 1.\nB.\nC.\nE.\nC.\n8.\nb.\nd.\nft.\nft.\nin.\nin.\nin\nin\n2, or 4\n2\n1\n1,859,500 lbs.\n0.0000108\n1,808,480 lbs.\n0.0000082\n2\n2, or 8\n8, or 2\n1,566,809 44\n0.0000100\n1,579,960 \"\n0.0000095\n4\n2, or &\n8, or 2\n1,584,820 \"\n0.0000087\n1,560,800 \"\n0.0000078\n2, or 4\n4\n2\n1,552,000 \"\n0.0000140\n1,501,200 of\n0.0000127\n2, or 4\n2\n2\n1,481,800 44\n0.0000108\n1,423,600 \"\n0.0000084\nMeans\n1,508,986 \"\n0.0000108\n1,474,798\n\"\n0.0000080\nSet No. 2.\nft.\nin.\nin.\nof\nor\n4\n8\n2\n1,277,729 lbs.\n0.0000084\n1,254,000 lbs.\n0.0000080\nof or 4\n2\n8\n1,295,984 \"\n0.0000089\n1,815,000 \"\n0.0000088\n2, or 4\n4\n2\n1,558,900 44\n0.0000110\n1,542,860 \"\n0.0000107\nor\n4\n2\n2\n1,561,822 \"\n0.0000084\n1,600,000 \"\n0.0000100\nMeans,\n1,423,609\n\"\n0.0000092\n1,427,965\n\"\n0.0000094\n347. Resistance to Detrusion. From the experiments of\nProf. Barlow, it appears that the resistance offered by the\nlateral adhesion of the fibres of fir, to a force acting in a\ndirection parallel to the fibres, may be estimated at 592 lbs.\nper square inch.\nMr. Tredgold gives the following as the results of experi-\nments on the resistance offered by adhesion to a force applied\nperpendicularly to the fibres to tear them asunder.\nOak\n2316 lbs. per square inch.\nPoplar\n1782\n\"\n\"\nLarch, 970 to 1700\n\"\n\"\n4\nDigitized by Google\nSTRENGTH OF CAST-IRON\n131\nV.\nSTRENGTH OF OAST-IRON.\nThe most recent experiments on the strength of this ma-\nterial are those of Mr. Hodgkinson. Those, particularly,\nmade by him on the subject of the strength of columns,\nand the most suitable form of cast-iron beains to sustain a\ntransversal strain, have supplied the engineer and architect\nwith the most valuable guide in adapting this material to\nthe various purposes of structures.\n348. Resistance to Extension.-From a few experiments\nmade by Mr. Rennie and Captain Brown, the tensile strength\nof cast iron varies from 7 to 9 tons per square inch.\nThe experiments of Mr. Hodgkinson upon both hot and\ncold blast iron give the tensile strength from 6 to 9 ₫ tons per\nsquare inch.\nFrom some experiments made on American cast iron, under\nthe direction of the Franklin Institute, the mean tensile\nstrength is 20834 lbs., or 91 tons per square inch.\n349. Resistance to Compressive Strain-The general\ncircumstances attending the rupture of this material by com-\npression, drawn from the experiments of Mr. Hodgkinson,\nhave already been given. The angle of the wedge resulting\nfrom the rupture is about 55°.\nThe mean crushing weight derived from experiments upon\nshort cylinders of hot blast iron was 121,685 lbs., or 54 tons\n61 cwt. per square inch.\nThat on short prisms of the same, with square bases,\n100,738 lbs., or 44 tons 191 cwt. per square inch.\nThat on short cylinders of cold blast iron was 125,403 lbs.,\nor 55 tons 191 cwt. per square inch.\nThat on short prisms of the same, having other regular\nfigures for their bases, was 100,631 lbs., or 44 tons 181 cwt.\nper square inch.\nMr. Hodgkinson remarks with respect to the forms of base\ndiffering from the circle \"In the other forms the difference\nof strength is but little; and therefore we may perhaps admit\nthat difference of form of section has no influence upon the\npower of a short prism to bear a crushing force.\"\nIn remarking on the circumstances attending the rupture,\nMr. Hodgkinson further observes : We may assume, there-\nfore, without assignable error, that in the crushing of short\nDigitized by\nGoogle\n132\nCIVIL ENGINEERING,\niron prisms of various forms, longer than the wedge, the angle\nof fracture will be the same. This simple assumption, if ad-\nmitted, would prove at once, not only in this material, but in\nothers which break in the same manner, the proportionality of\nthe crushing force in different forms to the area since the\narea of fracture would always be equal to the direct trans-\nverse area multiplied by a constant quantity dependent upon\nthe material.\"\nTable exhibiting the Ratio of the Tensilc to the Compres-\nsive Forces in Cast Iron, from Mr. Hodgkinson's Experi-\nments.\nCompressive force\nTensile force per\nDESCRIPTION OF METAL.\nper square inch.\nsquare inch.\nRatio.\nDevon iron,\nNo. 3. Hot blast\n145,435\n21,907\n6.638 : 1\nBuffery iron,\nNo. 1. Hot blast\n86,397\n13,434\n6.431 : 1\nDo.\n\"\nCold blast\n93,385\n17,466\n5.346 : 1\nCoed-Talen iron, No. 2. Hot blast\n82,734\n16,676\n4.961 : 1\nDo.\n\"\nCold blast\n81,770\n18,855\n4 337 : 1\nCarron iron,\nNo. 2. Hot blast\n108,540\n18,505\n8 037 : 1\nDo.\n\" Cold blast\n106,375\n16,683\n6.376 : 1\nCarron iron,\nNo. 3. Hot blast\n133,440\n17,755\n7.515 : 1\nDo.\n\"\nCold blast\n115.443\n14,200\n8.129 : 1\n350. Resistance of Cylindrical Columns. The experi-\nments under this head were made upon solid and hollow col-\numns, both ends of which were either flat or rounded, fixed or\nloose, or one end flat and the other rounded. In the case of\ncolumns with rounded ends, the pressure was applied in the\ndirection of the axis of the column.\nThe following extracts are made from Dr. Hodgkinson's\npaper on this subject, published in the Report of the British\nAssociation of 1840.\n\" 1st. In all long pillars of the same dimensions, the resist-\nance to crushing by flexure is about three times greater when\nthe ends of the pillars are flat than when they are rounded.\n\" 2d. The strength of a pillar, with one end rounded and\nthe other flat, is the arithmetical mean between that of a\npillar of the same dimensions with both ends round, and one\nwith both ends flat. Thus, of three cylindrical pillars, all of\nthe same length and diameter, the first having both its ends\nrounded, the second with one end rounded and one flat, and\nthe third with both ends flat, the strengths are as 1, 2, 3,\nnearly.\nDigitized by\nGoogle\nSTRENGTH OF CAST-IRON.\n133\n3d. A long, uniform, cast-iron pillar, with its ends firmly\nfixed, whether by means of disks or otherwise, has the same\npower to resist breaking as a pillar of the same diameter, and\nhalf the length, with the ends rounded or turned SO that the\nforce would pass through the axis.\n\"4th. The experiments show that some additional strength\nis given to a pillar by enlarging its diameter in the middle\npart; this increase does not, however, appear to be more than\none seventh or one eighth of the breaking weight.\n\" 5th. The index of the power of the diameter to which the\nstrength of long pillars with rounded ends is proportional, is\n3.76 nearly, and 3.55 in those with flat ends, as appeared from\nthe results of a great number of experiments ; or the strength\nof both may be taken as the 3.6 power of the diameter\nnearly.\n\" 6th. In pillars of the same thickness, the strength is in-\nversely proportional to the 1.7 power of the length nearly.\n\" Thus the strength of a solid pillar with rounded ends, the\ndiameter of which is d, and the length l, is as dⁿ\n\" The absolute strength of solid pillars, as appeared from\nthe experiments, are nearly as below.\n\" In pillars with rounded ends,\nStrength in tons = 14.9 ÈF\n\"In pillars with flat ends,\nStrength in tons = 44.16\n\" In hollow pillars nearly the same laws were found to ob-\ntain; thus, if D and d be the external and internal diameters\nof a pillar whose length is i, the strength of a hollow cylinder\nof which the ends were movable (as in the connecting-rod of\na steam-engine) would be expressed by the formula below.\nStrength in tons= 13 Dª⁰\n\" In hollow pillars, whose ends are flat, we had from experi-\nment as before,\nStrength in tons\n\" The formulse above apply to all pillars whose length is not\nless than about thirty times the external diameter; for pillars\nshorter than this, it is necessary to have recourse to the for-\nmula,' given under the head of STRENGTH OF TIMBER, for\nDigitized by Google\n134\nCIVIL ENGINEERING.\nshort pillars of timber, substituting for W and W in that for-\nmula, the proper values applicable to cast-iron.\"\n351. Similar Pillars. In similar pillars, or those whose\nlength is to the diameter in a constant proportion, the strength\nis nearly as the square of the diameter, or of any other linear\ndimension ; or, in other words, the strength is nearly as the\narea of the transverse section.\"\n\" In hollow pillars, of greater diameter at one end than the\nother, or in the middle than at the ends, it was not found\nthat any additional strength was obtained over that of cylin-\ndrical pillars.\"\n\"The strength of a pillar, in the form of the connecting\nrod of a steam-engine (that is, the transverse section pre-\nsenting the figure of a cross +) \" was found to be very\nsmall, perhaps not half the strength that the same metal\nwould have given if cast in the form of a uniform hollow\ncylinder.\"\n\" A pillar irregularly fixed, so that the pressure would be in.\nthe direction of the diagonal, is reduced to one third of its\nstrength. Pillars fixed at one end and movable at the other,\nas in those flat at one end and rounded at the other, break at\none third the length from the movable end therefore, to\neconomize the metal, they should be rendered stronger there\nthan in other parts.\"\n352. Long-continued Pressure on Pillars. \"To deter-\nmine the effect of a load lying constantly on a pillar, Mr.\nFairbairn had, at the writer's suggestion, four pillars cast,\nall of the same length and diameter. The first was loaded\nwith 4 cwt., the second with 7 cwt., the third with 10 cwt.,\nand the fourth with 13 cwt.; this last load was 19070 of what\nhad previously broken a pillar of the same dimensions, when\nthe weight was carefully laid on without loss of time. The\npillar loaded with 13 cwt. bore the weight between five and\nsix months, and then broke.\"\n353. General Properties of Pillars. \"In pillars of\nwrought-iron, steel, and timber, the same laws, with respect\nto rounded and flat ends, were found to obtain, as had been\nshown to exist in cast-iron.\"\nOf rectangular pillars of timber, it was proved experimen-\ntally that the pillar of greatest strength of the same material,\nis a square.\"\n354. Comparative Strength of Cast-Iron, Wrought-\nIron, Steel, and Timber. It resulted from the experi-\nments upon pillars of the same dimensions but of different\nmaterials, that if we call the strength of cast-iron 1000, we\nDigitized\nby\nGoogle\nSTRENGTH OF CAST-IRON.\n135\nshall have for wrought 1745, cast steel 2518, Dantzic oak\n108.8, red deal 78.5.' ,,\n355. Resistance to Transverse Strain. The following\ntables and deductions are drawn from the experiments of\nMessrs. Hodgkinson and Fairbairn, on hot and cold blast\niron, as published in their Reports to the British Association\nin 1837.\nTable exhibiting the results of experiments by Mr. Hodg-\nkinson on bars of hot blast iron 5 feet long, with a rect-\nangular sectional area; the bars resting horizontally on\nprops 4 feet 6 inches apart; the weight being applied at\nthe middle of the bar.\nEXPERIMENT 1.\nEXPERIMENT. 18.\nEXPERIMENT 14.\n-\n-\nI\nRectangular bar,\nRectangular bar,\nRectangular bar,\n1.00 inch broad,\n1.08 inches broad,\n1.02 inches broad,\n1.00 \" deep.\n8.00 \" deep,\n4.98 \" deep.\nWeight of bar, 15 lbs. 2 OE.\nWeight 78 lbs.\nWadght in\nlbs.\nDeflection in\ninches.\nSet, or defieo-\ntion when\nunloaded.\nWeight in\nlbs.\nDeflection in\ninches.\nSet in inches.\nWeightin\nlbs.\nDeflection in\ninches.\nSet in inches.\n16\n.037\nvisible\n1474\n-\n.001\n5867\n.127\n-\n23\n.052\nincreased\n1605\n.130\n.003\n6798\n.153\n.01\n30\n.070\n.001?\n1866\n.156\n.006\n7730\n.177\n-\n56\n.132\n.002\n2126\n.185\n.010\n8661\n.207\n-\n112\n.271\n.008\n2388\n.212\n.012\n9593\n.235\n-\n224\n.588\n.037\n2649\n.243\n.017\n10524\n.275\n.03\n336\n.940\n.087\n2910\n.272\n.022\n11087\nbroke\n-\n448\n1.860\n.181\n3172\n.807\n.030\n-\n-\n-\n469\nbroke\n-\n3433\n.340\n.038\n-\n-\nI\n-\n-\n-\n3694\n.378\n.050\n-\n-\nI\n-\n-\n-\n3956\nbroke\n-\n-\n-\nI\n.\nUltimate deflection\nUltimate deflection\nUltimate defiection\n1.444 inches.\n.416 inch.\n.299 inch.\n356. The following remarks are extracted from the same\nReport: \"I had remarked, in some of the experiments, that\nthe elasticity of the bars was injured much earlier than is\ngenerally conceived; and that instead of its remaining per-\nfect till one third, or upwards, of the breaking weight was\nlaid on, as is generally admitted by writers, it was evident\nthat fth, or less, produced in some cases a considerable set or\ndefect of elasticity ; and judging from its slow increase after-\nDigitized by Google\n136\nCIVIL ENGINEERING.\nResults of experiments, by the same, on the Transverse\nStrength of Cold Blast Iron; length of bars, and distance\nbetween the points of support the same as in the preced-\ning table.\nEXPERIMENT 1.\nEXPERIMENT 12.\nEXPERIMENT 18.\n-\nI\n-\nRectangular bar,\nRectangular bar,\nRectangular bar,\n1.025 inch deep,\n8.00 inches deep,\n4.98 inches deep,\n1.002 \" broad.\n1.02 \" broad.\n1.08 \" broad.\nWeight, 15 lbs. 6 OZ.\nWeight, 46 lbs. 8 OZ.\nWeight, 78 lbs.\nWelght by\nlbs.\nDeflection in\ninches.\nBet in\ninches.\nWalght by\nlbs.\nDeflection in\ninches.\nSet in\ninches.\nWelght ba\nlbs.\nDeflection in\ninches.\nSet in\ninches.\n16\n.033\nvisible\n1082\n.091\n.003\n4936\n.110\n.013\n30\n.062\nincreased\n1843\n.111\n.006\n5867\n.130\n-\n56\n.120\n.002\n1605\n.138\n.008\n6798\n.153\n.020\n112\n.240\n.007\n1866\n.164\n.010\n7730\n.179\n.025\n168\n.870\n.014\n2126\n.190\n.012\n8662\n.195\n-\n224\n.510\n.028\n2388\n.229\n.015\n9593\n.219\n.034\n280\n.649\n.041\n2649\n.250\n.019\n10525\n.250\n.043\n336\n.798\n.061\n2910\n.281\n.026\n10588\nbroke\n-\n892\n.953\n.084\n3172\n.310\n.031\n-\n-\n-\n448\n1.120\n.120\n3433\n.345\n.037\n-\n-\n-\n504\n1.310\n.170\n3694\n.378\n.046\n-\n-\n-\n514\nit bore\n-\n3825\nbroke\nI\n-\n-\n-\n518\nbroke\n-\n-\n-\n-\n-\n-\n-\nUltimate deflection\nUltimate deflection\nUltimate deflection\n1.36 inch.\n0.895 inch.\n0.252.\nwards, I was persuaded that it had not come on by a sudden\nchange, but had existed, though in a less degree, from a very\nearly period.\"\n\"From what has been stated above, deduced from experi-\nments made with great care, it is evident that the maxim of\nloading bodies within the elastic limit has no foundation in\nnature; but it will be considered as a compensating fact,\nthat materials will bear for an indefinite period a much\ngreater load than has hitherto been conceived.\"\n357. \"We may admit,\" from the mean results, \" that the\nstrength of rectangular bars is as the square of the depth.\"\n358. Effects of Time upon the Deflections caused by a\nPermanent Load on the Middle of Horizontal Bars. The\nfollowing table exhibits the results of Mr. Fairbairn's experi-\nments on this point. The experiments were made on\nDigitized by Google\nSTRENGTH OF CAST-IRON.\n137\nbars 5 feet long, 1.05 inch deep the one of cold blast iron,\n1.03 inch broad; the other of hot blast, 1.01 broad distance\nbetween the points of support 4 feet 6 inches. The constant\nweight suspended at the centre of the bars was 280 lbs. This\nweight remained on from March 11th, 1837, to June 23d,\n1838.\nCold blast iron.\nHot blast iron.\nRatio of increase of\nDeflection in\nDate of observation.\nTemp.\nDeflection in\ndeflections.\ninches.\ninches.\n.930\nMarch 11th, 1837,\n-\n1.064\n-\n.963\nJune 23d, 1838.\n78°\n1.107\n-\n.033\nIncrease,\n-\n.048\n1000 : 1308\n359. Mr. Fairbairn in his Report remarks on the above\nand like results: 'The hot blast bar in these experiments\nbeing more deflected than the cold blast, indicates that the\nparticles are more extended and compressed in the former\niron, with the same weight, than in the latter. This excess\nof deflection may in some degree account for the rapidity of\nincrease, which it will be observed is considerably greater in\nthe hot than in the cold blast bar.\"\n\" It appears from the present state of the bars (which indi-\ncate a slow but progressive increase in the deflections) that\nwe must at some period arrive at a point beyond their bearing\npowers; or otherwise to that position which indicates a cor-\nrect adjustment of the particles in equilibrium with the load.\nWhich of the two points we have in this instance attained is\ndifficult to determine; sufficient data, however, are adduced to\nshow that the weights are considerably beyond the elastic\nlimit, and that cast iron will support loads to an extent be-\nyond what has usually been considered safe, or beyond that\npoint where a permanent set takes place.\"\n360. Effects of Temperature. Mr. Fairbairn remarks:\n\" The infusion of heat into a metallic substance may render it\nmore ductile, and probably less rigid in its nature ; and I ap-\nprehend it will be found weaker, and less secure under the\neffects of heavy strain. This is observable to a considerable\nextent in the experiments\" on transverse strength \"ranging\nfrom 26° up to 190° Fahr.\"\n\"The cold blast at 26° and 190°, is in strength as 874 : 743.\nThe hot blast at 26° and 190°, is in strength as 811 : 731.\nDigitized by Google\n138\nCIVIL ENGINEERING.\nBeing a diminution in strength as 100 : 85 for the cold blast,\nand 100 to 90 for the hot blast, or 15 per cent. loss of strength\nin the cold blast, and ten per cent. in the hot blast.\"\n\" A number of the experiments made on No. 3 iron have\ngiven extraordinary and not unfrequently unexpected results.\nGenerally speaking, it is an iron of an irregular character,\nand presents less uniformity in its texture than either the first\nor second qualities; in other respects it is more retentive, and\nis often used for giving strength and tenacity to the finer\nmetals.\"\n\" At 212° we have in the No. 3 a much greater weight sus-\ntained than what is indicated by the No. 2 at 190° ; and at\n600° there appears in both hot and cold blast the anomaly of\nincreased strength as the temperature is advanced from boil-\ning water to melted lead, arising from the greater strength of\nthe No. 3 iron.\"\n361. From experiments made by Major Wade on American\ncast iron, and by Mr. Fairbairn on English cast iron, it appears\nthat the tenacity of the metal is increased both by remelting,\nand by prolonged fusion when kept in their certain limits.\nIt also appears from other experiments that repeated fusions\noccasion a heavy waste of material, and that if either remelt-\ning or prolonged fusion be carried too far the result will be\nan iron of a hard and brittle quality.\n362. Influence of Form upon the Transverse Strength\nof Cast Iron Beams. Upon no point, respecting the strength\nof cast iron, have the experiments of Mr. Hodgkinson led to\nmore valuable results to the engineer and architect, than upon\nthe one under this head. The following tables give the results\nof experiments on bars of a uniform cross-section (thus T)\ncast from hot and cold blast iron. The bars were 7 feet\nlong, and placed, for breaking, on supports 6 feet 6 inches\nasunder.\nDigitized by Google\nSTRENGTH OF CAST-IRON.\n139\nTable exhibiting the Results of Experiments on bars of Hot\nBlast Iron of the form of cross section as above.\nEXPERIMENT 4.\nEXPERIMENT 5.\nBar broken\nas shown\nBar broken\nas shown\nwith the rib downward.\nwith the rib upward.\nWeight in lbs.\nDeflection in\nDeflection in\nBet.\ninches.\nWeight in lbs.\ninches.\nSet.\n7\n.015\nvisible\n7\n-\nnot visible\n14\n.032\n.001\n14\n.025\nvisible\n21\n.046\n.002\n21\n.045\n.003\n28\n.064\n.004\n28\n.065\n.003\n56\n.130\n.005\n56\n.184\n.005\n112\n.273\n.020\n112\n.270\n.015\n168\n.444\n.035\n224\n.580\n.058\n224\n.618\n.058\n336\n.895\n.101\n280\n.813\n.093\n448\n1.224\n.155\n336\n1.030\n.130\n560\n1.585\n.235\n864\nbroke\n-\n672\n1.985\n.830\n-\n-\n-\n784\n2.410\n.490\n-\n-\n-\n896\n8.450\n.722\n-\n-\n-\n1008\n4.140\n1.040\n-\n-\n-\n1064\n-\n-\n-\n-\n-\n1120\nbroke\n-\nUltimate deflection 1.138 inches.\nFracture caused by a wedge 2.92 inches\nlong and 1.05 deep, of\nthis\nform flying out.\nUltimate deflection 4.880.\nNote. The annexed diagram shows the\na\nform of the uniform cross-section of the\nbars. The linear dimensions of the cross-\nF\nB\nsection in the two experiments were as fol-\nlows:-\nD\nB\nLength of parallelogram AB\n5 inches\n5 inches\nDepth\n\"\nAB\n0.30 \"\n0.30 \"\nTotal depth of bar\nCD 1.55 \"\nExpt. 4.\n1.56 \"\nExpt. 5.\nBreadth of rib\nDE 0.86 \"\n0.365 \"\nDigitized by Google\n140\nCIVIL ENGINEERING.\nTable exhibiting Results of Experiments on bars of Cold\nBlast Iron 5 feet long, of the same form of cross section\nas in preceding table.\nEXPERIMENT 4.\nEXPERIMENT 5.\nBar broken\nwith rib\nBar broken\nwith nb\ndownward.\nupward.\nDeflection in\nWeight in lbs.\nWeight in lbs.\nDeflection in\nSet.\ninches.\ninches.\nSet.\n112\n.03\n-\n112\n.03\n-\n224\n.07\n-\n224\n.07\n1\n336\n.11\n-\n336\n.11\n-\n892\n.13\n.005\n448\n.15\n-\n420\n.14\n.007\n560\n.19\n.005\n448\n.15\n.010\n616\n.21\n.010\n560\n.19\n.012\n672\n.23\n-\n672\n.23\n.015\n728\n-\n.015\n784\n.28\n.023\n784\n.27\n-\n896\n.33\n.030\n896\n.31\n-\n952\n.35\n-\n1008\n.35\n-\n980\nbroke\n-\n1120\n.39\n-\n-\n-\n-\n1344\n.48\n-\n-\n-\n-\n1568\n.57\n-\n-\n-\n-\n1792\n.67\n-\n-\n-\n-\n2016\n.80\n-\n-\n-\n-\n2240\n.95\n-\n-\n-\n-\n2296\nit bore\n-\n-\n-\n-\n2352\nbroke\n-\nUltimate deflection 36.\nUltimate deflection 1.08.\nFracture by a wedge breaking out as in\nExperiment 5, Hot Blast.\nNote. The linear dimensions of the cross-section of the bars\nin the above table were nearly the same as those in the pre-\nceding table, with the exception of the total depth CD, which\nin these last two experiments was 2.27 inches, or a little\nmore.\n363. The object had in view by Mr. Hodgkinson, in the\nexperiments recorded in the two preceding tables, was two-\nfold ; the one to ascertain the circumstances under which a\npermanent set, or injury to elasticity takes place ; the other\nto ascertain the effect of the form of cross section on the\ntransverse strength of cast iron. The following extracts from\nthe Report, give the principal deductions of Mr. Hodgkinson\non these points.\n\" In experiments 4 and 5 \" (on hot blast iron), \" which were\nDigitized by\nGoogle\nSTRENGTH OF CAST-IRON.\n141\non longer bars than the others, cast for this purpose, and for\nanother mentioned further on, the elasticity (in Expt. 4) was\nsensibly injured with 7 lbs., and in the latter (Expt. 5) with\n14 lbs., the breaking weights being 364 lbs., and 1120 lbs.\nIn the former of these cases a set was visible with By, and in\nthe other with 810 of the breaking weight, showing that there\nis no weight, however small, that will not injure the elasti-\ncity.\"\n\" When a body is subjected to a transverse strain, some of\nits particles are extended and others compressed; I was de-\nsirous to ascertain whether the above defect in elasticity arose\nfrom tension or compression, or both. Experiments 4 and 5\nshow this; in these a section of the casting, which was uni-\nform throughout, had the form i. During the experiments\nb\nthe broad part ab was laid horizontally upon supports ; the\nvertical rib c in the latter experiment being upward, in the\nformer downward. When it was downward the rib was ex-\ntended, when upward the rib was compressed. In both cases\nthe part ab was the fulcrum; it was thin, and therefore easily\nflexible; but its breadth was such that it was nearly inex-\ntensible and incompressible, comparatively, with the vertical\nrib. We may therefore assume, that nearly the whole flexure\nwhich takes place in a bar of this form, arises from the ex-\ntension or compression of the rib, according as it is downward\nor upward. In Expt. 4 we have extension nearly without\ncompression, and in Expt. 5 compression almost without ex-\ntension. These experiments were made with great care.\nThey show that there is but little difference in the quantity\nof set, whether it arises from tension or compression.\"\nThe set from compression, however, is usually less than\nthat from extension, as is seen in the commencement of\nthe two experiments, and near the time of fracture in that\nsubmitted to tension. The deflections from equal weights\nare nearly the same whether the rib be extended or compress-\ned, but the ultimate strengths, as appears from above, are\nwidely different.\"\n364. Form of Cast Iron Beam best adapted to Resist a\nTransverse Strain. The experiments of Mr. Hodgkinson\non this subject, published in the Memoirs of the Literary and\nPhilosophical Society of Manchester, Second Series, vol. 5,\nare of equal interest with those just detailed, both in their\ngeneral results and practical bearing. From these experi-\nments, the conclusion drawn is that the form of beam in the\nDigitized\nby\nGoogle\n142\nCIVIL ENGINEERING.\nannexed diagrams is the most favorable for resistance to\ntransverse strains.\nFig. a.\nFig. b.\nFig. a\nFig. a represents the plan, Fig. b\nthe elevation, and Fig. c the cross\nsection (enlarged) at the middle of\nthe beam. From the Figs. it will\nbe seen that the beam consists of\nthree parts; a bottom flanch of uni-\nform depth, but variable breadth,\ntapering from the centre towards\nthe extremities, where the points\nof support would be placed so as to\nform a portion of the common parabola on each side of the\naxis of the beam, the vertex of each parabola being at the\ncentre of the beam. The object of this form of flanch was to\nmake it, according to theory, the strongest, with the same\namount of material, to bear a weight uniformly distributed\nover it. The top flanch is of a like form, but of much small-\ner breadth and depth than the bottom one. The two are\nunited by a vertical rib of uniform depth and breadth.\nThe following are the relative dimensions of this form of\nbeam, which, from experiment, gave the most favorable\nresult.\nDistance of supports\n4 ft. 6 inches.\nTotal depth of beam\n0 \" 51 \"\nBreadth of top flanch at centre of beam\n2.33 \"\n\"\nbottom flanch\n\"\n6.66 \"\nUniform depth of top flanch\n0.31 \"\n\"\nbottom flanch\n0.66 \"\nThickness of vertical rib\n0.266\"\nTotal area of cross section\n6.4 square inch.\nWeight of beam\n71 lbs.\n\" This beam broke in the middle by compression with\n26084 lbs., or 11 tons 13 cwt., a wedge separating from its\nupper side.\"\nDigitized by Google\nSTRENGTH OF CAST-IRON.\n143\n\"The weights were laid gradually and slowly on, and the\nbeam had borne within a little of its breaking weight a con-\nsiderable time, perhaps half an hour.\"\n\"The form of the fracture and wedge is represented in the\nFig. b, where enf is the wedge, ef=5.1 inches, tn=3.9 inches,\nangle enf=82°.\"\n66 It is extremely probable, from this fracture, that the neu-\ntral point was at n, the vertex of the wedge, and therefore at\n4ths the depth of the beam, since 3.9= X 5} nearly.\"\nThe relative dimensions above given were arrived at by\n\" constantly making small additions\" to the bottom flanch,\nuntil a point was reached where resistance to compression\ncould no longer be sustained. The beams of this form, in all\nprevious experiments, having yielded by the bottom flanch\ntearing asunder.\nThe great strength of this form of cross section is an in-\ndisputable refutation of that theory which would make the\ntop and bottom ribs of a cast iron beam equal.\"\nThe form of cross section (as above) \" is the best which\nwe have arrived at for the beam to bear an ultimate strain.\nIf we adopt the form of beam (as above) I think we may\nconfidently expect to obtain the same strength with a saving\nof upwards of }th of the metal.\"\n365. Rules for determining the Ultimate Strength of Cast\nIron Beams of the above Forms. From the results of his ex-\nperiments, Mr. Hodgkinson has deduced the following very\nsimple formulæ, for determining the breaking weight, in tons,\nwhen applied at the middle of a beam.\nCall the breaking weight in tons, W.\nCall the area of the cross section of the bottom flanch, taken\nat the middle of the beam, a.\nCall the depth of the beam at the middle point, d.\nCall the distance between the supports, l.\nThen\nW=26ad,\nwhen the beam has been cast with the bottom flanch upward\nand\nW=24ad,\nwhen the beam has been cast on its side.\nThe working strain on cast iron beams subjected to direct\ncompression is placed by most authorities at from 1th to fth\nof the crushing weight, when the beam, a column for exam-\nDigitized by Google\n144\nCIVIL ENGINEERING.\nple, is not subjected to violent vibrations or shocks. In the\ncontrary case, particularly in beams subjected to a transverse\nstrain, it is recommended to reduce the working strain to 1ᵗʰᵗʰ\nthe crushing strain.\n366. Effect of Horizontal Impact upon Cast Iron Bars.\nThe following tables of experiments on this subject, and the\nresults drawn from them, are taken from a paper by Mr.\nHodgkinson, published in the Fifth Report of the British\nAssociation.\nThe bars under experiment were impinged upon by a\nweight suspended freely in such a position that, hanging ver-\ntically, it was in contact with the side of the bar. The blow\nwas given by allowing the weight to swing through different\narcs. The bars were so confined against lateral supports, that\nthey could take no vertical motion.\nTable of experiments on a cast iron bar, 4 ft. 6 in. long, 1 in\nbroad, 1/2 in. thick, weighing 71 lbs., placed with the broad-\nside against lateral supports 4 ft. asunder, and impinged\nupon by cast iron and lead balls weighiny 81 lbs., swinging\nthrough arcs of the radius 12 feet.\nImpact with leaden ball.\nImpact with iron ball.\nChord of are\nfallen through\nin feet.\nObserved chord\nof recoll of ball\nin inches.\nObserved defieo-\ntion of bar in\ninches,\nChord of are\nfallen through\nin feet.\nObserved chord\nof recoll of ball\nin inches.\nObserved defieo-\ntion of bar in\ninches.\n1\n6.5\n.24\n1\n6.5\n.23\n2\n13\n.46\n2\n14\n.46\n8\n19\n.73\n8\n20\n.65\n4\n27\n.97\n4\n29\n.98\n5\n34\n1.80\n5\n87\n1.32\n6\n47\n1.60\nB\n48\n1.65\n\" Before the experiments on impact were made upon this\nbar, it was laid on two horizontal supports 4 feet asunder, and\nweights gently laid on the middle bent it (in the same direc-\ntion that it was afterwards bent by impact) as below:\n28 lbs. bent it .37 inch.\n56 lbs. \"\n.77 inch. Elasticity a little injured.\"\nDigitized by Google\nSTRENGTH OF CAST-IRON.\n145\nTable of experiments on a cast iron bar 7 ft. long, 1.08 in.\nbroad and 1.05 in. thick, weighing 231 lbs., placed, as in\npreceding experiments, against supports 6 ft. 6 in.\nasunder, and bent by impacts in the middle. Impinging\nball of cast iron weighing 204 lbs. Radius of arcs 16\nfeet.\nImpact upon bar.\nImpact upon the\nweight.\nChord of are\nObserved deflec-\nChord of are\nObserved defieo-\nfallen through.\ntion in inches.\nfallen through.\ntion in inches.\n2\n.46\n2\n.31\n8\n.62\n8\n.43\n4\n.87\n4\n.69\n5\n1.03\n5\n.81\n6\n1.24\n6\n1.04\n7\n1.44\n7\n1.28\n8\n1.80\n8\n1.41\n-\n-\n9\n1.63\nThe results in the 3d and 4th columns of the above table\nwere derived from allowing the ball to impinge against &\nweight of 56 lbs., hung 80 as to be in contact with the bar.\n\" Before the experiments on impact, the beam was laid on\ntwo supports 6 ft. 6 in. asunder, and was bent .78 in. by 123\nlbs. (including the pressure from its own weight), applied\ngently in the middle.\"\nTables of experiments on two cast iron bars, 4 ft. 6 in. long,\nfull inch square, weighing 14 lbs. 10 02. nearly, placed\nagainst supports 4 feet apart, and impinged upon by a cast\niron ball weighing 44 lbs. Radius 16 ft.\nImpact in the middle.\nImpact at one-fourth the length from the middle\nof the bars.\nChords of ares in\nMean deflections\nChords of aros in\nMean deflections\nMean ratio of the\nof the two bars\nof the two bars\ndeflections in\nfeet.\nin inches.\nfeet.\nin inches.\nthe two cases.\n2\n.35\n2\n.24\n-\n8\n.55\n8\n.42\n-\n4\n.77\n4\n.52\n694\n5\n.95\n5\n.64\n-\n5.5\n1.05\n5.5\n.70\n-\n6\nBroke in the\n6\nBrok e at the\n-\nmiddle\npoint of impa t\n10\nDigitized by\nGoogle\n146\nCIVIL ENGINEERING.\nThe results in the 1st of the above tables are from bars\nstruck in the middle, those in the 2d table are from bars\nstruck at the middle point between the centre and extremity\nof the bar.\nFrom the above and other experiments the conclusion is\ndrawn, \" that a uniform beam will bear the same blow, whether\nstruck in the middle or half way between that and one end.\"\nFrom all the experiments it appears that the deflection is\nnearly as the chord of the arc fallen through, or as the velo-\ncity of impact.\"\nThe following conclusions are drawn from the experiments.\n(1.) \" If different bodies of equal weight, but differing con-\nsiderably in hardness and elastic force, be made to strike hori-\nzontally against the middle of a heavy beam supported at its\nends, all the bodies will recoil with velocities equal to one\nanother.\"\n(2.) If, as before, a beam supported at its ends be struck\nhorizontally by. bodies of the same weight, but different hard-\nness and elastic force, the deflection of the beam will be the\nsame whichever body be used.\"\n(3.) The quantity of recoil in a body, after striking\nagainst a beam as above, is nearly equal to (though somewhat\nbelow) what would arise from the full varying pressure of a\nperfectly elastic beam, as it recovered its form after deflec-\ntion.\"\nNote. This last conclusion is drawn from a comparison of\nthe results of experiment with those obtained from calcula-\ntion, in which the beam is assumed as perfectly elastic.\n(4.) \" The effect of bodies of different natures striking\nagainst a hard, flexible beam, seems to be independent of the\nelasticities of the bodies, and may be calculated, with trifling\nerror, on a supposition that they are inelastic.\"\n(5.) \"The power of a uniform beam to resist a blow given\nhorizontally, is the same in whatever part it is struck.\"\n367. From the results of the experiments of Messrs. Fair-\nbairn and Hodgkinson, on the properties of cold and hot blast\niron, it appears that the ratio of their resistances to impact is\n1000 to 1226.3, the resistance of cold blast being represented\nby 1000 : the resistance, or power of the beam to bear a hori-\nzontal impact, being measured by the product of its breaking\nweight from a transverse strain at the middle of the beam\nand its ultimate deflection. This measure, Mr. Hodgkinson\nremarks, \" supposes that all cast iron bars of the same dimen-\nsions, in our experiments, are of the same weight, and that\nthe deflection of a beam up to the breaking weight would be\nDigitized by Google\nSTRENGTH OF WROUGHT IRON.\n147\nas the pressure. Neither of these is true; they are only\napproximations; but the difference in the weights of cast iron\nbars of equal size is very little, and, taking them as the same,\nit may be inferred from my paper on Impact upon Beams\n(Fifth Report of the British Association) that the assump-\ntion above gives results near enough for practice.\"\nVI.\nSTRENGTH OF WROUGHT IRON.\nTHIS material, from its very extensive applications in\nstructures where a considerable tensile force is to be resisted,\nas in suspension bridges, iron ties, etc., has been the subject\nof a very great number of experiments. Among the many\nmay be cited those of Telford and Brown in England, Duleau\nin France, and the able and extensive series upon plate iron\nfor steam boilers, made under the direction of the Franklin\nInstitute, and published in the 19th and 20th vols. (New\nSeries) of the Journal of the Institute.\n368. Resistance to Tensile Strain. The tables on the\nnext page exhibit the tensile strength of this material under\nordinary temperatures, and in the different states in which it\nis used for structures.\nIt is remarked, in the Report of the Sub-committee, that\nthe inherent irregularities of the metal, even in the best speci-\nmens, whether of rolled or hammered iron, seldom fall short\nof 10 or 15 per cent. of the mean strength.\"\nFrom the same series of experiments, it appears that the\nstrength of rolled plate lenghthwise is about 6 per cent.\ngreater than its strength crosswise.\nIn the Tenth Report of the British Association in 1840,\nMr. Fairbairn has given the results of experiments on plate\niron by Mr Hodgkinson, from which it appears that the mean\nstrength of iron plates lengthwise is 22.52 tons.\nCrosswise \" 23.04 \"\nSingle-riveted plates \" 18,590 lbs.\nDouble-riveted plates \" 22,258 \"\nRepresenting the strength of the plate by 100.\nThe double-riveted plates will be\n70.\nThe single-riveted plates will be\n56.\nDigitized by\nGoogle\n148\nCIVIL ENGINEERING.\nTable exhibiting the Strength of Square and Round Bars of\nWrought Iron.\nLength of\nExtension be-\nBreaking\nTensile\nDESCRIPTION OF IRON.\npieces in\nfore rupture\nweight in\nstrength per\nAuthor.\nfeet.\nin inches.\ntons.\nsquare inch.\nBar 1 inch square, Welsh\n1\n22.75\n29\n29\nTelford.\n\"\n\"\nSwedish\n1\n0.875\n29\n29\n\"\nRound bar, 2 in. diam. \"\n1\n2.2\n100\n29.28\n\"\nBar, 1.81 inch square\n\"\n8.5\n0.19\n40.95\n28.75\nBrown.\n\" 1.19\n\"\n\"\n8.5\n8.00\n88.50\n28.75\n\"\nRound bar, 1.81 in. diam., Russian\n8.5\n2.25\n86.10\n26.50\n64\nBar, 1.25 inch square, Welsh\n8.5\n2.00\n88.05\n24.86\n\"\nRound bar, 2 in. diam.\n\"\n12.5\n18.50\n82.75\n26.88\n\"\nBars reduced in the middle by\nhammering to 0.875 in. square\n81.35\nBrunel.\n\"\n\"\n0.50\n\"\n80.80\n\"\nBar,\nMissouri\n21.88\ns Franklin\nInstitute.\n\" (alit rods)\n22.32\n\"\n\"\nTennessee\n28.25\n\"\n\"\nSalisbury, Connecticut.\n25.89\n\"\n64\nSwedish\n25.97\n\"\n\"\nCentre Co., Penn\n26.07\n\"\n\"\nLancaster Co., Penn\n26.18\n\"\n\" (cable iron)\nEnglish\n26.62\n\"\n\"\ndo. hammer-hardened\n\"\n81.70\n\"\n\"\nRussian\n88.95\n44\nWire, 0.888 in. diam. Phillipsburg\n37.58\n\"\n\"\n0.190\n\"\n\"\n32.98\n\"\n\"\n0.156\n\"\n\"\n89.80\n\"\n\"\n0.10\n\"\nEnglish\n85.81\nTelford.\nTable exhibiting the Mean Strength of Boiler Iron, per\nsquare inch in lbs., cut from plates with shears.\nProcess of manufacture.\nEdges filed uni-\nNotches filed into\nRough edge bar.\nformly.\nbar on each edge.\nPiled iron\n53,045\n56,081\n63,266\nHammered plate\n47,506\n55,584\n58,447\nPuddled iron\n52,341\n51,089\n62,420\nProfessor Barlow, in his Report to the Directors of the\nLondon and Birmingham Railroad (Journal of Franklin\nInstitute, July, 1835), states, as the results of his experiments,\nthat a bar of malleable iron one inch square is elongated the\n10.80oth part of its length by a strain of one ton ; that good\niron is elongated the 1000th part by a strain of 10 tons, and\nis injured by this strain, while indifferent or bad iron is in-\njured by a strain of 8 tons.\nFrom the Report made to the Franklin Institute, it appears\nthat the first set, or permanent elongation, may take place\nunder very different strains, varying with the character of the\nmaterial. The most ductile iron yields permanently to a low\nDigitized by Google\nSTRENGTH OF WROUGHT IRON.\n149\ndegree of strain. The extremes by which a permanent set is\ngiven vary between the 0.416 and 0.872 of the ultimate\nstrength; the mean of thirteen comparisons being 0.641.\nFrom the able series of experiments made by Mr. Kirkaldy\nat Glasgow, on the tensile strength of wrought iron, he has\narrived at the following general conclusions (Kirkaldy,\nExperiments on Wrought Iron and Steel, 2d Ed., 1866) :-\n1. The breaking strain does not indicate the quality, as\nhitherto assumed.\n2. A high breaking strain may be due to the iron being of\nsuperior quality, dense, fine, and moderately soft, or simply\nto its being very hard and unyielding.\n3. A low breaking strain may be due to looseness and\ncoarseness in the texture, or to extreme softness, although\nvery close and fine in quality.\n4. The contraction of area at fracture, previously overlook-\ned, forms an essential element in estimating the quality of\nspecimens.\n5. The respective merits of various specimens can be cor-\nrectly ascertained by comparing the breaking strain jointly\nwith the contraction of area.\n6. Inferior qualities show a much greater variation in the\nbreaking strain than superior.\n7. Greater differences exist between small and large bars\nin coarse than in fine varieties.\n8. The prevailing opinion of a rough bar being stronger\nthan a turned one is erroneous.\n9. Rolled bars are slightly hardened by being forged\ndown.\n10. The breaking strain and contraction of area of iron\nplates are greater in the direction in which they are rolled\nthan in a transverse direction.\n11. A very slight difference exists between specimens from\nthe centre and specimens from the outside of crank-shafts.\n12. The breaking strain and contraction of area are greater\nin those specimens cut lengthways out of crank-shafts than in\nthose cut crossways.\n13. Iron, when fractured suddenly, presents invariably a\ncrystalline appearance; when fractured slowly, its appearance\nis invariably fibrous.\n14. The appearance may be changed from fibrous to crys-\ntalline by merely altering the shape of specimen so as to\nrender it more liable to snap.\n15. The appearance may be changed by varying the treat-\nment so as to render the iron harder and more liable to snap.\nDigitized by\nGoogle\n150\nCIVIL ENGINEERING.\n16. The appearance may be changed by applying the\nstrain so suddenly as to render the specimen more liable to\nsnap, from having less time to stretch.\n17. Iron is less liable to snap the more it is worked and\nrolled.\n18. The \"skin,\" or outer part of the iron, is somewhat\nharder than the inner part, as shown by appearance of frac-\nture in rough and turned bars.\n19. The mixed character of the scrap-iron used in large\nforgings is proved by the singularly varied appearance of the\nfractures of specimens cut out of crank-shafts.\n20. The texture of various kinds of wrought iron is beauti-\nfully developed by immersion in dilute hydrochloric acid,\nwhich, acting on the surrounding impurities, exposes the\nmetallic portion alone for examination.\n21. In the fibrous fractures the threads are drawn out, and\nare viewed externally, whilst in the crystalline fractures the\nthreads are snapped across in clusters, and are viewed inter-\nnally or sectionally. In the latter cases the fracture of the\nspecimen is always at right angles to the length; in the\nformer it is more or less irregular; fracture is nearly free\nof lustre and unlike the crystalline appearance of iron sud-\ndenly fractured; the two, combined in the same specimen,\nare shown in iron bolts partly converted into steel.\n22. The little additional time required in testing those\nspecimens whose rate of elongation was noted had no inju-\nrious effect in lessening the amount of breaking strain, as\nimagined by some.\n23. The rate of elongation varies not only extremely in dif-\nferent qualities, but also to a considerable extent in speci-\nmens of the same brand.\n24. The specimens were generally found to stretch equally\nthroughout their length until close upon rupture, when they\nmore or less suddenly drew out, usually at one part only,\nsometimes at two, and, in a few exceptional cases, at three dif-\nferent places.\n25. The ratio of ultimate elongation may be greater in\nshort than in long bars in some descriptions of iron, whilst\nin others the ratio is not affected by difference in the\nlength.\n26. The lateral dimensions of specimens forms an impor-\ntant element in comparing either the rate of, or the ultimate\nelongations-a circumstance which has been hitherto over-\nlooked.\n27. Iron bolts, case-hardened, bore a less breaking strain\nDigitized by\nGoogle\nSTRENGTH OF WROUGHT IRON.\n151\nthan when wholly iron, owing to the superior tenacity\nof the small proportion of steel being more than counter-\nbalanced by the greater ductility of the remaining portion of\niron.\n28. Iron highly heated and suddenly cooled in water is\nhardened, and the breaking strain, when gradually applied,\nincreased, but at the same time it is rendered more liable to\nsnap.\n29. Iron, like steel, is softened, and the breaking strain re-\nduced by being heated and allowed to cool slowly.\n30. Iron, subjected to the cold-rolling process, has its\nbreaking strain greatly increased by being made extremely\nhard, and not by being consolidated,\" as previously sup-\nposed.\n31. Specimens cut out of crank-shaft are improved by\nadditional hammering.\n32. The galvanizing or tinning of iron plates produces no\nsensible effects on plates of the thickness experimented on.\nThe results, however, may be different should the plates be\nextremely thin.\n33. The breaking strain is materially affected by the shape\nof the specimen. Thus the amount borne was much less when\nthe diameter was uniform for some inches of the length than\nwhen confined to a small portion-a peculiarity previously\nunascertained and not even suspected.\n34. It is necessary to know correctly the exact conditions\nunder which any tests are made, before we can equitably\ncompare results obtained from different quarters.\n35. The startling discrepancy between experiments made\nat the Royal Arsenal, and by the writer, is due to the differ-\nence in the shape of the respective specimens, and not to the\ndifference in the two testing machines.\n36. In screwed bolts the breaking strain is found to be\ngreater when old dies are used in their formation than when\nthe dies are new, owing to the iron becoming harder by the\ngreater pressure required in forming the screw thread when\nthe dies are old and blunt, than when new and sharp.\n37. The strength of screw-bolts is found to be in propor-\ntion to their relative areas, there being only a slight difference\nin favor of the smaller compared with the larger sizes, instead\nof the very material difference previously imagined.\n38. Screwed bolts are not necessarily injured although\nstrained nearly to their breaking-point.\n39. A great variation exists in the strength of iron bars\nwhich have been cut and welded; whilst some bear almost as\nDigitized by\nGoogle\n152\nCIVIL ENGINEERING.\nmuch as the uncut bar, the strength of others is reduced fully\na third.\n40. Iron is injured by being brought to a white or welding\nheat if not at the same time hammered or rolled.\n41. The breaking strain is considerably less when the strain\nis applied suddenly instead of gradually, though some have\nimagined that the reverse is the case.\n42. The contraction of area is also less when the strain is\nsuddenly applied.\n43. The breaking strain is reduced when the iron is frozen\nwith the strain gradually applied, the difference between a\nfrozen and unfrozen bolt is lessened, as the iron is warmed by\nthe drawing out of the specimen.\n44. The amount of heat developed is considerable when the\nspecimen is suddenly stretched, as shown in the formation of\nvapor from the melting of the layer of ice on one of the spe-\ncimens, and also by the surface of others assuming tints of\nvarious shades of blue and orange, not only in steel, but also,\nalthough in a less marked degree, in iron.\n45. The specific gravity is found generally to indicate\npretty correctly the quality of specimens.\n46. The density of iron is decreased by the process of wire-\ndrawing, and by the similar process of cold-rolling, instead of\nincreased, as previously imagined.\n47. The density in some descriptions of iron is also de-\ncreased by additional hot-rolling in the ordinary way: in others\nthe density is very slightly increased.\n48. The density of iron is decreased by being drawn out\nunder a tensile strain, instead of increased, as believed by\nsome.\nThe breaking strain per square-inch of wrought iron is\ngenerally stated to be about twenty-five tons for bars, and\ntwenty tons for plates. This corresponds very nearly with\nthe results of the writer's experiments, of which the follow-\ning table presents a condensed summary :-\nHighest, lbs.\nLowest, lbs.\nMean. lbs.\nTons.\n188. Bars, rolled\n68,848\n44,584\n57,555 =254\n72. Angle-iron, etc\n63,715\n87,909\n54,729 =241\n167. Plates, lengthways\n62,544\n37,474\n50,737\n160. Plates, crossways\n60,756\n32,450\n46,171\n=214\nAlthough the breaking strain is generally assumed to be\nabout twenty-five tons for bars, and twenty tons for plates,\nvery great difference of opinion exists as to the amount of\nworking strain, or the load which can with safety be applied\nDigitized by Google\nSTRENGTH OF WROUGHT IRON.\n153\nin actual practice. The latter is variously stated at from a\nthird to a tenth. It will be observed that whilst much dis-\ncussion has arisen as to the amount of working strain, or the\nratio the load should bear to that of the breaking strain, the\nimportant circumstance of the quality of the iron, as in-\nfluencing the working strain, has been overlooked. The Board\nof Trade limits the strain to 5 tons, or 11,200 lbs. per square\ninch.\nIt must be abundantly evident, from the facts which have\nbeen produced, that the breaking strain, when taken alone,\ngives a false impression of, instead of indicating, the real\nquality of the iron, as the experiments which have been in-\nstituted reveal the somewhat startling fact, that frequently\nthe inferior kinds of iron actually yield a higher result than\nthe superior. The reason of this difference was shown to be\ndue to the fact that, whilst the one quality retained its ori-\nginal area, only very slightly decreased by the strain, the\nother was reduced to less than one-half. Now, surely this\nvariation, hitherto unaccountably completely overlooked, is of\nimportance as indicating the relative hardness or softness of\nthe material, and thus, it is submitted, forms an essential ele-\nment in considering the safe load that can be practically\napplied in various structures. It must be borne in mind that\nalthough the softness of the material has the effect of lessen-\ning the amount of the breaking strain, it has the very opposite\neffect as regards the working strain. This holds good for\ntwo reasons: first, the softer the iron the less liable it is to\nsnap; and second, fine or soft iron, being more uniform in\nquality, can be more depended upon in practice. Hence the\nload which this description of iron can suspend with safety\nmay approach much more nearly the limit of its breaking\nstrain than can be attempted with the harder or coarser sorts,\nwhere a greater margin must necessarily be left.\nSpecial attention is now solicited to the practical use that\nmay be made of the new mode of comparison introduced by\nthe writer, viz., the breaking strain per square inch of the\nfractured area of the specimen, insteud of the breaking strain\nper square inch of the original area.\nAs a necessary corollary to what he has just endeavored to\nestablish, the writer now submits, in addition, that the work-\ning strain should be in proportion to the breaking strain per\nsquare inch of fractured area, and not to the breaking strain\nper square inch of original area, as heretofore. He does not\npresume to say what that ratio should be, but he fully main-\ntains that some kinds of iron experimented on by him will\nDigitized by\nGoogle\n154\nCIVIL ENGINEERING.\nsustain with safety more than double the load that others can\nsuspend, especially in circumstances where the load is un-\nsteady, and the structure exposed to concussions, as in a ship,\nor to vibratory action, as in a railway bridge.\n369. Resistance to Compressive Strain. But few ex-\nperiments have been published on the resistance of this\nmaterial to compression. Rondelet states that it commences\nto yield under a pressure of about 70,800 lbs. per square inch,\nand that when the altitude of the specimen tried is greater\nthan three times the diameter of the base it yields by bending.\nMr. Hodgkinson states that the circumstances of its rupture\nfrom crushing indicate a law similar to what obtains in cast\niron.\nThe same rule for proportioning the working strain to the\ncrushing strain is followed in wrought iron subjected to com-\npression as in cast iron.\nResistance to a Transverse Strain. The following\ntables exhibit the circumstances of deflection from a transverse\nstrain on bars laid on horizontal supports; the weight being\napplied at the middle of the bar.\nThe table I. gives the results on bars 2 inches square, laid\non supports 33 inches asunder; table II. the results on bars\n2 inches deep, 1.9 in. broad, bearing as in table I.\nTABLE I.\nTABLE IL\nDeflections in\nDeflections in\nWeight in tons.\ninches for each\nWeight in tona.\ninches for each\nhalf ton.\nhalf ton.\n.75\n.020\n.250\n-\n1.00\n.020\n.50\n.016\n1.50\n.020\n1.00\n.022\n2.00\n.030\n1.50\n.020\n2.50\n.020\n2.00\n.026\n3.00\nSet\n2.25\n.018\n-\n-\n2.50\n.026\n-\n-\n2.75\n.038\n-\n-\n8.00\n.092\nThe above experiments were made by Professor Barlow,\nand published in his report already cited. He remarks on\nthe results in Table II., that the elasticity was injured by 2.50\ntons and destroyed by 3.00 tons.\n370. Trials were made to ascertain mechanically the posi-\ntion of the neutral axis on the cross section. Professor Bar-\nlow remarks on these trials, that \" the measurements obtained\nin these experiments being tension 1.6, compression 0.4, giv-\nDigitized by\nGoogle\nSTRENGTH OF WROUGHT IRON.\n155\ning exactly the ratio of 1 to 4 in rectangular bars. These re-\nsults seem the most positive of any hitherto obtained; still\nthere can be little doubt this ratio varies in iron of different\nqualities; but looking to the preceding experiments, it is\nprobably always from 1 to 3, to 1 to 5.\"\n371. Effects of Time on the Elongation of Wrought Iron\nfrom a Constant Strain of Extension. M. Vicat has given,\nin the Annales de Chimie et de Physique, vol. 54, some ex-\nperiments on this point, made on iron wires which had not\nbeen annealed, by subjecting four wires, respectively, to\nstrains amounting to the ±, the 1, the 1, and & of their tensile\nstrength, during a period of 33 months.\nFrom the results of these experiments it appears, that each\nwire, immediately upon the application of the strain to which\nit was subjected, received a certain amount of extension.\nThe first wire, which was subjected to a strain of 1th its\ntensile strength, was found at the end of the time in question\nnot to have acquired any increase of extension.\nThe second, submitted to dd its tensile strength, was elon-\ngated 0.027 in. per foot, independently of the elongation it at\nfirst received.\nThe third, subjected under like circumstances to a strain of\n1th its tensile strength, was elongated 0.40 in. per foot, be-\nsides its first elongation.\nThe fourth, similarly subjected to &ths the tensile strength,\nwas elongated 0.061, besides its first elongation.\nFrom observations made during the experiments, it was\nfound that, reckoning from the time when the first elongations\ntook place, the rapidity of the subsequent elongations was\nnearly proportional to the times; and that the elongations\nfrom strains greater than 1th the tensile strength are, after\nequal times. nearly proportional to the strains.\nM. Vicat remarks in substance, upon the results of these ex-\nperiments, that iron wire, when not annealed, commences to\nexhibit a permanent set when subjected to a strain between the\nt and 1 of its tensile strength, and that therefore it is rendered\nprobable that the wire ropes of a suspension bridge, which\nshould be subjected to a like strain, would, when the vibratory\nmotion to which such structures are liable is considered, yield\nconstantly from year to year, until they entirely gave way.\nM. Vicat further remarks, in substance, that the measure of\nthe resistance offered by materials to strains exerted only some\nminutes, or hours, is entirely relative to the duration of the\nexperiments. To ascertain the absolute measure of this re-\nsistance, which should serve as a guide to the engineer, the\nDigitized by Google\n156\nCIVIL ENGINEERING.\nmaterials ought to be subjected for some months to strains ;\nwhile observations should be made during this period, with\naccurate instruments, upon the manner in which they yield\nunder these strains.\nThe following tables, on the comparative strength of iron,\nsteel and hemp rope are taken from Stoney's work on the\nTheory of Strains, Vol. 11. The weights are given in\nEnglish units.\nHEMP.\nIRON.\nSTEEL.\nEQUIVALENT STRENGTH.\nCircumference,\ninchea.\nLbs. weight pr.\nfathom.\nCircumference,\ninches.\nLbs. weight pr\nfathom.\nCircumference,\ninches.\nLbs. weight pr.\nfathom.\nWorking load,\ncwts.\nTearing strain,\ntona.\n24\n2\n1\n1\n6\n2\n11\n11\n1\n1\n9\n3\n3t\n4\n14\n2\n12\n4\n14\n21\n11\n11\n15\n5\n41\n5\n1f\n3\n18\n6\n2\n81\n14\n2\n21\n7\n51\n7\n21\n4\n14\n21\n24\n8\n21\n4g\n27\n9\n6\n9\n24\n5\n11\n3\n30\n10\n21\n5}\n33\n11\n61\n10\n2f\n6\n2\n81\n36\n12\n24\n61\n2f\n4\n39\n13\n7\n12\n27\n7\n2t\n41\n42\n14\n8\n71\n45\n15\n71\n14\n31\n8\n24\n5\n48\n16\n8t\n81\n51\n17\n8\n16\n34\n9\n21\n57\n54\n18\n31\n10\n2f\n6\n60\n20\n81\n18\n34\n11\n24\n6}\n66\n22\n34\n12\n72\n24\n91\n22\n81\n18\n3t\n8\n78\n26\n10\n26\n4\n14\n84\n28\n41\n15\n3f\n9\n90\n30\n11\n80\n41\n16\n96\n32\n41\n18\n31\n10\n108\n36\n12\n34\n4f\n20\n34\n12\n120\n40\nDigitized by Google\nSTRENGTH OF WROUGHT IRON.\n157\nBESSEMER STEEL, MADE FROM RAIL-ENDS BY MARSH & CO. NOT TEMPERED.\nNo.\nBreaking\nstrain.\nStrength\nper square\ninch.\nFeet in the\nlb.\nStretch.\nPer cent. of\nlength.\nLength.\nDrawn from.\n6\n3472\n118,471\n10.15\n11\n2.4\n5.0788\n4-6.\nB\n3220\n110,563\n10.28\n4\n1.3\n4.975\n4-6.\n7\n3038\n114,549\n11.21\nto\n1.05\n4.9063\n47; large 7\n7\n3136\n122,880\n11.6\n11\n1.8\n5.1\n4-7.\n8\n2135\n109,034\n15.2\nt\n1.04\n4.9844\n4-8.\n9\n2184\n127,000\n17.3\n1\n0.35\n4.8646\n4-6 and 6-9.\n9\n1904\n109,770\n17.14\nt\n0.65\n4.823\n4-6 and 6-9.\n10\n1694\n117,567\n20.6\nt\n1.2\n4.8375\n4-10 S no annealing\n10\n1610\n111,718\n20.6\nto\n0.6\n4.8375\n4-10 1 between hard drawn.\n10\n1834\n130,493\n21.16\n4\n1\n4.96\n4-7 and 7-10 not drawn\nhard.\n11\n1407\n121,900\n25.7\nt\n0.8\n4.833\n4-8 and 8-11 not drawn\nhard.\n12\n1015\n121,679\n32.6\n**\n1.5\n4.6094\n4-7 7-10 and 10-12.\n13\n952\n131,055\n40.9\n1\n0.8\n5.1106\n4-7 7-10 and 10-18.\n14\n630\n114,508\n54\nt\n1.2\n5.078\n4-7 7-10 10-12 and 12-14.\n15\n560\n170,740\n62.5\nt\n0.85\n4.8854\n4-7 7-10 10-12 and 18-15.\n18\n466\n130,286\n88.17\nt\n0.6\n4.947\nGERMAN PUDDLED STEEL. FALKENWORTH ROCHER & CO. NOT TEMPERED.\nNo.\nBreaking\nstrain.\nStrength\nper square\ninch.\nFeet in the\nlb.\nStretch.\nPer cent. of\nlength.\nLength.\nDrawn from.\n8\n2226\n110,200\n14.75\nt\n0.6\n5.0625\n4-8. Drawn in Germany.\n9\n1778\n106,900\n17.87\nt\n0.82\n5 026\n4-9\n\"\n\"\n\"\n9\n1820\n108,700\n17.75\nt\n1.2\n4.9948\n4-9\n\"\n\"\n\"\nCAST-STEEL, PIANO WIRE. (M. PÖHLMANN, NUREMBERG.)\nPer\nNo.\nBreaking\nStrength per\nFeet in the\nStretch\ncent. of\nLength.\nDrawn from.\nStrain.\nsq. inch.\nlb.\nlength.\n14\n1624\n302,500\n55.4\n1f\n1.8\n5.1944\ndrawn wet, no an-\n14}\n1400\n299,225\n63.5\n2.6\n4.96\nnealing below\n15\n1008\n263,117\n70.8\n1₁ₕ\n1.8\n4.69\n10.\n15\n1078\n270,000\n74.5\nt\n1.6\n4.658\n16\n774\n249,700\n96.0\nt\n1.6\n4.5\n161\n812\n283,820\n103.8\n1½\n2.0\n4.865\n16}\n784\n275,525\n104.8\nt\n1,2\n4.9\n16+\n763\n261,576\n102.0\n18\n1.4\n4.78\nDigitized by Google\n158\nCIVIL ENGINEERING.\nCAST-STEEL. (JOHNSON, NEPHEW.)\nPer\nNo.\nBreaking\nStrength per\nFeet in the\nStretch.\ncent. of\nStrain.\nsq. inch.\nLength.\nDrawn from.\nlb.\nlength.\n8\n3220\n158,823\n14.67\n11\n2.2\n5.043\n4-8\n8\n3262\n160,000\n14.5\n1ts\n3\n5.0143\n4-8\n8\n3160\n1 &\n2\n5.026\n4-8\n~\nTempered.\n155,400\n14.6\nCAST-STEEL. (WEBSTER, HORSFALL.)\nPer\nNo.\nBreaking\nStrength per\nFeet in the\nStretch.\ncent. of\nStrain.\nlb.\nLength.\nDrawn from.\nsq. inch.\nlength.\n9\n2856\n167,601\n17.6\n1±\n2\n4.96\n9\n2812\n166,122\n17.6\n11\n1.8\n4.96\n4-8, then tem-\n.9\n2842\n168,506\n17.6\n11\n1.8\n4.96\npered and fin-\nished in 1 hole.\n10\n1988\n150,560\n22.6\nate\n1.4\n4.927\nThe following results were computed from experiments by\nthe late J. A. Roebling, the eminent engineer of the Niagara,\nCincinnati and other suspension bridges, on the comparative\nstrength of iron-wire rope and of hemp rope. The breaking\nweight being in tons of 2,000 lbs.\nTearing strain per\nNo.\nCircumference\nof wire rope in\ninches.\nArea of section\nin sq. inches.\nTrade number.\nCircumference\nof hemp rope\nin inches.\nArea of section\nin sq. inches.\nsquare inch in tons.\nWire\nHemp\nrope.\nrope.\n1\n4.9\n1.9\n4\n12\n11.45\n22.8\n3.8\n2\n3.91\n1.22\n6\n9.5\n7.18\n22.3\n3.78\n8\n2.98\n0.7\n8\n7\n3.9\n22.8\n4.1\n4\n4.00\n1.27\n12\n10\n7.95\n23.6\n3.77\n5\n2.98\n0.7\n15\n7.25\n4.18\n22.8\n3.82\nNote. Nos. 1, 2, 3, were made of what is known as fine\nwire ; Nos. 4, 5, of coarse wire.\n372. Effects of Temperature on the Tensile Strength\nof Wrought Iron. The experiments made under the direc-\ntion of the Franklin Institute, already noticed, have developed\nsome very curious facts of an anomalous character, with re-\nspect to the effect of an increase of temperature upon the\nDigitized by\nGoogle\nSTRENGTH OF WROUGHT IRON.\n159\nstrength of wrought iron. It was found that at high degrees\nof heat the tensile strength was greater up to a certain point\nthan was exhibited by the same iron at ordinary temperatures.\nThe Sub-committee in their Report remark: \" This circum-\nstance was noted at 212°, 392°, and 572°, rising by steps of\n180° each from 32°, at which last point some trials have been\nmade in melting ice. At the highest of these points, however,\nit was perceived that some specimens of the metal exhibited\nbut little, if any, superiority of strength over that which they\nhad possessed when cold, while others allowed of being heated\nnearly to the boiling-point of mercury, before they manifested\nany decided indications of a weakening effect from increase\nof temperature.\"\n\" It hence became apparent that any law, taking for a\nbasis the strength of iron in its ordinary condition, and at\ncommon temperatures, must be liable to great uncertainty, in\nregard to its application to different specimens of the metal.\nIt was evident that the anomaly above referred to must be\nonly apparent, and that the tenacity actually exhibited at 572°,\nas well as that which prevails while the iron is in the state in\nwhich it was left by forging or rolling, must be below its\nmaximum tenacity.\"\nFrom the experiments made upon several bars of the same\niron, it appeared that their \" maximum tenacity was 15.17 per\ncent. greater than their mean strength when tried cold.\"\nCalculating the maximum tenacity in other experiments\nfrom this standard, the Sub-committee have drawn up the\nfollowing table exhibiting the relations between diminutions\nfrom the maximum tenacity and the degrees of temperature\nby which they are caused, from which the curve representing\nthe law of these relations can be constructed.\nThe Sub-committee remark on the construction of the above\ntable: \" As some of the experiments which furnished the\nstandards of comparison for strength at ordinary temperatures\nwere made at 80, and as at this point small variations with re-\nspect to heat appear to affect but very slightly the tenacity of\niron, it was conceived that for practical purposes, at least, the\ncalculations might be commenced from that point.\"\n\" It will be found that with the exception of a slight anoma-\nly between 520° and 570°, amounting to -.08, the numbers\nexpressing the ratios between the elevations of temperature,\nand the diminutions of tenacity, constantly increase until we\nreach 932°, at which it is 2.97, and that from this point the\nratio of diminution decreases to the limits of our range of\ntrials, 1317°, where it is 2.14. It will also be observed, that\nDigitized by\nGoogle\n160\nCIVIL ENGINEERING.\nthe diminution of tenacity at 932°, where the law changes\nfrom an increasing to a decreasing rate of diminution, is\nalmost precisely one-third of the total, or maximum strength\nof the iron at ordinary temperatures.\"\nTABLE.\nObserved dimi-\nPower of the temperature\nNo. of the com-\nObserved tem-\nObserved tem-\nnution of to-\nwhich represents the di-\nparison.\nperatures.\nperatures-80°.\nnacity.\nminution of tenacity at\neach point.\n1\n520°\n440°\n.0738\n2.25\n2\n570\n490\n.0869\n2.17\n8\n596\n516\n.0899\n2.38\n4\n662\n582\n.1155\n2.67\n5\n770\n690\n.1627\n2.85\n6\n824\n744\n.2010\n2.94\n7\n982\n852\n.3324\n2.97\n8\n1030\n950\n.4478\n2.92\n9\n1111\n1031\n.5514\n2.63\n10\n1155\n1075\n.6000\n2.60\n11\n1237\n1157\n.6622\n2.41\n12\n1317\n1237\n.7001\n2.14\nMean 2.58\nFrom the mean of all the rates in the above table the fol-\nlowing rule is deduced : \" the thirteenth power of the temper-\nature above 80° is proportionate to the fifth power of the\ndiminution from the maximum tenacity.\"\nProfessor W. R. Johnson, a member of the Sub-committee,\nhas since applied the results developed in the preceding ex-\nperiments to practical purposes, in increasing the tenacity of\nwrought iron by subjecting it to tension under a high degree\nof temperature, before using it for purposes in which it will\nhave to undergo considerable strains, as, for example, in chain\ncables, etc.\nThis subject was brought by Prof. Johnson before the\nBoard of Navy Commissioners in 1841 ; subsequently, experi-\nments were made by him under direction of the Navy Depart-\nments the results of which, as exhibited in the following\ntable, were published in the Senate Public Documents (1),\n28th Congress, 2d Session, p. 641. Dec. 3, 1844.\nProf. Johnson in his letter remarks : \" It will be observed\nthat in these experiments the temperature has, with a view to\neconomy of time, been limited to 400°, whereas the best\nDigitized by\nGoogle\nSTRENGTH OF WROUGHT IRON.\n161\neffects of the process have generally been obtained heretofore\nwhen the heat has been as high as 575°.\"\nTable of the Effects of Thermo-tension on the Tenacity\nand Elongation of Wrought Iron.\nStrength af-\nGain of\nStrength\nter treating\nGain of\nstrength by\nKIND OF IRON.\nTotal gain\nof cold.\nwith Ther-\nlength.\nthe treat-\nof value.\nmo-tension.\nment.\nTredegar, No. 1, round iron\n60\n71.4\n6.51\n19.00\n25.51\nDo.\ndo.\n60\n72.0\n6.51\n20.00\n26.51\nTredegar, square bar iron\n60\n67.2\n6.77\n12.00\n18.77\nTredegar, No. 3, round iron\n58\n68.4\n5.263\n17.93\n23.19\nSalisbury, round (Ames')\n105.87\n121.0\n3.73\n14.29\n18.02\nMean,\n-\n-\n5.75\n16.64\n22.40\nFrom the experiments of Mr. Kirkaldy it appears that\n\" wrought iron is injured by being brought to a white heat if\nnot at the same time hammered or rolled.\"\nResistance of Wrought Iron and Steel to a Shearing Strain.\nFrom the experiments of Mr. Clark on plates joined by a\nsingle wrought-iron rivet, and those of Mr. Kirkaldy on steel\nrivets, it appears that the resistance to a shearing strain of the\nformer was very nearly equal to its tensile strength ; and for\nthe latter that it was about three-fourths of its tensile\nstrength.\n373. Resistance of Iron Wire to Impact. The follow-\ning table of experiments gives the results obtained by Mr.\nHodgkinson, by suspending an iron ball at the end of a wire\n(diameter No. 17), and letting another iron ball impinge\nupon it from different altitudes. The suspended and imping-\ning balls had holes drilled through them, through which the\nwire passed. A disk of lead was placed on the suspended\nball to receive the blow, and lessen the recoil from elasticity.\nThe following observations are made by Mr. Hodgkinson\n\" To ascertain the strength and extensibility of this wire, it\nwas broken in a very careful experiment with 2521 lbs., sus-\npended at its lower end, and laid gradually on. And to ob-\ntain the increment of a portion of the wire (length 24 ft. 8 in.)\nwhen loaded by a certain weight, it had 139 lbs. hung at the\nbottom, and when 89 lbs. were taken off the load, the wire\ndecreased in length .39 inch.\n11\nDigitized by Google\n162\nCIVIL ENGINEERING.\nTABLE\nLength of wire.\nWeight of stri-\nking ball.\nWeight of sus-\npended ball\nand lead.\nHeight fallen through by\nstriking ball.\nWire broke with\nball falling\nthrough.\nRemarks.\nft. in.\nlbs. O%.\nlbs. OZ.\n25 0\n5 14\n0 9\n2, 2½, 8, 8½, 4,\n43/2\n-\n-\n-\n(repeated) 2½, 8, 8½, 4, 4½,\n5\n4%\nNo lead.\n24 0\n6 0\n10 1\n7,\n7\n7\nThe wire usu-\n-\n-\n-\n(repeated with fresh wire,) 6,\n6½\nally broke near\n-\n-\n44 0\n1, 2, 8, 4, 5, 6, 6½, 7,\n7½\nthe point of im-\n-\n-\n80 8\n6, 6½, 7, 7½, 8, 8½, 9,\n9½\npact, and it was\n-\n-\n89 0\n8, 8½, 9, 9½, 10, 10½,\n11\nadjusted to its\n-\n-\n125 0\n8, 8½, 9, 9½, 10,\n10%\nlength, if fresh\n-\n40 0\n10\n1\n8, 4 inches,\n5 inches\nwire were not\n-\n-\n80 8\n2, 8, 4, 5, 6 inches,\n7 do.\nused by a reserve\nat the top.\n-\n-\n89\n0\n4, 5 inches,\n6 do.\nBroke one inch\n24 8\n85 0\n44 0\n2 inches,\n8 do.\nfrom top.\n\" Should it be suggested that the wire by being frequently\nimpinged upon would perhaps be much weakened, the author\nwould beg to refer to a paper of his on Chain Bridges, Man-\nchester Memoirs, 2d series, vol. 5, where it is shown that an\niron wire broken by pressure several times in succession is\nvery little weakened, and will nearly bear the same weight as\nat first.\"\n\"The first of the preceding experiments on wires are the\nonly ones from which the maximum can, with any approach\nto certainty, be inferred; and we see from them that the wire\nresisted the impulsion with the greatest effect when it was\nloaded at bottom with a weight, which, added to that of the\nstriking body, was a little more than one-third of the weight\nthat would break the wire by pressure.\"\n\"From these experiments generally, it appears that the wire\nwas weak to bear a blow when lightly loaded.\"\n\"These last experiments and remarks, and some of the pre-\nceding ones (on horizontal impact), \" show clearly the benefit\nof giving considerable weight to elastic structures subject to\nimpact and vibration.\"\n374. Resistance to Torsion of Wrought and Cast Iron.\n-The following table exhibits the results of experiments\nmade by Mr. Dunlop, at Glasgow, on round bars of wrought\niron. The twisting weights were applied with an arm of lever\n14 feet 2 inches.\nDigitized by Google\nSTRENGTH OF STEEL.\n163\nLength of bars\nDiameter of bare\nWeight in lbs. pro-\nin inches.\nin inchea.\nducing rupture.\n24\n2\n250\n21\n2t\n884\n8\n21\n408\n8\n24\n700\n4\nto\n1170\n5\n81\n1240\n5\n84\n1662\n5\n4\n1938\n6\n41\n2158\nTable of Experiments made by Mr. G. Rennie upon Cast\nand Wrought Iron. Weight applied at an arm of lever of\n2 feet.\nLength of\nSize of\nMean break-\nMATERIAL\nblocks in\nsectional\ning weight\ninches.\narea.\nin lbs.\nlbs.\n05,\nIron cast horisontally\n0\nH\n9\n15\n\"\nvertically\n0\n10\n10\n\"\nhorizontally\n+\n7\n8\n\"\n\"\nt\n8\n1\n\"\n\"\n1\n8\n8\n\"\nvertically\n+\n10\n1\n\"\n\"\nt\n8\n9\n\"\n\"\n1\n8\n5\n\"\n\"\n6\n+\n9\n12\n\"\nhorizontally\n0\n93\n12\n\"\n\"\n0\n74\n\"\n\"\n10\n52\nWrought iron (English)\n0\nH\n10\n2\n\"\n(Swedish)\n0\n9\n8\nVII.\nSTRENGTH OF STEEL.\n875. FROM experiments made in Sweden by a government\ncommission it appears that both the ductility and the strength\nof steel and iron are influenced by the amount of carbon they\ncontain.\nDigitized by Google\n164\nCIVIL ENGINEERING.\nThe experiments show that the hardest material has the\ngreatest strength both before and after a permanent set has\ntaken place from the force employed ; but its ductility is also\nthe least. The Bessemer steel in these experiments gave the\nsame results as the other processes for obtaining steel, the\nsame pig iron being used in each case.\nThe limit for the amount of carbon for the Bessemer steel\nis from 1.2 to 1.5 per cent. With a larger amount both the\nstrength and ductility was found to decrease. When the\namount of carbon does not exceed 0.4 per cent. the ductility\nof Bessemer steel is about the same as puddled iron from the\nsame pig iron, and as it is not only much stronger but more\ndense and homogeneous than the puddled material, it is de-\ncidedly superior for railway purposes.\nFrom the experiments of the same commission that the\nstrength both of iron and steel, subjected to strains between\nthe extremes of temperature of boiling water and freezing\nmercury, was greater during low than at ordinary tempera-\ntures.\nThe cheaper methods which have been introduced into the\nmanufacture of steel within but a few years past, have brought\nthis material within the class of the ordinary materials for\nengineering purposes ; as railroad bars, bridges, etc. ; and has\nled to a very extensive series of experiments upon its resist-\nance to the usual strains on building materials; among the\nmost noted of which are those of Mr. Fairbairn and of Mr.\nKirkaldy.\nThe results of Mr. Fairbairn's experiments, Report of the\nBritish Association, 1867, give for the mean rupturing strain\nfrom extension 106,848 lbs. per square inch ; and for com-\npression a mean rupturing strain of 225,568 lbs. per square\ninch.\nFrom the same series of experiments upon bars deflected\nunder moderate transverse strains the coefficient or modulus\nof elasticity deduced was 31,000,000 lbs. per square inch.\nFrom the experiments already referred to by Mr. Kirkaldy,\nthe following general conclusions were arrived at:-\n1. The breaking strain of steel, when taken alone, gives no\nclue to the real qualities of various kinds of that metal (74).\n2. The contraction of area at fracture of specimens of steel\nmust be ascertained as well as in those of iron (74).\n3. The breaking strain, jointly with the contraction of\narea, affords the means of comparing the peculiarity in various\nlots of specimens (74, 75).\n4. Some descriptions of steel are found to be very hard,\nDigitized by\nGoogle\nSTRENGTH OF STEEL.\n165\nand, consequently, suitable for some purposes, whilst others\nare extremely soft, and equally suitable for other uses (74,\n75, 78).\n5. The breaking strain and contraction of area of puddled\nsteel plates, as in iron plates, are greater in the direction in\nwhich they are rolled, whereas in cast steel they are less (74,\n75).\n6. Steel invariably presents, when fractured slowly, a silky\nfibrous appearance; when fractured suddenly the appearance\nis invariably granular, in which case the fracture is always at\nright angles to the length; when the fracture is fibrous, the\nangle diverges always more or less from 90° (139).\n7. The granular appearance presented by steel suddenly.\n8. Steel which previously broke with a silky fibrous ap-\npearance is changed into granular by being hardened (141).\n9. Steel is reduced in strength by being hardened in water,\nwhile the strength is vastly increased by being hardened in\noil (161, 162, 164).\n10. The higher steel is heated (without, of course, running\nthe risk of being burned) the greater is the increase of strength,\nby being plunged into oil (161, 162).\n11. In a highly converted or hard steel the increase in\nstrength and in hardness is greater than in a less converted or\nsoft steel (161, 162).\n12. Heated steel, by being plunged into oil instead of\nwater, is not only considerably hardened, but toughened by\nthe treatment (162).\n13. Steel plates hardened in oil and joined together with\nrivets are fully equal in strength to an unjointed soft plate,\nor the loss of strength by riveting is more than counter-\nbalanced by the increase in strength by hardening in oil\n(163).\n14. Steel rivets fully larger in diameter than those used in\nriveting iron plates of the same thickness being found to be\ngreatly too small for riveting steel plates, the probability is\nsuggested that the proper proportion for iron rivets is not, as\ngenerally assumed, a diameter equal to the thickness of the\ntwo plates to be joined (163).\n15. The shearing strain of steel rivets is found to be about\na fourth less than the tensile strain (163).\n16. The welding of steel bars, owing to their being so\neasily burned by slightly overheating, is a difficult and uncer-\ntain operation (181, 15).\n17. The most highly converted steel does not, as some may\nsuppose, possess the greatest density (196).\nDigitized\nby\nGoogle\n166\nCIVIL ENGINEERING.\n18. In cast steel the density is much greater than in pud-\ndled steel, which is even less than in some of the superior de-\nscriptions of wrought iron (196).\nFrom experiments made by Major Wade, late of the U.S.\nOrdnance Corps, the following results were obtained for the\ncrushing weights of cast iron on the square inch :-\nNot hardened\n198,944 lbs.\nHardened ; low temper\n354,544 \"\nHardened ; mean temper\n891,985 \"\nHardened ; high temper\n372,598 \"\nFrom contracts made by direction of Mr. James B. Eads,\nchief engineer of the Illinois and St. Louis bridge, at St.\nLouis, Missouri, the staves of the arches, the pins and plates\nare to be of the crucible cast steel of commerce. Those parts\nsubjected to compression are to withstand 60,000 pounds on\nthe square inch, and those subjected to a tensile strain 40,000\npounds on the square inch without permanent set, and all\nmust stand a tensile strain of 100,000 pounds on the square\ninch without fracture.\nThe modulus of elasticity of the steel not to be less than\n26,000,000 pounds, nor more than 30,000,000.\nVIII.\nSTRENGTH OF COPPER.\nTHE various uses to which copper is applied in construc-\ntions, render a knowledge of its resistance under various\ncircumstances a matter of great interest to the engineer.\n376. Resistance to Tensile Strain. The resistance of cast\ncopper on the square inch, from the experiments of Mr. G.\nRennie, is 8.51 tons, that of wrought copper reduced per\nhammer at 15:08 tons. Copper wire is stated to bear 27.30\ntons on the square inch. From the experiments made under\nthe direction of the Franklin Institute, already cited, the\nmean strength of rolled sheet copper is stated at 14.35 tons\nper square inch.\nResistance to Compressive Strain. Mr. Rennie's experi-\nments on cubes of one-fourth of an inch on the edge, give for\nthe crushing weight of a cube of cast copper 7,318 lbs., and\nof wrought copper 6,440 lbs.\nDigitized by Google\nSTRENGTH OF COPPER.\n167\n377. Effects of Temperature on Tensile Strength.-\nThe experiments already cited of the Franklin Institute,\nshow that the difference in strength at the lower tempera-\ntures, as between 60° and 90°, is scarcely greater than what\narises from irregularities in the structure of the metal at\nordinary temperatures. At 550° Fahr. copper loses one-\nfourth of its tenacity at ordinary temperatures, at 817° pre-\ncisely one-half, and at 1000° two-thirds.\nRepresenting the results of experiments by a curve of\nwhich the ordinates represent the temperatures above 32°, and\nthe abscissas the diminutions of tenacity arising from increase\nof temperature, the relations between the two will be thus\nexpressed the squares of the diminutions are as the cubes\nof the temperatures.\nIX.\nSTRENGTH OF OTHER METALS.\n378. MR. RENNIE states the tenacity of cast tin at 2.11 tons\nper square inch; and the resistance to compression of a\nsmall cube of 1 of an inch on an edge at 966 lbs.\nIn the same experiments, the tenacity of cast lead is stated\nat 0.81 tons per square inch; and the resistance of a small\ncube of same size as in preceding paragraph at 483 lbs.\nIn the same experiments, the tenacity of hard gun-metal is\nstated at 16.23 tons; that of fine yellow brass at 8.01 tons.\nThe resistance to compression of a cube of brass the same as\nbefore mentioned, is stated at 10,304 lbs.\nX.\nLINEAR CONTRACTION AND EXPANSION OF METALS AND OTHER\nMATERIALS FROM TEMPERATURE.\n379. Coefficients of Linear Expansion-The change of\nlength which takes place in a bar of any material estimated\nin fractional parts of its length at 0° Centigrade, for a\nDigitized by Google\n168\nCIVIL ENGINEERING.\nchange in temperature of 1° Centigrade, is termed the coeffi-\ncient of linear expansion, for the material in question.\nThe increase in length for other changes of temperature\nthan 1° is given by the following formula:-\nl = KNL,\nin which L is the length at 0° C.; N, the number of degrees\nabove 0°; K, the coefficient of linear expansion; and l the\nincrease of length due to N degrees above 0° C.\nTable of Coefficients of Linear Expansion for 1° C.\nCoefficients of\nlinear ex-\nDESCRIPTION OF MATERIAL\nAuthority.\npansion for\n1° C.\nMETALS.\nAntimony\nSmeaton\n000010833\nBismuth\n\"\n000013916\nBrass (supposed to be Hamburg plate brass)\nRamsden\n000018554\n\"\n(English plate, in form of a rod)\n\"\n000018928\n\" (English plate, in form of trough)\n\"\n000018949\n\"\n(cast) 1\nSmeaton\n000018750\n\" (wire)\n000019333\nCopper\nLaplace &\nLavoisier.\n}\n000017122\n\"\n\"\n000017224\nGold (de départ)\n\"\n000014660\n\" (standard of Paris, not annealed)\n\"\n000015515\n\"\n(\n\"\n\"\nannealed)\n\"\n000015186\nIron (cast)\nRamsden\n000011094\n\" (from a bar cast 2 inches square)\nAdie\n000011467\n\" (from a bar cast t an inch square)\n\"\n000011023\n\" (soft forged)\nan\nLaplace &\n}\n000012204\nLavoisier\n\" (round wire)\n\"\n000012350\n\" (wire)\nTroughton\n000014401\nLead\nan\nLaplace &\n~\n000028484\nLavoisier\n\"\nSmeaton\n000028066\nPalladium\nWollaston\n000010000\nPlatina\nDulong & Petit\n000008842\n\"\nTroughton\n000009918\nSilver (of cupel)\n{ Lavoisier\nLaplace &\n}\n000019097\n\"\n(Paris standard)\n\"\n000019086\n\"\nTroughton\n000020826\nSolder (white ; lead 2, tin 1)\nSmeaton\n000025053\n\"\n(spelter; copper 2, zinc 1)\n\"\n000020583\nSpeculum metal\n\"\n000019333\nDigitized by Google\nEXPANSION DUE TO TEMPERATURE.\n169\nCoefficients of\nlinear ex-\nDESCRIPTION OF MATERIALS.\nAuthority.\npansion for\n1° O.\nan\nLaplace &\nSteel (untempered)\nLavoisier\n}\n000010788\n\" (tempered yellow, annealed at 65° C.)\n\"\n000012395\n\" (blistered)\nSmeaton\n000011500\n\" (rod)\nRamsden\n000011447\nTin (from Malacca)\nLaplace &\nLavoisier\n}\n000019376\n\" (from Falmouth)\n\"\n000021729\nZino\nSmeaton\n000029416\nTIMBER.\n00000461\nBaywood (in the direction of the grain, dry).\nJoule\nto\n00000566\n00000428\nDeal (in the direction of the grain, dry)\nto\n00000488\nSTONE, BRICK, GLASS, CEMENT.\nArborath pavement\nAdie\n000008985\nBrick (best stock)\n\"\n000005502\n\" (fire)\n\"\n000004928\nCaithness pavement\n\"\n000008947\nCement (Roman)\n\"\n000014349\nGlass (English flint)\nLaplace &\n~\n000008117\nLavoisier\n\" (French with lead)\n\"\n000008720\nGranite (Aberdeen gray)\nAdie\n000007894\n\"\n(Peterhead red, dry)\n\"\n000008968\n\"\n(\n\"\n\"\nmoist)\n\"\n000009588\nGreenstone (from Katho)\n\"\n000008089\nMarble (Carrara moist)\n\"\n000011928\n\"\n(\ndry)\n\"\n000006539\n\"\n(black Galway)\n\"\n000004452\n\"\n(black, softer specimen, containing\n\"\nmore fossils)\n\"\n000004793\n\"\n(Sicilian, white moist)\n\"\n000014147\n\"\n(\n\"\n\"\ndry)\n\"\n000011041\nSandstone (from Craigleith quarry)\n\"\n000011748\nSlate (from Penrhyn quarry, Wales)\n\"\n000010876\nIt has been found from experiment that the absorption of\nwater in any manner decreases the coefficient of linear ex-\npansion in wood; and that, in some cases, in stone it in-\ncreases this coefficient, whilst in others a permanent increase\nof length took place from an increase of temperature.\nAn increase in temperature of 15° C. in cast iron, and 8°\nDigitized by Google\n170\nCIVIL ENGINEERING.\nC. in wrought iron will produce a strain of one ton of 2240\nlbs. on the square inch, when the two ends of the bar\nabut against a fixed object.\nXI.\nADHESION OF IRON SPIKES TO TIMBER.\n380. THE following tables and results are taken from an\narticle by Professor Walter R. Johnson, published in the\nJournal of the Franklin Institute, Vol. 19, 1837, giving the\ndetails of experiments made by him on spikes of various forms\ndriven into different kinds of timber.\nThe first series of experiments was made with Burden's\nplain square spike, the flanched, grooved, and swell spike, and\nthe grooved and swelled spike. The timber was seasoned\nJersey yellow pine, and seasoned white oak.\nFrom these experiments it results, that the grooved and\nswelled form is about 5 per cent. less advantageous than the\nplain, in yellow pine, and about 181 per cent. superior to the\nplain in oak. The advantage of seasoned oak over the sea-\nsoned pine, for retaining plain spikes, is as 1 to 1.9, and for\ngrooved spikes as 1 to 2.37.\nThe second series of experiments, in which the timber was\nsoaked in water after the spikes were driven, gave the follow-\ning results :-\nFor swelled and grooved spikes, the order of retentiveness\nwas: 1 locust; 2 white oak; 3 hemlock; 4 unseasoned chest-\nnut; 5 yellow pine.\nFor grooved spike without swell, the like order is: 1 un-\nseasoned chestnut; 2 yellow pine; 3 hemlock.\nThe swelled and grooved spike was, in all cases, found to\nbe inferior to the same spike with the swell filed off.\nThe third series of experiments gave the following results:\nThoroughly seasoned oak is twice, and thoroughly seasoned\nlocust 2ª times as retentive as unseasoned chestnut.\nThe forces required to extract spikes are more nearly pro-\nportional to the breadths than to either the thickness or the\nweights of the spikes. And, in some cases, a diminution of\nthickness with the same breadth of spike afforded a gain in\nretentiveness.\nDigitized by\nGoogle\nADHESION OF IRON SPIKES TO TIMBER.\n171\n\" In the softer and more spongy kinds of wood the fibres,\ninstead of being forced back longitudinally and condensed\nupon themselves, are, by driving a thick, and especially a\nrather obtusely-pointed spike, folded in masses backward and\ndownward so as to leave, in certain parts, the faces of the\ngrain of the timber in contact with the surface of the\nmetal.\"\n\" Hence it appears to be necessary, in order to obtain the\ngreatest effect, that the fibres of the wood should press the\nfaces as nearly as possible in their longitudinal direction, and\nwith equal intensities throughout the whole length of the\nspike.\"\nThe following is the order of superiority of the spikes from\nthat of the ratio of their weights and extracting forces respec-\ntively:-\n1. Narrow flat\n7.049 ratio of weight to extracting force.\n2. Wide flat\n5.712\n\"\n\"\n\"\n3. Grooved but not swelled.\n5.662\n\"\n\"\n\"\n4. Grooved and not notched.\n5.300\n\"\n\"\n\"\n5. Grooved and swelled\n4.624\n\"\n\"\n\"\n6. Burden's patent\n4.509\n\"\n\"\n\"\n7. Square hammered\n4.129\n\"\n\"\n\"\n8. Plain cylindrical\n3.200\n\"\n\"\n\"\n\" All the experiments prove, that when a spike is once\nstarted the force required for its final extraction is much less\nthan that which produced the first movement.\"\n\" When a bar of iron is spiked upon wood, if the spike be\ndriven until the bar compresses the wood to a great degree,\nthe recoil of the latter may become SO great as to start back\nthe spike for a short distance after the last blow has been\ngiven.\"\n342 From the fourth series of experiments it appears, that\nthe spike tapering gradually towards the cutting edge gives\nbetter results than those with more obtuse ends.\nThat beyond a certain limit the ratio of the weight of the\nspike to the extracting force begins to diminish; \" showing\nthat it would be more economical to increase the number\nrather than the length of the spikes for producing a given\neffect.\"\n\" That the absolute retaining power of unseasoned chestnut\non square or flat spikes of from two to four inches in length\nis a little more than 800 lbs. for every square inch of their\ntwo faces which condense longitudinally the fibres of the\ntimber.\"\nDigitized by\nGoogle\nCHAPTER III.\nMASONRY.\nI. CLASSIFICATION OF. II. CUT STONE MASONRY. III. RUB-\nBLE-STONE MASONRY. IV. BRICK MASONRY. V. FOUNDA-\nTIONS OF STRUCTURES ON LAND. VI. FOUNDATIONS OF\nSTRUCTURES IN WATER. VII. CONSTRUCTION OF MASONRY.\nSUMMARY.\nI.\nCLASSIFICATION OF MASONRY.\nMasonry defined and classified (Art. 881).\nII.\nOUT STONE MASONRY.\nDefinitions (Art. 383). Requisites of Strength (Arta 384-390). Bonds\n(Arts. 891-392). Cutting (Art. 393).\nIII.\nRUBBLE-STONE MASONRY.\nQuality (Art. 394). Construction (Arts. 895-397).\nIV.\nBRICK MASONRY.\nConstruction (Arts. 398-402). Concrete Walls (Arts. 408-416).\nDigitized by Google\nMASONEY.\n173\nV.\nFOUNDATIONS OF STRUCTURES ON LAND.\nFoundation defined (Art. 417). Importance (Art. 418). Classification of\nSoils (Art. 420). Foundations on Rock (Art. 421). In Stony Ground\n(Arts. 422-423). On Sand (Art. 424). Precautions against water (Art.\n425). In Compressible Soils (Arts. 426-429). In Marshy Soils (Art.\n430). On Piles (Art. 431). Pile Engines (Art. 432). Pile driving (Arts.\n432-434). Load placed on piles (Arts. 435-436). Piles prepared for\nfoundation (Arts. 437-439). On Sand (Art. 441). Precautions against\nLateral Yielding (Art. 443).\nVI.\nFOUNDATIONS OF STRUCTURES IN WATER.\nDifficulties (Art. 444). Use of Dams (Arts. 445-449). Use of Caisson (Art.\n450). Artificial Island (Art. 452). Protection against running water\n(Arts. 454-455). Pneumatic processes (Art. 456). Pneumatic piles\n(Arts. 457-458). Pneumatic Caissons (Art. 459).\nVII.\nCONSTRUCTION OF MASONEY.\nFoundation Courses (Arts. 461-463). Inverted arches (Art. 464). Compo-\nnent parts of structures of Masonry (Art. 467). Walls of Enclosures\n(Art. 468). Vertical Supports (Art. 469). Areas (Art. 470). Retaining\nWalls (Arts. 471-475). Form of Section of Retaining Walls (Arts. 476-\n478). Measures for increasing the Strength of Retaining Walls (Arts.\n479-488). Counterforts (Arts. 480-483). Relieving Arches (Art. 484).\nLintel (Art. 490). Plate-bande (Art. 491). Arches (Arts. 492-494).\nClassification of Arches (Art. 495). Cylindrical Arches (Arts. 496-502).\nOblique Arch (Arts. 502-508). Groined and Cloistered Arch (Arts. 504-\n505). Conical Arch (Art. 506). Conoidal Arch (Arts. 507-508). An-\nnular Arch (Art. 509). Dome (Art. 510). Arrangement of voussoirs\n(Arts. 511-513). Construction of Arches (Arts. 514-523). Rupture of\nArches (Arts. 524-527). Precautions to be observed in constructing\nArches (Arts. 528-533). Precautions against settling (Art. 584). Point-\ning (Arts. 535-537). Repairs of Masonry (Arts. 538-540). Effects of\nTemperature on Masonry (Art. 541).\nDigitized by\nGoogle\n174\nCIVIL ENGINEERING.\nI.\nCLASSIFICATION.\n381. MASONRY is the art of raising structures, in stone, brick,\nand mortar.\nMasonry is classified either from the nature of the ma-\nterial, as stone masonry, brick masonry, and mixed, or that\nwhich is composed of stone and brick; or from the manner in\nwhich the material is prepared, as cut stone or ashlar masonry,\nrubble-stone or rough masonry, and hammered stone masonry,\nor, finally, from the form of the material, as1regular mason-\nry, and irregular masonry.\nII.\nOUT STONE.\n382. MASONRY of cut stone, when carefully made, is stronger\nand more solid than that of any other class; but, owing to the\nlabor required in dressing or preparing the stone, it is also the\nmost expensive. It is therefore mostly restricted to those\nworks where a certain architectural effect is to be produced\nby the regularity of the masses, or where great strength is in-\ndispensable.\n383. Definitions. Before explaining the means to be used\nto obtain the greatest strength in cut stone, it will be neces-\nsary to give a few definitions to render the subject clearer.\nIn a wall of masonry the term face is usually applied to the\nfront of the wall, and the term back to the inside; the stone\nwhich forms the front, is termed the facing; that of the back,\nthe backing; and the interior, the filling. If the front, or\nback of the wall, has a uniform slope from the top to the bot-\ntom, this slope is termed the batter, or bâtir.\nThe term course is applied to each horizontal layer of stone\nin the wall: if the stones of each layer are of equal thickness\nthroughout it is termed regular coursing; if the thicknesses\nare unequal the term random, or irregular coursing, is ap-\nplied. The divisions between the stones, in the courses, are\nDigitized by Google\nCUT-STONE MASONRY.\n175\ntermed the joints ; the upper surface of the stones of each\ncourse is also sometimes termed the bed, or build.\nThe arrangement of the different stones of each course, or\nof contiguous courses, is termed the bond.\n384. Requisites of Strength. The strength of a mass of\ncut stone masonry will depend on the size of the blocks in\neach course, on the accuracy of the dressing, and on the bond\nused.\nThe size of the blocks varies with the kind of stone and the\nnature of the quarry. From some quarries the stone may be\nobtained of any required dimensions; others, owing to some\npeculiarity in the formation of the stone, only furnish blocks\nof small size. Again, the strength of some stones is so great\nas to admit of their being used in blocks of any size, without\ndanger to the stability of the structure, arising from their\nbreaking; others can only be used with safety when the length,\nbreadth, and thickness of the block bear certain relations to\neach other. No fixed rule can be laid down on this point;\nthat usually followed by builders is to make, with ordinary\nstone, the breadth at least equal to the thickness, and seldom\ngreater than twice this dimension, and to limit the length to\nwithin three times the thickness. When the breadth or the\nlength is considerable, in comparison with the thickness, there\nis danger that the block may break, if any unequal settling,\nor unequal pressure should take place. As to the absolute\ndimensions, the thickness is generally not less than one foot,\nnor greater than two; stones of this thickness, with the rela-\ntive dimensions just laid down, will weigh from 1000 to 8000\npounds, allowing, on an average, 160 pounds to the cubic foot.\nWith these dimensions, therefore, the weight of each block\nwill require a very considerable power, both of machinery and\nmen, to set it on its bed.\n385. For the coping and top courses of a wall the same\nobjections do not apply as to excess in length but this excess\nmay, on the contrary, prove favorable because the number\nof top joints being thus diminished, the mass beneath the co-\nping will be better protected, being exposed only at the joints,\nwhich cannot be made water-tight, owing to the mortar being\ncrushed by the expansion of the blocks in warm weather, and,\nwhen they contract, being washed out by the rain.\n386. The closeness with which the blocks fit is solely de-\npendent on the accuracy with which the surfaces in contact\nare wrought or dressed; if this part of the work is done in a\nslovenly manner, the mass will not only present open joints\nfrom any inequality in the settling; but, from the courses not\nDigitized by\nGoogle\n176\nCIVIL ENGINEERING.\nfitting accurately on their beds, the blocks will be liable to\ncrack from the unequal pressure on the different points of\nthe block.\n387. The surfaces of one set of joints should, as a prime\ncondition, be perpendicular to the direction of the pressure:\nby this arrangement there will be no tendency in any of the\nblocks to slip. In a vertical wall, for example, the pressure\nbeing downward, the surfaces of one set of joints, which are\nthe beds, must be horizontal. The surfaces of the other set\nmust be perpendicular to these, and, at the same time, perpen-\ndicular to the face, or to the back of the wall, according to\nthe position of the stones in the mass; two essential points\nwill thus be attained,-the angles of the blocks, at the top and\nbottom of the course, and at the face or back, will be right\nangles, and the block will therefore be as strong as the nature\nof the stone will admit. The principles here applied to a\nvertical wall, are applicable in all cases whatever may be the\ndirection of the pressure and the form of the exterior sur-\nfaces, whether plane or curved.\n388. A modification of this principle, however, may in some\ncases be requisite, arising from the strength of the stone. It\nis laid down as a rule, drawn from the experience of builders,\nthat no stone-work with angles less than 60° will offer suffi-\ncient strength and durability to resist accidents, and the effects\nof the weather. If, therefore, the batter of a wall should be\ngreater than 60°, which is about 7 perpendicular to 4 base,\nthe horizontal joints (Fig. 17) must not be carried out in the\nFig. 17-Represents the arrangement of stone with\nabutting, or elbow joints for very inclined sur-\nfaces.\nA, face of the block.\nc, elbow joint.\nB\nB, buttress block, termed a newell stone.\nsame plane to the face or back, but be broken off at right\nangles to it, so as to form a small abutting joint of about 4\ninches in thickness. As the batter of walls is seldom so great\nas this, except in some cases of sustaining walls for the side\nslopes of earthen embankments, this modification in the joints\nwill not often occur; for, in a greater batter, it will generally\nbe more economical, and the construction will be stronger, to\nplace the stones of the exterior in offsets, the exterior stone of\none course being placed within the exterior one of the course\nbelow it, SO as to give the required general direction of the\nDigitized by Google\nCUT-STONE MASONRY.\n177\nbatter. The arrangement with offsets has the further advan-\ntage in its favor of not allowing the rain water to lodge in the\njoint, if the offset be slightly bevelled off.\n389. Workmen, unless narrowly watched, seldom take the\npains necessary to dress the beds and joints accurately on\nthe contrary, to obtain what are termed close joints, they dress\nthe joints with accuracy a few inches only from the outward\nsurface, and then chip away the stone towards the back, or\ntail (Fig. 18), so that, when the block is set, it will be in con-\nB\nFig. 18-Represents a section of a wall in which the\nface is of cut stone, with the tails of the blocks\nthinned off, and the backing of rubble.\nA, section of face block.\nB, rubble backing.\ntact with the adjacent stones only throughout this very small\nextent of bearing surface. This practice is objectionable\nunder every point of view; for, in the first place, it gives an\nextent of bearing surface, which, being generally inadequate-\nto resist the pressure thrown on it, causes the block to splinter\noff at the joint; and in the second place, to give the block its.\nproper set, it has to be propped beneath by small bits of stone,\nor wooden wedges, an operation termed pinning-up, or under-\npinning, and these props, causing the pressure on the block\nto be thrown on a few points of the lower surface, instead of\nbeing equally diffused over it, expose the stone to crack.\n390. When the facing is of cut stone, and the backing of\nrubble, the method of thinning off the block may be allowed\nfor the purpose of forming a better bond between the rubble\nand ashlar; but, even in this case, the block should be dress-\ned true on each joint, to at least one foot back from the face.\nIf there exists any cause which would give a tendency to an\noutward thrust from the back, then instead of thinning off\nall the blocks towards the tail it will be preferable to leave\nthe tails of some thicker than the parts which are dressed.\n391. Various methods are used by builders for the bond of\ncut stone. The system termed headers and stretchers, in,\nwhich the vertical joints of the blocks of each course alter-\n12\nDigitized by Google\n178\nCIVIL ENGINEERING.\nnate with the vertical joints of the courses above and below\nit, or, as it is termed, break joints with them, is the most sim-\nple, and offers, in most cases, all requisite solidity. In this\nc\nFig. 19 is a vertical section of the sea walls used for pro-\ntecting the bluffs of the islands in Boston Harbor ex-\nposed to the action of the waves.\nA, Stone facing of heavy blocks well fitted and clamped.\nB, Concrete bed and backing.\nD\nC, Top wall well bonded.\nD, Natural soil back of concrete.\nsystem (Fig. 20), the blocks of each course are laid alter-\nnately with their greatest and least dimensions to the face of\nthe wall; those which present the longest dimension along\nthe face are termed stretchers; the others, headers. If the\nA\nB\na\na\nb\nb\nFig 20-Represents an elevation A. end vie\nB, and plan C, of a wall arranged as headers\nand stretchers.\na, stretchers.\nb, headers.\nC\na\nb\nheader reaches from the face to the back of the wall, it is\ntermed a through; if it only reaches part of the distance it\nis termed a binder. The vertical joints of one course are\neither just over the middle of the blocks of the next course\nbelow, or else, at least four inches on one side or the other of\nthe vertical joints of that course; and the headers of one\ncourse rest as nearly as practicable on the middle of the\nDigitized by Google\nOUT-STONE MASONEY.\n179\nstretchers of the course beneath. If the backing is of rubble,\nand the facing of cut stone, a system of throughs or binders,\nsimilar to what has just been explained, must be used.\nBy the arrangement here described, the facing and backing\nof each course are well connected and, if any unequal set-\ntling takes place, the vertical joints cannot open, as would be\nthe case were they in a continued line from the top to the\nbottom of the mass; as each block of one course confines the\nends of the two blocks on which it rests in the course\nbeneath.\n392. In masses of cut stone exposed to violent shocks, as\nthose of which light-houses, and sea-walls in very exposed\npositions are formed, the blocks of each course require to be\nnot only very firmly united with each other, but also with the\ncourses above and below them. To effect this, various means\nhave been used. The beds of one course are sometimes ar-\nranged with projections (Fig. 21) which fit. into correspond-\ning indentations of the next course. Iron cramps in the form\nof the letter S, or in any other shape that will answer the\nA\nC\nFig. 21-Represents\nan elevation, A,\nplan, B, and per-\nspective views, C\nand D, of two of\nthe blocks of a wall\nD\nin which the blocks\nare fitted with in-\ndents, and connect-\ned with bolts and\nB\ncramps of metal.\npurpose of giving them a firm hold on the blocks, are let into\nthe top of two blocks of the same course at a vertical joint,\nand are firmly set with melted lead, or with bolts, SO as to\nconfine the two blocks together. Holes are, in some cases,\ndrilled through several courses, and the blocks of these\ncourses are connected by strong iron bolts fitted to the holes.\nThe most noted examples of these methods of strengthen-\ning the bond of cut stone, are to be found in the works of the\nRomans which have been preserved to our time, and in two\ncelebrated modern structures, the Eddy-stone and Bell-rock\nlight-houses in Great Britain (Fig. 22).\nDigitized by Google\n180\nOIVIL ENGINEERING.\nFig. 22-Represents the manner of arranging stones of\nthe same course by dove-tail joints and joggling, taken\nfrom a horisontal section of the masonry of the Bell-\nrock light-house.\nFigs. 23, 24, 25, 26.-Plans and sections showing the\nmasonry bond and metal fastenings of some of the courses in\nthe Minot's ledge light-house.\n6249\nLANDING\n(0.)\nFig. 28.-Rock surface prepared for receiving foundation.\n393. The manner of dressing stone belongs to the stone-\ncutter's art, but the engineer should not be inattentive either\nto the accuracy with which the dressing is performed, or the\nmeans employed to effect it. The tools chiefly used by the\nworkman are the chisel, axe, and hammer for knotting. The\nusual manner of dressing a surface is to cut draughts around\nand across the stone with the chisel, and then to use the chisel,\nDigitized by Google\nCUT-STONE MASONRY.\n181\nthe axe with a serrated edge, or the knotting hammer, to work\ndown the intermediate portions into the same surface with the\ndraughts. In performing this last operation, the chisel and\nWELL\nROCK\nFig. 24.-Vertical section showing foundation courses and their metal fastenings.\nFig. 25.-Plan showing bond of stone and fastenings above the solid foundation courses,\nFig. 26-Vertical section and interior elevation above foundation courses.\naxe should alone be used for soft stones, as the grooves on the\nsurface of the hammer are liable to become choked by a soft\nDigitized by Google\n182\nCIVIL ENGINEERING.\nmaterial, and the stone may in consequence be materially in-\njured by the repeated blows of the workman. In hard stones\nthis need not be apprehended.\nIn large blocks which require to be raised by machinery, a\nhole, of the shape of an inverted truncated wedge, is cut to\nFig. X7-Represents A perspective\nview, A, of a block of stone with\ndraughts around the edges of its\nfaces, and the intermediate space\naxed, or knotted, and its tackling\nfor hoisting also the common\niron lewis, B, with its tackling.\na, draughts around edge of block.\nb, knotted part between draughts.\nc, iron bolts with eyes let into oblique\nholes cut in the block.\nP\nd and e, chain and rope tackling.\nn, n, side pieces of the lewis.\nB\no, centre piece of lewis with eye fast-\n0\nened to n n by a bolt.\nP, iron ring for attaching tackling.\nn\nn\nreceive a small iron instrument termed a lewis (Fig. 27), to\nwhich the rope is attached for suspending the block ; or else,\ntwo holes are cut obliquely into the block to receive bolts\nwith eyes for the same purpose.\nWhen a block of cut stone is to be laid, the first point to be\nattended to is to examine the dressing, which is done by\nplacing the block on its bed, and seeing that the joints fit\nclose, and the face is in its proper plane. If it be found that\nthe fit is not accurate, the inaccuracies are marked and the\nrequisite changes made. The bed of the course on which\nthe block is to be laid is then thoroughly cleansed from dust,\n&c., and well moistened, a bed of thin mortar is laid evenly\nover it, and the block, the lower surface of which is first\ncleansed and moistened, is laid on the mortar-bed, and well\nsettled by striking it with a wooden mallet. When the block\nis laid against another of the same course, the joint between\nthem is prepared with mortar in the same manner as the\nbed.\nDigitized by Google\nBRICK MASONRY.\n183\nIII.\nEUBBLE-STONE MASONRY.\n394. With good mortar, rubble work, when carefully exe-\ncuted, possesses all the strength and durability required in\nstructures of an ordinary character; and it is much less ex-\npensive than cut stone.\n395. The stone used for this work should be prepared\nsimply by knocking off all the sharp, weak angles of the\nblock; it is then cleansed from dust, &c., and moistened,\nbefore placing it on its bed. This bed is prepared by spread-\ning over the top of the lower course an ample quantity of\ngood ordinary-tempered mortar, into which the stone is firmly\nembedded. The interstices between the larger masses of stone\nare filled in by thrusting small fragments, or chippings of\nstone, into the mortar. Finally, the whole course may be\ncarefully grouted before another is commenced, in order to\nfill up any voids left between the full mortar and stone.\n396. To connect the parts well together, and to strengthen\nthe weak points, throughs or binders should be used in all the\ncourses; and the angles should be constructed of cut or ham-\nmered stone. In heavy walls of rubble masonry, the precau-\ntion, moreover, should be observed, to lay. the stones on their\nquarry-bed; that is, to give them the same position, in the\nmass of masonry, that they had in the quarry; as stone is\nfound to offer more resistance to pressure in a direction per-\npendicular to the quarry-bed than in any other. The direc-\ntions of the lamina in stratified stones show the position of the\nquarry-bed.\n397. Hammered stone, or dressed rubble, is stone roughly\nfashioned into regular masses with the hammer. The same\nprecautions must be taken in laying this kind of masonry as\nin the two preceding.\nIV.\nBRICK MASONRY.\n398. With good brick and mortar, this masonry offers great\nstrength and durability, arising from the strong adhesion be-\ntween the mortar and brick.\nDigitized by Google\n184\nCIVIL ENGINEERING.\n399. The bond used in brick-work is very various, depend-\ning on the character of the structure. The most usual kinds\nare known as the English and Flemish. The first consists in\narranging the courses alternately, entirely as .headers or\nstretchers, the bricks through the course breaking joints. In\nthe second the bricks are laid as headers and stretchers in\neach course. The first is stated to give a stonger bond than\nthe last; the bricks of which, owing to the difficulty of pre-\nventing continuous joints, either in the same or different\ncourses, are liable to separate, causing the face or the back to\nbulge outward. The Flemish bond presents the finer archi-\ntectural appearance, and is therefore preferred for the fronts\nof edifices.\n400. Timber and iron have both been used to strengthen\nthe bond of brick masonry. Among the most remarkable ex-\namples of their uses are the well, faced in brick, forming an\nentrance to the Thames Tunnel, the celebrated work of Mr.\nBrunel, and his experimental arch of brick, a description of\nwhich is given in the Civil Engineer and Architect's Journal,\nNo. 6, vol. I. In both these structures Mr. Brunel used pan-\ntile laths and hoop iron, in the interior of the horizontal\ncourses, to connect two contiguous courses throughout their\nlength. The efficacy of this method has been further fully\ntested by Mr. Brunel, in experiments made on the resistance\nto a transversal strain of a brick beam bonded with hoop iron,\naccounts of which, and of experiments of a like kind, are\ngiven by Colonel Pasley in his work on Limes, Calcareous\nCements, &c.\n401. The mortar-bed of brick may be either of ordinary or\nthin-tempered mortar; the last, however, is the best, as it\nmakes closer joints, and, containing more water, does not dry\nSO rapidly as the other. As brick has great avidity for water,\nit would always be well not only to moisten it before laying\nit, but to allow it to soak in water several hours before it is\nused. By taking this precaution, the mortar between the\njoints will set more firmly than when it imparts its water to\nthe dry brick, which it frequently does so rapidly as to render\nthe mortar pulverulent when it has dried.\n402. On this point the late General Totten, Chief of Engin-\neers, in his instructions for building brick masonry, observes:\n\" The want of cohesion\" between the brick and mortar, in the\ncase of some gun practice against brick embrasures, \" was\ndue to the interposition of dust, sometimes quite free, but\nmore generally composing a layer slightly cohering to the\nbody of the bricks. The process of laying must be to cause\nDigitized by Google\nBRICK MASONEY.\n185\nevery brick to be thoroughly soaked in water, and to be laid\nthe moinent it ceases to drip.\"\n403. Concrete Walls. The use of hydraulic concrete for\nthe construction of both solid and hollow walls for houses has\nvery much increased within a few years and it is claimed\nthat they are drier, stronger, and cheaper than walls of brick\nof equal thickness.\nIn some of the cheaper structures of this class put up in\nParis, the concrete was composed of one part in volume of\nPortland cement, and from five to eight parts of clean screen-\ned gravel from the size of pearl barley to that of peas; and in\nsome cases instead of gravel what is known as brick ballast,\nor the small fragments of ordinary brick from which all the\nfine dust is screened out, is used, taking eight parts of this to\none of Portland cement.\n404. For building walls of concrete where a scaffold is not\nnecessary it is only requisite to have a boxing formed of\nscantling and boards of the width of the wall within, between\nthe two sides of which the concrete is thrown in and rammed.\n405. For solid walls requiring a scaffolding, what is termed\nTall's bracket scaffolding is used. The concrete is laid with-\nA\nA\nB\nB\nFig. 28 represents a vertical section of the boxing for laying\nconcrete walls.\nb\nA, Boarding confined by clamp screws.\nB, Platform supported by brackets and clamp screws.\nc, Cylinder for forming flues in the wall.\nC\nin the boxing, which consist of boards, A, held together by\nclamp screws, b, which pass through hollow iron cones placed\nbetween the sides of the boxing, which, within, is of the same\nheight and width as the layer of concrete to be laid at a time.\nWhen the layer is finished the boxing is taken apart, and the\nholes left bv the cones when removed are used for secur-\ning the brackets of the scaffolding, which consists of triangu-\nlar frames, B, each formed of a vertical pin, a horizontal\nbeam to support the flooring, and an inclined strut to support\nthe outer end of the horizontal beam. The flooring, of suffi-\ncient width for the workmen, projects beyond the wall on each\nside, and the two parts without and within are held together\nDigitized by\nGoogle\n186\nCIVIL ENGINEERING.\nby clamp screws which pass through the holes. When cylin-\ndrical flues are to be left within the body of the wall, a cylin-\nder C, with a handle to it, of the requisite diameter, and the\nlength of the thickness of the layer, is placed in position, and\nthe concrete rammed well around it. When a new layer is\nto be laid the cylinder is drawn up from the one finished.\n406. For constructing either solid or hollow walls, an ap-\nparatus devised by Mr. Clarke of New Haven, Conn., termed\nClarke's adjustable frame for concrete building, is used. This\nB\na\nC\nD\nC\nb\nA\nA\nFig. 29. Vertical section of boxing for hollow walls of\nconcrete.\nA, Boxing confining concrete.\nB, Horizontal arm supporting the pieces σ.\nD, Vertical support of B.\na, Clamp screws confining C, σ.\n0, Board used for forming the void in the wall.\nconsists of a boxing of boards, A, for laying the concrete\nwhich is held together by frames, each composed of a hori-\nzontal piece, B, to which are affixed two vertical clamping\npieces, C, the interior piece being movable and capable of\nbeing adjusted by screws, the two pieces being held together\nby a clamp screw, a; the frames and boxing being attached\nto vertical supports, D, within the building, in which holes\nare arranged at suitable distances to admit of the frame be-\ning placed at the proper height. For hollow walls a wedge-\nshaped board, b, two inches and a half thick at its broad end,\nand two inches on the other, is used. This board has rect-\nangular notches of the width of a brick, and placed at twenty\ninches apart, cut into the narrow edge. This forms the core\nfor the hollow portion of the wall. The work is started or\ncontinued by placing the bricks in place lengthwise across the\nhollow SO as to tie the exterior and interior portions of the\nwall together. The core is then placed with its notches fitting\non the bricks, and secured in a vertical position, the concrete\nis filled in on each side between the sides of the boxing.\nWhen the layer is finished the core is drawn up.\nDigitized by Google\nBRICK MASONEY.\n187\nFor further applications of Coignet Béton, see Prof. Bar-\nnard's Report on the Paris Exposition of 1867, and Gen.\nGilmore's Paper, No. 19, on Béton Aggloméré.\n407. Uses of beton agglomere in Europe and else-\nwhere. The most important and costly work that has yet\nbeen undertaken in this material is a section, thirty-seven\nmiles in length, of the Vanne aqueduct, for supplying water\nto the city of Paris.\nThis aqueduct, which traverses the forest of Fontainebleau\nthrough its entire length, comprises two and a half to three\nmiles of arches, some of them as much as fifty feet in height,\nand eleven miles of tunnels, nearly all constructed of the mate-\nrial excavated, the impalpable sand of marine formation\nknown under the generic name of Fontainebleau sand. It in-\ncludes, also, eight or ten bridges of large span (seventy-five to\none hundred and twenty-five feet) for the bridging of rivers,\ncanals, and highways.\nThe smaller arches are full centre, and are generally of a\nuniform span of 39100 feet, with a thickness at the crown of\n15 inches. Their construction was carried on without inter-\nruption through the winter of 1868-'69 and the following\nsummer, and the character of the work was not affected by\neither extreme of temperature. The spandrels are carried\nup in open work to the level of the crown, and upon the\narcade thus prepared the aqueduct pipe is moulded in the\nsame material, the whole becoming firmly knit together into\na perfect monolith. The pipe is circular, 61 feet in interior\ndiameter, with a thickness of 9 inches at the top, and 12\ninches at the sides, at the water surface. The construction of\nthe arches is carried on about two weeks in advance of work\non the pipe, and the centres are struck about a week later.\nWater was let into a portion of this pipe in the spring of\n1869, and M. Belgrand, inspector-general of bridges and\nhighways, and director of drainage and sewers of the city\nof Paris, certified that \"the impermeability appeared com-\nplete.\"\n408. Another interesting application of this material has\nbeen made in the construction, completed or very nearly so, of\nthe light-house at Port Said, Egypt. It will be one hundred\nand eighty feet high, without joints, and resting upon a mon-\nolithic block of béton, containing nearly four hundred cubic\nyards.\n409. An entire Gothic church, with its foundations, walls,\nand steeple in a single piece, has been built of this material\nat Vesinet, near Paris. The steeple is one hundred and\nDigitized by Google\n188\nCIVIL ENGINEERING.\nthirty feet high, and shows no cracks or other evidences of\nweakness.\nM. Pallu, the founder, certifies that \" during the two years\nconsumed by M. Coignet in the building of this church, the\nbéton aggloméré, in all its stages, was exposed to rain and\nfrost, and that it has perfectly resisted all variations of tem-\nperature.\"\nThe entire floor of the church is paved with the same ma-\nterial, in a variety of beautiful designs, and with an agreeable\ncontrast of colors.\n410. In constructing the municipal barracks of Notre\nDame, Paris, the arched ceilings of the cellars were made\nof this béton, each arch being a single mass. The spans\nvaried from twenty-two to twenty-five feet, the rise, in\nin all cases, being one-tenth the span, and the thickness at\nthe crown 8.66 inches. In the same building the arched ceil-\nings of the three stories of galleries, one above the other,\nfacing the interior, and all the subterranean drainage, com-\nprising nearly six hundred yards of sewers, are also mono-\nliths of béton.\n411. Over thirty-one miles of the Paris sewers had been\nlaid in this material prior to June, 1869, at a saving of 20 per\ncent., on the lowest estimated cost, in any other kind of\nmasonry.\nThe composition of the béton was as follows :-\nSand, 5 measures.\nHydraulic lime, 1 measure.\nParis cement (said to be as good as Portland cement), to\nmeasure.\n412. The works above referred to were visited by the\nwriter in the month of February, 1870, and these statements\nare based upon close observation and personal knowledge.\nMany other interesting applications of this material were\nexamined, of which it is not deemed necessary to make any\nspecial mention, except that in combined stability, strength,\nbeauty, and cheapness they far surpass the best results that\ncould have been achieved by the use of any other materials,\nwhether stone, brick, or wood.\nIn the numerous and varied applications which have been\nmade of it in France, it has received the most emphatic com-\nmendations from the government engineers and architects.\n413. Its superiority to Rosendale concrete for common\nwork, such as foundations, the backing and hearting of walls,\nmagazine walls, and generally for all masonry protected by\nearth, and therefore not necessarily required to be of first\nDigitized by\nGoogle\nBRICK MASONEY.\n189\nquality, lies in its possessing greater strength and hardness at\nthe same cost, and consequently in its being proportionately\ncheaper when reduced to the same strength by increasing\nthe proportion of sand.\n414. Sea-water is nearly as good as fresh water for mix-\ning Portland cements, but injures the Rosendale and all\nargillo-magnesian cements very considerably.\n415. It is of great importance that the incorporation of the\nlime with the cement should be very thorough, in order to\ninsure a perfectly homogeneous mixture, and this can be ob-\ntained with greater certainty by triturating the two together\ninto a thick, viscous paste before the sand is added. In con-\nducting extensive operations the use of two mills of different\nsizes would perhaps be advantageous, the smaller one being\nemployed exclusively in the preparation of the matrix.\nThe following proportions may be relied upon to give\nCoignet bétons of good average quality:-\n1\n2\n3\n4\nCoarse and fine sand, by measure\n6\n67\n7\n71\nPortland cement, by measure.\n1\n1\n1\n1\nCommon lime-powder, by measure\nro\n+\n4\nto\n416. For foundations and other plain massive work not ex-\nposed to view, or where a smooth surface is not specially de-\nsired, a liberal amount of gravel and pebbles, or broken stone,\nmay be added to all of the bétons of the above table.\nThe following proportions will answer for such purposes:-\n1\n2\n8\n4\nCoarse and fine sand, by measure\n6\n6¥\n7\n71\nGravel and pebbles, by measure\n12\n13\n18\n14\nPortland cement, by measure\n1\n1\n1\n1\nCommon lime-powder, by measure\n10\nt\nt\n10\nSee General Gilmore's Report.\nDigitized by Google\n190\nCIVIL ENGINEERING.\nV.\nFOUNDATIONS OF STRUCTURES ON LAND.\n417. The term foundation is used indifferently either for\nthe lower courses of a structure of masonry, or for the artifi-\ncial arrangement, of whatever character it may be, on which\nthese courses rest. For more perspicuity, the term bed of the\nfoundation will be used in this work when the latter is de-\nsignated.\n418. The strength and durability of structures of masonry\ndepend essentially upon the bed of the foundation. In ar-\nranging this, regard must be had not only to the permanent\nefforts which the bed may have to support, but to those of an\naccidental character. It should, in all cases, be placed so far\nbelow the surface of the soil on which it rests, that it will not\nbe liable to be uncovered, or exposed ; and its surface should\nnot only be normal to the resultant of the efforts which it sus-\ntains, but this resultant should intersect the base of the bed\nSO far within it, that the portion of the soil between this point\nof intersection and the outward edge of the base shall be\nbroad enough to prevent its yielding from the pressure thrown\non it.\n419. The first preparatory step to be taken, in determining\nthe kind of bed required, is to ascertain the nature of the sub-\nsoil on which the structure is to be raised. This may be done,\nin ordinary cases, by sinking a pit; but where the subsoil is\ncomposed of various strata, and the structure demands extra-\nordinary precaution, borings must be made with the tools\nusually employed for this purpose.\n420. Classification of Soils.-With respect to foundations,\nsoils are usually divided into three classes:\nThe 1st class consists of soils which are incompressible, or,\nat least, so slightly compressible, as not to affect the stability\nof the heaviest masses laid upon them, and which, at the same\ntime, do not yield in a lateral direction. Solid rock, some\ntufas, compact stony soils, hard clay which yields only to the\npick or to blasting, belong to this class.\nThe 2d class consists of soils which are incompressible, but\nrequire to be confined laterally, to prevent them from spread-\ning out. Pure gravel and sand belong to this class.\nThe 3d class consists of all the varieties of compressible\nsoils ; under which head may be arranged ordinary clay, the\nDigitized by\nGoogle\nFOUNDATIONS OF STRUCTURES.\n191\ncommon earths, and marshy soils. Some of this class are\nfound in a more or less compact state, and are compressible\nonly to a certain extent, as most of the varieties of clay and\ncommon earth; others are found in an almost fluid state, and\nyield, with facility, in every direction.\n421. Foundations on Rock.-To prepare the bed for a\nfoundation on rock, the thickness of the stratum of rock\nshould first be ascertained, if there are any doubts respecting\nit: and if there is any reason to suppose that the stratum has\nnot sufficient strength to bear the weight of the structure, it\nshould be tested by a trial weight, at least twice as great as\nthe one it will have to bear permanently. The rock is next\nproperly prepared to receive the foundation courses by level-\nling its surface, which is effected by breaking down all pro-\njecting points, and filling up cavities, either with rubble ma-\nsonry or with béton; and by carefully removing any portions\nof the upper stratum which present indications of having been\ninjured by the weather. The surface, prepared in this man-\nner, should, moreover, be perpendicular to the direction of the\npressure; if this is vertical, the surface should be horizontal,\nand so for any other direction of the pressure. Should there,\nhowever, be any difficulty in so arranging the surface as to\nhave it normal to the resultant of the pressure, it may receive\na position such that one component of the resultant shall be\nperpendicular to it, and the other parallel; the latter being\ncounteracted by the friction and adhesion between the base\nof the bed and the surface of the rock. If, owing to a great\ndeclivity of the surface, the whole cannot be brought to the\nsame level, the rock must be broken into steps, in order that\nthe bottom courses of the foundation throughout, may rest on\na surface perpendicular to the direction of the pressure. If\nfissures or cavities are met with, of so great an extent as to\nrender the filling them with masonry too expensive, an arch\nmust then be formed, resting on the two sides of the fissure,\nto support that part of the structure above it.\nThe slaty rocks require most care in preparing them to re-\nceive a foundation, as their top stratum will generally be\nfound injured to a greater or less depth by the action of frost.\n422. Foundations in Stony Ground.-In stony earths and\nhard clay, the bed is prepared by digging a trench wide\nenough to receive the foundation, and deep enough to reach\nthe compact soil which has not been injured by the action of\nfrost; a trench from 4 to 6 feet. will generally be deep enough\nfor this purpose.\n423. In compact gravel and sand, where there is no lia-\nDigitized by Google\n192\nCIVIL ENGINEERING.\nbility to lateral yielding, either from the action of rain or any\nother cause, the bed may be prepared as in the case of stony\nearths. If there is danger from lateral yielding, the part on\nwhich the foundation is to rest must be secured by confining\nit laterally by means of sheeting piles, or in any other way\nthat will offer sufficient security.\n424. Foundations on Sand.-In laying foundations on\nfirm sand, a further precaution is sometimes resorted to, of\nplacing a. platform on the bottom of the trench, for the pur-\npose of distributing the whole weight more uniformly over it.\nThis, however, seems to be unnecessary; for if the bottom\ncourses of the masonry are well settled in their bed, there is\nno good reason to apprehend any unequal settling from the\neffect of the superincumbent weight: whereas, if the wood of\nthe platform should, by any accident, give way, it would leave\na part of the foundation without any support.\nWhen the sand under the bed is liable to injury from\nsprings they must be cut off, and a platform, or, still better,\nan area of béton, should compose the bed, and this should be\nconfined. on all sides between walls of stone, or béton sunk\nbelow the bottom of the bed.\n425. Precautions against Water.-If, in opening a trench\nin sand, water is found at a slight depth, and in such quan-\ntity as to impede the labors of the workmen, and the trench\ncannot be kept dry by the use of pumps or scoops, a row of\nsheeting piles must be driven on each side of the space occu-\npied by it, somewhat below the bottom of the bed, the sand\non the outside of the sheeting piles be thrown out, and its\nplace filled with a puddling of clay, to form a water-tight en-\nclosure round the trench. The excavation for the bed is then\ncommenced ; but if it be found that the water still makes\nrapidly at the bottom, only a small portion of the trench must\nbe opened, and after the lower courses are laid in this por-\ntion, the excavation will be gradually effected, as fast as the\nworkmen can execute the work, without difficulty from the\nwater.\n426. Foundations in Compressible Soils. The beds of\nfoundations in compressible soils require peculiar care, parti-\ncularly when the soil is not homogeneous, presenting more\nresistance to pressure in one point than in another; for, in\nthat case, it will be very difficult to guard against unequal\nsettling.\n427. In ordinary clay, or earth, a trench is dug of the pro-\nper width, and deep enough to reach a stratum beyond the\naction of frost the bottom of the trench is then levelled off\nDigitized by\nGoogle\nFOUNDATIONS OF STRUCTURES.\n193\nto receive the foundation. This may be laid immediately on\nthe bottom, or else upon a grillage and platform. In the\nfirst case, the stones forming the lowest course should be\nfirmly settled in their beds, by ramming them with a very\nheavy beetle. In the second a timber grating, termed a gril-\nlage (Fig. 30), which is formed of a course of heavy beams\nlaid lengthwise in the trench, and connected firmly by cross\npieces into which they are notched, is firmly settled in the\nbed, and the earth is solidly packed between the longitudinal\nand cross pieces; a flooring of thick planks, termed a plat-\nform, is then laid on the grillage, to receive the lowest course\nA\nFig. 80 represents the arrangement of a grillage and platform\nfitted on piles.\nA, masonry.\na\naa, piles.\nb, string-pieces.\na cross pieces.\nd, capping-piece.\na platform of plank\nof the foundation. The object of the grillage and platform\nis to diffuse the weight more uniformly over the surface of\nthe trench, to prevent any part from yielding.\n428. Repeated failures in grillages and platforms, arising\neither from the compression of the woody fibre or from a\ntransversal strain occasioned by the subsoil offering an unequal\nresistance, have impaired confidence in their efficacy. En-\ngineers now prefer beds formed of an area of béton, as offer-\ning more security than any bed of timber, either in a uni-\nformly or unequally compressible soil.\n429. The preparation of an area of béton for the bed of a\nfoundation, will depend on the circumstances of the case. In\nordinary cases the béton is thrown into the trench, and care-\nfully rammed in layers of 6 or 9 inches, until the mortar col-\nlects in a semi-fluid state on the top of the layer. If the\nbase of the bed is to be broader than the top, its sides must\nbe confined by boards suitably arranged for this purpose.\nWhenever a layer is left. incomplete at one end, and another\nis laid upon it, an offset should be left at the unfinished ex-\n13\nDigitized by Google\n194\nCIVIL ENGINEERING.\ntremity, for the purpose of connecting the two layers more\nfirmly when the work on the unfinished part is resumed.\nConsiderable economy may be effected, in the quantity of\nbéton required for the bed, by using large blocks of stone\nwhich should be so distributed throughout the layer that the\nbeetle will meet with no difficulty in settling the béton be-\ntween and around the blocks.\nWhen springs rise through the soil over which the béton is\nto be spread, the water from them must either be conveyed off\nby artificial channels, which will prevent it rising through the\nmass of béton and washing out the lime; or else strong cloth,\nprepared so as to be impermeable to water, may be laid over\nthe surface of the soil to receive the bed of béton.\nThe artificial channels for conveying off the water may be\nformed either of stone blocks with semi-cylindrical channels\ncut in them, or of semi-cylinders of iron, or tiles, as may be\nmost convenient. A sufficient number of these channels\nshould be formed to give an outlet to the water as fast as it\nrises.\nAn impermeable cloth may be formed of stout canvas,\nprepared with bituminous pitch and a drying oil. It is well\nto have the cloth doubled on each side with ordinary canvas\nto prevent accidents. The manner of settling the cloth on\nthe surface of the soil must depend on the circumstances of\nthe case.\nEach of the foregoing expedients for preventing the action\nof springs on an area of béton has been tried with success.\nWhen artificial channels are used, they may be completely\nchoked subsequently, by injecting into them a semi-fluid\nhydraulic cement, and the action of the springs be thus de-\nstroyed.\nFoundation beds of béton are frequently made without ex-\nhausting the water from the area on which they are laid. For\nthis purpose the béton is thrown in layers over the area, by\nusing either a wooden conduit reaching nearly to the position\nof the layer, or else by placing the béton (Fig. 31) in a box\nby which it is lowered to the position of the layer, and from\nwhich it is deposited so as not to permit the water to separate\nthe lime from the other ingredients.\nA conduit for immersing hydraulic concrete, formed of\nboiler iron, has been used on some of our public works. The\nbody of it is cylindrical, and made in sections which can be\nreadily successively fastened on or detached; the bottom,\nhaving the form of a conical frustum, is fastened to the low-\nest section of the body. The conduit is suspended vertically\nDigitized by Google\nFOUNDATIONS OF STRUCTURES.\n195\nfrom a movable crane, or crab engine, by a strong screw, by\nwhich it can be raised or lowered, so as to admit the concrete\nto escape from the body through the conical-shaped end, to\nbe spread and compressed by the movements of the crane and\nscrew.\na\nc\nFig. 81 represents an end\nview, A, of a semi-cylindrical\nbox for lowering béton in\nwater, and B the same view of\nthe box when opened to let the\nbéton fall through.\no, hinge around which the\nhalves of the box open.\na rope tackling for lowering\nB\nbox.\n1\nb, pin, or catch to fasten the\ntwo parts of the box.\nc, cord to detach the pin and\n0\nopen the box.\nShould it be found that springs boil up at the bottom, it\nmust be covered with an impermeable cloth.\n430. Foundations in Marshy Soils. In marshy soils the\nprincipal difficulty consists in forming a bed sufficiently firm\nto give stability to the structure, owing to the yielding nature\nof the soil in all directions.\nThe following are some of the dispositions that have been\ntried with success in this case. Short piles from 6 to 12 feet\nlong, and from 6 to 9 inches in diameter, are driven into the\nsoil as close together as they can be crowded, over an area\nconsiderably greater than that which the structure is to occu-\npy. The heads of the piles are accurately brought to a level\nto receive a grillage and platform; or else a layer of clay,\nfrom 4 to 6 feet thick, is laid over the area thus prepared with\npiles, and is either solidly rammed in layers of a foot thick,\nor submitted to a very heavy pressure for some time before\ncommencing the foundations. The object of preparing the\nbed in this manner is to give the upper stratum of the soil all\nthe firmness possible, by subjecting it to a strong compression\nfrom the piles; and when this has been effected, to procure a\nfirm bed for the lowest course of the foundation by the gril-\nlage, or clay bed by these means the whole pressure will be\nuniformly distributed throughout the entire area. This case\nis also one in which a bed of béton would replace, with great\nadvantage, either the one of clay, or the grillage.\nDigitized\nby\nGoogle\n196\nCIVIL ENGINEERING.\nThe purposes to which the short piles are applied in this\ncase is different from the object to be attained usually in the\nemployment of piles for foundations ; which is to transmit the\nweight of the structure that rests on the piles, to a firm in-\ncompressible soil, overlaid by a compressible one, that does\nnot offer sufficient firmness for the bed of the foundation.\n431. Foundations on Piles. When a firm soil is overlaid\nby one of a compressible character, and its distance below the\nsurface is such that it can be reached by piles of ordinary di-\nmensions, they should be used in preference to any other plan,\nwhen they can be rendered durable, on account of their\neconomy and the security they afford.\nTo prepare the bed to receive the foundations in this case,\nstrong piles are driven, at equal distances apart, over the en-\ntire area on which the structure is to rest. These piles are\ndriven until they meet with a firm stratum below the com-\npressible one, which offers sufficient resistance to prevent them\nfrom penetrating farther.\nPiles are generally from 9 to 18 inches in diameter, with a\nlength not above 20 times the diameter, in order that they\nmay not bend under the stroke of the ram. They are pre-\npared for driving by stripping them of their bark, and paring\ndown the knots, so that the friction, in driving, may be re-\nduced as much as possible. The head of the pile is usually\nencircled by a strong hoop of wrought iron, to prevent the pile\nfrom being split by the action of the ram. The foot of the\npile may receive a shoe formed of ordinary boiler iron, well\nfitted and spiked on ; or a cast-iron shoe of a suitable form\nfor penetrating the soil may be cast around a wrought-iron\nbolt, by means of which it is fastened to the pile.\nFig. 82 represents a section through the axis of a cast-iron shoe and wronght-\niron bolt for a pile.\n432. Screw Piles. In localities where it has been found im-\npracticable to resort to any of the usual means of foundations,\nas on sandpits, or on beds of a soft conglomerate formed\nof shells, clay, and the oxide of iron, such as are found on our\nSouthern coasts, iron screw piles have been used with success,\nparticularly for light-house structures of iron.\nDigitized by\nGoogle\nFOUNDATIONS OF STRUCTURES.\n197\nThese piles have the screws of different forms according to\nthe soil they are to be used in. The point being little or\nnothing, and the thread of the screw very broad, for loose\nFig. 84.\nFig. 85.\nFig. 38.\nA\nB\nB\nB\nFigs. 38, 34, 85. Elevations of screw piles for loose, firm and hard or rocky soil respectively.\nA, newel; B, thread of screw.\nsoils; the point becoming sharper and the thread of the screw\nmore narrow as the soil becomes harder.\nDisk Piles. In some parts of India this species of pile has\nbeen advantageously employed.\nA\nFig. 86. Elevation of a disk pile. A, shaft; B, disc : a, water-hole.\nB\nc\nThese piles are made hollow of iron, and have a circular\ndisk attached to the foot. A hole is made in the disk to\nallow water to pass through.\nPile Engines. A machine, termed a pile engine, is used\nfor driving piles. It consists essentially of two uprights\nfirmly connected at top by a cross piece, and of a ram, or\nmonkey of cast iron, for driving the pile by a force of per-\ncussion. Two kinds of engines are in use; the one termed a\ncrab engine, from the machinery used to hoist the ram to the\nheight from which it is to fall on the pile; the other the ring-\ning engine, from the monkey being raised by the sudden pull\nof several men upon a rope, by which the ram is drawn up a\nfew feet to descend on the pile.\nThe crab engine is by far the more powerful machine, but\non this account is inapplicable in some cases, as in the driving\nDigitized by Google\n198\nCIVIL ENGINEERING.\nof cast-iron piles, where the force of the blow might destroy\nthe pile; also in long slender piles it may cause the pile to\nspring SO much as to prevent it from entering the subsoil.\nThe steam pile driver is but a modification of the crab\nengine.\nA\nA\nC\nFig. 87 represents a front elevation of the gun-\nB\npowder pile driver.\nAA, guides.\nB, ram.\nC, socket in which piston I fits.\nD, cast-iron cylinder containing powder\nchamber E.\nF, socket to fit on head of pile.\nG, pile.\nK\nK, plunger of ram.\nL, lever to hold ram at any point on the\nguides.\nE\nD\nL\nShaw's gunpowder pile driver consists essentially of two\nuprights or guides, between which are placed the ram and\npowder chamber. The latter consists of a east-iron cylinder,\nhaving a socket in its lower end, and a powder chamber at\nthe upper. The ram differs from that in ordinary use only\nby having a plunger made to fit the powder chamber, at the\nbottom, and a cylindrical cavity at top, extending about half\nway down. At any convenient point on the guides is placed\na piston made to fit into the ram, to take the place of an air-\ncushion in taking up the recoil, in case the charge should be\ntoo great.\nWork is begun by placing the powder chamber on top of\nDigitized by Google\nFOUNDATIONS OF STRUCTURES.\n199\nthe pile to be driven, putting a cartridge in the chamber, and\nallowing the ram to fall. The explosion of the cartridge\nthrows the ram up and drives the pile down proportionally.\nAnother cartridge is thrown in and the operation repeated.\nThe only limit to the rapidity of the blows is the size of the\ncartridges and the rapidity with which they are supplied.\nD\nc\n1\nFlg. 88 represents the capstan for driving screw piles by hand.\nA, shaft of pile.\nB, acrew.\nC, capstan.\nD, taper of shaft to fit into socket of next section above.\nE, bolt fastening socket of shaft to taper of next section be-\nlow.\nFor driving screw-piles a capstan is fitted to the head of\nthe pile, and motion communicated to the pile either by men\ntaking hold of the capstan bars and walking around with\nthem, or by attaching an endless rope or chain to the extremi-\nties of the bars, and setting it in motion by machinery.\nFor setting disk-piles, water is forced down through the\nhole in the disk, and produces a scour from under the pile\nwhich gradually sinks to its place.\nThe manner of driving piles, and the extent to which they\nmay be forced into the subsoil, will depend on local circum-\nstances. It sometimes happens that a heavy blow will effect\nless than several slighter blows, and that piles after an inter-\nval between successive volleys of blows can with difficulty be\nDigitized by Google\n200\nCIVIL ENGINEERING.\nstarted at first. In some cases the pile breaks below the sur-\nface, and continues to yield to the blows by the fibres of the\nlower extremity being crushed. These difficulties require\ncareful attention on the part of the engineer. Piles should\nbe driven to an unyielding subsoil. The French civil engi-\nneers have, however, adopted a rule to stop the driving when\nthe pile has arrived at its absolute stoppage, this being mea-\nsured by the further penetration into the subsoil of about\n1ˢσᵗʰₛ of an inch, caused by a volley of thirty blows from a\nram of 800 lbs., falling from a height of 5 feet at each blow.\n433. If the head of a pile has to be driven below the level\nto which the ram descends, another pile, termed a punch, is\nused for the purpose. A cast-iron socket of a suitable form\nembraces the head of the pile and the foot of the punch, and\nthe effect of the blow is thus transmitted through the punch\nto the pile.\n434. When a pile, from breaking or any other cause, has\nto be drawn out, it is done by using a long beam as a lever\nfor the purpose; the pile being attached to the lever by a\nchain or rope, suitably adjusted.\n435. The number of piles required will be regulated by\nthe weight of the structure. Where the piles are driven to a\nfirm subsoil, they may be subjected to a working strain of\n1000 pounds to the square inch of cross section at top. In\nthe contrary case, and where the resistance offered results\nmainly from that of friction on the exterior of the piles, the\nworking strain should be reduced to 200 pounds to the square\ninch. The least distance apart at which the piles can be\ndriven with ease is about 21 feet between their centres. If\nthey are more crowded than this, they may force each other\nup as they are successively driven. When this is found to\ntake place, the driving should be commenced at the centre of\nthe area, and the pile should be driven with the butt end\ndownward.\n436. From experiments carefully made in France, it appears\nthat piles which resist only in virtue of the friction arising\nfrom the compression of the soil, cannot be subjected with\nsafety to a load greater than one-fifth of that which piles of\nthe same dimensions will safely support when driven into a\nfirm soil.\n437. After the piles are driven, they are sawed off to a\nlevel, to receive a grillage and platform for the foundation.\nA large beam, termed a capping, is first placed on the heads\nof the outside row of piles, to which it is fastened by means\nof wooden pins, or tree-nails, driven into an auger-hole made\nDigitized by Google\nFOUNDATIONS OF STRUCTURES.\n201\nthrough the cap, into the head of each pile. After the cap is\nfitted, longitudinal beams, termed string-pieces, are laid\nlengthwise on the heads of each row, and rest at each extrem-\nity on the cap, to which they are fastened by a dove-tail joint\nand a wooden pin. Another series of beams, termed cross-\npieces, are laid crosswise on the string-pieces, over the heads\nof each row of piles. The cross and string pieces are con-\nnected by a notch cut into each, so that, when put together,\ntheir upper surfaces may be on the same level, and they are\nfastened to the heads of the piles in the same manner as the\ncapping. The extremities of the cross-pieces rest on the cap-\nping, and are connected with it like the string-pieces.\nThe platform is of thick planks laid over the grillage, with\nthe extremity of each plank resting on the capping, to which,\nand to the string and cross pieces, the planks are fastened by\nnails.\nThe capping is usually thicker than the cross and string\npieces by the thickness of the plank; when this is the case, a\nrabate, about four inches wide, must be made on the inner\nedge of the capping, to receive the ends of the planks.\n438. An objection is made to the platform as a bed for the\nfoundation, owing to the want of adhesion between wood and\nmortar from which, if any unequal settling should take\nplace, the foundations would be exposed to slide off the plat-\nform. To obviate this, it has been proposed to replace the\ngrillage and platform by a layer of béton resting partly on\nthe heads of the piles, and partly on the soil between them.\nThis means would furnish a firm bed for the masonry of the\nfoundations, devoid of the objections made to the one of tim-\nber.\nTo counteract any tendency to sliding, the platform may be\ninclined if there is a lateral pressure, as in the case, for ex-\nample, of the abutments of an arch.\n439. In soils of alluvial formation, it is common to meet\nwith a stratum of clay on the surface, underlaid with soft\nmud, in which case the driving of short piles would be inju-\nrious, as the tenacity of the stratum of clay would be de-\nstroyed by the operation. It would be better not to disturb\nthe upper stratum in this case, but to give it as much firmness\nas possible, by ramming it with a heavy beetle, or by submit-\nting it to a heavy pressure.\nThe piers of the bridge over the Seekonk river are formed\nof clusters of piles driven through the mud to a firm subsoil.\nThese piles are of hard Southern or yellow pine, hewn to\ntwelve or fourteen inches square, according to the size of the\nDigitized by\nGoogle\n202\nCIVIL ENGINEERING.\nstick, throughout their whole length. They are arranged in\ngroups of twelve, except in five clusters under the draw.\nEight of the piles in the clusters of twelve have their outside\ncorners taken off to allow the flanges of the cylinders to pass\nA\nA\nE\nB\nB\nG\nFig. 89 represents a section and elevation of a pier of the Seekonk river bridge.\nA, outside cover of metal.\nB, clusters of wooden piles.\nC, inside filling of concrete.\nD, loose stone.\nE, slag.\nF, crust of shells.\nG, cross section of wooden clusters.\ndown by them. The piles forming each of these clusters are\nfirmly bolted together with inch and a quarter bolts. These\nclusters are incased with cast-iron cylinders, extending from\nten inches above the piling in the draw pier, and sixteen or\nDigitized by Google\nFOUNDATIONS OF STRUCTURES.\n203\ntwenty inches in the others, to four and six feet below the top\nof the crust. The cylinders are six and five feet in diameter\nfor the large and small clusters, and the void space left be-\ntween them and the clusters is filled in with good concrete.\n440. Piles and sheeting piles of cast iron have been used\nwith complete success in England, both for the ordinary pur-\nposes of cofferdams, and for permanent structures for wharf-\ning. The piles have been cast of a variety of forms; in some\ncases they have been cast hollow for the purpose of excavat-\ning the soil within the pile as it was driven, and thus facili-\ntate its penetration into the subsoil. Fig. 40 represents a\nhorizontal section of one of the more recent arrangements of\niron piles and sheeting piles.\ne\n6\nd\nd\nd\nd\nd\nFig. 40 represents a horizontal section of an arrangement of piles and sheeting piles of\ncast iron.\na, sheeting pile with a lap e to cover the joint between it and the next sheeting pile.\nb, piles with a lap on each side.\nc, sheeting pile lapped by pile and sheeting pile next it.\na ribs of piles and sheeting piles.\n441. Sand has also been used with advantage to form a bed\nfor foundations in a very compressible soil. For this purpose\na trench is (Fig. 40) excavated, and filled with sand ; the sand\nbeing spread in layers of about 9 inches, and each layer being\nfirmly settled by a heavy beetle, before laying the next. If\n=\nFig. 41 represents a section of a sand foun-\ndation bed and the masonry upon it.\nA, sand bed in a trench.\nB, masonry.\nwater should make rapidly in the trench, it would not be\npracticable to pack the sand in layers. Instead, therefore, of\nDigitized by\nGoogle\n204\nCIVIL ENGINEERING.\nopening a trench, holes about 6 feet deep, and 6 inches in\ndiameter (Fig. 42), should be made by means of a short pile,\nas close together as practicable; when the pile is withdrawn\nfrom the hole it is immediately filled with sand. To cause\nthe sand to pack firmly, it should be slightly moistened before\nplacing it in the holes or trench.\nB\nFig. 42.-Represents a section of a foun-\ndation bed made by filling holes with\nsand.\nA, holes filled with sand.\nB, masonry.\nSand, when used in this way, possesses the valuable prop-\nerty of assuming a new position of equilibrium and stability,\nshould the soil on which it is laid yield at any of its points.\nNot only does this take place along the base of the sand bed,\nbut also along the edges, or sides, when these are enclosed by\nthe sides of the trench made to receive the bed. This last\npoint offers also some additional security against yielding in a\nlateral direction. The bed of sand must, in all cases, receive\nsufficient thickness to cause the pressure on its upper surface\nto be distributed over the entire base.\n442. When, from the fluidity of the soil, the vertical pres-\nsure of the structure causes the soil to rise around the bed,\nthis action may be counteracted either by scooping out the\nsoil to some depth around the bed and replacing it by another\nof a more compact nature, well rammed in layers, or with any\nrubbish of a solid character; or else a mass of loose stone\nmay be placed over the surface exterior to the bed, whenever\nthe character of the structure will warrant the expense.\n443. Precautions against Lateral Yielding. The soils\nwhich have been termed compressible, strictly speaking, yield\nonly by the displacement of their particles either in a lateral\ndirection, or upward around the structure laid upon them.\nWhere this action arises from the effect of a vertical weight,\nuniformly distributed over the base of the bed, the preceding\nDigitized by Google\nFOUNDATIONS OF STRUCTURES.\n205\nmethods for giving permanent stability to structure present\nall requisite security. But when the structure is subjected\nalso to a lateral pressure, as, for example, that which would\narise from the action of a bank of earth resting against the\nback of a wall, additional means of security are demanded.\nOne of the most obvious expedients in this case is to drive\na row of strong square piles in juxtaposition immediately in\ncontact with the exterior edges of the bed. This expedient\nis, however, only of service where the piles attain either an\nincompressible soil, or one at least firmer than that on which\nthe bed immediately rests. For otherwise, as is obvious, the\npiles only serve to transmit the pressure to the yielding soil in\ncontact with them. But where they are driven into a firm\nsoil below, they gain a fixed point of resistance, and the only\ninsecurity they offer is either by the rupture of the piles, from\nthe cross strain upon them, or from the yielding of the firm\nsubsoil, from the same cause.\nIn case the piles reach a firm subsoil, it will be best to scoop\nout the upper yielding soil before driving the piles and to fill\nin between and around them with loose broken stone (Fig. 43).\nThis will give the piles greater stiffness, and effectually pre-\nvent them from spreading at top.\nFig. 48-Represents the manner of using\nloose stone to sustain piles and prevent\nthem from yielding laterally.\nA, section of the masonry.\nB, loose stone thrown around the piles, a.\nWhen the piles cannot be secured by attaining a firm sub-\nsoil, it will be better to drive them around the area at some\ndistance from the bed, and, as a further precaution, to place\nhorizontal buttresses of masonry at regular intervals from the\nbed to the piles. By this arrangement some additional secu-\nrity is gained from the counter-pressure of the soil enclosed\nDigitized by Google\n206\nCIVIL ENGIN RING.\nbetween the bed and the wall of piles. But it is obvious that\nunless the piles in this case are driven into a firmer soil than\nthat on which the structure rests, there will still be danger of\nyielding.\nIn using horizontal buttresses, the stone of which they are\nconstructed should be dressed with care; their extremities\nnear the wall of piles should be connected by horizontal\narches (Fig. 44), to distribute the pressure more uniformly;\nand where there is an upward pressure of the soil around the\nstructure, arising from its weight, the buttresses ought to be\nin the form of reversed arches.\nIn buttresses of this kind, as likewise in broad areas resting\non a very yielding soil, since as much danger is to be appre-\nhended from their breaking by their own weight as from any\nother cause, it must be carefully guarded against. Something\nmay be done for this purpose by ramming the earth around\nthe structure with a heavy beetle, when it can be made more\ncompact by this means; or else a part of the upper soil may\nbe removed, and be replaced by one of a more compact nature\nwhich may be rammed in layers.\nFig. 44 represents the manner of prevent-\ning a sustaining wall from yielding later-\nally to a thrust behind it, by using hori-\nsontal buttresses of reversed arches abut-\nting against vertical counter-arches.\nA, vertical section of wall, buttresses, and\ncounter arches.\nB, plan of wall, buttresses, and counter-\narches.\na, plan of wall.\nb, section of do.\na buttresses.\nd, counter-archea.\nB\nThe following methods, where they can be resorted to, and\nwhere the character of the structure will justify the expense,\nhave been found to offer the best security in the case in ques-\ntion.\nWhen the bed can be buttressed in front with an embank-\nDigitized by Google\nFOUNDATIONS OF STRUCTURES.\n207\nment, a low counter-wall (Fig. 45) may be built parallel to\nthe edge of the bed, and some 10 or 12 feet from it; between\nthis wall and the bed a reversed arch connecting the two may\nbe built, and a surcharge of earth of a compact character and\nwell rammed, may be placed against the counter-wall to act\nby its counter-pressure against the lateral pressure upon the\nbed.\ne\nFig. 45 represents the man-\nner of buttressing a sustain-\ning wall in front by the ao-\ntion of a counter-pressure of\nearth transmitted to the wall\nby a reversed arch.\na, section of sustaining wall.\nb, section of sustaining wall\nof embankment, d.\nc, section of reversed arch.\nd, section of embankment\nfrom which counter-pres-\nsure comes.\nc\ne, section of embankment be-\nhind sustaining wall.\nWhen the bed cannot be buttressed in front, as in quay\nwalls, a grillage and platform supported on piles (Fig. 46)\nmay be built to the rear from the back of the wall, for the\npurpose of supporting the embankment against the back of\nthe wall, and preventing the effect which its pressure on the\nsubsoil might have in thrusting forward the bed of the founda-\ntion.\nIn addition to these means, land ties of iron will give great\nadditional security, when a fixed point in rear of the wall can\nbe found to attach them firmly.\nFig. 46 represents the manner of re-\nlieving a sustaining wall from the\nlateral action caused by the pressure\nof an embankment on the subsoil by\nmeans of a platform built behind the\nwall.\nA, section of the wall.\nB, section of embankment.\na, piles supporting the grillage and plat-\nform of A.\nb, loose stone, forming a firm bed under\nthe platforms.\na piles supporting the platform d behind\nthe wall.\nDigitized by\nGoogle\n208\nCIVIL ENGINEERING.\nVI.\nFOUNDATIONS OF STRUCTURES IN WATER.\n444. In laying foundations in water, two difficulties have\nto be overcome, both of which require great resources and\ncare on the part of the engineer. The first is found in the\nmeans to be used in preparing the bed of the foundation\nand the second in securing the bed from the action of water,\nto insure the safety of the foundations. The last is generally\nthe more difficult problem of the two; for a current of water\nwill gradually wear away, not only every variety of loose soils,\nbut also the more tender rocks, such as most varieties of sand-\nstone, and the calcareous and argillaceous rocks, particularly\nwhen they are stratified, or are of a loose texture.\n445. To prepare the bed of a foundation in stagnant water\nthe only difficulty that presents itself is to exclude the water\nfrom the area on which the structure is to rest. If the depth\nof water is not over 4 feet, this is done by surrounding the\narea with an ordinary water-tight dam of clay, or of some\nother binding earth. For this purpose, a shallow trench is\nformed around the area, by removing the soft or loose stratum\non the bottom; the foundation of the dam is commenced by\nfilling this trench with the clay, and the dam is made by\nspreading successive layers of clay about one foot thick, and\npressing each layer as it is spread to render it more compact.\nWhen the dam is completed, the water is pumped out from\nthe enclosed area, and the bed for the foundation is prepared\nas on dry land.\n446. When the depth of stagnant water is over 4 feet, and\nin running water of any depth, the ordinary dam must be\nreplaced by the coffer-dam. This construction consists of\ntwo rows of plank, termed sheeting piles, driven into the soil\nvertically, forming thus a coffer-work, between which clay or\nbinding earth, termed the puddling, is filled in, to form a\nwater-tight dam to exclude the water from the area enclosed.\nThe arrangement, construction, and dimensions of coffer-\ndams depend on their specific object, the depth of water, and\nthe nature of the subsoil on which the coffer-dam rests.\nWith regard to the first point, the width of the dam be-\ntween the sheeting piles should be SO regulated as to serve as\na scaffolding for the machinery and materials required about\nthe work. This is peculiarly requisite where the coffer-dam en-\nDigitized by Google\nFOUNDATIONS OF STRUCTURES.\n209\ncloses an isolated position removed from the shore. The\ninterior space enclosed by the dam should have the requisite\ncapacity for receiving the bed of the foundations, and such\nmaterials and machinery as may be required within the dam.\nThe width or thickness of the coffer-dam, by which is\nunderstood the distance between the sheeting piles, should be\nsufficient not only to be impermeable to water, but to form,\nby the weight of the puddling, in combination with the resis-\ntance of the timber-work, a wall of sufficient strength to resist\nthe horizontal pressure of the water on the exterior, when the\ninterior space is pumped dry. The resistance offered by the\nweight of the puddling to the pressure of the water can be\neasily calculated; that offered by the timber-work will depend\nupon the manner in which the framing is arranged, and the\nmeans taken to stay or buttress the dam from the enclosed\nspace.\nThe most simple and the usual construction of a coffer-dam\nc\nb\nFig. 47-represents a seo-\ntion of the ordinary oof-\nfer-dam.\na, main piles.\nb. wale or string pieces.\nB\nn.\nc, cross pieces.\na\nd, sheeting piles.\na guide string pieces for\nsheeting piles.\nA, puddling.\nB, interior space.\n(Fig. 47) consists in driving a row of ordinary straight piles\naround the area to be enclosed, placing their centre lines about\n4 feet asunder. A second row is driven parallel to the first,\nthe respective piles being the same distance apart; the dis-\ntance between the centre lines of the two rows being so regu-\nlated as to leave the requisite thickness between the sheeting\npiles for the dam. The piles of each row are connected by a\nhorizontal beam of square timber, termed a string or wale\npiece, placed. a foot or two above the highest water line, and\n14\nDigitized by Google\n210\nCIVIL ENGINEERING.\nnotched and bolted to each pile. The string pieces of the\ninner row of piles are placed on the side next to the area\nenclosed, and those of the outer row on the outside. Cross\nbeams of square timber connect the string pieces of the two\nrows upon which they are notched, serving both to prevent\nthe rows of piles from spreading from the pressure that may\nbe thrown on them and as a joisting for the scaffolding. On\nthe opposite sides of the rows interior string pieces are placed,\nabout the same level with the exterior, for the purpose of\nserving both as guides and supports for the sheeting piles.\nThe sheeting piles being well jointed are driven in juxtaposi-\ntion, and against the interior string pieces. A third course\nof string or ribbon pieces of smaller scantling confine, by\nmeans of large spikes, the sheeting piles against the interior\nstring pieces.\nAs has been stated, the thickness of the dam and the dimen-\nsions of the timber of which the coffer-work is made will de-\npend upon the pressure due to the head of water, when the\ninterior space is pumped dry. For extraordinary depths, the\nengineer would not act prudently were he to neglect to verify\nby calculation the equilibrium between the pressure and re-\nsistance; but for ordinary depths under 10 feet, a rule fol-\nlowed is to make the thickness of the dam 10 feet; and for\ndepths over 10 feet to give an additional thickness of one foot\nfor every additional depth of three feet. This rule will give\nevery security against filtrations through the body of the dam,\nbut it might not give sufficient strength unless the scantling\nof the coffer-work were suitably increased in dimensions.\nIn very deep tidal water, coffer-dams have been made in\noffsets, by using three rows of sheeting piles for the purpose\nof giving greater thickness to the dam below the low-water\nlevel. In such cases strong square piles closely jointed and\ntongued and grooved, should be used in place of the ordinary\nsheeting piles.\nBesides providing against the pressure of the head of water,\nsuitable dimensions must be given to the sheeting piles, in\norder that they may sustain the pressure arising from the pud-\ndling when the interior space is emptied of water. This\npressure against the interior sheeting piles may be further\nincreased by that of the exterior water upon the exterior\nsheeting piles, should the pressure of the latter be greater\nthan the former. To provide more securely against the effect\nof these pressures, intermediate string pieces may be placed\nagainst the interior row of piles before the sheeting piles are\ndriven; and the opposite sides of the dam on the interior may\nDigitized by\nGoogle\nFOUNDATIONS OF STRUCTURES.\n211\nbe buttressed by cross pieces reaching across the top string\npieces, and by horizontal beams placed at intermediate points\nbetween the top and bottom of the dam.\nThe main inconvenience met with in coffer-dams arises\nfrom the difficulty of preventing leakage under the dam. In\nall cases the piles must be driven into a firm stratum, and the\nsheeting piles should equally have a firm footing in a tena-\ncious compact substratum. When an excavation is requisite\non the interior, to uncover the subsoil on which the bed of the\nfoundation is to be laid, the sheeting piles should be driven\nat least as deep as this point, and somewhat below it if the\nresistance offered to the driving does not prevent it.\nThe puddling should be formed of a mixture of tenacions\nclay and sand, as this mixture settles better than pure clay\nalone. Before placing the puddling, all the soft mud and\nloose soil between the sheeting piles should be carefully ex-\ntracted; the puddling should be placed in and compressed in\nlayers, care being taken to agitate the water as little as prac-\nticable.\nWith requisite care coffer-dams may be used for founda-\ntions in any depth of water, provided a water-tight bottoming\ncan be found for the puddling. Sandy bottoms offer the\ngreatest difficulty in this respect, and when the depth of\nwater is over 5 feet, extraordinary precautions are requisite\nto prevent leakage under the puddling.\nWhen the depth of water is over 10 feet, particularly where\nthe bottom is composed of several feet of soft mud, or of loose\nsoil, below which it will be necessary to excavate to obtain a\nfirm stratum for the bed of the foundation, additional precau-\ntions will be requisite to give sufficient support to the interior\nsheeting piles against the pressure of the puddling, to provide\nagainst leakage under the puddling, and to strengthen the\ndam against the pressure of the exterior water, when the inte-\nrior space is pumped dry and excavated. The best means for\nthese ends, when the locality will admit of their application,\nis to form the exterior of the dam, as has already been de-\nscribed, by using piles and sheeting piles, giving to the latter\nadditional points of support, by intermediate string pieces\nbetween the one at top and the bottom of the water ; and to\nform a strong framing of timber for a support to the interior\nsheeting piles, giving to it the dimensions of the area to be\nenclosed. The framework (Fig. 48) may be composed of\nupright square beams, placed at suitable distances apart, de-\npending on the strength required, upon which square string\npieces are bolted at suitable distances from the top to the\nDigitized by\nGoogle\n212\nCIVIL ENGINEERING.\nbottom, the bottom string resting on the surface of the mud.\nThe string pieces, serving as supports for the sheeting piles,\nmust be on the sides of the uprights towards the puddling,\nand their faces in the same vertical plane. Between each\ne\nd\n0\nPL\nn\nFig. 48 Represents a\nsection of the coffer-\nb\ndam used for the\nB\nPotomac aqueduct.\na, main exterior piles.\na\n0\nb, strong square beams\nTL\ncorresponding to a\nA\non which the wales\nn. n are notched and\nbolted.\n0\nc, sheeting piles.\nn\nd, top wale on main\ne\nC\npiles.\nn\na crosspieces.\n0\ni, guide and supporting\nstring pieces for\nsheeting piles.\n00, horizontal shores\nbuttressing opposite\nG\nsides of dam.\nA, puddling.\nB, interior space.\nC, mud, etc.\nD. rock bottom.\nD\npair of opposite uprights horizontal shores may be placed at\nthe points opposite the position of the string pieces, to in-\ncrease the resistance of the dam to the pressure of the water\nthe top shores extending entirely across the dam, and being\nnotched on the top string pieces. The interior shores must\nbe so arranged that they can be readily taken out as the ma-\nsonry on the interior is built up, replacing them by other\nshores resting against the masonry itself.\n447. Caisson and Cribwork Coffer-dams. In the con-\nstruction of the foundations for the piers and abutments of\nthe Victoria tubular iron railroad bridge over the river Saint\nLawrence, at Montreal, the engineers had to contend against\nunusual difficulties in a rocky bottom covered with boulders,\nwhich prevented the use of piles; and in a swift current,\nbringing down in the spring of the year enormous fields of\nice, the effects of which none of the ordinary methods of\ncaisson or coffer-dams could have withstood.\nThese difficulties were successfully met, in some cases by\nthe use of a large water-tight caisson, shown in plan (Fig. 49),\nand in cross-section (Fig. 51), of such a form and dimensions\nas to leave a sufficient interior area, between its interior sides,\nDigitized by Google\nFOUNDATIONS OF STRUCTURES.\n213\nfor a coffer-dam, and for the ground to be occupied for the\nconstruction of the foundations of the pier. In others (Fig.\n51), where, from the velocity of the current, the caissons,\nfrom their great bulk, proved unmanageable, by enclosing the\narea to be occupied by crib-work, sunk upon the bottom and\nheavily laden with stone; and exterior to this forming a\nsecond similar enclosure; and then, by means of sheeting\npiles, supported against the opposite sides of these two en-\nclosures, forming a coffer-dam between them.\n100\nA\nB\nA\nFig. 49. Plan of caisson.\nB, Detached end.\nA, A, sides of caisson.\nC, Puddling.\nD, Plan of pier of bridge.\nThe caisson (Fig. 49) consisted of two parts, the two sides\nand up-stream wedge-shaped head, and a rectangular-shaped\nportion B, which fitted in between the two sides, forming the\ndown-stream end, and which could be detached and floated\noff when it became necessary to remove the entire caisson.\nThe caisson (Fig. 50) was flat-bottomed, with vertical sides ;\nand it was provided with a strong flat deck, to receive the\nworkshops, machinery, and materials for pumping, dredging,\nand the construction of the masonry.\nWhen placed in position, it was moored to a loaded, sunken\ncrib-work up-stream; and, besides the exterior guide-piles,\nlong two-inch iron bolts were inserted into holes drilled into\nthe solid rock, through vertical holes bored through the piles.\nIn this way, through the bearing of the piles on the bottom,\nthe foothold given by the bolts and the mooring-tackle, the\nDigitized by Google\n214\nCIVIL ENGINEERING.\ncaisson, when sunk, was solidly secured against accidents from\nrafts, or other floating bodies.\nA\nC\nD\nFig. 50. Cross-section of Fig. 49.\nC', Cross-section of puddling and sheeting.\nA', Cross-section of caisson.\nD', Foundation courses of pier.\nThe interior sides of the coffer-dam were strongly buttress-\ned by horizontal beams, to withstand the pressure of the water.\nThese beams were removed, and their places supplied by\nshorter buttresses placed between the sides of the coffer-dam\nand pier as the masonry was carried up.\nThe cribwork dams were constructed of a number of cribs.\neach about forty feet in length, which were placed end to end\nto form the sides of the enclosures, and strongly connected\nwith each other. Some of these were constructed on shore,\nand towed to their positions. Some were constructed in the\nwater behind mooring cribs, and others upon the ice during\nthe winter, and sunk in position.\nA flooring (Fig. 51) was made, about midway between the\ntop and bottom of the cribs, to receive the blocks of stone with\nwhich the cribs were loaded, to secure them from the effects\nof the pressure of the ice in its spring movement, and the\ncollision of floating bodies.\nThe caissons were not of adequate strength to resist the\ncrush of the ice, and had to be pumped out and removed to a\nsecure position before the closing of the river. The cribs\nwere planked over at top, and remained in place as long as re-\nquired for the work.\n448. When the bed of a river presents a rocky surface, or\nDigitized by Google\nFOUNDATIONS OF STRUCTURES.\n215\nrock covered with but a few feet of mud, or loose soil, cases\nmay occur in which it will be more economical and equally\nsafe to lay a bed of béton without exhausting the water from\nthe area to be built on ; enclosing the area, before throwing\nin the béton, by a simple coffer-work formed of a strong\nB\nFig. 51. Cross section of cribwork dams.\nB, Exterior crib.\nA, Interior crib.\nC, Puddling and sheeting piles,\nframework of uprights and horizontal beams and sheeting\npiles. The framework (Fig. 52) in this case is composed of\nuprights connected by string pieces in pairs; each pair is\nnotched and bolted to the uprights, a sufficient interval being\nleft between them for the insertion of the sheeting piles. To\nsecure the framework to the rock, it may be requisite to drill\nholes in the rock to receive the foot of each upright. The\nholes may be drilled by means of a long iron bar, termed a\njumper, which is used for this purpose, or else the ordinary\ndiving-bell may be employed. This machine is very service-\nable in all similar constructions where an examination of\nwork under water is requisite, or in cases where it is neces-\nsary to lay masonry under water. The framework is put\ntogether on land, floated to its position, and settled upon the\nrock; the sheeting piles are then driven into close contact\nwith the surface of the rock.\n449. The convenience and economy resulting from the use\nof béton for the beds of structures raised in water have led\nGeneral Treussart to propose a plan for laying beds of this\nmaterial, and then to take advantage of their strength and\nimpermeability to construct a coffer-dam upon them, in order\nto carry on the superstructure with more care. To effect\nthis, the space to be occupied by the bed (Fig. 53) is first en-\nclosed by square piles, driven in juxtaposition and secured at\ntop by a string piece. The mud and loose soil are then\nscooped from the enclosed area to the firm soil on which the\nDigitized by\nGoogle\n216\nCIVIL ENGINEERING.\nbed of béton is to be laid. The bed of béton is next laid\nwith the usual precautions, and while it is still soft a second\nrow of square piles is driven into it, also in juxtaposition, and\nb\nFig. 52 represents a coffer-work for confining béton.\nA, Section of coffer-work and béton.\nB, Plan of coffer-work.\na, a', square uprights connected by horisontal beams, b D,\nbolted to them in pairs.\nc, c, sheeting piles inserted between the beams b, b' and\nB\nthe uprights a, a'.\nd, d', iron rods connecting opposite sides of coffer-work.\nb\nat a suitable distance from the first for the thickness of the\ndam ; these are also secured at top by a string piece. Cross\npieces are notched upon the string pieces, to secure the rows of\npiles and form a scaffolding. An ordinary puddling is placed\nin between the rows of piles, and the interior space is pumped\ndry.\nShould the soil under the bed of béton be permeable, the\npressure of the water on the base of the bed may be sufficient\nto raise the bed and the dam upon it, when the water is taken\nfrom the interior space. A proper calculation will show\nwhether this danger is to be apprehended, and should it be,\nDigitized by Google\nFOUNDATIONS OF STRUCTURES.\n217\na provisional weight must be placed on the dam, or the bed\nof béton, before exhausting the interior.\nc\nb\nb\nD\nB\na\na\nFig. 53 represents a section of Gen-\nC\neral Treussart's dam.\nA, bed of béton.\nB, puddling of dam.\nC, masonry of structure.\na, square piles.\nb, wale pieces.\nc, cross pieces.\n450. When the depth of water is great, or when, from the\npermeability of the soil at the bottom, it is difficult to pre-\nvent leakage, a coffer-dam may be a less economical method\nof laying foundations than the caisson. The caisson (fig. 54.)\nis a strong water-tight vessel having a bottom of solid heavy\ntimber, and vertical sides so arranged that they can be readi-\nly detached from the bottom. The following is the usual\narrangement of the caisson, it, like the coffer-dam, being sub-\nject to changes to suit it to the locality. The bottom of the\ncaisson, serving as a platform for the foundation course of\nthe masonry, is made level and of heavy timber laid in juxta-\nposition, the ends of the beams being confined by tenons and\nscrew-bolts to longitudinal capping pieces of larger dimen-\nsions. The sides of the box are usually vertical. The sides\nare formed of upright pieces of scantling covered with thick\npiank, the seams being carefully calked to make the caisson\nwater-tight. The lower ends of the uprights are inserted\ninto shallow mortises made in the capping. The arrange-\nment for detaching the sides is effected in the following\nmanner: Strong hooks of wrought iron are fixed to the bot-\ntom of the caisson at the sides of the capping piece, corre-\nsponding to the points where the uprights of the sides are in-\nDigitized by Google\n218\nCIVIL ENGINEERING.\nserted into this piece. Pieces of strong scantling are laid\nacross the top of the caisson, resting on the opposite uprights,\nupon which they are notched. These cross pieces project\nbeyond the sides, and the projecting parts are perforated by\nan auger-hole, large enough to receive a bolt of two inches in\nFig. 54 represents a cross\nsection and interior end\nview of a caisson. The\nboards in this figure are rep-\nresented as let into grooves\nin the vertical pieces, in-\nstead of being nailed to them\non the exterior.\na, bottom beams let into\nb\ngrooves in the capping.\nb, square uprights to sustain\nthe boards.\nc, cross pieces resting on b.\nd, iron rods fitted to hooks at\nbottom and nuts at top.\ne, longitudinal beams to stay\nthe cross pieces c.\nA, section of the majonry.\ndiameter. The object of these cross pieces is twofold ; the\nfirst is to buttress the sides of the caisson at top against the\nexterior pressure of the water; and the second is to serve as\na point of support for a long bolt, or rod of iron, with an eye\nat the lower end, into which the hook on the capping piece is\ninserted, and a screw at top, to which a nut or female screw\nis fitted, and which, resting on the cross pieces as a point of\nsupport, draws the bolt tight, and, in that way, attaches the\nsides and bottom of the caisson firmly together.\nA bed is prepared to receive the bottom of the caisson, by\nlevelling the soil on which the structure is to rest, if it be of\na suitable character to receive directly the foundation; or by\ndriving large piles through the upper compressible strata of\nthe soil to the firm stratum beneath. The heads of the piles\nare sawed off on a level to receive the bottom of the caisson.\nTo settle the caisson on its bed, it is floated to and moored\nover it; and the masonry of the structure is commeneed and\ncarried up, until the weight grounds the caisson. The caisson\nshould be SO contrived, that it can be grounded, and after-\nwards raised, in case that the bed is found not to be accurately\nlevelled. To effect this, a small sliding gate should be placed\nin the side of the caisson, for the purpose of filling it with\nDigitized by\nGoogle\nFOUNDATIONS OF STRUCTURES.\n219\nwater at pleasure. By means of this gate, the caisson can be\nfilled and grounded, and by closing the gate and pumping out\nthe water, it can be set afloat.\nAfter the caisson is settled on its bed, and the masonry of\nthe structure is raised above the surface of the water, the sides\nare detached by first unscrewing the nuts and detaching the\nrods and then taking off the top cross pieces. By first filling\nthe caisson with water, this operation of detaching the sides\ncan be more easily performed.\n451. To adjust the piles before they are driven, and to pre-\nvent them from spreading outward by the operation of driving,\na strong grating of heavy timber, formed by notching cross\nand longitudinal pieces on each other, and fastening them\nfirmly together, may be resorted to. This grating is arranged\nin a similar manner to a grillage; only the square compart-\nments between the cross and string pieces are larger, SO that\nthey may enclose an area .for 4 or 9 piles; and instead of a\nsingle row of cross pieces, the grating is made with a double\nrow, one at top, the other at the bottom, embracing the string\npieces on which they are notched.\nThe grating may be fixed in its position at any depth under\nwater, by a few provisional piles, to which it can be attached.\n452. Where the area occupied by a structure is very con-\nsiderable, and the depth of water great, the methods which\nhave thus far been explained cannot be used. In such cases,\na firm bed is made for the structure, by forming an artificial\nisland of loose heavy blocks of stone, which are spread over\nthe area, and receive a batter of from one perpendicular to\none base, to one perpendicular and six base, according to the\nexposure of the bed to the effects of waves. This bed is\nraised several feet above the surface of the water, according\nto the nature of the structure, and the foundation is com-\nmenced upon it.\n453. It is important to observe, that, where such heavy masses\nare laid upon an untried soil, the structure should not be com-\nmenced before the bed appears entirely to have settled ; nor\neven then if there be any danger of further settling taking\nplace from the additional weight of the structure. Should\nany doubts arise on this point, the bed should be loaded with\na provisional weight, somewhat greater than that of the con-\ntemplated structure, and this weight may be gradually re-\nmoved, if composed of other materials than those required\nfor the structure, as the work progresses.\n454. To give perfect security to foundations in running\nwater, the soil around the bed must be protected to some ex-\nDigitized by\nGoogle\n220\nCIVIL ENGINEERING.\ntent from the action of the current. The most ordinary\nmethod of effecting this is by throwing in loose masses of\nbroken stone of sufficient size to resist the force of the cur-\nrent. This method will give all required security, where the\nsoil is not of a shifting character, like sand and gravel. To\nsecure a soil of this last nature, it will in some cases be neces-\nsary to scoop out the bottom around the bed to a depth of\nfrom 3 to 6 feet, and to fill this excavated part with béton,\nthe surface of which may be protected from the wear arising\nfrom the action of the pebbles carried over it by the current,\nby covering it with broad flat flagging stones.\n455. When the bottom is composed of soft mud to any\ngreat depth, it may be protected by enclosing the area with\nsheeting piles, and then filling in the enclosed space with frag-\nments of loose stone. If the mud is very soft, it would be\nadvisable, in the first place, to cover the area with a grillage,\nor with a layer of brushwood laid compactly, to serve as a\nbed for the loose stone, and thus form a more stable and solid\nmass.\n456. Pneumatic Processes.-By this term we understand\nthose methods of obtaining foundations in water, in which\nexternal or internal atmospheric pressure is the active agent.\nThese processes are divided into two classes, viz. the\nplenum pneumatic and the vacuum pneumatic, the former\nterin being applied to the case where the pressure of con-\ndensed air is employed to drive the water out, and the latter,\nwhere the pressure of the atmosphere is employed to drive\nthe water into a vacuum.\n457. Pneumatic Piles.-This appellation has been given\nto cylinders of cast-iron, used in the place of ordinary piles to\nreach a firm subsoil below the bed of a river, suitable for the\ncharacter of the superstructure to rest upon it, which, being\nmade air-tight on the sides and top, but left open at the bot-\ntom, are sunk to the required depth, by rapidly withdrawing\nthe air within them, by methods to be described, and thus\ncausing the water to rush in through the open bottom, remo-\nving in its flow the subsoil in contact with the lower end of\nthe cylinder, and allowing it to sink by its own weight, thus\nbelonging to the vacuum pneumatic class.\nThe cylinders are cast and put together very much in the\nsame manner as ordinary water-pipes; being composed of\nlengths of from six to ten feet, each of which has an interior\nflange at each end, with holes for screw-bolts, by means of\nwhich and a disk of india-rubber, inserted between the con-\nnecting flanges, the joints are made air and water tight.\nDigitized by\nGoogle\nFOUNDATIONS OF STRUCTURES.\n221\nIn me first essays at this mode of foundation, the cylinders\nwere sunk by simply exhausting the internal air, in the ordi-\nnary way, above the water-level. The results, however, were\nnot satisfactory, as the pile sunk very slowly.\nThe next step (Fig. 55) was to connect an air-tight cylin-\ndrical vessel, D, by means of a tube A, with a stop-cock,\nwith the interior of the pile A, and also with the air-pump,\nby another tube leading to the pump from the other end. In\norder to sink the pile, the communication between it and the\nexhaust chamber D was first closed, and that between this\nchamber and air-pump opened. The air was then drawn\nfrom D until a sufficient vacuum was produced, when the\nM\nW\nC\nD\nD\nN\nC\nA\nFig. 55.-Longitudinal section\nof a pneumatic pile A. air-\nlock C, and exhaust vessel\nD.\nA\nB\nB\nA. exhaust tube between A\nand D.\nB, water discharge-tube.\nC, equilibrium tube between\nthe lock and chamber of\nthe pile.\nD, equilibrium tube between\nlock and exterior air.\nM, upper man-hole and\nvalves.\nN, lower man-hole and\n0\nvalves.\nW, windlass and gearing,\nE, concrete underpinning as\npractised at Harlem bridge.\ncommunion with the pump was closed, and that with the pile.\nopened, allowing the air to flow from it into the chamber with\nconsiderable velocity. This sudden disturbance of the equi-\nlibrium between the external and internal pressures on the\nDigitized by Google\n222\nCIVIL ENGINEERING.\npile caused it to descend instantaneously and rapidly, as if\nstruck on the top by a heavy blow, the descent continuing\nfrequently many feet until an equilibrium among the forces\nwas restored.\nWhen the resistance to the further descent of the pile was\nfound to be too great, either from some obstruction met with\nat the bottom, or from the tenacity of the soil itself, the inge-\nnious expedient was hit upon to force the water from within\nthe pile, by pumping air into it, and thus enable workmen\nto descend to the bottom and remove the soil or other ob-\nstruction to the descent. The plan devised for this purpose\nwas to fit another air-tight iron cylindrical vessel C to the\ntop of the pile, of sufficient diameter and height to hold\nseveral workmen, and a windlass W, arranged with an end-\nless rope and buckets for raising the excavated soil into the\nchamber C.\nThe chamber, which has received the name of an air-lock\nfrom its functions, was provided with an upper man-hole M at\ntop for entering the lock, and one N in the bottom for enter-\ning the pile. Each man-hole had two air-tight valves, one\nopening outwards, the other inwards. Two tubes, C and D,\nwith stop-cocks, furnished an air-passage between the air of\nthe pile and that of the lock, and between the latter and the\nexternal air. A syphon-shaped water-discharge tube B, with\na stop-cock, leads from below the level of the inner water\nsurface through the bottom and side of the lock.\nThe operation of sinking the pile by first exhausting the\nair from the exhaust chamber D, was the same in this case\nas in the preceding; the upper valves of either man-hole be-\ning closed, and all communication between the external air\nand the interior of the pile being cut off by means of the\nstop-cocks.\nWhen it became necessary to descend to the bottom of the\npile, to remove the soil or any obstruction, the lower valve of\nthe lower man-hole, with the tube C, were closed; the dis-\ncharge tube, B, left open; and the air forced into the pile,\nby the pumps, through the tube A; the increased pressure\nupon the water surface caused the water to rise in the tube\nB, and flow out at the other end.\nWhen all the water was discharged in this way, the lower\nvalve of the upper man-hole, and tubes A, B, and D were\nclosed; the tube C was then opened, through which the con-\ndensed air in the pile flowed into the lock, until the density\nof the air in it and in the pile became the same; the lower\nvalve of the lower man-hole was then opened, to allow the\nDigitized by\nGoogle\nFOUNDATIONS OF STRUCTURES.\n223\nworkmen to descend, and the excavated soil to be raised into\nthe lock-chamber.\nTo take the excavated material out of the lock, the lower\nman-hole under valve and the tube C are closed, and the tube\nD opened; the condensed air of the lock flows out, and the\nupper man-hole lower valve is opened.\nIn some of the more recent cases of the application of\npneumatic piles, the exhaust-chamber and the discharge\nwater-pipe have been suppressed ; condensed air being alone\nused, both to force the internal water out through the open\nbottom of the pile, to allow the workmen to excavate within,\nand also to produce a scour below the lower end, from the\nrush of the water back into the pile, by allowing the con-\ndensed air to escape rapidly from it. For this purpose\na tube leads from the air-pumps through the side and bottom\nof the air-lock, into the pile, to supply the compressed air.\nAnother pipe with a stop-cock leads through the side and\nbottom of the lock, from the external air to the interior of\nthe pile, through which the condensed air in the pile can be\ndischarged. The upper and lower man-holes have each an\nunder valve. Two equilibrium-tubes with stop-cocks, one\nforming a connection between the interior of the pile and the\nair-lock, the other leading through the side of the lock to the\nexternal air, furnish the means of bringing the air of the\nlock to the same density as that within the pile, or that of\nthe atmosphere.\nTo force out the water, the lower man-hole, the condensed\nair discharge pipe, and the condensed air equilibrium-tube\nare closed, and the air then forced into the pile by the\npumps.\nTo excavate the internal soil, the workmen enter the lock,\nclose the upper man-hole and the upper equilibrium-tube,\nand open the lower equilibrium-tube. This establishes an\nequilibrium between the air of the lock and that of the pile,\nand the workmen can then descend into the pile and exca-\nvate the soil.\nTo remove the excavated soil which has been raised into\nthe lock, the lower man-hole and lower equilibrium-tube are\nclosed, and the upper equilibrium-tube opened, which estab-\nlishes an equilibrium between the air of the lock and that of\nthe: atmosphere. The upper man-hole then being opened,\nthe material in the lock can be carried out.\nTo produce a scour under the pile to allow it to sink, the\nworkmen leave the pile and lock; the condensed air dis-\ncharge-pipe is then opened, and by the rush of the water\nDigitized by Google\n224\nCIVIL ENGINEERING.\ninto the pile all obstruction to the movement of the pile is\nremoved from its lower end.\n458. Double Air-Locks. In some of the more recent ap-\nplications of condensed air in Europe, air-locks in pairs have\nbeen used to save time.\nN\nW\nW\nD\nC\nB\nB\nA\nM\nB\nA\nFig. 56.-Longitudinal section of pile A,\nbell or working-chamber B, and air-locks\nC. D, used at the bridge at Szegedin,\nover the river Theise, Hungary.\nA, water discharge-pipe.\nA\nB, equilibrium tubes of air-lock.\nC, elevation of air-lock.\n0\nD, longitudinal section of air-lock.\nM, hoisting-gear in the bell.\nN, hoisting-gear for air-lock.\nW, counterpoise to compressed air.\n0\nA\nThe arrangements in this case (fig. 56) consist of a work-\ning chamber, B, termed the bell, which is a large air-tight\niron cylindrical vessel fastened to the head of the pile, in\nwhich there is sufficient room for a hoisting apparatus, M,\nand several workmen, to raise the excavated soil to the level\nof the air-locks; of two small air-locks, D and C, which are\ninserted into the bell about two-thirds of their length ; of a\nsyphon-shaped water discharge-pipe A; and of a windlass N\nto raise the excavated soil out of the locks.\nEach lock has a man-hole, with an undervalve on top, for\nDigitized by Google\nFOUNDATIONS OF STRUCTURES.\n225\nentering the lock, and a vertical door on the side for enter-\ning the bell. Each is provided with two sets of equilibrium\nvalves, so arranged that they can be opened by a person from\nwithin the bell or the lock, to establish an equilibrium\nbetween the air in them ; or from the outside of the lock, or\nthe inside, to establish an equilibrium between the external\nair and that of the lock.\nThe air in the pile is condensed by air-pumps in the usual\nway.\nThe hoisting-engine in the bell has its gearing so arranged\nthat the filled buckets can be delivered alternately into the\nlocks, and from there be taken by the gearing of the windlass\nabove. In the example represented by Fig. 56, a weight, W,\nformed of cast-iron bars, resting on brackets cast on the out-\nside of the bell, forms a counter-pressure to the interior con-\ndensed air.\nThe pile is sunk by opening a condensed air-pipe leading to\nthe external air, the lower portions of water discharge-pipe\nhaving been removed, and, with the tools used in excavating,\nplaced within the bell.\nThe descent of the pile at each discharge of the condensed\nair depends upon the nature of the strata met with. In very\ncompact clay the descent will, in some instances, be only a\nfew inches in several discharges; while in sandy or gravelly\nstrata it will descend as much, at times, as twelve or more\nfeet. This is owing to the difference between the effect of\nthe scour, and the resistance offered by the friction on the\nexterior surface of the pile. The resistances in sand and\ngravel being much less than in stiff clay. It has been found,\nin some cases, that two or three feet of a compact clay soil.\nleft within the piles at the bottom would prevent the scour\nand the further descent of the pile when the condensed air\nwas discharged.\nThe piles are placed in position by a suitable hoisting-\ngearing raised upon a strong scaffolding; and in their descent\nare kept in a vertical position by guides placed in connection\nwith the scaffolding. Great precautions have to be taken in\nmanaging the descent of the pile, when it is approaching the\ndepth to which it is wished to sink it, so as to keep the top.\nsurface of each on the same level.\nIn the first applications of pneumatic piles, cast-iron cylin-\nders of small diameters were used; as many being sunk as\nthe resistance of the substratum upon which they rested re-\nquired to support the base of the superstructure. Subse-\nquently the diameters of the cylinders were enlarged, to\n15\nDigitized by\nGoogle\n226\nCIVIL ENGINEERING.\nenable the soil to be excavated from the interior, and be\nreplaced with hydraulic concrete. In some instances the\nconcrete simply rested upon the bottom of the excavation.\nIn others, wooden piles were driven within the cylinder some\ndistance below its lower end, and the concrete thrown in to\nrest upon the heads of the piles.\nHarlem Bridge.-In the Harlem Bridge the piles were six\nfeet in diameter, and cast in lengths of ten feet. The air-\nlock was of the same diameter as the piles, and six feet high;\nthe valves or man-holes twenty inches in diameter. The most\nnoticeable feature in this part of the structure, is the expedient\nof using an underpinning of plank and concrete, to obtain a\nwider spread of the foundation bed, and a greater bearing\nsurface for the superstructure to rest on. For this purpose,\nplank five feet long, three inches wide, and one inch and a\nquarter thick (Fig. 55) were forced under the bottom of the\npile, in sections of three feet wide on opposite sides, and in\nan inclined direction, SO as to gain an additional spread of\nfoundation base of two feet around and beyond the pile.\nThese formed a temporary roofing, from beneath which the\nsoil was rapidly removed, and the excavated space filled in\nwith concrete. Finding great inconvenience in this process,\nfrom the rapidity with which the water and sand came in on\nthe sides, an additional condensation was given to the com-\npressed air of six to ten feet extra water pressure; this was\nfound to counteract the external pressure, so as to allow the\nexcavations to be carried on with facility.\nThe refuse gas-pipes which were used to convey the com-\npressed air down between the bottom of the concrete and the\nunderlying soil, as well as giving it a passage between the\noutside of the pipes and the body of the concrete, were dis-\ntributed through the concrete about a foot apart.\nThe bottom of the foundation in this example was thirty\nfeet below the surface of the river-bed, and fifty below\ntide.\nAn opinion has obtained, from the condition in which the\nhydraulic concrete was found in a pile accidentally fractured,\nin which it had lain for some time, that this material did not\nharden when subjected to the great pressure of the water\nfrom the bottom. A remedy, it is stated, has been found for\nthis by using a portion of fragments of a porous brick in a\ndry state instead of stone, in the composition of the con-\ncrete, as was done in the case of the piers of the bridge at\nSzegedin, in Hungary ; and by inserting in the body of the\nconcrete half-inch gas-pipes, through which the compressed\nDigitized by\nGoogle\nPNEUMATIC PILES.\n227\nair was diffused throughout the mass, as practised at the\nHarlem Bridge by Mr. McAlpine.\nBridge over the Theis s.-The soil below the bed of the\nriver Theiss, at Szegedin, is alluvial, and found in alternate\nstrata of compact clay and sand to an indefinite depth. The\ncurrent throughout its course is sluggish, having a surface velo-\ncity at Szegedin, during the highest stage of the waters, of from\nthree to three and a half feet. The rise and fall of the water\nare both very gradual; the highest stage being about twenty-\nsix feet, and the mean level about sixteen feet. The arched\nribs and other superstructure of the bridge were of wrought-\niron plates. Each pier was formed of two piles, or columns,\nfilled with béton, as above described; and each supporting\none track of the railroad. They were cast in lengths of six\nfeet, and ten feet in diameter, and one inch and one-tenth in\nthickness. The piles were sunk to the depth of about thirty\nfeet below the surface of the bed; and about forty feet below\nthe ordinary low-water level. Their height corresponded to\nthe highest water level, or nearly thirty-three feet above the\npresumed scour of the bed.\nThe interior excavation of the soil was carried down to the\nfirst joint, or six feet from the bottom of the column. To\ncompress the soil below the column to sustain better the su-\nperincumbent weight, twelve piles of pine were driven within\nthe column to a depth of twenty feet below the bottom.\nThe air-locks were each about six feet six inches in height,\nand two feet nine inches in diameter.\nTo provide against the scour of the current, the entire pier\nwas enclosed by a row of square sheeting-piles, driven to the\nlevel of the bottom of the columns, and about two feet from\nthem. The space between these piles and columns, to the\ndepth of ten feet below the bed level, was filled with hydraulic\nconcrete; and the piles were surrounded by loose stone with\na spread of about ten feet from the piles.\nAs large quantities of hydraulic concrete are required for\nfilling the piles, the method pursued in Germany, and as\npractised at the bridge at Szegedin, for mixing the mortar and\nfragments of brick or stone, commends itself for its economy,\nand the thoroughness with which the materials are incor-\nporated. A wooden cylinder about twelve feet long, and four\nfeet diameter, made and hooped like a barrel, and lined with\nsheet-iron, placed in an inclined position of I's to the horizon,\nwas made to revolve by a band set in motion by a steain-en-\ngine, from fifteen to twenty revolutions in a minute. The\ncylinder was fed by a hopper at the upper end, into which\nDigitized by Google\n228\nCIVIL ENGINEERING.\nthe materials were thrown, and they were discharged thor-\noughly mixed and ready for use into wheelbarrows at the\nlower end. It is stated that this simple machine delivered\nfrom 280 to 350 cubic feet in ten hours.\nThe concrete is usually thrown down into the pile from the\nbell or lock. At the bridge at Szegedin the double locks\nwere, alternately, nearly filled with the concrete, and it was\nraked out from them and thrown into the pile; care being\ntaken to work it in well by hand, around the flanges and\njoints.\nFig. 57.\nC\nFig. 57.-Longitudinal section of the cais-\nson and masonry of a pier of a railroad\nbridge over the Scarff, at L'Orient,\nFrance.\nFig. 58.-Plan.\nA, working-chamber for excavating soil.\nB, interior elevation of caisson.\nC, C, elevation of the bells containing the\ndouble air-locks.\nD, D, cylinders for communication between\nbells and working-chamber.\nFig. 58.\nOF\nBridge over the Savannah River on the line of the\nCharleston and Savannah Rail Road. The air-locks on\nthese piles were similar to the Harlem plan. Light was\nadmitted into the air-lock by means of large bulls-eye glasses,\nand thence into the body of the pile in the same way, but\nthis mode was found to be worthless, on account of the mud\nin the bottom of the air-lock which covered the glass. The\nengineer employed a secondary small air lock so that the\nmaterial which was brought into the main one could be dis-\ncharged at any time, and thus the work go on with less\ninterruption, and the bulls-eyes became more serviceable.\nWith the secondary air-lock the work progressed more rapidly;\nthe ratio for a given amount of work being\nTime by old air-lock 14\nTime by new air-lock 5\nBy a fortunate discovery the engineer discovered that the\npressure of the air in the pile was sufficient to force sand from\nDigitized by Google\nPNEUMATIC CAISSONS.\n229\nthe bottom of the pile through a vertical pipe to a height\nabove the surface of the water outside the works. A sort of\ntelescopic tube was attached to the lower end of a pipe so\nthat it could be easily moved downward as the excavation\nprogressed. This greatly facilitated the progress of the work,\nfor it was found that to do a given amount of work the ratio\nwas\nTime by old air-lock\n14\nTime by blowing out sand =\n28\nThis mode of excavation has been adopted to some extent in\nthe caissons of the East River Bridge. This process also\nsecures thorough ventilation. The same plan has also been\nused in the Omaha Bridge and Leavenworth Bridge with\nequally good results.\nIt is sometimes very difficult to keep the tubes vertical.\nWhen they begin to incline efforts should be made immedi-\nately to bring them to an erect position. In some cases\nwedges or blocks placed under the lower side and suddenly\nrelieving the pressure will correct the evil. An ingenious\nmode was adopted by the engineer of the Omaha Bridge. He\nbored several holes through the tubes on the upper side,\nthrough which the compressed air escaped and thus disturbed\nthe soil and relieved the pressure on that side so that it would\nsink faster. Strong levers have been used to pull on the top\nwhilst the tube was sinking, but not with very marked re-\nsults. In at least one very obstinate case, in which the holes\non the upper side, combined with the action of a strong lever,\ndid not alone effect the desired result, a ram was used in\ncombination with the other devices and the erect position was\nquickly secured. The jar produced by the ram whilst the\ntube was sinking seemed to give great effect to the other\ndevices.\nGen. W. S. Smith, who had charge of the construction of\nthe foundations of the Omaha and Leavenworth Bridges, is of\nopinion that a pneumatic caisson, surmounted by masonry, is\ncheaper and better than pneumatic pile piers, but it 18 evident\nthat circumstances may often determine which is preferable\nin any particular case.\n459. Pneumatic Caissons. The application of compressed\nair for laying foundations has been further extended in some\nof the railroad bridges recently constructed in Europe ; by\nusing wrought-iron caissons of sufficient dimensions to serve\nas an envelope, or jacket, for the masonry of an entire pier;\nand gradually sinking the whole to the requisite depth, by\nexcavating the soil within the pier to the desired level.\nDigitized by Google\n230\nCIVIL ENGINEERING.\nThe caissons (Figs. 57, 58) for this purpose were divided\ninto two compartments.\nThe lower A (Fig. 57), which served as a chamber for the\nworkmen, for excavating the soil, was strongly roofed at top,\nwith iron bars and iron sheeting, to bear the weight of the\nmasonry that rested upon it; and was securely buttressed on\nthe sides to resist the inward pressure of the soil on the out-\nside. The upper chamber, B, served as an ordinary caisson,\nfitting closely to the masonry on the sides, and rising suffi-\nciently above it to exclude the water during the construction\nof the masonry: the body of which, composed of béton with\na facing of stone, was gradually raised as the caisson was sunk\nthrough the earth overlying a bed of rock upon which the\npier was finally to rest.\nThe working chamber A was connected with two bells C,\nC, by two vertical iron cylinders D, D (Fig. 57), for each\nbell; these cylinders serving as a communication between the\nworking-chamber and bells, for the passage of the workmen\nfrom one to the other, for raising the excavated soil, and as a\npassage for the compressed air forced in by the air-pumps.\nEach bell contained two air-locks for communicating be-\ntween it and the exterior; and a hoisting gearing for the\nexcavated soil; the filled buckets ascending through one\ncylinder, and the empty ones descending through the other.\nThe lower chamber, the bottom of which was open, was\nkept filled with compressed air of sufficient density to exclude\nthe water, and enable the workmen to excavate the soil.\nThe caisson was gradually sunk, by the weight of the\nsuperincumbent mass, as the soil below was removed.\nSo soon as the rock-bed was reached, the surface was\nthoroughly cleaned off, and levelled under the edges of the\nbottom of the caisson, and the chamber A was gradually\nfilled in with masonry closely up to its roof. Finally the\ncylinders D were removed, and the wells occupied by them\nin the body of the pier, filled with béton.\nAs a matter of interest, on the subject of laying founda-\ntions by means of pneumatic piles and caissons, a few addi-\ntional facts in connection with the examples above cited will\nnot be out of place here.\nBridge over the Scorff. In the example of the bridge at\nL'Orient over the Scorff, the river-bed is a stratum of mud,\nforty-six feet in depth, resting upon a surface of hard schis-\ntoze rock more or less inclined and uneven. The level of\nmean tide is about sixty feet above the rock surface; that of\nthe highest tide seventy feet.\nDigitized by Google\nPNEUMATIC CAISSONS.\n231\nThe caissons used in this example were designed for the\npiers of a stone bridge, and were about forty feet long and\ntwelve feet broad. The bells, or upper working chambers,\nwere ten feet high and eight feet in diameter; the lower\nworking-chamber ten feet high; and the cylinders, for com-\nmunication between them, two feet and a half in diameter.\nThe caissons were built of sheet-iron, in zones decreasing in\nthickness from the top to the bottom; but not having been\nbuttressed within against the pressure of the water, as the\nlower working-chamber was, they yielded and got out of\nshape.\nIn a subsequent structure of nearly the same dimensions,\nfor a railroad bridge at Nantes, the same failure took place,\nand precautions were then taken against it by the insertion of\ncross-stays, which were removed as the masonry was carried\nup. In the caissons used in this case, the bells and air-locks\nwere made larger. Each air-lock had three separate com-\npartments; one for the passage of the workmen which could\ncontain four men; one for the barrows by which the excavated\nsoil was removed, and one for the concrete to fill up the\nlower working chamber, when the excavation was completed.\nSt. Louis Bridge. The caissons for the two piers of this\nbridge differ in no material respect, so that a description of\none will equally apply to the other. The air-chambers are\nnine feet high, the sides being formed of 2-inch plate iron in\nthe larger, and §-inch in the smaller. The air-chamber is\nsimply a huge diving-bell of the full size of the pier. The\niron plates K, K (Fig. 59), forming its roof, are of 1-inch\nthickness. Transversely over this and riveted firmly to it\nare thirteen iron girders L, at intervals of five and a half feet.\nBeneath the roof two massive timber girders C, C (Figs. 59\nand 60), in an opposite direction to the iron ones, divide the\nair-chamber into three nearly equal parts. Communication\nbetween the three divisions is had through openings made for\nthis purpose in the girders. These timber girders are\nintended to rest on the sand and support the roof from below.\nThe sides of the air-chambers are strongly braced with plate\niron brackets O O, stiffened with angle iron. Between the\nbrackets is placed all around the chamber a course of strong\ntimbers, the bottom of which is level with that of the girders,\nintended to rest on the sand and assist in supporting the\nweight. The support given by the timbers, together with the\nbuoyant power of the compressed air in the chamber and the\nfriction of the sand on the sides, is the only means relied on\nto sustain the pier in its gradual descent to the rock.\nDigitized by Google\n232\nCIVIL ENGINEERING.\nFig. 59.\nM\nB\nA\nK\nH\n0\nA\nB\nA\nA/F\n0\nH\nA\nB\nN\nFig. 60.\nMc\nD\nH\nH\nB\nA\nA\nE\nFig. 59-Represents the plan of the caisson of the East pier of the Illinois and St. Louis Bridge.\nFig. 60 represents transverse section of the same. A. air-locks. B, air-chamber. C, timber\ngirders. D, discharge of sand. E, sand-pumps. F, main entrance shaft. G, side shafts. H,\niron sides. I, bracing for H. K, iron deck or roof. L, iron girders, o, strengthening girders.\nDigitized by Google\nPNEUMATIC CAISSONS.\n233\nThe air-locks A A, heretofore as a rule placed above the\nsurface of the water, are located within the roof of the air-\nchamber, and access is had to them through brick wells F, G,\nthus avoiding the inconvenience and delay of adding new\njoints under the locks.\nThe sand-pumps E are placed on the roof of the chamber,\ntheir suction pipes extending through the chamber to the\nsand. The action of these pumps is very simple. A stream\nof water is forced down the pipe B, (Fig. 61), and discharged\nnear the sand into the pipe A, through\nFig. 61.\nthe annular jet C. The jet creates\na vacuum below it, by which the sand\nis drawn into the second pipe, the lower\nend of which is in the sand, and the\nforce of the jet carries it up to the\nmouth of the pump so soon as it passes\nC.\nThe abutments at the east end of the\nbridge (Figs. 61 a and 61 b) differed in\nsome of the details of their construction\nfrom the piers.\nA\nB\nFig. 61 a.\nS\nB\nB\nor\nM\nor\n[\nS\nor\nM\nE\nI\nE\nP\nP\nG\nG\nO\nK\nS\nFig. 61 a, is a part plan and part section of the east abut-\nment of the St. Louis Bridge. Fig. 61 0, is a vertical section\nof the same.\nI, is the main shaft.\nKK, the side shafts.\nMM, iron girders.\n00, the air-locks.\nFig. 61, represents a vertical seo-\nPP, the air-chamber.\ntion of a sand-pump.\nQQ, the timber girdera.\nA, pump barrel.\nRR, the timber deck.\nB, injection pipe.\nSS, the iron sheeting.\nC, annular jet.\nTT, the timber sides of the caisson.\nDigitized by\nGoogle\n234\nCIVIL ENGINEERING.\nFig. 61 b.\nS\nS\nM\nM\nK\nN\nN\n0\n0\nP\nS\nS\nThe main shaft had two air-locks at the lower end, each 8\nfeet in diameter, having about four times the capacity of the\none used in the piers. There were also two other shafts and\nair-locks which were introduced to secure additional safety.\nThis caisson was probably sunk to a greater depth than any\nother in the world by the pneumatic process.\nIt was sunk to the native rock, which was 136 feet below\nhigh-water mark, and 94 below the extreme low-water mark.\nIt was about 110 feet below the surface of the water at the\ntime it was completed. It was extremely hazardous to the\nhealth and even lives of workmen to be kept under the pres-\nsure of over three atmospheres for a long time. The greatest\nsecurity was found in changing them every three or four\nhours.\nCandles burned very readily at this depth and pressure.\nAfter a depth of about 80 feet was reached, the candles were\ninclosed in a strong glass globe, the inside of which communi-\ncated with one of the shafts, and the pressure was regulated\nby a small tube passing through the globe and containing a\ncheck valve. In this way the candles burned in an atmos-\nphere whose pressure was about the same as the external air.\n(See London Engineering, 1870 and 1871.)\nEast River Bridge. The caisson for this bridge is com-\nposed almost wholly of wood. The air-chamber (Fig. 62) is\nnine feet six inches high, the roof being made of fifteen\ncourses of timbers, one foot thick, the lower five (A) being\nDigitized by Google\nCAISSON OF EAST RIVER BRIDGE.\n235\nlaid solid, the upper ten (C) crossing in alternate layers, and\nplaced about a foot apart, the spaces between the timbers being\nfilled with concrete. The sides (B) of the air-chamber are V\nshape, made very solid, nine feet thick at top, and eight inches\nat the bottom, which is heavily shod with iron. Between\nE\nD\nF\nC\nC\nA\nB\nH\nFig. 62 represents a vertical section of the Brooklyn Caisson of the East River Bridge.\nA, lower timber courses of roof, laid solid.\nB, timber sides of air-chamber.\nC, upper timber courses of roof, laid crosswise, and spaces filled in with concrete.\nD, masonry of pier.\nE, dam to prevent water from reaching shafts.\nF, air-shaft and lock.\nG, supply shaft,\nH, excavation shaft.\nI, heavy timber partitions.\nK, air-chamber.\nthe fourth and fifth courses of the roof is laid a sheet of tin,\nwhich is continued down underneath the outside sheathing.\nThe air-chamber is divided into six compartments by heavy\ntimber girders. The shafts through which the heavy material\nis raised extend below the level of the excavation at the\nbottom, and are constantly open; but the compressed air is\nprevented from escaping by a column of water, which is\nmaintained at nearly the same height as the water in the river\nby the pressure of the compressed air. If the pressure of the\nair should be made to greatly exceed that at which it is ordi-\nnarily maintained, it would blow all the water out of the shaft\nDigitized by Google\n236\nCIVIL ENGINEERING.\nand the air would entirely escape, but every necessary pre-\ncaution was used to keep a proper pressure of the air. An ac-\ncident of this kind once took place in the Brooklyn caisson.\nVII.\nCONSTRUCTION OF MASONRY.\n460. Under this head will be comprised whatever relates\nto the manner of determining the forms and dimensions of\nthe most important elementary components of structures of\nmasonry, together with the practical details of their construc-\ntion.\n461. Foundation Courses. As the object of the founda-\ntions is to give greater stability to the structure by diffusing\nits weight over a broad surface, their breadth, or spread,\nshould be proportioned both to the weight of the structure\nand to the resistance offered by the subsoil. In a perfectly\nunyielding soil, like hard rock, there will be no increase of\nstability by augmenting the base of the structure beyond\nwhat is strictly necessary for stability in a lateral direction\nwhereas in a very compressible soil, like soft mud, it would\nbe necessary to make the base of the foundation very broad,\nso that by diffusing the weight over a great surface, the sub-\nsoil may offer sufficient resistance, and any unequal settling\nbe obviated.\n462. The thickness of the foundation course will depend\non the spread; the base is made broader than the top for mo-\ntives of economy. This diminution of the volume (Fig. 63)\nFig. 68-Section of foundation courses and superstructure.\nA, batter.\nB, offsets.\nC, superstructure.\nis made either in steps, termed offsets, or else by giving a\nuniform batter from the base to the top.\nWhen the foundation has to resist only a vertical pressure,\nDigitized by Google\nFOUNDATIONS.\n237\nan equal batter is given to it on each side; but if it has to\nresist also a lateral effort, the spread should be greater on the\nside opposed to this effort, in order to resist its tendency,\nwhich would be to cause a yielding on that side.\n463. The bottom course of the foundations is usually\nformed of the largest sized blocks, roughly dressed off with\nthe hammer; but if the bed is compressible, or the surfaces\nof the blocks are winding, it is preferable to use blocks of a\nsmall size for the bottom course; because these small blocks\ncan be firmly settled, by means of a heavy beetle, into close\ncontact with the bed, which cannot be done with large-sized\nblocks, particularly if their under surface is not perfectly\nplane. The next course above the bottom one should be of\nlarge blocks, to bind in a firm manner the smaller blocks of\nthe bottom course, and to diffuse the weight more uniformly\nover them.\n464. When a foundation for a structure rests on isolated\nsupports, like the pillars, or columns of an edifice, an in\nverted or counter-arch, (Fig. 64,) should connect the top\ncourse of the foundation under the base of each isolated\nsupport, so that the pressure on any two adjacent ones may\nbe distributed over the bed of the foundation in the interval\nbetween them. This precaution is obviously necessary in\ncompressible soils.\nB\nFig. 64.-Section of vertical\nsupports on reversed arches.\nA, reversed arch.\nA\nB, vertical supports.\nC, bed of stone.\nThe reversed arch is also used to give greater breadth to\nthe foundations of a wall with counterforts, and in cases\nwhere an upward pressure from water, or a semi-fluid soil\nrequires to be counteracted. In the former case the reversed\narches are turned under the counterforts; in the latter they\nform the points of support of the walls of the structure.\n465. The angles of the foundations should be formed of\nthe most massive blocks. The courses should be carried up\nuniformly throughout the foundation, to prevent unequal\nsettling in the mass.\nThe stones of the top course of the foundation should be\nDigitized by Google\n238\nCIVIL ENGINEERING.\nsufficiently large to allow the course of the superstructure\nnext above to rest on the exterior stones of the top course.\n466. Hydraulic mortar should be used for the foundations,\nand the upper courses of the structure should not be com-\nmenced until the mortar has partially set throughout the\nentire foundation.\n467. Component parts of Structures of Masonry.\nThese may be divided into several classes, according to the\nefforts they sustain; their forms and dimensions depending on\nthese efforts.\n1st. Those which sustain only their own weight, and are not\nliable to any cross strain upon the blocks of which they are\nformed, as the walls of enclosures.\n2d. Those which, besides their own weight, sustain a verti-\ncal pressure arising from a weight borne by them, as the walls\nof edifices, columns, the piers of arches, &c.\n3d. Those which sustain lateral pressures, and cross strains\nupon the blocks, arising from the action of the earth, water,\nframes or arches.\n4th. Those which sustain a vertical upward, or downward\npressure, and a cross strain, as areas, lintels, &c.\n5th. Those which transfer the pressure they directly receive\nto lateral points of supports, as arches.\n468. Walls of Enclosure. Walls for these purposes\nmay be built of brick, rubble, or dry stone.\nBrick walls are usually built vertically upon the two faces\nand their thickness cannot be less than that of one brick.\nRubble stone walls should never receive a thickness less\nthan 18 inches when the two faces are vertical. Rondelet, in\nhis work l'Art de Bâtir, lays down a rule that the mean\nthickness of both rubble and brick walls should be of their\nheight ; but rubble stone walls are rarely made so thin as this.\nDry stone walls should not-receive a less thickness than two\nfeet. When their height exceeds 12 feet, their mean thick-\nness should not be less than to of the height.\nStone walls are usually built with sloping faces. The batter\nshould not be greater, when the stones are cemented with\nmortar, than one base to six perpendicular, in order that the\nrain may run rapidly from the surface, and that the wall be\nnot too much exposed to decay from the germination of seeds\nwhich may lodge in the joints.\nThe batter is arranged either by building the wall in offsets\nfrom top to bottom, or by a uniform surface. In either case,\nthe thickness of the wall at top should not be less than from\n8 to 12 inches.\nDigitized by Google\nRETAINING WALLS.\n239\nWhen a wall is built with an equal batter on each face, and\nthe thickness at the top and the mean thickness are fixed, the\nbase of the wall, or its thickness at the bottom, will be found\nby subtracting the thickness at top from twice the mean thick-\nness. This rule evidently makes the batter of the wall de-\npend upon the two preceding dimensions.\nThe mean thickness of long walls may be advantageously\ndiminished by placing counterforts, or buttresses, upon each\nface at equal distances along the line of the wall. These are\nspurs of masonry projecting some length from the wall, and\nare firmly connected with it by a suitable bond. The horizon-\ntal section of the counterforts may be rectangular; their\nheight should be the same as that of the wall.\n469. Vertical Supports. These consist of walls, columns,\nor pillars, according to circumstances. The dimensions of\nthe courses of masonry which compose the supports should be\nregulated by the weight borne. If, as in the walls of edifices,\nthe resultant of the efforts sustained by the wall should not\nbe vertical, it must not intersect the base of the wall so near\nthe outer edge, that the stone forming the lowest course would\nbe in danger of being crushed.\nCross walls between the exterior walls, as the partition\nwalls of edifices, should be regarded as counterforts which\nstrengthen the main walls.\n470. Areas. The term area is applied to a mass of\nmasonry, usually of a uniform thickness, laid over the ground\nenclosed by the foundations of walls. It seldom happens that\nareas have an upward pressure to sustain. Whenever this\noccurs, as in the case of the bottoms of cellars in communica-\ntion with a head of water which causes an upward pressure,\nthe thickness and arrangement of the area should be regulated\nto resist this pressure. When the pressure is considerable, an\narea of uniform thickness may not be sufficiently strong to en-\nsure safety; in this case an inverted arch must be used. The\nfoundation of the Capitol building at Albany, N. Y., rests on\nan immense area, which is formed of successive layers of\nbroken stone and concrete, making an area of several feet in\nthickness. The first stones of the piers are very large and\nflat and nearly cover the whole area so that there is little\nor no danger of an upward pressure.\n471. Retaining or Sustaining Walls. These terms are\napplied to walls which sustain a lateral pressure from an\nembankment, or a head of water.\n472. Retaining walls may yield by sliding either along the\nbase of the foundation courses, or along one of the horizontal\nDigitized by\nGoogle\n240\nCIVIL ENGINEERING.\njoints, or by rotation about the exterior edge of some one of\nthe horizontal joints, or the line of fracture may be oblique\nto the base.\n473. The determination of the form and dimensions of a\nretaining wall for an embankment of earth is a problem of\nconsiderable intricacy, and the mathematical solutions which\nhave been given of it have generally been confined to particu-\nlar cases, for which approximate results alone have been ob-\ntained; these, however, present sufficient accuracy for all\npractical purposes within the limits to which the solutions are\napplicable. Among the many solutions of this problem, those\ngiven by M. Poncelet, of the Corps of French Military En-\ngineers, in a Memoir on this subject, published in the Mé-\nmorial de C Officier du Génie, No. 10, present a degree of re-\nsearch and completeness which peculiarly characterize all\nthe writings of this gentleman, and have given to his produc-\ntions a claim to the fullest confidence of practical men.\nThe following formula, applicable to cases of rotation about\nthe exterior edge of the lowest horizontal joint, are taken from\nthe memoir above cited.\nCalling H, the height BC (Fig. 65) of a wall of uniform\nthickness, the face and back being vertical.\nG\n(!h)\nP\nD\nST\nFig. 65.-Represents a section 0 of a retaining wall\nwith the face and back vertical.\nN\nP, section of the embankment above the wall.\n5\no\nA\nB\nh, the mean height CG of the embankment, retained by the\nwall, above the top of the wall.\nc, the berm DI, or distance between the foot of the embank-\nment and the outer edge of the top of the wall.\na, the angle between the line of the natural slope BN of the\nearth of the embankment and the vertical BG.\nf\n=cot. a, the co-efficient of friction of the earth of the em-\nbankment.\nw, the weight of a cubic foot of the earth.\nDigitized by Google\nRETAINING WALLS.\n241\nw', the weight of a cubic foot of the masonry of the wall.\n#\nb, the base AB, or thickness of the wall at bottom.\nThen,\nb=0.74 tan. 0.56c tan. a(^\nThe above formula gives the value of the base of a wall\nwith vertical faces, within a near degree of approximation to\nthe true result, only when the values of the quantities which\nenter into it are confined within certain limits. These limits\nare as follows: for h, between 0 and H; c, between 0 and\nJH; f, between 0.6 and 1.4, which correspond to values of a\nof 70° and 35°, being in the one case the angle which the line\nof the natural slope of very fine dry sand assumes, and in the\nother of heavy clayey earth; and for w, between w', and fw'.\nBesides these limits, the formula also rests on the assumption\nthat the moment of the pressure against the wall is 1.912\ntimes the moment of strict equilibrium between it and the\nwall. This excess of stability given to the wall supposes an\nexcess of resistance above the pressure against it equal to\nwhat obtains in the retainiug walls of Vauban, for fortifica-\ntions which have now stood the test of more than a century\nwith security.\n474. Having by the preceding formula calculated the\nvalue of b for a vertical wall, the base b' of another wall, pre-\nsenting equal stability, but having a batter on the face, the\nback being vertical, which is the usual form of the cross sec-\nD\nFlg. 66-Represents & section 0 of a retaining wall with\na sloping face AD.\nP, section of the embankment,\no\nA\ntion of retaining walls, can be calculated from the following\nnotation and formula.\nCalling (Fig. 66) b' the base of the sloping wall.\n16\nDigitized by Google\n242\nCIVIL ENGINEERING.\nAd\nn\n=\nDd\nthe batter, or ratio of the base of the slope to the.\nperpendicular, or height of the wall.\nThen,\n6'= b + &nH.\n475. With regard to sliding either on the base of the\nfoundation courses, or on the bed of any of the horizontal\njoints of the wall, M. Poncelet shows, in the memoir cited,\nby a comparison of the results obtained from calculations\nmade under the suppositions both of rotation and sliding,\nthat no danger need be apprehended from the latter, when\nthe dimensions are calculated to conform to the former, so\nlong as the limits of h are taken between 0 and 4H ; particu-\nlarly if the precantion be taken to allow the mortar of the\nmasonry to set firmly before forming the embankment behind\nthe wall.\n476. Mr. C.S. Constable read a paper before the American\nSociety of Civil Engineers in New York, in 1873, in which he\nshowed by means of a model and experiments that the prism\nwhich produces the maximum thrust or pressure was less than\nGCD. The wall, when composed of blocks, will not turn\nover bodily about the outer edge, but there will be a broken\nline of fracture as shown by the heavy line in (Fig. 67), the\ngeneral direction of which corresponds to the natural slope\nG\nB\nD\nFig. 67-0 G is the back of the wall.\nC E represents the natural slope of the\nearth. G CD the prism which gives\nI\nthe maximum pressure. AB a line\nparallel to o D.\nE\nA\n:\nC\nof the earth, although the two have not necessarily the same\ndirection. This being the case, it is evident that a portion of\nthe prism GCD will not be active in overturning the wall, but\non the other hand will prevent, or tend to prevent, a portion\nof the back of the wall from moving with the main part.\nAs a result of this investigation it is evident that the for-\nmulas which are founded on the supposition that the whole of\nthe prism GCD is active in producing a rotation of the wall\nDigitized by Google\nRETAINING WALLS.\n243\nerr on the safe side, and give an unnecessarily large margin\nfor safety.\nHis experiments also showed that the wall might start to\nfall but not fall, and that it required considerable jarring to\ncause it to fall. When the movement began the face did not\nremain plane but became curved. This shows why in prac-\ntice walls have assumed a curved face, and yet stand securely\nfor many years. After a slight movement has taken place,\nthe pressure due to the earth is slightly relieved, and the\nwhole mass takes up a new position of equilibrium, until\nfinally the earth nearly supports itself.\n477. Form of Section of Retaining Walls. The more\nusual form of cross section is that in which the back of the\nwall is built vertically, and the face with a batter varying\nbetween one base to six perpendicular, and one base to\ntwenty-four perpendicular. The former limit having been\nadopted, for the reasons already assigned, to secure the joints\nfrom the effects of weather; and the latter because a wall\nhaving a face more nearly vertical is liable in time to yield\nto the effects of the pressure, and lean forward.\n478. The most advantageous form of cross section for\neconomy of masonry is the one (Fig. 68) termed a leaning\nP\nD\nC\nFig. 68-Represents a section o of & leaning retaining\nwall with a sloping face AD and the back BC coun-\nter-sloped.\no\nretaining wall. The counter slope, or reversed batter of the\nback of the wall, should not be less than six perpendicular to\none base. In this case strength requires that the perpendi-\ncular let fall from the centre of gravity of the section upon\nthe base, should fall so far within the inner edge of the base,\nthat the stone of the bottom course of the foundation may\npresent sufficient surface to bear the pressure upon it.\n479. Walls with a curved batter (Fig. 69) both upon the\nface and back, have been used in England, by some engineers,\nfor quays. They present no peculiar advantages in strength\nDigitized by Google\n244\nCIVIL ENGINEERING.\nover walls with plane faces and backs, and require particular\ncare in arranging the bond, and fitting the stones or bricks\nof the face.\nD\nFig. 69-Represents a section A of a wall with a\ncurved face and back, and an elevation B of the\ncounterforts.\nC, water.\nD, embankment behind the wall.\na, fender beams of timber.\n480. Measures for increasing the Strength of Retain-\ning Walls. These consist in the addition of counterforts,\nin the use of relieving arches, and in the modes of forming\nthe embankment.\n481. Counterforts give additional strength to a retaining\nwall in several ways. By dividing the whole line of the wall\ninto shorter lengths between each pair of counterforts, they\nprevent the horizontal courses of the wall from yielding to the\npressure of the earth, and bulging outward between the ex-\ntremities of the walls ; by receiving the pressure of the earth\non the back of the counterfort, instead of on the correspond-\ning portion of the back of the wall, its effect in producing\nrotation about the exterior foot of the wall is diminished; the\nsides of the counterforts acting as abutments to the mass of\nearth between them may, in the case of sand, or like soil,\ncause the portion of the wall between the counterforts to be\nrelieved from a part of the pressure of the earth behind it,\nowing to the manner in which the particles of sand become\nbuttressed against each other when confined laterally, and\noffer a resistance to pressure.\n482. The horizontal section of counterforts may be either\nrectangular or trapezoidal. When placed against the back of\na wall, the rectangular form offers the greater stability in the\ncase of rotation, and is more economical in construction; the\ntrapezoidal form gives a broader and therefore a firmer con-\nDigitized by Google\nRETAINING WALLS.\n245\nnection between the wall and counterfort than the rectangular,\na point of some consideration where, from the character of\nthe materials, the strength of this connection must mainly de-\npend upon the strength of the mortar used for the masonry.\n483. Counterforts have been chiefly used by military engi-\nneers for the retaining walls of fortifications, termed revête-\nments. In regulating their form and dimensions, the practice\nof Vauban has generally been followed, which is to make the\nhorizontal section of the counterfort trapezoidal, making the\nheight of the trapezoid ef (Fig. 70), which corresponds to the\nC\nB\nFig. 70-Represents a section A and plan D of a wall, and an\nelevation B, and plan E of a trapesoidal counterfort.\nD\nb\nlength of the counterfort, two-tenths of the height of the\nwall added to two feet, the base of the trapezoid ab corre-\nsponding to the junction of the counterfort and back of the\nwall, one-tenth of the height added to two feet, and the side\ncd which corresponds to the back of the counterfort equal to\ntwo-thirds of the base ab. The counterforts are placed from\n15 to 18 feet from centre to centre along the back of the\nwall, according to the strength required.\n484. In adding counterforts to walls, the practice has ge-\nnerally been to regard them only as giving additional stability\nto the wali, and not as a means of diminishing its volume of\nmasonry of which the addition of the counterforts ought to\nadmit.\n485. Relieving Arches are so termed from their preventing\na portion of the embankment from resting against the back\nDigitized by Google\n246\nCIVIL ENGINEERING.\nof the wall, and thus relieving it from a part of the pressure.\nThey consist (Fig. 71) of one or more tiers of brick arches\nM\nN\nFig. 71-Bepresents a section M and an eleva-\ntion N ofa wall and relieving arches in three\ntiers.\nA, section of the wall.\na c, a sections of the arches through their\ncrowns.\nd, d, interior elevations of counterforts serving\nas piers of the arohes.\ne, e, interior end elevations of arches.\nbuilt upon counterforts, which act as the piers of the arches.\nIn arranging a combination of relieving arches and their\npiers, the latter, like ordinary counterforts, are placed about\n18 feet apart between their centre lines; their length should\nbe SO regulated that the earth behind them resting on the\narches, and falling under them with the natural slope, shall\nnot reach the wall between the arch and the foot of the back\nof the wall below the arch. The thickness of the arches, as\nwell as that of the counterforts, will depend upon the weight\nwhich the arches sustain. The dimensions of the wall will\nbe regulated by the decreased pressure against it caused by\nthe action of the arches, and the point at which this pressure\nacts.\n486. Whenever it becomes necessary to form the embank-\nment before the mortar of the retaining wall has had time to\nset firmly, the portion of the embankment next to the wall\nmay be of a compact binding earth placed in layers inclining\ndownward from the back of the wall, and well rammed ; or\nof a stiff mortar made either of clay, or sand, with about 10th\nin bulk of lime. Instead of bringing the embankment di-\nrectly against the back of the wall, dry stone, or fascines may\nbe laid in to a suitable depth back from the wall for the same\npurpose. The precaution, however, of allowing the mortar\nto set firmly before forming the embankment, should never be\nomitted except in cases of extreme urgency, and then the\nbond of the masonry should be arranged with peculiar care,\nto prevent disjunction along any of the horizontal joints.\n487. Walls built to sustain a pressure of water should be\nregulated in form and dimensions like the retaining walls of\nembankments. The buoyant effort of the water must be\ntaken into account in determining the dimensions of the\nwall, whenever the masonry is so placed as to be partially\nimmersed in the water.\nDigitized by\nGoogle\nARCHES.\n247\n488. Heavy walls, and even those of ordinary dimensions,\nwhen exposed to moisture, should be laid in hydraulic mortar.\nGrout has been tried in laying heavy rubble walls, but with\ndecided want of success, the successive drenchings of the\nstone causing the sand to separate from the lime, leaving\nwhen dry a weak porous mortar. When the stone is laid in\nfull mortar, grout may be used with advantage over each\ncourse, to fill any voids left in the mass.\n489. Beton has frequently been used as a filling between\nthe back and facing of water-tight walls; it presents no ad-\nvantage over walls of cut, or rubble stone laid in hydraulic\nmortar, and causes unequal settling in the parts, unless great\ncare is taken in the construction.\n490. When a weight, arising from a mass of masonry or\nearth, rests upon two or more isolated supports, that portion\nof it which is distributed over the space, or bearing between\nany two of the supports, may be borne by a block of stone,\ntermed a lintel, laid horizontally upon the supports, by a\ncombination of blocks termed a plate-bande, so arranged as to\nresist, without disjunction, the pressure upon them; or by an\narch.\n491. Lintel. Owing to the slight resistance of stone to a\ncross strain, and to shocks, lintels of ordinary dimensions\ncannot be used alone with safety, for bearings over five or\nsix feet. For wider bearings, a slight brick arch is thrown\nacross the bearing above the lintel, and thus relieves it from\nthe pressure of the parts above.\n492. Plate-bande. The plate-bande is a combination of\nblocks cut in the form of truncated wedges. From the form\nof the blocks, the pressure thrown upon them causes a lateral\npressure which must be sustained either by the supports, or\nby some other arrangement (Fig. 72).\nFig. 79-Represents a cross\nsection of a plate-bande,\nshowing the manner in\nwhich the voussoirs A, A\nand B are cut and con-\nnected by metal cramps.\nab, tie of wronght iron for\nthe plate-bande fastened\nto the bolts cd, let into\nthe piers of the plate-\nbande.\nThe plate-bande should be used only for narrow bearings,\nas the upper edges of the blocks at the acute angles are liable\nto splinter from the pressure. If the bearing exceeds 10\nfeet, the plate-bande should be relieved from the pressure\nDigitized by\nGoogle\n248\nCIVIL ENGINEERING.\nby a brick arch above it. Additional means of strengthening\nthe plate-bande are sometimes used by forming a broken joint\nbetween the blocks, or by a projection made on the face of\none block to fit into a corresponding indent in the adjacent\none, or by connecting the blocks with iron bolts.\nWhen, from any cause, the supports cannot be made suffi-\nciently strong to resist the lateral pressure of the plate-bande,\nthe extreme blocks must be united by an iron bar, termed a\ntie, suitably arranged to keep the blocks from yielding.\n493. Arches. The arch is a combination of wedge-shaped\nblocks, termed arch stones, or voussoirs, truncated towards\nthe angle of the wedges by a curved surface which is usually\nnormal to the surfaces of the joints between the blocks.\nThis inferior surface of the arch is termed the soffit. The\nupper, or outer surface of the arch is termed the back\n(Fig. 73).\nM\nN\nf\nB\ne\nme\nn\nc\ne\ne\ne\nB\ne\nB\ne\na\nd\n6\n0\ng\ng\ny\ng\nP\ne\nFig. 73-Represents an elevation M of the head of a right cylindrical arch,\nand a section N through the crown of the arch A, with an elevation B of\nthe soffit and the face C of the abutment.\nab, span of the arch.\ndc, rise.\nacb, curve of the intrados.\ne, e, voussoirs forming ring courses of heads.\nf, key stone.\ng, cushion stone of abutment.\nmn, crown of the arch.\nop, springing line.\n494. The extreme blocks of the arch rest against lateral\nsupports, termed abutments, which sustain both the vertical\npressure arising from the weight of the arch stones, and the\nweight of whatever lies upon them ; also the lateral pressure\ncaused by the action of the arch.\n495. In a range, or series of arches placed side by side,\nthe extreme supports are termed the abutments, the interme-\ndiate supports which sustain the intermediate arches and the\nhalves of the two extreme ones are termed piers. When the\nsize of the arches is the same, and their springing lines are\nDigitized by Google\nARCHES.\n249\nin the same horizontal plane, the piers receive no other pres-\nsure but that arising from the weight of the arches.\n496. Arches are classified, from the form of the soffit, into\ncylindrical, conical, conoidal, warped, annular, groined, clois-\ntered, and domes. They are also termed right, oblique, or\naskew, and rampant, from their direction with respect to a\nvertical, or horizontal plane.\n497. Cylindrical, groined and cloistered arches are formed by\nthe intersections of two or more cylindrical arches. The\nspan of the arches may be different, but the rise is the same\nin each. The axes of the cylinders will be in the same plane,\nand they may intersect under any angle.\nThe groined arch (Fig. 74) is formed by removing those\nM\nFig. 74-Represents the plan of the soffit\nand the right sections M and N of the cyl-\nn\ninders forming a groined arch.\naa, pillars supporting the arch.\nbc, groins of the soffit\nB\nom, mn, edges of coursing joints.\nA, key-stone of the two arches formed of\nm\none block.\nB, B, groin stones of one block below the\nkey-stone forming a part of each arch.\nportions of each cylinder which lie under the other and be-\ntween their common curves of intersection; thus forming a\nprojecting, or salient edge on the soffit along these curves.\nThe cloistered arch (Fig. 75) is formed by removing those\nportions of each cylinder which are above the other and ex-\nterior to their common intersection, forming thus re-entering\nangles along the same lines.\n498. The planes of the joints in both of these arches are\nplaced in the same manner as in the simple cylindrical arch.\nThe inner edges of the corresponding course of voussoirs in\neach arch are placed in the same plane parallel to that of the\naxes of the cylinders. The portions of the soffit in each cyl-\ninder, corresponding to each course of voussoirs, which form\neither the groin in the one case, or the re-entering angle in\nthe other, are cut from a single stone, to present no joint\nalong the common intersection of the arches, and to give\nthem a firmer bond.\nDigitized by\nGoogle\n250\nCIVIL ENGINEERING.\nM\nA\n0\nm\n11\n0\nFig. 75-Represents a section M of the vonssoirs and an\nN\nelevation of the soffit of & cloistered arch with a plan\nN of the soffit.\nB\nA, A, voussoirs.\nmn, edge of coursing joint.\no, o, edges of heading joints.\nk\nB, B, abutments of the arches.\nacb, curve of the groin.\nB\ne\nC, C, groin stones of one block.\nB\nB\n499. When the spans at the two ends of an arch are un-'\nequal, but the rise is the same, then the soffit of the arch is\nmade of a conoidal surface. The curves of right section at\nthe two ends may be of any figure, but are usually taken\nfrom some variety of the elliptical, or oval curves. The\nsoffit is formed by moving a line upon the two curves, and\nparallel to the plane containing their spans\nThe conoidal arch belongs to the class with warped soffits.\nA variety of warped surfaces may be used for soffits accord-\ning to circumstances; the joints and the bond depending on\nthe generation of the surface.\n500. In arranging the joints in conoidal arches, the heading\njoints are contained in planes perpendicular to the axis of\nthe arch. The coursing joints are also formed of plane sur-\nfaces, so arranged that the portion of the joint corresponding\nto each block is formed by a plane normal to the conoid at\nthe middle point of the lower edge of the block. In this way\nthe joints of the string course will not be formed of contin-\nuous surfaces. To make them so, it would be necessary to\ngive them the form of warped surfaces, which present more\ndifficulty in their mechanical execution, and not sufficient ad-\nvantages over the method just explained to compensate for\nhaving them continuous.\n501. The annular arch is formed by revolving the plane of\na semi-circle, or semi-oval, or other curve, about a line drawn\nDigitized by Google\nARCHES.\n251\nwithout the figure and parallel to the rise of the arch (Fig.\n76). One series of joints in this arch will be formed by\nconical surfaces passing through the inner edges of the\nstones which correspond to the string courses; and the other\nseries will be planes passed through the axis about which the\nsemi-circle is revolved. This last series should break joints\nwith each other.\nC\nFig. 76-Repro-\nsents a plan M of\nthe abutments A\nand B, and the\nsoffit C of an an-\nnular arch.\nN, right section\nof the arch.\na, position of\nvertical axis\nsround which\nthe section N is\nrevolved.\n502. The soffit of a dome is usually formed by revolving\nthe quadrant of one of the usual curves of cylindrical arches\naround the rise of the curve; or else by revolving the semi-\ncurve about the line of the span, and taking the half of the\nsurface thus generated for the soffit of the dome. In the\nfirst of these cases the horizontal section of the dome at the\nspringing line will be a circle; in the second the entire curve\nof the semi-curve by which the soffit is generated. The plan\nof domes inay also be of regular polygonal figures, in which\ncase the soffit will be a polygonal-cloistered arch formed of\nequal sections of cylinders (Fig. 77). The joints and the\nbond are determined in the same manner as in other arches.\nI\n503. The voussoirs which form the ring course of the\nheads, in ordinary cylindrical arches, are usually terminated\nby plane surfaces at top and on the sides, for the purpose of\nconnecting them with the horizontal courses of the head which\nDigitized by Google\n252\nCIVIL ENGINEERING.\nA\nA\nTh\nB\nFig. 77-Represents a section M of the voussoirs and\nan elevation of the soffit, with a plan N of the soffit of\nan octagonal-cloistered dome.\nThe letters refer to the same parts as in Fig. 75.\nB\nlie above and on each side of the arch (Figs. 78 and 79).\nThis connection may be arranged in a variety of ways. The two\npoints to be kept in view are, to form a good bond between\nthe voussoirs and horizontal courses, and to give a pleasing\nFig. 78-Represents a manner of connecting the voussoirs and\nhorizontal courses in an oval arch.\no, a are examples of voussoirs with elbow joints.\n0\nFig. 79-Represents a mode of arranging the voussoirs and\nhorizontal courses in flat segment arches.\narchitectural effect by the arrangement. This connection\nshould always give a symmetrical appearance to the halves of\nthe structure on each side of the crown. To effect these\nseveral objects it may be necessary, in cases of oval arches, to\nmake the breadth of the voussoirs unequal, diminishing\nusually those near the springing lines.\n504. In small arches the voussoirs near the springing line\nare SO cut as to form a part also of the horizontal course (see\nFig. 78), forming what is termed an elbow joint. This plan\nis objectionable, both because there is a waste of material in\nforming a joint of this kind, and the stone is liable to crack\nwhen the arch settles.\n505. The forms and dimensions of the voussoirs should be\ndetermined both by geometrical drawings and numerical\nDigitized by Google\nARCHES.\n253\ncalculation, whenever the arch is important, or presents any\ncomplication of form. The drawings should, in the first place,\nbe made to a scale sufficiently large to determine the parts\nwith accuracy, and from these, pattern drawings giving the\nparts in their true size may be made for the use of the mason.\nTo make the pattern drawings, the side of a vertical wall, or\na firm horizontal area may be prepared, with a thin coating\nof mortar, to receive a thin smooth coat of plaster of Paris.\nThe drawing may be made on this surface in the usual man-\nner, by describing the curve either by points from its calcu-\nlated abscissas and ordinates, or, where it is formed of circular\narcs, by using the ordinary instrument for describing such\narcs when the centres fall within the limits of the prepared\nsurface. In ovals the positions of the extreme radii should be\naccurately drawn either from calculation, or construction.\nTo construct the intermediate normals, whenever the centres\nof the arcs do not fall on the surface, an arc with a chord of\nabout one foot may be set off on each side of the point\nthrough which the normal is to be drawn, and the chord of\nthe whole arc, thus set off, be bisected by a perpendicular.\nThis construction will generally give a sufficiently accurate\npractical result for elliptical and other curves of a large size.\n506. The masonry of arches may be either of dressed stone,\nrubble, or brick.\nIn wide spans, particularly for oval and other flat arches,\ncut stone should alone be used. The joints should be dressed\nwith extreme accuracy. As the voussoirs have to be sup-\nported by a framing of timber, termed a centre, until the\narch is completed, and as this structure is liable to yield, both\nfrom the elasticity of the materials and the number of joints\nin the frame, an allowance for the settling in the arch, arising\nfrom these causes, is sometimes made, in cutting the joints of\nthe voussoirs false, that is, not according to the true position\nof the normal, but from the supposed position the joints will\ntake when the arch has settled thoroughly. The object of\nthis is to bring the surfaces of the joints into perfect contact\nwhen the arch has assumed its permanent state of equilibrium,\nand thus prevent the voussoirs from breaking by unequal\npressures on their coursing joints. This is a problem of con-\nsiderable difficulty, and it will generally be better to cut the\njoints true, and guard against settling and its effects by giving\ngreat stiffness to the centres, and by placing between the\njoints of those voussoirs, where the principal movement takes\nplace in arches, sheets of lead suitably hammered to fit the\njoint and yield to any pressure.\nDigitized by Google\n254\nCIVIL ENGINEERING.\n507. The manner of laying the voussoirs demands peculiar\ncare, particularly in those which form the heads of the arch.\nThe positions of the inner edges of the voussoirs are deter-\nmined by fixed lines, marked on the abutments, or some\nother immovable object, and the calculated distances of the\nedges from these lines. These distances can be readily set\noff by means of the level and plumb-line. The angle of each\njoint can be fixed by a quadrant of a circle, connected with a\nplumb-line, on which the position of each joint is marked.\n508. Brick may be used alone, or in combination with cut\nstone, for arches of considerable size. When the thickness of\na brick arch exceeds a brick and a half, the bond from the\nsoffit outward presents some difficulties. If the bricks are\nlaid in concentric layers, or shells, a continuous joint will be\nformed parallel to the surface of the soffit, which will proba-\nbly yield when the arch settles, causing the shells to separate\n(Fig. 80). If the bricks are laid like ordinary string courses,\nN\nFig. 80-Represents an end\nview, M, of a brick arch\nbuilt with blocks, C, and\nshells, A and B.\nN, represents the manner\nof arranging the courses\nof brick forming the\ncrown of the arch.\nforming continuous joints from the soffit outward, these joints,\nfrom the form of the bricks, will be very open at the back,\nand, from the yielding of the mortar, the arch will be liable\nto injury in settling from this cause. To obviate both of these\ndefects, the arch may be built partly by the first plan and\npartly by the second, or as it is termed in shells and blocks.\nThe crown, or key of the arch should be laid in a block, in-\ncreasing the breadth of the block by two bricks for each\ncourse from the soffit outward. These bricks should be laid\nin hydraulic cement, and be well wedged with pieces of thin\nhard slate between the joints.\n509. When a combination of brick and cut stone is used, the\nDigitized by\nGoogle\nARCHES.\n255\nring courses of the heads, with some intermediate ring courses,\nthe bottom string courses, the keystone course, and a few in-\ntermediate string courses, are made of cut stone (Fig. 81), the\nD\nFig. 81 Repre-\nsents a cross seo-\ntion of a stone\nsegment arch,\na\ncapped with\nbrick and beton.\nA. stone voussoirs.\nB and D, brick and\nbeton capping.\nC, abutment.\nE, cushion stone.\nintermediate spaces being filled in with brick. The brick\nportions of the soffit may, if necessary, be thrown within the\nstone portions, forming plain caissons.\n510. The centres of large arches should not be struck until\nthe whole of the mortar has set firmly. After the centres\nare struck, the arch is allowed to assume its permanent state\nof equilibrium, before any of the superstructure is laid.\n511. When the heads of the arch form a part of an exterior\nsurface, as the faces of a wall, or the outer portions of a\nbridge, the voussoirs of the head ring courses are connected\nwith the horizontal courses, as has been explained ; the top\nsurface of the voussoirs of the intermediate ring courses are\nusually left in a roughly dressed state to receive the courses\nof masonry termed the capping (see Fig. 81), which rests\nupon the arch between the walls of the head. Before laying\nthe capping, the joints of the voussoirs on the back of the\narch should be carefully examined, and, wherever they are\nfound to be open from the settling of the arch, they should\nbe filled up with soft-tempered mortar, and by driving in\npieces of hard slate. The capping may be variously formed\nof rubble, brick, or beton. Where the arches are exposed to\nthe filtration of rain water, as in those used for bridges and\nthe casemates of fortifications, the capping should be of beton\nlaid in layers, and well rammed, with the usual precautions\nfor obtaining a solid homogeneous mass.\n512. The difficulty of forming water-tight cappings of\nmasonry has led engineers, within a few years back, to try a\ncoating of asphalte upon the surface of beton. The surface\nDigitized by Google\n256\nCIVIL ENGINEERING.\nof the beton capping is made uniform and smooth by the\ntrowel, or float, and the mass is allowed to become thoroughly\ndry before the asphalte is laid. Asphalte is usually laid on in\ntwo layers. Before applying the first, the surface of the\nbeton should be thoroughly cleansed of dust, and receive a\ncoating of mineral tar applied hot with a swab. This appli-\ncation of hot mineral tar is said to prevent the formation of\nair bubbles in the layers of asphalte which, when present,\npermit the water to percolate through the masonry. The first\nlayer of asphalte is laid on in squares, or thin blocks, care\nbeing taken to form a perfect union between the edges of\nthe squares by pouring the hot liquid along them in forming\neach new one. The surface of the first layer is made uni-\nform, and rubbed until it becomes smooth and hard with an\nordinary wooden float. In laying the second layer, the same\nprecautions are taken as for the first, the squares breaking\njoints with those of the first. Fine sand is strewed over the\nsurface of the top layer, and pressed into the asphalte before\nit becomes hard.\nCoverings of asphalte have been used both in Europe and\nin our military structures for some years back with decided\nsuccess. There have been failures, in some instances, arising\nin all probability either from using a bad material, or from\nsome fault of workmanship.\n513. In a range of arches, like those of bridges, or case-\nmates, the capping of each arch is shaped with two inclined\nsurfaces, like a common roof. The bottoms of these surfaces,\nby their junction, form gutters where the water collects, and\nfrom which it is conveyed off in conduits, formed either of\niron pipes, or of vertical openings made through the masonry\nof the piers which communicate with horizontal covered\ndrains. A small arch of sufficient width to admit a man to\nexamine its interior, or a square culvert, is formed over the\ngutter. When the spaces between the head walls above the\ncapping is filled in with earth, a series of drains running\nfrom the top, or ridge of the capping, and leading into the\nmain gutter drain, should be formed of brick. They may be\nbest made by using dry brick laid flat, and with intervals left\nfor the drains, these being covered by other courses of dry\nbrick with the joints in some degree open. The earth is filled\nin upon the upper course of bricks, which should be 80 laid\nas to form a uniform surface.\n514. From observations taken on the manner in which\nlarge cylindrical arches settle, and experiments made on a\nsmall scale, it appears that in all cases of arches where the\nDigitized by\nGoogle\nARCHES.\n257\nrise is equal to or less than the half span they yield (Fig. 82)\nby the crown of the arch falling inward, and thrusting out-\nward the lower portions, presenting five joints of rupture,\none at the keystone, one on each side of it which limit the\nportions that fall inward, and one on each side near the\nspringing lines which limit the parts thrust outward. In\nFig. 89-Represents the manner in which flat arches\nyield by rupture.\no, joint of rupture at the keystone.\nm, m, joints of rupture below the keystone.\nn, n, joints of rupture at springing lines.\npointed arches, or those in which the rise is greater than the\nhalf span, the tendency to yielding is, in some cases, differ-\nent; here the lower parts may fall inward (Fig. 83), and\nthrust upward and outward the parts near the crown.\nFig. 88-Represents the manner in which pointed\narches may yield.\nThe letters refer to same points as in Fig. 82.\nn\nThe angle which a line drawn from the centre of the arch\nto the joint of rupture makes with a vertical line is called\nthe angle of rupture. This term is also used when the arch\nis stable, or when there is no joint of rupture, in which case\nit refers to that point about which there is the greatest ten-\ndency to rotate. It may also be defined as including that\nportion of the arch near the crown which will cause the\ngreatest thrust or horizontal pressure at the crown. This\nthrust tends to crush the voussoirs at the crown, and also to\noverturn. the abutments about some outer joint. The thrust\nis rarely sufficient to crush ordinary stone. The most com-\nmon mode of failure is by rupturing, or turning about a joint.\nIn very thick arches rupture may take place from slipping\non the joints.\n515. The joints of rupture below the keystone vary in\narches of different thicknesses and forms, and in the same\narch with the weight it sustains.\n516. The problem for finding the joints of rupture by cal-\nculation, and the consequent thickness of the abutments ne-\ncessary to preserve the arch from yielding, has been solved\n17\nDigitized by Google\n258\nCIVIL ENGINEERING.\nby a number of writers on the theory of the equilibrium of\narches, and tables for effecting the necessary numerical cal-\nculations have been drawn up from their results to abridge\nthe labor in each case.\n517. In cloistered arches the abutments may be less than\nin an ordinary cylindrical arch of the same length; and in\ngroined arches, in calculating the resistance offered by the\nabutments, the counter resistance offered by the weight of\none portion in resisting the thrust of the other, must be taken\ninto consideration.\n518. When abutments, as in the case of edifices, require to\nbe of considerable height, and therefore would demand ex-\ntraordinary thickness, if used alone to sustain the thrust of\nthe arch, they may be strengthened by the addition to their\nweight made in carrying them up above the imposts like the\nbattlements and pinnacles in Gothic architecture; by adding\nto them ordinary, full, or arched buttresses, termed flying\nbuttresses or by using ties of iron connecting the voussoirs\nnear the joints of rupture below the keystone. Tie-rods are\nevidently the safest expedient. The employment of these\ndifferent expedients, their forms and dimensions, will depend\non the character of the structure and the kind of arch. The\niron tie, for example, cannot be hidden from view except in\nthe plate-bande, or in very flat segment arches, and wherever\nits appearance would be unsightly some other expedient must\nbe tried.\nCircular rings of iron have been used to strengthen the\nabutments of domes, by confining the lower courses of the\ndome and relieving the abutment from the thrust.\n519. In a range of arches of unequal size, the piers will\nhave to sustain a lateral pressure occasioned by the unequal\nhorizontal thrust of the arches. In arranging the form and\ndimensions of the piers this inequality of thrust must be\nestimated for, taking also into consideration the position of\nthe imposts of the unequal arches.\n520. Precautions against Settling. One of the most dif-\nficult and important problems in the construction of masonry,\nis that of preventing unequal settling in parts which require\nto be connected but sustain unequal weights, and the conse-\nquent ruptures in the masses arising from this cause. To\nobviate this difficulty requires on the part of the engineer no\nsmall degree of practical tact. Several precautions must be\ntaken to diminish as far as practicable the danger from un-\nequal settling. Walls sustaining heavy vertical pressures\nshould be built up uniformly, and with great attention to the\nDigitized by Google\nARCHES.\n259\nbond and correct fitting of the courses. The materials should\nbe uniform in quality and size hydraulic mortar should\nalone be used ; and the permanent weight not be laid on the\nwall until the season after the masonry is laid. As a farther\nprecaution, when practicable, a trial weight may be laid upon\nthe wall before loading it with the permanent one.\nWhere the heads of arches are built into a wall, particularly\nif they are designed to bear a heavy permanent weight, as\nan embankment of earth, the wall should not be carried up\nhigher than the imposts of the arches until the settling of the\nlatter has reached its final term; and as there will be danger\nof disjunction between the piers of the arches and the wall at\nthe head, from the same cause, these should be carried up in-\ndependently, but SO arranged that their after-union may be\nconveniently effected. It would moreover be always well to\nsuspend the building of the arches until the season follow-\ning that in which the piers are finished, and not to place the\npermanent weight upon the arches until the season following\ntheir completion.\n521. Pointing. The mortar in the joints near the surfaces\nof walls exposed to the weather should be of the best hydrau-\nlic lime, or cement, and as this part of the joint always\nrequires to be carefully attended to, it is usually filled, or as\nit is termed pointed, some time after the other work is finish-\ned. The period at which pointing should be done is a dis-\nputed subject among builders, some preferring to point while\nthe mortar in the joint is still fresh, or green, and others not\nuntil it has become hard. The latter is the more usual and\nbetter plan. The mortar for pointing should be poor, that is,\nhave rather an excess of sand ; the sand should be of a fine\nuniform grain, and but little water be used in tempering the\nmortar. Before applying the pointing, the joint should be\nwell cleansed by scraping and brushing out the loose matter,\nand then be well moistened. The mortar is applied with a\nsuitable tool for pressing it into the joint, and its surface is\nrubbed smooth with an iron tool. The practice among our\nmilitary engineers is to use the ordinary tools for calking in\napplying pointing; to calk the joint with the mortar in the\nusual way, and to rub the surface of the pointing until it be-\ncomes hard. To obtain pointing that will withstand the\nvicissitudes of our climate is not the least of the difficulties\nof the builder's art. The contraction and expansion of the\nstone either causes the pointing to crack, or else to separate\nfrom the stone, and the surface water penetrating into the\ncracks thus made, when acted upon by frost, throws out the\nDigitized by Google\n260\nCIVIL ENGINEERING.\npointing. Some have tried to meet this difficulty by giving\nthe surface of the pointing such a shape, and so arranging it\nwith respect to the surfaces of the stones forming the joint,\nthat the water shall trickle over the pointing without enter-\ning the crack, which is usually between the bed of the stone\nand the pointing.\n522. The term flash pointing is sometimes applied to a\ncoating of hydraulic mortar laid over the face or back of a\nwall, to preserve either the mortar joints, or the stone itself,\nfrom the action of moisture, or the effects of the atmosphere.\nMortar for flash pointing should also be made poor, and when\nit is used as a stucco to protect masonry from atmospheric\naction, it should be made of coarse sand, and be applied in a\nsingle uniform coat over the surface, which should be prepared\nto receive the stucco by having the joints thoroughly cleansed\nfrom dust and loose mortar, and being well moistened.\nNo pointing of mortar has been found to withstand the\neffects of weather in our climate on a long line of coping.\nWithin a few years a pointing of asphalte has been tried on\nsome of our military works, and has given thus far promise\nof a successful issue.\n523. Stucco exposed to weather is sometimes covered with\npaint, or other mixtures, to give it durability. Coal tar has\nbeen tried, but without success in our climate. M. Raucourt\nde Charleville, in his work Traité des Mortiers, gives the\nfollowing compositions for protecting exposed stuccoes, which\nhe states to succeed well in all climates. For important work,\nthree parts of linseed oil boiled with one-sixth of its weight\nof litharge, and one part of wax. For common works, one\npart of linseed oil, one-tenth of its weight of litharge, and\ntwo or three parts of resin.\nThe surfaces must be thoroughly dry before applying the\ncompositions, which should be laid on hot with a brush.\n524. Repairs of Masonry. In effecting repairs in mason-\nry, when new work is to be connected with old, the mortar\nof the old should be thoroughly cleaned off wherever it is in-\njured along the surface where the junction is effected, and\nthe surface thoroughly wet. The bond and other arrange-\nments will depend upon the circumstances of the case; the\nsurfaces connected should be fitted as accurately as practical\nble, SO that by using but little mortar, no disunion may take\nplace from settling.\n525. An expedient, very fertile in its applications to hy-\ndraulic constructions, has been for some years in use among\nthe French engineers, for stopping leaks in walls and renew-\nDigitized by Google\nFOUNDATIONS.\n261\ning the beds of foundations which have yielded, or have been\notherwise removed by the action of water. It consists in in-\njecting hydraulic cement into the parts to be filled, through\nholes drilled through the masonry, by means of a strong sy-\nringe. The instruments used for this purpose (Fig. 83 a) are\nusually cylinders of wood, or of cast iron ; the bore uniform,\nexcept at the end, which is terminated with a nozle of the\nusual conical form; the piston is of wood, and is driven down\nby a heavy mallet. In using the syringe, it is adjusted to\nthe hole; the hydraulic cement in a semi-fluid state poured\nB\nFig. 88 a-Represents the arrangements for in-\njecting hydraulic cement under a wall.\nA, section of the wall with vertical holes a c\ndrilled through it.\nB, syringe and piston for injecting the cement\ninto the space C under the wall.\nA\nC\ninto it; a wad of tow, or a disk of leather being introduced\non top before inserting the piston. The cement is forced in\nby repeated blows on the piston.\n526. A mortar of hydraulic lime and fine sand has been\nused for the same purpose ; the lime being ground fresh from\nthe kiln, and used before slaking, in order that by the in-\ncrease of volume which takes place from slaking, it might fill\nmore compactly all interior voids. The use of unslaked lime\nhas received several ingenious applications of this character ;\nits after expansion may prove injurious when confined. The\nuse of sand in mortar for injections has by some engineers\nbeen condemned, as from the state of fluidity in which the\nmortar must be used, it settles to the bottom of the syringe,\nand thus prevents the formation of a homogeneous mass.\n527. Effects of Temperature on Masonry. Frost is the\nmost powerful destuctive agent against which the engineeer\nhas to guard in constructions of masonry. During severe\nDigitized by Google\n262\nCIVIL ENGINEERING.\nwinters in the northern parts of our country, it has been as-\ncertained, by observation, that the frost will penetrate earth\nin contact with walls to depths exceeding ton feet; it there-\nfore becomes a matter of the first importance to use every\npracticable means to drain thoroughly all the ground in con-\ntact with masonry, to whatever depths the foundations may\nbe sunk below the surface; for if this precaution be not\ntaken, accidents of the most serious nature may happen to the\nfoundations from the action of the frost. If water collects in\nany quantity in the earth around the foundations, it may be\nnecessary to make small covered drains under them to con-\nvey it off, and to place a stratum of loose stone between the\nsides of the foundations and the surrounding earth to give it\na free downward passage.\nIt may be laid down as a maxim in building, that mortar\nwhich is exposed to the action of frost before it has set, will\nbe 80 much damaged as to impair entirely its properties.\nThis fact places in a stronger light what has already been re-\nmarked, on the necessity of laying the foundations and the\nstructure resting on them in hydraulic mortar, to a height of\nat least three feet above the ground; for, although the mortar\nof the foundations might be protected from the action of the\nfrost by the earth around them, the parts immediately above\nwould be exposed to it, and as those parts attract the mois-\nture from the ground, the mortar, if of common lime, would\nnot set in time to prevent the action of the frosts of winter.\nIn heavy walls the mortar in the interior will usually be se-\ncured from the action of the frost, and masonry of this char-\nacter might be carried on until freezing weather commences;\nbut still in all important works it will be by far the safer\ncourse to suspend the construction of masonry several weeks\nbefore the ordinary period of frost.\nDuring the heats of summer, the mortar is injured by a\ntoo rapid drying. To prevent this the stone, or brick, should\nbe thoroughly moistened before being laid and afterwards,\nif the weather is very hot, the masonry should be kept wet until\nthe mortar gives indications of setting. The top course should\nalways be well moistened by the workmen on quitting their\nwork for any short period during very warm weather.\nThe effects produced by a high or low temperature on mor-\ntar in a green state are similar. In the one case the freezing\nof the water prevents a union between the particles of the\nlime and sand; and in the other the same arises from the\nwater being rapidly evaporated. In both cases the mortar\nwhen it has set is weak and pulverulent.\nDigitized\nby\nGoogle\nCHAPTER IV.\nFRAMING.\n528. FRAMING is the art of arranging beams of solid mate-\nrials for the various purposes to which they are applied in\nstructures. A frame is any arrangement of beams made for\nsustaining strains.\n529. That branch of framing which relates to the combina-\ntions of beams of timber is denominated Carpentry.\n530. Timber and iron are the only materials in common\nuse for frames, as they are equally suitable to resist the vari-\nous strains to be met with in structures. Iron, independently\nof offering greater resistance to strains than timber, possesses\nthe further advantage of being susceptible of receiving the\nmost suitable forms for strength without injury to the mate-\nrial; while timber, if wrought into the best forms for the\nobject in view, may, in some cases, be greatly injured in\nstrength.\n531. The object to be attained in framing is to give, by a\nsuitable combination of beams, the requisite degree of strength\nand stiffness demanded by the character of the structure,\nunited with a lightness and an economy of material of which\nan arràngement of a massive kind is not susceptible. To\nattain this end, the beams of the frame must be of such forms,\nand be so combined that they shall not only offer the greatest\nresistance to the efforts they may have to sustain, but shall\nnot change their relative positions from the effect of these\nefforts.\n532. The forms of the beams will depend upon the kind\nof material used, and the nature of the strain to which it\nmay be subjected, whether of tension, compression, or a cross\nstrain.\n533. The general shape given to the frame, and the com-\nbinations of the beams for this purpose, will depend upon\nthe object of the frame and the directions in which the efforts\nact upon it.\nIn frames of timber, for example, the cross sections of each\nbeam are generally uniform throughout, these sections being\neither circular, or rectangular, as these are the only simple\nDigitized by Google\n264\nCIVIL ENGINEERING.\nforms which a beam can receive without injury to its strength.\nIn frames of cast-iron, each beam may be cast into the most\nsuitable form for thestrength required, considering the econo-\nmy of the material.\n534. In combining the beams, whatever may be the gen-\neral shape of the frame, the parts which compose it must, as\nfar as practicable, present triangular figures, each side of the\ntriangles being formed of a single beam; the connection of\nthe beams at the angular points, termed the joints, being so\narranged that no yielding can take place. In all combina-\ntions, therefore, in which the principal beams form polygonal\nfigures, secondary beams must be added, either in the direc-\ntions of the diagonals of the polygon, or so as to connect each\npair of beams forming an angle of the polygon, for the pur-\npose of preventing any change of form of the figure, and of\ngiving the frame the requisite stiffness. These secondary\npieces receive the general appellation of braces. When they\nsustain a strain of compression they are termed struts; when\none of extension, ties.\n535. As one of the objects of a frame is to transmit the\nstrain it directly receives to firm points of support, the beams\nof which it is formed should be so combined that this may\nbe done in the way which shall have the least tendency to\nchange the shape of the frame and to fracture the beams.\n536. The points of support of a frame may be either\nabove or below it. In the former case, the frame will con-\nsist of a suspended system, in which the polygon will assume\na position of stable equilibrium, its sides being subjected to a\nstrain of extension. In the latter case the frame, if of a\npolygonal form, must satisfy the essential conditions already\nenumerated, in order that its state of equilibrium shall be\nstable.\n537. The object of the structure will necessarily decide\nthe general shape of the frame, as well as the direction of\nthe strains to which it will be subjected. An examination,\ntherefore, of the frames adapted to some of the more usual\nstructures will be the best course for illustrating both the\npreceding general principles and the more ordinary combina-\ntions of the beams and joints.\n538. Frames for Cross Strains. The parts of a frame\nwhich receive a cross strain may be horizontal, as the beams,\nor joists of a floor; or inclined, as the beams, or rafters\nwhich form the inclined sides of the frame of a roof. The\npressure producing the cross strain may either be uniformly\ndistributed over the beams, as in the cases just cited, or it\nDigitized by\nGoogle\nFRAMING.\n265\nmay act only at one point, as in the case of a weight laid\nupon the beam.\nIn all of these cases the extremities of the beam should be\nfirmly fixed against immovable points of support; the longer\nside of the rectangular section of the beain should be par-\nallel to the direction of the strain, as this is the best position\nfor strength.\nIf the distance between the points of support, or the bear-\ning, be not great, the framing may consist simply of a row\nof parallel beams of such dimensions, and placed so far asun-\nder as the strain borne may require. When the beams are\nh\nFig. 84-Represents a cross section of horizontal beams a, a braced\nby diagonal battens b.\nnarrow, or the depth of the rectangle considerably greater\nthan the breadth (Fig. 84), short struts of batteris may be\nplaced at intervals between each pair of beams, in a diagonal\ndirection, uniting the bottom of the one with the top of the\nother, to prevent the beams from twisting, or yielding late-\nrally. This also increases the stiffness of the structure by\ndistributing the strains.\n539. When the bearing and strain are BO great that a sin-\ngle beam will not present sufficient strength and stiffness, a\ncombination of beams, termed a built beam, which may be\nsolid, consisting of several layers of timber laid in juxtapo-\nsition, and firmly connected together by iron bolts and straps\n-or open, being formed of two beams, with an interval be-\ntween them, so connected by cross and diagonal pieces, that\na strain upon either the upper or lower beam will be trans-\nmitted to the other, and the whole system act under the effect\nof the strain like a solid beam.\n540. Solid built Beams. In framing solid built beams,\nthe pieces in each course (Fig. 85) are laid abutting end to\nFig. 85-Represents a solid built beam\nof three courses, the pieces of each\ncourse breaking joints and confined\nby iron hoops.\nend with a square joint between them, the courses breaking\njoints to form a strong bond between them. The courses\nare firmly connected either by iron bolts, formed with a\nscrew and nut at one end to bring the courses into close con-\nDigitized by\nGoogle\n266\nCIVIL ENGINEERING.\ntact, or else by iron bands driven on tight, or by iron stirrups\n(Fig. 86) suitably arranged with screw ends and nuts for the\nsame purpose.\nFig. 86-Represents an iron stirrup or hoop with nuts or female screws\nc which confine the cross piece of the stirrup b.\nWhen the strain is of such a character that the courses\nwould be liable to work loose and slide along their joints, the\nbeams of the different courses may be made with shallow in-\ndentations (Figs. 87, 88), accurately fitting into each other ;\nFig. 87-Represents a solid built beam\nof three courses arranged with in-\ndents and confined by iron hoops.\na\nb\nb\nFig. 88-Représents a solid built beam, the top part being of two pieces b, b which abut\nagainst a broad fiat iron bolt a, termed a king bolt.\nor shallow rectangular notches (Fig. 89) may be cut across\neach beam, being so placed as to receive blocks, or keys of\nFig. 89-Represents a solid built beam\nwith keys b, b of hard wood between\nthe courses.\nhard wood. The keys are sometimes made of two wedge-\nFig. 90-Represents the keys in the form of double,\nc\nor folding wedges a, b let into a shallow notch\nb\nin the beam a\nshaped pieces (Fig. 90), for the purpose of causing them to\nfit the notches more closely, and to admit of being driven\ntight upon any shrinkage of the woody fibre.\nThe joints between the courses may be left slightly open\nwithout impairing in an appreciable degree the strength of\nthe combination. This is a good method in beains exposed o\nDigitized by Google\nFRAMING.\n267\nmoisture, as it allows of evaporation from the free circulation\nof the air through the joints. Felt, or stout paper saturated\nwith mineral tar, has been recommended to secure the joints\nfrom the action of moisture. The prepared material is so\nplaced as to occupy the entire surface of the joint, and the\nwhole is well screwed together.\n541. Joints. A joint is the surface between two pieces\nwhich come in contact with each other, and which are connected\ntogether. The form and arrangement of joints will depend\nupon the relative position of the beams joined, and the object\nof the joint.\nIn all arrangements of joints, the axes of the beams con-\nnected should lie in the same plane in which the strain upon\nthe frame acts; and the combination should be so arranged\nthat the parts will accurately fit when the frame is put to-\ngether, and that any portion may be displaced without dis-\nconnecting the rest. The simplest forms most suitable to the\nobject in view will usually be found to be the best.\nIn adjusting the surfaces of the joints an allowance should\nbe made for any settling in the frame which may arise either\nfrom the shrinking of the timber in seasoning while in the\nframe, or from the fibres yielding to the action of the strain.\nThis is done by leaving sufficient play in the joints when the\nframe is first set up, to admit of the parts coming into per-\nfect contact when the frame has attained its final settling.\nJoints formed of plane surfaces present more difficulty in\nthis respect than curved joints, as the bearing surfaces in the\nlatter case will remain in contact should any slight change\ntake place in the relative positions of the beams from settling;\nwhereas in the former a slight settling might cause the strains\nto be thrown upon a corner, or edge of the joint, by which\nthe bearing surfaces might be crushed, and the parts of the\nframework wrenched asunder from the leverage which such\na circumstance might occasion.\nThe surface of a joint subjected to pressure should be as\ngreat as practicable, to secure the parts in contact from being\ncrushed by the strain; and the surface should be nearly per-\npendicular to the direction of the strain to prevent sliding.\nA thin plate of iron, or lead, may be inserted between the\nsurfaces of joints where, from the magnitude of the strain,\none of them is liable to be crushed by the other, as in the\ncase of the end of one beam resting upon the face of another.\n542. Folding wedges, and pins, or tree-nails, of hard wood,\nare used to bring the surfaces of joints firmly to their bear-\nings, and retain the parts of the frame in their places. The\nDigitized by Google\n268\nCIVIL ENGINEERING.\nwedges are inserted into square holes, and the pins into auger-\nholes made through the parts connected. As the object of\nthese accessories is simply to bring the parts connected into\nclose contact, they should be carefully driven, in order not to\ncause a strain that might crush the fibres.\nTo secure joints subjected to a heavy strain, bolts, straps,\nand hoops of wrought iron are used. These should be placed\nin the best direction to counteract the strain and prevent the\nparts from separating; and wherever the bolts are requisite\nthey should be inserted at those points which will least weaken\nthe joint.\n543. Joints of Beams united end to end. When the axes\nof the beams are in the same right line, the form of the joint\nwill depend upon the direction of the strain. If the strain is\none of compression, the ends of the beams may be united by\na square joint perpendicular to their axes, the joint being\nsecured (Fig. 91) by four short pieces 80 placed as to embrace\na\nb\nd\nFig. 91-Represents the manner in which the end joint of two beams a and b is fished or\nsecured by side pieces c and d bolted to them.\nthe ends of the beams, and being fastened to the beams and\nto each other by bolts. This arrangement, termed fishing a\nbeam, is used only for rough work. It may also be used\nwhen the strain is one of extension; in which case the short\npieces (Fig. 92) may be notched upon the beams, or else keys\nFig. 99-Represents a fished joint in which the side pieces c and d are either let into the\nbeams or secured by keys e, a\nof hard wood, inserted into shallow notches made in the beams\nand short pieces, may be employed to give additional security\nto the joint.\nA joint termed a scarf may be used for either of the fore-\ngoing purposes. This joint may be formed either by halving\nDigitized by Google\nFRAMING.\n269\nd\nFig. 93-Represents a scarf joint secured by iron plates a a keys, d, d, and bolts.\nthe beams on each other near their ends (Fig. 93), and se-\ncuring the joints by bolts, or straps; or else by so arranging\nthe ends of the two beams that each shall fit into shallow\ntriangular notches cut into the other, the joint being secured\nby iron hoops. This last method is employed for round\ntimber.\n544. When beams united at their ends are subjected to\na cross strain, a scarf joint is generally used, the under\npart of the joint being secured by an iron plate confined\nto the beams by bolts. The scarf for this purpose may\nbe formed simply by halving the beams near their ends;\nbut a more usual and better form (Fig. 94) is to make\nd\nz\nc\nFig. 94-Represents a scarf joint for a cross strain secured at bottom by a piece of tim-\nber c confined to the beams by iron hoops d, a and keys e, c.\nthe portion of the joint at the top surface of the beams per-\npendicular to their axes, and about one third of their depth ;\nthe bottom portion being oblique to the axis, as well as the\nportion joining these two.\nWhen the beams are subjected to a cross strain and to one\nof extension in the direction of their axes, the form of the\nscarf must be suitably arranged to resist each of these strains.\nThe one shown in Fig. 95 is a suitable and usual form for\na\nc\nb\nFig. 95-Represents a scarf joint arranged to resist a cross strain and one of extension. The\nbottom of the joint is secured by an iron plate confined by bolts. The folding wedge key\ninserted at c serves to bring all the surfaces of the joints to their bearings.\nthese objects. A folding wedge key of hard wood is in-\nserted into a space left between the parts of the joint which\ncatch when the beams are drawn apart. The key serves to\nbring the surfaces of the joints to their bearings, and to form\nan abutting surface to resist the strain of extension. In this\nDigitized by Google\n270\nCIVIL ENGINEERING.\nform of scarf the surface of the joint which abuts against\nthe key will be compressed; the portions of the beams just\nabove and below the key will be subjected to extension.\nThese parts should present the same amount of resistance, or\nhave an equality of cross section. The length of the scarf\nshould be regulated by the resistance with which the timber\nemployed resists detrusion compared with its resistance to\ncompression and extension.\n545. When the axes of beams form an angle between'\nthem, they may be connected at their ends either by halving\nthem on each other, or by cutting a mortise in the centre\nof one beam at the end, and shaping the end of the other to\nfit into it. See Fig. 97.\n546. Joints for connecting the end of one beam with\nthe face of another. The joints used for this purpose\nare termed mortise and tenon joints. Their form will\ndepend upon the angle between the axes of the beams.\nA\nFig. 96-Represents a mortise and tenon\njoint when the axes of the beams are per-\na\npendicular to each other.\na, tenon on the beam A.\nb, mortise in the beam B.\na pin to hold the parts together.\nB\nWhen the axes are perpendicular to each other, the mor-\ntise (Fig. 96) is cut into the face of the beam, and the end\nof the other beam is shaped into a tenon to fit the mortise.\nA\nFig. 97-Represents a mortise and tenon\njoint when the axes of the beams are\noblique to each other. A notch whose\nsurfaces ab and bc are at right angles is\nout into the beam B, and a shallow mortise\nd is cut below the surface bc. The end of\nc\nthe beam A is arranged to fit the notch and\n6\nmortise in B. The joint is secured by a\nB\nscrew bolt.\nWhen the axes of the beams are oblique to each other, a\ntriangular notch (Fig. 97) is usually cut into the face of\nDigitized by Google\nFRAMING.\n271\none beam, the sides of the notch being perpendicular to\neach other, and a shallow mortise is cut into the lower\nsurface of the notch; the end of the other beam is suitably\nshaped to fit the notch and mortise.\nThe direction of the strain and the effect it may produce\nupon the joint must in all cases regulate its form. In some\ncases the circular joint may be more suitable than those\nforms which are plane surfaces; in others a double tenon\nmay be better than the simple joint.\n547. Tie Joints. These joints are used to connect beams\nwhich cross, or lie on each other. The simplest and strong-\nest form of tie joint consists in cutting a notch in one or both\nof the beams to connect them securely. But when the beams\ndo not cross, but the end of one rests upon the other, a notch\nof a trapezoidal form (Fig. 98) may be cut in the lower beam\nB\nFig. 98-Represents an ordinary dove-tail joint secured by\noc\na pin at c.\nto receive the end of the upper, which is suitably shaped to\nfit the notch. This, from its shape, is termed a dove-tail\njoint. It is of frequent use in joinery, but is not suitable\nfor heavy frames where the joints are subjected to consider-\nable strains, as it soon becomes loose from the shrinking of\nthe timber.\n548. Open built Beams. In framing open built beams,\nthe principal point to be kept in view is to form such a con-\nnection between the upper and lower solid beams, that they\nshall be strained uniformly by the action of a strain at any\npoint between the bearings. This may be effected in various\nways, (Fig. 99.) The upper and lower beams may consist\nFig. 99-Represents an open\nbuilt beam A and B are\nthe top and bottom rails or\nstrings; a, a, cross pieces,\neither single or in pairs; b,\ndiagonal braces in pairs; c,\nsingle diagonal braces.\neither of single beams or of solid built beams; these are con-\nnected at regular intervals by pieces at right angles to them,\nbetween which diagonal pieces are placed. By this arrange-\nDigitized by Google\n272\nCIVIL ENGINEERING.\nment the relative position of all the parts of the frame will\nbe preserved, and the strain at any point will be brought to\nbear upon the intermediate points.\n549. Framing for intermediate Supports. Beams of\nordinary dimensions may be used for wide bearings when\nintermediate supports can be procured between the extreme\npoints.\nThe simplest and most obvious method of effecting this is\nto place upright beams, termed props, or shores, at suitable\nintervals under the supported beam.\nWhen the props would interfere with some other arrange-\nment, and points of support can be procured at the extremi-\nties below those on which the beam rests, inclined struts (Fig.\n100) may be used. The struts must have a suitably formed\nstep at the foot, and be connected at top with the beam by a\nsuitable joint.\nIn some cases the bearing may be diminished by placing\nFig. 100-Represents a horizontal beam σ sup-\nported near the middle by inclined struts A, A.\nA\non the points of support short pieces, termed corbels (Fig. 101),\nand supporting these near their ends by struts.\nFig. 101-Represents a\nhorizontal heam c sup-\nported by vertical\nposts a a with corbel\npieces d,d and inclined\nstruts e, 6 to diminish\nthe bearing.\nIn other cases a portion of the beam, at the middle, may\nbe strengthened by placing under it a short beam, called a\nFig. 109-Represents a\nhorizontal beam c,\nstrengthened by a\nstraining beam f and\ninclined struts c,a\nstraining beam (Fig. 102), against the ends of which the\nstruts abut.\nDigitized by Google\nFRAMING.\n273\nWhenever the bearing may require it the two preceding\narrangements (Fig. 103) may be used in connection.\nFig. 108-Represents a combination of Figa. 101 and 102.\nIn all combinations with struts, a lateral thrust will be\nthrown on the point of support where the foot of the strut\nrests. This strain must be provided for in proportioning the\nsupports.\n550. When intermediate supports can be procured only\nabove the beam, an arrangement must be made which shall\nanswer the purpose of sustaining the beam at its interme-\ndiate points by suspension. The combination will depend\nupon the number of intermediate points required.\nWhen the beam requires to be supported only at the mid-\ndle, it may be done as shown in Fig. 104. If the suspending\npiece be of iron, it must be arranged at one end with a screw\nand nut. When the support is of timber, a single beam,\ncalled a king post, (Fig. 104,) may be used, against the head\nFig. 104-Represents a\nhorizontal beam 0\nsupported in its mid-\nc\ndle by a king post ,\nsuspended from the\nstruts a a\nof which the two inclined pieces may abut; the foot of the\npost is connected with the beam by a bolt, an iron stirrup, or\na suitable joint. Instead of the ordinary king post, two\nbeams may be used; these are placed opposite to each other\nand bolted together, embracing between them the supported\nbeam and the heads of the inclined beams which fit into shal-\nlow notches cut into the supporting beams. Pieces arranged\n18\nDigitized by Google\n274\nCIVIL ENGINEERING.\nin this manner for suspending portions of a frame receive the\nname of suspension preces, or bridle pieces.\nWhen two intermediate points of support are required, they\nmay be obtained as shown in Fig. 105. The suspension\nH\n9\nFig. 105-Represents a beam c\nsupported at two points by\nposts g, g suspended from the\nstruts e, 6 and straining beam\nh.\npieces in this case may be either posts, termed queen posts,\narranged like a king post, iron rods, or bridle pieces. This\ncombination may be used for very wide bearings, (Fig. 106,)\nby suitably increasing the number of inclined pieces and\nstraining beam.\ng\nc\ng\nFig. 106-Represents a beam 0 suspended from a combination of strute and straining beams\nby posts v, g.\n551. Experiments on the Strength of Frames. Experi-\nmental researches on this point have been mostly restricted\nto those made with models on a comparatively small scale,\nowing to the expense and difficulty attendant upon experi-\nments on frames having the form and dimensions of those\nemployed in ordinary structures.\nAmong the most remarkable experiments on a large scale,\nare those made by order of the French government at Lori-\nent, under the direction of M. Riebell, the superintending\nengineer of the port, and published in the Annales Mari\ntimes et Coloniales, Feb. and Nov., 1837.\nThe experiments were made by first setting up the frame\nto be tried, and, after it had settled under the action of its\nDigitized by Google\nFRAMING.\n275\nown weight, suspending from the back of it, by ropes placed\nat equal intervals apart, equal weights to represent a load\nuniformly distributed over the back of the frame.\nThe results contained in the following table are from ex-\nperiments on a truss (Fig. 107) for the roof of a ship shed.\nThe truss consisted of two rafters and a tie beam, with sus-\nFig. 107.\n+\nI\npension pieces in pairs, and diagonal iron bolts, which were\nadded because it was necessary to scarf the tie beam. The\nspan of the truss was 651 feet; the rafters had a slope of 1\nperpendicular to 4 base. The thickness of the beams, meas-\nured horizontally, was about 21 inches, their depth about 18\ninches. The amount of the settling at each rope was ascer-\ntained by fixed .graduated vertical rods, the measures being\ntaken below a horizontal line marked 0.\nAmount of settling on the right of\nthe ridge below the horisontal 0,\nin inches.\nWEIGHTS BORNE BY THE TRUSE.\nAt 18 inches from\nthe ridge.\nAt 4 ft. 6 in. from\nthe ridge.\nAt 8 ft. from the\nridge.\nAt 10 ft. from the\nridge.\nAt 15 ft. from the\nridge.\nWeight uniformly distributed, 1654 lbs\n0.15\n0.15\n0.15\n0.15\n0.15\nDo.\ndo.\n8680 lbs\n1.6\n1.7\n1.9\n1.8\n1.1\nDo.\ndo.\n1654 lbs. and 1368 lbs.\nsus-\npended from the centre of the frame\n0.4\n0.5\n0.4\n0.8\n0.2\n8680 lbs., uniformly distributed, and 1868 lbs. from the\ncentre\n2.0\n2.1\n2.3\n2.1\n1.2\nThe following table gives the results of experiments made\non frames of the usual forms of straight and curved timber\nfor roof trusses. The curved pieces were made of two thick-\nnesses, each 31 inches. The numbers in the fifth column\ngive the ratios between the weight of the frame and that of\nthe weight borne by which the elasticity was not impaired.\nDigitized by Google\n276\nCIVIL ENGINEERING.\nDESCRIPTION OF THE FRAMES.\nI Span, or bearing.\nRise, or versed sine.\nDepth of beams.\nHorisontal breadth of\nbeams.\nRatios between weight\nin lbs. of frame, and\nthat of the load borne.\nWeight borne without\nimpairing elasticity of\nthe wood.\nWeight by which the\nelasticity was visibly\nchanged.\nFrame formed of two rafters and a tie beam\n25 ft.\n8 ft.\n8.5 in.\n8.1 in.\n14.80\n2300\n3916\nDo.\ndo.\ndo.\nand suspension pieces in pairs, (Fig. 108)\n8.88\n2770\n5590\nFrame of a segment arch confined by a tie\nbeam, (Fig. 109)\n54 ft.\n11 ft.\n12 in.\n7 in.\n8.85\n6520\n12940\nDo.\ndo.\ndo.\nwith suspension pieces in pairs, (Fig. 110)\n2.82\n9500\n18077\nFrame of a segment arch with rafters con-\nfined at their foot by a tie piece, (Fig.111)\n8.91\n6111\n21896\nFrame of a full centre arch confined by a tie\nbeam\n50 ft.\n25 ft.\n1.00\n4886\n5161\nDo.\ndo.\ndo.\nwith suspension pieces in pairs\n0.91\n7828\n8158\nFig. 108.\no\no\no\nFig. 109.\nFig. 110.\nDigitized by Google\nFRAMING.\n277\nFig. 111.\n0\nc\nFig. 112-Represents a wooden arch A formed of a solid built beam of three\ncourses which support the beams c, o by the posts g, g which are formed\nof pieces in pairs.\n3, b, inclined struts to strengthen the aroh by relieving it of a part of the\nload on the beams a a\na.\na\nB\na\nFig. 118-Represents a wooden arch of a solid built beam A which supports\nthe horizontal beam B by means of the ponts a, a. The arch is let into\nthe beam B, which acts as a tie to confine its extremities.\n552. Wooden arches may also be formed by fastening to-\ngether several courses of boards, giving the frame a polygo-\nnal form, (Fig. 114,) corresponding to the desired curvature,\nand thon shaping the outer and inner edges of the arch to the\nproper curve. Each course is formed of boards cut into\nDigitized by Google\n278\nCIVIL ENGINEERING.\nFig. 114-Bepresents an elevation A of a\nwooden arch formed of short pieces a, b\nwhich abut end to end and break joints.\nB represents a perspective view of this com-\nbination, showing the manner in which\nthe parts are keyed together.\nsharp lengths, depending on the curvature required; these\npieces abut end to end, the joints being in the direction of\nthe radii of curvature, and the pieces composing the different\ncourses break joints with each other. The courses may be\nconnected either by jibs and keys of hard wood; or by iron\nbolts. This method is very suitable for all light framework\nwhere the pressure borne is not great.\nWooden arches are chiefly used for bridges and roofs.\nThey serve as intermediate points of support for the framing\non which the roadway rests in the one case, and the roof\ncovering in the other. In bridges the roadway may lie either\nabove the arch, or below it; in either case vertical posts,\niron rods, or bridles connect the horizontal beams with the\narch.\n553. The greatest strain in wooden arches takes place\nnear the springing line this part should, therefore, when\npracticable, be relieved of the pressure that it would directly\nreceive from the beams above it by inclined struts, so arranged\nas to throw this pressure upon the lateral supports of the\narch.\nThe pieces which compose a wooden arch may be bent into\nany curve. The one, however, usually adopted is an arc of a\ncircle, as the most simple for the mechanical construction of\nthe framing, and presenting all desirable strength.\nDigitized by Google\nCHAPTER V.\nBRIDGES.\nI. CLASSIFICATION. II. STONE BRIDGES. III. WOODEN\nBRIDGES. IV. CAST-IRON BRIDGES. V. WEOUGHT-\nIRON TRUSS BRIDGES. VI. TUBULAR BRIDGES. VII.\nSUSPENSION BRIDGES. VIII. SWING BRIDGES. IX.\nAQUEDUCT BRIDGES.\nI.\nCLASSIFICATION.\n554. A bridge is a structure for supporting a roadway over\na body or stream of water, or over a depression in the earth.\nIf the structure is over a depression in which there is\nusually no water, it is called a viaduct.\nIf the structure supports a water-way, it is called an aque-\nduct, and if the aqueduct is over a river, it is sometimes\ncalled an aqueduct-bridge.\nBridges may be classed according to their mechanical\nfeatures; in which case we have-\n1. Arches.\n2. Trussed bridges.\n3. Tubular bridges.\n4. Suspension bridges.\nThey may also be classed according to the materials which\ncompose them; as Stone, Wood, and Iron.\nThe former is more convenient for the purposes of analy-\nsis, but the latter will be used in this work.\nIL\nSTONE BRIDGES.\n555. A stone bridge consists of a roadway which rests upon\none or more arches, usually of a cylindrical form, the abut-\nments and piers of the arches being of sufficient height and\nstrength to secure them and the roadway from the effects of\nan extraordinary rise in the water-course.\nDigitized by Google\n280\nCIVIL ENGINEERING.\n556. The general location of a bridge will depend upon\nthe approaches, and the particular locality may be modified\nby the character of the banks, the soil or subsoil, and the\nbends in the stream. High embankments and deep excava-\ntions will naturally be avoided, if possible. The faces of the\npiers and abutments should be nearly or quite parallel to the\nthread of the stream.\n557. Survey. With whatever considerations the locality\nmay have been selected, a careful survey must be made not\nonly of it, but also of the water-course and its environs for\nsome distance above and below the point which the bridge\nwill occupy, to enable the engineer to judge of the probable\neffects which the bridge, when erected, may have upon the\nnatural regimen of the water-course.\nThe object of the survey will be to ascertain thoroughly\nthe natural features of the surface, the nature of the subsoil\nof the bed and banks of the water-course, and the character\nof the water-course at its different phases of high and low\nwater, and of freshets. This information will be embodied\nin a topographical map; in cross and longitudinal sections of\nthe water-course and the substrata of its bed and banks, as\nascertained by soundings and borings; and in a descriptive\nmemoir which, besides the usual state of the water-course,\nshould exhibit an account of its changes, occasioned either\nby permanent or by accidental causes, as from the effects of\nextraordinary freshets, or from the construction of bridges,\ndams, and other artificial changes either in the bed or banks.\n558. Water-way. When the natural water-way of a river\nis obstructed by any artificial means, the contraction, if con-\nsiderable, will cause the water, above the point where the\nobstruction is placed, to rise higher than the level of that\nbelow it, and produce a fall, with an increased velocity\ndue to it, in the current between the two levels. These\ncauses, during heavy freshets, may be productive of serious\ninjury to agriculture, from the overflowing of the banks of\nthe water-course ;-may endanger if not entirely suspend\nnavigation, during the seasons of freshets ;-and expose any\nstructure which, like a bridge, forms the obstruction, to ruin,\nfrom the increased action of the current upon the soil around\nits foundations. If, on the contrary, the natural water-way is\nenlarged at the point where the structure is placed, with the\nview of preventing these consequences, the velocity of the\ncurrent, during the ordinary stages of the water, will be de-\ncreased, and this will occasion deposits to be formed at the\npoint, which, by gradually filling up the bed, might, on a\nDigitized by Google\nLOCATION OF BRIDGES.\n281\nsudden rise of the water, prove a more serious obstruction\nthan the structure itself; particularly if the main body of the\nwater should happen to be diverted by the deposit from its\nordinary channels, and form new ones of greater depth\naround the foundations of the structure.\nThe water-way left by the structure should, for the reasons\nabove, be so regulated that no considerable change shall be\noccasioned in the velocity of the current through it during the\nmost unfavorable stages of the water.\n559. For the purpose of deciding upon the most suitable\nvelocity for the current through the contracted water-way\nformed by the structure, the velocity of the current and its\neffects upon the soil of the banks and bed of the natural water-\nway should be carefully noted at those seasons when the water\nis highest; selecting, in preference, for these observations, those\npoints above and below the one which the bridge is to occupy,\nwhere the natural water-way is most contracted.\n560. The velocity of the current at any point may be ascer-\ntained by the simple process of allowing a light ball, or float\nof some material, like white wax, or camphor, whose specific\ngravity is somewhat less than that of water, to be carried along\nby the current of the middle thread of the water-course, and\nnoting the time of its passage between two fixed stations.\n561. From the velocity at the surface, ascertained in this\nway, the average, or mean velocity of the water, which flows\nthrough the cross-section of any water-way between the sta-\ntions where the observations are taken, is nearly four-fifths of\nthe velocity at the surface.\nHaving the mean velocity of the natural water-way, that of\nthe artificial water-way will be obtained from the following\nexpression,\nv=m⁻v,\nII\nin which 8 and v represent, respectively, the area and mean\nvelocity of the artificial water-way; S and V, the same data of\nthe natural water-way; and m a constant quantity, which, as\ndetermined from various experiments, may be represented by\nthe mixed number 1,097.\nWith regard to the effect of the increased velocity on the\nbed, there are no experiments which directly apply to the\ncases usually met with. The following table is drawn up from\nexperiments made in a confined channel, the bottom and sides\nof the channel being formed of rough boards :-\nDigitized by Google\n282\nCIVIL ENGINEERING.\nStages of accumu-\nVelocity of\nNature of the bottom which just bears\nSpecific gravity\nlation termed\nriver in feet\nsuch velocities.\nof the mate-\nper second.\nrial.\n8.2\nOrdinary floods\nAngular stones, the size of a hen's egg\n2.25\n2.17\nRounded pebbles one inch in diameter\n2.614\n1.07\nGravel of the size of garden beans.\n2.545\nUniform tenors\n0.62\nGravel of the size of peas\n2.545\n0.71\nCoarse yellow sand\n2.36\nGliding\n0.851\nSand, the grains the size of aniseeds\n2.545\nDull\n0.26\nBrown potters' clay\n2.64\n562. Bays. As a general rule, there should be an odd\nnumber of bays, whenever the width of the water-way is too\ngreat to be spanned by a single arch. Local circumstances\nmay require a departure from this rule; but when departed\nfrom, it will be at the cost of architectural effect; since no\nsecondary feature can occupy the central point in any archi-\ntectural composition without impairing the beauty of the\nstructure to the eye; and as the arches are the main features\nof a stone bridge, the central point ought to be occupied by\none of them.\nThe width of the bays will depend mainly upon the char-\nacter of the current, the nature of the soil upon which the\nfoundations rest, and the kind of material that can be obtained\nfor the masonry.\nFor streams with a gentle current, which are not subject to\nheavy freshets, narrow bays, or those of a medium size may\nbe adopted, because, even a considerable diminution of the\nnatural water-way will not greatly affect the velocity under\nthe bridge, and the foundations therefore will not be liable to\nbe undermined. The difficulty, moreover, of laying the foun-\ndations in streams of this character is generally inconsiderable.\nFor streams with a rapid current, and which are, moreover,\nsubject to great freshets, wide bays will be most suitable, in\norder, by procuring a wide water-way, to diminish the danger\nto the points of support, in placing as few in the stream as\npracticable.\n563. Classification of Arches. Arches are classed, ac-\ncording to their concave surface, as: cylindrical, conical,\nconoidal, warped, annular, groined, cloistered, and domes.\nA right arch is one in which the axis is perpendicular to\nthe face and an oblique arch is one in which the axis is not\nperpendicular to the face.\nA rampant arch is one in which the axis is not in a horizon-\ntal plane.\n564. Surfaces of the Arch. The soffit is the inner con-\ncave surface.\nDigitized by Google\nARCHES.\n283\nThe back is the external surface.\nThe face of the arch is the end surface.\n565. Lines of the Arch. The springing lines are the in-\ntersections of the soffit with the abutment ; as a', c', Fig. 121.\nIn Fig. 115, B is the projection of a springing line.\nThe span is the chord of the curve of right section, as\nDB, Fig. 115.\nc\nFig. 115-Represents an oval curve of\nthree centres, the ares of which are\neach 60°.\nDB, span of the curve,\nD\nAC, rise.\nP\nB\nP. o, and R, centres of the ares of 60°.\nDCB is the intrados.\no\nThe axis of the arch is the line passing through the centres\nof the span.\nThe rise is the versed sine of the curve of right section, as\nAC, Fig. 115.\nThe intrados is the intersection of the soffit with the face\nof the arch, as DOB.\nThe extrados is the intersection of the back of the arch\nwith the face.\nThe intrados may be defined as the inner curve of a verti-\ncal right section, and the extrados as the outer one.\nThe crown is the highest line of the soffit.\nThe coursing joints are those lines which run lengthwise of\nthe arch, and separate the several courses of the stones.\nThe heading or ring joints are those lines which separate\nthe stones, and are nearly or quite parallel to the face of the\narch.\n566. Volumes of the Arch. The blocks of stone which\nform the body of the arch are called voussoirs.\nThe keystone is the highest stone of the arch.\nThe impost stones are the highest stones of the abutment,\nand upon which the arch directly rests.\nDigitized by Google\n284\nCIVIL ENGINEERING.\n567. Cylindrical Arch. This is the most usual and\nthe simplest form of arch. The soffit consists of a portion\nof a cylindrical surface. When the section of the cylin-\nder perpendicular to the axis of the arch, termed a right\nsection, cuts from thequrface a semicircle, the arch is termed\na full centre arch; when the section is an arc less than a\nsemicircle, it is termed a segmental arch; when the section\ngives a semi-ellipse, it is termed an elliptical arch ; when the\nsection gives a curve resembling a semi-ellipse, formed of arcs\nof circles tangent to each other, the arch is termed an oval,\n(Fig. 115, or basket handle), and is called a curve of three,\nFig. 116-Represents the half of a pointed curve of\nfour centres,\nab, half span.\nbc, rise,\nm and n, centres of the half curve ac.\nb\nm\nc\nm\nb\nFig. 117-Represents the half of an obtuse or surbased\ncurve of four centres,\nab, half span.\nbc, rise.\nm and n, centres of the half curve ac.\nfive, seven, etc., centres. In order to make the curve horizon-\ntal at the crown and symmetrical in reference to a vertical\nline through the centre, there must be an odd number of arcs.\nWhen the intrados is composed of two arcs meeting at the\nhighest point of the curve, it is called a pointed, (Fig. 116,)\nor an obtuse or surbased arch, (Fig. 117.)\nDigitized by Google\nARCHES.\n285\n568. Oblique Arches. If the obliquity of the arch is\nsmall, it may be constructed like the right arch, but when the\nobliquity is considerable, or in other words when the angle\nbetween the axis and face is considerably less or greater than\n90 degrees, the pressure upon the voussoirs near the end of the\nspringing lines would be very oblique to the beds, and at the\nacute angles would tend to force the voussoirs out of place if\nthe coursing joints are made parallel to the axis. To obviate\nthis defect the coursing joints are inclined to the cylindrical\nelements, as will now be explained.\nAn ideal mode of determining the coursing joints is to\nconceive the arch to be intersected by an indefinite number\nof vertical planes parallel to the face, thus making an indefi-\nnite number of curves like the end ones. Then begin at any\npoint, as d, Fig. 118, and pass a line along the soffit so as to\ncut all the former curves at right angles, and we have an\nideal coursing joint. The line d c, Fig. 118, represents such\na line. Other similar curves are also shown. The equation\nof these when developed is logarithmic. They are all asymp-\ntotes to the springing line. The plan of these curves is shown\nin Fig. 119. A suitable number of vertical intersections may\nbe selected for determining the ring-joints, portions of which\nonly are used, as b a, Fig. 118, and b', a', Fig. 119.\nFig. 118.\nA\na\nd\nc\nFlg. 118-Elevation of an oblique\nB\narch, in which the coursing joints\nd c, etc., are normal to the ring-\njointa, b a, etc.\nB is the abutment.\nA the filling over the back.\nFig. 119-Plan of the oblique arch\nshown in Fig. 118, showing the plan\nof the coursing joint and heading\njoints,\nC\nFig. 119.\nDigitized by Google\n286\nCIVIL ENGINEERING.\nThis mode of determining the coursing joints is very ob-\njectionable in practice, because the voussoirs must constantly\nvary in width as we pass from one end to the other; and as\nthe bed-surfaces are warped, it makes it exceedingly difficult\nto make the voussoirs of proper shape.\nThe method of making the coursing joints nearly or quite\nparallel to each other, sometimes called the English method,\nis more simple, and gives as good results as the preceding\nmethod.\nFig. 120.\nA\nTHE\nOF\nFig. 120 is the\nplan of an oblique\nDEVELOPMENT\narch.\nit 1 is the axis, a\nc the springing\nline. a & the face;\na b and c A the de-\nn\nvelopment of the\nPLAN.\nintrados of\noblique section.\nb\nThe right seo-\ntion, mf, is the\nare of a circle; A\ni\n7\nf and \" are hor-\nizontal projec-\n6\ntions of heading\n5\njoints; J R is the\ndevelopment of\n4\nthe joint A J. g\nh\nof c 8, eto., are\n2\nSUFFIT.\nthe developments\nm\nof coursing\njoints.\n1\nFig. 121 is the\nelevation of an\na\noblique arch, of\nwhich Fig. 120 is\nthe plan.\na c' o is the sof-\nELEVATION.\n7\nfit.\na c' is the spring-\ning line.\nc' o, spiral cours-\ning joint.\nc is a point di-\nb\nrectly below the\na\naxis. from which\nall the joints, as\nC\nP o, in the face\nradiate.\nFig. 121.\nFig. 121 is the elevation of such an oblique arch, and Fig.\n120 is the plan. The system here shown is sometimes called\n\" Buck's System.\" In order to construct this system\ngraphically, we conceive that the soffit is developed, or\nrolled out about the springing line a c. Let mf be a right\nDigitized by Google\nSTONE BRIDGES.\n287\nsection (which is here supposed to be circular). Conceive\nthat.it is revolved down to coincide with the horizontal plane,\nand that the circumference is divided into a convenient num-\nber of equal parts, and through the points of division conceive.\nthat cylindrical elements are drawn, as shown in the plan.\nIn the development the circumference of the semicircle will\nbecome the line fb, and the cylindrical elements will be, as\nshown, parallel to the springing line ac. From the points\nwhere the horizontal projections of the cylindrical elements\nintersect the face a k, draw lines parallel to fb, and note their\nintersections with the developed position of the cylindrical\nelements, and the curve a d b through these points will be the\ndevelopment of the intrados of oblique section. In a similar\nway find c A.\nJoin a b with a straight line, and divide it into as many\nequal parts as there are to be voussoirs in the face. In the\nfigure there are eight such parts. When there is an even\nnumber there will be a joint at the crown, but when an odd\nnumber there will be the appearance of a keystone at the\ncrown. From c at the end of the springing-line a c\ndraw a perpendicular c d to the line a b, and if it passes\nthrough one of the divisions previously determined on a b, we\nproceed with the construction but if it does not, we make\nsuch a change in the data as will make it perpendicular.\nThis may be done in several ways. We may erect a perpen-\ndicular to u b from the joint which is nearest the foot of the\nperpendicular previously drawn, and note where it inter-\nsects the springing-line, and change the length of the arch so\nthat it will pass through that point. Or we may change the\nobliquity of the arch, or change the number of divisions of\nthe line ab. If the foot of the perpendicular should fall near\na division, the line may be changed so as to pass through the\npoint and leave it slightly out of a perpendicular. We might\nalso disregard the condition that the perpendicular d c should\npass through the end of the springing-line a c; but this is ob-\njectionable, because the opposite sides of the arch would then\nnot be alike.\nHaving fixed the position of cd, we proceed to draw lines\nthrough the several points of division of a b, parallel to c d. It\nshould be observed that points through which these parallel\nlines are drawn are on the straight line a db, and not on the\ncurved line a 1, 2, etc. The parallel lines thus drawn are the\ncoursing joints. The development of the ring joints fn, etc.,\nare perpendicular to the developed coursing joints, and hence\nwill be normal to each other in their true position in the\nDigitized by Google\n288\nCIVIL ENGINEERING.\narch; and hence it is evident that the intrados in oblique\nsection a b will not be perpendicular to the coursing joints.\nAnd since the projection of the face is a straight line, ak, it\nis evident that the horizontal projection of a ring joint will be\na curved line fh, the position of which may be determined\nby reversing the process by which a 1 2 b was found. The\nhorizontal projection of the coursing joints will also be curved\nlines.\nThis construction evidently makes the divisions a 1-12-23,\netc., on the curved line adb, unequal. The space a 1 on\nthe development is laid off on the are in the elevation from a.\nThe space 1-2 is next laid off, and 80 on. By developing the\nextrados and determining the points of division on the back\nof the arch, we may construct the radial lines in the face of\nthe arch. These lines are slightly curved in the arch, but it\nis found, by constructing the arch on a large scale, that the\nchords of the arcs o p, etc., all pass through a common point\nC. The coursing joints and ring joints in the elevation are\neasily determined from the plan.\nThe bed-surfaces of the voussoirs may be generated by con-\nceiving a radial line to pass through one corner of them\n(which will be normal to the soffit) and moved along on a\ncoursing joint, keeping it constantly normal to the soffit.\nThis line will generate a true helicoidal surface. The end\nsurfaces of the voussoirs are generated in a similar way by\nmoving a radial line along a ring joint, and hence these sur-\nfaces are also helicoidal. The lengths of the end voussoirs,\nmeasured on the back of the arch next to the oblique angles,\nwill be shorter than those next to the acute angles, while all\nthose in the body of the arch will be like each other.\nMr. Hart, an English author, proposed a method which\ndiffered from the one above explained in the following par-\nticulars: The spaces in the curved line a db were made equal\nto each other; the coursing joints were straight, and passed\nthrough the points of division at the opposite ends of the arch\nin the developed intrados ; hence, the coursing joints in this\nsystem are not parallel to each other. Another distinction is,\nthe ring joints and end-faces of all the voussoirs are parallel\nto the end of the arch, and hence the end-faces are plane.\nThis might simplify the construction, but it does not use the\nmaterial from which the voussoirs are eut as economically as\nthe preceding system. In this system the bed-surfaces are\nhelicoidal, as in the preceding system. The preceding system\nseems to be thoroughly scientific and quite as easily executed\nas the latter, or of any other conceivable system in which the\nDigitized\nby\nGoogle\nSTONE BRIDGES.\n289\njoints are spiral. In practice, templets and bevels are made, in\norder to guide the workmen in making the angles and surfaces\nof the voussoirs.\n569. Arched Bridges. Cylindrical arches with any of the\nusual forms of curve of intrados may be used for bridges.\nThe selection will be restricted by the width of the bay, the\nhighest water-level during freshets, the approaches to the\nbridge, and the architectural effect which may be produced\nby the structure, as it is more or less exposed to view at the\nintermediate stages between high and low water.\nOval and segment arches are mostly preferred to the full\ncentre arch, particularly for medium and wide bays, for the\nreasons that, for the same level of roadway, they afford a more\nample water-way under them, and their heads and spandrels\noffer a smaller surface to the pressure of the water during\nfreshets than the full centre arch under like circumstances.\nThe level of the springing lines will depend upon the rise\nof the arches, and the height of their crowns above the water-\nlevel of the highest freshets. The crown of the arches should\nnot, as a general rule, be less than three feet above the high-\nest known water-level, in order that a passage-way may be\nleft for floating bodies descending during freshets. Between\nthis, the lowest position of the crown, and any other, the rise\nshould be 80 chosen that the approaches, on the one hand,\nmay not be unnecessarily raised, nor, on the other, the spring-\ning lines be placed 80 low as to mar the architectural effect\nof the structure during the ordinary stages of the water.\nWhen the arches are of the same size, the axis of the road-\nway and the principal architectural lines which run lengthwise\nalong the heads of the bridge, as the top of the parapet, the\ncornice, etc., etc., will be horizontal, and the bridge, to use a\ncommon expression, be on a dead level throughout. This has\nfor some time been a favorite feature in bridge architecture,\nfew of the more recent and celebrated bridges being without\nit, as it is thought to give a character of lightness and bold-\nness to the structure.\n570. Centres. Before an arch is constructed a strong sup-\nport or framework is erected to support the arch until the\nwork is completed. This support is called the centering of\nthe arch. It must be made strong, and so as to settle as little\nas possible while the masonry is being erected; and in arches\nof long span it must be so erected and supported that it\nmay be removed without causing local or cross strains in\nthe arch. To accomplish this, the centering should be re-\nmoved from the entire soffit at the same time. It is espe-\n19\nDigitized by Google\n290\n.CIVIL .ENGINEERING.\ncially detrimental to relieve one side whilst the other side is\nfirmly supported.\n571. Means used for striking Centres. When the arch is\ncompleted the centres are detached from it, or struck. To\neffect this in large centres an arrangement of wedge blocks\nis used, termed the striking-plates, by means of which the\ncentre may be gradnally lowered and separated from the\nsoffit of the arch. This arrangement consists (Fig. 125) in\nforming steps upon the upper surface of the beam which\nforms the framed support to receive a wedge-shaped block,\non which another beam, having its under surface also ar-\nranged with steps, rests. The struts of the rib either abut\nagainst the upper surface of the top beam, or else are inserted\ninto cast-iron sockets, termed shoe-plates, fastened to this\nsurface. The centre is struck by driving back the wedge\nblock.\n572. When the struts rest upon intermediate supports be-\ntween the abutments, double or folding wedges may be\nplaced under the struts, or else upon the back pieces of the\nribs under each bolster. The latter arrangement presents\nthe advantage of allowing any part of the centre to be eased\nfrom the soffit, instead of detaching the whole at once as in\nthe other methods of striking wedges. This method was\nemployed for the centres of Grosvenor Bridge (Fig. 124),\nover the river Dee at Chester, and was perfectly successful\nboth in allowing a gradual settling of the arch at various\npoints, and in the operation of striking.\n573. A novel application of sand to the striking of centres\nhas lately been made with success. Vessels containing the\nsand are placed on the supports for the centres, and are so\narranged near the bottom that the sand can be allowed to run\nout slowly when the time comes for striking. The centres\nare placed on these vessels and keyed up in the usual way.\nTo lower them, the sand is allowed to run out and let the\ncentres gradually down. This method has the advantage of\nsteadiness of lowering each rib of the centre, and of not\nallowing one to come down more rapidly than the others.\nAfter the sand has all run out, the centres can be taken down\nin the ordinary manner.\n574. For small light arches (Fig. 122) the ribs may be\nformed of two or more thicknesses of short boards, firmly\nnailed together; the boards in each course abutting end to\nend by a joint in the direction of the radins of curvature of\nthe arch, and breaking joints with those of the other course.\nThe ribs are shaped to the form of the intrados of the arch,\nDigitized by Google\nSTONE BRIDGES.\n291\nto receive the bolsters, which are of battens cut to suitable\nlengths and nailed to the ribs.\nb\nFig. 123-Represents the rib of a centre for\nlight arches.\na, a, rib formed of planks.\nb, b, bolster pieces which receive the masom-\nry.\n575. For heavy arches with wide spans, when firm inter-\nmediate points of support can be procured between the abut-\nments, the back pieces (Fig. 123) may be supported by shores\nFig. 198-Represents the\nrib of a centre with in-\ntermediate points of\nsupport.\na, back pieces of the rib\nwhich receive the bol-\nsters J.\nb, b, struts which support\nc\nthe back pieces.\ne, a, braces.\na solid beam resting on\na\nthe intermediate sup-\nports d, d, which re-\nceive the ends of the\nstruts b b.\nplaced under the blocks in the direction of the radii of curva-\nture of the arch, or of inclined struts (Fig. 124) resting on the\npoints of support. The shores, or struts, are prevented from\nbending by braces suitably placed for the purpose.\nIf intermediate points of support cannot be obtained, a\nbroad framed support must be made at each abutment to\nreceive the extremities of the struts that sustain the back\npieces. The framed support (Fig. 125) consists of a heavy\nbeam laid either horizontally or inclined, and is placed at that\njoint of the arch (the one which makes an angle of about\n30° with the horizon) where the voussoirs, if unsupported\nbeneath, would slide on their beds. This beam is borne by\nshores, which find firm points of support on the foundations\nof the abutment.\nThe back pieces of the centre (Fig. 125) may be supported\nby inclined struts, which rest immediately upon the framed\nsupport, one of the two struts under each block resting upon\none of the framed supports, the other on the one on the oppo-\nDigitized by Google\n292\nCIVIL ENGINEERING.\nA\nFig. 124-Represents a part of the rib of Grosvenor Bridge over the Dee at Chester. Span 200\nfeet.\nA, A, intermediate points of support.\na, a, a, struts resting upon cast-iron sockets on the supports A.\nb, b, two courses of plank each 4½ inches thick bent over the struts a, a, to the form of the\narch, the courses breaking joints.\nc, c, folding wedges laid upon the back pieces b of each rib to receive the bolsters on which\nthe voussoirs are laid.\nsite side, the two struts being so placed as to make equal\nangles with the radius of curvature of the arch drawn through\nthe middle point of the block. Bridle pieces, placed in the\ndirection of the radius of curvature, embrace the blocks and\nstruts in the usual manner, and prevent the latter from sag-\nging. This combination presents a figure of invariable form,\nas the strain at any one point is received by the struts and\ntransmitted directly to the fixed points of support. It has\nthe disadvantage of requiring beams of great length when the\nspan of the arch is considerable, and of presenting frequent\ncrossing of the struts where notches will be requisite, and the\nstrength of the beams thereby diminished.\nThe centre of Waterloo Bridge, over the Thames (Fig. 125),\nwas framed on this principle. To avoid the inconveniences\nresulting from the crossing of the struts, and of building\nbeams of sufficient length where the struts could not be pro-\ncured from a single beam, the device was adopted of receiv-\ning the ends of several struts at the points of crossing into\na large cast-iron socket suspended by a bridle piece.\n576. When the preceding combination cannot be employed,\na strong truss (Fig. 126), consisting of two inclined struts,\nresting upon the framed supports, and abutting at top against\na straining beam, may be formed to receive the ends of some\nDigitized by Google\nCENTERS FOR ARCHES.\n293\nn.\nFig. 125-Represents a part of & rib of Waterloo Bridge over the Thames.\na, a, b, three heavy beams, forming the striking plates, which with the shores A, A, form the,\nframed support for the struts of the centre.\n.\na a strute abutting against the blocks g, g placed under the joints of the back pieces S. J.\nd, d, bridle or radial pieces in pairs which are confined at top and bottom between the hori-\nzontal ties \" \" of the riba, also in pairs.\na, a cast-iron sockets.\n176, m, bolsters of the centre resting on the back pieces f.\na\nFig. 126-Represents a frame\nfor a rib in which the two\nb\ninclined struts b, b and the\nstraining beams c form in-\ntermediate supports for\nsome of the struts that sup-\nort the back pieces a a.\n6 and d are the framed ex-\ntreme supports\nof the struts which support the back pieces. This combina-\ntion, and all of a like character, require that the arch should\nnot be constructed more rapidly on one side of the centre\nthan on the other, as any inequality of strain on the two\nhalves of the centre would have a tendency to change the\nshape of the frame, thrusting it in the direction of the greater\nstrain.\nDigitized by Google\n294\nCIVIL ENGINEERING.\n577. Style of Architecture. The design and construction\nof a bridge should be governed by the same general princi-\nples as \"y other architectural composition. As the object of\na bridge is to bear heavy loads, and to withstand the effects\nof one of the most destructive agents with which the engineer\nhas to contend, the general character of its architecture\nshould be that of strength. It should not only be secure, but\nto the apprehension appear SO. It should be equally removed\nfrom Egyptian massiveness and Corinthian lightness; while,\nat the same time, it should conform to the features of the\nsurrounding locality, being more ornate and carefully wrought\nin its minor details in a city, and near buildings of a sump-\ntuous style, than in more obscure quarters; and assuming\nevery shade of conformity, from that which would be in\nkeeping with the humblest hamlet and tamest landscape to\nthe boldest features presented by Nature and Art. Sim-\nplicity and strength are its natural characteristics; all orna-\nment of detail being rejected which is not of obvious utility,\nand suitable to the point of view from which it must be seen ;\nas well as all attempts at boldness of general design which\nmight give rise to a feeling of insecurity, however unfounded\nin reality. The heads of the bridge, the cornice, and the\nparapet should generally present an unbroken outline; this,\nhowever, may be departed from in bridges where it is desira-\nble to place recesses for seats, 80 as not to interfere with the\nfootpaths; in which case a plain buttress may be built above\neach starling to support the recess and its seats, the utility of\nwhich will be obvious, while it will give an appearance of\nadditional strength when the height of the parapet above the\nstarlings is at all considerable.\n578. Construction. The methods of laying the founda-\ntions of structures of stone, &c., described under the article\nof Masonry, are alike applicable to all structures which come\nunder this denomination.\n579. Various expedients have been tried to secure the bed\nof the natural water-way around and between the piers;\namong the most simple and efficacious of which is that of\ncovering the surface to be protected by a bed of stone broken\ninto fragments of sufficient bulk to resist the velocity of the\ncurrent in the bays, if the soil is of an ordinary clayey mud\nbut, if it be of loose sand or gravel, the surface should be\nfirst covered by a bed of tenacious clay before the stone be\nthrown in. The voids between the blocks of stone, in time,\nbecome filled with a deposit of mud, which, acting as a\ncement, gives to the mass a character of great durability.\nDigitized by Google\nSTONE BRIDGES.\n295\n580. The foundation courses ot the piers should be formed\nof heavy blocks of cut stone bonded in the most careful\nmanner, and carried up in offsets. The faces of the piers\nshould be of cut stone well bonded. They may be built\neither vertically, or with a slight batter. Their thickness at\nthe impost should be greater than what would be deemed\nsufficient under ordinary circumstances; as they are exposed\nto the destructive action of the current, and of shocks from\nheavy floating bodies; and from the loss of weight of the\nparts immersed, owing to the buoyant effort of the water,\ntheir resistance is decreased. The most successful bridge\narchitects have adopted the practice of making the thickness\nof the piers at the impost between one sixth and one eighth\nof the span of the arch. The thickness of the piers of the\nbridge of Neuilly, near Paris, built by the celebrated Perronet,\nwhose works form an epoch in modern bridge architecture, is\nonly one ninth of the span, its arches also being remarkable\nfor the boldness of their curve.\n581. The usual practice is to give to all the piers the same\nproportional thickness. It has, however, been recommended\nby some engineers to give sufficient thickness to a few of the\npiers to resist the horizontal thrust of the arches on either side\nof them, and thus secure a part of the structure from ruin,\nshould an accident happen to any of the other piers. These\nmasses, to which the name abutment piers has been applied,\nwould be objectionable from the diminution of the natural\nwater-way that would be caused by their bulk, and from the\nadditional cost for their construction, besides impairing the\narchitectural effect of the structure. They present the\nadvantage, in addition to their main object, of permitting the\nbridge to be constructed by sections, and thus procure an\neconomy in the cost of the wooden centres for the arches.\n582. The projection of the starlings beyond the heads of\nthe bridge, their form, and the height given to them above\nthe springing lines, will depend upon local circumstances.\nAs the main objects of the starlings are to form a fender or\nguard to secure the masonry of the spandrels, &c., from\nbeing damaged by floating bodies, and to serve as a cut-water\nto turn the current aside, and prevent the formation of whirls,\nand their action on the bed around the foundations, the form\ngiven to them should subserve both these purposes. Of the\ndifferent forms of horizontal section which have been given\nto starlings (Figs. 127, 128, 129, 130), the semi-ellipse, from\nexperiments carefully made, with these ends in view, appears\nbest to satisfy both objects.\nDigitized by\nGoogle\n296\nCIVIL\nFig. 127.\nFig. 128,\nB\nFiga. 127, 128, and 129-Repre:\nsent horizontal sections of\nstarlings A of the more usual\nforms, and part of the pier B\nabove the foundation courses.\nrig. 129.\nFig. 180 represents the plan of\nFig. 180.\nthe hood of a starling laid in\ncourses, the general shape be-\ning that of the quarter of a\nsphere.\nA\nB\nThe up and down stream starlings, in tidal rivers not sub-\nject to freshets and ice, usually receive the same projections,\nwhich, when their plan is a semi-ellipse, must be somewhat\ngreater than the semi-width of the pier. Their general verti-\ncal outline is columnar, being either straight or swelled (Figs.\n131, 132, 133, 134). They should be built as high as the ordi-\nFlg. 181-Represents in elevation starlings A, their hoods B, the vonsmoirs C. the spandrels\nD, and the combination of their courses and joints with each other in an oval arch of three\ncentres.\nE, parapet; F, cornice.\nnary highest water-level. They are finished at top with a cop-\ning stone to preserve the masonry from the action of rain,\n&c. : this stone, termed the hood, may receive a conical, a\nspheroidal, or any other shape which will subserve the object\nin view, and produce a pleasing architectural effect, in keep-\ning with the locality.\nDigitized by Google\nSTONE BRIDGES.\n297\nR\nI\nFig. 189-Represents in elevation the combinations of the same elements as in Fig. 181 for a\nfist segmental arch.\nR\n0\n702\nFig. 188- Represents in elevation the combinations of the same elements as in Fig. 182, from\nthe bridge of Neuilly, and oval of eleven centres,\nom, curve of intrados.\non, are of circle traced on the head of the bridge.\n0\nFig. 134-Represents a cross section\nand elevation through the crown\nof Fig. 182, showing the ar-\nrangement also of the roadway,\nfootpaths, parapet, and cornice.\nDigitized by Google\n298\nCIVIL ENGINEERING.\nIn streams subject to freshets and ice, the up-stream star-\nlings should receive a greater projection than those down\nstream, and, moreover, be built in the form of an inclined\nplane (Fig. 135) to facilitate the breaking of the ice, and its\npassage through the arches.\nD\nFig. 185-Represents a side elevation\nand plan N of a pier of the Poto-\nmac aqueduct, arranged with an\nfoe-breaker starling.\nc\nA, up-stream starling, with the in-\nP\nclined ice-breaker D, which rises\nfrom the low-water level above\nthat of the highest freshets.\nB, down-stream starling.\n0, face of pier.\nE, top of pier.\nF, horizontal projection of top of\nice breaker.\nGG, horizontal projection of faces\nof pier and starlings.\nN\nG\nG\nE\nF\nG\n583. Where the banks of a water-course spanned by a\nbridge are so steep and difficult of access that the roadway\nmust be raised to the same level with their crests, security\nfor the foundation, and economy in the construction demand\nthat hollow or open piers be used instead of a solid mass of\nmasonry. A construction of this kind requires great pre-\ncaution. The facing courses of the piers must be of heavy\nblocks dressed with extreme accuracy. The starlings must\nbe built solid. The faces must be connected by one or more\ncross tie-walls of heavy, well-bonded blocks; the tie-walls be-\ning connected from distance to distance vertically by strong\ntie-blocks; or, if the width of the pier be considerable, by a\ntie-wall along its centre line.\n584. The foundations, the dimensions, and the form of the\nabutments of a bridge will be regulated upon the same princi-\nples as the like parts of other arched structures; a judicious\nconformity to the character of strength demanded by the\nDigitized by Google\nSTONE BRIDGES.\n299\nstructure and to the requirements of the localitv. being ob-\nserved. The wails which at the extremities 01 the oridge\nform the continuation of the heads, and sustain the embank-\nments of the approaches,-and which, from their widening\nout from the general line of the heads, so as to form a gradual\ncontraction of the avenue by which the bridge is approached,\nare termed the wing-walls,-serve as firm buttresses to the\nabutments. In some cases the back of the abutment is ter-\nminated by a cylindrical arch (Fig. 136) placed on end, or\nhaving its right-line elements vertical, which connects the\nB\nC\nB\nFig. 186-Represents a horizontal section of\nan abutment A, with curved wing-walls B,\nB, connected with a central buttress C,\nand a cross tie-wall D.\nA\nA\nB\nB\nFig. 187-Represents a hori-\nsontal section of an abut-\nment A, with straight wing-\nwalls B, B, terminated by\nreturn-walls C, C. D, central\nC\nbuttrews.\ntwo wing-walls. In others (Fig. 137) a rectangular-shaped\nbuttress is built back from the centre line of the abutment,\nand is connected with the wing-walls either by horizontal\narches, or by a vertical cross tie-wall.\n585. The wing-walls may be either plane surface walls\n(Fig. 138) arranged to make a given angle with the heads of\nthe bridge, or they may be curved surface-walls presenting\ntheir concavity (Fig. 145) or their convexity to the exterior ;\nor of any other shape, whether presenting a continuous or a\nbroken surface, that the locality may demand.\n586. The arches of bridges demand great care in propor-\nDigitized by Google\n300\nCIVIL ENGINEERING.\nM\nFig. 188-Represents an elevation M and plan N of a\nportion of a single arch bridge with straight wing-\nwalls sustaining an embankment across the valley of\nthe water-course.\na, a', face of wing-wall.\n8, b', side slope of emhankment.\na c', top of wing-wall.\no, o', fender or guard stones.\nb'\nN\nb'\ntioning the dimensions of the voussoirs, and procuring accu-\nracy in their forms, as the strength of the structure, and the\npermanence of its figure, will chiefly depend upon the atten-\ntion bestowed on these points. Peculiar care should be given\nin arranging the masonry above the piers which lies between\nthe two adjacent arches. In some of the more recent bridges,\n(Fig. 139,) this part is built up solid but a short distance\nabove the imposts, generally not higher than a fourth of the\nrise, and is finished with a reversed arch to give greater se-\ncurity' against the effects of the pressure thrown upon it.\nThe backs of the arches should be covered with a water-\ntight capping of beton, and a coating of asphaltum.\n587. The entire spandrel courses of the heads are usually\nnot laid until the arches have been uncentred, and have set-\ntled, in order that the joints of these courses may not be sub-\nject to any other cause of displacement than what may arise\nfrom the effects of variations of temperature upon the arches.\nThe thickness of the head-walls will depend upon the\nmethod adopted for supporting the roadway. If this be by a\nfilling of earth between the head-walls, then their thickness\nmust be calculated not only to resist the pressure of the earth\nwhich they sustain, but allowance must also be made for the\nDigitized by Google\nSTONE BRIDGES.\n301\nFig. 189-Represents a longitudinal section of a portion of a pier and foundations, and of an\narch and its centre of the new London bridge over the Thames.\nA, finish of solid spandrel with reversed arch.\nB, wedge of striking plates.\nC, recess over the starlings for seats.\neffects of the shocks of floating bodies in weakening the bond,\nand separating the blocks from their mortar-bed. The more\napproved methods of supporting the roadway, except for very\nflat segment arches, are to lay the road materials either upon\nbroad flagging stones (Figs. 139, 140,) which rest upon thin\nbrick walls built parallel to the head-walls, and supported by\nthe piers and arches; or by small arches, (Fig. 141) for\nwhich these walls serve as piers; or by a system of small\ngroined arches supported by pillars resting upon the piers\nDigitized by Google\n302\nCIVIL ENGINEERING.\nFlg. 140-Represents a profile of\nFig. 189 through the centre of\nthe pier, showing the arrange-\nment of the roadway and its\ndrainage, &c.\nA, section of masonry of pier and\nspandrel.\nb, b, sections of walls parallel to\nhead-wall, which support the\nflagging stone on which the\nroadway is laid.\na section of head-wall and but-\ntress above the starling d.\na footpath.\nJ, recess for seats over the but-\nn\ntrees,\na, cornice and parapet.\n98, vertical conduit in the pier\ncommunicating with two oth-\ners under the roadway from\nthe side channels.\nand main arches. When either of these methods is used, the\nhead-walls may receive a mean thickness of one fifth of their\nheight above the solid spandrel.\n588. Superstructure. The superstructure of a bridge con-\nsists of a cornice, the roadway and footpaths, &c., and a par-\napet.\nThe object of the cornice is to shelter the face of the head-\nwalls from rain. To subserve this purpose, its projection be-\nyond the surface to be sheltered should be the greater as the\naltitude of the sheltered part is the more considerable. This\nrule will require a cornice with supporting blocks, (Fig. 142,)\ntermed modillions, below it, whenever the projecting part\nwould be actually, or might seem, insecure from its weight.\nThe height of the cornice, including its supports, should gen-\nerally be equal to its projections; this will often require more\nor less of detail in the profile of the cornice, in order that it\nmay not appear heavy. The top surface of the cornice should\nbe a little above that of the footpath, or roadway, and be\nslightly sloped outward; the bottom should be arranged with\na suitable tarmier, or drip, to prevent the water from finding\na passage along its under surface to the face of the wall.\n589. The parapet surmounts the cornice, and should be high\nenough to secure vehicles and foot-passengers from accidents,\nwithout however intercepting the view from the bridge. The\nparapet is usually a plain low wall of cut stone, surmounted\nby a coping slightly rounded on its top surface. In bridges\nwhich have a character of lightness, like those with flat seg-\nment arches, the parapet may consist of alternate panels of\nDigitized by Google\nSTONE BRIDGES.\n303\nFg. 141-Represents a section through the axis of a pier of bridge built of stone with brick\nfilling, showing the arrangement for supporting the roadway on small arobes,\nFig. 149-Represents a section through the crown\nof an arch, showing the cornice a, modillion 0,\nparapet a and footpath d.\nA, key-stones.\nB, side elevation of soffit,\nB\nplain wall and balustrades, provided this arrangement be\notherwise in keeping with the locality. The exterior face of\nthe parapet should not project beyond that of the heads. The\nblocks of which it is formed, and particularly those of the\ncoping, should be firmly secured with copper or iron cramps.\n590. Strong and durable stone, dressed with the chisel, or\nhammer, should alone be used for the masonry of bridges\nwhere the span of the arch exceeds fifty feet. The interior of\nDigitized by Google\n304\nCIVIL ENGINEERING.\nB\nFig. 148-Represents an elevation of a pier, a portion of two arches, and the centre of the\nbridge of which Fig. 141 is the section.\nA, face of starling.\nB, hood.\nC, voussoirs with chamfered joints,\nthe piers, and the backing of the abutments and head-walls,\nmay, for economy, be of good rubble, provided great atten-\ntion be bestowed upon the bond and workmanship. For me-\ndium and small spans a mixed masonry of dressed stone and\nrubble, or brick, may be used; and, in some cases, brick alone.\nIn all these cases (Figs. 141, 143) the starlings,-the founda-\ntion courses,-the impost stone,-the ring courses, at least of\nthe heads,-and the key-stone, should be of good dressed stone.\nThe remainder may be of coursed rubble, or of the best brick,\nDigitized by Google\nSTONE BRIDGES.\n305\nfor the facing, with good rubble or brick for the fillings and\nbackings. In a mixed masonry of this character the courses\nof dressed stone may project slightly beyond the surfaces of\nthe rest of. the structure. The architectural effect of this\narrangement is in some degree pleasing, particularly when\nthe joints are chamfered; and the method is obviously useful\nin structures of this kind, as protection is afforded by it to the\nsurfaces which, from the nature of the material, or the char-\nacter of the work, offer the least resistance to the destructive\naction of floating bodies Hydraulic mortar should alone be\nused in every part of the masonry of bridges.\nM\nN\nFig. 144-Elevation M and plan N, showing the manner of arranging the embankments of\nthe approaches, when the head-walls of the bridge are simply prolonged.\na, a', side slope of embankment,\nb, b', dry stone facing of the embankment where its end is rounded off, forming a quarter of a\ncone finish.\nJ.J. flight of steps for foot-passengers to ascend the embankment.\nc, c', embankment arranged as above, but simply sodded.\nd, d', facing of dry stone for the side slopes of the banks.\na c', facing of the bottom of the stream.\n591. Approaches. The approaches should be SO made as\nto procure an easy and safe access to the bridge, and not ob-\nstruct unnecessarily other channels of communication.\nWhen several avenues meet at & bridge, or where the width\nof the roadway of a direct avenue is greater than that of the\nbridge, the approaches are made by gradually widening the\noutlet from the bridge, until it attains the requisite width,\nby means of wing-walls of any of the usual forms that may\n20\nDigitized by Google\n306\nCIVIL ENGINEERING.\nsuit the locality. The form of wing-wall (Fig. 145) present-\ning a concave surface outward is usually preferred when suited\nto the locality, both for its architectural effect and its strength.\nWhen made of dressed stone it is of more difficult construc-\ntion and more expensive than the plane surface wall.\nM\nFig. 145-Represents an elevation M and plan\nN of a ourved face wing-wall.\nA, front view of wing-wall.\nN\nB, B', slope of embankment.\n592. Water-wings. To secure the natural banks near the\nbridge, and the foundations of the abutments from the action\nof the current, a facing of dry stone or of masonry should be\nlaid upon the slope of the banks, which should be properly\nprepared to receive it, and the foot of the facing must be se-\ncured by a mass of loose stone blocks spread over the bed\naround it, in addition to which a line of square-jointed piles\nmay be previously driven along the foot. When the face of\nthe abutment projects beyond the natural banks, an embank-\nment faced with stone should be formed, connecting the face\nwith points on the natural banks above and below the bridge.\nBy this arrangement, termed the water-wings, the natural\nwater-way will be gradually contracted to conform to that\nleft by the bridge.\n593. Enlargement of Water-way. In the full centre and\noval arches, when the springing lines are placed low, the\nspandrels present a considerable surface and obstruction to\nthe current during the higher stages of the water. This not\nonly endangers the safety of the bridge, by the accumulation\nof drift-wood and ice which it occasions, but, during these\nepochs, gives a heavy appearance to the structure. To rem-\nedy these defects the solid angle, formed by the heads and\nthe soffit of the arch, may be truncated, the base of the cunei-\nform-shaped mass taken away being near the springing lines\nDigitized by Google\nSTONE BRIDGES.\n307\nof the arch, and its apex near the crown. The form of the\ndetached mass may be variously arranged. In the bridge of\nNeuilly, which is one of the first where this expedient was\nresorted to, the surface, marked F, (Figs. 133, 134) left by\ndetaching the mass in question, is warped, and lies between\ntwo plane curves, the one an arc of a circle no, traced on the\nhead of the bridge, the other an oval, m o 0 p, traced on the\nsoffit of the arch. This affords a funnel-shaped water-way to\neach arch, and, during high water, gives a light appearance\nto the structure, as the voussoirs of the head ring-course have\nthen the appearance of belonging to a flat segmental arch.\n594. General Remarks. The architecture of stone bridges\nhas, within a somewhat recent period, been carried to a very\nhigh degree of perfection, both in design and in mechanical\nexecution. France, in this respect, has given an example to\nthe world, and has found worthy rivals in the rest of Europe,\nand particularly in Great Britain. Her territory is dotted\nover with innumerable fine monuments of this character,\nwhich attest her solicitude as well for the public welfare as\nfor the advancement of the industrial and liberal arts. For\nher progress in this branch of architecture, France is mainly\nindebted to her School and her Corps of Ponts et Chaussées,\ninstitutions which, from the time of her celebrated engineer\nPerronet, have supplied her with a long line of names, alike\neminent in the sciences and arts which pertain to the profes-\nsion of the engineer.\nEngland, although on some points of mechanical skill per-\ntaining to the engineer's art the superior of France, holds the\nsecond rank to her in the science of her engineers. Without\nestablishments for professional training corresponding to\nthose of France, the English engineers, as a body, have, until\nwithin a few years, labored under the disadvantage of having\nnone of those institutions which, by creating a common bond\nof union, serve not only to diffuse science throughout the\nwhole body, but to raise merit to its proper level, and frown\ndown alike, through an enlightened esprit de corps, the as-\nsumptions of ignorant pretension, and the malevolence of\npetty jealousies.\nAmong the works of this class, in this country, may be\ncited the railroad bridge, called the Thomas Viaduct, over\nthe Patapsco, on the line of the Baltimore and Washington\nrailroad, designed and built by Mr. B. H. Latrobe, the engi-\nneer of the road. This is one of the few existing bridge\nstructures with a curved axis. The engineer has very hap-\npily met the double difficulty before him, of being obliged\nDigitized by\nGoogle\n308\nCIVIL ENGINEERING.\nto adopt a curved axis, and of the want of workmen suffi-\nciently conversant with the application of working drawings\nof a rather complicated character, by placing full centre\ncylindrical arches upon piers with a trapezoidal horizontal\nsection. This structure, with the exception of some minor\ndetails in rather questionable taste, as the slight iron parapet\nrailing, for example, presents an imposing aspect, and does\ngreat credit to the intelligence and skill of the engineer at\nthe time of its construction, but recently launched in a new\ncareer. The fine single arch, known as the Carrolton Via\nduct, on the Baltimore and Ohio railroad, is also highly\ncreditable to the science and skill of the engineer and me-\nchanics under whom it was raised. One of the largest\nbridges in the United States, designed and partly executed\nin stone, is the Potomac Aqueduct at Georgetown, where the\nChesapeake and Ohio canal intersects the Potomac river.\nThis work, to which a wooden superstructure has been made,\nwas built under the superintendence of Captain Turnbull of\nthe U. S. Topographical Engineers.\n595. The following table contains a summary of the prin-\ncipal details of some of the more noted stone bridges of\nEurope:\nNAME OF\nRiver.\nBHIDGE.\nForm of Arch.\nNumber of\narches.\nSpan of widest\nspan.\nRise.\nDepth of key-\nstone.\nWidth between\nthe heads,\nName of Engl-\nneer.\nDate.\nVieille-Brionde\nAllier.\nSegment.\n1\n178\n69\n5.8\n1454\nGrenier & Estone.\nRialto\n**\n1\n98.6\n23\n1578\nMichel Angelo,\nClaix\nDrac.\n\"\n1\n150\n54\n3.1\n1611\nNeuilly\nScine,\nElliptical.\n5\n127.9\n81.9\n5.3\n47.9\n1774\nPerronet.\nLavaur\nAgout,\n1\n160.5\n10.9\n1775\nSaget.\nSaint-Maxence\nOise,\nSegment.\n8\n76.7\n6\n5\n41.5\n1784\nPerronet.\nGignac\nErault.\nElliptical.\n1\n160\n44\n6.5\n1798\nGaripuy.\nJena\nSeine.\nSegment.\n5\n91.8\n10.8\n4.6\n43.7\n1811\nLamandé.\nRouen\nSeine.\n5\n101.7\n13.7\n4.6\n49.2-\n1813\nLamandé.\nWaterloo\nThames.\nElliptical.\n9\n120\n35\n4.9\n45\n1816\nRennie.\nGloncester\nSevern.\n1\n150\n54\n4.5\n35\n1827\nTelford.\nLondon\nThames.\n\"\n5\n152\n37.8\n5\n56\n1831\nRennie.\nTurin\nDora Riparia.\nSegment.\n1\n147.6\n18\n4.9\n40\nMosca.\nGrosvenor\nDee.\n**\n1\n200\n42\n4\n1888\nHartley.\n596. Among the recent French bridges, presenting some\ninteresting features in their construction, may be cited that\nof Souillac over the Dordogne. The river at this place hav-\ning a torrent-like character, and the bed being of lime-stone\nrock with a very uneven surface, and occasional deep fissures\nfilled with sand and gravel, the obstacle to using either the\ncaisson, or the ordinary coffer-dam for the foundations, was\nvery great. The engineer, M. Vicat, so well known by his\nDigitized by Google\nSTONE BRIDGES.\n309\nresearches upon mortar, etc., devised, to obviate these difficul-\nties, the plan of enclosing the area of each pier by a coffer-\nwork accurately fitted to the surface of the bed, and of filling\nthis with beton to form a bed for the foundation courses.\nThis he effected, by first forming a framework of heavy tim-\nber, 80 arranged that thick sheeting-piles could be driven\nclose to the bottom, between its horizontal pieces, and form a\nwell-jointed vessel to contain the semi-fluid material for the\nbed. After this coffer-work was placed, the loose sand and\ngravel was scooped from the bottom, the asperities of the\nsurface levelled, and the fissures were voided, and refilled\nwith fragments of a soft stone, which it was found could be\nmore compactly settled, by ramming, in the fissures, than a\nlooser and rounder material like gravel. On this prepared\nsurface, the bed of beton, which was from 12 to 15 feet in\nthickness, was gradually raised, by successive layers, to with-\nin a few feet of the low-water level, and the stone superstruc-\nture then laid upon it, by using an ordinary coffer-dam that\nrested on the framework around the bed. In this bridge, as\nin that of Bordeaux, a provisional trial-weight, greater than\nthe permanent load, was laid upon the bed, before com-\nmencing the superstructure.\nTo give greater security to foundations, they may be sur-\nrounded with a mass of loose stone blocks thrown in and\nallowed to find their own bed. Where piles are used and\nproject some height above the bottom, besides the loose stone,\na grating of heavy timber, placed between and enclosing the\npiling, may be used to give it greater stiffness and prevent\noutward spreading. In streams of a torrent character, where\nthe bed is liable to be worn away, or shifted, an artificial\ncovering, or apron of stone laid in mortar, has, in some cases,\nbeen used, both under the arches and above and below\nthe bridge, as far as the bed seemed to require this protec-\ntion. At the bridge of Bordeaux loose stone was spread\nover the river-bed between the piers, and it has been found\nto answer perfectly the object of the engineer, the blocks\nhaving, in a few years, become united into a firm mass by\nthe clayey sediment of the river deposited in their interstices.\nAt the elegant cast-iron bridge, built over the Lary, near\nPlymouth, resort was had to a similar plan for securing the\nbed, which is of shifting sand. The engineer, Mr. Rendel,\nhere laid, in the first place, a bed of compact clay upon the\nsand bed between the piers, and imbedded in it loose stone.\nThis method, which for its economy is worthy of note, has\nfully answered the expectations of the engineer.\nDigitized by Google\n310\nCIVIL ENGINEERING.\nIII.\nWOODEN BRIDGES.\n597. Abutments. The abutments and piers of wooden\nbridges may be either of stone or of timber. Stone sup-\nports are preferable to those of timber, both on account of\nthe superior durability of stone, and of its offering more\nsecurity than frames of timber against the accidents to which\nthe piers of bridges are liable from freshets, ice, &c.\n598. Wooden abutments may be formed by constructing\nwhat is termed a crib-work, which consists of large pieces of\nsquare timber laid horizontally upon each other, to form the\nupright or sloping faces of the abutment. These pieces are\nhalved into each other at the angles, and are otherwise firmly\nconnected together by diagonal ties and iron bolts. The space\nenclosed by the crib-work, which is usually built up in the\nmanner just described, only on three sides, is filled with earth\ncarefully rammed, or with dry stone, as circumstances may\nseem to require.\nA wooden abutment of a more economical construction\nmay be made, by partly imbedding large beams of timber\nplaced in a vertical or an inclined position, at intervals of a few\nfeet from each other, and forming a facing of thick plank to\nsustain the earth behind the abutment. Wooden piers may\nalso be made according to either of the methods here laid\ndown, and be filled with loose stone, to give them sufficient\nstability to resist the forces to which they may be exposed\nbut the method is clumsy, and inferior, under every point of\nview, to stone piers, or to the methods which are about to be\nexplained.\n599. The simplest arrangement of a wooden pier consists\n(Fig. 146) in driving heavy square or round piles in a single\nrow, placing them from two to four feet apart. These upright\npieces are sawed off level, and connected at top by a horizon-\ntal beam, termed a cap, which is either mortised to receive a\ntenon made in each upright, or else is fastened to the uprights\nby bolts or pins. Other pieces, which are notched and bolted\nin pairs on the sides of the uprights, are placed in an inclined\nor diagonal position, to brace the whole system firmly. The\nseveral uprights of the pier are placed in the direction of the\nthread of the current. If thought necessary, two horizontal\nbeams, arranged like the diagonal pieces, may be added to\nthe system just below the lowest water-level. In a pier of\nthis kind, the place of the starlings is supplied by two in-\nDigitized by\nGoogle\nPILE FOUNDATIONS.\n311\nclined beams on the same line with the uprights, which are\ntermed fender-beams.\nB\nd\nC\nc\nc\nFig. 146-Elevation of a wooden pier.\na, a, piles of substructure.\nb, b, capping of piles arranged to receive the ends of the uprights a a which support the\nstring-pieces 4 1.\na, upper fender beam.\na, lower fender beam.\n1, horizontal ties bolted in pairs on the uprights.\n0, g, diagonal braces bolted in pairs on the uprights.\nA, capping of the uprights placed under the string pieces,\nA, roadway.\nB, parapet.\n600. A strong objection to the system just described, arises\nfrom the difficulty of replacing the uprights when in a state\nof decay. To remedy this defect, it has been proposed to\n5\n5\nN\nFig. 147-Plan 0, elevation M, and cross section N,\nshowing the arrangement of the capping of the\nfoundation piles with the uprights.\na, piles.\nb, capping of four beams bolted together.\na uprights.\n--\n-\na\ndrive large piles in the positions to be occupied by the uprights\n(Fig. 147), to connect these piles below the low-water level\nby four horizontal beams, firmly fastened to the heads of the\npiles, which are sawed off at a proper height to receive the\nDigitized by Google\n312\nCIVIL ENGINEERING.\nhorizontal beams. The two top beams have large square\nmortises to receive the ends of the uprights, which rest on\nthose of the piles. The rest of the system may be construct-\ned as in the former case. By this arrangement the uprights,\nwhen decayed, can be readily replaced, and they rest on a\nsolid substructure not subject to decay; shorter timber also\ncan be used for the piers than when the uprights are driven\ninto the bed of the stream.\n601. In deep water, and especially in a rapid current, a\nsingle row of piles might prove insufficient to give stability\nto the uprights; and it has therefore been proposed to give\na sufficient spread to the substructure to admit of bracing the\nuprights by struts on the two sides. To effect this, three\npiles (Fig. 148) should be driven for each upright; one just\nunder its position, and the other two on each side of this, on\na line perpendicular to that of the pier. The distance be-\ntween the three piles will depend on the inclination and\nlength that it may be deemed necessary to give the struts. The\nheads of the three piles are sawed off level, and connected\nby two horizontal clamping pieces below the lowest water.\nFig. 148-Elevation of the arrangement of a wide\nfoundation for a wooden pier.\nd\nd\na, upright.\nb, b, piles of the foundation.\n€\na c, capping of the piles.\nd, d, struts to strengthen the uprights.\nc\nc, e, clamping pieces bolted in pairs on the uprights.\nb\nb\nA square mortise is left in these two pieces, over the middle\npile, to receive the uprights. The uprights are fastened to-\ngether at the bottom by two clamping pieces, which rest on\nthose that clamp the heads of the piles, and are rendered\nfirmer by the two struts.\n602. In localities where piles cannot be driven, the uprights\nof the piers may be secured to the bottom by means of a gra-\nting, arranged in a suitable manner to receive the ends of the\nuprights. The bed, on which the grating is to rest, having\nbeen suitably prepared, it is floated to its position, and sunk\neither before or after the uprights are fastened to it, as may\nbe found most convenient. The grating is retained in its\nplace by loose stone. As a farther security for the piers, the\nuprights may be covered by a sheathing of boards, and the\nspaces between the sheathing be filled in with gravel.\n603. As wooden piers are not of a suitable form to resist\nDigitized by Google\nPILE FOUNDATIONS.\n313\nheavy shocks, ice-breakers should be placed in the stream,\nopposite to each pier, and at some distance from it. In\nstreams with a gentle current, a simple inclined beam (Fig.\n149) covered with thick sheet-iron, and supported by uprights\nd\nM\nFig. 149-Elevation M and plan N of a simple ice-\nbreaker.\na, a, foundation piles.\nb, b, capping of piles,\na a uprights.\nd, inclined fender-beam shod with iron.\na\nN\nand diagonal pieces, will be all that is necessary for an ice-\nbreaker. But in rapid currents a crib-work, having the form\nof a triangular pyramid (Fig. 150), the up-stream edge of\nM\nFig. 150-Elevation M and plan N of the\nframe of an ice-breaker to be filled in\nwith broken stone.\nN\nwhich is covered with iron, will be required, to offer sufficient\nresistance to shocks. The crib-work may be filled in, if it be\ndeemed advisable, with blocks of stone.\n604. In determining the length of the span the engineer\nmust take into consideration the fact that wooden bridges\nrequire more frequent repairs than those of stone, arising\nDigitized by Google\n314\nCIVIL ENGINEERING.\nfrom the decay of the material, and from the effects of shrink-\ning and vibrations upon the joints of the frames, and that the\ndifficulty of replacing decayed parts, and readjusting the\nframework, increases rapidly with the span.\n605. Bridge-frames may be divided into two general classes.\nTo the one belong all those combinations, whether of straight or\nof curved timber, that exert a lateral pressure upon the abut-\nments and piers, and in which the superstructure is generally\nabove the bridge-frame. To the other, those combinations\nwhich exert no lateral pressure upon the points of support,\nand in which the roadway, &c., may be said to be suspended\nfrom the bridge-frame.\n606. Definitions of some of the terms employed in\nbridge nomenclature.\nA Chord is the upper or lower member in a truss. It ex-\ntends from end to end of the structure. There are usually two\nchords, an upper and a lower chord. These may be parallel,\nas in Figs. 157 and 167, or the upper one may be curved\n(arched) and the lower one horizontal, or both may be curved.\nThese pieces by some English writers are called booms, and by\nothers stringers. The lower chord is often called a tie. The\nupper chord is sometimes called a straining beam.\nA Tie is a piece which connects two parts and is subjected\nto tension.\nA Strut is a general term which is applied to a piece in a\ntruss which is subjected to compression. In proportioning it,\nit is treated as a pillar. In its more restricted sense, it is a\nshort piece which is subjected to compression.\nA Tie-Strut, or Strut-Tie, is a piece which may be sub-\njected to tension and compression at different times, under\ndifferent conditions of loading.\nA Braceis an inclined piece which is subjected to compres-\nsion. It is an inclined strut. In bridges, braces are some-\ntimes distinguished as main-braces and counter-braces. This\nFig. 151.\nUPPER\nCHORD\nBRACE\nLOWER\nCHORD\nDigitized by\nGoogle\nWOODEN BRIDGES.\n315\ndistinction is quite unnecessary in an analytical point of view,\nas will be seen hereafter, but it is 80 common in practice that\nit will not do to ignore it.\nA Main-Brace is a brace which inclines from the end of a\ntruss towards the centre, as in Fig. 151.\nA Counter-Brace is one which inclines from the centre\nand towards the ends. In the same panel the counter-brace\ninclines the opposite way from the main-brace. See Fig. 151.\nA Tie-Brace performs the office of both main and counter-\nbrace; it is the same as a Tie-Strut.\n607. Long's Truss. This was one of the first trusses of\nthis country in which a scientific arrangement of the parts\nwas observed. It was composed entirely of wood, even iron\nbolts for splicing the main beams being avoided. It consists\nin forming both the upper and lower beams (Fig. 152) of\nthree parallel beams, sufficient space being left between the\na\nA\na\nD\nC\nC\nE\na\nB\nFig. 159-Represents a panel of Long's truss.\nA and B, top and bottom strings of three courses,\nC, C, posts in pairs.\nD, braces in pairs.\nE, counter-brace single.\na, a, mortises where jibs and keys are inserted.\nF, jib and key of hard wood.\nDigitized by Google\n316\nCIVIL ENGINEERING.\none in the centre and the other two to insert the cross pieces,\ntermed the posts; the posts consist of beams in pairs placed\nat suitable intervals along the strings, with which they are\nconnected by wedge blocks, termed jibs and keys, which are\ninserted into rectangular holes made through the strings,\nand fitting a corresponding shallow notch cut into each post.\nA brace connects the top of one post with the foot of the\none adjacent by a suitable joint. Another diagonal piece,\ntermed the counter-brace, is placed crosswise between the two\nbraces and their posts, with its ends abutting against the\ncentre beam of the upper and lower strings. The counter-\nbraces are connected with the posts and braces by wooden\npins, termed tree-nails.\nIn wide bearings, the strings require to be made of several\nbeams abutting end to end; in this case the beams should\nbreak joints, and short beams should be inserted between the\ncentre and exterior beams wherever the joints occur, to\nstrengthen them.\nThe beams in this combination are all of uniform cross\nsection, the joints and fastenings are of the simplest kind,\nand the parts are well distributed to call into play the\nstrength of the strings, and to produce uniform stiffness and\nstrain.\n608. Town's Truss.-The combination of Mr. Town\n(Fig. 153) consists in two main strings, each formed of two or\nFig 153.-Represents an elevation A, and end view, B,\nof a portion of Town's truss.\na, a, top strings.\nb, b, bottom strings.\nc, a diagonal braces.\nthree parallel beams of two thicknesses breaking joints. Be-\ntween the parallel beams are inserted a series of diagonal\nbeams crossing each other. These diagonals are connected\nwith the strings and with each other by tree-nails. When\nthe strings are formed of three parallel beams, diagonal\npieces are placed between the centre and exterior beams, and\ntwo intermediate strings are placed between the two courses\nof diagonals.\nThis combination, commonly known as the lattice truss, is\nof very easy mechanical execution, the beams being of a uni-\nDigitized by Google\nWOODEN BRIDGES.\n317\nform cross section and length. The strains upon it are borne\nby the tree-nails, and when used for structures subjected to\nvariable strains and jars, it loses its stiffness and sags between\nthe points of support. It is more commendable for its\nsimplicity than scientific combination.\n609. Howe's Truss.-This truss consists of (Fig. 154) an\nupper and lower string, each formed of several thicknesses\nof beams placed side by side and breaking joints. On the\nupper side of the lower string and the lower side of the\nupper, blocks of hard wood are inserted into shallow notches ;\nthe blocks are bevelled off on each side to form a suitable\npoint of support, or step for the diagonal pieces. One series.\nof the diagonal pieces are arranged in pairs, the others are\nsingle and placed between those in pairs. Two strong bolts\nof iron, which pass through the blocks, connect the upper\nand lower strings, and are arranged with a screw cut on one\nend and a nut to draw the parts closely together.\nThis combination presents a judicious arrangement of the\nparts. The blocks give abutting surfaces for the braces su-\nperior to those obtained by the ordinary forms of joint for\nthis purpose. The bolts replace advantageously the timber\ne\nd\nFig. 154 - Represents\nan elevation of a por-\ntion of Howe's truss.\ncl\na, top string.\nb, bottom strings.\nc, c, diagonal braces in\npairs,\nd, single braces.\ne, e, steps of hard wood\nfor braces,\nJ.J. iron rods with nuts\nand screws,\nC\nposts, and in case of the frame working loose and sagging,\ntheir arrangement for tightening up the parts is simple and\nefficacious.\n610. Schuylkill Bridge.-This bridge, designed and\nbuilt by L. Wernwag, has the widest span of any wooden\nDigitized by Google\n318\nCIVIL ENGINEERING.\nFig 86 is a perspective view of a part of one panell\nof the Howe truss, and shows quite clearly how\nthe parts are arranged. For an analysis of\nthese structures, see Wood's Treatise on Bridges\nand Roofs. I\nbridge in this country. The bridge-frame (Fig. 155) consisted\nB\nFig. 155-Represents a side view of a portion of the open-ourved rib of the\nbridge over the Schnylkill at Philadelphia.\nA, lower curved built beam.\nB, top beam.\na, a, posta,\na c, diagonal braces,\no, \", iron diagonal ties.\nm, m, iron stays anchored in the abutment C.\nof five ribs. Each rib is an open-built beam formed of a\nbottom curved solid-built beam and of a single top beam,\nwhich are connected by radial pieces, diagonal braces, and\ninclined iron stays. The bottom curved beam is composed\nof three concentric solid-built beams, slightly separated from\neach other, each of which has seven courses of curved scant-\nling in it, each course 6 inches thick by 13 inches in breadth ;\nthe courses, as well as the concentric beams, being firmly\nunited by iron bolts, &c. A roadway that rests upon the\nbottom curved ribs is left on each side of the centre rib, and\na footpath between each of the two exterior ribs. The bridge\nwas covered in by a roof and a sheathing on the sides.\n611. Burr's Truss.-Burr's plan, which (Fig. 156) consists\nDigitized by Google\nWOODEN BRIDGES.\n319\nin forming each rib of an open-built beam of straight timber,\nand connecting with it a curved solid-built. beam formed of\ntwo or more thicknesses of scantling, between which the\nb\nd\nd\nd\nb\nb\nOX\nox\nOX\nOX\nFig. 156-Represents a side view of a\na, a plate of the side frame.\nportion of a rib of Burr's bridge.\n0, o, floor girders on which the flooring,\na, a, arch timbers,\njoists and flooring boards rest.\nd, a, queen-posts.\n98, n, check braces,\nb, b, braces.\n4, 4, tie-beams of roof.\na c, chords,\nA, portion of pier.\nframework of the open-built beam is clamped. The open-\nbuilt beam consists of a horizontal bottom beam of two\nthicknesses of scantling, termed the chords, between which\nare secured the uprights, termed the queen posts,-of a single\ntop beam, termed the plate of the side frame, which rests\nupon the uprights, with which it is connected by a mortise\nand tenon joint,-and of diagonal braces and other smaller\nbraces, termed check braces, placed between the uprights.\nFig. 157.\nThe curved-built beam, termed the arch-timbers, is bolted\nupon the timbers of the open-built beam. The bridge-frame\nDigitized by Google\n320\nCIVIL ENGINEERING.\nmay consist of two or more ribs, which are connected and\nstiffened by cross ties and diagonal braces. The roadway-\nflooring is laid upon cross pieces, termed the floor girders,\nwhich may either rest upon the chords, or else be attached at\nany intermediate point between them and the top beam.\nThe roadway and footpaths may be placed in any position\nbetween the several ribs.\n612. Pratt's Truss. This truss (Fig. 157) has the same\ngeneral form as Howe's, but differs in its details. The ver-\nticals here are wooden posts instead of iron rods, and the\ndiagonals are iron ties instead of wooden braces.\n613. MoCallum's Truss. This truss (Fig. 158) is a modi-\nFig. 158.\nfication of Howe's, the essential difference of which consists\nin a curved upper chord instead of a horizontal one. The\nlong braces at the end-called arch braces,-are not essential\nto this system. This system is stiffer than similar ones having\nhorizontal chords.\n614. A simple but effective structure, shown in Fig. 159,\nFig. 159.\nDigitized by Google\nWOODEN BRIDGES.\n321\nhas been in use for some time on the N. Y. State canals for\ncommon road bridges, and for crossings on farms. There\nare no counter-braces, which, as may readily be shown, are\nunnecessary for short spans. (See Wood's Treatise on Bridges\nand Roofs, pp. 120 and 121.) The lower timber may be\nspliced, or in any other manner made continuous throughout.\nAnother timber, which is placed on this, extends over two or\nfour of the central bays. The verticals, which are iron rods,\nare made divergent, as shown in Fig. 159a.\nA\n159 a. Cross section of a New York State\ncanal bridge.\nA, upper chord.\nB, lower chord.\na, b, suspending rods, which incline out-\nward.\nC, a floor-girder.\nb\nd, a diagonal rod.\na\nB\nc\n615. Wooden Arches. A wooden arch may be formed by\nbending a single beam (Fig. 160) and confining its extremi-\nc\n6\nFig. 160 - Represents a horizontal\nbeam c supported at its middle\npoint by a bent beam b.\na\nties to prevent it from resuming its original shape. A beam\nin this state presents greater resistance to a cross strain than\nwhen straight, and may be used with advantage where great\nstiffness is required, provided the points of support are of\nsufficient strength to resist the lateral thrust of the beam.\nThis method can be resorted to only in narrow bearings.\nFor wide arches a curved-built beam must be adopted; and\nfor this purpose a solid (Figs. 161 and 162) or an open-built\nbeam may be used, depending on the bearing to be spanned\nby the arçh. In either case the curved beams are built in\n21\nDigitized by Google\n322\nCIVIL ENGINEERING.\nthe same manner as straight beams, the pieces of which they\nare formed being suitably bent to conform to the curvature\nof the arch, which may be done either by steaming the pieces,\nby mechanical power, or by the usual method of softening the\nwoody fibres by keeping the pieces wet while subjected to\nthe heat of a light blaze.\nFig, 161.\nFig. 161-Represents a wooden arch A, formed of a solid-built beam of three\ncourses, which support the beams c, c by the posts g, g, which are formed\nof pieces in pairs.\nb, b, inclined strute to strengthen the arch by relieving it of a part of the\nload on the beams c, c.\nFig. 162.\na.\na\nB\nFig. 162-Represents a wooden arch of a solid-built beam A, which supports\nthe horizontal beam B by means of the posts a, a. The arch is let into\nthe beam B, which acts as a tie to confine its extremities.\n616. The number of ribs in the bridge-frame will depend\non the general strength required by the object of the struc-\nture, and upon the class of frame adopted. In the first\nclass, in which the roadway is usually above the frames, any\nrequisite number of ribs may be used, and they may be\nplaced at equal intervals apart, or else be SO placed as to give\nthe best support to the loads which pass over the bridge. In\nthe second class, as the frame usually lies entirely, or projects\npartly above the roadway, &c., if more than two ribs are re-\nquired, they are SO arranged that one or two, as circumstances\nmay demand, form each head of the bridge, and one or two\nmore are placed midway between the heads, so as to leave a\nsufficient width of roadway between the centre and adjacent\nribs. The footpaths are usually, in this case, either placed\nDigitized by Google\nWOODEN BRIDGES.\n323\nbetween the two centre ribs, or, when there are two exterior\nribs, between them.\n617. In frames which exert a lateral pressure against the\nabutments and piers, the lowest points of the framework\nshould be so placed as to be above the ordinary high-water\nlevel; and plates of some metal should be inserted at those\npoints, both of the frame and of the supports, where the\neffect of the pressure might cause injury to the woody fibre.\n618. The roadway usually consists of a simple flooring\nformed of cross joists, termed the roadway-bearers, or floor-\ngirders, and flooring-boards, upon which a road-covering\neither of wood or stone is laid. A more common and better\narrangement of the roadway, now in use, consists in laying\nlongitudinal joists of smaller scantling upon the roadway-\nbearers, to support the flooring-boards. This method pre-\nserves more effectually than the other the roadway-bearers\nfrom moisture. Besides, in bridges which, from the position\nof the roadway, do not admit of vertical diagonal braces to\nstiffen the framework, the only means, in most cases, of\neffecting this object is in placing horizontal diagonal braces\nbetween each pair of roadway-bearers. For like reasons,\nstone road-coverings for wooden bridges are generally re-\njected, and one of plank used, which, for a horse-track, should\nbe of two thicknesses, so that, in case of repairs, arising from\nthe wear and tear of travel, the boards resting upon the\nflooring-joists may not require to be removed. The footpaths\nconsist simply of a slight flooring of sufficient width, which\nis usually detached from and raised a few inches above the\nroadway surface.\n619. When the bridge-frame is beneath the roadway, a\ndistinct parapet will be requisite for the safety of passengers.\nThis may be formed either of wood, of iron, or of the two\ncombined. It is most generally made of timber, and con-\nsists of a hand and foot rail connected by upright posts and\nstiffened by diagonal braces. A wooden parapet, besides the\nsecurity it gives to passengers, may be made to add both to\nthe strength and stiffness of the bridge, by constructing it of\ntimber of a suitable size, and connecting it firmly with the\nexterior ribs.\n620. In bridge-frames in which the ribs are above the road-\nway, a timber sheathing of thin boards will be requisite on the\nsides, and a roof above, to protect the structure from the\nweather. The tie-beams of the roof-trusses may serve also as\nties for the ribs at top, and may receive horizontal diagonal\nbraces to stiffen the structure, like those of the roadway-\nDigitized by Google\n324\nCIVIL ENGINEERING.\nbearers. The rafters, in the case in which there is no centre\nrib, and the bearing, or distance between the exterior ribs, is\nSO great that the roadway-bearers require to be supported in\nthe middle, may serve as points of support for suspension\npieces of wood, or of iron, to which the middle point of the\nroadway-bearers may be attached.\n621. The frame and other main timbers of a wooden bridge\nwill not require to be coated with paint, or any like compo-\nsition, to preserve them from decay when they are roofed\nand boarded in to keep them dry. When this is not the case,\nthe ordinary preservatives against atmospheric action may be\nused for them. The under surface and joints of the planks\nof the roadway may be coated with bituminous mastic when\nused for a horse-track; in railroad bridges a metallic cover-\ning may be suitably used when the bridge is not traversed by\nhorses.\n622. Wooden bridges can produce but little other archi-\ntectural effect than that which naturally springs up in the\nmind of an educated spectator in regarding any judiciously-\ncontrived structure. When the roadway and parapet are\nabove the bridge-frame, a very simple cornice may be formed\nby a proper combination of the roadway-timbers and flooring,\nwhich, with the parapet, will present not only a pleasing ap-\npearance to the eye, but will be of obvious utility in covering\nthe parts beneath from the weather. In covered bridges, the\nmost that can be done will be to paint them with a uniform\ncoat of some subdued tint. At best, from their want of\nheight as compared with their length, covered wooden bridges\nmust, for the most part, be only unsightly, and also apparent-\nly insecure structures when looked at from such a point of\nview as to embrace all the parts in the field of vision; and\nany attempt, therefore, to disguise their true character, and\nto give them by painting the appearance of houses, or of stone\narches, while it must fail to deceive even the most ignorant,\nwill only betray the bad taste of the architect to the more en-\nlightened judge.\nThe art of erecting wooden bridges has been carried to\ngreat perfection in almost every part of the world where\ntimber has, at any period, been the principal building mate-\nrial at the disposal of the architect; but iron at the present\nday is fast taking the place of wood in the more important\nbridges.\n623. The following Table contains the principal dimen-\nsions of some of the most celebrated American and European\nwooden bridges:\nDigitized by Google\nWOODEN BRIDGES.\n325\nNumber of\nWidth of\nNAME, ETC., OF BRIDGE.\nRise or depth\nbays.\nwidest bay.\nof rib.\nWettengen bridge.\n1\n390 ft.\n-\nBridge of Schaffhausen\n2\n193 \"\n-\nBridge of Kandel\n1\n166 \"\n-\nBridge of Bamberg\n1\n208 \"\n16.9 ft.\nBridge of Freysingen\n2\n153 \"\n11.6 \"\nEssex bridge\n1\n250 \"\n-\nUpper Schuylkill bridge\n1\n340 \"\n20 \"\nMarket-street bridge\n3\n195 \"\n12 \"\nTrenton bridge\n5\n200 \"\n27\n\"\nColumbia bridge\n29\n200 \"\n-\nRichmond bridge\n19\n153 \"\n15.4 \"\nSpringfield bridge.\n7\n180 \"\n18 \"\nSusquehanna bridge\n10\n250 \"\n-\nIV.\nCAST-IRON BRIDGES.\n624. Bridges of cast iron admit of even greater bold-\nness of design than those of timber, owing to the superiority,\nboth in strength and durability, of the former over the\nlatter material; and they may therefore be resorted to under\ncircumstances very nearly the same in which a wooden struc-\nture would be suitable.\n625. The abutments and piers of cast-iron bridges should\nbe built of stone, as the corrosive action of salt water, or\neven of fresh water when impure, would in time render\niron supports of this character insecure; and timber, when\nexposed to the same destructive agents, is still less durable\nthan cast iron.\n626. The curved ribs of cast-iron bridge-frames have under-\ngone various modifications and improvements. In the earlier\nbridges, they were formed of several concentric arcs, or\ncurved beams, placed at some distance asunder, and united\nby radial pieces the spandrels being filled either by con-\ntiguous rings, or by vertical pieces of cast iron upon which\nthe roadway bearers were laid.\nIn the next stage of progress towards improvement, the\ncurved ribs were made less deep, and were each formed of\nseveral segments, or panels cast separately in one piece, each\npanel consisting of three concentric arcs connected by radial\npieces, and having flanches, with other suitable arrangements,\nfor connecting them firmly by wrought-iron keys, screw-bolts,\n&c. ; the entire rib thus presenting the appearance of three\nconcentric arcs connected by radial pieces. The spandrels\nwere filled either with panels formed like those of the curved\nDigitized by Google\n326\nCIVIL ENGINEERING.\nribs, with iron rings, or with a lozenge-shaped reticulated\ncombination. The ribs were connected by cast-iron plates\nand wrought-iron diagonal ties.\nIn the more recent structures, the ribs have been com-\nposed of voussoir-shaped panels, each formed of a solid thin\nplate with flanches around the edges; or else of a curved\ntubular rib, formed like those of Polonceau, or of Dela-\nfield, described further on. The spandrel-filling is either a\nreticulated combination, or one of contiguous iron rings.\nThe ribs are usually united by cast-iron tie-plates, and\nbraced by diagonal ties of cast and wrought iron.\n609. The roadway-bearers and flooring may be formed\neither of timber, or of cast iron. In the more recent struc-\ntures in England, they have been made of the latter material\nthe roadway-bearers being cast of a suitable form for strength,\nand for their connection with the ribs; and the flooring-\nplates being of cast-iron.\nThe roadway and footpaths, formed in the usual manner,\nrest upon the flooring-plates.\nThe parapet consists, in most cases, of a light combina-\ntion of cast or wrought iron, in keeping with the general\nstyle of the structure.\n627. The English engineers have taken the lead in this\nbranch of architecture, and, in their more recent structures,\nhave carried it to a high degree of mechanical perfection\nand architectural elegance. Among the more celebrated\ncast-iron bridges in England, that of Coalbrookdale belongs\nto the first epoch above mentioned; those of Staines and\nSunderland to the second; and to the third, the bridge\nof Southwark at London; that of Tewkesbury over the\nSevern; that over the Lary near Plymouth, and a number of\nothers in various parts of the United Kingdom.\nThe French engineers have not only followed the lead\nset them by the English, but have taken a new step, in\nthe tubular-shaped ribs of M. Polonceau. The Pont des\nArts at Paris, a very light bridge for foot-passengers only,\nand which is a combination of cast and wrought iron, belongs\nto their earliest essays in this line; the Pont Austerlitz,\nalso at Paris, which is a combination similar to those of\nStaines and Sunderland, belongs to their second epoch; and\nthe Pont du Carrousel, in the same city, built upon Polon-\nceau's system, with several others on the same plan, belong\nto the last.\nIn the United States a commencement can hardly be said\nto have been made in this branch of bridge architecture;\nDigitized by Google\nCAST-IRON BRIDGES.\n327\nthe bridge of eighty feet span, with tubular ribs, constructed\nby Major Delafield at Brownsville, stands almost alone,\nand is a step contemporary with that of Polonceau in France.\nThe following Table contains a summary description of\nsome of the most noted European cast-iron bridges:\nNAME OF BRIDGE.\nRiver.\nNo. of\nSpan in\nRise in\nNo. of\nDate.\nEngineer.\narches.\nfeet.\nfeet.\nribe.\nCoalbrookdale\nSevern\n1\n100.5\n40\n5\n1779\n-\nWearmonth\nWear\n1\n240\n30\n6\n1796\nBurdon.\nStaines.\n1\n181\n16.5\n-\n1802\n-\nAusterlits\nSeine\n5\n106.6\n10.6\n7\n1805\nLamandé.\nVauxhall\nThames\n9\n78\n-\n9\n1816\nWalker.\nSouthwark\nThames\n8\n240\n24\n8\n1818\nRennie.\nTewkesbury\nSevern\n1\n170\n17\n6\n-\nTelford.\nLary\nLary\n5\n100\n14.5\n5\n1827\nRendel.\nCarrousel\nSeine\n8\n150\n16\n5\n1838\nPolonceau.\n628. Iron Arches. Cast-iron arches may be used for the\nsame objects as those of timber. The frames for these pur-\nposes consist of several parallel ribs of uniform dimensions,\nwhich are cast into an arch form, the ribs being connected\nby horizontal ties, and stiffened by diagonal braces. The\nweight of the superstructure is transmitted to the curved\nribs in a variety of ways; most usually by an open cast-\niron beam, the lower part of which is so shaped as to rest\nupon the curved rib, and the upper part suitably formed for\nthe object in view. These beams are also connected by ties,\nand stiffened by diagonal braces.\nEach rib, except for narrow spans, is composed of several\npieces, or segments, between each pair of which there is a\nB\nB\nFig. 168-Repre-\nsents a portion\nof a cast-iron\nplate arch with\nan open cast-iron\nbeam.\nA, A, segments of\nthe arch.\nA\nB, B, panels of the\nopen beam con-\nnected at the\njoints a b.\nA\nDigitized by Google\n328\nCIVIL ENGINEERING.\njoint in the direction of the radius of curvature. The forms\nand dimensions of the segments are uniform. The segments\nare usually either solid (Fig. 163) or open plates of uniform\nthickness, having a flauch of uniform breadth and depth at\neach end, and on the entrados and intrados. The flanch serves\nboth to givestrength to the segment and to form the connection\nbetween the segments and the parts which rest upon the rib.\nThe ribs are connected by tie-plates, which are inserted be-\ntween the joints of the segments, and are fastened to the seg-\nments by iron screw bolts, which pass through the end flanches\nof the segments and the tie-plate between them. The tie-\nplates may be either open or solid; the former being usually\npreferred on account of their superior lightness and cheapness.\nThe framework of the ribs is stiffened by diagonal pieces,\nwhich are connected either with the ribs or the tie-plates.\nThe diagonal braces are cast in one piece, the arms being\nribbed, or feathered, and tapering from the centre towards\nthe ends in a suitable manner to give lightness combined with\nstrength.\nThe open beams (Fig. 163), which rest upon the curved ribs,\nare cast in a suitable number of panels; the joint between\neach pair being either in the direction of the radii of the arch,\nor else vertical. These pieces are also cast with flanches, by\nwhich they are connected together, and with the other parts\nof the frame. The beams, like the ribs, are tied together and\nstiffened by ties and diagonal braces.\nBeams of suitable forms for the purposes of the structure\nare placed either lengthwise or crosswise upon the open\nbeams.\n629. Curved ribs of a tubular form have, within a few years\nback, been tried with success, and bid fair to supersede the\nordinary plate rib, as with the same amount of metal they\ncombine more strength than the flat rib.\nThe application of tubular ribs was first made in the United\nStates by Major Delafield of the U.S. Corps of Engineers, in\nan arch for a bridge of 80 feet span. Each rib was formed of\nnine segments; each segment (Fig. 164) being cast in one\npiece, the cross section of which is an elliptical ring of uni-\nform thickness, the transverse axis of the ellipse being in\nthe direction of the radius of curvature of the rib. A broad\nelliptical flanch with ribs, or stays, is cast on each end of the\nsegment, to connect the parts with each other; and three\nchairs, or saddle-pieces, with grooves in them, are cast upon\nthe entrados of each segment, and at equal intervals apart, to\nreceive the open beam which rests on the curved rib.\nDigitized by Google\nCAST-IRON BRIDGES.\n329\nThe ribs are connected by an open tie plate (Fig. 164).\nRaised elliptical projections are cast on each face of the tie\nplate, where it is connected with the segments, which are\nadjusted accurately to the interior surface of each pair of\nsegments, between which the tie plate is embraced. The\nsegments and plate are fastened by screw bolts passed\nthrough the end flanches of the segments.\nc\nb\nb\nb\nB\nZ\n6\nFig. 164-Represents a side view A, and a cross section and end view B, through a saddle-piece\nof the tubular arch of Major Delafield.\na, a (Fig. A), a side view, and (Fig. B) an end view of the elliptical flanches of the end of each\nsegment.\nb, b, shoulders, or ribs to strengthen the flanches against lateral strains.\ns tie-plate, between the ribs.\nJ, (Fig. B) side view of the rim of the tie-plate fitted to the interior of the tube.\nd, d, (Fige. A. and B) saddle-pieces to receive the open beams of a form similar to Fig. 163,\nwhich rest on the tubular ribs.\ne, cross section of the rib through the saddle-piece.\nThe tie plates form the only connection between the curved\nribs; the broad-ribbed flanches of the segments, and the\nraised rims of the tie plates inserted into the ends of the\ntubes, giving all the advantages and stiffness of diagonal\npieces.\n630. Tubular ribs with an elliptical cross section have\nbeen used in France for many of their bridges. They were\nfirst introduced but a few years back by M. Polonceau, after\nDigitized by Google\n330\nCIVIL ENGINEERING.\nd\nB\ne\n0\nFig. 165.-Represents a side view A, and a cross section and end view B, through a joint of M.\nPolonceau's tubular arch.\na, a. top flanch, b, b. bottom flanch of the semi-segments united along the vertical joint od\nthrough the axis of the rib.\ng n, side view of the joint between the flanches a, . of two semi-segments.\nm, inner side of the flanches.\nc, cross section of a semi-segment and top and bottom flanches.\nf, J. thin wedges of wrought iron placed between the end flanches of the semi-segments to bring\nthe parts to their proper bearing.\nwhose designs the greater part of these structures have been\nbuilt. According to M. Polonceau's plan, each rib consists\nof two symmetrical parts divided lengthwise by a vertical\njoint. Each half of the rib is composed of a number of\nsegments SO distributed as to break joints, in order that when\nthe segments are put together there shall be no continuous\ncross joint through the ribs.\nThe segments (Fig. 165) are cast with a top and bottom\nflanch, and one also at each end. The halves of the rib are\nconnected by bolts through the upper and lower flanches,\nand the segments by bolts through the end flanches.\nFor the purposes of adjusting the segments and bringing\nthe rib to a suitable degree of tension, flat pieces of wrought\niron of a wedge shape are driven into the joints between the\nsegments, and are confined in the joints by the bolts which\nfasten the segments and which also pass through these\nwedges.\nTo. connect the ribs with each other, iron tubular pieces\nare placed between them, the ends of the tubes being suita-\nbly adjusted to the sides of the ribs. Wrought-iron rods\nwhich serve as ties pass through the tubes and ribs, being\narranged with screws and nuts to draw the ribs firmly against\nthe tubular pieces. Diagonal pieces of a suitable form are\nDigitized by Google\nCAST-IRON BRIDGES.\n331\nplaced between the ribs to give them the requisite degree of\nstiffness.\nIn the bridges constructed by M. Polonceau according to\nthis plan, he supports the longitudinal beams of the roadway\nby cast-iron rings which are fastened to the ribs and to\neach other, and bear a chair of suitable form to receive the\nbeams.\n631. Open cast-iron beams are seldom used except in com-\nbination with cast-iron arches. Those of wrought iron are\nfrequently used in structures. They may be formed of a\ntop and bottom rail connected by diagonal pieces, forming the\nordinary lattice arrangement, or a piece bent into a curved\nFig. 166-Represents an open beam\nd\nof wrought iron consisting of a top\nand bottom rail a and b, with an\nintermediate curved piece, the\nwhole secured by the pieces a c, in\npairs bolted to them.\nd, e, and I represent the parts of a\ntruss of a curved light roof, con-\nnected with the open beam; and\nalso the manner in which the\nwhole are secured to the wall.\ne\n0\nform may be placed between the rails, or any other suitable\ncombination (Fig. 166) may be used which combines lightness\nwith strength and stiffness.\n632. Effects of Temperature on Stone and Cast-iron\nBridges. The action of variations of temperature upon\nmasses of masonry, particularly in the coping, has already been\nnoticed. The effect of the same action upon the equilibrium\nof arches was first observed by M. Vicat in the stone bridge\nbuilt by him at Souillac, in the joints of which periodical\nchanges were found to take place, not only from the ranges\nof temperature between the seasons, but even daily. Similar\nphenomena were also very accurately noted by Mr. George\nRennie in a stone bridge at Staines.\nFrom these recorded observations the fact is conclusively\nestablished, that the joints of stone bridges, both in the arches\nDigitized by Google\n332\nCIVIL ENGINEERING.\nand spandrels, are periodically affected by this action, which\nmust consequently at times throw an increased amount of\npressure upon the abutments, but without, under ordinary\ncircumstances, any danger to the permanent stability of the\nstructure.\nWhen iron was first proposed to be employed for bridges,\nobjections were brought against it on the ground of the effect\nof changes of temperature upon this metal. The failure in\nthe abutments of the iron bridge at Staines was imputed to\nthis cause, and like objections were seriously urged against\nother structures about to be erected in England. To put\nthis matter at rest, observations were very carefully made by\nSir John Rennie upon the arches of Southwark bridge, built\nby his father. From these experiments it appears that the\nmean rise of the centre arch at the crown was about 40th of\nan inch for each degree of Fahr., or 1.25 inches for 50° Fahr.\nThe change of form and increase of pressure arising from\nthis cause do not appear to have affected in any sensible\ndegree the permanent stability either of this structure, or of\nany of a like character in Europe.\nV.\nIRON TRUSSED BRIDGES.\n633. AMONG the earliest and most meritorious of the iron\nbridges of this country is Whipple's Trapezoidal Truss (see\nFig. 167). So far as the arrangement of ties and struts are\nconcerned it is similar to the Pratt Truss.\nFig. 167.-The upper chord is of cast-iron and made in sections, the length of each piece be-\ning equal to the length of a bay. The lower chord is composed of a succession of links (see\nFig. 168), which receive cast-iron blocks at their ends. The cast-iron blocks form steps for\nsecuring the lower ends of the vertical posts. The posts have openings near the middle of\ntheir length. through which the main and counter-ties pass. The posts are trussed at the\nmiddle, as shown in the figure.\nIn this truss the end members are inclined, SO that the\ngeneral form of the outline is that of a trapezoid. All un-\nDigitized by\nGoogle\nIRON BRIDGES.\n333\nnecessary members are omitted, and hence comparatively few\ncounter-ties are used. In the Fig. only two are shown-one\neach side of the centre. The number of counter-ties depends\nupon the relation of the moving load to that of the weight of\nthe bridge (see articles 107 and 108 of Wood's Treatise on\nBridges and Roofs).\nThe lower chord is sometimes made of links of iron (Fig.\n168), which pass over cast-iron blocks under the vertical\nFig 168.-One of the links of the lower\nchord.\nposts (Fig. 169). The lower chord may be, and at the pres-\nFig 169.-A joint in the lower chord of a Whipple Truss.\nent day often is, made of eye-bars (Fig. 170). The proper\nFig. 170.-One end of an eye-bar used in tension members of bridges\nand roofs.\nform and dimensions of the eyes and the proper size of the\npins has been the subject of considerable experiment.\nAt first it was supposed that the total section on both sides\nof the eye should equal half the section of the pin, but ex-\nperiments quickly showed that when made in this proportion\nthe eyes would tear out before the shearing strength of the\npin was reached. According to some experiments made by\nSir Charles Fox, he concluded that it was best to make the\nbearing surface between the pin and concave surface of the\neye about equal to the least section of the link; or, in other\nwords, the diameter of the pin should equal about two-thirds\nof the diameter of the link.\nThis rule, however, is not rigidly adhered to by our most\neminent bridge builders. Each has a rule of his own. Some\nmake the eye thicker than the link ; others make them some-\nwhat pear-shaped by adding material back of the eye (Fig.\n171) ; while still others make them of the form shown in Fig.\n172.\nFig 171.-Form of eye-bar.\nDigitized by\nGoogle\n33+\nCIVIL ENGINEERING.\nBut in all cases the total section of the material through\nthe eye is made to exceed that through the bar, and the sec-\ntion of the pin also exceeds that of the bar.\nFig. 172-Another form of eye-bar.\n634. Modifications of Whipple's Truss. Different\nbridge builders have modified the details of Whipple's Truss,\nso as to suit their convenience or fancy, or to make them con-\nform with modern practice. It is useless to attempt to give\nall these modifications. They have, however, given rise to\ncertain names of bridges, such as the Murphy-Whipple\nbridge, Linville bridge, Jones's bridge, etc., etc.\n635. Linville Bridge. This bridge, the details of which\n(Figs. 173 and 174) have been very thoroughly and carefully\nworked out, has a wide reputation.\nThe improvements consist in employing tubular forms of\nwrought iron for members used to resist compressive strains,\nand weldless eye-bars to resist tensile strains, by this means\neconomizing material and reducing the dead weight of the\nstructures. In the accompanying details of the chords, struts,\nand ties, and the floor system and lateral connections, some of\nthe leading principles of the Linville truss are illustrated.\nThe upper chords A, are composed of channel ([) bars\nand I beams, to which are riveted top plates, and sometimes\nbottom plates, forming a tubular compressive member of\ngreat strength. When the lower plate is used, elliptical holes\nare cut out in order to admit of painting the interior. The\nchords are generally made in sections, one panel in length.\nThe connection between the suspension ties and upper chords\nare effected by means of angle blocks, through which pass\nthe suspension ties, with enlarged screw threads and nuts for\nadjustment, or by means of pins passing through the chords,\nand through loops or eyes on the suspension ties.\nThe struts B are circular or polygonal tubes (Fig. 174a),\ncomposed of two or more rolled bars united by rivets through\nflanges, or by transverse tie-bolts passing through the struts\nbetween the flanges. The struts are generally swelled and\nopened to allow the interior to be repainted in order to pre-\nvent their rapid destruction by oxydation.\nThe lower chords are made by upsetting the enlarged eye\nends, by compressing them when highly heated into moulds\nor dies. They are afterwards forged and rewelded under a\nhammer.\nDigitized by Google\nIRON BRIDGES.\n335\nH\nH\nJ\nJ\nA\nH.\nB\nB\nD\nD\nE\nG\nG\nD\nC\nF\nF\nF\nK\nK\nK\nI\nFiga. 178, 174-Details of Linville's trues. Fig. 178 is a cross section, and Fig. 174 a right\nsection of a portion of the trues.\nAA, upper chord, composed of channel bars ([) and I sections. B, the post. (See Fig.\n174 A.) CO, the lower chord. DD, the lower end of a main tie; and H H, the upper end of\na main tie.\nE is a counter-tie.\nG G, bases of the posts or struts.\nII, suspenders for supporting cross-ties.\nJ, cross horizontal diagonal tie,\nK, horizontal diagonal tie,\n1\nDigitized by Google\n336\nCIVIL ENGINEERING.\nB\nFig. 174 A-Cross section of one of the forms of post used in a Lin-\nville truss.\nThese weldless chords and tubular posts have, in many\ncases, superseded older forms. The lower chords CC disposed\nat each side of the suspension ties D, and counter-tie E, and\nbetween ribs in the bases G of the posts or struts, are effect-\nually combined with the struts and ties by means of a con-\nnecting-pin. The tendency to bend the connecting-pin is\nobviated by this distribution of the strains.\nThe pin can fail only by shearing.\nFrom the connecting-pins depend loops or suspenders, II,\nwhich support the rolled cross-girders F, that sustain the track-\nstringers and track. The upper lateral struts of wrought or\ncast iron are secured at the connecting-pins, the ties being\nattached to an eye-plate, or in a jaw-nut secured to the con-\nnecting-pins.\nThe lateral ties J are adjusted by means of sleeve-nuts with\nright and left hand-screws.\nThe lower laterals K K are attached to the cross girders,\nand adjusted in a similar manner.\nThe bases and capitals of the posts are made either of\nwrought or cast iron.\nTo secure greater efficiency in the struts by dispensing\nwith the round bearing, and at the same time retain the pin\nFig. 175-An Arched Truss after the general plan of Whipple's. The lower chords or tie-\nrods pass through the ends of the arch, and are secured by nuts on the ends of the rods.\nDigitized by Google\nIRON BRIDGES.\n337\nconnection between the chords and ties, the lower chords\nare brought compactly together between and outside of the\nsuspension-ties and suspenders, and a bearing provided on the\nupper edges of the chords for the lower ends of the posts.\nThe upper ends also have a flat bearing.\n636. Arched Truss. Fig. 175 shows the general form\nof a Whipple Arched Truss. The upper chord is composed\nof hollow tubes, made in sections of about a panel length.\n637. Bollman's Truss. The general outline of Bollman's\nTruss is shown in Fig. 176.\nD\nE\nH\nI\nK\nB\nc\nF\nG\nJ\nL\nFig 176-Bollman's Trues. A D, D B, etc., are sections of the uppper chord-oast iron and\nusually hollow. D C, E F, etc., are hollow cast-iron posts. A C, 0 B; A F, F B, etc., are\ntension rods; D F, o E, etc., are panel rods,\nOne of the leading features of this bridge is, the load at\neach post or joint is carried directly to the supports at the\nends by means of a pair of tension (or suspension) rods.\nThus a load at E is supported by the post E F, and is thence\nsupported by the rods A F and F B. The panel rods D F,\nE C, E G, etc., serve to keep the upper chord in place, and\nin case of an undue strain upon, or failure of, one of the long\nsuspension-rods, may transmit the strains to the other mem-\nbers of the truss.\nThe suspension rods being of unequal length will be\nunequally elongated or contracted by the same strain, or\nby changes in the temperature. In order to prevent severe\ncross strains upon the posts due to these causes, the suspension-\nrods are connected to the lower ends of the.posts by means\nof a link which is a few inches in length, and which permits\nof a small lateral movement at the ends of the rods without\nany corresponding movement of the posts. The suspension-\nrods are made of flat iron, and pass through the ends of the\nupper chord where they are secured by means of pins which\npass through the ends of the chords.\nIf the roadway passes above the upper chord, it is called a\ndeck bridge, and the lower chord may be dispensed with.\n22\nDigitized by Google\n338\nCIVIL ENGINEERING.\nBut if it passes on the level of the lower chord (Fig. 176a.)\nthe lower chord may be simply suspended upon the posts;\nand not be depended upon for resisting tension. The lower\nchord in this case may also be entirely dispensed with; for\ncross-ties, or joists, may be secured to the posts and longi-\ntudinal joints be placed upon them. If the lower chord is\nused and is made continuous so as to resist tension, it vir-\nFig. 170a.\ntually changes it into a Whipple truss in which the long sus-\npension-rods are unnecessary members. Still, in this case,\nthe truss-especially the panel rods, are not so proportioned\nas to make it safe to omit the long suspension-rods.\n638. Fink Truss. The outline or skeleton of a Fink truss\nis shown in Fig. 177.\nV,\nA\na\nb\nc\nD\nd\ne\nB\ng\nh\nc\nFig. 177-Fink Trues. A B the upper chord, g I the lower chord, a o, B A, etc., are posts,\nA C, C B long suspension-rods. A A, A D, etc., secondary suspension-rods.\nThis truss consists of a primary system of king posts, A C\nB, Fig. 177 ; two secondary systems, A h D and D k B; four\ntertiary systems, A g b, b i D, Dj e, and e l B, and 80 on.\nDigitized by Google\nIRON BRIDGES.\n339\nThe posts, suspension-rods and chords may be similar in\ndetail to the systems previously described.\nThe noted Louisville bridge, across the Ohio River at\nLouisville, is made upon this plan.\nDIMENSIONS OF THE LOUISVILLE BRIDGE.\nIt is 5,294 feet long, divided into the following spans from\ncentre to centre of piers:\nKentucky abutment\n32.5 feet.\n2 spans of 50 feet\n100.0 \"\n1. pivot-draw over canal\n264.0 \"\n4 spans of 149.6\n598.4 \"\n2 spans of 180.0\n360.0 \"\n2 spans of 210.0\n420.0 \"\n2 spans of 227.0\n454.0 \"\n1 span of 370.0\n370.0\n\"\n6 spans of 245.5\n1,473.0 \"\n1 span of 400\n400.0 \"\n3 spans of 180\n540.0 \"\n1 span of 149.6\n149.6 \"\n1 span of 100\n100.0 \"\nIndiana abutment\n32.5 \"\nTotal length\n5,294.0 \"\n639. Post's Truss. The main peculiarity of this truss is\nin its form. The upper ends of the posts are carried towards\nthe centre of the bridge, an amount equal to half a bay, and\nas all the bays are equal the posts in each half of the truss are\nall parallel to each other (Fig. 178).\nH\nC'\nI\nA\nA\nB\nB\nc\nc\nE\nG\nD\nD\nFig. 178-Side view of panels of a Post Truss. A A are struts. BB, main ties. 0 0, counter\nties. E E, bottom chords. IL top chords. D, ends of floor-beams. G, lower horizontal\ndiagonal ties. α, upper horizontal diagonal ties.\nDigitized by Google\n340\nCIVIL ENGINEERING.\nCENTRE\nE\nc\nD\nc\nE\nX\n-\nCENTRE\nAd\nX\nFig. 179-Plan of the roadway. G G are brace-rods. E E, bottom chord. D are floor-\nbeams.\nC'\nH\n>\nFig. 180-Plan of the top of the bridge. I, top chord. H, cross-tie or strut. G, upper hori-\nmontal tie.\nB\nA\nB\nc\nD\nK\nE\nc\nFig. 181-Shows details at a joint of the lower chord. F is a cast-iron block for receiving\nthe ends of the horizontal tie-rods. K is an iron bolt which passes through the ends of the\nlinks which form the lower chord. The other letters refer to the same parts as in the preced-\ning figures.\nDESCRIPTION OF POST'S IRON BRIDGE.\nA A (Figs. 178, 179, 180 and 181)-Are the struts, com-\nposed of two rolled-iron channel bars, with plates riveted on\ntheir flanges, forming a hollow column having a rectangular\ncross-section. The struts are swelled in the centre by spring-\nDigitized by Google\nIRON BRIDGES.\n341\ning the channel-bars and having the plates sheared to the\nrequired shape.\nThe bearings of the struts upon the pins (K) are of either\ncast or wrought iron, and are enclosed between the side-plates,\nand abut against the channel-bars, and are riveted to both.\nThe pin holes are bored through shoes and plates.\nB B-Are the main ties, or main suspension braces, and\nare made of flat bar-iron with die-forged heads at the ends,\nbored out to fit the pins.\nC C-Are the counter ties, made of round iron, with\nforged eyes at the ends to receive the pins, and having turn-\nbuckles at a convenient distance from the bottom end, for\npurposes of adjustment.\nD D-Are the floor-beams, suspended in pairs from the\nchord pins at each panel point, by means of eye-bolts or by\nstirrups passing over the chord pins and under a bolt through\nthe webs of the beams.\nE E-Are the bottom chord bars or links, made of flat bar-\niron, with die-forged heads, and bored holes for the chord\npins. The sizes of the bars in the respective panels are de-\ntermined by the strains, the first and second panels having\ntwo bars, the third and fourth having four bars each, the fifth\nand sixth having six bars each, etc., to the centre of the span.\nF-Is a bottom lateral brace angle block of cast iron, fas-\ntened to the ends of the floor-beams, which form the bottom\nlateral strut.\nG G-Are the lateral brace-rods, of round iron, having\nscrews and nuts at their ends, for adjustment.\nH H-Are top lateral struts, made of rolled-iron I beams,\nor channel bars in pairs. These struts have a cast-iron shoe\nat their ends, and are bolted to the top plate of the top chord,\nby bolts passing through shoes, top plate of chord, and through\nthe joint box in the top chord. The top lateral brace rods\npass through the cast-iron shoes, with nuts on the outside,\nI I-Are the top chords. When made of wrought iron\nthey are composed of channel bars with covering plate rivet-\ned to the flanges on the top, and bars riveted at intervals\nacross the bottom flanges, either diagonally or straight across\nto keep the channel bars in line. Additional sectional area is\nobtained by riveting plates on the inside of the channel bars.\nThe top chords are made in panel lengths, with their ends\nsquared by machinery to insure true bearings-and when of\ncast iron have a rectangular cross-section, with the inside\ncored out to obtain the necessary sectional area to provide for\nthe compression strain.\nDigitized by Google\n342\nCIVIL ENGINEERING.\nThe connection of the struts and main and counter braces\nis made by means of a pin passing through a cast-iron box\nwhich encloses the mall, the length of the pin being just equal\nto the width of the box. The top-chord sections have a recess\nwhich fits over the box, and when the connection is made in\nthe box the pieces of top chord are laid on, and cover the\nwhole. The joint is then secured by the bolts which pass\nthrough the top lateral strut, top chord and joint box.\nDESCRIPTION OF POST'S \" COMBINATION\" OR \" COMPOSITE\" BRIDGE.\nThis bridge is composed partly of wood and partly of iron,\nas shown in Figs. 181a, 1816, and 181c.\nA, A-Top chord, packed and framed as shown in Figs.\n181a and 1816.\nB B-Struts, framed with square end at the top entering and\nabutting against joint box E (Fig. 1813) and fitted at bottom\nends into strut shoe K (Fig. 181c).\nA\nA\nIm\nD\nc\nC\nB\nH\nFig. 181a.\nC C-Main suspension ties, of square, round or flat iron,\nwith eye at lower end and screw at upper end, passing through\njoint box E, secured by nuts.\nD D-Counter braces, of square or round iron, made sim-\nilar to main ties.\nE E-Cast-iron joint boxes enclosed in top chord, and\nreceiving the struts, main ties and counters.\nThis box has a flange around the bottom to support the\nweight of the top chord, which lies upon and is bolted to it.\nDigitized by Google\nIRON BRIDGES.\n343\nF F-Bottom chord links of flat iron, with heads at each\nend, bored to receive the pins (Fig. 181c).\nE\nD\nA\nB\nc\nFig. 181b.\nc\nB\nc\nB\nH\nD\nC\nK\nH\nF\nI\nG\nF\nFig. 181c.\nG G-Rolled iron floor-beams, suspended to chord pins.\nH H-Bottom lateral ties, round iron rods with screws.\nI I-Bottom lateral angle block, cast iron.\nK-Cast-iron strut shoes, having sockets to receive struts\nDigitized by Google\n344\nCIVIL ENGINEERING.\nand drilled holes for chord pins passing through flanges or\nribs below the sockets.\n640. Alleghany River Bridge at Pittsburgh, Pa. This\nis a lattice iron bridge (Fig. 182), and is similar to several\nFig. 182.\nother structures which have been made in this country. There\nis a similar one on the New York Central Railroad, at Sche-\nnectady, N. Y., and another near Rome, of the same State.\n641. St. Louis and Illinois Bridge. This noted structure\nmight properly be called a steel arch. It is now in course of\nerection, and is to consist of three spans, the central one of\nwhich is 515 feet, and each of the end ones 497 feet. There\nare eight arches in each span, arranged in sets of two and\ntwo; and in each set one arch is directly over the other, and\nthe two are trussed together by link-bars. The arches are\ncomposed of steel tubes, which are made of steel staves, as\nwill now be explained.\nAll the steel in this structure is of the very best quality.\nThe standard fixed for it by the Chief Engineer, Capt. Eads,\nwas so high as to make it almost impossible for our best steel\nmanufacturers to produce it. The coefficient of elasticity was\nDigitized by Google\nIRON BRIDGES.\n345\nE\nE\nD\nc\nc\nA\n.\nA\na\na\nb\nc\nc\nb\nB\nB\nG\nC\nFig. 188-Section of a tube, St. Louis and Illinois Bridge. a a is a steel caseing about\nthree-eighths of an inch thick, which is lapped over, and riveted like the plates of a steam-boller,\n0, b are steel staves which are forced into the caseing.\nA A, Figs. 188 and 184, are cross-rods for connecting the arches together laterally.\nB BB are diagonal rods in a vertical, for connecting the upper arch in one set to the lower\narch in the adjacent set.\n0 CC are diagonal rods in the plane of the tubes, for connecting the joint of one set with\nthe joint which 18 in advance of or back of the corresponding joint in the adjacent set,\nD is a vertical diagonal rod for trussing the roadway.\nEE are trussed vertical posta, the lower ends of which are secured to the arch, and the\nupper ends support the roadway.\nE\nE\nD\nF\nF\nFig. 184-Is a cross-section of two arches\nC\nC\nof the bridge. Two sets of tubes which\nform the arch are shown, also the posts\nA\nand rods which have been described above.\na\nF F is the track for & railroad; the car-\nc\nriage road passing above this.\nc\nB\nB\nB\nB\nc\nC\na\nDigitized by Google\n346\nCIVIL ENGINEERING.\nto be between 26,000,000 pounds and 30,000,000 pounds, and\nit was to sustain a strain of 60,000 pounds, without producing\na permanent set.\nAll the workmanship is of a higher order than is usual in\nbridge construction. Special machines and tools were made\nfor making the several joints. An error of one thirty-second\nof an inch might, in most cases, be very troublesome, if not\nfatal.\nE\nF\nFig. 185-Shows a side view of a portion of\nthe arch.\nc\na\nG G are diagonal posts which are trussed,\nas shown in Fig. 188, for connecting the two\narches together. The other letters refer to\nthe same parts as in Figa. 188 and 184,\nc\nC\na\nc\nH\nI\nFig. 186-Shows a cross-sectien of a por-\ntion of the upper roadway.\nII is the carriage-way.\nH is the side-walk.\nE\nE\nD\nThe tubes are straight throughout their length, but the\nends are planed off in the direction of the radius of the arch,\nso that the arch is really a polygon having short sides. Seve-\nral rectangular annular grooves are cut near the ends of each\ntube; and after the tubes are put in place, their ends abut-\nting against each other, they are joined, and firmly secured\nby means of a heavy and nicely-fitted iron coupling. In\nthis way the arch is made continuous. A strong steel pin\nDigitized by Google\nTUBULAR BRIDGES.\n347\npasses through the coupling and the ends of the tubes, one\nhalf of the pin being in each tube. One length of tube is\nput up at a time, and is connected to all the others, which\nare properly placed by cross-rods, A A, Figs. 183 and 184,\nand also diagonal rods 0 C and B B. The diagonals G G\nare also secured. These are secured to the pins c c, Fig. 185.\nThe vertical posts E E, which support the railroad, are trussed\nby means of diagonal bars, as shown in Fig. 184. Each skew-\nback of the arch is secured to the abutments by means of two\nsix-inch steel rods or bolts, which pass through the wrought-\niron skew-backs, and several feet into the masonry. This\nbridge, when completed, will be one of the most remarkable\nstructures of its kind in the world, and can hardly fail to es-\ntablish many important principles in iron structures.\n642. Kuilenberg Bridge. The span of this bridge is about\nthe same as that of the St. Louis and Illinois bridge, as will\nbe seen from the following dimensions. The lower chord of\nthis bridge (Fig. 187) is horizontal, and the upper chord is\nFig. 187-Kuilenberg Bridge. Span between the abutments, 152 meters. Total length, in-\ncluding the parts on the abutments, 156.8 meters (about 515 feet). Length of each bay, 4\nmeters, Depth of the trues at the centre, 29 meters.\nthe arc of a circle, the radius of which is 809 feet. It is of\nthe general plan of the Pratt or Whipple systems, only that\nthe upper chord is curved.\nVI.\nTUBULAR BRIDGES.\n643. Tubular Frames of Wrought-iron. Except for the\nobvious application to steam boilers, sheet iron had not been\nconsidered as suitable for structures demanding great strength,\nfrom its apparent deficiency in rigidity; and although the\nprinciple of gaining strength by a proper distribution of the\nmaterial, and of giving any desirable rigidity by combinations\nadapted to the object in view, were at every moment acted\nupon, from the ever-increasing demands of the art, engineers\nseem not to have looked upon sheet iron as suited to such\nDigitized by Google\n348\nCIVIL ENGINEERING.\npurposes, until an extraordinary case occurred which seemed\nabout to baffle all the means hitherto employed. The occa-\nsion arose when it became a question to throw a bridge of\nrigid material, for a railroad, across the Menai Straits; sus-\npension systems, from their flexibility, and some actual fail-\nures, being, in the opinion of the ablest European engineers,\nunsuitable for this kind of communication.\nRobert Stephenson, who for some years held the highest\nrank among English engineers, appears, from undisputed tes-\ntimony, to have been the first to entertain the novel and bold\nidea of spanning the Straits by a tube of sheet iron, supported\non piers, of sufficient dimensions for the passage within it of\nthe usual trains of railroads. The preliminary experiments\nfor testing the practicability of this conception, and the work-\ning out of the details of its execution, were left chiefly in the\nhands of Mr. William Fairbairn, to whom the profession owes\nmany valuable papers and facts on professional topics. This\ngentleman, who, to a thorough acquaintance with the mode\nof conducting such experiments, united great zeal and judg-\nment, carried through the task committed to him proceed-\ning step by step, until conviction so firm took the place of\napprehension, that he rejected all suggestions for the use of\nany auxiliary means, and urged, from his crowning experi-\nment, reliance upon the tube alone as equal to the end to be\nattained.\nNumerous experiments were made by him upon tubes of\ncircular, elliptical, and rectangular cross-section. The object\nchiefly kept in view in these experiments was to determine\nthe form of cross-section which, when the tube was submitted\nto a cross strain, would present an equality of resistance in the\nparts brought into compression and extension. It was shown,\nat an early stage of the operations, that the circular and ellip-\ntical forms were too weak in the parts submitted to compres-\nsion, but that the elliptical was the stronger of the two; and\nthat, whatever form might be adopted, extraordinary means\nwould be requisite to prevent the parts submitted to compres-\nsion from yielding, by \"puckering\" and doubling. To meet\nthis last difficulty, the fortunate expedient was hit upon of\nmaking the part of the main tube, upon which the strain of\ncompression was brought, of a series of smaller tubes, or cells\nof a curved or a rectangular cross-section. The latter form of\nsection was adopted definitively for the main tube, as having\nyielded the most satisfactory results as to resistance; and also\nfor the smaller tubes, or cells, as most easy of construction\nand repair.\nDigitized by Google\nTUBULAR BRIDGES.\n349\nAs a detail of each of these experiments would occupy\nmore space than can be given in this work, that alone of the\ntube which gave results that led to the forms and dimensions\nadopted for the tubular bridges subsequently constructed, will\nbe given in this place.\n644. Model Tube. The total length of the tube was 78\nfeet. The distance, or bearing between the points of support\non which it was placed to test its strength, was 75 ft. Total\ndepth of the tube at the middle, 4 ft. 61 in. Depth at each\nextremity, 4 ft. Breadth, 2 ft. 8 in.\nThe top of the tube was composed of a top and bottom\nplate, formed of pieces of sheet iron, abutting end to end, and\nconnected by narrow strips riveted to them over the joints.\nThese plates were 2 ft. 11 ₫ in. wide. They were 61 in. apart,\nand connected by two vertical side plates and five interior\ndivision plates, with which they were strongly joined by\nangle irons, riveted to the division plates, and to the top and\nbottom plates where they joined. Each cell, between two di-\nvision plates and the top and bottom plates, was nearly 6 in.\nwide. The sides of the tube were made of plates of sheet\niron similarly connected; their depth was 3 ft. 6& in. A\nstrip of angle iron, bent to a curved shape, and running from\nthe bottom of each end of the tube to the top just below the\ncellular part, was riveted to each side to give it stiffness. Be-\nsides this, precautions were finally taken to stiffen the tube\nby diagonal braces within it. The bottom of the tube was\nformed of sheets, abutting end to end, and secured to each\nother like the top plates; a continuous joint, running the en-\ntire length of the tube along the centre line of the bottom,\nwas secured by a continuous strip of iron on the under side,\nriveted to the plates on each side of the joint. The entire\nwidth of the bottom was 2 ft. 11 in.\nThe sheet iron composing the top cellular portion was 0.147\nin. thick; that of the sides 0.099 in. thick. The bottom of the\ntube at the final experiments, to a distance of 20 ft. on each\nside of the centre, was composed of two thicknesses of sheet\niron, each 0.25 in. thick, the joints being secured by strips\nabove and below them, riveted to the sheets the remainder,\nto the end of the tube, was formed of sheets 0.156 in. thick.\nThe total area of sheets composing the top cellular portion\nwas 24.024 in., that of the bottom plates at the centre portion,\n22.450 in.\nThe general dimensions of the tube were one sixth those of\nthe proposed structure. Its weight at the final experiment,\n13,020 lbs.\nDigitized\nby\nGoogle\n350\nCIVIL ENGINEERING.\nThe experiments, as already stated, were conducted with a\nview to obtain an equality between the resistances of the parts\nstrained by compression and those extended ; with this object,\nat the end of each experiment, the parts torn asunder at the\nbottom were replaced by additional pieces of increased\nstrength.\nThe following table exhibits the results of the final experi-\nments :-\nNo. of Experiments.\nWeight in lbs.\nDeflection in inches.\n1\n20,006\n0.55\n2\n35,776\n0.78\n3\n48,878\n1.12\n4\n62,274\n1.48\n5\n77,534\n1.78\n6\n92,299\n2.12\n7\n103,350\n2.38\n8\n114,660\n2.70\n9\n132,209\n3.05\n10\n138,060\n3.23\n11\n143,742\n3.40\n12\n148,443\n3.58\n13\n153,027\n3.70\n14\n157,728\n3.78\n15\n161,886\n3.88\n16\n164,741\n3.98\n17\n167,614\n4.10\n18\n171,144\n4.23\n19\n173,912\n4.33\n20\n177,088\n4.47\n21\n180,017\n4.55\n22\n183,779\n4.62\n23\n186,477\n4.72\n24\n189,170\n4.81\n25\n192,892\nThe tube broke with the weight in the 25th experiment ;\nthe cellular top yielding by puckering at about 2 feet from\nthe point where the weight was applied. The bottom and\nsides remained uninjured.\nThe ultimate deflection was 4.89 in.\n645. Britannia Tubular Bridge. Nothing further than a\nsuccinct description of this marvel of engineering will be\nattempted here, and only with a view of showing the arrange-\nment of the parts for the attainment of the proposed end.\nDigitized by\nGoogle\nTUBULAR BRIDGES.\n851\nIt differs in its general structure from the model tube, chiefly\nin having the bottom formed like the top, of rectangular cells,\nand in the means taken for giving stiffness to the sides.\nThe total distance spanned by the bridge is 1,489 ft. This\nis divided into four bays, the two in the centre being each\n460 ft., and the one at each end 230 ft. each.\nThe tube is 1,524 ft. long. Its bearing on the centre pier\nis 45 ft. ; that on the two intermediate 32 ft.; and that on\neach abutment 17 ft. 6 in. The height of the tube at the\ncentre pier is 30 ft. ; at the intermediate piers 27 ft.; and at\nthe ends 23 ft. This gives to the top of the tube the shape\nof a parabolic curve.\no\nof\n0\nb\nb\nh\nI\nFig. 188-Represents a vertical cross-section of the Britannia Bridge.\nA, interior of bridge.\nB, cells of top cellular beam.\nC, cells of bottom cellular beam.\na, top plates of top and bottom beams.\nb, bottom plates of top and bottom beams.\nc, division plates of top and bottom beams.\nd and a strips riveted over the joints of top and bottom plates.\no, angle irons riveted to a, b, and c.\na, plates of sides of the tube 4.\nA, exterior I irons riveted over vertical joints of g.\n4, interior T irons riveted over vertical joints of a, and bent at the angles of 4, and extend-\ning beyond the second cell of the top beam, and beyond the first of the bottom beam.\nse, triangular pieces on each side of & and riveted to them.\nDigitized by Google\n352\nCIVIL ENGINEERING.\nThe cellular top (Fig. 188) is divided into eight cells B, by\ndivision plates c, connected with the top a, and bottom b, by\nangle irons o, riveted to the plates connected. The different\nsheets composing the plates a and b abut end to end length-\nwise the tube; and the joints are secured by the strips d and\ne, riveted to the sheets by rivets that pass through the interior\nangle irons.\nThe sheets of which this portion is composed are each 6 ft.\nlong, and 1 ft. 9 in. wide; those at the centre of the tube are\nHths of an inch thick: they decrease in thickness towards\nthe piers, where they are 18ths of an inch thick. The division\nplates are of the same thickness at the centre, and decrease\nin the same manner towards the piers. The rivets are 1 inch\nthick, and are placed 3 in. apart from centre to centre. The\ncells are 1 ft. 9 in. by 1 ft. 9 in., so as to admit a man for\npainting and repairs.\nThe cellular bottom is divided into six cells C, each of\nwhich is 2 ft. 4 in. wide by 1 ft. 9 in. in height. To diminish,\nas far as practicable, the number of joints, the sheets for the\nsides of the cells were made 12 ft. long. To give sufficient\nstrength to resist the great tensile strain, the top and bottom\nplates of this part are composed of two thicknesses of sheet\niron, the one layer breaking joint with the other. The joints\nover the division plates are secured by angle irons o, in the\nsame manner as in the cellular top. The joints between the\nsheets are secured by sheets 2 ft. 8 in. long placed over them,\nwhich are fastened by rivets that pass through the triple\nthickness of sheets at these points. The rivets, for attaining\ngreater strength at these points, are in lines lengthwise of the\ncell. The sheets forming the top and bottom plates of the\ncells are 1°6ᵗʰs of an inch at the centre of the tube, and de-\ncrease to 1'gths at the ends. The division plates are 1°cths in\nthe middle, and 18ths at the ends of the tube. The rivets of\nthe top and bottom plates are 11 in. in diameter.\nFig. 189-Represents a horizontal cross-section of the T irons and side plates.\nD, cross-section near centre of bridge.\nE, cross-section near the piers.\no, plates of the sides.\nh, exterior irons.\n4 interior T irons.\nDigitized by Google\nTUBULAR BRIDGES.\n353\nThe sides of the tube (Fig. 188) between the cellular top\nand bottom are formed of sheets g, 2 ft. wide ; the lengths of\nwhich are so arranged that there are alternately three and four\nplates in each panel, the sheets of each panel abutting end\nto end, and forming a continuous vertical joint between the\nadjacent panels. These vertical joints are secured by strips\nof iron, h and i, of the T cross-section, placed over each side\nof the joint, and clamping the sheets of the adjacent panels\nbetween them. The T irons within and without are firmly\nriveted together with 1-inch rivets, placed at 3 in. between\ntheir centres. Over the joints, between the ends of the sheets\nin each panel, pieces of sheet iron are placed on each side,\nand connected by rivets. The sheets of the panels at the\ncentre of the tube are 1°0ths of an inch thick ; they increase\nto 18ths to within about 10 ft. of the piers, where their thick-\nness is again increased and the T irons are here also increased\nin thickness, being composed of a strip of thick sheet iron,\nclamped between strips of angle iron which extend from the\ntop to the bottom of the joints. The object of this increase\nof thickness, in the panels and T irons at the piers, is to give\nsufficient rigidity and strength to resist the crushing strain at\nthese points.\nThe T irons on the interior are bent at top and bottom, and\nextended as far as the third cell from the sides at top, and to\nthe second at bottom. The projecting rib of each in the\nangles is clamped between two pieces, n, of sheet iron, to\nwhich it is secured by rivets, to give greater stiffness at the\nangles of the tube.\nThe arrangement of the ordinary T irons and sheets of the\npanels is shown in cross-section by D, Fig. 189 and that of the\nlike parts near the piers by E, same Fig.\nFor the purpose of giving greater stiffness to the bottom,\nand to secure fastenings for the wooden cross sleepers that\nsupport the longitudinal beams on which the rails lie, cross\nplates of sheet iron, half an inch thick, and 10 in. in depth,\nare laid on the bottom of the tube, from side to side, at every\nfourth rib of the T iron, or 6 ft. apart. These cross plates are\nsecured to the bottom by angle iron, and are riveted also to\nthe T iron.\nThe tube is firmly fixed to the central pier, but at the inter-\nmediate piers and the abutments it rests upon saddles sup-\nported on rollers and balls, to allow of the play from con-\ntraction and expansion by changes of temperature.\nThe following tabular statements give the details of the\ndimensions, weights, etc., of the Britannia Bridge.\n23\nDigitized by Google\n354\nCIVIL ENGINEERING.\nFeet.\nPlates\nAngle\nT\nRivet\nCast-\niron\niron.\nTotal\niron.\niron.\ntons.\ntons.\ntons.\ntons.\ntons.\ntons.\nTotal length of each tube\n1524\n\"\n\"\nof tubes for each line\n8048\nGreatest span of bay\n460\nHeight of tubes at the middle\n80\n\"\nintermediate piers\n27\n\"\n\"\nends\n28\nExtreme width of tubes\n14%\nNumber of rivets in one tube\n882,000\nComputed weight of tube 274 ft. long\n450\n109\n70\n60\n689\n\"\n\"\n8 tubes 274 ft. long\n1850\n827\n210\n180\n2067\n\"\n\"\n1 tube 472 ft. long.\n965\n188\n139\n108\n1400\n\"\n\"\n8 tubes 472 ft. long\n2895\n564\n417\n824\n4200\n\"\n\"\n1 tube over pier 32 ft. long\n64\n26\n10\n7\n107\n\"\n\"\n\"\n\"\n64\n26\n10\n7\n107\nFrames and beams\n2000\n2000\nTotal weight\n5788\n1240\n856\n686\n2000\n10,570\n646. Formula for reducing the Breaking Weight of\nWrought Iron Tubes.\nRepresenting by A, the total area in inches of the cross-\nsection of the metal.\n\"\n\"\nd, the total depth in inches of the tube.\n\"\n\"\ni, the length in inches between the points\nof support.\n\"\n\"\nC, a constant to be determined by ex-\nperiment.\n\"\n\" W, the breaking weight in tons.\nThen the relations between these elements, in tubes of\ncylindrical, elliptical and rectangular cross-section, will be\nexpressed by\nW=C Ad\nThe mean value for C for cylindrical tubes, deduced from\nseveral experiments, was found to be 13.03; that for ellipti-\ncal tubes, 15.3; and that for rectangular tubes, 21:5.\n647. Victoria Bridge. This bridge is located near Mon-\ntreal. It is a tubular bridge, a cross-section of which is shown\nin Fig. 190. It is the largest bridge of its kind in existence.\nIt consists of twenty-four openings of 242 feet each, and a\ncentral span of 330 feet, and the total length of the tube, in-\ncluding the width of the abutments, is 6,538. The em-\nbankment forming the approach at the Montreal end is 1,200\nfeet long, and at the south end it is 800 feet, making a total\nlength, including the approaches, of nearly 8,000 feet.\nThe centre span is level, but each side of the centre the\nbridge falls on a grade of 40 feet per mile.\nDigitized by\nGoogle\nTUBULAR BRIDGES.\n355\nA\nB\nc\nC\nD\nH\nF\nQ\nE\nFig. 190-Victoria Bridge.\nWeb plates and top plates at centre of tube.\nA, tie bar 6\" x 0\".75\nB, web plate.\nC C, cover plates.\nD, top plates.\nE, bottom plates.\nF, heavy wooden beams on which rail H rests.\nG, cross timber to connect beams F.\nA\nFig. 190 A-is an enlarged view of a\npart of one of the upper cells. The\nB\nletters apply to the same parts as in\nthe preceding Figure.\nA is the top plate.\nc\nD shows two continuous plates, and\nC C, two joint plates.\nO\nC\nEach tube covers two openings, being fixed in the centre,\nand free to expand or contract on the adjacent piers. They\nare 16 feet wide and 19 feet deep at their ends, and gradually\nDigitized by Google\n356\nCIVIL ENGINEERING.\nL\nK\nFig. 190 B-Is a section on the line D D of Fig. 190.\nK is a vertical side plate.\nLL are angle irons which are riveted to the side plates.\nL\nSec. on D.D.\nE\nFig. 190 C-Section of the bottom plates B of Fig. 190. There are three continuous plates\nand four joint plates.\nincrease in depth to the middle, where they are 16 feet wide\nby 21 feet 8 inches deep. The total length of each of these\ndouble tubes is,\nOn the centre pier\n16 feet.\nTwo openings in the clear\n484 \"\nResting on the east pier\n8\n\"\nResting on the west pier\n8\n\"\nTotal\n516 feet.\nThe weight of each tube of 516 feet is about 644 tons. At\neach end are seven expansion rollers, each 6 inches in diame-\nter, upon which the tubes rest. The rollers which are turned\nrest on planed cast-iron bed plates.\nThe centre pier is 24 feet wide, the remaining ones each\n16 feet wide at the top.\nThe work of laying the foundation was begun in 1854, and\nthe centre tube was put in place in March, 1859.\nThe scaffolding for the centre tube rested on the ice in the\nriver, which began to move the day after the tube was put\nin place. From a record which had been kept of the break-\ning up of the ice, it was presumed that it would remain sound\nseveral days longer than it did.\nThe foundations were made on the solid rock by means of\ncoffer-dams. Two kinds were used, one a floating dam, and\nthe other a permanent crib-work; and each possessed certain\nadvantages over the other which was peculiar to itself and to\nthe objects which were to be accomplished.\nDigitized by Google\nVII.\nSUSPENSION BRIDGES.\n648. The use of flexible materials, as cordage and the like,\nto form a roadway over chasms and narrow water-courses,\ndates from a very early period; and structures of this char-\nacter were probably among the first rude attempts of ingenu-\nity, before the arts of the carpenter and mason were suf-\nficiently advanced to be made subservient to the same ends.\nThe idea of a suspended roadway, in its simplest form, is one\nthat would naturally present itself to the mind, and its con-\nsequent construction would demand only obvious means and\nbut little mechanical contrivance; but the step from this\nstage to the one in which such structures are now found,\nsupposes a very advanced state both of science and of its\napplication to the industrial arts, and we accordingly find\nthat bridge architecture, under every other guise, was brought\nto a high degree of perfection before the suspension bridge,\nas this structure is now understood, was attempted.\nWith the exception of some isolated cases which, but in the\nmaterial employed, differed little from the first rude struc-\ntures, no recorded attempt had been made to reduce to syste-\nmatic rules the means of suspending a roadway now in use,\nuntil about the year 1801, when a patent was taken out in\nthis country for the purpose, by Mr. Finlay, in which the\nmanner of hanging the chain supports, and suspending the\nroadway from it, are specifically laid down, differing, in no\nvery material point, from the practice of the present day in\nthis branch of bridge architecture. Since then, a number\nof structures of this character have been erected both in the\nUnited States and in Europe, and, in some instances, valleys\nand water-courses have been spanned by them under circum-\nstances which would have baffled the engineer's art in the em-\nployment of any other means.\nA suspension bridge consists of the supports, termed piers,\nfrom which the suspension chains are hung; of the anchoring\nmasses, termed the abutments, to which the ends of the sus-\npension chains are attached; of the suspension chains, termed\nthe main chains, from which the roadway is suspended of\nthe vertical rods, or chains, termed the suspending-chains, etc.,\nwhich connect the roadway with the main chains; and of the\nroadway.\n649. Bays. The natural water-way may be divided into\nDigitized by Google\n358\nCIVIL ENGINEERING.\nany number of equal-sized bays, depending on local circum-\nstances, and the comparative cost of high or low piers, and\nthat of the main chains, and the suspending-rods.\nA bridge with a single bay of considerable width presents\na bolder and more monumental character, and its stability,\nall other things being equal, is greater, the amplitude from\nundulations caused by a movable load being less than one of\nseveral bays.\n650. A chain or rope, when fastened at each extremity to\nfixed points of support, will, from the action of gravity,\nassume the form of a catenary in a state of equilibrium,\nwhether the two extremities be on the same or different levels.\nThe relative height of the fixed supports may therefore be\nmade to conform to the locality.\n651. The ratio of the versed sine of the arc to its chord, or\nspan, will also depend, for the most part, on local circum-\nstances and the object of the suspended structure. The\nwider the span, or chord, for the same versed sine, the greater\nwill be the tension along the curve, and the more strength\nwill therefore be required in all the parts of the cable. The\nreverse will obtain for an increase of versed sine for the same\nspan ; but there will be an increase in the length of the curve.\n652. The chains may either be attached at the extremities\nof the curve to the fixed supports, or piers ; or they may rest\nupon them (Figs. 191, 192), being fixed into anchoring masses,\nb\nd\nc\na\nm\nn\nFig. 191-Represents a chain arch a b c d e, resting upon two piers f f, and anchored at the\npoints a and 6, from which a horizontal beam 973 n is suspended by vertical chains, or rods.\na\nc\nf\n71\nFig. 199-Represents the manner in which the system may be arranged when a single pier is\nplaced between the extreme points of the bearing.\nor abutments, at some distance beyond the piers. Local\ncircumstances will determine which of the two methods will\nbe the more suitable. The latter is generally adopted, partic-\nularly if the piers require to be high, since the strain upon\nthem from the tension might, from the leverage, cause rup-\nDigitized by\nGoogle\nSUSPENSION BRIDGES.\n359\nture in the pier near the bottom, and because, moreover, it\nremedies in some degree the inconveniences arising from\nvariations of tension caused either by a movable load or\nchanges of temperature. Piers of wood, or of cast iron,\nmovable around a joint at their base, have been used instead\nof fixed piers, with the object of remedying the same incon-\nveniences.\n653. When the chains pass over the piers and are anchored\nat some distance beyond them, they may either rest upon\nsaddle-pieces of cast iron, or upon pulleys placed on the\npiers.\n654. The position of the anchoring points will depend upon\nlocal circumstances. The two branches of the chain may\neither make equal angles with the axis of the pier, thus assum-\ning the same curvature on each side of it, or else the extrem-\nity of the chain may be anchored at a point nearer to the base\nof the pier. In the former case the resultant of the tensions\nand weights will be vertical and in the direction of the axis\nof the pier, in the latter it will be oblique to the axis, and\nshould pass so far within the base that the material will be-\nsecure from crushing. When the cable is secured to a sad-\ndle, and the saddle is free to move horizontally on the top of\nthe pier, the resultant forces would still be vertical if there\nwere no frictional resistance to the movement of the saddle.\nIn all cases, whether the inclinations of the cable on the oppo-\nsite sides of the pier are equal or not, the frictional resistance\nunder the saddle when it is moving will cause a horizontal\nforce tending to overturn the pier.\n655. The anchoring points are usually masses of masonry\nof a suitable form to resist the strain to which they are sub-\njected. They may be placed either above or below the sur-\nface of the ground, as the locality may demand. The kind\nof resistance offered by them to the tension on the chain will\ndepend upon the position of the chain. If the two branches\nof the chain make equal angles with the axis of the pier, the\nresistance offered by the abutments will mainly depend upon\nthe strength of the material of which they are formed. If\nthe branches of the chain make unequal angles with the axis\nof the pier, the branch fixed to the anchoring mass is usually\ndeflected in a vertical direction, and SO secured that the weight\nof the abutment may act in resisting the tension on the chain.\nIn this plan fixed pulleys placed on very firm supports will\nbe required at the point of deflection of the chain to resist the\npressure arising from the tension at these points.\nWhenever it is practicable the abutment and pier should be\nDigitized by Google\n360\nCIVIL ENGINEERING.\nsuitably connected to increase the resistance offered by the\nformer.\nThe connection between the chains and abutments should\nbe SO arranged that the parts can be readily examined. The\nchains at these points are sometimes imbedded in a paste of\nfat lime to preserve them from oxidation.\n656. The chains may be placed either above or below the\nstructure to be supported. The former gives a system of\nmore stability than the latter, owing to the position of the\ncentre of gravity, but it usually requires high piers, and the\nchain cannot generally be SO well arranged as in the latter to\nsubserve the required purposes. The curves may consist of\none or more chains. Several are usually preferred to a single\none, as for the same amount of- metal they offer more resist-\nance, can be more accurately manufactured, are less liable to\naccidents, and can be more easily put up and replaced than a\nsingle chain. The chains of the curve may be placed either\nside by side, or above each other, according to circumstances.\n657. The cables may be formed either of chains, of wire\ncables, or of bands of hoop iron. Each of these methods has\nfound its respective advocates among engineers. Those who\nprefer wire cables to chains urge that the latter are more\nliable to accidents than the former, that their strength is less\nuniform and less in proportion to their weight than that of\nwire cables, that iron bars are more liable to contain con-\ncealed defects than wire, that the proofs to which chains are\nsubjected may increase without, in all cases, exposing these\ndefects, and that the construction and putting up of chains is\nmore expensive and difficult than for wire cables. The op-\nponents of wire cables state that they are open to the same\nobjections as those urged against chains, that they offer a\ngreater amount of surface to oxidation than the same volume\nof bar iron would, and that no precaution can prevent the\nmoisture from penetrating into a wire cable and causing rapid\noxidation.\nThat in this, as in all like discussions, an exaggerated de-\ngree of importance should have been attached to the objec-\ntions urged on each side was but natural. Experience, how-\never, derived from existing works, has shown that each\nmethod may be applied with safety to structures of the\nboldest character, and that wherever failures have been met\nwith in either method, they were attributable to those faults\nof workmanship, or to defects in the material used, which\ncan hardly be anticipated and avoided in any novel applica-\ntion of a like character. Time alone can definitively decide\nDigitized by\nGoogle\nSUSPENSION BRIDGES.\n361\nupon the comparative merits of the two methods, and how\nfar either of them may be used with advantage in the place\nof structures of more rigid materials.\n658. The chains of the curves may be formed of either\nround, square, or flat bars. Chains of flat bars have been\nmost generally used. These are formed in long links which\nare connected by short plates and bolts. Each link consists\nof several bars of the same length, each of which is perforated\nwith a hole at each end to receive the connecting bolts. The\nbars of each link are placed side by side, and the links are\nconnected by the plates which form a short link, and the bolts.\nThe links of the portions of the chain which rest upon the\npiers may either be bent, or else be made shorter than the\nothers to accommodate the chain to the curved form of the\nsurface on which it rests.\n659. The vertical suspension bars may be either of round\nor square bars. They are usually made with one or more\narticulations, to admit of their yielding with less strain to the\nbar to any motion of vibration or of oscillation. They may\nbe suspended from the connecting bolts of the links, but the\npreferable method is to attach them to a suitable saddle-piece\nwhich is fitted to the top of the chain and thus distributes the\nstrain upon the bar more uniformly over the bolts and links.\nThe lower end of the bar is suitably arranged to connect it\nwith the part suspended from it.\n660. The wire cables are composed of wires laid side by\nside, which are brought to a cylindrical shape and confined\nby a spiral wrapping of wire. To form the cable several\nequal-sized ropes, or yarns, are first made. This may be\ndone by cutting all the wires of the length required for the\nyarn, or by uniting end to end the requisite number of wires\nfor the yarn, and then winding them around two pieces of\nwrought or of cast iron, of a horse-shoe shape, with a suitable\ngorge to receive the wires, which are placed as far asunder\nas the required length of the yarn. The yarn is firmly\nattached at its two ends to the iron pieces, or cruppers, and\nthe wires are temporarily confined at intermediate points by\na spiral lashing of wire. Whichever of the two methods be\nadopted, great care must be taken to give to every wire of the\nyarn the same degree of tension by a suitable mechanism.\nThe cable is completed after the yarns are placed upon the\npiers and secured to the anchoring ropes or chains; for this\npurpose the temporary lashings of the yarns are undone, and\nall the yarns are united and brought to a cylindrical shape\nand secured throughout the extent of the cable, to within a\nDigitized by\nGoogle\n362\nCIVIL ENGINEERING.\nshort distance of each pier, by a continuous spiral lashing of\nwire.\nThe part of the cable which rests upon the pier is not\nbound with wire, but is spread over the saddle-piece with a\nuniform thickness.\n661. The suspension ropes are formed in the same way as\nthe cables; they are usually arranged with a loop at each end,\nformed around an iron crupper, to connect them with the\ncables, to which they are attached, and to the parts of the\nstructure suspended from them by suitable saddle-pieces.\n662. To secure the cables from oxidation the iron wires are\ncoated with varnish before they are made into yarns, and\nafter the cables are completed they are either coated with the\nusual paints for securing iron from the effects of moisture, or\nelse covered with some impermeable material.\n663. Piers. Those are commonly masses of masonry in the\nshape of pillars, or columns, that rest on a common foundation,\nand are usually connected at the top. The form given to the\npier, when of stone, will depend in some respects on the\nlocality. Generally it is that of the architectural monument\nknown as the Triumphal Arch; an arched opening being\nformed in the centre of the mass for the roadway, and some-\ntimes two others of smaller dimensions, on each side of the\nmain one, for approaches to the footpaths of the bridge.\nPiers of a columnar, or of an obelisk form, have in some\ninstances been tried. They have generally been found to be\nwanting in stiffness, being subject to vibrations from the\naction of the chains upon them, which in turn, from the re-\nciprocal action upon the chains, tends very much to increase\nthe amplitude of the vibrations of the latter. These effects\nhave been observed to be the more sensible as the columnar\npiers are the higher and more slender.\nCast-iron piers, in the form of columns connected at top by\nan entablature, have been tried with success, as also have been\ncolumnar piers of the same material SO arranged, with a joint\nat their base, that they can receive a pendulous motion at top\nto accommodate any increase of tension upon either branch\nof the chain resting on them.\nThe dimensions of piers will depend upon their height and\nthe strain upon them. When built of stone, the masonry\nshould be very carefully constructed of large blocks well\nbonded, and tied by metal cramps. The height of the piers\nwill depend mostly on the locality. When of the usual forms,\nthey should at least be high enough to admit the passage of\nvehicles under the arched way of the road.\nDigitized by\nGoogle\nSUSPENSION BRIDGES.\n363\n664. Abutments. The forms and dimensions of the abut-\nments will depend upon the manner in which they may be\nconnected with the chains. When the locality will admit of the\nchains being anchored without deflecting them vertically, the\nabutments may be formed of any heavy mass of rough\nmasonry, which, from its weight, and the manner in which it\nis imbedded, have sufficient strength to resist the tension in\nthe direction of the chain. If it is found necessary to deflect\nthe chains vertically to secure a good anchoring point, it will\nalso generally be necessary to build a mass of masonry of an\narched form at the point where the deflection takes place,\nwhich, to present sufficient strength to resist the pressure\ncaused by the resultant of the tension on the two branches of\nthe chain, should be made of heavy blocks of cut stone well\nbonded. If the abutments are not too far from the founda-\ntions of the piers, it will be well to connect the two, in order\nto give additional resistance to the anchoring points.\n665. Main Chains, etc. The suspending curves, or arches,\nmay be made of chains formed of flat or round iron, or may\nconsist of wire cables constructed in the usual manner.\nThe main chains of the earlier suspension bridges were\nformed of long links of round iron made in the usual way ;\nbut, independently of the greater expense of these chains,\nthey were found to be liable to defects of welding, and the\nlinks, when long, were apt to become misshapen under a great\nstrain, and required to be stayed to preserve their form.\nChains formed of long links of flat bars, usually connected by\nshorter ones, as coupling links, have on these accounts super-\nseded those of the ordinary oval-shaped links.\nThe breadth of the chains has generally been made uniform,\nbut in some bridges erected in England by Mr. Dredge, the\nchains are made to increase uniformly in breadth, by increas-\ning the number of bars in a link, from the centre to the points\nof suspension. In addition to this change in the form of the\nmain chains, Mr. Dredge places the suspending chains in a\nvertical plane parallel to the axis of the bridge, but obliquely\nto the horizon, inclining each way from the points of suspen-\nsion towards the centre of the curve. This system has never\ncome into general use. At the present day nearly all cables.\nof suspension bridges are made of wire.\nSome of the links of the main chains should be arranged\nwith adjusting screws, or with keys, to bring the chains to the\nproper degree of curvature when set up.\nThe chains may either be attached to, or pass over a mo-\nvable cast-iron saddle, seated on rollers on the top of the piers,\nDigitized by Google\n364\nCIVIL ENGINEERING.\nso that it will allow of sufficient horizontal displacement to\npermit the chains to accommodate themselves to the effects\nof a movable load on the roadway. The same ends may be\nattained by attaching the chains to a pendulum bar suspended\nfrom the top of the pier.\nThe chains are firmly connected with the abutments, by\nbeing attached to anchoring masses of cast iron, arranged in\na suitable manner to receive and secure the ends of the\nchains, which are carefully imbedded in the masonry of the\nabutments. These points, when under ground, should be so\nplaced that they can be visited and examined from time to\ntime.\n666. Suspending-Chains. The suspending-rods, or chains,\nshould be attached to such points of the main chains and the\nroadway-bearers, as to distribute the load uniformly over the\nmain chains, and to prevent their being broken or twisted off\nby the oscillations of the bridge from winds, or movable\nloads. They should be connected by suitably-arranged ar-\nticulations, with a saddle piece bearing upon the back of the\nmain chain, and at bottom with the stirrup that embraces the\nroadway-bearers.\nThe suspending-chains are usually hung vertically. In\nsome recent bridges they have been inclined inward to give\nmore stiffness to the system.\n667. Roadway. Transversal road way-bearersare attached\nto the suspending-chains, upon which a flooring of timber is\nlaid for the roadway. The roadway-bearers, in some in-\n\"stances, have been made of wrought iron, but timber is now\ngenerally preferred for these pieces. Diagonal ties of\nwrought iron are placed horizontally between the roadway-\nbearers to brace the frame-work.\nThe parapet may be formed in the usual style either of\nwrought iron, or of timber, or of a combination of cast iron\nand timber. Timber alone, or in combination with cast iron,\nis now preferred for the parapets; as observation has shown\nthat the stiffness given to the roadway by a strongly-trussed\ntimber parapet limits the amplitude of the undulations caused\nby violent winds, and secures the structure from danger.\nIn some of the more recent suspension bridges, a trussed\nframe, similar to the parapet, has been continued below the\nlevel of the roadway, for the purpose of giving greater se-\ncurity to the structure against the action of high winds.\nWhen the roadway is above the chains, any requisite num-\nber of single chains may be placed for its support. Frames\nformed of vertical beams of timber, or of columns of cast\nDigitized by Google\nSUSPENSION BRIDGES.\n365\niron united by diagonal braces, rest upon the chains, and sup-\nport the roadway-bearers placed either transversely or\nlongitudinally.\n668. Vibrations. The undulatory or vibratory motions of\nsuspension bridges, caused by the action of high winds, or\nmovable loads, should be reduced to the smallest practicable\namount, by a suitable arrangement of bracing for the road-\nway-timbers and parapet, and by chain-stays attached to the\nroadway and to the basements of the piers, or to fixed points\non the banks whenever they can be obtained.\nCalculation and experience show that the vibrations caused\nby a movable load decrease in amplitude as the span in-\ncreases, and, for the same span, as the versed sine decreases.\nThe heavier the roadway, also, all other things being the same,\nthe smaller will be the amplitude of the vibrations caused by\na movable load, and the less will be their effect in changing\nthe form of the bridge.\nThe vibrations caused by a movable load seldom affect the\nbridge in a hurtful degree, owing to the elasticity of the\nsystem, unless they recur periodically, as in the passage of a\nbody of soldiers with a cadenced march. Serious accidents\nhave been occasioned in this way; also by the passage of cat-\ntle, and by the sudden rush of a crowd from one side of the\nbridge to the other. Injuries of this character can only be\nguarded against by a proper system of police regulations.\nChain-stays may either be attached to some point of the\nroadway and to fixed points beneath it, or else they may be in\nthe form of a reversed curve below the roadway. The former\nis the more efficacious, but it causes the bridge to bend in a\ndisagreeable manner at the point where the stay is attached,\nwhen the action of a movable load causes the main chains to\nrise. The more oblique the stays, the longer, more expensive,\nand less effective they become. Stays in the form of a re-\nversed curve preserve better the shape of the roadway under\nthe action of a movable load, but they are less effective in\npreventing vibrations than the simple stay. Neither of these\nmethods is very serviceable, except in narrow spans. In wide\nspans, variations of temperature cause considerable changes\nin the length of the stays, which makes them act unequally\nupon the roadway; this is particularly the case with the re-\nversed curve. Both kinds should be arranged with adjusting\nscrews, to accommodate their length to the more extreme\nvariations of temperature.\nEngineers at present generally agree that the most effica-\ncious means of limiting the amplitude, and the consequent\nDigitized by\nGoogle\n366\nCIVIL ENGINEERING.\ninjurious effects of undulations, consists in a strong combina-\ntion of the roadway-timbers and flooring, stiffened by a trussed\nparapet of timber above the roadway, and in some cases in\nextending the framework of the parapet below it. These\ncombinations present, in appearance and reality, two or more\nopen-built beams, as circumstances may demand, placed paral-\nlel to each other, and strongly connected and braced by the\nframework of the roadway, which are supported at inter-\nmediate points by the suspending rods or chains. The\nmethod of placing the roadway-framing at the central line of\nthe open-built beams, presents the advantage of introducing\nvertical diagonal braces, or ties, between the beams beneath\nthe roadway-frame. The main objections to these combina-\ntions is the increased tension thrown upon the chains from\nthe greater weight of the framework. This increase of ten-\nsion, however, provided it be kept within proper limits, so far\nfrom being injurious, adds to the stability and security of the\nbridge, both from the effects of undulations and of vibra-\ntions from shocks.\nAs a farther security to the stability of the structure, the\nframework of the roadway should be firmly attached at the\ntwo extremities to the basements of the piers.\n669. Preservative Means. To preserve the chains from\noxidation on the surface, and from rain or dews which may\nlodge in the articulations, they should receive several coats of\nminium, or of some other preparation impervious to water,\nand this should be renewed from time to time, and the forms\nof all the parts should be the most suitable to allow the free\nescape of moisture.\nWires for cables can be preserved from oxidation, until they\nare made into ropes, by keeping them immersed in some alka-\nline solution. Before making them into ropes, they should\nbe dipped several times in boiling linseed oil, prepared by\npreviously boiling it with a small portion of litharge and\nlampblack. The cables should receive a thick coating of the\nsame preparation before they are put up, and finally be\npainted with white-lead paint, both as a preservative means,\nand to show any incipient oxidation, as the rust will be de-\ntected by its discoloring the paint.\n670. Proofs of Suspension Bridges. From the many\ngrave accidents, accompanied by serious loss of life, which\nhave taken place in suspension bridges, it is highly desirable\nthat some trial-proof should be made before opening such\nbridges to the public, and that, moreover, strict police regu-\nlations should be adopted and enforced, with respect to them,\nDigitized by Google\nSUSPENSION BRIDGES.\n367\nto guard against the recurrence of such disasters as have seve-\nral times taken place in England, from the assemblage of a\ncrowd upon the bridge. In France, and on the continent\ngenerally, where one of the important duties of the public\npolice is to watch over the safety of life, under such circum-\nstances, regulations of this character are rigidly enforced.\nThe trial-proof enacted in France for suspension bridges, be-\nfore they are thrown open for travel, is about 40 lbs. to each\nsuperficial foot of roadway in addition to the permanent\nweight of the bridge. This proof is at first reduced to one-\nhalf, in order not to injure the masonry of the points of sup-\nport during the green condition of the mortar. It is made\nby distributing over the road surface any convenient weighty\nmaterial, as bricks, pigs of iron, bags of earth, etc. Besides\nthis after-trial, each element of the main chains should be\nsubjected to a special proof to prevent the introduction of un-\nsound parts into the system. This precaution will not be\nnecessary for the wire of a cable, as the process of drawing\nalone is a good test. Some of the coils tested will be a guar-\nantee for the whole.\nFrom experiments made at Geneva, by Colonel Dufour, one\nof the earliest and most successful constructors of suspension\nbridges on the Continent, it appears that wrought bar iron\ncan sustain, without danger of rupture, a shock arising from\na weight of 44 lbs., raised to a height of 3.28 feet on each,\n.0015dths of an inch of cross-section, when the bar is strained\nby a weight equal to one-third of its breaking weight and he\nconcludes that no apprehension need be entertained of injury\nto a bridge from shocks caused by the ordinary transit upon\nit, which has been subjected to the usual trial of a dead weight\nand that the safety, in this respect, is the greater as the bridge\nis longer, since the elasticity of the system is the best pre-\nservative from accidents due to such causes. Mr. Whoeler,\nan engineer in Germany, concluded, after a long series of\ncarefully conducted experiments, that good wrought iron\nwould sustain any number of continuous shocks, provided\nthat it was in no case strained more than 10,000 pounds per\nsquare inch of section.\n671. Durability. Time is the true test of the durability\nof the structures under consideration. So far as experience\ngoes there seems to be no reason to assign less durability to\nsuspension than to cast-iron or even stone bridges, if their re-\npairs and the proper means of preserving them from decay\nare attended to. Doubts have been expressed as to the dura-\nbility of wire cables, but these seem to have been set at rest\nDigitized by Google\n368\nCIVIL ENGINEERING.\nby the trials and examinations to which a bridge of this kind,\nerected by Colonel Dufour, at Geneva, was subjected by him\nafter twenty years' service. It was found that the undulations\nwere greater than when the bridge was first erected, owing to\nthe shrinking of the roadway-frame; but the main cables,\nand suspending-ropes, even at the loops in contact with the\ntimber, proved to be as sound as when first put up, and free\nfrom oxidation ; and the whole bridge stood another very\nsevere proof without injury.\nThe following succinct descriptions of the principal ele-\nments of some of the most celebrated suspension bridges of\nchains, and wire cables, of remarkable span, are taken from\nvarious published accounts.\n672. Bridge over the Tweed near Berwick. This is the\nfirst large suspension bridge erected in Great Britain. It\nwas constructed upon the plans of Capt. Brown, who took\nout a patent for the principles of its construction.\nSpan\n449 feet.\nVersed sine\n30 \"\nNumber of main-chains 12, six being placed on each side of\nthe roadway, in three ranges of two chains each, above\neach other.\nThe chains are composed of long links of round iron, 2\ninches in diameter, and are 15 feet long. They are connected\nby coupling-links of round iron, 11 inch diameter, and\nabout 7 inches long, by means of coupling bolts.\nThe roadway is borne by suspending-rods of round iron,\nwhich are attached alternately to the three ranges of chains.\nThe roadway-bearers are of timber, and are laid upon longi-\ntudinal bars of wrought iron, which are attached to the sus-\npension-rods.\n673. Menai Bridge, erected after the designs of Mr. Tel-\nford. Opened in 1826.\nSpan\n579.8 feet.\nVersed sine\n43\n\"\nNumber of main-chains 16, arranged in sets of 4 each, ver-\ntically above each other.\nNumber of bars in each link, 5.\nLength of links, 10 feet.\nBreadth of each bar, 31 inches depth, 1 inch.\nCoupling-links, 16 inches long, 8 inches broad, and 1 inch\ndeep.\nCoupling-bolts, 3 inches in diameter.\nTotal area of cross-section of the main-chain, 260 square\ninches.\nDigitized by\nGoogle\nSUSPENSION BRIDGES.\n369\nThe main-chains are fastened to their abutments by an-\nchoring-bolts 9 feet long and 6 inches in diameter, which are\nsecured in cast-iron grooves. The abutments, which are un-\nderground, and reached by suitable tunnels, are the solid rock.\nUpon the tops of the piers are cast-iron saddles, upon\nwhich the main-chains rest. The base of the saddle, which\nis fitted with grooves to receive them, rests upon iron rollers\nplaced on a convex cylindrical bed of cast iron, shaped like\nthe bottom of the base of the saddle, to admit of a slight\ndisplacement of the chains from movable loads or changes\nof temperature.\nThe roadway is divided into two carriage-ways, each 12\nfeet wide, and a footpath 4 feet wide between them. The\nroadway-framing consists of 444 wrought-iron roadway-\nbearers, 31 inches deep and 1 inch thick, which are sup-\nported at the centre points of each of the carriage-ways by\nan inverted truss, consisting of two bent iron ties which sup-\nport a vertical bar placed under the roadway-bars at the\npoints just mentioned. The platform of the roadway is\nformed of two thicknesses of plank. The first, 3 inches thick,\nis laid on the roadway-bearers and fastened to them. This\nis covered by a coating of patent felt soaked in boiling tar.\nThe second is two inches thick and spiked to the first.\nThe roadway is suspended by articulated rods attached to\nstirrups on the roadway-bearers and to the coupling-bolts of\nthe main-chains.\nThe piers are 152 feet high above the high-water level.\nThey have an arched opening leading to the roadway, and\nthe masses on the sides of the arch are built hollow, with a.\ncross-tie partition wall between the exterior main walls.\nThe parapet is of wrought-iron vertical and parallel bars.\nconnected by a network.\nThis bridge was seriously injured by a violent gale, which\ngave so great an oscillation to the main-chains that they were\ndashed against each other, and the rivet-heads of the bolts\nwere broken off. To provide against similar accidents, a\nframework of cast-iron tubes, connected by diagonal pieces,\nwas fastened at intervals between the main-chains, by cross-\nties of wrought-iron rods, which passed through the tubes,\nand were firmly connected with the exterior chains. Subse-\nquently to this addition, a number of strong timber roadway-\nbearers were fastened at intervals to those of iron, as the\niron roadway-bearers were found to have been bent, and in\nsome instances broken, by the undulatory motion of the:\nbridge in heavy gales.\n24\nDigitized by Google\n370\nCIVIL ENGINEERING.\nThe total suspending weight of this bridge, including the\nmain-chains, roadway, and all accessories, is stated at 643\ntons 151 cwt.\n674. The Fribourg Bridge of wire thrown across the\nvalley of the Sarine, opposite Fribourg, was erected in 1832,\nby M. Chaley, a French engineer.\nSpan\n870.32 feet.\nVersed sine\n63.26 \"\nThere are 4 main cables, 2 on each side of the road, of\nthe same elevation, and about 11 inch asunder. Each cable\nis composed of 1056 wires, each about 0.118 inch in diameter,\nwhich are firmly connected and brought to cylindrical shape\nby a spiral wire wrapping. The diameter of the cable varies\nfrom 5 to 51 inches. The cables pass over 3 fixed pulleys on\nthe top of the piers, upon which they are spread out without\nligatures, and are each attached to two other cables of half\ntheir diameter, which are anchored at some distance from the\npiers, in vertical pits, passing over a fixed pulley where they\nenter the mouth of the pit.\nThe suspending-ropes are of wire a size smaller than that\nused for the cables. Their diameter is nearly one inch. They\nare formed with a loop at each end, fastened around a crup-\nper-shaped piece of cast iron, that forms an eye to connect\nthe rope with the hook of the stirrup affixed to the roadway-\nbearers, and to a saddle-piece of wrought iron, for each rope,\nthat rests on the two main cables.\nThe roadway-bearers are of timber, being deeper in the\ncentre than at the two ends, the top surface being curved to\nconform to a slight transverse curvature given to the surface\nof the carriage-way they are placed about 5 feet between\ntheir centre lines, every fourth one projecting about 3 feet\nbeyond the ends of the others, to receive an oblique wrought-\niron stay to maintain the parapet in its vertical position. The\ncarriage-way, which is about 151 feet wide, is formed of two\nthicknesses of plank. The foot-paths, which are 6 feet wide,\nare raised above the surface of the carriage-way, and rest\nupon longitudinal beams of large dimensions, the inner one of\nwhich is firmly secured to the roadway-bearers by stirrups\nwhich embrace them, and the exterior one is fastened to the\nsame pieces by long screw-bolts, which pass through the top\nrail of the parapet. The roadway has a slight curvature from\nthe centre to the two extremities, along the axis, the centre\npoint being from 18 inches to about 3 feet higher than the\nends, according to the variations of temperature. The main\nDigitized by\nGoogle\nSUSPENSION BRIDGES.\n371\ncables at the centre are brought down nearly in contact with\nthe roadway-timbers.\nThe parapet is an open-built beam, consisting of a top rail,\nthe bottom rail being the longitudinal exterior beam of the\nfootpath, and of diagonal pieces which are mortised into the\ntwo rails; the whole being secured by the iron bolts that\npass through the roadway-bearers and the top rail. This\ncombination of the parapet with the inclination towards the\naxis of the roadway given to the suspending-ropes, gives great\nstiffness to the roadway and counteracts both lateral oscilla-\ntions and longitudinal undulations.\nThe piers consist of two pillars of solid masonry, about 66\nfeet high above the level of the roadway, which are united, at\nabout 33 feet above the same level, by a full centre arch,\nhaving a span of nearly 20 feet, and which forms the top of\nthe gateway leading to the bridge.\n675. Hungerford and Lambeth Bridge, erected over the\nThames, upon the plans of Mr. Brunel.\nThis bridge, designed for foot-passengers only, has the\nwidest span of any chain bridge erected up to this period.\nSpan\n6761 feet.\nVersed sine\n50 \"\nThe main chains are 4 in number, two being placed on\neach side of the bridge, one above the other. These chains\nare formed entirely of long links of flat bars; the links near\nthe centre of the curve having alternately ten and eleven bars\nin each, and those near the piers alternately eleven and twelve\nbars. The bars are 24 feet long, 7 inches in depth, and 1 inch\nthick. They are connected by coupling-bolts, 4g inches in\ndiameter, which are secured at each end by cast-iron nuts, 8\ninches in diameter, and 28 inches thick. The extremity of\neach chain is connected with a cast-iron saddle-piece, by bolts\nwhich pass through the vertical ribs of the saddle-piece, of\nwhich there are 15. The bottom of the saddle rests on 50\nfriction-rollers, which are laid on a firm horizontal bed of cast-\niron. The saddle can move 18 inches horizontally, either way\nfrom the centre, and thus compensate for any inequality of\nstrain on the main chains, either from a load, or from vari-\nations of temperature.\nThe side main-chains are attached in like manner to the sad-\ndle, and anchored at the other extremity in an abutment of\nbrickwork. The anchorage (Fig. 193) is arranged by passing\nthe chains through a strong cast-iron plate, and securing the\nends of the bars by keys. The anchoring-plate is retained in\nDigitized by Google\n372\nCIVIL ENGINEERING.\nits place by two strong cast-iron beams, against which the\nstrain upon the plate is thrown.\nFig. 198-Shows the manner in which the\nside main-chains are anchored.\nA, inclined shaft for the chains leading to\nB\nthe arched chamber B of the anchorage.\n6\na, a, two main-chains, passed through the\ncast-iron holding-plate b and fastened be-\nhind it by keys.\na c, cross sections of the cast-iron girders\nwhich retain b.\nThe suspending-rods (Fig. 194) are connected with both the\nFig. 194-Shows an eleva-\ntion M and cross section\nN of the connection be-\ntween the main-chains\nand suspending-rods,\n0\na, a, upper main-chain.\nP\nb, b, joint of lower main-\nP\nchain.\na suspending-rod with a\na\nforked head to receive the\nplate d, hung by stirrup-\n109\nstraps 6 and f. respective-\n9\nly, to the coupling-bolt of\nthe links and to the two\nbolts g, fastened to the sad-\ndle h on top of the upper\nmain-chain.\nD\n4\nN\nW\nY\nupper and lower main-chains; to the upper by a saddle-piece\nand bolts, and to the coupling-bolt of the lower by an arrange-\nment of articulations, which allows an easy play to the rods ;\nat the bottom (Fig. 195) they are connected by a joint with a\nbolt that fastens firmly the roadway-timbers.\nThe roadway-timbers consist of a strong longitudinal bottom\nbeam, upon which the road way-bearers are notched ; these last\npieces are in pairs, the two being so far apart that the bolts con-\nnecting with the suspending-rods by a forked head can pass be-\ntween them ; the flooring-plank is laid upon the roadway-bear-\ners; and a top longitudinal beam, which forms the bottom rail\nof the parapet, is secured to the bottom beam by the con-\nnecting bolt. Wrought-iron diagonal ties are placed horizon-\nDigitized by Google\nSUSPENSION BRIDGES.\n373\ntally below the flooring, to brace the whole of the timbers be-\nneath.\nFig. 195-Shows an elevation of the roadway-timbers.\na, bottom longitudinal beam.\nb, b, roadway-bearers in pairs.\nc, platform.\nd, top longitudinal beam forming the bottom rail of the para-\npet.\nb\nb\ne, bolt, with a forked head to receive the end of the suspending-\nrod, which is keyed beneath and secures the beams, etc.\no, wrought-iron horizontal diagonal ties.\nThe roadway is 14 feet wide. It slopes from the centre\npoint along the axis to the extremities, being 4 feet higher in\nthe centre than at the two last points.\nThe piers are in the form of towers, resembling the Italian\nbelfry. They are of brick, 80 feet high, and so constructed\nand combined with the top saddles, that they have to sustain\nno other strain than the vertical pressure from the main-chains.\nThe whole weight of the structure, with an additional load\nof 100 lbs. per square foot of the roadway, would throw about\n1,000 tons on each pier. The tension on the chains from this\nload is calculated at about 1,480 tons ; while the strain which\nthey can bear without impairing their strength is about 5,000\ntons.\n676. Monongahela Wire Bridge. This bridge, erected\nat Pittsburgh, Penn., upon plans, and under the superintend-\nence of the late Mr. Roebling, has 8 bays, varying between\n188 and 190 feet in width. It is one of the more recent of\nthese structures in the United States.\nThe roadway of each bay is supported by two wire cables,\nof 41 inches in diameter, and by diagonal stays of wire rope,\nattached to the same point of suspension as the cables, and\nconnecting with different points of the roadway-timbers.\nThe ends of the cables of each bay are attached to pendulum-\nbars, by means of two, oblique arms, which are united by\njoints to the pendulum-bars. These bars are suspended from\nthe top of 4 cast-iron columns, inclining inwards at top,\nwhich are there firmly united to each other ; and, at bottom,\nanchored to the top of a stone pier built up to the level of\nthe roadway timbers. The side columns of each frame\nare connected throughout by an open lozenge-work of cast\nDigitized by Google\n374\nCIVIL ENGINEERING.\niron. The front columns have a like connection, leaving a\nsufficient height of passage-way for foot-passengers.\nThe framework of 4 columns on each side is firmly con-\nnected at the top by cast-iron beams, in the form of an entab-\nlature. A carriage-way is left between the two frames, and a\nfootpath between the two columns forming the fronts of each\nframe.\nThe points of suspension of the cables are over the centre\nline of the footpaths; and the cables are inclined so far in-\nward that the centre point of the curve is attached just out-\nside of the carriage-way. The suspending-ropes have a like\ninward inclination, the object in both cases being to add stiff-\nness to the system, and diminish lateral oscillations.\nThe roadway consists of a carriage-way 22 feet wide, and\ntwo footpaths each 5 feet wide. The roadway-bearers are\ntransversal beams in pairs, 35 feet long, 15 inches deep, and\n41 inches wide. They are attached to the suspending-ropes.\nThe flooring consists of 21-inch plank, laid longitudinally\nover the entire roadway-surface; and of a second thickness of\n21-inch oak plank laid transversely over the carriage-way.\nThe parapet, which is on the principle of Town's lattice,\nextends so far below the roadway-bearers that they rest and\nare notched on the lowest chord of the lattice. A second\nchord embraces them on top, and finally a third chord com-\npletes the lattice at the top. The object of adopting this form\nof parapet was to increase the resistance of the roadway to\nundulations.\n677. Niagara Railroad and Highway Suspension Bridge.\nThis remarkable structure, like the Aqueduct suspension\nbridge at Pittsburgh, was constructed by Roebling; and for\nboldness of plan, and skill in the execution of its details,\nis every way worthy of the professional ability of this distin-\nguished engineer.\nDesigned to afford a passage-way over the Niagara river,\nboth for railroad and common road traffic, it consists essen-\ntially of two platforms (Fig. 196), one above the other, and\nabout fifteen feet apart; the upper serving as the railroad\ntrack, and the lower for ordinary vehicles; the two being con-\nnected by a lattice girder on each side ; and the whole bridge-\nframe being suspended from four main wire cables, two of\nwhich are connected with the upper platform, and two with\nthe lower, by suspension-rods and wire ropes attached to the\nroadway-bearers, or joists of the platforms.\nEach platform consists of a series of roadway-bearers in\npairs; the lower covered by two thicknesses of flooring-plank,\nDigitized by Google\nSUSPENSION BRIDGES.\n375\nthe upper by one thickness ; the portion of the latter imme-\ndiately under the railroad track having a thickness of four\ninches, and the remainder on each side but two inches.\nc'\nc'\nD\nA\nC\nB'\nD\n25\nA\nH\nC\nE\nF\nF\nc\nc\nN\nC\nC\nM\nB\nD\nde\nB\ndo\nB\nA\nx\nFig. 196-Cross section of Niagara Bridge.\nA, railway track and beams.\nc, lower main cables.\nB, lower platform for common road.\no, upper main cables.\nC, Diagonal truss.\nD, suspension ropes.\nD, parapet.\nE, wrought-iron braces.\nA, lower roadway bearers.\nF, wooden braces.\nA, upper roadway bearers.\nG, beams of longitudinal railway bearers.\nB, lower flooring.\nH, longitudinal braces between roadway bearers.\nB', upper flooring.\nN, horizontal rail between posts.\nThe lattice-girders consist of vertical posts in pairs, the\nends of which are clamped between the roadway-bearers ;\nand of diagonal wrought-iron rods with screws at each end,\nwhich pass through cast-iron plates fastened above the road-\nway-bearers of the upper platform, and below those of the\nlower, and are brought to a proper bearing by nuts on each\nend. A horizontal rail of timber is placed between the posts\nof the lattice at their middle points to prevent flexure.\nDigitized by Google\n376\nCIVIL ENGINEERING.\nD\n00000\nA\nThe\nT\nT\nN\nM\nx\nFig. 197-Side elevation of Niagara Bridge.\nA', A', ends of roadway bearers.\nD, parapet.\nM, ports in pairs.\nN, rail between posts.\nT, diagonal Iron brace rods.\nThe roadway-bearers and flooring of the upper platform\nare solidly clamped between four solid built beams or gird-\ners; two above the flooring, which rest on cross supports;\nand two, corresponding to those above, below the roadway-\nbearers; the upper and lower corresponding beams, with\nlongitudinal braces in pairs between the roadway-bearers and\nresting on the lower beams, being firmly connected by screw-\nbolts. The rails are laid upon the top beams.\nA strong parapet, on the plan of Howe's truss, is placed on\neach side of the upper platform.\nWrought-iron and wooden braces connect the posts and the\ntwo platforms.\nThe piers (Fig. 198) consist of four obelisk-shaped pillars,\nwhich are sixty feet high ; the base of each being a square of\nfifteen feet sides; and the top one of eight feet sides. The\npedestal of each pillar is a square of about seventeen feet\nside at top, and having a batir of one foot vertically to one\nhorizontally, or 12, on each of its faces. The height of the\nDigitized by Google\nSUSPENSION BRIDGES.\n377\n8\nFig. 196-End elevation of piers and con-\nnecting arch of bridge.\nA\nA, shaft of the pier.\nB, pedestal.\nC, connecting arch.\nD, arched way for common road.\n15'\nc\n17\"\nD\nB\n20\npedestals on the United States side of the river being twenty-\neight feet, and on the Canadian side eighteen feet. An arch-\nway below the level of the railroad connects the two pedestals.\nThe main cables pass over saddles placed on rollers, on\nthe tops of the piers, and they are fastened at their ends\n(Fig. 199) to chains formed of links of wrought-iron bars,\nwhich, passing through abutments of masonry, and down into\nshafts made into the solid rock below, are there each firmly\nattached to an anchoring-plate of cast iron.\nBesides the usual suspending-rods of the bridge, a number\nof wire ropes, termed over-floor stays, connect the portions of\nthe upper platform adjacent to the piers with the saddles at\nthe top of the piers; and the lower platform is in like manner\nconnected with the rocky banks of the river by a number of\nlike stays. The object of both being to resist the action of\nhigh winds upon the platform, and to give the bridge more\nrigidity.\nEach of the main cables is formed of seven smaller ones or\nstrands. The whole bound together in the usual manner by\na wire wrapping. Each strand contains 520 wires in its\ncross-section, sixty of which make an area of one square inch.\nThe main cables to which the roadway-bearers of the upper\nplatform are attached are deflected laterally towards the\naxis of the bridge, and thus limit the range of lateral oscilla-\ntions. This provision, the lattice structure of the sides and\nthe parapet, the over and under floor stays, the deep longitu-\ndinal girders of the railway track, the slight camber or longi-\nDigitized by Google\n378\nCIVIL ENGINEERING.\n4\nA\nC\nB\nFig. 199-Side view of anohor-chain.\nA, masonry of buttress.\nB, natural rock bed.\nC, shaft and masonry for chains.\nD, anchoring-plate.\ntudinal curvature from the ends of the bridge to the centre,\nand its own weight, give to the whole structure that degree\nof rigidity and stability which are its marked characteristics,\nas contrasted with suspension bridges usually.\nSome of the principal dimensions of the means of suspen-\nsion are given in the following statement :\nSpan of both cables between axis of piers, 821] feet.\nVersed sine of cables of lower platform, 64 feet.\nVersed sine of cables of upper platform, 54 feet.\nDiameter of each cable, 10 inches.\nArea of cross-section of each cable, 60.4 square inches.\nArea of cross-section of upper links of anchor-chains, 372\nsquare inches.\nUltimate strength of anchor-chains, 11,904 tons.\nNumber of wires in the four cables, 14,560.\nAverage strength of one wire, 1,648 lbs.\nUltimate strength of the four cables, 12,000 tons.\nPermanent weight borne by the cables, 1,000 tons.\nLength of anchor-chains, 66 feet.\nLength of upper cables, 1,261 feet.\nDigitized by Google\nSUSPENSION BRIDGES.\n379\nLength of lower cables, 1,193 feet.\nNumber of suspenders, 624.\nNumber of over-floor stays, 64.\nNumber of under-floor stays, 56.\nLength of platforms between piers, 800 feet.\nHeight of railway track above middle stage of water, 245\nfeet.\n678. East River Bridge. The East River Bridge, which is\nnow in process of erection, will, when completed, be the\nlongest span suspension bridge which has been erected up to\nthis date. It will form a suspended highway connecting\nNew York and Brooklyn cities. The terminus in New York\ncity will be opposite City Hall, in Chatham street; and in\nBrooklyn in the square bounded by Fulton, Sands, Washing-\nton, and Prospect streets. Its total length will be 5,989 feet.\nThe central span will cross the river without impeding navi-\ngation, in'a single span of 1,595 feet 6 inches from centre to\ncentre of tower.\nOn each side of the central opening on the land sides there\nwill be spans supported by the land cables of 930 feet each.\nThe remaining distances, which form the approaches, will be\nsupported by iron girders and trusses, and will rest at short\nintervals upon small piers of masonry or iron columns,\nlocated within the blocks of buildings which will be crossed\nand occupied. These pillars will form part of the walls\nneeded for the division of the occupied ground into stores,\ndwellings, or offices.\nThe grade from the New York terminus to the centre of\nthe bridge will be three feet and three inches per hundred\nfeet, and the same on the Brooklyn side from the centre of\nthe bridge to the anchorage, but the grade of the Brook-\nlyn approach will be two feet and nine inches per hundred\nfeet.\nThe floor of the bridge will be 85 feet in width from out\nto out. The floor is divided into five spaces by six lines of\niron trusses. The outer spaces will be in the clear eigh-\nteen feet each, and will accommodate each two lines of iron\ntramways for ordinary vehicle travel, as well as for street cars,\ndrawn singly by horses, or in pairs by light dummies. The\nnext two spaces will be thirteen feet two inches wide each,\nprovided with an iron track for running of two passenger\ntrains back and forward alternately. These trains will be at-\ntached to an endless wire rope, propelled by a stationary en-\ngine, which will be located on the Brooklyn side, underneath\nthe floor, the two tracks being operated like an inclined plane,\nDigitized by Google\n380\nCIVIL ENGINEERING.\nwith a speed of twenty miles per hour, the whole transit occu-\npying only five minutes from terminus to terminus.\nThe central or fifth division of the bridge floor will form a\npromenade for foot travel, fifteen feet in width. It will be\nelevated five feet above the roadway, affording a view over\nboth sides of the bridge.\nThe roadway will pass the towers at an elevation of 119\nfeet, and the centre of the main span will be 135 feet above\nmean high tide, or 140 feet above mean low water.\nThe width of the roadway, from outside to outside, will be\n85 feet.\nThe bridge will be supported by four main cables, each 16\ninches in diameter, composed of galvanized tempered cast-\nsteel wire, No. 6 gauge, having a strength of 160 pounds per\nsquare inch of section. There will also be 104 stays to aid\nthe cables.\nThe total weight of the structure, including the cables, is\nestimated to be 5,000 tons.\nThis grand structure was devised, and works superintended\ntill his death, by the late John A. Roebling. It is now engi-\nneered by his son Col. W. A. Roebling.\nVIII.\nMOVABLE BRIDGES.\n679. The term movable bridge is commonly applied to a\nplatform supported by a framework of timber or of cast\niron, by means of which a communication can be formed or\ninterrupted at pleasure between any two points of a fixed\nbridge, or over any narrow water-way. These bridges are\ngenerally denominated draw-bridges, but this term is now, for\nthe most part, confined to those movable bridges which can\nbe raised or lowered by means of a horizontal axis, placed\neither at one extremity of the platform, or at some inter-\nmediate point between the two ends, and a counterpoise which\nis so connected with the platform in either case, that the\nbridge can be easily manœuvred by a small power acting\nthrough the intermedium of some suitable mechanism ap-\nplied to the counterpoise. The term turning or swinging\nbridge is used when the bridge is arranged to turn horizon-\ntally around a vertical axis placed at a point between its two\nends, so that the parts on each side of the axis balance each\nother; and the term rolling bridge is applied when the bridge,\nDigitized by\nGoogle\nMOVABLE BRIDGES.\n381\nresting upon rollers, can be shoved forward or backward hori-\nzontally, to open or interrupt the passage.\nTo the above may be added another class of movable\nbridges used for the same purpose, which consist of a plat-\nform supported by a boat, or other buoyant body, which can\nbe placed in or withdrawn from the water-way as circum-\nstances may require.\n680. Draw-Bridges. When the horizontal axis of this\ndescription of bridge is placed at the extremity of the plat-\nform, the bridge is manœuvred by attaching a chain to the\nother extremity, which is connected with a counterpoise and\na suitable mechanism, by which the slight additional power\nrequired for raising the bridge can be applied.\nFig. 200-Shows the manner\nb\nof manœuvring a draw-\nbridge either by a framed\nlever, or by a counterpoise\nsuspended from a spiral\neccentric.\nA, abutment.\ni\na, section of the platform.\nb, framed lever.\na chain attached to the ends\no\nof the lever and the plat-\nm\nform.\nh\nd, strut movable around its\nlower end.\ne, bar with an articulation\ng\nat each end that confines\nn\nthe strut to the platform.\n1, spiral eccentric connected\nwith the counterpoise g by\na chain passing over the\ngorge of the eccentric.\nA, chain for raising the\na\nbridge, one end of which\nis attached to the extremity\nof the platform, and the\nother to the axle of the\nA\neccentric.\nt, fixed pulley over which the\nd\nchain A is passed.\nm, wheel fixed to the axle\nof the ecoentric for the\npurpose of turning it by\nmeans of animal power\napplied to the endless\nchain n.\nA number of ingenious contrivances have been put in\npractice for these purposes. They consist usually either of a\ncounterpoise of invariable weight, connected with additional\nanimal motive-power, which acts with constant intensity, but\nwith a variable arm of lever; or of a counterpoise of vari-\nable weight, which is assisted by animal motive-power acting\nwith an invariable arm of lever. In some cases the bridge is\nworked with a less complicated combination, by dispensing\nDigitized by Google\n382\nCIVIL ENGINEERING.\nwith a counterpoise, and applying animal motive-power, of\nvariable intensity, acting with a constant or a variable arm of\nlever.\nAmong the combinations of the first kind the most simple\nconsists in placing a framed lever (Fig. 200) revolving on a\nhorizontal axis above the platform. The anterior part of the\nframe is connected with the movable extremity of the plat-\nform by two chains. The posterior portion, which forms the\ncounterpoise, has chains attached to it by which the lever can\nbe worked by men.\nWhen the locality does not admit of this arrangement, the\nchain attached to the movable end of the platform may be\nconnected with a horizontal axle above the platform, to which\nis also attached a fixed eccentric of a spiral shape (Fig. 200),\nconnected with a chain that passes over its gorge and sustains\na counterpoise of invariable weight. Upon the same axle an\nordinary wheel is hung, over the gorge of which passes an\nendless chain to manœuvre the bridge by animal power.\nFig. 201-Shows the ar-\nrangement of a draw-\nbridge with a variable\nJc\ncounterpoise.\nA and B, abutments.\ng, variable counterpoise\nz\nformed of a chain with\nflat links, one end of\nwhich is attached to a\nfixed point, and the\nother to the chain c at-\ntached to the movable\nend of the platform.\n1, fixed pulley over which\nthe chain c passes 10\nthe small wheel k fixed\non a horizontal shaft,\nto which is also attach-\ned the wheel m and\na\nthe endless chain n\nB\nfor manceuvring the\nbridge.\nOf the combinations of variable counterpoises the mechan-\nism of M. Poncelet, which has been successfully applied in\nmany instances in France for the draw-bridges of military\nworks, is one of the most simple in its arrangement and con-\nstruction. The movable end of the platform (Fig. 201) is\nconnected by a common chain, that passes over the gorge of a\nwheel hung upon a horizontal shaft above the platform, with\nanother chain of variable breadth, formed of flat bar links,\nwhich forms the counterpoise. The chain counterpoise is at-\ntached at its other extremity to a fixed point in such a way,\nthat when the platform ascends a portion of the weight of\nthe chain is borne by this fixed point ; and thus the weight of\nDigitized by\nGoogle\nMOVABLE BRIDGES.\n383\nthe counterpoise decreases as the platform rises. The system\nis manœuvred by an endless chain passed over the gorge of a\nwheel hung upon the horizontal shaft.\nFor light platforms a counterpoise may be dispensed with,\nand the bridge may be manœuvred by connecting the chain\nattached to the movable end of the platform to a horizontal\nshaft, which is turned by the usual tooth-work combinations.\nWhen the locality does not admit of manœuvring the\nFig. 209-Shows the ar-\nrangement of a draw-\nB\nbridge where the coun-\nterpoise is formed by\nprolonging back the\nplatform.\nA, abutment.\nB, well of a suitable form\nfor manoeuvring the\nbridge.\na, chain-stay to keep the\nplatform firm when the\nbridge is down.\nbridge by a chain connected with some point above the\nframework, the platform (Fig. 202) is continued back, from\ntwo-thirds to three-fifths its length, from the face of the\nabutment, to form a counterpoise for the platform of the\nbridge. The horizontal axis of the bridge is placed near the\nface of the abutment, and a well ofa suitable shape to re-\nceive the posterior portion of the platform that forms the\ncounterpoise is formed behind the abutment.\nThe mechanism for working the bridge may consist of a\nchain and capstan below the platform-counterpoise, or of a\nsuitable combination of tooth-work.\nIn bridges of a single platform, the movable extremity,\nwhen the bridge is lowered, rests on the opposite abutinent,\nand no intermediate support will be required for the struc-\nture if the framework be of sufficient strength; but when\na double bridge, consisting of two platforms, is used, the plat-\nforms (Fig. 200) should be supported near their movable ends,\nwhen the bridge is down, by struts movable around the joint\nby which they are connected with the face of the abutments.\nThese struts are so connected with the bridge that they are\ndetached from it and drawn up when it is raised, and fall back\ninto their places, abutting against blocks near the movable end\nof the platform, when the bridge is down. By these arrange-\nments the chains for working the bridge are relieved from a\nDigitized by Google\n384\nCIVIL ENGINEERING.\nportion of the strain when the bridge is down, and it is also\nrendered more firm.\nWhen the counterpoise is formed by the rear part of the\nplatform, additional security may be given to the bridge when\ndown by attaching two chains beneath the platform, and se-\ncuring them to anchoring-points at the bottom of the well.\nIn some cases a heavy bar, fitted to staples beneath connected\nwith the timbers of the platform, is used for the same pur-\npose.\nIn double bridges the two platforms when lowered should\nabut against each other, giving a slight elevation to the cen-\ntre of the bridge. This not only gives greater stiffness, but\nis favorable to detaching the platforms when the bridge is to\nbe raised.\nFor draw, and every kind of movable bridge, temporary\nbarriers should be erected on each side at the entrance upon\nthe bridge, to prevent accidents by persons attempting to\ncross the bridge before it is properly secured when lowered.\n681. Turning-bridges. These bridges revolve horizontally\nupon a vertical shaft or gudgeon below the platform, which\nis usually thrown far enough back from the face of the abut-\nment to place the side of the bridge, when brought round,\njust within this face. The weights of the parts of the bridge\naround the shaft should balance each other.\nn\nb\nn\na\n(O)\n(O)\nFig. 208-Represents the arrangement of a turning-bridge.\na, platform of the bridge.\n0, vertical posts to which the iron stays n n are attached.\nc, vertical shaft or gudgeon on which the bridge turna.\n0 o, conical rollers.\nTo support and manœuvre the bridge (Fig. 203) a circular\nring of iron, or roller-way, of less diameter than the breadth\nof the bridge, and concentric with the vertical shaft, is firmly\nimbedded in masonry. Fixed rollers, in the shape of trun-\ncated cones, are attached at equal distances apart to the frame-\nwork of the platform beneath, and rest upon the roller-way.\nDigitized by Google\nSWING BRIDGES.\n385\nThe bridge is worked by a suitably arranged tooth-work, or\nby a chain and capstan. In some cases cast-iron balls, rest-\ning on a grooved roller-way, and fitting into one of corre-\nsponding shape fixed beneath the platform, have been used\nfor manœuvring the bridge.\nThe ends of the bridge are cut in the shape of circular arcs\nto fit recesses of a corresponding form in the abutments, so\narranged as not to impede the play of the bridge.\nIn double-turning bridges the two ends of the platforms\nwhich come together should be of a curved shape. The plat-\nforms should be sustained from beneath by struts, like those\nused for draw-bridges, which can be detached and drawn into\nrecesses when the passage is interrupted; or else they may\nbe arranged with a ball-and-socket joint at their lower ex-\ntremity, so as to be brought round with the bridge. For the\npurpose of giving additional strength and security to the\nbridge, iron stays are, in some cases, attached on each side of\nthe platform near the extremities, and connected with verti-\ncal posts placed in a line with the vertical shaft.\nTurning-bridges may be made either of timber or of cast\niron; the latter material is the more suitable, as admitting of\nmore accuracy of workmanship, and not being liable to the\nderangements caused by the shrinking or warping of frame-\nwork of timber.\n682. Swing Bridge at Providence, R. I. The details of\nthis bridge are worthy of special study. An account of it\nis published in the London Engineering for March 21st,\n1873. Fig. 204 is an elevation of the bridge, and the right-\nhand half of Fig. 205 is a plan of the truss work under the\nroadway, and the left-hand half the plan of the roadway and\ntruss work. Fig. 206 is a section of the turn-table for sup-\nporting the bridge. An essential part is the four compound\nradial arms, G G, F F, Fig. 206, the lower parts of which\nare of cast-iron compression members, and the upper parts\nof two wrought-iron rods each.\nThe whole structure rests upon a nest of conical rollers, I I\n(Fig. 206), upon which it turns as it moves about. There are\nseveral small wheels b, b, b, which are under the turn-table,\nand serve only to steady it in case it tends to tip in any di-\nrection.\nThe strains on the several members were computed under\nthree hypotheses, viz. : 1st. The strains due to the weight of\nthe truss only when the draw was open. These strains were\nassumed to be the same as when it was closed and unloaded,\nfor no part of the weight of the bridge was supposed to be\n25\nDigitized by Google\n386\nFir. 201.\nA\nc\nc\nD\nD\nB\nGEIRDER\nE\n6\n6\nB\n19\n\"\nR\nFOREST\nE\nP\nTIAIO\na\na\na\na\nE\nM\nN\n0\nFig. 205.\nDigitized by Google\nFign. 204 and 205-The elevation and plan of the swing bridge over Point Street, at Providence, Rhode Island. Total span 250 feet.\nDepth at the centre 25 feet, and at the ends 9 feet. The part A 0 of the upper chord is subjected to tension only, and is composed of\ntension bars only ; but the part 0 D may be subjected to both tension and compression, and is made to remist both strains. The three end\npanels only require counter-ties. E is a pin for securing the bridge in place when it is closed. a, a, a, are tie rods after the plan of a\nWhipple Truss, The part M N is subjected to compression only, and the part N 0 to both tension and compression, a c, a are main the\nrods; d, d, counter-tie rods, P, the foundation for the turn table, b, b, the seat for steady wheels.\n387\nK\nF\nDigitized by Google\nC\nJ\nJ\nF\nSWING BRIDGES.\nH\nC\n6\nST\nFig. 206-Is the turn-table. 3, 0, b, are rollers for guiding the turn-table to keep it from overturning. They serve to steady it.\nThe whole weight rests upon a nest of conical rollers I I, upon which the table turns.\nH is a central block for supporting the table.\nG G is a cast-iron arm, which is supported at its outer end by the wrought-iron radial arms FF (four in number). JJ is the wheel\nfor opening the draw. A shaft extends from J J upwards to the floor K, to which a lever is attached. Two men can easily open and\nclose the draw.\n388\nCIVIL ENGINEERING.\nsupported at its ends, although the ends were pinned to keep\nthem from rising when only one part was loaded. 2d. One\nhalf was supposed to be loaded while the other end was held\ndown by the pin and 3d. The bridge was supposed to be\nloaded uniformly throughout.\nThe call for proposals specified that the rolling load should\nbe 3,200 lbs. per lineal foot of the bridge, and that the\nwrought iron should not be strained in tension to exceed\n12,000 lbs. per square inch, or in compression 8,000 lbs. per\nsquare inch. The following tables give the results of the\noriginal computations for the strains and the dimensions of\nthe pieces used. The engineer, Charles McDonald, of New\nYork City, states that a review of the computations after the\nstructure was completed, confirmed the general results, al-\nthough in some cases the actual strains exceed those previ-\nously determined by a small amount. Although the analysis\nshows (see Table II.), that there is compression on the fourth\nand fifth bay of the upper chord, yet there is no tendency to\na strain on the counter-diagonals in those panels. The incli-\nnation of the upper chord acts as a brace and thus prevents\nany strain in the direction of the counter-tie in those panels.\nTABLE No. I.-Showing Total Strains on Parts when the Bridge is Open,\nbut Unloaded.\n(The sign plus is for compression and minus for tension.)\nNumber of\nCounter-\nTop Chord.\nBottom Chord.\nVerticals.\nBay.\nDiagonals.\nties.\nlb.\nlb.\nlb.\nlb.\nlb.\nEnd\nnil.\n+ 6,073\nnil\n- 8,427\nnil\n2\n- 6,223\n+ 19,577\n+ 4,407\n- 20,900\n\"\n8\n- 19,941\n+ 87,735\n+ 18,532\n- 80,868\n\"\n4\n- 88,263\n+ 59,688\n+ 22,565\n- 40,800\n5\n- 60,280\n+ 85,759\n+ 82,227\n- 51,340\n6\n- 86,800\n+116,189\n+ 42,702\n- 62,600\n7\n-116,600\n+151,625\n+ 55,047\n- 75,875\n8\n-151,860\n+193,249\n+ 68,463\n- 90,350\n9\n-193,400\n+242,624\n+ 84,090\n-107,637\nCentre\n-242,624\n+242,624\n+ 98,625\nnil\nDigitized by Google\nSWING BRIDGES.\n389\nTABLE No. II-Showing Total Strains on Parts with Bridge Closed and\none-half fully Loaded, the Unloaded end being Latched.\nNumber of\nBay.\nTop Chord.\nBottom Chord.\nVerticals.\nCounter-\nDiagonals.\nties.\nlb.\nlb.\nlb.\nlb.\nlb.\nLoaded end\n+ 69,500\nnil\n+ 64,500\nnil\n- 81,080\n2\n+ 83,610\n- 67,480\n+ 21,500\nnil\n- 27,000\n8\n+ 88,110\n- 69,800\nnil\nnil\nnil\n4\n+ 69,977\n- 41,600\n+ 17,718\n- 52,249\n5\n+ 42,000\nnil\n+ 40,365\n- 81,910\n6\nnil\n+ 53,800\n+ 64,500\n-110,674\n7\n- 54,000\n+120,337\n+ 92,690\n-141,580\n8\n-120,520\n+201,326\n+123,440\n-175,770\n9\n-201,480\n+299,587\n+158,187\n-214,100\nCentre\n-299,587\n+304,868\n{ +193,500\n+160,010\n~\n- 60,560\n9\n-249,140\n+304,868\n+ 96,480\n-121,916\n8\n-201,954\n+248,943\n+ 79,520\n-103,670\n7\n-161,500\n+201,637\n+ 65,190\n- 86,618\n6\n-126,120\n+160,915\n+ 51,800\n- 73,141\n5\n- 95,240\n+125,360\n+ 41,036\n- 61,061\n4\n- 67,713\n+ 94,800\n+ 80,984\n- 51,000\n8\n- 42,962\n+ 66,778\n+ 22,400\n- 41,955\nnil\n2\n- 20,600\n+ 42,178\n+ 14,500\n- 34,240\nnil\nUnloaded end\nnil\n+ 20,098\nnil\n- 27,752\nnil\nTABLE No. III-Showing Total Strains on Parts with Bridge closed and\nfully Loaded.\nNumber of\nTop Chord.\nBottom Chord.\nVerticals.\nDiagonals.\nCounter-\nBay.\nties.\nlb.\nlb.\nlb.\nlb.\nlb.\nEnd\n+ 52,130\nnil\n+ 48,425\nnil\n- 60,810\n2\n+ 55,774\n- 50,611\n+ 10,500\nnil\n- 18,500\n8\n+ 55,100\n- 84,940\nnil\n- 26,727\nnil\n4\n+ 85,480\nnil\n+ 24,157\n- 64,732\n5\nnil\n- 47,644\n+ 48,425\n- 94,383\n6\n- 47,930\n+107,600\n+ 74,621\n-123,840\n7\n-108,000\n+180,500\n+104,688\n-155,073\n8\n- -180,779\n+268,200\n+136,540\n-190,800\n9\n--268,400\n+374,421\n+172,803\n-231,560\nCentre\n-874,421\n+374,420\n+209,625\nnil\nDigitized by Google\nTABLE No. IV.-Showing Dimensions of Principal Parts and their Effective Sectional Areas.\n390\nTop Chord.\nBottom Chord.\nVerticals.\nDiagonals.\nCounter-ties.\nNo. of Bay.\nOf what Composed.\nSectional\nArea.\nOf what Composed.\nSectional\nArea.\nSectional\nArea.\nOf what Composed.\nSectional\nArea.\nOf what Composed.\nSectional\nArea.\nsq. in.\nsq. in.\nsq. in.\nsq. in.\na. in.\nTwo 6 in.\nchannel bars\nEnd\n}\nTwo 12 in.\n12.11\nTwo bars,\nTwo bars,\nan\n}\n17.6\n10.0\n-\n2.53\n1td in. X\n6.57\n1 in. cover\nchannel bars\n1t in. X 11 in\n11th in.\nplates.\n2\ndo.\n14.11\ndo.\n17.6\n5.75\nTwo bars,\n2.82\nOne bar,\n2.64\n11th in. X 1-28 in.\n14 in X 14 in.\n3\ndo.\n14.11\ndo.\n17.6\n5.75\nTwo bars,\n3.78\nOne bar,\n1.0\n11 in. X 11 in.\n1 in, X 1 in.\n4\ndo.\n12.11\ndo.\n17.6\n5.75\nTwo bars,\n5.28\nnone\n14 in. X 14 in.\n*ONTHRENIONS TIAIO\nTwo bars,\n5\ndo.\n12.11\ndo.\n17.6\n7.5\n8.0\n\"\n2 in. X 2 in.\nThree 4 in. X\nTwo 12 in. chan-\n6\n1 in bars,\n9.75\nnel bars, to in.\n24.28\n10.0\nFour bars,\n10.56\n\"\nswelled.\ncover plates\n1f in. x 14 in.\nFour bars\nTwo 12 in. chan-\nDigitized by\n7\n111 in. x\n11.4\nnel bars, t in.\n30.96\n12.8\nFour bars,\n12.25\n\"\n111 in.\ncover plates\n11 in. x 11 in.\nThree bars,\nFour 12 in. chan-\n8\n2126 in. X\n14.35\nnel bars, T6 in.\n41.88\n17.0\nan\n$\nFour bars,\n~\n15.01\n\"\n22 in.\n111 in. X 18 in.\nGoogle\ncover plates\nFour bars,\nFour 12 in. chan-\n9\n21% in. X\n21.4\nnel bars, t in.\n54.69\n22.25\nFour bars,\n18.06\n\"\ncover plates\n21 in x 21 in.\n216 in.\nFive bars,\nCentre\nD₁₆ in. X\n29.7\ndo.\n54.69\n26.8\n{\nTwo bars,\n9.08\n\"\n21 in. x 2f in.\n2120 in.\nAQUEDUOT BRIDGES.\n891\n683. Rolling-bridges. These bridges are placed upon\nfixed rollers, so that they can be moved forward or backward,\nto interrupt or open the communication across the water-\nway. The part of the bridge that rests upon the rollers,\nwhen the passage is closed, must form a counterpoise to the\nother. The mechanism usually employed for manceuvring\nthese bridges consists of tooth-work, and may be 80 arranged\nthat it can be worked by one or more persons standing on the\nbridge. Instead of fixed rollers turning on axles, iron balls,\nresting in a grooved roller-way, may be used, a similar roller-\nway being affixed to the framework beneath.\n684. Boat-bridge. A movable bridge of this kind may\nbe made by placing a platform to form a roadway upon a\nboat, or a water-tight box of a suitable shape. This bridge\nis placed in, or withdrawn from the water-way, as circum-\nstances may require, a suitable recess or mooring being ar-\nranged for it near the water-way when it is left open.\nA bridge of this character cannot be conveniently used in\ntidal waters, except at certain stages of the water. It may\nbe employed with advantage on canals in positions where a\nfixed bridge could not be placed.\nIX.\nAQUEDUCT-BRIDGES.\n685. In aqueducts and aqueduct-bridges of masonry, for\nsupplying reservoirs for the wants of a city, or for any other\npurpose, the volume of water conveyed being, generally\nspeaking, small, the structure will present no peculiar diffi-\nculties beyond affording a water-tight channel. This may be\nmade either of masonry, or of cast-iron pipes, according to\nthe quantity of water to be delivered. If formed of masonry,\nthe sides and bottom of the channel should be laid in the\nmost careful manner with hydraulic cement, and the surface\nin contact with the water should receive a coating of the\nsame material, particularly if the stone or brick used be of a\nporous nature. This part of the structure should not be\ncommenced until the arches have been uncentred and the\nheavier parts of the structure have been carried up and have\nhad time to settle. The interior spandrel-filling, to the level\nof the masonry which forms the bottom of the water-way,\nmay either be formed of solid material, of good rubble laid\nin hydraulic cement, or of beton well settled in layers; or a\nsystem of interior walls, like those used in common bridges\nDigitized by\nGoogle\n392\nCIVIL ENGINEERING.\nfor the support of the roadway, may be used in this case for\nthe masonry of the water-way to rest on.\n686. In canal aqueduct-bridges of masonry, as the volume\nof water required for the purposes of navigation is much\ngreater than in the case of ordinary aqueducts, and as the\nstructure has to be traversed by horses, every precaution\nshould be taken to procure great solidity, and secure the\nwork from accidents.\nSegment arches of medium span will generally be found\nmost suitable for works of this character. The section of\nthe water-way is generally of a trapezoidal form, the bottom\nline being horizontal, and the two sides receiving a slight\nbatir; its dimensions are usually restricted to allow the pas-\nsage of a single boat at a time. On one side of the water-\nway a horse or tow-path is placed, and on the other a narrow\nfootpath. The water-way should be faced with a hard cut-\nstone masonry, well bonded to secure it from damage from\nthe passage of the boats. The space between the facing of\nthe water-way, termed the trunk of the aqueduct, and the\nhead-walls, is filled in with solid material, either of rubble or\nof beton.\nA parapet-wall of the ordinary form and dimensions sur-\nmounts the tow and foot paths.\nThe approach to an aqueduct-bridge from a canal is made\nby gradually increasing the width of the trunk between the\nwings, which, for this purpose, usually receives a curved\nshape, and narrowing the water-way of the canal 80 as to\nform a convenient access to the aqueduct. Great care should\nbe taken to form a perfectly water-tight junction between\nthe two works.\n687. When cast iron or timber is used for the trunk of an\naqueduct-bridge, the abutments and piers should be built of\nstone. The trunk, which, if of cast iron, is formed of plates\nwith fianches to connect them, or, if of timber, consists of\none or two thicknesses of plank supported on the outside by\na framing of scantling, may be supported by a bridge-frame\nof cast iron, or of timber, or be suspended from chains or\nwire cables.\nThe tow-path may be placed either within the water-way,\nor, as is most usually done, without. It generally consists of\na simple flooring of plank laid on cross-joists supported from\nbeneath by suitably-arranged framework.\nDigitized by\nGoogle\nROOFS.\n893\nCHAPTER VI.\nROOFS.\n688. A Roof, in common language, is the covering over a\nstructure, the chief object of which is to protect the building\nagainst the effects of snow and rain. It is composed of\nboards, shingles, slate, mastic, or other suitable materials.\nE\nc\nD\nF\nG\nFig. 207.\nThe inclined pieces AC, and BC, Fig. 207, which support\nthe roof are called rafters. When the roof is light, the roof\nboards DE are placed directly upon the rafters, but when the\nrafters are far apart, say more than four feet, small pieces a,\nb, c, and d, called purlins,* are placed across the rafters for\nthe purpose of receiving the roof proper. AB is a tie, and\nF and G represent the ends of posts. The frame ABC is\ncalled a roof truss.\n689. Roof Trusses have a great variety of forms, and\ndiffer greatly in the details of their construction. All the\ntrusses which have been discussed in the preceding pages are\nsuitable for this purpose in many cases. Some other forms\nare given in the following pages.\n690. General Data. A roof truss is required to carry\nits own weight, the weight of the purlins, the weight of the\nPurlin beams are sometimes placed under the rafters.\nDigitized by Google\n394\nCIVIL ENGINEERING.\nroof above them, the force of the wind, the weight of snow\nwhen there is any, and in some cases certain local or concen-\ntrated loads, such as floors, machinery, and the like, which\nare suspended from the roof trusses.\n691. The Weight of Snow. Freshly fallen snow weighs\nfrom five to twelve lbs. per cubic foot, although snow which\nis saturated with water weighs much more. Some say that\nsnow is equivalent to from to to 1 of its depth in water,\nwhile others say that it may be equivalent to ± its depth of\nwater.\nEuropean engineers consider that six lbs. per square foot\nis sufficient for snow, and eight lbs. for the pressure of the\nwind, making fourteen lbs. for both. Trautwine thinks that\nnot less than twenty lbs. should be allowed in the United\nStates.\n692. The Force of the Wind. According to Mr.\nSmeaton, the pressure of the wind directly against a flat sur-\nface in a hurricane may be 32 lbs. per square foot. Tred-\ngold recommends an allowance of 40 lbs. per square foot.\nA gange in Girard College broke under a strain of 42 lbs. per\nsquare foot, whilst a tornado was passing near by. During\nthe severest gale on record at Liverpool, England, there was\na pressure of 42 lbs. per square foot directly upon a flat sur-\nface. During a very violent gale in Scotland, a wind-gauge\nonce indicated 45 lbs. per square foot. Buildings which are\nmore or less protected will not be subjected to such high\npressures.\nf\nd\nd\na\na\nFig. 208-Represents a roof trues for medium spans.\na, tie-beam of trues.\nb, 3, principal rafters framed into tie-beam and the king post a and confined at thank\nfoot by an iron strap.\nd, d, struts.\ns, e, purlins supporting the common rafters 1, f.\n693. The truss of a roof, for ordinary bearings, consists\n(Fig. 208) of a horizontal beam termed the tie-beam, with\nwhich the inclined beams, termed the principal rafters, are\nconnected by suitable joints. The principal rafters may\nDigitized by Google\nROOFS.\n395\neither abut against each other at the top or ridge, or against\na king post. Inclined struts are in some cases placed be-\ntween the principal rafters and king post, with which they\nare connected by suitable joints.\nFor wider bearings the short rafters (Fig. 209) abut against\na straining beam at the top. Queen posts connect these pieces\nwith the tie-beam. A king post connects the straining beam\nwith the top of the short rafters; and struts are placed at\nsuitable points between the rafters and king and queen posts.\nFig. 209-Represents a roof truss for wide\nspans.\na, tie-beam.\nb, b, principal rafters,\nc, short rafters abutting against the strain-\ning beam d.\ne and f, king and queen posts in pairs.\ns, g, purlins supporting common rafters R.\nIn each of these combinations the weight of the roof\ncovering and the frames is supported by the points of support.\nThe principal rafters are subjected to cross and longitudinal\nstrains, arising from the weight of the roof covering and from\ntheir reciprocal action on each other. These strains are\ntransmitted to the tie-beam, causing a strain of tension upon\nit. The struts resist the cross strain upon the rafters and\nprevent them from sagging; and the king and queen posts\nprevent the tie and straining beams from sagging and give\npoints of support to the struts. The short rafters and strain-\ning beam form points of support which resist the cross strain\non the principal rafters, and support the strain on the queen\nposts.\n694. Ties and Braces for Detached Frames. When a\nseries of frames concur to one end, as, for example, the main\nbeams of a bridge, the trusses of a roof, ribs of a centre, etc.,\nthey require to be tied together and stiffened by other beams\nto prevent any displacement and warping of the frames.\nFor this purpose beams are placed in a horizontal position\nand notched upon each frame at suitable points to connect\nthe whole together; while others are placed crossing each\nother, in a diagonal direction, between each pair of frames,\nwith which they are united by suitable joints, to stiffen the\nframes and prevent them from yielding to any lateral effort.\nBoth the ties and the diagonal braces may be either of single\nbeams, or of beams in pairs, so arranged as to embrace\nbetween them the part of the frames with which they are\nconnected.\nDigitized by Google\n396\nCIVIL ENGINEERING.\n695. Iron Roof Trusses. Frames of iron for roofs have\nbeen made either entirely of wrought iron, or of a combina-\ntion of wrought and cast iron, or of these two last materials\ncombined with timber. The combinations for the trusses of\nroofs of iron are in all respects the same as in those for tim-\nber trusses. The parts of the truss subjected to a cross strain,\nor to one of compression, are arranged to give the most suit-\no\no\na\na\n01\nn\no\n©\n1.\n-\no\na\nO\nb\nc\na\nb\na\nb\na\no\nM\nm\no\ne\ne\nI\nFig. 210-Represents the half of a trues for the same building composed of wrought and\ncast iron.\na, a, feathered struts of cast-iron.\nb, b, suspension bars in pairs.\nm, 18, tie and straining bars.\na e, and f, J, cross sections of beams resting in the cast-iron sockets connected with the sus-\npension bars.\nable forms for strength, and to adapt them to the object in\nview. The parts subjected to a strain of extension, as the\ntie-beam and king and queen posts, are made either of\nwrought iron or timber, as may be found best adapted to the\nparticular end proposed.\nThe joints are in some cases arranged by inserting the ends\nDigitized by Google\nROOFS.\n397\nof the beams, or bars, in cast-iron sockets, or shoes of a suita-\nble form; in others the beams are united by joints arranged\nlike those for timber frames, the joints in all cases being\nsecured by wrought-iron bolts and keys. (Figs. 210. 211 and\n212.)\n0°\nFig. 211-Represents the half of a trues of wrought iron for the new Houses of Parliament,\nEngland. The pieces of this trues are formed of bars of a rectangular section. The joints\nare secured by cast-iron sockets, within which the ends of the bars are secured by screw\nbolts.\n696. Fig. 213 shows a very common form of the roofs of\ngas-houses.\nThis here shown is supposed to be made entirely of iron\nAt the ridge is a ventilator to allow the escape of gases.\nThe manner of joining the parts is sufficiently shown in the\nfigure.\nDigitized by Google\n398\nCIVIL ENGINEERING.\nFig. 219-Represents the are\nrangements of the parts at\nthe joint c in Fig. 210.\nA, side view of the pleces\nand joint.\na, principal rafter of the\ncross section B.\n3, common rafter of the cross\nsection C.\na cross section of purlins and\njoint for fastening the com-\nmon rafters to the purlins.\nd\nd, cast-iron socket arranged\nto confine the pieces a, 4,\na.e.\nF\nE\nB\na\nA\nd\na\nD\nc\nFig. 218.-Ordinary roof of a gas-house. A, B, is the main rafter.\na, α' a\" are vertical tie-roda.\nb, b' 6\" are braces,\nC, D, is the main tie.\nE, F, is the ventilator.\n697. Fig. 214 shows a mode of secondary trussing. A is a\nstrut for supporting the middle of the main rafter. The\nlower end of A is secured to a block which is supported by\nthe tie-rods B and D. The tie-rods C and D serve the office\nof a single tie for supporting the lower end of E. In this\nDigitized by Google\nROOFS.\n399\nway the rod D performs a double office. It may be question-\nable whether this arrangement is as good as it would be to\nhave one continuous rod pass from E to F, and another\nrod (D) to act with B.\nD\nc\nE\nFig. 214-A is a strut, the lower end of which is supported by the ties B and D. o and D\nserve the office of a continuous the for supporting the lower end of the strut R\nIt may be observed that in this Fig. the tie-rods are in-¹\nclined and much longer than the struts, which is the reverse\nof the condition in Fig. 213. If iron only is used the arrange-\nment of Fig. 214 will generally be the most economical,\nbut if wooden struts are used the plan of Fig. 213 may be\npreferable.\nFig. 215.\n698. Depot Roof Truss. Fig. 215 shows a truss which\nhas been used in many cases for supporting the roofs of depots\nand of other large buildings. The passenger depot of the\nDigitized by Google\n400\nCIVIL ENGINEERING.\nMichigan Central Railroad at Chicago was built after this\nplan. It was destroyed by the great fire in 1871. The plan\nof the arch is a Howe truss, having curved wooden chords,\nwooden braces and iron ties to connect the two chords. The\ntruss formed an arch, the thrust of which was resisted by a\nlong horizontal tie-rod.\nThe same style was adopted in the new roof over the depot\nat Troy, New York; and the Grand Central Depot in New\nYork City.\n699. A novel plan was used in making the roof over the\nrolling-mills at Milwaukee, Wis. An arch was made of\nboards so placed as to break joints and form a rib about a\nfoot wide and eighteen inches deep, and one hundred and\neighty feet span. The boards were bolted together so as to\nmake the rib continuous, and then the upper part of the arch\nwas trussed after the Howe plan. The main objects of this\nplan were cheapness and to secure the whole inclosed area\nfree from posts or other similar obstructions. But it was\nfound that the arch was too weak, especially when required\nto carry the large ventilator which was placed over it, and\nposts were afterwards added.\n700. Roofs and Domes. In some cases-especially in state\nbuildings-domes are placed upon roofs for architectural effect.\nFig. 216.\nC\nE\n4-9\n1 Yours.\nthe\nthe\n-\nA\n0\nNIL.\nSM.\n10-12\nc\n(+\n1/2m\n1 /201\nMIA.\n13-13\nA\nR\nR\na\n10-18\nFig. 217.\nFign. 216 and 217-Are two trusses, which are made in pairs, and are placed fourteen inches\napart, for supporting part of the dome (octagonal) of the State capitol at Montpelier, Vt.\na a a are the short timbers for connecting the two trusses.\nA is a timber resting upon the cross pieces a a a.\nC is a post of the dome resting upon the piece A.\nSpan, sixty-seven feet four inches.\nDigitized by Google\nROOFS.\n401\nP\nFig. 218-Boof over the large hall of the University of Michigans\nUU\nC C\n0\nDigitized by Google\n402\nCIVIL ENGINEERING.\nThe dome of the State capitol, Vermont, rests upon wooden\ntrusses (Figs. 216 and 217), having a span of sixty-seven feet\nfour inches. The trusses are supported at the ends only. They\nare placed in pairs, fourteen inches apart. The Fig. shows\ntwo pairs. They are connected by short cross beams, a a;\nupon which rest other timbers, A, for receiving the posts, C,\nof the dome. It is profitable for the student to make a careful\nstudy of the details of this structure.\nWhere the thrust is severe especial care should be taken to\nsecure a good bearing for the ends of the timbers. The lower\nends of the main rafters tend to shear the main tie at its ends,\nand to prevent this action they should enter the tie at a\nreasonable distance from its ends. The bearing pieces are of\nwhite oak, and the rest of the timber is spruce. The trusses\nare constructed differently, because the posts of the dome\nbear upon them in different places.\n701. Roof over the large hall of the University of\nMichigan. This truss and dome presents a very novel fea-\nture (Fig. 218), inasmuch as a part of the dome rests directly,\nor nearly so, upon the posts which support the roof, while the\nother part rests directly upon the trusses which support the\nroof. The span is eighty feet in the clear, and the depth of the\ntrusses is sixteen feet. The main rafters are pieces of solid\npine fourteen inches wide by sixteen inches deep. They are\nnot of equal length, the longer ones having a horizontal run\nof forty-seven feet, and the shorter ones thirty-three feet.\nThe secondary trussing is distributed according to the strains.\nThe dome is thirty feet in diameter at the base.\nThe ceiling of the large hall being attached directly to\ntrusses, it was necessary to make very strong trusses, 80 that\nthe action of the wind upon the dome, and also the effect of\nthe changes of temperature might not 80 disturb the trusses\nby causing them to deflect, as to destroy the ceiling. (For a\ncomputation of the parts, see Wood's Bridges and Roofs, pp.\n194-211.\nDigitized by Google\nROADS.\n403\nCHAPTER VII.\nROADS.\nL COMMON ROADS. II. RAILROADS.\n702. In establishing a line of internal communication of\nany character, whether it be an ordinary road, railroad, or\ncanal, the main considerations to which the attention of the\nengineer must be directed in the outset are: 1, the probable\ncharacter and amount of traffic over the line; 2, the wants of\nthe community in the neighborhood of the line; 3, the nat-\nural features of the country, between the points of arrival\nand departure, as regards their adaptation to the proposed\ncommunication.\nAs the last point alone comes exclusively within the prov-\nince of the engineer's art, and within the limits prescribed to\nthis work, attention will be confined solely to its consideration.\n703. Reconnaissance. A thorough examination and study\nof the ground by the eye, termed a reconnaissance, is an in-\ndispensable preliminary to any more accurate and minute\nsurvey by instruments, to avoid loss of time, as by this more\nrapid operation any ground unsuitable for the proposed line\nwill be as certainly detected by a person of some experience,\nas it could be by the slow process of an instrumental survey.\nBefore, however, proceeding to make a reconnaissance, a care-\nful inspection of the general maps of that portion of the\ncountry through which the communication is to pass will\nfacilitate, and may considerably abridge the labors of the en-\ngineer; as from the natural features laid down upon them,\nparticularly the direction of the water-courses, he will at once\nbe able to detect those points which will be favorable, or\notherwise, to the general direction selected for the line. This\nwill be sufficiently evident when it is considered-1, that the\nwater-courses are necessarily the lowest lines of the valleys\nthrough which they flow, and that their direction must also be\nthat of the lines of greatest declivity of their respective val-\nleys; 2, that from the position of the water-courses the posi-\ntion also of the high grounds by which they are separated\nnaturally follows, as well as the approximate position at least\nDigitized by Google\n404\nCIVIL ENGINEERING.\nof the ridges, or highest lines of the high grounds, which\nseparate their opposite slopes, and which are at the same time\nthe lines of greatest declivity common to these slopes, as the\nwater-courses are the corresponding lines of the slopes that\nform the valleys.\nKeeping these facts (which are susceptible of rigid mathe-\nmatical demonstration) in view, it will be practicable, from a\ncareful examination of an ordinary general map, if accurately\nconstructed, not only to trace, with considerable accuracy, the\ngeneral direction of the ridges from having that of the water-\ncourses, but also to detect those depressions in them which\nwill be favorable to the passage of a communication intended\nto connect two main or two secondary valleys. The follow-\ning illustrations may serve to place this subject in a clearer\naspect.\nIf, for example, it be found that on any portion of a map\nthe water-courses seem to diverge from or converge towards\none point, it will be evident that the ground in the first case\nmust be the common source or supply of the water-courses,\nand therefore the highest and in the second case that it is\nthe lowest, and forms their cominon recipient.\nIf two water-courses flow in opposite directions from a com-\nmon point, it will show that this is the point from which they\nderive their common supply, at the head of their respective\nvalleys, and that it must be fed by the slopes of high grounds\nabove this point; or, in other words, that the valleys of the\ntwo water-courses are separated by a chain of high grounds,\nwhich, at the point where it crosses them, presents a depres-\nsion in its ridge, which would be the natural position for a\ncommunication connecting the two valleys.\nIf two water-courses flow in the same direction and parallel\nto each other, it will simply indicate a general inclination of\nthe ridge between them, in the same direction as that of the\nwater-courses. The ridge, however, may present in its course\nelevations and depressions, which will be indicated by the\npoints in which the water-courses of the secondary valleys,\non each side of it, intersect each other on it and these will\nbe the lowest points at which lines of communication, through\nthe secondary valleys, connecting the main water-courses,\nwould cross the dividing ridge.\nIf two water-courses flow in the same direction, and paral-\nlel to each other, and then at a certain point assume divergent\ndirections, it will indicate that this is the lowest point of the\nridge between them.\nIf two water-courses flow in parallel but opposite directions,\nDigitized by\nGoogle\nCOMMON ROADS.\n405\ndepressions in the ridge between them will be shown by\nthe meeting of the water-courses of the secondary valleys on\nthe ridge; or by an approach towards each other, at any point,\nof the two principal water-courses.\nFurnished with the data obtained from the maps, the char-\nacter of the ground should be carefully studied both ways\nby the engineer, first from the point of departure to that of\narrival, and then returning from the latter to the former, as\nwithout this double traverse natural features of essential im-\nportance might escape the eye.\n704. Surveys. From the results of the reconnaissance,\nthe engineer will be able to direct understandingly the requi-\nsite surveys, which consist in measuring the lengths, determin-\ning the directions, and ascertaining both the longitudinal and\ncross levels of the different routes, or, as they are termed,\ntrial-lines, with sufficient accuracy to enable him to make a\ncomparative estimate both of their practicability and cost.\nAs the expense of making the requisite surveys is usually but\na small item compared with that of constructing the commu-\nnication, no labor should be spared in running every practica-\nble line, as otherwise natural features might be overlooked\nwhich might have an important influence on the cost of con-\nstruction.\n705. Map and Memoir. The results of the surveys are\naccurately embodied in a map exhibiting minutely the topo-\ngraphical features and sections of the different trial-lines,\nand in a memoir which should contain a particular descrip-\ntion of those features of the ground that cannot be shown on\na map, with all such information on other points that may\nbe regarded as favorable, or otherwise, to the proposed com-\nmunication; as, for example, the nature of the soil, that of\nthe water-courses met with, etc., etc.\n706. Location of Common Roads. In selecting among\nthe different trial-lines of the survey the one most suitable to\na common road, the engineer is less restricted, from the\nnature of the conveyance used, than in any other kind of\ncommunication. The main points to which his attention\nshould be confined are: 1, to connect the points of arrival\nand departure by the most direct, or shortest line; 2, to\navoid unnecessary ascents and descents, or, in other words, to\nreduce the ascents and descents to the smallest practicable\nlimit; 3, to adopt such suitable slopes, or gradients, for the\naxis, or centre line of the road, as the nature of the convey-\nance may demand; 4, to give the axis such a position with\nregard to the surface of the ground and the natural obstacles\nDigitized by\nGoogle\n406\nCIVIL ENGINEERING.\nto be overcome, that the cost of construction for the excava-\ntions and embankments required by the gradients, and for\nthe bridges and other accessories, shall be reduced to the\nlowest amount.\n707. Deviations from the right line drawn on the map, be-\ntween the points of arrival and departure, will be often de-\nmanded by the natural features of the ground. In passing\nthe dividing ridges of main, or secondary valleys, for ex-\nample, it will frequently be found more advantageous, both\nfor the most suitable gradients, and to diminish the amount\nof excavation and embankment, to cross the ridge at a lower\npoint than the one in which it is intersected by the right line,\ndeviating from the right line either towards the head, or\nupper part of the valley, or towards its outlet, according to\nthe advantages presented by the natural features of the\nground, both for reducing the gradients and the amount of\nexcavation and embankment.\nWhere the right line intersects either a marsh or water-\ncourse, it may be found less expensive to change the direction,\navoiding the marsh, or intersecting the water-course at a\npoint where the cost of construction of a bridge, or of the\napproaches to it, will be more favorable than the one in\nwhich it is intersected by the right line.\nChanges from the direction of the right line may also be\nfavorable for the purpose of avoiding the intersection of\nsecondary water-courses; of gaining a better soil for the\nroadway; of giving a better exposure of its surface to the\nsun and wind; or of procuring better materials for the road-\ncovering.\nBy a careful comparison of the advantages presented by\nthese different features, the engineer will be enabled to\ndecide how far the general direction of the right line may be\ndeparted from with advantage to the location. By choosing\na more sinuons course the length of the line will often not\nbe increased to any very considerable degree, while the cost\nof construction may be greatly reduced, either in obtaining\nmore favorable gradients, or in lessening the amount of ex-\ncavation and embankment.\n708. When the points of arrival and departure are upon\ndifferent levels, as is usually the case, it will seldom be prac-\nticable to connect them by a continual ascent. The most\nthat can be done will be to cross the dividing ridges at their\nlowest points, and to avoid, as far as practicable, the intersec-\ntion of considerable secondary valleys which might require\nany considerable ascent on one side and descent on the other.\nDigitized by\nGoogle\nCOMMON ROADS.\n407\n709. The gradients upon common roads will depend upon\nthe kind of material used for the road-covering, and upon the\nstate in which the road-surface is kept. The gradient in all\ncases should be less than the angle of repose, or of that in-\nclination of the axis of the road in which the ordinary\nvehicles for transportation would remain at a state of rest, or,\nif placed in motion, would descend by the action of gravity\nwith nniform velocity.\nThe gradients corresponding to the angle of repose have\nbeen ascertained by experiments made upon the various road-\ncoverings in ordinary use, by allowing a vehicle to descend\nalong a road of variable inclination until it was brought to a\nstate of rest by the retarding force of friction; also, by as-\ncertaining the amount of force, termed the force of traction,\nrequisite to put in motion a vehicle with a given load on a\nlevel road.\nThe following are the results of experiments made by Mr.\nMacneill, in England, to determine the force of traction for\none ton upon level roads :-\nNo. 1. Good pavement, the force of traction is\n33 lbs.\n\"\n2. Broken-stone surface laid on an old flint road\n65 \"\n\"\n3. Gravel road.\n147 \"\n\" 4. Broken-stone surface on a rough pavement\nbottom\n46 \"\n\" 5. Broken-stone surface on a bottom of beton\n46 \"\nFrom this it appears that the angle of repose in the first\ncase is represented by IIIO or 6'8 nearly; and that the slope\nof the road should therefore not be greater than one perpendic-\nular to sixty-eight in length; or that the height to be overcome\nmust not be greater than one sixty-eighth of the distance be-\ntween the two points measured along the road, in order that\nthe force of friction may counteract that of gravity in the\ndirection of the road.\nA similar calculation will show that the angle of repose in\nthe other cases will be as follows :\nNo. 2\n1 to\n35 nearly.\n\" 3\n1 to\n15 \"\n\" 4 and 5\n1 to\n49\n\"\nThese numbers, which give the angle of repose between 8to\nand to for the kinds of road-covering Nos. 2 and 4 in most\nordinary use, and corresponding to a road-surface in good\norder, may be somewhat increased, to from to to 8'3' for the\nordinary state of the surface of a well-kept road, without\nthere being any necessity for applying a brake to the wheels\nin descending, or going out of a trot in ascending. The\nDigitized by\nGoogle\n408\nCIVIL ENGINEERING.\nsteepest gradient that can be allowed on roads with a broken-\nstone covering is about to, as this, from experience, is found\nto be about the angle of repose upon roads of this character\nin the state in which they are usually kept. Upon a road\nwith this inclination, a horse can draw at a walk his usual\nload for a level without requiring the assistance of an extra\nhorse; and experience has farther shown that a horse at the\nusual walking pace will attain, with less apparent fatigue, the\nsummit of a gradient of to in nearly the same time that he\nwould require to reach the same point on a trot over a gra-\ndient of 3'8.\nA road on a dead level, or one with a continued and uni-\nform ascent between the points of arrival and departure, where\nthey lie upon different levels, is not the most favorable to the\ndraft of the horse. Each of these seems to fatigue him more\nthan a line of alternate ascents and descents of slight gra-\ndients; as, for example, gradients of Ito, upon which a horse\nwill draw as heavy a load with the same speed as upon a hori-\nzontal road.\nThe gradients should in all cases be reduced as far as prac-\nticable, as the extra exertion that a horse must put forth in\novercoming heavy gradients is very considerable ; they should\nas a general rule, therefore, be kept as low at least as 3'8,\nwherever the ground will admit of it. This can generally be\neffected, even in ascending steep hill-sides, by giving the axis\nof the road a zigzag direction, connecting the straight por-\ntions of the zigzags by circular arcs. The gradients of the\ncurved portions of the zigzags should be reduced, and the\nroadway also at these points be widened, for the safety of ve-\nhicles descending rapidly. The width of the roadway may\nbe increased about one-fourth, when the angle between the\nstraight portions of the zigzags is from 120° to 90° ; and the\nincrease should be nearly one-half where the angle is from\n90° to 60°.\n710. Having laid down upon the map the approximate loca-\ntion of the axis of the road, a comparison can then be made\nbetween the solid contents of the excavations and embank-\nments, which should be so adjusted that they shall balance\neach other, or, in other words, the necessary excavations shall\nfurnish sufficient earth to form the embankments. To effect\nthis, it will frequently be necessary to alter the first location,\nby shifting the position of the axis to the right or left of the\nposition first assumed, and also by changing the gradients\nwithin the prescribed limits. This is a problem of very con-\nsiderable intricacy, whose solution can only be arrived at by\nDigitized by\nGoogle\nCOMMON ROADS.\n409\nsuccessive approximations. For this purpose, the line must\nbe subdivided into several portions, in each of which the\nequalization should be attempted independently of the rest,\ninstead of trying a general equalization for the whole line at\nonce.\nIn the calculations of solid contents required in balancing\nthe excavations and embankments, the most accurate method\nconsists in subdividing the different solids into others of the\nmost simple geometrical forms, as prisms, prismoids, wedges,\nand pyramids, whose solidities are readily determined by the\nordinary rules for the mensuration of solids. As this pro-\ncess, however, is frequently long and tedious, other methods\nrequiring less time, but not so accurate, are generally pre-\nferred, as their results give an approximation sufficiently\nnear the true for most practical purposes. They consist in\ntaking a number of equidistant profiles, and calculating the\nsolid contents between each pair, either by multiplying the\nhalf sum of their areas by the distance between them, or else\nby taking the profile at the middle point between each pair,\nand multiplying its area by the same length as before. The\nlatter method is the more expeditious; it gives less than the\ntrue solid contents, but a nearer approximation than the for-\nmer, which gives more than the true solid contents, whatever\nmay be the form of the ground between each pair of cross\nprofiles.\nIn calculating the solid contents, allowance must be made\nfor the difference in bulk between the different kinds of earth\nwhen occupying their natural bed and when made into em-\nbankment. From some careful experiments on this point\nmade by Mr. Elwood Morris, a civil engineer, and published\nin the Journal of the Franklin Institute, it appears that light\nsandy earth occupies the same space both in excavation and\nembankment; clayey earth about one-tenth less in embankment\nthan in its natural bed ; gravelly earth also about one-twelfth\nless ; rock in large fragments about five-twelfths more, and\nin small fragments about six-tenths more.\n711. Another problem connected with the one in question\nis that of determining the lead, or the mean distance to which\nthe earth taken from the excavations must be carried to form\nthe embankments. From the manner in which the earth is\nusually transported from the one to the other, this distance is\nusually that between the centre of gravity of the solid of ex-\ncavation and that of its corresponding embankment. What-\never disposition may be made of the solids of excavation, it\nis important, so far as the cost of their removal is concerned,\nDigitized by Google\n410\nCIVIL ENGINEERING.\nthat the lead should be the least possible. The solution of\nthe problem under this point of view will frequently be ex-\ntremely intricate, and demand the application of all the re-\nsources of the higher analysis. One general principle,\nhowever, is to be observed in all cases, in order to obtain an\napproximate solution, which is, that in the removal of the\ndifferent portions of the solid of excavation to their corre-\nsponding positions on that of the embankment, the paths\npassed over by their respective centres of gravity shall not\ncross each other either in a horizontal or vertical direction.\nThis may in most cases be effected by intersecting the solids\nof excavation and embankment by vertical planes in the\ndirection of the removal, and by removing the partial\nsolids between the planes within the boundaries marked out\nby them.\n712. The definitive location having been settled by again\ngoing over the line, and comparing the features of the ground\nwith the results furnished by the preceding operations, gene-\nral and detailed maps of the different divisions of the defini-\ntive location are prepared, which should give, with the\nutmost accuracy, the longitudinal and cross sections of the\nnatural ground, and of the excavations and embankments,\nwith the horizontal and vertical measurements carefully writ-\nten upon them, so that the superintending engineer may have\nno difficulty in setting out the work from them on the\nground.\nIn addition to these maps, which are mainly intended to\nguide the engineer in regulating the earth-work, detailed\ndrawings of the road-covering, of the masonry and carpentry\nof the bridges, culverts, etc., accompanied by written specifi-\ncations of the manner in which the various kind of work is\nto be performed, should be prepared for the guidance both\nof the engineer and workmen.\n713. With the data furnished by the maps and drawings,\nthe engineer can proceed to set out the line on the ground.\nThe axis of the road is determined by placing stont stakes or\npickets at equal intervals apart, which are numbered to corre-\nspond with the same points on the map. The width of the\nroadway and the lines on the ground corresponding to the\nside slopes of the excavations and embankments are laid out\nin the same manner, by stakes placed along the lines of the\ncross profiles.\nBesides the numbers marked on the stakes, to indicate their\nposition on the map, other numbers, showing the depth of the\nexcavations, or the height of the embankments from the sur-\nDigitized by\nGoogle\nCOMMON ROADS.\n411\nface of the ground, accompanied by the letters Cut. Fill. to\nindicate a cutting, or a filling, as the case may be, are also\nadded to guide the workmen in their operations. The posi-\ntions of the stakes on the ground, which show the principal\npoints of the axis of the road, should, moreover, be laid down\non the map with great accuracy, by ascertaining their bear-\ning and distances from any fixed and marked objects in their\nvicinity, in order that the points may be readily found should\nthe stakes be subsequently misplaced.\n714. Earth-Work. This term is applied to whatever re-\nlates to the construction of the excavations and embankments,\nto prepare them for receiving the road-covering.\n715. In forming the excavations, the inclination of the side\nslopes demands peculiar attention. This inclination will de-\npend on the nature of the soil, and the action of the atmos-\nphere and internal moisture upon it. In common soils, as\nordinary garden earth formed of a mixture of clay and sand,\ncompact clay, and compact stony soils, although the side\nslopes would withstand very well the effects of the weather\nwith a greater inclination, it is best to give them two base to\none perpendicular, as the surface of the roadway will, by this\narrangement, be well exposed to the action of the sun and\nair, which will cause a rapid evaporation of the. moisture on\nthe surface. Pure sand and gravel may require a greater\nslope, according to circumstances. In all cases where the\ndepth of the excavation is great, the base of the slope should\nbe increased. It is not usual to use any artificial means to\nprotect the surface of the side slopes from the action of the\nweather; but it is a precaution which, in the end, will save\nmuch labor and expense in keeping the roadway in good or-\nder. The simplest means which can be used for this purpose\nconsist in covering the slopes with good sods (Fig. 219), or\nc\nFig. 219. Cross-section of a road in\nexcavation.\nB\nA, road-surface.\nB\nB, side slopes,\nC, top surface-drain.\nelse with a layer of vegetable mould about four inches thick,\ncarefully laid and sown with grass-seed. These means will\nbe amply sufficient to protect the side slopes from injury\nwhen they are not exposed to any other causes of deteriora-\ntion than the wash of the rain, and the action of frost on the\nordinary moisture retained by the soil.\nThe side slopes form usually an unbroken surface from the\nDigitized by Google\n412\nCIVIL ENGINEERING.\nfoot to the top. But in deep excavations, and particularly in\nsoils liable to slips, they are sometimes formed with horizon-\ntal offsets, termed benches, which are made a few feet wide,\nand have a ditch on the inner side to receive the surface\nwater from the portion of the side slope above them. These\nbenches catch and retain the earth that may fall from the\nportion of the side slope above.\nWhen the side slopes are not protected, it will be well, in\nlocalities where stone is plenty, to raise a small wall of dry\nstone at the foot of the slopes, to prevent the wash of the\nslopes from being carried into the roadway.\nA covering of brushwood, or a thatch of straw, may also be\nused with good effect but, from their perishable nature, they\nwill require frequent renewal and repairs.\nIn excavations through solid rock, which does not disinte-\ngrate on exposure to the atmosphere, the side slopes might be\nmade perpendicular; but as this would exclude, in a great\ndegree, the action of the sun and air, which is essential to\nkeeping the road-surface dry and in good order, it will be\nnecessary to make the side slopes with an inclination, varying\nfrom one base to one perpendicular, to one base to two per-\npendicular, or even greater, according to the locality; the in-\nclination of the slope on the south side in northern latitudes\nbeing greatest, to expose better the road-surface to the sun's\nrays.\nThe slaty rocks generally decompose rapidly on the sur-\nface, when exposed to moisture and the action of frost. The\nside slopes in rocks of this character may be cut into steps\nFig. 220.\n(Fig. 220), and then be covered by a layer of vegetable\nmould sown in grass-seed, or else the earth may be sodded in\nthe usual way.\n716. The stratified soils and rocks, in which the strata have\na dip, or inclination to the horizon, are liable to slips, or to\ngive way by one stratum becoming detached and sliding on\nanother, which is caused either from the action of frost, or\nfrom the pressure of water, which insinuates itself between\nDigitized by Google\nCOMMON ROADS.\n413\nthe strata. The worst soils of this character are those formed\nof alternate strata of clay and sand; particularly if the clay\nis of a nature to become semi-fluid when mixed with water.\nThe best preventives that can be resorted to in these cases\nare to adopt a thorough system of drainage, to prevent the\nsurface-water of the ground from running down the side\nslopes, and to cut off all springs which run towards the road-\nway from the side slopes. The surface-water may be cut off\nby means of a single ditch (Fig. 219) made on the up-hill side\nof the road, to catch the water before it reaches the slope of\nthe excavation, and convey it off to the natural water-courses\nmost convenient; as, in almost every case, it will be found\nthat the side slope on the down-hill side is, comparatively\nspeaking, but slightly affected by the surface-water.\nWhere slips occur from the action of springs, it frequently\nbecomes a very difficult task to secure the side slopes. If the\nsources can be easily reached by excavating into the side\nslopes, drains formed of layers of fascines or brush-wood may\nbe placed to give an outlet to the water, and prevent its action\nupon the side slopes. The fascines may be covered on top\nwith good sods laid with the grass side beneath, and the exca-\nvation made to place the drain be filled in with good earth well\nrammed. Drains formed of broken stone, covered in like\nmanner on top with a layer of sod to prevent the drain from\nbecoming choked with earth, may be used under the same\ncircumstances as fascine drains. Where the sources are not\nisolated, and the whole mass of the soil forming the side\nslopes appears saturated, the drainage may be effected by\nexcavating trenches a few feet wide at intervals to the depth\nof some feet into the side slopes, and filling them with broken\nstone, or else a general drain of broken stone may be made\nthroughout the whole extent of the side slope by excavating\ninto it. When this is deemed necessary, it will be well to\narrange the drain like an inclined retaining-wall, with but-\ntresses at intervals projecting into the earth farther than the\ngeneral mass of the drain. The front face of the drain\nshould, in this case, also be covered with a layer of sods with\nthe grass side beneath, and upon this a layer of good earth\nshould be compactly laid to form the face of the side slopes.\nThe drain need only be carried high enough above the foot\nof the side slope to tap all the sources; and it should be sunk\nsufficiently below the roadway-surface to give it a secure\nfooting.\nThe drainage has been effected, in some cases, by sinking\nwells or shafts at some distance behind the side slopes, from\nDigitized by Google\n414\nCIVIL ENGINEERING.\nthe top surface to the level of the bottom of the excavation,\nand leading the water which collects in them by pipes into\ndrains at the foot of the side slopes. In others a narrow\ntrench has been excavated, parallel to the axis of the road,\nfrom the top surface to a sufficient depth to tap all the sources\nwhich flow towards the side slope, and a drain formed either\nby filling the trench wholly with broken stone, or else by ar-\nranging an open conduit at the bottom to receive the water\ncollected, over which a layer of brushwood is laid, the re-\nmainder of the trench being filled with broken stone.\n717. In forming the embankments (Fig. 221), the side\nB\nFig. 221.\nslopes should be made with a less inclination than that which\nthe earth naturally assumes; for the purpose of giving them\ngreater durability, and to prevent the width of the top sur-\nface, along which the roadway is made, from diminishing by\nevery change in the side slopes, as it would were they made\nwith the natural slope. To protect the side slopes more ef-\nfectually, they should be sodded, or sown in grass-seed; and\nthe surface-water of the top should not be allowed to run\ndown them, as it would soon wash them into gullies, and de-\nstroy the embankment. In localities where stone is plenty, a\nsustaining wall of dry stone may be advantageously substi-\ntuted for the side slopes.\nTo prevent, as far as possible, the settling which takes\nplace in embankments, they should be formed with great\ncare; the earth being laid in successive layers of about four\nfeet in thickness, and each layer well settled with rammers.\nAs this method is very expensive, it is seldom resorted to ex-\ncept in works which require great care, and are of trifling ex-\ntent. For extensive works, the method usually followed, on\naccount of economy, is to embank out from one end, carrying\nforward the work on a level with the top surface. In this\ncase, as there must be a want of compactness in the mass, it\nwould be best to form the outsides of the embankment first,\nand to gradually fill in towards the centre, in order that the\nearth may arrange itself in layers with a dip from the sides\ninwards: this will in a great measure counteract any ten-\ndency to slips outward. The foot of the slopes should be se-\nDigitized by\nGoogle\nCOMMON ROADS.\n415\ncured by buttressing them either by a low stone wall, or by\nforming a slight excavation for the same purpose.\n718. When the axis of the roadway is laid out on the side\nslope of a hill, and the road-surface is formed partly by exca-\nvating and partly by embanking out, the usual and most\nsimple method is to extend out the embankment gradually\nalong the whole line of excavation. This method is insecure,\nand no pains therefore should be spared to give the embank-\nment a good footing on the natural surface upon which it\nrests, particularly at the foot of the slope. For this purpose\nthe natural surface (Fig. 222) should be cut into steps, or off-\nFig. 222,\nsets, and the foot of the slope be secured by buttressing it\nagainst a low stone wall, or a small terrace of carefully ram-\nmed earth.\nIn side-formings along a natural surface of great inclina-\ntion, the method of construction just explained will not be\nsufficiently secure; sustaining-walls must be substituted for\nthe side slopes, both of the excavations and embankments.\nThese walls may be made simply of dry stone, when the stone\ncan be procured in blocks of sufficient size to render this kind\nof construction of sufficient stability to resist the pressure of\nthe earth. But when the blocks of stone do not offer this\nsecurity, they must be laid in mortar (Fig. 223), and hydrau-\nlic mortar is the only kind which will form a safe construc-\ntion. The wall which supplies the slope of the excavation\nshould be carried up as high as the natural surface of the\nground; the one that sustains the embankment should be\nbuilt up to the surface of the roadway; and a parapet-wall\nshould be raised upon it, to secure vehicles from accidents in\ndeviating from the line of the roadway.\nA road may be constructed partly in excavation and partly\nin embankment along a rocky ledge, by blasting the rock,\nDigitized by Google\n416\nCIVIL ENGINEERING.\nwhen the inclination of the natural surface is not greater than\none perpendicular to two base ; but with a greater inclination\nthan this, the whole should be in excavation.\nD\nC\nFig. 228.-Cross section of a road in steep\nside-forming.\nA, filling.\nB, sustaining-wall of filling.\nC, breast-wall of cutting.\nD, parapet-wall of footpath.\nB\n719. There are examples of road constructions, in localities\nlike the last, supported on a framework, consisting of hori-\nzontal pieces, which are firmly fixed at one end by being let\ninto holes drilled in the rock, and are sustained at the other\nby an inclined strut underneath, which rests against the rock\nin a shoulder formed to receive it.\n720. When the excavations do not furnish sufficient earth\nfor the embankments, it is obtained from excavations termed\nside-cuttings, made at some place in the vicinity of the em-\nbankment, from which the earth can be obtained with most\neconomy.\nIf the excavations furnish more earth than is required for\nthe embankment, it is deposited in what is termed spoil-bank,\non the side of the excavation. The spoil-bank should be\nmade at some distance back from the side slope of the exca-\nvation, and on the down-hill side of the top surface; and\nsuitable drains should be arranged to carry off any water\nthat might collect near it and affect the side slope of the ex-\ncavation.\nThe forms to be given to side-cuttings and spoil-banks will\ndepend, in a great degree, upon the locality: they should, as\nfar as practicable, be such that the cost of removal of the\nearth shall be the least possible.\n721. Drainage. A system of thorough drainage, by which\nthe water that filters through the ground will be cut off from\nthe soil beneath the roadway, to a depth of at least three feet\nbelow the bottom of the road-covering, and by which that\nwhich falls upon the surface will be speedily conveyed off,\nDigitized by Google\nCOMMON ROADS.\n417\nbefore it can filter through the road-covering, is essential to\nthe good condition of a road.\nThe surface-water is conveyed off by giving the surface of\nthe roadway a slight transverse convexity, from the middle\nto the sides, where the water is received into the gutters, or\nside-channels, from which it is conveyed by underground\naqueducts, termed culverts, built of stone or brick and usually\narched at top, into the main drains that communicate with\nthe natural water-courses. This convexity is regulated by\nmaking the figure of the profile an ellipse, of which the semi-\ntransverse axis is 15 feet, and the semi-conjugate axis 9 inches;\nthus placing the middle of the roadway nine inches above the\nbottom of the side channels. This convexity, which is as great\nas should be given, will not be sufficient in a flat country to\nkeep the road-surface dry; and in such localities, if a slight\nlongitudinal slope cannot be given to the road, it should be\nraised, when practicable, three or four feet above the general\nlevel; both on account of conveying off speedily the surface-\nwater, and exposing the surface better to the action of the\nwind.\nTo drain the soil beneath the roadway in a level country,\nditches, termed open side drains (Fig. 224), are made paral-\nc\nD\nFig. 294.-Cross-section of broken-stone road-covering.\nA, road-surface.\nB, side channels.\nC, footpath.\nD, covered drains, or culverts, leading from side channels to the side drains E.\nlel to the road, and at some feet from it on each side. The\nbottom of the side drains should be at least three feet below\nthe road-covering; their size will depend on the nature of the\nsoil to be drained. In a cultivated country the side drains\nshould be on the field side of the fences.\nAs open drains would be soon filled along the parts of a\nroad in excavation, by the washings from the side-slopes,\ncovered drains, built either of brick or stone, must be substi-\ntuted for them. These drains (Fig. 225) consist simply of a\nflooring of flagging stone, or of brick, with two side walls of\n27\nDigitized by\nGoogle\n418\nCIVIL ENGINEERING.\nrubble, or brick masonry, which support a top covering of\nflat stones, or of brick, with open joints, of about half an\ninch, to give a free passage-way to the water into the drain.\nThe top is covered with a layer of straw or brushwood; and\nclean gravel, or broken stone, in small fragments, is laid over\nthis, for the purpose of allowing the water to filter freely\nthrough to the drain, without carrying with it any earth or\nsediment, which might in time accumulate and choke it.\nThe width and height of covered drains will depend on the\nmaterials of which they are built, and the quantity of water\nto which they yield a passage.\nFig. 225,-Cross-section of a covered drain.\nA, drain.\na, a, side walls.\nb, top stones.\nA\nc, bottom stones.\nd, broken stone or large gravel laid over brush.\nBesides the longitudinal covered drains in cuttings, other\ndrains are made under the roadway which, from their form,\nare termed cross mitre drains. Their plan is in shape like\nthe letter V, the angular point being at the centre of the\nroad, and pointing in the direction of its ascent. The angle\nshould be so regulated that the bottom of the drain shall not\nhave a greater slope along either of its branches, than one\nperpendicular to one hundred base, to preserve the masonry\nfrom damage by the current. The construction of mitre\ndrains is the same as the covered longitudinal drains. They\nshould be placed at intervals of about 60 yards from each\nother.\nIn some cases surface drains, termed catch-water drains,\nare made on the side slopes of cuttings. They are run up\nobliquely along the surface, and empty directly into the cross\ndrains which convey the water into the natural water-courses.\nWhen the roadway is in side-forming, cross drains of the\nordinary form of culverts are made to convey the water from\nthe side channels and the covered drains into the natural\nwater-courses. They should be of sufficient dimensions to\nconvey off a large volume of water, and to admit a man to\npass through them so that they may be readily cleared out,\nor even repaired, without breaking up the roadway over\nthem.\nThe only drains required for embankments are the ordi-\nDigitized by Google\nCOMMON ROADS.\n419\nnary side channels of the roadway, with occasional culverts to\nconvey the water from them into the natural water-courses.\nGreat care should be taken to prevent the surface-water from\nrunning down the side slopes, as they would soon be washed\ninto gullies by it.\nVery wet and marshy soils require to be thoroughly drained\nbefore the roadway can be made with safety. The best\nsystem that can be followed in such cases is to cut a wide\nand deep open main-drain on each side of the road, to con-\nvey the water to the natural water-courses. Covered cross\ndrains should be made at frequent intervals, to drain the soil\nunder the roadway. They should be sunk as low as will ad-\nmit of the water running from them into the main drains,\nby giving a slight slope to the bottom each way from the\ncentre of the road to facilitate its flow.\nIndependently of the drainage for marshy soils, they will\nrequire, when the subsoil is of a spongy, elastic nature, an\nartificial bed for the road covering. This bed may, in some\ncases, be formed by simply removing the upper stratum to a\ndepth of several feet, and supplying its place with well-\npacked gravel, or any soil of a firm character. In other cases,\nwhen the subsoil yields readily to the ordinary pressure that\nthe road-surface must bear, a bed of brushwood, from 9 to 18\ninches in thickness, must be formed to receive the soil on\nwhich the road-covering is to rest. The brushwood should be\ncarefully selected from the long straight slender shoots of the\nbranches or undergrowth, and be tied up in bundles, termed\nfascines, from 9 to 12 inches in diameter, and from 10 to 20\nfeet long. The fascines are laid in alternate layers crosswise\nand lengthwise, and the layers are either connected by pick-\nets, or else the withes, with which the fascines are bound, are\ncut to allow the brushwood to form a uniform and compact bed.\nThis method of securing a good bed for structures on a\nweak wet soil has been long practised in Holland, and ex-\nperience has fully tested its excellence.\n722. Road-coverings. The object of a road-covering being\nto diminish the resistances arising from collision and friction,\nand thereby to reduce the force of traction to the least prac-\nticable amount, it should be composed of hard and durable\nmaterials, laid on a firm foundation, and present a uniform,\neven surface.\nThe material in ordinary use for road-coverings is stone,\neither in the shape of blocks of a regular form, or of large\nround pebbles, termed a pavement, or broken into small an-\ngular masses; or in the form of gravel.\nDigitized by\nGoogle\n420\nCIVIL ENGINEERING.\n723. Pavements. The pavements in most general use in\nour country are constructed of rounded pebbles, known as\npaving stones, varying from 3 to 8 inches in diameter, which\nare set in a form, or bed of clean sand or gravel, a foot or\ntwo in thickness, which is laid upon the natural soil excavated\nto receive the form. The largest stones are placed in the\ncentre of the roadway. The stones are carefully set in the\nform, in close contact with each other, and are then firmly\nsettled by a heavy rammer until their tops are even with the\ngeneral surface of the roadway, which should be of a slightly\nconvex shape, having a slope of about to from the centre\neach way to the sides. After the stones are driven, the road-\nsurface is covered with a layer of clean sand, or fine gravel,\ntwo or three inches in thickness, which is gradually worked\nin between the stones by the combined action of the travel\nover the pavement and of the weather.\nThe defects of pebble pavements are obvious, and con-\nfirmed by experience. The form of sand or gravel, as\nusually made, is not sufficiently firm it should be made in\nseparate layers of about 4 inches, each layer being moistened\nand well settled either by ramming, or passing a heavy roller\nover it. Upon the form prepared in this way a layer of\nloose material of two or three inches in thickness may be\nplaced to receive the ends of the paving stones. From the\nform of the pebbles, the resistance to traction arising from\ncollision and friction is very great.\nPavements termed stone tramways have been tried in some\nof the cities of Europe, both for light and heavy traffic.\nThey are formed by laying two lines of long stone blocks for\nthe wheels to run on, with a pavement of pebble for the horse-\ntrack between the wheel-tracks. In crowded thoroughfares\ntramways offer but few if any advantages, as it is impracticable\nto confine the vehicles to them, and when exposed to heavy\ntraffic they wear into ruts. The stone blocks should be care-\nfully laid on a very firm bottoming, and particular attention\nis requisite to prevent ruts from forming between the blocks\nand the pebble pavement.\nStone suitable for pavements should be hard and tongh, and\nnot wear smooth under the action to which it is exposed.\nSome varieties of granite have been found in England to\nfurnish the best paving blocks. In France, a very fine-grained\ncompact gray sandstone of a bluish cast is mostly in use for\nthe same purpose, but it wears quite smooth.\nThe sand used for forms should be clean and free from peb-\nbles and gravel of a larger grain than about two-tenths of an\nDigitized by Google\nCOMMON ROADS.\n421\ninch. The form should be made by moistening the sand, and\ncompressing it in layers of about four inches in thickness,\neither by ramming, or by passing over each layer several times\na heavy iron roller. Upon the top layer about an inch of\nloose sand may be spread to receive the blocks; the joints\nbetween which, after they are placed, should be carefully\nfilled with sand.\nThe sand form, when carefully made, presents a very firm\nand stable foundation for the pavement.\nWooden pavements, formed of blocks of wood of various\nshapes, have been tried in England and several of our cities\nwithin the last few years, and notwithstanding they decay in\na few years, yet they are extensively used in many of our large\ncities. The travel upon them is so free from noise, and the\nsurface is so smooth, that, on those streets where the haulage\nof heavy articles is not excessive, many property holders prefer\nto renew a wooden pavement every eight or ten years, than be\nannoyed with the noise and the roughness of stone pavements.\nThey are especially desirable upon those streets which are oc-\ncupied by residences.\nAsphaltic pavements have undergone a like trial, and\nhave been found to fail after a few years' service. This\nmaterial is farther objectionable as a pavement in cities where\nthe pavements and sidewalks have frequently to be disturbed\nfor the purposes of repairing, or laying down sewers, water-\npipes, and other necessary conveniences for a city.\nThe best system of pavement is that which has been\npartially put in practice in some of the commercial cities of\nEngland, the idea of which seems to have been taken from the\nexcellent military roads of the Romans, vestiges of which re-\nmain at the present day in a good state.\nB\nC\nA\nFig. 226.-Paved road-covering.\nA, pavement.\nC, curb-stone.\nB, flagging of side-walk.\nIn constructing this pavement, a bed (Fig. 226) is first pre-\npared, by removing the surface of the soil to the depth of a\nfoot or more, to obtain a firm stratum; the surface of this bed\nreceives a very slight convexity, of about two inches to ten\nfeet, from the centre to the sides of the roadway. If the soil\nis of a soft clayey nature, into which small fragments of\nDigitized by Google\n422\nCIVIL ENGINEERING.\nbroken stone would be easily worked by the wheels of vehicles,\nit should be excavated a foot or two deeper to receive a form\nof sand, or of clean fine gravel. On the surface of the bed\nthus prepared, a layer of small broken stone, four inches\nthick, is laid; the dimensions of these fragments should not\nbe greater than two and a half inches in any direction; the\nroad is then opened to vehicles until this first layer becomes\nperfectly compact; care being taken to fill up any ruts with\nfresh stone, in order to obtain a uniform surface. A second\nlayer of stone, of the same thickness as the first, is then laid\non, and treated in the same manner; and finally a third layer.\nWhen the third layer has become perfectly compact, and is\nof a uniform surface, a layer of fine clean gravel, two and a\nhalf inches thick, is spread evenly over it to receive the\npaving stones. The blocks of stone are of a square shape, and\nof different sizes, according to the nature of the travelling\nover the pavement. The largest size are ten inches thick,\nnine inches broad, and twelve inches long; the smallest are\nsix inches thick, five inches broad, and ten inches long.\nEach block is carefully settled in the form, by means of a\nheavy beetle; it is then removed in order to cover the side of\nthe one against which it is to rest with hydraulic mortar;\nthis being done, the block is replaced, and properly adjusted.\nThe blocks of the different courses across the roadway should\nbreak joints. The surface of the road is convex; the con-\nvexity being determined by making the outer edgessix inches\nlower than the middle, for a width of thirty feet.\nThis system of pavement fulfils in the best manner all the\nrequisites of a good road-covering, presenting a hard even\nsurface to the action of the wheels, and reposing on a firm\nbed formed by the broken-stone bottoming. The mortar-\njoints, so long as they remain tight, will effectually prevent\nthe penetration of water beneath the pavement; but it is\nprobable, from the effect of the transit of heavily-laden\nvehicles, and from the expansion and contraction of the stone,\nwhich in our climate is found to be very considerable, that\nthe mortar would soon be crushed and washed out.\nIn France, and in many of the large cities of the continent,\nthe pavements are made with blocks of rough stone of a cubi-\ncal form measuring between eight and nine inches along the\nedge of the cube. These are laid on a form of sand of only a\nfew inches thick when the soil beneath is firm; but in bad soils\nthe thickness is increased to from six to twelve inches. The\ntransversal joints are usually continuous, and those in the\ndirection of the axis of the road break joints. In some cases\nDigitized by Google\nCOMMON ROADS.\n423\nthe blocks are so laid that the joints make an angle of 45° with\nthe axis of the roadway, one set being continuous, the other\nbreaking joints with them. By this arrangement of the\njoints, it is said that the wear upon the edges of the blocks,\nby which the upper surface soon assumes a convex shape, is\ndiminished. It has been ascertained by experience that the\nwear upon the edges of the blocks is greatest at the joints\nwhich run transversely to the axis when the blocks are laid in\nthe usual manner. From the experiments of M. Morin, to\nascertain the influence of the shape of stone blocks on the\nforce of traction, it was found that the resistance offered by a\npavement of blocks averaging from five to six inches in\nbreadth, measured in the direction of the axis of the road-\nway, and about nine inches in length, was less than in one of\ncubical blocks of the ordinary size.\nPavements in cities must be accompanied by sidewalks\nand crossing-places for foot-passengers. The sidewalks are\nmade of large flat flagging-stone, at least two inches thick,\nlaid on a form of clean gravel well rammed and settled. The\nwidth of the sidewalks will depend on the street being more\nor less frequented by a crowd. It would, in all cases, be well\nto have them at least twelve feet wide they receive a slope,\nor pitch, of one inch to ten feet, towards the pavement, to\nconvey the surface-water to the side channels. The pavement\nis separated from the sidewalk by a row of long slabs set on\ntheir edges, termed ourb-stones, which confine both the flag-\nging and paving stones. The curb-stones form the sides of\nthe side channels, and should for this purpose project six\ninches above the outside paving stones, and be sunk at least\nfour inches below their top surface; they should, moreover,\nbe flush with the upper surface of the sidewalks, to allow the\nwater to run over into the side channels, and to prevent acci-\ndents which might otherwise happen from their tripping\npersons passing in haste.\nThe crossings should be from four to six feet wide, and be\nslightly raised above the general surface of the pavement, to\nkeep them free from mud.\n724. Broken-stone Road-covering. The ordinary road-\ncovering for common roads, in use in this country and Eu-\nrope, is formed of a coating of stone broken into small frag-\nments, which is laid either upon the natural soil, or upon a\npaved bottoming of small irregular blocks of stone. In\nEngland these two systems have their respective partisans;\nthe one claiming the superiority for road-coverings of stone\nbroken into small fragments, a method brought into vogue\nDigitized by Google\n424\nCIVIL ENGINEERING.\nsome years since by Mr. McAdam, from whom these roads\nhave been termed macadamized; the other being the plan\npursued by Mr. Telford in the great national roads construct-\ned in Great Britain within about the same period.\nThe subject of road-making has within the last few years\nexcited renewed interest and discussion among engineers\nin France; the conclusion, drawn from experience, there\ngenerally adopted is, that a covering alone of stone broken\ninto small fragments is sufficient under the heaviest traffic\nand most frequented roads. Some of the French engineers\nrecommend, in very yielding clayey soils, that either a paved\nbottoming after Telford's method be resorted to, or that the\nsoil be well compressed at the surface before placing the\nroad-covering.\nThe paved bottom road-covering on Telford's plan (Fig.\n225), is formed by excavating the surface of the ground to a\nsuitable depth, and preparing the form for the pavement with\nthe precautions as for a common pavement. Blocks of stone\nof an irregular pyramidal shape are selected for the pave-\nment, which, for a roadway 30 feet in width, should be seven\ninches thick for the centre of the road, and three inches\nthick at the sides. The base of each block should not\nmeasure more than five inches, and the top not less than four\ninches.\nThe blocks are set by the hand, with great care, as closely\nin contact at their bases as practicable; and blocks of a\nsuitable size are selected to give the surface of the pavement\na slightly convex shape from the centre outwards. The\nspaces between the blocks are filled with chippings of stone\ncompactly set with a small hammer.\nA layer of broken stone, four inches thick, is laid over this\npavement, for a width of nine feet on each side of the centre\nno fragment of this layer should measure over two and a half\ninches in any direction. A layer of broken stone of smaller\ndimensions, or of clean coarse gravel, is spread over the wings\nto the same depth as the centre layer.\nThe road-covering, thus prepared, is thrown open to vehi-\ncles until the upper layer has become perfectly compact;\ncare having been taken to fill in the ruts with fresh stone,\nin order to obtain a uniform surface. A second layer, about\ntwo inches in depth, is then laid over the centre of the road-\nway ; and the wings receive also a layer of new material laid\non to a sufficient thickness to make the outside of the roadway\nnine inches lower than the centre, by giving a slight convexi-\nty to the surface from the centre outwards. A coating of\nDigitized by\nGoogle\nCOMMON ROADS.\n425\nclean coarse gravel, one inch and a half thick, termed a\nbinding, is spread over the surface, and the road-covering is\nthen ready to be thrown open to travelling.\nThe stone used for the pavement may be of an inferior\nquality, in hardness and strength, to that placed at the surface,\nas it is but little exposed to the wear and tear occasioned by\ntravelling. The surface-stone should be of the hardest kind\nthat can be procured. The gravel binding is laid over the\nsurface to facilitate the travelling, whilst the under stratum\nof stone is still loose; it is, however, hurtful, as, by working\nin between the broken stones, it prevents them from setting\nas compactly as they would otherwise do.\nIf the roadway cannot be paved the entire width, it should,\nat least, receive a pavement for the width of nine feet on\neach side of the centre. The wings, in this case, may be\nformed entirely of clean gravel, or of chippings of stone.\nFor roads which are not much travelled, like the ordinary\ncross roads of the country, the pavement will not demand so\nmuch care; but may be made of any stone at hand, broken\ninto fragments of such dimensions that no stone shall weigh\nover four pounds. The surface-coating may be formed in the\nmanner just described.\n725. In forming a road-covering of broken stone alone,\nthe bed for the covering is arranged in the same manner as\nfor the paved bottoming: a layer of the stone, four inches in\nthickness, is carefully spread over the bed, and the road is\nthrown open to vehicles, care being taken to fill the ruts, and\npreserve the surface in a uniform state until the layer has be-\ncome compact; successive layers are laid on and treated in\nthe same manner as the first, until the covering has received\na thickness of about twelve inches in the centre, with the\nordinary convexity at the surface.\n726. Gravel Roads. Where good gravel can be procured\nthe road-covering may be made of this material, which should\nbe well screened, and all pebbles found in it over two and a\nhalf inches in diameter, should be broken into fragments of\nnot greater dimensions than these. A firm level form having\nbeen prepared, a layer of gravel, four inches in thickness, is\nlaid on, and, when this has become compact from the travel,\nsuccessive layers of about three inches in thickness are laid\non and treated like the first, until the covering has received\na thickness of sixteen inches in the centre and the ordinary\nconvexity.\nThe Superintending Engineer of Central Park, of. New\nYork City, Mr. W. H. Grant, made experiments upon Telford,\nDigitized by Google\n426\nCIVIL ENGINEERING.\nMcAdam, and gravel roads in the Park, and he came to the\nconclusion that the gravel roads, as there constructed, were\nbetter for the purposes of park roads than either of the\nothers. (Journal of the Franklin Institute, 1867. Vol. 84,\np. 233.)\nThe gravel roads which were constructed by him had a\nrubble, or broken-stone foundation, over which was passed a\nvery heavy roller; and upon which was placed layers of gravel\nwhich were thoroughly rolled. In some cases screened\ngravel was used, and in others gravel directly from the bed.\nPaved foundations for receiving the gravel make the road\nmuch more durable, although the original cost is considerably\nincreased thereby. Roads of this kind, which are constantly\nused, should be frequently repaired, and the additional layers\nof gravel should be thoroughly pressed with a heavy roller.\nFor detailed information, see Journal of the Franklin Insti-\ntute, 1867. Vol. 83, pp. 100, 153, 233, 297 and 391, and Vol.\n84, pp. 233 and 311.\n727. As has been already stated, the French civil engineers\ndo not regard a paved bottoming as essential for broken-stone\nroad-coverings, except in cases of a very heavy traffic, or where\nthe substratum of the road is of a very yielding character.\nThey also give less thickness to the road-covering than the\nEnglish engineers of Telford's school deem necessary allow-\ning not more than six to eight inches to road-coverings for\nlight traffic, and about ten inches only for the heaviest traffic.\nIf the soil upon which the road-covering is to be placed is\nnot dry and firm, they compress it by rolling, which is done\nby passing over it several times an iron cylinder, about six\nfeet in diameter, and four feet in length, the weight of which\ncan be increased, by additional weights, from six thousand to\nabout twenty thousand pounds. The road material is placed\nupon the bed, when well compressed and levelled, in layers\nof about four inches, each layer being compressed by passing\nthe cylinder several times over it before a new one is laid on.\nIf the operation of rolling is performed in dry weather, the\nlayer of stone is watered, and some add a thin layer of clean\nsand, from four to eight tenths of an inch in thickness, over\neach layer before it is rolled, for the purpose of consolidating\nthe surface of the layer, by filling the voids between the\nbroken-stone fragments. After the surface has been well\nconsolidated by rolling, the road is thrown open for travel,\nand all ruts and other displacement of the stone on the sur-\nface are carefully repaired, by adding fresh material, and\nlevelling the ridges by ramming.\nDigitized by Google\nCOMMON ROADS.\n427\nGreat importance is attached by the French engineers to\nthe use of the iron cylinder for compressing the materials of\na new road, and to minute attention to daily repairs. It is\nstated that by the use of the cylinder the road is presented\nat once in a good travelling condition; the wear of the ma-\nterials is less than by the old method of gradually consoli-\ndating them by the travel; the cost of repairs during the\nfirst year is diminished ; it gives to the road-covering a more\nuniform thickness, and admits of its being thinner than in the\nusual method.\nThe iron roller is now moved by a locomotive, to which it\nis attached by a suitable gearing, that admits of reversing, so\nas to travel backward and forward over the road surface.\n728. Asphaltic Roadways and Sidewalks. In pre-\nparing roadways with an asphaltic surface, the ground or\nsubsoil is first made level crosswise, and very compact, by\nrolling it with a heavy cylinder. Upon this a bed of hy-\ndraulic concrete, consisting of one part in volume of hy-\ndraulic mortar, to two and a quarter parts in volume of\ngravel, is laid to the thickness of two and a half inches.\nThis foundation is allowed to become perfectly hard and dry\nbefore the asphalt is laid over it.\nThe asphaltic rock reduced to powder by the ordinary pro-\ncess is uniformly spread over the concrete bed, the surface of\nwhich should be thoroughly dry before receiving the mastic,\nto the depth of two to two and a half inches. This will pro-\nduce a layer of packed material varying from one and three-\nquarters to two inches in thickness.\nThe packing is done with hot irons or pestles, worked by\nhand, and applied lightly, so as to produce a uniform smooth\nsurface. After the upper bed is compressed in this manner\nto a proper thickness, a thin coat of fine dry powder, the\nsiftings of earth or of mineral coal ashes, is spread over the\nsurface to fill up inequalities, and the surface is again\nsmoothed over by a flat-iron, heated nearly to a red heat;\nand, whilst the asphalt is still hot, it is rolled with polished\niron rollers, the lighter, weighing four hundred and forty\npounds, being first applied, and then a heavier, weighing\nthree thousand pounds.\nIn recommencing work on an unfinished portion, the part\nto which the fresh material is to be joined is first thoroughly\ncleansed from dust, and hot asphalt poured over it.\nFor sidewalks the asphaltic rock is reduced to a powder,\neither by crushing it under rollers or by roasting; this is\nthen sifted through wire gauze, with meshes of one-tenth of\nDigitized by\nGoogle\n428\nCIVIL ENGINEERING.\nan inch. This powder is thoroughly incorporated with hot\nmineral tar, in the usual way, in the proportions of about\nthree hundred and thirty pounds of tar to four thousand four\nhundred pounds of powder. This mixture, termed mastic,\n,\ncan be cast into moulds of suitable size and kept for use.\nTo one hundred pounds of this mixture five or six pounds\nof mineral tar are added. A portion, about three per cent.\nof the mastic, of the mineral tar is first heated in an iron\ncylinder, and then one-third of the mastic thoroughly incor-\nporated with it by stirring with an iron rod, one per cent.\nmore of the tar is then added, and next another third of the\nmastic, and the remaining portions are stirred in in like\nmanner. When the whole is melted one-half the gravel is\nstirred in, and then the remaining half in the same way.\nIn warm climates the mixture may receive a larger dose of\ngravel.\nWhen the subsoil is compact and dry a layer of concrete\nof one inch and a half in thickness is spread over it, and\ncovered by a layer of mortar half an inch thick; and over\nthis, when thoroughly dry, a coat of one inch and six-tenths\nof the prepared mastic concrete.\nWhen the soil is not hard, it should be rammed or rolled\nto make it so before receiving the hydraulic concrete, which,\nin this case, is three inches and a half thick, the other two\ncourses being the same as before.\nThe mastic, whilst hot, is spread uniformly with wooden\ntrowels over the mortar bed; and before it has cooled fine\nsand is sifted over the surface.\nIn some cases, instead of a bed of hydraulic concrete and\nmortar to receive the mastic concrete, one of hot gravel,\nmixed up with a small dose of mineral tar, is laid, and over\nthis a layer of concrete mastic, formed of the fine siftings of\nmineral coal ashes, mixed np with heated mineral tar, is laid\nto form the top coating. This, in like manner, may receive\na sifting of fine sand. Rollers are used in this case to give\ncompactness to the bed and the upper layer.\n729. Materials and Repairs. The materials for broken-\nstone roads should be hard and durable. For the bottom\nlayer a soft stone, or a mixture of hard and soft, may be\nused, but on the surface none but the hardest stone will with-\nstand the action of the wheels. The stone should be care-\nfully broken into fragments of nearly as cubical a form as\npracticable, and be cleansed from dirt and of all very small\nfragments. The broken stone should be kept in depots at\nconvenient points along the line of the road for repairs.\nDigitized by\nGoogle\nCOMMON ROADS.\n429\nToo great attention cannot be bestowed upon keeping the\nroad-surface free from all accumulation of mud and even\nof dust. It should be constantly cleaned by scraping and\nsweeping. The repairs should be daily made by adding fresh\nmaterial upon all points where hollows or ruts commence to\nform. It is recommended by some that when fresh material\nis added, the surface on which it is spread should be broken\nwith a pick to the depth of half an inch to an inch, and the\nfresh material be well settled by ramming, a small quantity\nof clean sand being added to make the stone pack better.\nWhen not daily repaired by persons whose sole business it is\nto keep the road in good order, general repairs should be\nmade in the months of October and April, by removing all\naccumulations of mud, cleaning out the side channels and\nother drains, and adding fresh material where requisite.\nThe importance of keeping the road-surface at all times\nfree from an accumulation of mud and dust, and of preserv-\ning the surface in a uniform state of evenness, by the daily\naddition of fresh material, wherever the wear is sufficient to\ncall for it, cannot be too strongly insisted upon. Without\nthis constant supervision, the best constructed road will, in a\nshort time, be unfit for travel, and with it the weakest may at\nall times be kept in a tolerably fair state.\n730. Cross Dimensions of Roads. A road thirty feet in\nwidth is amply sufficient for the carriage-way of the most fre-\nquented thoroughfares between cities. A width of forty, or\neven sixty feet, may be given near cities, where the greater\npart of the transportation is effected by land. For cross roads\nand others of minor importance, the width may be reduced\naccording to the nature of the case. The width should be\nat least sufficient to allow two of the ordinary carriages of\nthe country to pass each other with safety. In all cases, it\nshould be borne in mind that any unnecessary width increases\nboth the first cost of construction, and the expense of annual\nrepairs.\nVery wide roads have, in some cases, been used, the centre\npart only receiving a road-covering, and the wings, termed\nsummer roads, being formed on the natural surface of the\nsubsoil. The object of this system is to relieve the road-cov-\nering from the wear and tear occasioned by the lighter kind\nof vehicles during the summer, as the wings present a more\npleasant surface for travelling in that season. But little is\ngained by this system under this point of view; and it has\nthe inconvenience of forming during the winter a large\nquantity of mud, which is very injurious to the road-covering.\nDigitized by Google\n430\nCIVIL ENGINEERING.\nThere should be at least one foot-path, from five to six feet\nwide, and not more than nine inches higher than the bottom\nof the side channels. The surface of the foot-path should\nhave a pitch of two inches, towards the side channels, to\nconvey its surface-water into them. When the natural soil is\nfirm and sandy, or gravelly, its surface will serve for the foot\npath; but in other cases the natural soil must be thrown out\nto a depth of six inches, and the excavation be filled with fine\nclean gravel.\nTo prevent the foot-path from being damaged by the cur-\nrent of water in the side channels, its slide slope, next to the\nside channel, must be protected by a facing of good sods, or\nof dry stone.\nAs it is of the first importance, in keeping the road-way in\na good travelling state, that its surface should be kept dry, it\nwill be necessary to remove from it, as far as practicable, all\nobjects that might obstruct the action of the wind and the\nsun on its surface. Fences and hedges along the road should\nnot be higher than five feet; and no trees should be suffered\nto stand on the road-side of the side-drains, for independently\nof shading the road-way, their roots would in time throw up\nthe road-covering.\n731. Plank-Roads. Plank-roads were very popular a few\nyears since. The road was carefully graded, then stringers\n-one on each side-were imbedded in the earth, and upon\nthese were laid planks, three or four inches thick, forming a\ncontinuous floor. When the planks are new and well laid\nthis makes a very agreeable road for haulage and for pleasure\nrides, but when the planks become worn and displaced it\nmakes a very disagreeable road. As a general thing they\nhave been abandoned, except in certain localities where they\nare maintained on account of peculiar circumstances. A\ngood gravel road has been found to be more profitable, and\nin the long run makes a much better road. Many plank-\nroads have been changed to McAdam or to Telford roads.\nII.\nRAILWAYS.\n732. A railway, or railroad, is a track for the wheels of\nvehicles to run on, which is formed of iron bars placed in\ntwo parallel lines and resting on firm supports.\n733. Rails. The iron ways first laid down, and termed\ntramways, were made of narrow iron plates, cast in short\nDigitized by\nGoogle\nRAILWAYS.\n431\nlengths, with an upright flanch on the exterior to confine the\nwheel within the track. The plates were found to be de-\nficient in strength, and were replaced by others to which a\nvertical rib was added under the plate. This rib was of uni-\nform breadth, and of the shape of a semi-ellipse in elevation.\nThis form of tramway, although superior in strength to the\nfirst, was still found not to work well, as the mud which ac-\ncumulated between the flanch and the surface of the plate\npresented a considerable resistance to the force of traction.\nTo obviate this defect, iron bars of a semi-elliptical shape in\nFig. 227-Represents a cross-section a, of the flah-bellied\nrail of the Liverpool and Manchester Railway, and the\nmethod in which it is secured to its chair. The rail is\nformed with a slight projection at bottom, which fits\ninto a corresponding notch in the side of the chair b.\nAn iron wedge c is inserted into a notch on the opposite\nside of the chair, and confines the rail in its place.\nelevation, which received the name of edge-rails, were sub-\nstituted for the plates of the tramway. The cross-sections of\nthese rails are of the form shown in Fig. 227, the top surface\nbeing slightly convex, and sufficiently broad to preserve the\ntire of the wheel from wearing unevenly. This change in\nthe form of the rail introduced a corresponding one in the\ntires of the wheels, which were made with a flanch on the\ninterior to confine them within the rails of the track.\nThe cast-iron edge-rail was found upon trial to be subject\nto many defects, arising from the nature of the material.\nAs it was necessary to cast the rails in short lengths of three\nor four feet, the tract presented a number of joints, which\nrendered it extremely difficult to preserve a uniform surface.\nThe rails were found to break readily, and the surface upon\nwhich the wheels ran wore unevenly. These imperfections\nfinally led to the substitution of wrought iron for cast iron.\n734. The wrought-iron rails first brought into use received\nnearly the same shape in cross-section and elevation as the\ncast-iron rail. They were formed by rolling them out in a\nrolling-mill so arranged as to give the rail its proper shape.\nThe length of the rail was usually fifteen feet, the bottom of\nFig. 228-Represents a side elevation of a portion of\na flah-bellied rail.\nit (Fig. 228) presenting an undulating outline so disposed as\nto give the rail a bearing point on supports placed three feet\napart between their centres. This form, known as the fish-\nbelly rail, was adopted as presenting the greatest strength for\nDigitized by\nGoogle\n432\nCIVIL ENGINEERING.\nthe same amount of metal. It has been found on trial to be\nliable to many inconveniences. The rails break at about\nnine inches from the supports, or one fourth of the distance\nbetween the bearing points, and from the curved form of the\nbottom of the rail they do not admit of being supported\nthroughout their length.\n735. The form of rail at present in most general use is\nknown by the name of the parallel, or straight rail, the top\nand bottom of the rail being parallel ; or as the T, or H rail,\nfrom the form of the cross-section.\nA variety of forms of cross-section are to be met with in\nthe parallel rail. The more usual form is that (Fig. 229) in\nFig. 229-Represents a cross-section a\nof a parallel rail of the form generally\nadopted in the U. States. The rail\nmay be confined to its chair b by\ntwo wooden keys c on each side,\nwhich are formed of hard compressed\nwood. At the present time two iron\nstraps are used instead of the keys c\nc, which are firmly bolted to the rails.\nThis form is called a fish-joint. In\nthis case the projection b is omitted.\nA very great variety of splices are in\nuse.\nwhich the top is shaped like the same part in the fish-belly\nrail, the bottom being widened out to give the rail a more\nstable seat on its supports. In some cases the top and bot-\ntom are made alike to admit of turning the rail. The great-\nest deviation from the usual form is in the rail of the Great\nWestern Railway in England (Fig. 230), and the Grand\nTrunk in Canada; but this form is rapidly going out of use.\nFig. 280-Represents a cross-section of the rail of the Great\nWestern Railway in England. This rail is laid on a continu-\nous support, and is fastened to it by screws on each side of\nthe rail. A piece of tarred felt was inserted between the\nbase of the rail and its support.\nThe dimensions of the cross-section of a rail should be such\nthat the deflection in the centre between any two points of\nsupport, caused by the heaviest loads upon the track, should\nnot. be so great as to cause any very appreciable increase of\nresistance to the force of traction. The greatest deflection,\nas laid down by some writers, should not exceed three-hun-\ndredths of an inch for the usual bearing of three feet between\nthe points of support. The top of the rail is usually about\ntwo and a half inches broad, and an inch in depth. This has\nbeen found to present a good bearing surface for the wheels,\nand sufficient strength to prevent the top from being crushed\nDigitized by\nGoogle\nRAILWAYS.\n433\nby the weight upon the rail. The thickness of the rib varies\nbetween half an inch to three-fourths of an inch and the\ntotal depth of the rail from three to five inches. The thick-\nness and breadth of the bottom have been varied according to\nthe strength and stability demanded by the traffic.\n736. Steel Rails. Rails made entirely of steel, or of\nwrought iron, with a thin bar of steel forming the top surface,\nor steel-top, or steel-headed rails as they are termed, from their\nsuperior strength and durability, are coming into general use\nin replacing the worn-out wrought-iron rails of old roads.\nSteel obtained from any of the usual processes, either cast,\npuddled, or Bessemer steel, may be used for the steel heads\nof rails.\nFrom the experience of Swedish engineers it appears that\nsolid Besseiner steel rails of the best charcoal pig-iron may be\nmade 10 per cent. lighter than the best English wrought-iron\nrails, a result which has been carried into practice on the\nAustrian railways.\nThe durability of iron rails appears to depend principally\nupon the perfection of the welding, the chief cause of their\nwant of durability arising from the lamination caused by im-\nperfect welding.\nFormerly wrought-iron rails were made partly by hammer-\ning and partly by rolling. At present rolling alone is used,\nand the results are said to be more satisfactory, whilst the pro-\ncess of manufacture is more simple.\nThe resistance to wear of rails, from English experience, it\nis said, may be measured by the product of the speed and of\nthe weight passing over them. The rule proposed for the\nwork that rails may be subjected to is 220,000,000 tons trans-\nported at the rate of one mile per hour. The length of\ntime that iron rails will last in any given case will be found by\nmultiplying the number of tons transported by the rate of\nspeed per hour and dividing by 220.\n737. Supports. The rails are laid upon supports of tim-\nber or stone. The supports should present a firm, unyield-\ning bed to the rails, so as to prevent all displacement, either\nin a lateral or a vertical direction, from the pressure thrown\nupon them.\nConsiderable diversity is to be met with in the practice of\nengineers on this point. On the earlier roads, heavy stone\nblocks were mostly used for supports, but these were found to\nrequire great precautions to render them firm, and they were,\nmoreover, liable to split from the means taken to confine the\nrails to them. Timber is generally preferred to stone. It\n28\nDigitized by Google\n434\nCIVIL ENGINEERING.\naffords a more agreeable road for travel, and gives a better\nlateral support to the rails than store blocks, and the wear\nupon the locomotive and other machinery is less severe.\nThe usual method of placing timbersupports is transversely\nto the track, each support, termed a sleeper, or cross-tie,\nbeing formed of a piece of timber six or eight inches square.\nThe ordinary distance between the centre lines of the sup-\nports is three feet for rails of the usual dimensions. With a\ngreater bearing, rails of the ordinary dimensions do not pre-\nsent sufficient stiffness. The sleepers, when formed of round\ntimber, should be squared on the upper and lower surface.\nOn some of the recent railways in England, sleepers present-\ning in cross section a right-angled triangle have been used,\nthe right angle being at the bottom. They are represented to\nbe more convenient in setting, and to offer a more stable sup-\nport than those of the usual form. The sleepers are placed\neither upon the ballasting of the roadway, or upon longitudi-\nnal beams laid beneath them along the line of the rails. The\nlatter is indispensable upon new embankments to prevent the\nends of the sleepers from settling unequally. Thick plank,\nabout eight inches broad and three or four inches thick, is\nusually employed for the longitudinal supports of the sleepers.\nOn some of the more recent railways in England, the rails\nhave been laid upon longitudinal beams, presenting a con-\ntinuous support to the rail, the beams resting upon cross-ties.\n738. Ballast. A covering of broken stone, of clean coarse\ngravel, or of any other material that will allow the water to\ndrain off freely, is laid upon the natural surface of the excava-\ntions and embankments, to form a firm foundation for the\nsupports. This has received the appellation of the ballast.\nIts thickness is from nine to eighteen inches. Open or broken-\nstone drains should be placed beneath the ballasting to convey\noff the surface water. The parts of the ballasting upon which\nthe supports rest should be well rammed, or rolled; and it\nshould be well packed beneath and around the supports.\nAfter the rails are laid, another layer of broken stone or\ngravel should be added, the surface of which should be\nslightly convex and about three inches below the top of the\nrails.\n739. Temporary Railways of Wood and Iron. On the\nfirst introduction of railways into the United States, the tracks\nwere formed of flat iron bars laid upon longitudinal beams.\nThe iron bars were about two and a half inches in breadth,\nand from one-half to three-fourths of all inch in thickness, the\ntop surface being slightly convex. They were placed on the\nDigitized by\nGoogle\nRAILWAYS.\n435\nlongitudinal beams, a little back from the inner edge, the\nside of the beam near the top being bevelled off, and were\nfastened to the beam by screws or spikes, which passed\nthrough elliptical holes with a countersink to receive the\nheads of the spikes; the holes receiving this shape to allow\nof the contraction and expansion of the bar, without displac-\ning the fastenings. The longitudinal beams were supported\nby cross sleepers, with which they were connected by wedges\nthat confined the beams in notches cut into the sleepers to re-\nceive them. The longitudinal beams were usually about six\ninches in breadth, and nine inches in depth, and in as long\nlengths as they could be procured. The joints between the\nbars were either square or oblique, and a piece of iron or zinc\nwas inserted into the beams at the joint, to prevent the end\nof the rail from being crushed into the wood by the wheels.\nIn some instances the bars were fastened to long stone\nblocks, but this method was soon abandoned, as the stone was\nrapidly destroyed by the action of the wheels besides which,\nthe rigid nature of the stone rendered the travelling upon it\nexcessively disagreeable.\nThis system of railway, whose chief recommendation is\neconomy in the first cost, has gradually given place to the\nsolid rail. Besides the want of durability of the structure, it\ndoes not possess sufficient strength for a heavy traffic.\n740. Gauge. The distance between the two lines of rails\nof a track, termed the gauge, which has been adopted for the\ngreat majority of the railways in England, and also with us,\nis 4 feet 81 inches. This gauge appears to have been the re-\nsult of chance, and it has been followed in the great majority\nof cases up to the present time, owing to the inconvenience\nthat would arise from the adoption of a different gauge upon\nnew lines. The greatest deviation yet made from the estab-\nlished gauge is in that of the Great Western Railway, in\nwhich the gauge is seven feet. Engineers are generally\nagreed that with a wider gauge the wheels of railway cars\ncould be made of greater diameter than they now receive,\nand be placed outside of the cars instead of under them as at\npresent; the centre of gravity of the load might be placed\nlower, and more steadiness of motion and greater security at\nhigh velocities be attained. All roads having a gauge above\n4 feet 81 inches are inclined rather to reduce them to that\ngauge or use a third rail SO as to run the cars of that gauge\nover their own.\nWithin the last four or five years the subject of roads of\nvery narrow gauge has been much discussed. The advan-\nDigitized by Google\n436\nCIVIL ENGINEERING.\ntages principally claimed for roads of this kind are: 1st,\ngreat reduction in first cost; 2d, allowing steeper grades and\ncurves of smaller radius; 3d, less wear and tear on the road\non account of the rolling stock being much lighter; 4th, the\nratio of live to dead weight is much less. Some lines have\nbeen made with a 2}-foot gauge, but the advocates of narrow\ngauge` generally recommend a 3-foot gauge. The latter is\nthe gauge of the Denver and Texas narrow-gauge road.\nIn a double track the distance between the two tracks is\ngenerally the same as the gauge; and the distance between\nthe outside rail of a track, and the sides of the excavation,\nor embankment, is seldom made greater than six feet, as this\nis deemed sufficient to prevent the cars from going over an\nembankment were they to run off the rails.\n741. On all straight portions of a track, the supports should\nbe on a level transversely, and parallel to the plane of the\ntrack longitudinally. The top surface of the rail should in-\ncline inward, to conform to the conical form of the wheels\nthis is now usually effected by giving the chair the requisite\npitch, or by forming the top surface with the requisite bevel\nfor this purpose.\n742. Curves. In the curved portions of a track the cen-\ntrifugal force tends to force the carriage towards the outside\nrail of the curve, and by elevating the outer rail the force of\ngravity tends to draw it towards the inside rail. From the\nabove conditions of equilibrium the elevation which the ex-\nterior rail should receive above the interior can be readily\ncalculated. The method adopted is to give the exterior rail\nan elevation sufficient to prevent the flanch of the wheel from\nbeing driven against the side of the rail when the car is mov-\ning at the highest supposed velocity or, in other words, to\ngive the inclined plane across the track, on which the wheels\nrest, an inclination such that the tendency of the wheels to\nslide towards the interior rail shall alone counteract the cen-\ntrifugal force.\n743. Sidings, etc. On single lines of railways short por-\ntions of a track, termed sidings, are placed at convenient in-\ntervals along the main track, to enable cars going in opposite\ndirections to cross each other, one train passing into the siding\nand stopping while the other proceeds on the. main track.\nOn double lines arrangements, termed crossings, are made to\nenable trains to pass from one track into the other, as circum-\nstances may require. The position of sidings and their\nlength will depend entirely on local circumstances, as the\nlength of the trains, the number daily, etc.\nDigitized by Google\nRAILWAYS.\n437\nThe manner generally adopted, of connecting the main\ntrack with a siding, or a crossing, is very simple. It consists\n(Fig. 231) in having two short lengths of the opposite rails\nFig. 281 Represents\nthe aliding switches,\nc\n10\nc\nor rails, for connect-\ning a siding with the\na\nmain track.\na, a, rails connected\nc\nby an iron rod b, by\ne\nc\nwhich they can be\nturned around the\nb\na\nd\njoints o, o.\na c, rails of main\ntrack.\na, d, rails of siding.\nof the main track, where the siding or crossing joins it,\nmovable around one of their ends, so that the other can be\ndisplaced from the line of the main track, and be, joined\nwith that of the siding, or crossing, on the passage of a car\nout of the main track. These movable portions of rails are\nconnected and kept parallel by a long cross-bolt, to the end\nM\nd\nd\n0\n0\no\nc\nc\na\nc\n0\nO\nO\na\no\nO\no\na\nO\n0\nd\nO\nO\no\nO\no\nd\no\nC\na a a\nN\nc\no\nFig. 2-Represents a plain M, and section N, of a fixed crossing plate. The plate A is of\ncast-iron, with vertical ribs c, c, on the bottom, to give it the requisite strength. Wrought-\niron bars a, a, placed in the lines of the two intersecting rails d, d, are firmly screwed to\nthe plate; a sufficient space being left between them and the rails for the flanch of the\nwheel to pass.\nof which a vertical lever is attached to draw them forward, or\nshove them back.\nAt the point where the rails of the two tracks intersect, a\ncast-iron plate, termed a crossing-plate (Fig. 232), is placed to.\nconnect the rails. The surface of the plate is arranged either\nwith grooves in the lines of the rails to admit the flanch of\nthe wheel in passing, the tire running upon the surface of the\nplate; or wrought-iron bars are affixed to the surface of the\nplate for the same purpose.\nThe angle between the rails of the main tracks and those\nof a siding or crossing, termed the angle of deflection, should\nnot be greater than 2° or 3°. The connecting rails between\nDigitized by Google\n438\nCIVIL ENGINEERING.\nthe straight portions of the tracks should be of the shape of\nan S curve, in order that the passage may be gradually\neffected. At the present time switch rails and frogs of pecu-\nliar construction are in use, which are so made and arranged\nas to leave the main track unbroken, 80 that if the switch is\nwrongly placed the train on the main track will not run off.\nThere are many devices for securing this result.\n744. Turn-plates. Where one track intersects another\nunder a considerable angle, it will be necessary to substitute\nfor the ordinary method of connecting them, what is termed\na turn-plate, or turn-table. This consists of a strong circular\nplatform of wood or cast iron, movable around its centre by\nmeans of conical rollers beneath it running upon iron roller-\nways. Two rails are laid upon the platform to receive the\ncar, which is transferred from one track to the other by turn-\ning the platform sufficiently to place the rails upon it in the\nsame line as those of the track to be passed into.\n745. Street crossings. When a track intersects a road, or\nstreet, upon the same level with it, the rail must be guarded\nby cast-iron plates laid on each side of it, sufficient space be-\ning left between them and the rail for the play of the flanch.\nThe top of the plates should be on a level with the top of the\nrail. Wherever it is practicable a drain should be placed be-\nneath, to receive the mud and dust which, accumulating be-\ntween the plates and rail, might interfere with the passing of\nthe cars along the rails.\n746. Gradients. From various experiments upon the\nfriction of cars upon railways, it appears that the angle of\nrepose is about 20, but that in descending gradients much\nsteeper, the velocity due to the accelerating force of gravity\nsoon attains its greatest limit and remains constant, from the\nresistance caused by the air.\nThe limit of the velocity thus attained upon gradients of\nany degree, whether the train descends by the action of grav-\nity alone, or by the combined action of the motive-power of\nthe engine and gravity, can be readily determined for any\ngiven load. From calculation and experiment it appears that\nheavy trains may descend gradients of 1¹₀, without attaining\na greater velocity than about 40 or 50 miles an hour, by al-\nlowing them to run freely without applying the brake to\ncheck the speed. By the application of the brake, the velo-\ncity may be kept within any limit of safety upon much steeper\ngradients. The only question, then, in comparing the ad-\nvantages of different gradients, is one of the comparative cost\nbetween the loss of power and speed, on the one hand, for\nDigitized by Google\nRAILWAYS.\n439\nascending trains on steep gradients, and that of the heavy ex-\ncavations, tunnels, and embankments on the other, which\nmay be required by lighter gradients.\nIn distributing the gradients along a line, engineers are\ngenerally agreed that it is more advantageous to have steep\ngradients upon short portions of the line, than to overcome\nthe same difference of level by gradients less steep upon\nlonger developments.\n747. In steep gradients, where locomotive power cannot be\nemployed, stationary power is used, the trains being dragged\nup, or lowered, by ropes connected with a suitable mechan-\nism, worked by stationary power placed at the top of the\nplane. The inclined planes, with stationary powers, gener-\nally receive a uniform slope throughout. The portion of the\ntrack at the top and bottom of the plane should be level for\na sufficient distance back, to receive the ascending or descend-\ning trains. The axes of the level portion should, when prac-\nticable, be in the same vertical plane as that of the axis of the\ninclined plane.\nSmall rollers, or sheeves, are placed at suitable distances\nalong the axis of the inclined plane, upon which the rope\nrests.\nWithin a few years back flexible bands of rolled hoop-iron\nhave been substituted for ropes on some of the inclined\nplanes of the United States, and have been found to work\nwell, presenting more durability and being less expensive\nthan ropes.\nOn very steep gradients the expedient of a third rail\nin the centre of the track, and raised rather above the plane\nof the other two rails, has been used. Two horizontal wheels\nunderneath the locomotive run on this rail, and may be\ntightened to any desirable degree of compression on it. In\nthis way a gradient of 440 feet per mile is used over Mont\nCenis. Without the intermediate rail grades as steep as 280,\nand in one case 304 feet per mile, have been ascended by\nmeans of the adhesive power of the locomotive only. But\nsuch grades will never be sought; on the other hand,\nthey will be avoided when possible. Grades of 50 and 60\nfeet to the mile are very common. The maximum grade\nallowable by law on the Central Pacific Railroad is the\nsame as that of the Baltimore and Ohio Railroad, viz., 116\nfeet per mile.\n748. Tunnels. The choice between deep cutting and tun-\nnelling, will depend upon the relative cost of the two, and the\nnature of the ground. When the cost of the two methods\nDigitized by Google\n440\nCIVIL ENGINEERING.\nwould be about equal, and the slopes of the deep cut are not\nliable to slips, it is usually more advantageous to resort to\ndeep cutting than to tunnelling. So much, however, will de-\npend upon local circumstances, that the comparative advan-\ntages of the two methods can only be decided upon under-\nstandingly when these are known.\n749. The operations in Tunnelling will depend upon the\nnature of the soil. The work is commenced by setting out, in\nthe first place, with great accuracy upon the surface of the\nground, the profile line contained in the vertical plane of the\naxis of the tunnel. At suitable intervals along this line\nvertical pits, termed working shafts, are sunk to a level with\nthe top, or crown of the tunnel. The shafts and excavations,\nwhich form the entrances to the tunnel, are connected, when\nthe soil will admit of it, by a small excavation termed a\nheading, or drift, usually five or six feet in width, and seven\nor eight feet in height, which is made along the crown of\nthe tunnel. After the drift is completed, the excavation for\nthe tunnel is gradually enlarged; the excavated earth is\nraised through the working shafts, and at the same time\ncarried out at the ends. The dimensions and form of the cross\nsection of the excavation will depend upon the nature of\nthe soil and the object of the tunnel as a communication.\nIn solid rock the sides of the excavation are usually vertical;\nthe top receives an arched form ; and the bottom is horizontal.\nIn soils which require to be sustained by an arch, the excava-\ntion should conform as nearly as practicable to the form of\ncross section of the arch.\nIn tunnels through unstratified rocks, the sides and roof\nmay be safely left unsupported; but in stratified rocks there\nis danger of blocks becoming detached and falling; wherever\nthis is to be apprehended, the top of the tunnel should be\nsupported by an arch.\nTunnelling in loose soils is one of the most hazardous\noperations of the miner's art, requiring the greatest precau-\ntions in supporting the sides of the excavations by strong\nrough framework, covered by a sheathing of boards, to secure\nthe workmen from danger. When in such cases the drift\ncannot be extended throughout the line of the tunnel, the\nexcavation is advanced only a few feet in each direction\nfrom the bottom of the working shafts, and is gradually\nwidened and depended to the proper form and dimensions to\nreceive the masonry of the tunnel, which is immediately\ncommenced below each working shaft, and is carried forward\nin both directions towards the two ends of the tunnel.\nDigitized by\nGoogle\nRAILWAYS.\n441\n750. Masonry of Tunnels. The cross section of the arch\nof a tunnel (Fig. 233) is usually an oval segment, formed of\nFig. 288-Represents the general form of\nthe cross section c of a brick arch for\ntunnels.\na, a, askew-back stone between the sides\nof the arch and the bottom inverted\narch.\narcs of circles for the sides and top, resting on an inverted\narch at bottom. The tunnels on some of the recent railways\nin England are from 24 to 30 feet wide, and of the same\nheight from the level of the rails to the crown of the arch.\nThe usual thickness of the arch is eighteen inches. Brick\nlaid in hydraulic cement is generally used for the masonry,\nan askew-back course of stone being placed at the junction of\nthe sides and the inverted arch. The masonry is constructed\nin short lengths of about twenty feet, depending, however,\nupon the precautions necessary to secure the sides of the ex-\ncavation. As the sides of the arch are carried up, the frame-\nwork supporting the earth behind is gradually removed, and\nthe space between the back of the masonry and the sides of\nthe excavation is filled in with earth well rammed. This\noperation should be carefully attended to throughout the\nwhole of the backing of the arch, so that the masonry may\nnot be exposed to the effects of any sudden yielding of the\nearth around it.\n751. The earth at the ends of the tunnel is supported by a\nretaining wall, usually faced with stone. These walls, termed\nthe fronts of the tunnel, are generally finished with the\nusual architectural designs for gateways. To secure the ends\nof the arch from the pressure of the earth above them, cast-\niron plates of the same shape and depth as the top of the\narch, are inserted within the masonry, a short distance from\nDigitized by Google\n442\nCIVIL ENGINEERING.\nthe ends, and are secured by wrought-iron rods firmly\nanchored to the masonry at some distance from each end.\n752. The working shafts. which are generally made cylin-\ndrical and faced with brick, rest upon strong curbs of cast\niron, inserted into the masonry of the arch. The diameter of\nthe shaft within is ordinarily nine feet.\n753. The ordinary difficulties of tunnelling are greatly in-\ncreased by the presence of water in the soil through which\nthe work is driven. Pumps, or other suitable machinery for\nraising water, placed in the working shafts, will in some\ncases be requisite to keep them and the drift free from water\nuntil an outlet can be obtained for it at the ends, by a drain\nalong the bottom of the drift. Sometimes, when the water is\nfound to gain upon the pumps at some distance above the\nlevel of the crown of the tunnel, an outlet may be obtained\nfor it by driving above the tunnel a drift-way between the\nshafts, giving it a suitable slope from the centre to the two\nextremities to convey the water off rapidly.\nIn tunnels for railways, a drain should be laid under the\nbalasting along the axis, upon the inverted arch of the bottom.\nTunnelling in rock is greatly facilitated at the present\nday by power-drilling-machines, which are driven by com-\npressed air. By this means they are able to advance three\ntimes as fast as by hand labor. The compressed air greatly\nfacilitates ventilation. The Mont Cenis tunnel (nearly 7 miles\nlong) and the Hoosac tunnel (about 4 miles long) have been\ndriven in this way, and the St. Godard tunnel (nearly 13 miles\nlong) is now in process of construction on the same plan.\n754. The following extracts are made from a series of\npapers, published in the London Engineering, from Oct. 7,\n1870, to December 30, 1870, giving a translation of a work\nby Baron von Weber, Director of the State Railways of Sax-\nony, with running comments by the translator, detailing the\nexperiments made by the author, and giving his deductions\nfrom them, on the Stability of the Permanent Way.\nBaron von Weber desired, in the first place, to ascertain\nwhat was the minimum thickness which would be given to\nthe web of a rail, in order that the latter might still possess\na greater power of resistance to lateral forces than the fasten-\nings by which it was secured to the sleepers.\n755. Resistance of Rail to Lateral Forces. From the\nexperiments the result was deduced, that the least thickness\never given to the webs of rails in practice is more than suf-\nficient, and that if it were possible to roll webs 1 in. thick,\nsuch webs would be amply strong, if it were not that there\nDigitized by\nGoogle\nRAILWAYS.\n443\nwould be a chance of their being torn at the points where\nthey are traversed by the fish-plate bolts. Baron von Weber\nconcludes that webs 1 in. or 1/2 in. thick are amply strong\nenough for rails of any ordinary height, and that in fact the\nwebs should be made as thin as the process of rolling, and\nas the provision of sufficient bearing for the fish-plate bolts\nwill permit.\n756. Stability of the Permanent Way. The stability of\na permanent way structure in a longitudinal direction, is con-\nsidered by Baron von Weber as depending upon the bed-\nding of the sleepers in the ballast, the friction of the rails up-\non the sleepers, the strength of the spikes or other fastenings,\nand, lastly, upon the strength of the connections between the\nends of the rails. These connections have, in the first place,\nto keep the heads of the rails in their proper position with re-\ngard to each other; next, to give to the joint a certain amount\nof rigidity and finally, to insure that the horizontal or verti-\ncal deflections of the two rails connected take place together.\nOf the many forms of connections which have from time to\ntime been proposed for rails, but two practically fulfil the con-\nditions just mentioned, these two being the joint chair and\nthe fish-joint, in their various modifications and forms.\nWe now come to the researches made by Baron von Weber\nto determine the power of permanent way structures to resist\nforces tending to displace the entire system. Baron von\nWeber states that as the speed of trains was increased on Ger-\nman railways, there was noticed a peculiar and dangerous\ndisplacement of the permanent way, this displacement taking\nplace chiefly where trains pass from straight to curved por-\ntions of the line, or from curved portions to level and straight\nlengths, over which they passed at an increased speed. It was\nalso observed that the displacements at the first-mentioned\npoints-displacements which consisted in the shifting of the\nline towards the convex side of the curves-were caused prin-\ncipally by engines having long wheel bases and a compara-\ntively light load on the leading wheels; while the displace-\nment of the straight portions of the lines was due mainly to\nthe action of powerful engines with short wheel bases and\nconsiderable overhang on each end. In this latter case the\nhorizontal oscillations which produced the displacements were\nalmost always found to arise from the effect of vertical im-\npact due to a loose joint or some local settlement in the line,\nthe engine being thus not merely caused to lurch heavily side-\nways, but being also made to oscillate in a vertical plane, thus\nalternately relieving and increasing the loads on the leading\nDigitized by Google\n444\nCIVIL ENGINEERING.\nand trailing wheels. Under these circumstances, when the\nflange of the leading wheel struck the rail laterally at the\nsame time that the load on the latter was decreased by the\nmomentary relief of the leading wheel from a portion of the\nweight it ought to carry, there was a greater displacement\nthan there otherwise would have been owing to the dimin-\nished friction between the permanent way structure and its\nfoundation. Both the classes of displacements to which we\nhave referred were found to be less in permanent way struc-\ntures possessing considerable vertical rigidity than in those\nof a more flexible character.\n757. Experiments on the Power of Permanent Way-\nstructures to resist Horizontal Displacements of the\nentire System. These experiments were made to obtain\nanswers to the five following questions:-\na. What is the resistance offered by a well-bedded sleeper\nof average size against lateral displacement in the ballast\nb. What is the resistance of the whole structure against\ndisplacement at one point, and what is the influence of the\nballast and bedding, on and in which the structure rests, upon\nthis resistance?\nc. How far does the filling against the ends of the sleepers\nincrease this resistance?\nd. To what extent is the resistance to lateral displacement\nincreased by the load on the structure?\ne. How far does the application of piles or stones, etc.,\netc., increase this resistance?\nThe deductions to be made from the experiments referring\nto questions a and b, Baron von Weber considers to be\nas follows: 1st. The resistance of unloaded well-bedded per-\nmanent way-structures is comparatively small, a lateral\npressure of from 30 to 50 centners being sufficient to break\nthe connection between the sleeper and the ground. This\npressure is less than that which would be exerted by the\ncentrifugal force due to the passage of a 25-ton locomo-\ntive through a curve of 1,000 feet radius, at a speed of 30\nmiles per hour, supposing that this centrifugal force was not\ncounteracted by superelevation of the exterior rail. 2d. The\nnature of the ballast in which the sleepers of unloaded per-\nmanent way-structures are bedded has no important influence\non the resistance to lateral displacement. 3d. The pressure\nrequisite for producing the horizontal displacement of an un-\nloaded structure increases until this displacement has reached\na certain amount, generally between 12 and 18 millimetres\n(from 0.472 in. to 0.708 in.), when the further displacement\nDigitized by\nGoogle\nRAILWAYS.\n445\nup to 50 to 75 millimetres (2 in. to 3 in.) is produced without\nany considerable augmentation in the pressure, until finally\na considerable tension is set up in the different parts of the\nstructure.\nBaron von Weber's conclusions from the experiments re-,\nferring to question c are as follows: 1st. That the filling\nof ballast against the ends of the sleepers, up to the top\nsurface of the latter, has an insignificant influence upon\nthe resisting power of the structure to lateral displacement,\nparticularly if the structure is unloaded, and if a one-sided\ntilting is possible.' 2d. That if the ballast is not filled against\nthe ends of the sleepers, the elasticity of the rails will bring\nback the structure into its original position, on the removal\nof the pressure, even after considerable displacement, as in\nthis case small portions of ballast cannot fall between the\nend of the shifted sleeper and the undisturbed end filling,\nas is the case when the practice of filling up against the ends\nis followed.\nWe now come to the experiments made by Baron von\nWeber to obtain an answer to question d. It was, of course,\nrequisite, in order that a proper comparison might be insti-\ntuted, that these experiments should be conducted under cir-\ncumstances as nearly as possible identical with those which\nexisted when the resistance of displacement of the unloaded\nstructure was investigated; and in selecting portions of per-\nmanent way for the last-mentioned experiments, therefore,\nsuch lengths were chosen as would afford space for the experi-\nments with the loaded structure, without introducing any\nvariations in bedding, firmness of the ballast, etc., etc.\nThe results of seven sets of trials show that the resistance\nof the structure to lateral displacement was increased almost\ntenfold by the load of twenty-seven tons; and that lateral\npressures which produced in the unloaded structure displace-\nments entirely inadmissible in practice, did not affect the\nloaded structure in any perceptible degree. The portion of\nthe unloaded structure shifted by the press in the above ex-\nperiments weighed almost exactly 21 tons, while the total mass\nmoved, including the filling against the ends of the sleepers,\nweighed 3 tons; and taking this into consideration, it appeared\nas if the resistance to displacement varied directly-as indeed\nit might have been supposed it would do-as the weight\nresting on the ground.\nBaron von Weber's conclusion with regard to this subject\nis, that the force required to produce the lateral displace-\nment of a permanent way-structure is directly proportionate\nDigitized by Google\n446\nCIVIL ENGINEERING.\nto the weight by which the structure is pressed upon the\nground.\n758. Experiments relating to Question e. In con-\nsidering the influence of piles or stakes driven into the ballast\nagainst the ends of the sleepers to prevent lateral shifting of\nthe latter, Baron von Weber remarks that the resisting power\nof such piles has been very differently \" estimated by rail-\nway engineers, but that as far as he is aware the advantages\nor disadvantages attending the use of such piles has never\nbeen ascertained by experiment. Many elements evidently\nexercise an influence on the lateral displacement of piles\ndriven vertically into the ground, and experiments made\nwith a view of ascertaining the lateral resistance of such\npiles can only show in a very general manner how far the ad-\nvantages derived from their use will counterbalance the\nextra expense they involve. The results obtained by experi-\nment are moreover liable to great variations. Thus, a pile\ndriven deeply into solid, loamy soil, offers in dry weather\ngreat resistance to lateral displacement, whereas after a\nshower of rain-not strong enough to soak into the ground,\nbut capable of penetrating the narrow crack formed between\nthe pile and surrounding earth by the vibrations caused by\nthe traffic-the upper end of the pile can be moved, by the\napplication of a comparatively small force, to an extent suffi-\ncient to render it useless as a means of lateral support for the\nsleeper. Thus Baron von Weber has found that piles which,\nin dry weather, require a force of from 15 to 20 cwt. to shift\ntheir heads laterally through a distance of one inch, could be\nmoved to the same extent by the force of about 5 cwt. after\na shower of rain lasting barely one hour.\nThe elements by which the lateral stability of such piles as\nthose we are now considering is affected are: the diameter,\nlength, and section of the pile, the description of wood of\nwhich it is made, and the nature of ground into which it is\ndriven. To determine the influence of all these elements in\ntheir various combinations a very extensive series of experi-\nments would have been required, and Baron von Weber\ntherefore confined his researches to ascertaining the maxi-\nmum resistance of such stakes as are used on the Saxon\nstate railways, availing himself, however, of all available\nopportunities of noticing the resistance under unfavorable\ncircumstances.\nThe principle was laid down that a displacement of the top\nof a pile to the extent of 10 millimetres (=0.39 in.) should\nbe considered as inconsistent with its further usefulness.\nDigitized by\nGoogle\nRAILWAYS.\n447\nIn this series of trials the pressure acted against a number\nof oak stakes, some of round and some of square section, and\nvarying from 2 ft. 11½ in. to 3 ft. 11± in. long. The ground\nwas solid sand or mixed gravel, and some of the stakes had\nbeen in use for a considerable time, while others were driven\nexpressly for the experiments. The results showed that a\npressure of from 3 cwt. to 5 cwt. was quite sufficient to pro-\nduce the lateral displacement of 10 millimetres (=0.39 in.)\nwhilst a pressure of 7 cwt. almost forced the stakes out of the\nground. These experiments showed, therefore, that in\nground of this kind piles driven against the ends of the\nsleepers could not exercise the least influence upon the\nstability of the permanent way-structure.\nIn these trials the pressure acted against a pile 4 in. in\ndiameter and 2 ft. 111 in. long, driven into a heavy loamy\nballast, which had been laid down about ten years over the\nbroken-stone bedding of an old line. The results which we\nsubjoin show that the resisting power of such a pile would be\nof but little use for increasing the lateral stability of the\nstructure.\nThree trials were made on a pile 4 in. square and 4 ft.\n11 in. long, driven into the same ground as the pile tested in\nthe last series of experiments.\nThe results showed that the length and section of the pile\nexercise an important influence on its resistance to lateral\npressure. It was found in these last two series of experiments\nthat when the displacement of the piles became great, the\nground behind them cracked radially and rose considerably\nwhile, when the cracks reached certain dimensions, it was\nfound that no increase of pressure was required to produce\na further displacement of the piles.\nBaron von Weber's conclusions, drawn from the experi-\nments relating to question e, are as follows: 1st. That the\nresistance of piles driven into sandy or other light ground is\nso insignificant that the use of such piles under such circum-\nstances will not produce an increased stability of the structure\nagainst lateral displacement 2d. That the resistance of piles\ndriven into heavy solid ground is much greater than that of\npiles driven into sandy ground; but that even in the former\ncase the piles must be driven rather closely if they are to\nafford any efficient resistance to small lateral displacements\nof the permanent way-structure ; 3d. The resisting power of\npiles, and especially their resistance to small displacements,\nincreasing with their length, and in a more rapid ratio than\nthe latter, it is considered that no piles, to produce an effect\nDigitized by\nGoogle\n448\nCIVIL ENGINEERING.\ncommensurate with their cost, should have a length of less\nthan 5 ft. and 5th. The signs of considerable displacements\nof piles may, under certain circumstances, disappear after\nthe causes of these displacements have been removed, with-\nout, however, the piles regaining their former stability.\n759. Experiments to determine the power of perma-\nnent way-structures to resist the loosening of the rails\nfrom the sleepers. It is remarked by Baron von Weber\nthat in investigating the stability of the connection between\nrails and sleepers, it has to be borne in mind that the re-\nsistance of the rails to displacement depends upon three\nthings, viz. : First, the holding power of the fastenings\n(bolts, spikes, etc., etc.) by which the rails are secured to the\nsleepers; second, to the increased friction between the base\nof the rails and the sleepers which is caused by a load stand-\ning on the rails and, third, by the friction between the rails\nand the wheels, this friction causing the axles to form ties be-\ntween the two lines of rails on which their wheels rest. It\nwill thus be seen that the gauge of a line of rails is pre-\nserved not merely by the fastenings securing the rails to the\nsleepers, but also by other forces of considerable importance\nacting both on the top and bottom of the rails.\nThe passage of the rolling stock is considered by Baron\nvon Weber to produce on the rails the following effects :-\n1. Under all circumstances a vertical pressure tending to\nforce the rails into the sleepers, the latter yielding to this\nforce in all cases where they are not made of materials of\nvery high resisting powers, such as stone or iron. Wooden\nsleepers are of course compressed by the vertical pressure of\nthe trains, and one point to be determined, therefore, is-\n760. (e) To what extent are sleepers of various forms and\nmaterials compressed by the loads acting on the rails ?\n2. There is a horizontal pressure resulting, in the case of\ncurves, partly from centrifugal force and partly from the\nrigidity of the rolling stock, and, in the case of straight lines,\nfrom the oscillation of the vehicles. This horizontal pres-\nsure-which may, however, change into a pressure acting at\na more or less acute angle to the surface of the sleepers—\ntends to alter the position of the rail on the sleeper in two\nways, namely: first, by shifting the rail on the sleeper with-\nout altering the inclination of the former; and, second, by\ncanting the rail and causing it to turn on a point situated\nmore or less near to its outer edge, according to the com-\npressibility of the sleeper. The first of these two kinds of\ndisplacement is resisted by the horizontal resistance of the\nDigitized by Google\nRAILWAYS.\n449\nspikes or other fastenings, by the friction between the wheel\nand the rail, and by the friction between the base of the rail\nand the sleeper, and the question to be answered by the ex-\nperiments relating to this kind of displacement, therefore,\n18-\n761. (f) What power is required to displace a fastened\nand loaded rail horizontally on its sleepers ?\nThe second kind of displacement just mentioned, or cant-\ning of the rails outwards, is. resisted by the direct holding\npower of the fastenings connecting the rail to the sleeper,\nand by the friction between the wheel and rail. The ques-\ntions to be answered by the investigations relating to this\nmatter, therefore, are-\n(g) What force is required to draw the spikes out of the\nsleepers ? and\n(h) What force is required to overcome the combined re-\nsistance due to the holding power of the spikes in the sleep-\ners, and the friction between the rails and wheels?\nThe following sets of experiments were carried out by\nBaron von Weber, in order to obtain answers to the above\nquestions:-\nThe most striking result obtained is the deterioration of\nthe sleepers under the influence of the traffic at the points\nwhere the rails rest upon them. Thus it will be seen that\nin the case of the fir sleepers the average compressions under\nthe load, at the unused and old bearing surfaces respectively,\nwere 5.3 and 9.7 mils.; while the average permanent com-\npressions were 1.1 and 2.6 mils., the latter results being\nabout double the former.\nAnother remarkable result is the actual amount of the\ncompression, this amount averaging as much as 5.3 millime-\ntres 0.208 in.) for new and sound fir sleepers, and 9.7 mil-\nlimetres (=0:382 in.) for fir sleepers averaging five years old.\nBaron von Weber considers that these results point to the\nnecessity of employing rigid rails, so as to distribute the\neffects of the pressure of the rolling stock as far as possible\nover a number of supports, and that they also show the ad-\nvantage of employing sleepers of hard timber.\nThe results of the first group of experiments relating to\nquestion (e) Baron von Weber summarizes as follows:-\n1. That sound fir sleepers 140 millimetres (=5.5 in.) thick\nand 200 millimetres (=7.87 in.) wide are compressed, on an\naverage, one millimetre (0.039 in.) by a load of 5.6 kilogram-\nmes per square centimetre (=79.6 lb. per square inch), it\nbeing supposed that they have not before been subjected to\n29\nDigitized by\nGoogle\n450\nCIVIL ENGINEERING.\nsuch a load. At places where rails have already been bear-\ning upon the sleepers for some time, this compression is in-\ncreased to one millimetre for each load of 4 kilogrammes\nper square centimetre (=56.88 lb. per square inch).\n2. The action of the trains increases considerably the com-\npressibility of the sleepers at the points where the rails bear\nupon them.\n3. That the compressibility of wooden sleepers-and espe-\ncially of fir sleepers-is so great, that it is necessary to dis-\ntribute the pressure of the trains upon the sleepers as far as\npossible by the employment of rigid rails.\n4. That increasing the number of sleepers in order to in-\ncrease the carrying power of a permanent way, is, theore-\ntically and economically, a wrong mode of obtaining that\nend.\n5. That in the event of lateral pressure being brought to\nbear against the head of the rail, the resisting power of fir\nsleepers is not sufficiently great to prevent a canting of the\nrail consequent upon the impression of one side of the base\ninto the sleeper. Hence momentary alterations in the gauge\nare allowed, these alterations disappearing, however, on the\nremoval of the lateral pressure, and leaving no traces on the\nspikes, sleepers, or rails.\n6. The compression of fir sleepers under the bases of the\nrails is so great that the cellular structure of the wood is\nslowly destroyed, and a cutting or indentation of the sleepers\nat the points of bearing takes place, this action being accele-\nrated when the upper fibres of the wood have been more or\nless deprived of their elasticity by the action of the weather.\nThe above conclusions are justified by Baron von Weber's\nfurther investigations.\nBaron von Weber's deductions from the second group of\nexperiments relating to question (e) are as follows:-\n1. When the influence of the rigidity of the rail, etc., upon\nthe transference of the pressure of the rolling load to the\nsleeper is taken into account, it may be considered that the\ncompression of the sleeper itself takes place in the same\nmanner under the action of either a steadily applied or a roll-\ning load.\n2. That the sinking of well-bedded sleepers into the ground\non which they rest is proportionately insignificant even under\nthe action of considerable rolling stock.\n3. That if the base of the rail has a bearing surface of 220\nsquare centimetres (= 321 square inches) upon a sound fir\nsleeper between four and six years old, and 140 millimetres\nDigitized by\nGoogle\nRAILWAYS.\n451\n(= 5.5 inches) thick, a load of 1,500 kilogrammes applied\nthrough the rail will compress the sleeper one millimetre.\nOr, in other words, a load of about 7 kilogrammes per square\ncentimetre (= 99.54 lb. per square inch) will produce the\ncompression just mentioned on those parts of the sleepers\nwhich have already been frequently exposed to that during a\nconsiderable time.\nAlthough the series of experiments we have just described\nare not extensive, Baron von Weber considers that the follow-\ning deductions may be drawn from them: 1st. That the re-\nsistance of the spikes to the horizontal displacement of the\nrails upon the sleepers is proportionately so insignificant that\nmost of the movements of the rolling stock which would be\ncapable of producing a displacement of the rails on the\nsleepers would suffice to overcome this resistance; and, 2d.\nThat the power of resistance of the spikes to horizontal dis-\nplacement decreases, after that displacement has once begun,\nin a more rapid ratio than the displacement itself increases;\nand hence that the continued action of the rolling stock will\nproduce generally greater displacements than a sudden and\ngreat pressure or force.\n762. Herr Funk's Experiments on the Resisting Power\nof Railway Spikes. The experiments made by Herr Funk\non the holding power of railway spikes constitute, as we re-\nmarked, one of the most important investigations of the kind\never carried out, the experiments being directed, not merely to\nascertaining the power of the spikes to resist a force tending\nto draw them straight out of the timber, but also to deter-\nmining their resistance to lateral displacement. The effect of\nmodifications in the forms of the spikes, and variations in the\nnature of the timber into which they were driven were also\ntaken into consideration.\nThe resisting power of railway spikes depends chiefly-\n1. Upon the kind of timber of which the sleeper is formed,\nand the condition of the latter.\n2. Upon the shape and dimensions of the spikes.\n3. Upon the mode of driving them into the sleepers.\nThe following results are derived from the above investi-\ngations, and from former experience gained in the construc-\ntion and maintenance of permanent way-structures:-\n1. Sleepers made of oak are preferable to those made of\nfir and deal, not only on account of their greater durability,\nbut also on account of the greater resisting power which they\ngive to the spikes. Although experience has not yet suf-\nficiently proved the proportionate durability of prepared oak,\nDigitized\nby\nGoogle\n452\nCIVIL ENGINEERING.\nfir, and pine sleepers, it is, nevertheless, advisable to use\noak sleepers, even in cases where the prices for the oak\nare 11 or 1ª times as high as those for the softer kinds of\nwood.\n2. Joint sleepers, where a great resisting power of the\nspikes is especially necessary, ought to be made of oak, even\nin those cases where that timber costs about 2 or 21 times as\nmuch as fir or pine. If the difference of the price, how-\never, is still greater, the joint sleepers of fir ought to be\nmade larger, in order to enable a greater resisting power\nto be obtained for the spikes by giving the latter additional\nlength.\n3. If the intermediate sleepers are made of fir, one or two\nof these sleepers-according to whether 15 or 21 ft. rails\nare used-ought to have two spikes on the outside of the rail\nbase, or small bedplates, 3 or 4 inches wide, should be adopted,\nin order to increase the resisting power of the spikes against\nlateral pressure, and especially to bring the inside spike also\ninto action. The number of these outside spikes or bedplates\nought to be increased in curves of small radii on the outer\nline of rails, or ought to be provided with a bedplate with\ntwo holes.\n4. The impregnation of the sleepers with chloride of zinc\ndoes not influence the resisting power of the spikes, but this\npower seems to be a little less for newly prepared sleepers\nwhich are still completely saturated with water.\n5. The bellied spikes possess the smallest resisting power,\nthis power being only 0.7 or 0.9 of that for prismatic spikes\nof the same weight.\n6. No favorable result is obtained by twisting the spikes or\nby jagging their edges.\n7. The resisting power of double pyramidal spikes of short\nlength is for deal about 1 greater than that of straight pris-\nmatic spikes of the same weight; this advantage does not\nexist, however, in the case of spikes of greater length, nor\nwhen the spikes are driven into oak.\n8. The simple pyramidal spikes and the prismatic spikes, if\nboth are driven equally deep into the wood, offer the same re-\nsisting power against being drawn out of the timber, whilst,\nif the same volume of both is driven into the wood, the\nholding power of the former is for oak and for long spikes\nabout to, and for deal and for shorter spikes about 1\ngreater than the resisting power of prismatic spikes. But\nwith respect to the resisting power against lateral displace-\nments within the limits important for permanent way-struc-\nDigitized\nby\nGoogle\nRAILWAYS.\n453\ntures, the prismatic spikes are in a similar proportion stronger\nthan pyramidal spikes.\n9. The pyramidal spikes costing about 20 per cent. more\nthan prismatic spikes of the same weight, the advantage of\nthe smaller volume of iron driven into the wood for the ne-\ncessary depth of 5 or 6 inches (found by experience to be a\nsufficient depth for the spiking of rails), is completely com-\npensated; the prismatic spikes are, therefore, preferable to\npyramidal spikes, as the former, besides their greater resisting\npower against lateral pressure, have not the great disadvan-\ntage of the latter spikes of becoming, when once loosened,\nsoon entirely powerless.\n763. Baron von Weber's Experiments on the Re-\nsisting Power of Spikes. The experiments above de-\nscribed being of a very satisfactory kind, Baron von Weber's\nresearches were conducted so as to deal with questions to\nwhich Herr Funk's experiments did not relate, and they\nwere especially carried out for the purpose of ascertaining\nthe influence of the pressure of the wheels against the\nrails upon the resisting power of the spikes.\nThe average results deduced by Baron von Weber, from the\nexperiments we have recorded, are that, in the case of the fir\nsleepers, a force of about 1,850 lbs., and in the case of oak\nsleepers, a force of about 3,000 lbs. was required for drawing\nthe spikes. As the latter had 73 square centimetres, or 11.3\nsquare inches, of surface in contact with the timbers, the\nforces required for drawing the spikes were:\nPounds per square inch\nof surface.\nIn fir sleepers\n163.2\nIn oak sleepers\n269.6\nThese values for the holding power are much less than those\nfound by von Kaven and Funk, and there is also somewhat\nless difference between the respective holding powers in fir\nand oak than was shown by the researches of those experi-\nmenters. Baron von Weber, however, considers-and we agree\nwith him-that the difference between von Kaven and Funk's\nresults and his own are fully accounted for by the fact that\nin the latter experiments the spikes were not merely subjected\nto a pull in the direction of their axes, but were exposed also\nto lateral pressure, the pull being exerted on the underside of\nthe nose or head. Baron von Weber considers also that, from\nthe fibres of oak having less flexibility than those of fir, this\nDigitized by\nGoogle\n454\nCIVIL ENGINEERING.\nlateral pressure would produce greater loosening of the spikes\nin the former than in the latter timber, and hence there would\nbe less difference in the holding power of the spikes in the\ntwo kinds of sleepers, than was shown by the researches of\nformer experimenters, who applied a direct pull to the spikes.\nThis fact shows, as is remarked by Baron von Weber, that\nresults of direct practical value can only be obtained by ex-\nperiments carried out under the circumstances which exist in\nactual practice, and he considers, for this reason, that the\nvalues for the holding power of spikes deduced from his re-\nsearches are more reliable for practical use than those ob-\ntained from previous experiments.\n764. Experiments on the effects of Bedplates. After\nthe preceding experiments had been carried out, it became de-\nsirable, in order to complete the inquiries relating to the in-\nfluence of the means usually adopted for effecting the con-\nnection between the rails and sleepers, that some experiments\nshould be made to ascertain the effect of interposing rolled\niron bedplates between the sleepers and rails. Such bed-\nplates are generally supposed to serve three purposes. Thus,\nfirst, they render the spikes driven into the sleepers on both\nsides of the rail dependent on each other, it being impossible\nfor one to be displaced without the other being displaced\nalso; and thus it might be expected à priori that the resist-\nance of the spikes to lateral displacement would be doubled.\nSecond, the plates prevent the impression of the edge of the\nrail into the sleeper, an action which is often the reason for\nthe rail canting; and, third, they practically increase the\nbearing surface of the base of the rail upon the sleeper.\nIn this series of trials, two pieces of rails were fastened, at\nthe usual gauge apart, upon three fir sleepers, and between\nthe rails and the central sleepers were placed bedplates of the\nFig. 284.\nFig. 235.\nshape shown in Figs. 234 and 235. The\nspikes fitted the holes in the plate well, and\nat the same time pressed firmly against\nthe bases of the rails. The plates were\narranged in such a manner that the side of\none hole was placed towards the inside of\nthe rails, and the press acted against the\nPlan of bed-\nSection of\nplate.\nbedplate.\nheads of the rails directly above the\nplates.\nThe effect of the plates in the above experiment was very\nclear, and they evidently increased the resistance of the spikes\nto lateral displacement until the latter has been drawn out of\nthe timber. In fact, the pressure required to loosen tb\nDigitized by Google\nRAILWAYS.\n455\nstructure was more than double that necessary in the case of\nthe structure without plates.\nIn this case, the rails were fixed upon two sleepers, bed-\nplates being interposed between the former and the latter,\nand the press being placed so as to act upon the heads of the\nrails midway between the two sleepers.\nThe prevention of the lateral displacement of the rails re-\nsulting from the use of plates, was in the above instance the\ncause of a greater stability of the heads of the rails, but it at\nthe same time had the effect of causing the more rigid struc-\nture to become loosened with a less widening of the gauge\nand a less pressure than was the case with the more elastic\nstructure without plates. But the deferred loosening of the\nstructure without plates was practically of no value, for be-\nfore the loosening took place the gauge had been widened to\nsuch an extent that the line would have been unfit for use.\nIn these trials the rails were fastened upon four sleepers with\nbedplates, and the press acted against the heads of the rails\nin the middle between the central sleepers.\nThe loosening of the structure with plates took place at\na smaller widening of the gauge, but at a much greater pres-\nsure than that of the structure without plates; and the resist-\nance of the structure was in fact increased by the use of the\nbedplates more than 60 per cent.\nIn this series the rails were fastened down to five sleepers,\nbedplates being interposed, but two arrangements of the\nplates were tested. In the first case, all the bedplates were\narranged in the same manner as in the previous experiments,\nthat is, with the side traversed by one spike placed inside\nbut in the second case, the plates on the three central sleepers\nwere turned SO that the side having two spikes was next the\ncentre of the line. Thus six extra spikes were made to act\nagainst the canting of the rails, whilst the total number of\nspikes securing the rails to the sleepers remained the same.\nThe second arrangement was tested for the purpose of ascer-\ntaining the most advantageous method of placing the plates\nto secure stability of the structure.\nThe above experiments showed that the stability of the struc-\nture was practically the same for both positions of the plates,\nup to a pressure of 80 centners 9,075 lbs.). The spikes\nin the normal arrangements then became loose, while the other\narrangement with two spikes inside the rails on each of the\nthree central sleepers allowed a further widening of the\ngauge up to 38 millimetres (=1.496 in.) before the resisting\npower of the fastening ceased. The second arrangement of\nDigitized by\nGoogle\n456\nCIVIL ENGINEERING.\nthe plates thus offered a greater resistance to the destruction of\nthe structure than that in which single spikes were placed in-\nside the rails.\n765. The general deductions drawn by Baron von Weber\nfrom all the experiments relating to question (g), namely,\nWhat force is required to draw the spikes out of the sleepers ?\nare as follows :-\n1. That the force, in pounds, required to draw out of tim-\nber rail-spikes of the usual form-that is to say, square pris-\nmatic spikes with chisel points-is to be found, if the strain\nacts directly in the direction of the axis of the spike, by mul-\ntiplying the area of the surface of the spike in contact with\nthe timber by the following numbers:-\nFor fir, .300 lbs.\nper square inch of surface of the driven portion of\n\" oak, 600 \"\nthe spike.\n\"\nfir,\n47\n\"\nper square centimetre of surface of the driven portion\n\" oak, 94 \"\nof the spike.\nIf, however, the force acts laterally as well as in the direc-\ntion of the axis, as is generally the case in practice, the mul-\ntipliers become as follows :-\nFor fir, 150 lbs.\nper square inch of surface of the driven portion of the\n\" oak, 270 \"\nspike.\n\"\nfir,\n25\n\"\nper square centimetre of surface of the driven por-\n\" oak, 42 \"\ntion of the spike.\n2. That spikes driven into a sleeper for the second time\nafter the holes in the timber have been filled up, offer at\nfirst greater resistance than spikes driven into new sleepers.\n3. That but very small forces are required to produce a\nwidening of the gauge to the extent of 6 or 10 millimetres\n(0.236 in. or 0.394 in.) as such amounts of widening are with-\nin the limits of elasticity of the structure, and require no\nloosenings of the fastenings.\n4. That a lateral pressure of 80 centners (= 9,075 lbs.) at\nthe most, acting against one point of the head of the rails, is\nsufficient to produce either a canting or lateral displacement\nof the rails to such an extent that the structure at this point\nis completely and permanently loosened.\n5. That the force required for the further spreading and\nfinal destruction of the structure is much less than that neces-\nsary for the first loosening, the former being seldom more\nthan 75 per cent. of the latter.\n6. That the resistance of the structure to a pressure acting\nagainst one point of the head of a rail does not increase in\nDigitized by Google\nRAILWAYS.\n457\ndirect proportion to the number of sleepers to which the rail\nis fastened, but that the elasticity of the rail and consequent\ntorsion permits the fastenings upon the several sleepers to be\nloosened successively. The resistance of the rails to torsional\nstrains may, however, enable the fastenings at any one point\nto receive such support from the adjoining fastenings that the\nresistance to canting at that point may be doubled.\n7. That if the elasticity of the rails is very great, a widen-\ning of the gauge to the extent of 25 millimetres (=0.984 in.)\nmay be produced without remaining permanent or without\nshowing signs of having occurred after the pressure has been\nremoved. This is more likely to happen if the widening of\nthe gauge is produced by the canting of the rails than if it is\ndue to their lateral displacement on the sleepers; in the latter\ncase the displacement of the fastenings would be visible,\nwhilst in the former a slight raising of the spikes in the di-\nrection of their axis would only be observed under very\nfavorable circumstances.\n8. That in the case of structures having the joints of the\ntwo lines of rails arranged opposite each other on the same\nsleeper, the points on which the joints occur offer considera-\nbly less resistance to a widening of the gauge than is the case\nwhen the rails are disposed so as to break joint, the propor-\ntionate resisting powers in the two cases being about as 7\nto 10. Thus a permanent way, having the joints of the two\nlines of rails opposite each other, has as many points as there\nare joints, at which the lateral stability or power to resist\nwidening of the gauge, is but I'ᵈ of' that at the joints\nof the structure having the rails disposed so as to break joint.\nThis is of importance with respect to accidents originating\nfrom the widening of the gauge.\n9. That the application of bedplates between the rails and\nsleepers increases-under otherwise equal circumstances-the\npower of resistance of the structure to lateral displacement\nof the rails; but that the loosening of the fastenings takes\nplace with a smaller displacing movement.\nWe now come to the experiments relating to question (h),\nnamely: \" What force is required to overcome the total re-\nsistance due to the combination of the holding power of the\nspikes in the sleepers and the friction between the rails and\nwheels?\nThe trials just recorded are, as Baron von Weber justly\nobserves, very instructive, for they prove that the friction\nbetween the rails and the sleepers, plus the resistance of the\noutside spikes, is sufficient to keep the rails in their places, even\nDigitized by Google\n458\nCIVIL ENGINEERING.\nwhen the pressure against the heads is such as to cause the\ncanting of the rails to an extent sufficient to render the line\nunfit for traffic. The experiments also show that the inside\nspikes afford proportionately little resistance, and that they\nrepresent the weakest points of the structure. In fact, the\nfastened and loaded rails showed, under the influence of the\nsame displacing power, displacements which were certainly\nnot less than those obtained in the case of the structure in\nwhich the inside spikes had been loosened.\nNothing now remained connected with this part of Baron\nvon Weber's investigations but to collect facts showing the in-\nfluence of the state of the surface of the rails upon the stabil-\nity of the structure.\n766. The deductions made by him from the experiments\nrelating to the question (h), \" What force is required to\novercome the total resistance due to the combination of the\nholding power of the spikes in the sleepers and the friction\nbetween the rails and wheels?' are as follows :-\n1. That the resisting power of the rails to lateral forces is\nconsiderably increased through the friction between the\nwheels and rails, this friction causing the axle to form a kind\nof tie between the two rails.\n2. That if the load upon the rail is more than 9,075 lbs.\nper wheel or vehicle, the resisting power of the rails to\ncanting due to the friction just mentioned is greater than\nthat due to the spiking of the rails in the ordinary way to fir\nsleepers.\n3. That the resistance of the rails to lateral displacement\non the sleepers is increased by the load on the rails in the\nproportion of 0.33 of that load; whence, in the case of rails\ncarrying the load of 6,806 lbs. per wheel, the resistance of the\nrails to lateral displacement on the sleepers due to the load,\nis greater than that due to the resisting power of the spikes.\n4. That if the load be more than 9,075 lbs. per wheel, the\nfrictional resistances cause the rails to be supported at top\nand bottom against both canting and lateral displacement,\nand the support thus afforded is more effective than that due\nto the ordinary spiking.\n5. That the forces tending to produce canting and lateral\ndisplacement due to the horizontal oscillations of the rolling\nstock, can only be resisted (at least in most cases) by the com-\nbined action of the spikes, the friction between the wheels\nand rails, and the friction between the rails and sleepers.\n6. That if, therefore, the load upon one point of the struc-\nture be partially or entirely removed by the undue vertical\nDigitized by\nGoogle\nRAILWAYS.\n459\noscillation of a vehicle, whilst, at the same time, a lateral\noscillation of the vehicle takes place, the stability of the\nstructure against the pressure due to this lateral oscillation\ndepends solely upon the insufficient resisting power of the\nspikes, and the lateral distortion and displacement are the un-\navoidable consequences. This last deduction is, as Baron\nvon Weber justly considers, one of very great importance,\nand, in fact, the experimental researches upon which it is\nfounded may be said to prove the cause which leads to the\nserpentine displacements of the rails but too frequently met\nwith on straight portions of a line of railway, particularly if\nthe line is one of light construction, or is traversed by loco-\nmotives having considerable overhang at the leading and\ntrailing ends. If such a portion of a line contains a sleeper\nbadly bedded, which sinks uniformly throughout its entire\nlength under the influence of a passing load, the vehicle pass-\ning over it will make but a heavy vertical oscillation, having\nno influence upon the lateral resisting power. of the structure.\nBut if the sleeper sinks under one rail more deeply than un-\nder the other, the oscillation of the vehicle will be at once\nhorizontal and vertical, and the load will be removed more or\nless, first from the trailing and then from the leading axle,\nthus causing the lateral pressure due to the horizontal oscilla-\ntions to be exerted through the tires of the wheels with full\npower against the rails.\nIn such a case it is almost unavoidable that the point of\nthe unloaded, or partially unloaded, structure should be dis-\nplaced laterally; but this displacement having once occurred,\nthe oscillations of the passing vehicles become so consider-\nable, both in a horizontal and vertical direction, that the dis-\nplacement of the rail is soon repeated, and only favorable\ncircumstances, such as coincidence of the oscillations, can\nthen produce a uniform motion of the vehicles. The dis-\nplacements just referred to are considered by Baron von\nWeber to be most dangerous, both for the stability of the\nstructure, and the passage of the trains, because their original\ncauses can only be discovered with great difficulty, even\nwhen the permanent way is most carefully maintained.\n767. Notwithstanding the great value of the results ob-\ntained from the experiments we have already described, it is\nundeniable that some of the main questions relating to the sta-\nbility of permanent way-structures can only be finally an-\nswered by ascertaining the amount of the momentary deflec-\ntions and displacements of the rails which actually occur when\na line is subjected to the action of passing trains, but which\nDigitized by Google\n460\nCIVIL ENGINEERING.\ndisappear either entirely, or almost entirely, after the action\nwhich causes them ceases, and which are thus, under ordinary\ncircumstances, likely to escape observation.\nThe momentary deflections and displacements just referred\nto may be divided into two classes, namely, those which ap-\nparently disappear on the removal of the load, and those\nwhich disappear absolutely. To the first class belong those\ndeflections and displacements which, although causing a\ngreater or less loosening of the structure, are yet within the\nlimits of elasticity of the rails, so that the latter, after the pas-\nsage of the train, return to their normal positions, and there\nare only left to make the movements which have taken place,\nthe small lateral displacements of the spikes, or small impres-\nsions of the sleepers by the bases of the rails. Such marks of\ndisplacements are likely to escape any but very careful in-\nspection; yet, taken altogether, they may allow to the rails\nan amount of play or \"liberty to cant which may produce\ndangerous results. The second class of momentary displace-\nments, on the other hand, consists of those which take place\nwithin the limits of elasticity of the permanent way-structure\nas a whole, all the parts returning to their normal positions on\nthe removal of the cause of the disturbance. Such momen-\ntary alterations as these in the positions of the rails occur less\nfrequently than those of the former class, but they may never-\ntheless become dangerous under certain circumstances which\nwill be spoken of hereafter.\nWe now come to the deductions drawn by Baron von Weber,\nfrom the results of the various series of experiments recorded\nby us in the preceding articles of the present series. It is\nthe opinion of the Baron that the tendency of advanced rail-\nway practice is to abandon the ordinary system of iron or\nsteel rails fixed on wooden sleepers for the use of permanent\nway-structures formed of iron alone, and he considers that\nultimately lines of rails will be constructed as continuous gir-\nders, strong enough to resist all the actions of the rolling\nstock, and resisting directly upon properly prepared ground,\nwithout the intervention of intermediate members or perish-\nable materials. \"Looking back,\" he says, \" upon the experi-\nmental researches, we are struck by an extraordinary fact, the\nremarkable character of which is enhanced by the circum-\nstance that it has been little known and still less taken into\nconsideration. This fact is that heavy trains and powerful\nengines have already ran longer than the age of the present\ngeneration upon lines or structures, the flexibility of which is\nBO great that every wheel leaves its impression, and every 06-\nDigitized by Google\nRAILWAYS.\n461\ncillation produces a displacement; and of which the stability\n-as far as it depends upon the resisting power of its mechan-\nical parts-is SO small in proportion to the disturbing influ-\nences brought to bear upon it, that almost any one of these\ninfluences would destroy the structure if it were not that the\nvery load itself increased the stability through the agency of\nthe friction between the wheels and the rails. It would be\nquite unworthy of engineers and engineering science to reply\nthat as the traffic has for a long period been satisfactorily car-\nried on lines possessing such flexibility, that, therefore, it is of\nno importance whence the stability coines, so long as it is there\nwhen required. We might as well state that the neighborhood\nof a certain powder-mill is free from danger, because explo-\nsions have occurred but rarely during the last five-and-thirty\nyears.\"\n763. Deductions of Baron von Weber from tabulated\nresults. Baron von Weber makes a series of deductions which\nare worthy of the careful attention of both locomotive superin-\ntendents and engineers in charge of permanent way. These\ndeductions are in substance as follows:-\n1. That, as is well known, six-wheeled locomotives, when\nrunning, oscillate round their central axle, a dipping or\nplunging motion taking place towards the leading and trail-\ning end alternately. Thus the loads upon the leading and\ntrailing springs vary according to the oscillations, and conse-\nquently the pressures exerted by the leading and trailing\nwheels upon the rails vary also.\n2. That in the case of engines on which the experiments\nwere made the greatest load imposed in this manner upon the\nsprings exceeded the normal load by 103 per cent. (the in-\ncrease of load being from 70 to 160 centners per wheel) in\nthe case of the leading springs, and by 74 per cent. (the in-\ncrease being from 115 to 200 centners per wheel) in the case\nof the trailing springs.\n3. That the maximum loads just mentioned are much\ngreater than that laid down by the rules acknowledged by\nGerman railways, namely, a maximum of 130 centners per\nwheel. Thus in determining the strength of permanent way-\nstructures this great increase of the pressure sometimes exer-\ncised upon the rails should be taken into consideration.\n4. That the load upon the springs is sometimes reduced\nduring the running of the engine to about 7 per cent. of the\nnormal load (the reduction being from 72 to 5 centners) in\nthe case of the leading springs, and to 26 per cent. of the\nnormal load (from 114 to 30 centners) in the case of the\nDigitized\nby\nGoogle\n462\nCIVIL ENGINEERING.\ntrailing springs. The decrease, or even sometimes the almost\nentire removal of the load from the leading springs is sur-\nprising. The experiments, of which an account has just been\ngiven, prove that the permanent way is momentarily sub-\njected to far greater loads than it is ordinarily supposed to\ncarry, and further that it is sometimes almost entirely relieved\nof its load as above stated. It appears also certain that there\nexist horizontal oscillations of the vehicles produced at first\nby partially vertical oscillations, and there thus exists the\ngreatest probability of the coincidence of such a relief from\nload as has just been mentioned, with a horizontal oscillation\ntowards the rail from which the load has just been removed,\nthe result being a displacement of the permanent way, as,\nunder the circumstances supposed, the opposition offered by\nthe latter is but that due to its mechanical structure. The\nexperiments on the stability of permanent way already de-\nscribed, together with the investigations of the variations of\nload on the wheels of the engines, explain in a satisfactory\nmanner the causes of many cases of widening of the gauge\nand displacement of the structure previously considered\ninexplicable.\n5. The difference between the maximum and minimum\nloads resting at different times on the same spring varies by\nmore than double the normal load in the case of the leading\nwheels; but seldom by more than 40 per cent. of that load\nin the case of the trailing wheels, a circumstance which indi-\ncates that the real centre of oscillation of the masses forming\nthe engine is situated between the driving and trailing axle,\nand not over the former.\n6. That the extreme amounts of variation in the loads on\nthe leading and trailing springs were found to occur in an\nengine the construction of which would have least justified\nthe expectation of their taking place. This engine was the\n\" Prometheus,\" in which the wheel base differed very little\nfrom the length of the boiler, and in which about 60 per\ncent. of the load was removed from the leading wheel, while\nthat on the trailing wheels was reduced to 77 per cent. of the\nnormal load. This fact points strongly to the danger often\nattendant upon placing a great load upon the driving axle,\nif the latter is situated under the centre of the engine.\n769. Sleepers. The preservation of sleepers by chemical\nprocesses is always the subject of experiment on one or another\nof our railways. The practice, however, is not general in\nthis country, because the mashing of the rail into the sleeper\nusually destroys it in advance of decay. In England, the\nDigitized by Google\nRAILWAYS.\n463\nbearings of the chains used with the double-headed rail on\nevery sleeper are SO extended, that the mechanical injury of\nthe wood is quite small. Prevention against decay-usually\nimmersion in coal-tar-is therefore generally practised. The\ninsufficient bearing offered by sleepers to the rails is thus,\ndirectly and indirectly, the cause of their rapid destruction.\nIt is stated that placing the sleepers closer than, say two feet\napart between centres, would prevent the convenient tamping\nof the ballast. It is objected to the longitudinal sleeper, that the\nrail lying parallel with the fibre of the wood, mashes into it\nmore easily than into the cross-sleeper. These objections to\ninsufficient bearing are not inherent in either system, but arise\nfrom improper construction. Thoroughly good ballast would\nnot require continual tamping. It is even proposed by some\nof our most experienced engineers to cover the ballast with\na coating of coal-tar and gravel, to absolutely exclude water,\nand thus prevent not only decay, but washing, freezing, heav-\ning, settling-all destroying elements but vibration and wear.\nIn this case the timber bearings under the rails should be\nalmost continuous, to prevent wear both on the ballast and\non the rail. The mashing of rails into timbers, either longi-\ntudinals or cross-sleepers, is largely due to the want of stiff-\nness in the rails themselves. The low n rails on the Great\nWestern of England are the most notable examples of this\nkind of failure. If the iron wasted in the thick stem and\npear-head of our worst shaped rails were put into the height\nof stem, their resistance to deflection would be doubled, this\nresistance being as the cube of the depth.\nThere is a growing conviction among engineers, that the\nlongitudinal system will become standard. It offers twice to\nthree times as much bearing for the rail as the cross-sleeper\nsystem. The whole strength of a longitudinal is added to the\nstrength of the rail, considered as a beam to carry the load.\nThe strength of the cross-sleeper in this direction is wholly\nwasted. The longitudinal is almost certain to prevent the\ndisplacement of a broken rail. This system has never been\ntried on a large scale, with a high, stiff rail. It requires bet-\nter ballast, and more thorough adjustment than the other\nsystem. Independent points of support, like the isolated\nends of cross-sleepers, that can be blocked up or let down at\npleasure, without reference to the rest of the superstructure,\nare the indispensable accompaniment of bad ballasting and\nimperfect drainage. But they are unsuited to any system of\nhomogeneous, continuous, and permanent way.\nIron sleepers are coming into use in countries where tim-\nDigitized by Google\n464\nCIVIL ENGINEERING.\nber is very costly and unsuitable, and are the subjects of\nvarious experiments in England.\nThe great defect of all imperishable sleepers, whether stone\nor iron, has been want of elasticity. An anvil under a rail,\nand especially under a joint, is as bad if not worse than an\ninsufficient support.\n770. Rail-Joints. The selection of joint fastenings for\nthe ends of rails is somewhat dependent upon the weight of\nrail required, and hence upon the traffic. After twenty years\nof competitive trial with every variety of fastening, the sim-\nple \"fish-joint\"-an iron splice on each side of the rail-has\nbecome standard in Europe, and is gaining ground here. It\nis the lightest and strongest fastening that can be applied,\nwhen rails are high, and properly shaped to receive it. The\nold difficulty of nuts jarring loose has been overcome by the\nuse of elastic washers. Fishing a pear-headed rail, three or\nthree and a half inches high, would be perfectly useless. For\nlight rails, and for steel rails (to save weakening them by\npunching), and as an auxiliary to the fish-joint, the new\nReeves' fastening-a light clamp upon the contiguous flanges\nof two rails-is coming largely into use. The mere chair or\nseating for the ends of rails is no longer considered safe nor\neconomical for lines of heavy traffic. Although there is\nroom for farther experiment, it cannot be said that the de-\nmand for a good rail-joint has not been met.\n771 Steel Rails-The Results. Bessemer steel rails\nhave been in regular and extensive use abroad over ten years.\nFor several years large trial-lots have been laid on various\nAmerican roads having heavy traffic.\n772. The Wear of Steel Rails. As no steel rails are re-\nported to have worn out on our roads, the comparative dura-\nbility of steel and iron cannot be absolutely determined.\nA great number of instances of the comparative wear of\nsteel were cited. In one case twenty-three iron rails had been\nworn out, where a steel rail, laid end to end with the iron,\nwas not yet worn down. In other cases the wear was seven-\nteen to one. It is conceded that any steel rail will outlast\nsix iron rails. In fact, the remarkable wearing qualities of\nsteel rails have never been doubted or questioned.\n773. Breakage of Steel Rails. Some steel rails of Eng-\nlish, French, and American manufacture have broken in\nservice. In several cases the cause has been ascertained by\nthe direct analysis of the broken rail. The cause was phos-\nphorus. In some other cases, where analyses were not made,\nthe general character of the iron used has been ascer-\nDigitized by Google\nHAILWAYS.\n485\ntained, and the trouble has been inferred to be phosphorus,\nor, in some cases, an excess of silicon. It is well known to\nsteel makers that a very minute proportion of phosphorus\n(above 0.2 per cent.) will make Bessemer steel brittle. In\nother cases rails have broken at the mark of the \"gag,\" or\ninstrument for straightening the rail cold. The rails had not\nbeen properly hot-straightened, or were finished at too low'\na heat. More rails have broken through punched fish-bolt\nholes, and at punched nicks in the flange, than at any other'\nplaces. Experiments prove that punching a hole in a steel\nrail which is sufficiently hard to wear well, weakens it.\nIn the absence of further official information, it is fair to\nassume that the breakage of steel rails is only a small per-\ncentage of the breakage of iron rails. Indeed, the latter is\nof daily occurrence, and is rarely considered by the public,\nexcept when lives are lost, and not always by railway man-\nagers when they make contracts.\n774. Tests and Improvements. The punching of steel\nrails has been abandoned. Several kinds of power and hand\ndrilling machines have been introduced, that do the work\nrapidly and well. The loss from the neutral axis of a rail,\nof the little material necessary to let a bolt through, cannot\nsensibly weaken it. To prevent the rails from creeping, the\nengineer of the Pennsylvania railway pins them to several\nsleepers by means of 1 inch holes drilled in the flange.\nThere are also other and better devices for preventing end\nmovement, which do not weaken the rail at all. The grand\nadvantage of steel, for service under concussion and wear, is\nits homogeneity. Having been cast from a liquid state, it is\nsound and uniform, and free from the laminations and layers\nof cinder and numerous welds which characterize wrought\niron, especially the low grades of wrought iron usually put\ninto rails.\n775. Improved Traction upon Steel Rails. It has been\ntoo much the practice of railway managers to consider only\nthe increased durability of steel. A less striking, but per-\nhaps equally important advantage is, that it has double the\nstrength and more than double the stiffness of iron.\nThe great and constant resistance to traction, and the wear\nand tear of track, wheels, and running gear, due to the deflec-\ntion of rails between the sleepers and the perpetual series of\nresulting concussions, may be much reduced, or practically\navoided, by the use of rails of twice the ordinary stiffness;\nin such a case, however, reasonably good ballasting and\nsleepers would be essential. When a whole series of sleep-\n80\nDigitized by Google\n466\nCIVIL ENGINEERING.\ners sinks bodily into the mud, the consideration of deflection\nbetween the sleepers is a premature refinement. If the\nweight of steel rails is decreased in proportion to their\nstrength, these advantages of cheaper traction and mainte-\nnance will not, of course, be realized. The best practice, here\nand abroad, is to use the same weight for steel as had been\nformerly employed for iron.\n776. Steel-headed Rails. Many attempts have been made\nin England, on the Continent, and in this country, to produce\na good steel-headed rail, and not without success. Puddled\nsteel heads have all the structural defects of wrought iron,\nas they are not formed from a cast, and hence homogeneous\nmass, but are made by the wrought-iron process, and are, in\nfact, a high\" steely wrought iron. They are, however, a\ngreat improvement upon ordinary iron, although probably\nlittle cheaper than cast-steel heads. Rolling a plain cast-steel\nslab upon an iron pile has not proved successful. The weld\ncannot be perfected on so large a scale, and the steel peels\noff under the action of car wheels. Forming the steel slab\nwith grooves, into which the iron would dovetail when the\npile was rolled into a rail, has been quite successful.\nDigitized by Google\nCANALS.\n467\nCHAPTER VIII.\nCANALS.\n777. Canals are artificial channels for water, applied to the\npurpose of inland navigation; for the supply of cities with\nwater; for draining; for irrigation, &c., &c.\n778. Navigable canals are divided into two classes: 1st.\nCanals which are on the same level throughout their entire\nlength, as those which are found in low level countries.\n2d. Canals which connect two points of different levels, which\nlie either in the same valley, or on opposite sides of a dividing\nridge. This class is found in broken countries, in which it is\nnecessary to divide the entire length of the canal into several\nlevel portions, the communication between which is effected\nby some artificial means. When the points to be connected\nlie on opposite sides of a dividing ridge, the highest reach,\nwhich crosses the ridge, is termed the summit level.\n779. 1st CLASS. The surveying and laying out a canal in a\nlevel country, are operations of such extreme simplicity as to\nrequire no particular notice in this place.\nThe cross section of this class (Fig. 236) presents usually a\nA\nFig. 286-Cross section of a canal in level cutting.\nA, water-way.\nB, tow-paths.\nC, berms.\nD, side-drains.\nE, puddling of clay or sand.\nwaterway, or channel of a trapezoidal form, with an embank-\nment on each side, raised above the general level of the\ncountry, and formed of the excavation for the water-way.\nThe level, or surface of the water, is usually above the natural\nsurface, sufficient thickness being given to the embankments\nto prevent the filtration of the water through them, and to re-\nsist its pressure. This arrangement has in its favor the advan-\ntage of economy in the labor of excavating and embanking,\nDigitized by Google\n468\nCIVIL ENGINEERING.\nsince the cross section of the cutting may be so calculated as\nto furnish the necessary earth for the embankment; but it\nexposes the surrounding country to injury, from accidents\nhappening to the embankments.\nThe relative dimensions of the parts of the cross section\nmay be generally stated as follows; subject to such modifica-\ntions as each particular case may seem to demand.\nThe width of the water-way, at bottom, should be at least\ntwice the width of the boats used in navigating the canal; so\nthat two boats, in passing each other, may, by sheering to-\nwards the sides, avoid being brought into contact.\nThe depth of the water-way should be at least eighteen\ninches greater than the draft of the boat, to facilitate the\nmotion of the boat, particularly if there are water-plants\ngrowing on the bottom.\nThe side slopes of the water-way, in compact soils, should\nreceive a base at least once-and-a-half the altitude, and pro-\nportionally more as the soil is less compact.\nThe thickness of the embankments, at top, is seldom regu-\nlated by the pressure of the water against them, as this, in\nmost cases, is inconsiderable, but to prevent filtration, which,\nwere it to take place, would soon cause their destruction. A\nthickness from four to six feet, at top, with the additional\nthickness given by the side slopes at the water surface, will,\nin most cases, be amply sufficient to prevent filtrations. A\npathway for the horses attached to the boats, termed a tow-\npath, which is made on one of the embankments, and a foot-\npath on the other, which should be wide enough to serve as\nan occasional tow-path, give a superabundance of strength to\nthe embankments.\nThe tow-path should be from ten to twelve feet wide, to\nallow the horses to pass each other with ease ; and the foot-\npath at least six feet wide. The height of the surfaces of\nthese paths, above the water surface, should not be less than\ntwo feet, to avoid the wash of the ripple; nor greater than\nfour feet and a half, for the facility of the draft of the horses\nin towing. The surface of the tow-path should incline slightly\noutward, both to convey off the surface water in wet weather,\nand to give a firmer footing to the horses, which naturally\ndraw from the canal.\nThe side slopes of the embankment vary with the character\nof the soil : towards the water-way they should seldom be less\nthan two base to one perpendicular; from it, they may, if it be\nthought necessary, be less. The interior slope is usually not\ncarried up unbroken from the bottom to the top; but a hori-\nDigitized\nby\nGoogle\nCANALS.\n469\nzontal space, termed a bench, or berm, about one or two feet\nwide, is left, about one foot above the water surface, between\nthe side slope of the water-way and the foot of the embank-\nment above the berm. This space serves to protect the upper\npart of the interior side slope, and is, in some cases, planted\nwith such shrubbery as grows most luxuriantly in aquatic\nlocalities, to protect more efficaciously the banks by the sup-\nport which its roots give to the soil. The side slopes are\nbetter protected by a revêtement of dry stone. Aquatic plants\nof the bulrush kind have been used, with success, for the\nsame purpose; being planted on the bottom, at the foot of\nthe side slope, they serve to break the ripple, and preserve\nthe slopes from its effects.\nThe earth of which the embankments are formed should be\nof a good binding character, and perfectly free from vegetable\nmonld, and all vegetable matter, as the roots of plants, &c.\nIn forming the embankments, the vegetable mould should be\ncarefully removed from the surface on which they are to rest\nand they should be carried up in uniform layers, from nine\nto twelve inches thick, and be well rammed. If the charac-\nter of the earth, of which the embankments are formed, is\nsuch as not to present entire security against filtration, a pud-\ndling of clay, or fine sand, two or three feet thick, may be\nlaid in the interior of the mass, penetrating a foot below the\nnatural surface. Sand is useful in preventing filtration caused\nby the holes made in the embankments near the water sur-\nface by insects, moles, rats, &c.\nSide drains must be made, on each side, a foot or two from\nthe embankments, to prevent the surface water of the natural\nsurface from injuring the embankments.\n780. 2d CLASS. This class will admit of two subdivisions:\n1st. Canals which lie throughout in the same valley 2d.\nCanals with a summit level.\nLocation. In laying out canals, belonging to the first sub-\ndivision, the engineer must be guided in his choice by the\nrelative expense of construction on the two sides of the valley\nwhich will depend on the quantity of cutting and filling, the\nmasonry for the culverts, &c., and the nature of the soil as\nadapted to holding water. All other things being equal, the\nside on which the fewest secondary water-courses are found\nwill, generally speaking, offer the greatest advantage as to\nexpense, but it may happen that the secondary water-courses\nwill be required to feed the canal with water, in which case\nit will be necessary to lay out the line on the side where they\nare found most convenient, and in most abundance.\nDigitized\nby\nGoogle\n470\nCIVIL ENGINEERING.\n781. Cross section. The side formations of excavations\nand embankments require peculiar care, particularly the lat-\nter, as any crevices, when they are first formed, or which may\ntake place by settling, might prove destructive to the work.\nIn most cases, a stratum of good binding earth, lining the\nwater-way throughout to 'the thickness of about four feet, if\ncompactly rammed, will be found to offer sufficient security,\nif the substructure is of a firm character, and not liable to\nsettle. Fine sand has been applied with success to stop the\nleakage in canals. The sand for this purpose is sprinkled, in\nsmall quantities at a time, over the surface of the water, and\ngradually fills up the outlets in the bottom and sides of the\ncanal. But neither this nor puddling has been found to an-\nswer in all cases, particularly where the substructure is formed\nof fragments of rocks offering large crevices to filtrations, or\nis of a marly nature. In such cases it has been found neces-\nsary to line the water-way throughout with stone, laid in hy-\ndraulic mortar. A lining of this character (Fig. 237), both\nB\nB\nD\nFig. 287-Cross section of a canal in side outting lined with masonry.\nA. water-way.\nB, tow-paths.\nD, embankment.\na, masonry lining.\nat the bottom and sides, formed of flat stones, about four in-\nches thick, laid on a bed of hydraulic mortar, one inch thick,\nand covered by a similar coat of mortar, making the entire\nthickness of the lining six inches, has been found to answer\nall the required purposes. This lining should be covered, both\nat bottom and on the sides, by a layer of good earth, at least\nthree feet thick, to protect it from the shock of the boats,\nstriking either of those parts.\nThe cross section of the canal and its tow-paths in deep cut-\nting (Fig. 238) should be regulated in the same way as in\ncanals of the first class; but when the cuttings are of consid-\nerable depth, it has been recommended to reduce both to the\ndimensions strictly necessary for the passage of a single boat.\nDigitized by Google\nCANALS.\n471\nFig. 288-Cross section of a canal in deep outting.\nE, side slopes of cutting.\nBy this reduction there would be some economy in the exca-\nvations; but this advantage would, generally, be of too tri-\nfling a character to be placed as an offset to the inconveni-\nences resulting to the navigation, particularly where an active\ntrade was to be carried on.\n782. Summit level. As the water for the supply of the\nsummit level of a canal must be collected from the ground\nthat lies above it, the position selected for the summit level\nshould be at the lowest point practicable of the dividing ridge,\nbetween the two branches of the canal. In selecting this\npoint, and the direction of the two branches of the canal, the\nengineer will be guided by the considerations with regard to\nthe natural features of the surface, which have already been\ndwelt upon.\n783. Supply of water. The quantity of water required\nfor canals with a summit level, may be divided into two por-\ntions. 1st. That which is required for the summit level, and\nthose levels which draw from it their supply. 2d: That\nwhich is wanted for the levels below those, and which is fur-\nnished from other sources.\nThe supply of the first portion, which must be collected at\nthe summit level, may be divided into several elements: 1st.\nThe quantity required to fill the summit level, and the levels\nwhich draw their supply from it. 2d. the quantity required\nto supply losses, arising from accidents; as breaches in the\nbanks, and the emptying of the levels for repairs. 3d. The\nsupplies for losses from surface evaporation, from leakage\nthrough the soil, and through the lock gates. 4th. The quan-\ntity required for the service of the navigation, arising from\nthe passage of the boats from one level to another. Owing\nto the want of sufficient data, founded on accurate observa-\ntions, no precise amount can be assigned to these various ele-\nments which will serve the engineer as data for rigorous cal-\nculation.\nThe quantity required, in the first place, to fill the summit\nlevel and its dependent levels, will depend on their size, an\nDigitized by Google\n#72\nCIVIL ENGINEERING.\nelement which can be readily calculated; and upon the quan-\ntity which would soak into the soil, which is an element of a\nvery indeterminate character, depending on the nature of the\nsoil in the different levels.\nThe supplies for accidental losses are of a still less deter-\nminate character.\nTo calculate the supply for losses from surface evaporation,\ncorrect observations must be made on the yearly amount of\nevaporation, and the quantity of rain that falls on the sur-\nface; as the loss to be supplied will be the difference be\ntween these two quantities.\nWith regard to the leakage through the soil, it will depend\non the greater or less capacity which the soil has for holding\nwater. This element varies not only with the nature of the\nsoil, but also with the shorter or longer time that the canal\nmay have been in use; it having been found to decrease with\ntime, and to be, comparatively, but trifling in old canals. In\nordinary soils it may be estimated at about two inches in\ndepth every twenty-four hours, for some time after the canal\nis first opened. The leakage through the gates will depend\non the workmanship of these parts. From experiments by\nMr. Fisk, on the Chesapeake and Ohio canal, the leakage\nthrough the locks at the summit level, which are 100 feet\nlong, 15 feet wide, and have a lift of 8 feet, amounts to\ntwelve locks full daily, or about 62 cubic feet per minute.\nThe monthly loss upon the same canal, from evaporation and\nfiltration, is about twice the quantity of water contained in\nit. From experiments made by Mr. J. B. Jervis, on the Erie\ncanal, the total loss, from evaporation, filtration, and leakage\nthrough the gates, is about 100 cubic feet per minute, for\neach mile.\nIn estimating the quantity of water expended for the ser-\nvice of the navigation, in passing the boats from one level to\nanother, two distinct cases require examination: 1st. Where\nthere is but one lock between two levels, or in other words,\nwhen the locks are isolated. 2d. When there are several\ncontiguous locks, or as it is termed, a flight of locks between\ntwo levels.\n784. A lock is a small basin just large enough to receive\na boat, in which the water is usually confined on the sides by\ntwo upright walls of masonry, and at the ends by two gates,\nwhich open and shut, both for the purpose of allowing the\nboat to pass, and to cut off the water of the upper level from\nthe lower, as well as from the lock while the boat is in it. To\npass a boat from one level to the other-from the lower to the\nDigitized by Google\nCANALS.\n473\nmmm\nFig. & 289-Is a plan of the present enlarged form of one-half of a double lock on the Etis 1\nCanal.\nDigitized by Google\n474\nCIVIL ENGINEERING.\nupper end, for example-the lower gates are opened, and the\nboat having entered the lock they are shut, and water is drawn\nfrom the upper level, by means of valves, to fill the lock and\nraise the boat; when this operation is finished, the upper gates\nare opened, and the boat is passed out. To descend from the\nupper level, the lock is first filled ; the upper gates are then\nopened, and the boat passed in ; these gates are next shut, and\nthe water is drawn from the lock by valves, until the boat is\nlowered to the lower level, when the lower gates are opened\nand the boat is passed out.\nIn the two operations just described, it is evident, that for\nthe passage of a boat, up or down, a quantity of water must\nbe drawn from the upper level to fill the lock to a height\nwhich is equal to the difference of level between the surface\nof the water in the two ; this height is termed the lift of the\nlock, and the volume of water required to pass a boat up or\ndown is termed the prism of lift. The calculation, therefore,\nfor the quantity of water requisite for the service of the navi-\ngation, will be simply that of the number of prisms of lift\nwhich each boat will draw from the summit level in passing\nup or down.\n785. In calculating the expenditure for locks in flights, a\nnew element, termed the prism of draught, must be taken into\naccount. This prism is the quantity of water required to float\nthe boat in the lock when the prism of lift is drawn off and\nis evidently equal in depth to the water in the canal, unless it\nshould be deemed advisable to make it just sufficient for the\ndraught of the boat, by which a small saving of water might\nbe effected.\n786. Locks in flights may be considered under two points\nof view, with regard to the expenditure of water : the first,\nwhere both the prism of lift, and that of draught, are drawn\noff for the passage of a boat ; or second, where the prisms of\ndraught are always retained in the locks. The expenditure,\nof course, will be different for the two cases.\nGreat refinements in the calculation of such cases should\nnot be made, but the engineer should confine himself to mak-\ning an ample allowance for the most unfavorable cases, both\nas regards the order of passage and the number of boats.\n787. Feeders and Reservoirs. Having ascertained, from\nthe preceding considerations, the probable supply which\nshould be collected at the summit level, the engineer will\nnext direct his attention to the sources from which it may be\nprocured. Theoretically considered, all the water that drains\nfrom the ground adjacent to the summit level, and above it,\nDigitized by Google\nCANALS.\n475\nmight be collected for its supply but it is found in practice\nthat channels for the conveyance of water must have certain\nslopes, and that these slopes, moreover, will regulate the sup-\nply furnished in a certain time, all other things being equal.\nIn making, however, the survey of the country, from which\nthe water is to be supplied to the summit level, all the ground\nabove it should be examined, leaving the determination of the\nslopes for after considerations. The survey for this object\nconsists in making an accurate delineation of all the water-\ncourses above the summit level, and in ascertaining the quan-\ntity of water which can be furnished by each in a given time.\nThis survey, as well as the measurement of the quantity of\nwater furnished by each stream, which is termed the gauging,\nshould be made in the driest season of the year, in order to as-\ncertain the minimum supply.\n788. The usual method of collecting the water of the\nsources, and conveying it to the summit level, is by feeders.\nand reservoirs. The feeder is a canal of a small cross section,\nwhich is traced on the surface of the ground with a suitable\nslope, to convey the water either into the reservoir, or direct\nto the summit level. The dimensions of the cross section,\nand the longitudinal slope of the feeder, should bear certain\nrelations to each other, in order that it shall deliver a certain\nsupply in a given time. The smaller the slope given to the\nfeeder, the lower will be the points at which it will intersect\nthe sources of supply, and therefore the greater will be the\nquantity of water which it will receive. This slope, however,\nhas a practical limit, which is laid down at four inches in\n1,000 yards, or nine thousand base to one altitude; and the\ngreatest slope should not exceed that which would give the\ncurrent a greater mean velocity than thirteen inches per sec-\nond, in order that the bed of the feeder may not be injured.\nFeeders are furnished like ordinary canals, with contrivances\nto let off a part, or the whole, of the water in them, in cases\nof heavy rains, or for making repairs.\nBut a small proportion of the water collected by the feed-\ners is delivered at the reservoir; the loss from various causes\nbeing much greater in them than in canals. From observa-\ntions made on some of the feeders of canals in France, which\nhave been in use for a long period, it appears that the feeder\nof the Briare canal delivers only about one-fourth of the water\nit gathers from its sources of supply ; and that the annual loss\nof the two feeders of the Languedoo canal amounts to 100\ntimes the quantity of water which they can contain.\n789. A Reservoir is a large pond, or body of water, held in\nDigitized by Google\n476\nCIVIL ENGINEERING.\nreserve for the necessary supply of the summit level. A reser-\nvoir is usually formed by choosing a suitable site in a deep\nand narrow valley, which lies above the summit level, and\nerecting a dam of earth, or of masonry, across the outlet of\nthe valley, or at some more suitable point, to confine the\nwater to be collected. The object to be attained, in this case,\nis to embody the greatest volume of water, and at the same\ntime present the smallest evaporating surface, at the smallest\ncost for the construction of the dam.\nIt is generally deemed best to have two reservoirs for the\nsupply, one to contain the greater quantity of water, and the\nother, which is termed the distributing reservoir, to regulate\nthe supply to the summit level. If, however, the summit\nlevel is very capacious, it may be used as the distributing\nreservoir.\nThe proportion between the quantity of water that falls\nupon a given-surface, and that which can be collected from\nit for the supply of a reservoir, varies considerably with the\nlatitude, the season of the year, and the natural features of\nthe locality. The drainage is greatest in high latitudes, and\nin the winter and spring seasons; with respect to the natural\nfeatures, a wooded surface with narrow and deep valleys will\nyield a larger amount than an open flat country.\nBut few observations have been made on this point by en-\ngineers. From some by Mr. J. B. Jervis, in reference to the\nreservoirs for the Chenango canal, in the State of New York,\nit appears that in that locality about two-fifths of the quan-\ntity of rain may be collected for the supply of a reservoir.\nThe proportion usually adopted by engineers is one-third.\nThe loss of water from the reservoir by evaporation, filtra-\ntion, and other causes, will depend upon the nature of the,\nsoil, and the exposure of the water surface. From observa-\ntions made upon some of the old reservoirs in England and\nFrance, it appears that the daily loss averages about half an\ninch in depth.\n790. The dams of reservoirs have been variously con-\nstructed: in some cases they have been made entirely of\nearth (Fig. 240) in others, entirely of masonry; and in\nothers, of earth packed in between several parallel stone\nwalls. It is now thought best to use either earth or masonry\nalone, according to the circumstances of the case; the com-\nparative expense of the two methods being carefully con-\nsidered.\nEarthen dams should be made with extreme care, of the\nbest binding earth, well freed from everything that might\n,\nDigitized by\nGoogle\nCANALS.\n477\nB\nd\nFig. 940-Bepresents the section of a dam with three discharging culverta,\nA, body of the dam.\nB, pond.\na, a, a, culverts, with valves at their inlets, which discharge into the vertical well b.\na c, a grooves, in the faces of the side-walls, which form the entrance to the culverts, for stop-\nplank.\nd, stop-plank dam across the outlet of the bottom culvert, to dam back the water into the\nvertical well.\na, parapet wall on top of the dam.\ncause filtrations. A wide trench should be excavated to the\nfirm soil, to receive the base of the dam ; and the earth should\nbe carefully spread and rammed in layers not over a foot\nthick. As a farther precaution, it has in some instances been\nthought necessary to place a stratum of the best clay pud-\ndling in the centre of the dam, reaching from the top to three\nor four feet below the base. The dam may be from fifteen\nto twenty feet thick at top. The slope of the dam towards\nthe pond should be from three to six base to one perpendic-\nular; the reverse slope need only be somewhat greater than\nthe natural slope of the earth.\nThe slope of dams exposed to the water is usually faced\nwith dry stone, to protect the dam from the action of the\nsurface ripple. This kind of facing has not been found to\nwithstand well the action of the water when agitated by high\nwinds. Upon some of the more recent earthen dams erected\nin France, a facing of stone laid in hydraulic mortar has been\nsubstituted for the one of dry stone. The plan adopted for\nthis facing (Fig. 241) consists in placing a series of low walls,\nFig. 241-Represents the method of\nfacing the pond slope of a dam,\nwith low walls placed in offsets.\nA, body of the dam.\na, a, a, low walls the faces of which\nare built in offsets.\n0, b, top surface of the offsets be-\ntween the walls, covered with\nstone alabs laid in mortar.\na top of dam faced like the offects\nb.\na parapet wall.\nDigitized by Google\n478\nCIVIL ENGINEERING.\nin offsets above each other, along the slope of the dam, cover-\ning the exposed surface of each offset, between the top of one\nwall and the foot of the next, with a coating of slab-stone laid\nin mortar. The walls are from five to six feet high. They\nare carried up in small offsets upon the face, and are made\neither vertical, or leaning, on the back. The width of the off-\nsets of the dam, between the top of one wall and the foot of\nthe next, is from two to three feet.\nAn arched culvert, or a large cast-iron pipe, placed at some\nsuitable point of the base of the dam, which can be closed or\nopened by a valve, will serve for drawing off the requisite\nsupply of water, and for draining the reservoir in case of re-\npairs.\nThe culvert should be strongly constructed, and the earth\naround it be well puddled and rammed, to prevent filtrations.\nIts size should be sufficient for a man to enter it with ease.\nThe valves may be placed either at the entrance of the cul-\nvert, or at some intermediate point between the two ends.\nGreat care should be taken in their arrangement, to secure\nthem from accidents.\nWhen the depth of water in a reservoir is considerable, sev-\neral culverts should be constructed (Fig. 240), to draw off the\nwater at different levels, as the pressure upon the lower valves\nin this case would be very great when the reservoir is full.\nThey may be placed at intervals of about twelve feet above\neach other, and be arranged to discharge their water in a com-\nmon vertical shaft. In this case it will be well to place a dam\nof timber at the outlet of the bottom culvert, in order to keep\nit filled with water, to prevent the injury which the bottom\nof it might receive from the water discharged from the upper\nculverts.\nThe side walls which retain the earth at the entrance to the\nculverts should be arranged with grooves to receive pieces\nof scantling laid horizontally between the walls, termed stop-\nplanks, to form a temporary dam, and cut off the water of the\nreservoir, in case of repairs to the culverts, or to the face of\nthe dam.\nThe valves are small sliding gates, which are raised and\nlowered by a rack and pinion, or by a screw. The cross sec-\ntion of the culvert is contracted by a partition, either of ma-\nsonry or timber, at the point where the valve is placed.\n791. Dams of masonry are water-tight walls, of suitable\nforms and dimensions to prevent filtration, and resist the\npressure of water in the reservoir. The most suitable cross-\nsection is that of a trapezoid, the face towards the water being\nDigitized by\nGoogle\nCANALS.\n479\nvertical, and the exterior face inclined with a suitable batter\nto give the wall sufficient stability. The wall should be at\nleast four feet thick at the water line, to prevent filtration,\nand this thickness may be increased as circumstances may seem\nto require. Buttresses should be added to the exterior facing,\nto give the wall greater stability.\n792. Suitable dispositions should be made to relieve the\ndam from all surplus water during wet seasons. For this pur-\npose arrangements should be made for cutting off the sources\nof supply from the reservoir ; and a cut, termed a waste-weir\n(Fig 242), of suitable width and depth, should be made at some\npoint along the top of the dam, and be faced with stone, or\nwood, to give an outlet to the water over the dam. In high\ndams the total fall of the water should be divided into several\npartial falls, by dividing the exterior surface over which the\nwater runs into offsets. To break the shock of the water up-\non the horizontal surface of the offset, it should be kept cov-\nered with a sheet of water retained by a dam placed across\nits outlet.\na\nA\nb\nFig. 949-Represents a section of a waste-weir divided into two falls.\nA, body of the dam.\na, top of the waste-weir.\nb, pool, formed by a stop-plank dam at c, to break the fall of the water.\na, covering of loose stone to break the fall of the water from the pool above.\n793. In extensive reservoirs, in which a large surface is ex-\nposed to the action of the winds, waves might be forced over\nthe top of the dam, and subject it to danger; in such cases\nthe precaution should be taken of placing a parapet wall to-\nwards the outer edge of the top of the dam, and facing the\ntop throughout with flat stones laid in mortar.\n794. Lift of locks. The engineer is not always left free\nto select between the two systems-that of isolated locks and\nlocks in flights; for the form of the natural surface of the\nground may compel him to adopt a flight of locks at certain\npoints. As to the comparative expense of the two methods,\na flight is in most cases cheaper than the same number of\nsingle locks, as there are certain parts of the masonry which\nDigitized by Google\n480\nCIVIL ENGINEERING.\ncan be suppressed. There is also an economy in the suppres-\nsion of the small gates, which are not needed in flights. It is,\nhowever, more difficult to secure the foundations of combined\nthan of single locks from the effects of the water, which forces\nits way from the upper to the lower level under the locks.\nWhere an active trade is carried on, a double flight is some-\ntimes arranged; one for the ascending, the other for the\ndescending boats. In this case the water which fills one flight\nmay, after the passage of the boat, be partly used for the other,\nby an arrangement of valves made in the side wall separating\nthe locks.\nThe lift of locks is a subject of importance, both as regards\nthe consumption of water for the navigation, and the economy\nof construction. Locks with great lifts, as may be seen from\nthe remarks on the passage of boats, consume more water\nthan those with small lifts. They require also more care in\ntheir construction, to preserve them from accidents, owing to.\nthe great pressure of water against their sides. The expense.\nof construction is otherwise in their favor; that is, the ex-\npense will increase with the total number of locks, the\nheight to be ascended being the same. The smallest lifts are\nseldom less than five feet, and the greatest, for ordinary\ncanals, not over twelve medium lifts of seven or eight feet\nare considered the best under every point of view. This is a\npoint, however, which cannot be settled arbitrarily, as the\nnature of the foundations, the materials used, the embank-\nments around the locks, the changes in the direction of the\ncanal, caused by varying the lifts, are so many modifying\ncauses, which should be carefully weighed before adopting a\ndefinite plan.\nThe lifts of a flight should be the same throughout; but in\nisolated locks the lifts may vary according to circumstances.\nIf the supply of water from the summit level requires to be\neconomized with care, the lifts of locks which are furnished\nfrom it may be less than those lower down.\n795. Levels. The position and the dimensions of the\nlevels must be mainly determined by. the form of the natural\nsurface. Those points are naturally chosen to pass from one\nlevel to another, or as the positions for the locks, where there\nis an abrupt change in the surface.\nA level, by a suitable modification of its cross section, can\nbe made as short as may be deemed desirable; there being\nbut one point to be attended to in this, which is, that a boat\npassing between the two locks, at the ends of the level, will\nhave time to enter either lock before it can ground, on the\nDigitized\nby\nGoogle\nCANALS.\n481\na\nM\n10\nA\nFig. 243-Represents a plan M, and a section N, through the axis of a single lock laid on a be-\nton foundation.-A, lock-chamber. B, fore-bay. C, tail-bay. a, a, chamber-walls. b, b,\nrecesses or chambers in the side walls for upper gates. c, c, lower-gate chambers. d, d, lift\nwall and upper mitre sill. a, a, lower mitre sill. A, A, tail walls. o, o, head walls. m, m,\nupper wing, or return walls. n, 22, lower wing walls. D, body of masonry,under the fore-bay.\n31\nDigitized by Google\n482\nCIVIL INGINERING.\nsupposition that the water drawn off to fill the lower lock,\nwhile the boat is traversing the level, will just reduce the\ndepth to the draught of the boat.\n796. Locks. Å lock (Fig. 243) may be divided into three\ndistinct parts: 1st. The part included between the two gates,\nwhich is termed the chamber. 2d. The part above the upper\ngates, termed the fore, or head-bay. 3d. The part below the\nlower gates, termed the aft, or tail-bay.\n797. The lock chamber must be wide enough to allow an\neasy ingress and egress to the boats commonly used on the\ncanal ; a surplus width of one foot over the width of the boat\nacross the beam is usually deemed sufficient for this purpose.\nThe length of the chamber should be also regulated by that\nof the boats; it should be such, that when the boat enters the\nlock from the lower level, the tail-gates may be shut without\nrequiring the boat to unship its rudder.\nThe plan of the chamber is usually rectangular, as this form\nis, in every respect, superior to all others. In the cross seetion\nof the chamber (Fig. 244), the sides receive generally a slight\nA\nB\nA\nFig. 344-Represents a section of Fig. 248, through the\nchamber.\nA, A, chamber walls.\nB, chamber formed with all inverted-arch bottom.\nbatter; as when so arranged they are found to give greater fa-\ncility to the passage of the boat than when vertical. The bot-\ntom of the chamber is either flat or curved; more water will\nbe required. to fill the flat-bottomed chamber than the curved,\nbut it will require less masonry in its construction.\n798. The chamber is terminated just within the head gates\nby a vertical wall, the plan of which is usually curved. As\nthis wall separates the upper from the lower level, it is\ntermed the tiftwall; it is usually of the same height as the\nlift of the levels. The top of the lift-wall is formed of cut\nstone, the vertical joints of which are normal to the curved\nface of the wall this top course projects from six to nine\ninches above the bottom of the upper level, presenting an\nangular point, for the bottom of the head-gates, when shut,\nto rest against. This is termed the mitre-sill. Various de-\ngrees of opening have been given to the angle between the\ntwo branches of the mitre-sill; it is, however, generally so\nDigitized by Google\nCANALS\n483\ndetermined, that the perpendicular of the isosceles triangle,\nformed by the two branches, shall vary between one-fifth and\none-sixth of the base.\nAs stone mitre-sills are liable to injury from the shock of\nthe gate, they are now usually constructed of timber (Fig. 245),\nFig. 945-Represents a plan of a wooden mitre-sill,\nand a horisontal section of a lock-gate (Fig. 246)\nclosed.\na, a, mitre-sill framed with the pieces b and c, and\nfirmly fastened to the side walls A, A.\na, section of quoin posts of lock-gate.\na section of mitre posts.\nby framing two strong beams with the proper angle for the\ngate when closed, and securing them firmly upon the top of\nthe lift-wall. It will be well to place the top of the mitre-\nsill on the lift-wall a little lower than the bottom of the\ncanal, to preserve it from being struck by the keel of the boat.\non entering or leaving the lock.\n799. The cross section of the chamber walls is usually\ntrapezoidal; the facing receives a slight batter. The cham-\nber walls are exposed to two opposite efforts; the water in\nthe lock on one side, and the embankment against the wall\non the other. The pressure of the embankment is the greater\nas well as the more permanent effort of the two. The di-\nmensions of the wall must be regulated by this pressure.\nThe usual manner of doing this, is to make the wall four feet\nthick at the water line of the upper level, to secure it against\nfiltration; and then to determine the base of the batter, so\nthat the mass of masonry shall present sufficient stability to\ncounteract the tendency of the pressure. The spread, and\nother dimensions of the foundations, will be regulated accord-\ning to the nature of the soil, in the same way as in other\nstructures.\n800. The bottom of the chamber, as has been stated, may\nbe either flat or curved. The flat bottom is suitable to very\nfirm soils, which will neither yield to the vertical pressure of\nthe chamber walls, nor admit the water to filter from the\nupper level under the bottom of the lock. In either of the\ncontrary cases, the bottom should be made with an inverted\narch, as this form will oppose greater resistance to the up-\nward pressure of the water under the bottom, and will serve\nto distribute the weight of the walls over the portion of the\nfoundation under the arch. The thickness of the masonry of\nDigitized by Google\n484\nCIVIL ENGINEERING.\nthe bottom will depend on the width of the chamber and\nthe nature of the soil. Were the soil a solid rock, no bottom-\ning would be requisite; if it is of soft mud, a very solid bot-\ntoming, from three to six feet in thickness, might be re-\nquisite.\n801 The principal danger to the foundations arises from\nthe water which may filter from the upper to the lower level,\nunder the bottom of the lock. One preventive for this, but\nnot an effectual one, is to drive sheeting piles across the canal\nat the end of the head-bay; another, which is more expensive,\nbut more certain in its effects, consists in forming a deep\ntrench of two or three feet in width, just under the head-bay,\nand filling it with beton, which unites at the top with the\nmasonry of the head-bay. Similar trenches might be placed\nunder the chamber were it considered necessary.\n802. The lift-wall usually receives the same thickness as\nthe chamber walls; but, unless the soil is very firm, it would\nbe more prudent to form a general mass of masonry under\nthe entire head-bay, to a level with the base of the chamber\nfoundations, of which mass the lift-wall should form a part.\n803. The head-bay is enclosed between two parallel walls,\nwhich form a part of the side walls of the lock. They are\nterminated by two wing walls, which it will be found most\neconomical to run back at right angles with the side walls.\nA recess, termed the gate-chamber, is made in the wall of the\nhead-bay; the depth of this recess should be sufficient to\nallow the gate, when open, to fall two or three inches within\nthe facing of the wall, so that it may be out of the way when\na boat is passing; the length of the recess should be a few\ninches more than the width of the gate. That part of the\nrecess where the gate turns on its pivot is termed the hollow\nquoin; it receives what is termed the heel, or quoin-post of\nthe gate, which is made of a suitable form to fit the hollow\nquoin. The distance between the hollow quoins and the face\nof the lift-wall will depend on the pressure against the mitre-\nsill, and the strength of the stone, eighteen inches, will gener-\nally be found amply sufficient.\nThe side walls need not extend more than twelve inches\nbeyond the other end of the gate-chamber. The wing walls\nmay be extended back to the total width of the canal, but it\nwill be more economical to narrow the canal near the lock,\nand to extend the wing walls only about two feet into the\nbanks, or sides. The dimensions of the side and wing walls\nof the head-bay are regulated in the same way as the cham-\nber walls.\nDigitized\nby\nGoogle\nCANALS.\n485\nThe bottom of the head-bay is flat, and on the same level\nwith the bottom of the canal; the exterior course of stones\nat the entrance to the lock should be so jointed as not to\nwork loose.\n804. The gate-chambers for the lower gates are made\nin the chamber walls; and it is to be observed, that the bot-\ntom of the chamber, where the gates swing back, should be\nflat, or be otherwise arranged not to impede the play of the\ngates.\n805. The side walls of the tail-bay are also a part of\nthe general side walls, and their thickness is regulated as in\nthe preceding cases. Their length will depend chiefly on\nthe pressure which the lower gates throw against them when\nthe lock is full; and partly on the space required by the\nlock-men in opening and shutting gates manœuvred by the\nbalance beam. A calculation must be made for each par-\nticular case, to ascertain the most suitable length. The side\nwalls are also terminated by wing walls, similarly arranged\nto those of the head-bay. The points of junction between\nthe wing and side walls should, in both cases, either be\ncurved, or the stones at the angles be rounded off. One or\ntwo perpendicular grooves are sometimes made in the side\nwalls of the tail-bay, to receive stop-planks, when a tempo-\nrary dam is needed, to shut off the water of the lower level\nfrom the chamber, in case of repairs, etc. Similar arrange-\nments might be made at the head-bay, but they are not indis-\npensable in either case.\nThe strain on the walls at the hollow quoins is greater\nthan at any other points, owing to the pressure at those\npoints from the gates, when they are shut, and to the action\nof the gates when in motion; to counteract this, and\nstrengthen the walls, buttresses should be placed at the back\nof the walls in the most favorable position behind the quoins\nto subserve the object in view.\nThe bottom of the tail-bay is arranged, in all respects, like\nthat of the head-bay.\n806. The top of the side walls of the lock may be from\none to two feet above the general level of the water in the\nupper reach; the top course of the masonry being of heavy\nlarge blocks of cut stone, although this kind of coping is not\nindispensable, as smaller masses have been found to suit the\nsame purpose, but they are less durable. As to the masonry\nof the lock in general, it is only necessary to observe that\nthose parts alone need be of cut stone where there is great\nwear and tear from any cause, as at the angles generally ; or\nDigitized by Google\n486\nCIVIL ENGINEERING.\nwhere an accurate finish is indispensable, as at the hollow\nquoins. The other parts may be of brick, rubble, beton, etc.,\nbut every part should be laid in the best hydraulic mortar.\n807. The filling and emptying the lock chamber have\ngiven rise to various discussions and experiments, all of which\nhave been reduced to the comparative advantages of letting\nthe water in and off by valves made in the gates themselves,\nor by culverts in the side walls, which are opened and shut\nby valves. When the water is let in through valves in. the\ngates, its effects on the sides and bottom of the chamber are\nfound to be very injurious, particularly in high lift-walls;\nbesides the inconvenience resulting from the agitation of the\nboat in the lock. To obviate this, in some degree, it has been\nproposed to give the lift-wall the form of an inclined curved\nsurface, along which the water might descend without pro-\nducing a shock on the bottom.\n808. The side culverts are small arched conduits, of a\ncircular or an elliptical cross section, which are made in the\nmass of masonry of the side walls, to convey the water from\nthe upper level to the chamber. These culverts, in some\ncases, run the entire length of the side walls, on a level with\nthe bottom of the chamber, from the lift-wall to the end of\nthe tail-wall, and have several outlets, leading to the chamber.\nThey are arranged with two valves, one to close the mouth\nof the culvert, at the upper level, the other to close the out-\nlet from the chamber, to the lower level. This is, perhaps,\none of the best arrangements for side culverts. They all\npresent the same difficulty in making repairs when out of\norder, and they are moreover very subject to accidents.\nThey are therefore on these accounts inferior to valves in the\ngates.\n809. It has also been proposed, to avoid the inconveniences\nof culverts, and the disad vantages of lift-walls, by suppress-\ning the latter, and gradually increasing the depth of the\nupper level to the bottom of the chamber. This method\npresents a saving in the mass of masonry, but the gates will\ncost more, as the head and tail gates must be of the same\nheight. It would entirely remove the objection to valves in\nthe gates, as the current through them, in this case, would\nnot be sufficiently strong to injure the masonry.\n810. The bottom of the canal below the lock should be pro-\ntected by what is termed an apron, which is a covering of\nplank laid on a grillage, or else one of brushwood and dry\nstone. The sides should also be faced with timber or dry stone.\nThe length of this facing will depend on the strength of the\nDigitized\nby\nGoogle\nCANALS.\n487\ncurrent; generally not more than from fifteen to thirty feet\nfrom the lock will require it. The entrance to the head-bay\nis, in some cases, similarly protected, but this is unnecessary,\nas the current has but a very slight effect at that point.\n811. Locks constructed of timber and dry stone, termed\ncomposite-locks, are to be met with on several of the canals of\nthe United States. The side walls are formed of dry stone\ncarefully laid ; the sides of the chamber being faced with\nplank nailed to horizontal and upright timbers, which are firm-\nly secured to the dry stone walls. The walls rest upon a plat-\nform laid upon heavy beams placed transversely to the axis\nof the lock. The bottom of the chamber usually receives a\ndouble thickness of plank. The quoin-posts and mitre-sills\nare formed of heavy beams.\n812. Lock Gates. A lock gate (Fig. 246) is composed of\nE\nm\nFig. 246-Represents\nthe elevation of a\nlock-gate closed.\na, a, quoin-pests.\nb, mitre-posts.\na c, cross pieces\nframed into-a and\na\nc\na\nb, and firmly con-\nb\nnected with them\nby wrought-iron\nplates.\no, plank or sheath-\ning of the gate.\nd, valve.\nm,m, balance-beams.\nd\nd\ntwo leaves, each leaf consisting of a solid framework covered\non the side towards the water with thick plank made water-\ntight. The frame usually consists of two uprights, of several\nhorizontal cross pieces let. into the uprights, and sometimes a\ndiagonal piece or brace, intended to keep the frame of an in-\nvariable form, is added. The upright, around which the leaf\nturns, termed the quoin or heel-post, is rounded off on the back\nto fit in the hollow quoin; it is made slightly eccentric with it,\nso that it may turn easily without rubbing against the quoin ;\nits lower end rests on an iron gudgeon, to which it is fitted by\na corresponding indentation in an iron socket on the end ; the\nupper extremity is secured to the side walls by an iron collar,\nwithin which the post turns. The collar is so arranged that\nit can be easily fastened to, or loosened from, two iron bars,\nDigitized by Google\n488\nCIVIL ENGINEERING.\ntermed anchor-irons, which are firmly attached by bolts, or a\nlead sealing, to the top course of the walls. One of the anchor-\nirons is placed in a line with the leaf when shut, the other in\na line with it when open, to resist most effectually the strain\nin those two positions of the gate. The opposite upright,\ntermed the mitre-post, has one edge bevelled off to fit against\nthe mitre-post of the other leaf of the gate.\n813. A long heavy beam, termed a balance-beam, from its\npartially balancing the weight of the leaf, rests on the quoin-\npost, to which it is secured, and is mortised with the mitre-\npost. The balance-beam should be about four feet above the\ntop of the lock, to be readily manceuvred; its principal use\nbeing to open and shut the leaf.\n814. The top cross piece of the gate should be about on a\nlevel with the top of the lock; the bottom cross piece should\nswing clear of the bottom of the lock. The position of the\nintermediate cross pieces may be made to depend on their\ndimensions: if they are of the same dimensions, they should\nbe placed nearer together at the bottom, as the pressure of the\nwater is there greatest; but, by making them of unequal di-\nmensions, they may be placed at equal distances apart; this,\nhowever, is not of much importance except for large gates,\nand considerable depths of water.\nThe plank may be arranged either parallel to the uprights,\nor parallel to the diagonal brace in the latter position they\nwill act with the brace to preserve the form of the frame.\n815. A wide board, supported on brackets, is often affixed\nto the gates, both for the manœuvre of the machinery of the\nvalves, and to serve as a foot-bridge across the lock. The\nvalves are small gates which are arranged to close the open-\nings made in the gates for letting in or drawing off the water.\nThey are arranged to slide up and down in grooves, by the\naid of a rack and pinion, or a square screw or they may be\nmade to open or shut by turning on a vertical axis, in which\ncase they are termed paddle gates. The openings in the up-\nper gates are made between the two lowest cross pieces. In\nthe lower gates the openings are placed just below the surface\nof the water in the reach. The size of the opening will\ndepend on the time in which it is required to fill the lock.\n816. Accessory Works. Under this head are classed those\nconstructions which are not a part of the canal proper, although\ngenerally found necessary on all canals: as the culverts for\nconveying off the water-courses which intersect the line of the\ncanal; the inlets of feeders for the supply of water; aqueduct\nbridges, etc., etc.\nDigitized by Google\nCANALS.\n489\n817. Culverts. The disposition to be made of water-courses\nintersecting the line of the canal will depend on their size,\nthe character of their current, and the relative positions of\nthe canal and stream.\nSmall brooks which lie lower than the canal may be con-\nveyed under it through an ordinary culvert. If the level of\nthe canal and brook is nearly the same, it will then be neces-\nsary to make the culvert in the shape of an inverted syphon,\nand it is therefore termed a broken-back culvert. If the\nwater of the brook is generally limpid, and its current gentle,\nit may, in the last case, be received into the canal. The\ncommunication of the brook, or feeder, with the canal, should\nbe so arranged that the water may be shut off, or let in at\npleasure, in any quantity desired. For this purpose a cut is\nmade through the side of the canal, and the sides and bottom\nof the cut are faced with masonry laid in hydraulic mortar.\nA sliding gate, fitted into two grooves made in the side walls,\nis manœuvred by a rack and pinion, so as to regulate the\nquantity of water to be let in. The water of the feeder, or\nbrook, should first be received in a basin, or reservoir, near\nthe canal, where it may deposit its sediment before it is drawn\noff. In cases where the line of the canal is crossed by a tor-\nrent, which brings down a large quantity of sand, pebbles,\netc., it may be necessary to make a permanent structure over\nthe canal, forming a channel for the torrent; but if the dis-\ncharge of the torrent is only periodical, a movable channel\nmay be arranged, for the same purpose, by constructing a\nboat with a deck and sides to form the water-way of the tor-\nrent. The boat is kept in a recess in the canal near the point\nwhere it is used, and is floated to its position, and sunk when\nwanted.\n818. Aqueduots, etc. When the line of the canal is inter-\nsected by a wide water-course, the communication between\nthe two shores must be effected either by a canal aqueduct\nbridge, or by the boats descending from the canal into the\nstream. As the construction of aqueduct bridges has already\nbeen considered, nothing farther on this point need here be\nadded. The expedient of crossing the stream by the boats\nmay be attended with many grave inconveniences in water-\ncourses liable to freshets, or to considerable variations of level\nat different seasons. In these cases locks must be so arranged\non each side, where the canal enters the stream, that boats\nmay pass from the one to the other under all circumstances\nof difference of level between the two. The locks and the\nportions of the canal which join the stream must be secured\nDigitized by Google\n490\nCIVIL ENGINEERING.\nagainst damage from freshets by suitable embankments; and,\nwhen the summer water of the stream is so low that the\nnavigation would be impeded, a dam across the stream will\nbe requisite to secure an adequate depth of water during this\nepoch.\n819. Canal-Bridges. Bridges for roads over a canal, termed\ncanal-bridges, are constructed like other structures of the\nsame kind. In planning them the engineer should endeavor\nto give sufficient height to the bridge to prevent those acci-\ndents, of but too frequent occurrence, from persons standing\nupright on the deck of the passage-boat while passing under\na bridge.\nA novel device, which, on account of its diminutive size, is\nhardly worthy of the name of a bridge, is used for crossing\nthe canal at Williamsport, Pennsylvania. It is really a small\npivot bridge, so constructed that a boat may push it open either\nway as desired as it passes through, and which will close itself\nafter the boat has passed. As it opens it moves up an in-\nelined plane, SO that its weight will aid in closing it. A\nweight, which is attached to a rope at one end, the rope\npassing over a pulley and attached to the bridge at the other,\nis also employed in closing it.\n820. Waste-Weir. Waste-weirs must be made along the\nlevels to let off the surplus water. The best position for them\nis at points where they can discharge into natural water-\ncourses. The best arrangement for a waste-weir is to make\na cut through the side of the canal to a level with the bottom\nof it, so that. in case of necessity, the waste-weir may also\nserve for draining the level. The sides and bottom of the cnt\nmust be faced with masonry, and have grooves left in them\nto receive stop-plank, or a sliding gate, over which the sur-\nplus water is allowed to flow, under the usual circumstances,\nbut which can be removed, if it be found necessary, either\nto let off a larger amount of water, or to drain the level\ncompletely.\n821. Temporary Dams. In long levels an accident hap-\npening at any one point might cause serious injury to the\nnavigation, besides a great loss of water. To prevent this, in\nsome measure, the width of the canal may be diminished, at\nseveral points of a long level, to the width of a lock, and the\nsides, at these points, may be faced with masonry, arranged\nwith grooves and stop-planks, to form a temporary dam for\nshutting off the water on either side.\n822. Tide, or Guard Lock. The point at which a canal\nenters a river requires to be selected with judgment. Gen-\nDigitized\nby\nGoogle\n-CANALS.\n491\nerally speaking, a bar will be found in the principal water-\ncourse at or below the points where it receives its affluents.\nWhen the canal, therefore, follows the valley of an affluent,\nits outlet should be placed below the bar, to render its navi-\ngation permanently secure from obstruction. A large basin\nis usually formed at the outlet, for the convenience of com-\nmerce; and the entrance from this basin to the canal, or from\nthe river to the basin, is effected by means of a lock with\ndouble gates, so arranged that a boat can be passed either\nway, according as the level in the one is higher or lower than\nthat in the other. A lock 80 arranged is termed a tide or\nguard lock, from its uses. The position of the tail of this\nlock is not indifferent in. all cases where it forms the outlet to\nthe river; for, were the tail placed пр stream, it would be\nmore difficult to pass in or out than if it were down stream.\n823. The general dimensions of canals and their locks in\nthis country and in Europe, with occasional exceptions, do not\ndiffer in any considerable degree.\nEnglish Canals. Two classes of canals are to be met\nwith in England, differing materially in their dimensions.\nThe following are the usual dimensions of the cross section\nof the largest size, and those of their locks\nWidth of section at the water level, from 36 to 40 feet.\nWidth at bottom\n24 \"\nDepth\n5 \"\nLength of lock between mitre sills\n75. to 80 \"\nWidth of chamber\n15\n\"\nThe Caledonian canal, in Scotland, which connects Loch\nEil on the Western sea with Murray Firth on the Eastern, is\nremarkable for its size, which will admit of the passage of\nfrigates of the second class. The following are the principal\ndimensions of the cross section of the canal and its locks :-\nWidth of canal at the water level\n110 feet.\nWidth at bottom\n50 \"\nDepth of water\n20 \"\nWidth of berm\n6 \"\nLength of loek between mitre-sills\n180 \"\nWidth of chamber at top\n40 \"\nLift of lock.\n8 \"\nThe side walls of the locks are built with a curved batter,\nthey are of the uniform thickness of 6 feet, and are strength-\nened by counterforts, placed about 15 feet apart, which are\n4 feet wide and of the same thickness. The bottom of the\nchamber is formed with an inverted arch.\nDigitized by Google\n492\nCIVIL ENGINEERING.\nFrench Canals. In France the following uniform system\nhas been established for the dimensions of canals and their\nlocks :-\nWidth of canal at water level\n52 feet.\nWidth at bottom\n33 to 36 \"\nDepth of water\n5 \"\nLength of lock between mitre-sills.\n115 \"\nWidth of lock.\n17 \"\nThe boats adapted to these dimensions are from 105 to 108\nfeet long, 161 feet across the beam, and have 2 draught of 4\nfeet.\nWidth of canal at top\n50 feet.\nWidth at bottom\n30 \"\nDepth of water\n5 \"\nLength of locks\n100 \"\nWidth of locks.\n15\n\"\nThe Rideau canal, which connects Lake Ontario with the\nRiver Ottawa, is arranged for steam navigation. A consider-\nable portion of this line consists of slack-water navigation,\nformed by connecting the natural water-courses between the\noutlets of the canal. The length of the locks on this canal is\n134 feet between the mitre-sills, and their width 33 feet.\nThe Welland canal, between lakes Erie and Ontario, as ori-\nginally constructed, received the following dimensions :-\nWidth of canal at top\n56 feet.\nWidth at bottom\n24 \"\nDepth of water\n8 \"\nLength of locks between mitre-sills\n110 \"\nWidth of locks\n22 \"\nThe canals and locks made to avoid the dangerous rapids\nof the St. Lawrence are in all respects among the largest in\nthe world. The following are the dimensions of the por-\ntion of the canal and the locks between Long Sault and Corn-\nwall :-\nWidth of canal at top\n132 feet.\nWidth at bottom\n100 \"\nDepth of water\n8 \"\nWidth of tow-path.\n12 \"\nLength of locks between mitre-sills.\n200 \"\nWidth of locks at top\n56.6 \"\nWidth of locks at bottom\n43 \"\nA berm of 5 feet is left on each side between the water-\nDigitized by Google\nCANALS.\n493\nway and the foot of the interior slope of the tow-path. The\nheight of the tow-path is 6 feet above the berm. By increas-\ning the depth of water in the canal to 10 feet, the water-line\nat top can be increased to 150 feet.\nThe dimensions of the Erie canal as enlarged are :-\nWidth of canal at top, with bench walls\n81 feet.\nWidth of canal at top, without bench walls. 75 \"\nWidth of canal at water surface\n70\n\"\nWidth of canal at bottom, with bench walls. 42\n\"\nWidth of canal at bottom, without bench\nwalls\n521 \"\nDepth of water\n7 \"\nWidth of tow-path\n14 \"\nWidth of locks at top\n18 \" 10 in.\nWidth of locks at bottom\n17 \" 41 in.\nLength of lock (between mitre-sills)\n110 \"\n824. Locomotion on Canals. In early times boats were\ndrawn or pushed along by servants or slaves. In civilized\ncountries horses and mules have been chiefly used. A few\nyears since several attempts were made to use steam power,\nby driving the boat like a propeller, and although it would\ndo the work, yet it was mostly abandoned after a few months.\nThe wheel created such a disturbance in the water as caused\nit to wash the banks and thus damage them.\nA system, known as the Belgian system, has been quite\nextensively used in some of the European countries. It con-\nsists of a cable which passes from one end of the canal to the\nother, and is sunk in it. It is wound around a wheel which\nis at one end of the boat. Steam power is applied to turn\nthe wheel, and, as the friction of the rope on the wheel pre-\nvents it from slipping, it will take up the cable on one side of\nthe wheel and let it out on the other, and thus draw the boat\nalong. One of the objections to this plan is, it requires a\nlarge amount of slack cable to accommodate a large traffic,\nand every boat must draw in all the slack every time it passes\nover the canal.\nDuring the winter of 1870-71 the Legislature of the State\nof New York offered a prize of $100,000 to the party who\nwould make an acceptable mode of applying steam for pro-\npelling canal boats on the canals, and no plan was to be con-\nsidered which involved the Belgian system. The engineer in\ncharge of this project states that in round numbers a thousand\nplans, coming from all parts of the world, have been presented,\nbut up to the present time the prize has not been awarded.\nDigitized by Google\n494\nCIVIL ENGINEERING.\nCHAPTER IX.\nRIVERS.\n825. Natural features of Rivers. All rivers present the\nsame natural features and phenomena, which are more or less\nstrongly marked and diversified by the character of the re-\ngion through which they flow. Taking their rise in the high-\nlands, and gradually descending thence to some lake, or sea,\ntheir beds are modified by the nature of the soil of the val-\nleys in which they lie, and the velocities of their currents are\naffected by the same cause. Near their sources, their beds\nare usually rocky, irregular, narrow, and steep, and their\ncurrents are rapid. Approaching their outlets, the beds be-\ncome wider and more regular, the declivity less, and the cur-\nrent more gentle and uniform. In the upper portions of the\nbeds, their direction is more direct, and the obstructions met\nwith are usually of a permanent character, arising from the\ninequalities of the bottom. In the lower portions, the beds\nassume a more tortuous course, winding through their val-\nleys, and forming those abrupt bends, termed elbows, which\nseem subject to no fixed laws; and here are found those ob-\nstructions, of a more changeable character, termed bars,\nwhich are caused by deposites in the bed, arising from the\nwear of the banks by the current.\n826. The relations which are found to exist between the\ncross section of a river, its longitudinal slope, the nature of\nits bed, and its volume of water, are termed the regimen of\nthe river. When these relations remain permanently invari-\nable, or change insensibly with time, the river is said to have\na fixed regimen.\nMost rivers acquire in time a fixed regimen, although peri-\nodically, and sometimes accidentally, subject to changes from\nfreshets caused by the melting of snow, and heavy falls of\nrain. These variations in the volume of water thrown into\nthe bed cause corresponding changes in the velocity of the\ncurrent, and in the form and dimensions of the bed. These\nchanges will depend on the character of the soil, and the\nwidth of the valley. In narrow valleys, where the banks do\nnot readily yield to the action of the current, the effects of\nDigitized by Google\n495\nany variation of velocity will only be temporarily. to deepen.\nthe bed. In wide valleys, where the soil of the banks is\nmore easily worn by the current than the bottom, any in-\ncrease in the volume of water will widen the bed; and if\none bank yields. more than the other, an elbow will be\nformed, and the position of the bed will be gradually shifted\ntowards the concave side of the elbow.\n827. The formation of elbows occasions also variations in\nthe depth and velocity of the water. The greatest depth is\nfound at the concave side. At the straight portions which\nconnect two elbows, the depth is found to decrease, and the\nvelocity of the current to increase. The bottom of the bed\nthus presents a series of undulations, forming shallows and\ndeep pools, with rapid and gentle currents.\n828. Bars are formed at. those points, where from any\ncause the velocity of the current receives a sudden check.\nThe particles suspended in the water, or borne along over the\nbottom of the bed by the current, are deposited at these\npoints, and continue to accumulate, until, by the gradual fil-\nling of the bed, the water acquires sufficient velocity to bear\nfarther on the particles that reach the bar, when the river at\nthis point acquires and retains a fixed regimen, until die-\nturbed by some new cause.\n829. The points at which these changes of velocity usually\ntake place, and near which bars are found, are at the junc-\ntion of a river with its affluents, at those points where the\nbed of the river receives a considerable increase in width, at\nthe straight portions of the bed between elbows, and at the\nontlet of the river to the sea. The character of the bars will\ndepend upon that of the soil of the banks, and the velocity\nof the current. Generally speaking, the bars in the upper\nportions of the bed will be composed of particles which are\nlarger than those by which they are formed lower down.\nThese accumulations at the mouths of large rivers form in\ntime extensive shallows, and great obstructions to the dis-\ncharge of the water during the seasons of freshets. The\nriver then, not finding a sufficient outlet by the ordinary\nchannel, excavates for itself others through the most yielding\nparts of the deposites. In this manner are formed those\nfeatures which characterize the outlets of many large rivers,\nand which are termed delta, after the name given to the pe-\nculiar shape of the outlets of the Nile.\n830. River Improvements. There is no subject that\nfalls within the province of the engineer's art, that presents\ngreater difficulties and more uncertain issues than the im-\nDigitized by\nGoogle\n496\nCIVIL ENGINEERING.\nprovement of rivers. Ever subject to important changes in\ntheir regimen, as the regions by which they are fed are\ncleared of their forests and brought under cultivation, one\ncentury sees them deep, flowing with an equable current, and\nliable only to a gradual increase in volume during the sea-\nsons of freshets; while the next finds their beds a prey to\nsudden and great freshets, which leave them, after their vio-\nlent passage, obstructed by ever shifting bars and elbows.\nBesides these revolutions brought about in the course of\nyears, every obstruction temporarily placed in the way of the\ncurrent, every attempt to guard one point from its action by\nany artificial means, inevitably produces some corresponding\nchange at another, which can seldom be foreseen, and for\nwhich the remedy applied may prove but a new cause of\nharm. Thus, a bar removed from one point is found gradu-\nally to form lower down; one bank protected from the cur-\nrent's force transfers its action to the opposite one, on any\nincrease of volume from freshets, widening the bed, and\nfrequently giving a new direction to the channel. Owing\nto these ever varying causes of change, the best weighed\nplans of river improvement sometimes result in complete\nfailure.\n831. In forming a plan for a river improvement, the\nprincipal objects to be considered by the engineer, are, 1st.\nThe means to be taken to protect the banks from the action\nof the current. 2d. Those to prevent inundations of the sur-\nrounding country. 3d. The removal of bars, elbows and other\nnatural obstructions to navigation. 4th. The means to be re-\nsorted to for obtaining a suitable depth of water for boats, of\na proper tonnage, for the trade on the river.\n832. Means for protecting the banks. To protect the\nbanks, either the velocity of the current in-shore must be de-\ncreased so as to lessen its action on the soil; or else a facing\nof some material sufficiently durable to resist its action must\nbe employed. The former method may be used when the\nbanks are low and have a gentle declivity. The simplest plan\nfor this purpose consists either in planting such shrubbery on\nthe declivity as will thrive near water; or by driving down\nshort pickets and interlacing them with twigs, forming a kind\nof wicker-work. These constructions break the force of the\ncurrent, and diminish its velocity near the shore, and thus\ncause the water to deposit its finer particles, which gradually\nfill out and strengthen the banks. If the banks are high, and\nare subject to cave in from the action of the current on their\nbase, they may be either cut down to a gentle declivity, as in\nDigitized by\nGoogle\nRIVERS.\n497\nthe last case or else they may receive a slope of nearly 45°,\nand be faced with dry stone, care being taken to secure the\nbase by blocks of loose stone, or by a facing of brush and stone\nlaid in alternate layers.\n833. Measures against inundations. At the points in\nthe course of a river where inundations are to be apprehend-\ned, the water-way, if practicable, should be increased all\nobstructions to the free discharge of the water below the point\nshould be removed; and dikes of earth, usually termed levées,\nshould be raised on each side of the river. By increasing the\nwater-way a temporary improvement only will be effected\nfor, except in the season of freshets, the velocity of the cur-\nrent at this point will be so much decreased as to form de-\nposites, which, at some future day, may prove a cause of\ndamage. In confining the water between levées, two methods\nhave been tried the one consists in leaving a water-way strict-\nly necessary for the discharge of freshets; the other in giving\nthe stream a wide bed. The Po in Italy and the Mississippi\npresent examples of the former method; the effect of which\nin both cases has been to raise the bed of the stream so much\nthat in many parts the water is habitually above the natural\nsurface of the country, leaving it exposed to serious inunda-\ntions should the levées give way. The other method has been}\ntried on the Loire in France, and observation has proved that\nthe general level of the bed has not sensibly risen for a long\nseries of years; but it has been found that the bars, which are\nformed after each freshet, are shifted constantly by the next,'\nSO that when the waters have subsided to their ordinary state,\nthe navigation is extremely intricate from this cause. Other\nmeans have been tried, such as opening new channels at the\nexposed points, or building dams above them to keep the\nwater back; but they have all been found to afford only a tem-\nporary relief.\n834. Elbows. The constant wear of the bank, and shift-\ning of the channel towards the concave side of elbows, have\nled to various plans for removing the inconveniences which\nthey present to navigation. The method which has been\nmost generally tried for this purpose consists in building out\ndikes, termed wing-dams, from the concave side into the\nstream, placing them either at right angles to the thread of\nthe current, or obliquely down stream, 80 as to deflect the cur-\nrent towards the opposite shore.\nWing-dams are usually constructed either of blocks of\nstone, of crib-work formed of heavy timbers filled in with\nbroken stone, or of alternate layers of gravel and fascines.\n32\nDigitized by Google\n498\nCIVIL ENGINEERING.\nWithin a few years back, wing-dams, consisting simply of a\nseries of vertical frames, or ribs (Fig. 247), strongly con-\nnected together, and covered on the up-stream side by thick\nplank, which present a broken inclined plane to the current,\nthe lower part of which is less steep than the upper, have\nbeen used upon the Po, with, it is stated, complete success,\nfor arresting the wear of a bank by the current. These\ndams are placed at some distance above the point to be pro-\ntected, and their plan is slightly convex on the up-stream side.\n6\n9\nFig. 247-Represents a section of the timber wing-dams on the Po, formed of plank nailed on\nthe inclined pieces of the ribs.\na b and bc, inclined faces of the dam, the first making an angle of 63°, and the second of 23°\nwith the horizon.\na and e pieces of the rib.\nI and g horizontal pieces connecting the ribs.\nWing-dams of the ordinary form and construction are now\nregarded, from the experience of a long series of years on the\nRhine, and some other rivers in Europe, as little seviceable,\nif not positively hurtful, as a river improvement, and the\nabandonment of their use has been strongly urged by engi-\nneers in France.\nThe action of the current against the side of the dam\ncauses whirls and counter-currents, which are found to un-\ndermine the base of the dam, and the bank adjacent to it.\nShallows and bars are formed in the bed of the stream, near\nthe dam, by the débris borne along by the current after it\npasses the dam, giving very frequently a more tortuous course\nto the channel than it had naturally assumed in the elbow.\nDigitized by\nGoogle\nRIVERS.\n499\nThe best method yet found of arresting the progress of an\nelbow is to protect the concave bank by a facing of dry\nstone, formed by throwing in loose blocks of stone along the\nfoot of the bank, and giving them the slope they naturally\nassume when thus thrown in.\nWing-walls were put into the Hudson River many years\nsince for the purpose of removing the bars and improving\nthe stream for navigable purposes. The result has been that\nthey produced a scour in the narrowed part of the stream\nwhich removed the sand and other materials of the bar to\npoints lower down in the stream where it was again depos-\nited; thus removing the previous obstruction only to produce\na worse one in a new place.\nGen. Totten, in an able report to the Government on the\nimprovement of rivers having bars, showed very clearly the\nerror of attempting to improve rivers by means of wing-dams.\nHe recommended the establishment of a uniform channel by\nlongitudinal dikes, made of continuous piles or of walls of\nmasonry. This plan has been adopted more recently and\nwith good results.\n835. Elbows upon most rivers finally reach that state of\ndevelopment in which the wear upon the concave side, from\nthe action of the current, will be entirely suspended, and the\nregimen of the river at these points will remain stable. This\nstate will depend upon the nature of the soil of the banks\nand bed, and the character of the freshets. From observa-\ntions made upon the Rhine, it is stated that elbows, with a\nradius of curvature of nearly 3,000 yards, preserve a fixed\nregimen; and that the banks of those which have a radius of\nabout 1,500 yards are seldom injured, if properly faced.\n836. Attempts have, in some cases, been made to shorten\nand straighten the course of a river, by cutting across the\ntongue of land that forms the convex bank of the elbow, and\nturning the water into a new channel. It has generally been\nfound that the stream in time forms for itself a new bed of\nnearly the same character as it originally had.\n837. Bars. To obtain a sufficient depth of water over\nbars, the deposite must either be scooped up by machinery,\nand be conveyed away, or be removed by giving an increased\nvelocity to the current. When the latter plan is preferred,\nan artificial channel is formed, by contracting the natural\nway, confining it between two low dikes, which should rise\nonly a little above the ordinary level of low water, so that a\nsufficient outlet may be left for the water during the season\nof freshets, by allowing it to flow over the dams.\nDigitized by Google\n500\nCIVIL ENGINEERING.\nIf the river separates into several channels at the bar, dams\nshould be built across all except the main channel, so that by\nthrowing the whole of the water into it the effects of the cur-\nrent may be greater upon the bed.\nThe longitudinal dikes, between which the main channel\nis confined, should be placed as nearly as practicable in the\ndirection which the channel has naturally assumed. If it be\ndeemed advisable to change the position of the channel, it\nshould be shifted to that side of the bed which will yield most\nreadily to the action of the current.\n838. In situations where large reservoirs can be formed\nnear the bar, the water from them may be used for removing\nit. For this purpose an outlet is made from the reservoir, in\nthe direction of the bar, which is closed by a gate that turns\nupon a vertical axis, and is so arranged that it can be sudden-\nly thrown open to let off the water. The chase of water\nformed in this way sweeping over the bar will prevent the\naccumulation of deposites upon it. This plan is frequently\nresorted to in Europe for the removal of deposites that accu-\nmulate at the mouth of harbors in those localities where, from\nthe height to which the tide rises, a great head of water can be\nobtained in the reservoirs.\n839. In the improvement of the mouths of rivers which\nempty into the sea through several channels, no obstruction\nshould be placed to the free ingress of the tides through all\nthe channels. If the main channel is subject to obstructions\nfrom deposites, dams should be built across the secondary\nchannels, which may be SO arranged with cuts through them,\nclosed by gates, that the flood-tide will meet with no obstruc-\ntion from the gates, while the ebb-tide, causing the gates to\nclose, will be forced to recede through the main channel,\nwhich, in this way, will be daily scoured, and freed from de-\nposites by the ebb current. The same object may be effected\nby building dams without inlets across the secondary channels,\ngiving them such a height that at a certain stage of the flood-\ntide the water will flow over them and fill the channels above\nthe dams. The portion of water thus dammed in will be\nforced through the main channel at the ebb.\n840. When the bed is obstructed by rocks, it may be deep-\nened by blasting the rocks, and removing the fragments with\nthe assistance of the diving-bell and other machinery.\n841. In some of our rivers, obstructions of a very danger-\nous character to boats are met with, in the trunks of large\ntrees which are embedded in the bottom at one end, while the\nother is near the surface they are termed snags and sawyers\nDigitized by\nGoogle\nRIVERS.\n501\nby the boatmen. These obstructions have been very success-\nfully removed, within late years, by means of machinery, and\nby propelling two heavy boats, moved by steam, which are\nconnected by a strong beam across their bows, so that the\nbeam will strike the snag, and either break it off near the\nbottom or uproot it. Other obstructions, termed rafts, form-\ned by the accumulation of drift-wood at points of a river's\ncourse, are also found in some of our western rivers. These\nare also in process of removal, by cutting through them by\nvarious means which have been found successful.\n842. Slack-water Navigation. When the general depth\nof water in a river is insufficient for the draught of boats of\nthe most suitable size for the trade on it, an improvement,\ntermed slack-water or lock and dam navigation, is resorted\nto. This consists in dividing the course into several suitable\nponds, by forming dams to keep the water in the pond at a\nconstant head; and by passing from one pond to another by\nlocks at the ends of the dams.\n843. The position of the dams, and the number requisite,\nwill depend upon the locality. In streams subject to heavy\nfreshets, it will generally be advisable to place the dams at\nthe widest parts of the bed, to obtain the greatest outlet for the\nwater over the dam. The dams may be built either in a\nstraight line between the banks and perpendicular to the\nthread of the current, or they may be in a straight line ob-\nlique to the current, or their plan may be convex, the convex\nsurface being up-stream, or it may be a broken line present-\ning an angle up-stream. The three last forms offer a greater\noutlet than the first to the water that flows over the dain, but\nare more liable to cause injury to the bed below the stream,\nfrom the oblique direction which the current may receive,\narising from the form of the dam at top.\n844. The cross section of a dam is usually trapezoidal, the\nface up-stream being inclined, and the one down-stream\neither vertical or inclined. When the down-stream face is\nvertical, the velocity of the water which flows over the dam\nis destroyed by the shock against the water of the pond below\nthe dam, but whirls are formed which are more destructive\nto the bed than would be the action of the current upon it\nalong the inclined face of a dam. In all cases the sides and\nbed of the stream, for some distance below the dam, should\nbe protected from the action of the current by a facing of dry\nstone, timber, or any other construction of sufficient dura-\nbility for the object in view.\n845. The dams should receive a sufficient height only to\nDigitized by Google\n502\nCIVIL ENGINEERING.\nmaintain the requisite depth of water in the ponds for the\npurposes of navigation. Any material at hand, offering suffi-\ncient durability against the action of the water, may be re-\nsorted to in their construction. Dams of alternate layers of\nbrush and gravel, with a facing of plank, fascines, or dry\nstone, answer very well in gentle currents. If the dam is ex-\nposed to heavy freshets, to shocks of ice, and other heavy\nfloating bodies, as drift-wood, it would be more prudent to\nform it of dry stone entirely, or of crib-work filled with stone;\nor, if the last material cannot be obtained, of a solid crib-work\nalone. If the dam is to be made water-tight, sand and gravel\nin sufficient quantity may be thrown in against it in the\nupper pond. The points where the dam joins the banks,\nwhich are termed the roots of the dam, require particular at-\ntention to prevent the water from filtering around them.\nThe ordinary precaution for this is to build the dam some\ndistance back into the banks.\n846. The safest means of communication between the\nponds is by an ordinary lock. It should be placed at one\nextremity of the dam, an excavation in the bank being made\nfor it, to secure it from damage by floating bodies brought\ndown by the current. The sides of the lock and a portion of\nthe dam near it should be raised sufficiently high to prevent\nthem from being overflowed by the heaviest freshets. When\nthe height to which the freshets rise is great, the leaves of\nthe head gates should be formed of two parts, as a single leaf\nwould, from its size, be too unwieldy, the lower portion being\nof a suitable height for the ordinary manœuvres of the lock;\nthe upper, being used only during the freshets, are so ar-\nranged that their bottom cross pieces shall rest, when the\ngates are closed, against the top of the lower portions. An\narrangement somewhat similar to this may be made for the\ntail gates, when the lifts of the locks are great, to avoid the\ndifficulty of manœuvring very high gates, by permanently\nclosing the upper part of the entrance to the lock at the tail\ngates, either by a wall built between the side walls, or by a\npermanent framework, below which a sufficient height is left\nfor the boats to pass.\n847. A common, but unsafe method of passing from one\npond to another, is that which is termed flashing; it consists\nof a sluice in the dam, which is opened and closed by means\nof a gate revolving on a vertical axis, which is so arranged\nthat it can be manœuvred with ease. One plan for this pur-\npose is to divide the gate into two unequal parts by an axis,\nand to place a valve of such dimensions in the greater, that\nDigitized by\nGoogle\nRIVERS.\n503\nwhen opened the surface against which the water presses\nshall be less than that of the smaller part. The play of the\ngate is thus rendered very simple; when the valve is shut,\nthe pressure of water on the larger surface closes it against\nthe sides of the sluice; when the valve is opened, the gate\nswings round and takes a position in the direction of the cur-\nrent. Various other plans for flashing, on similar principles,\nare to be met with.\n848. When the obstruction in a river cannot be overcome\nby any of the preceding means, as for example in those con-\nsiderable descents in the bed known as rapids, where the\nwater acquires a velocity so great that a boat can neither\nascend nor descend with safety, resort must be had to a canal\nfor the purpose of uniting its navigable parts above and\nbelow the obstruction.\nThe general direction of the canal will be parallel to the\nbed of the river. In some cases it may occupy a part of the\nbed by forming a dike in the bed parallel to the bank, and\nsufficiently far from it to give the requisite width to the canal.\nWhatever position the canal may occupy, every precaution\nshould be taken to secure it from damage by freshets.\n849. A lock will usually be necessary at each extremity of\nthe canal where it joins the river. The positions for the ex-\ntreme locks should be carefully chosen, so that the boats can\nat all times enter them with ease and safety. The locks\nshould be secured by guard gates and other suitable means\nfrom freshets; and if they are liable to be obstructed by de-\nposites, arrangements should be made for their removal either\nby a chase of water, or by machinery.\nIf the river should not present a sufficient depth of water\nat all seasons for entering the canal from it, a dain will be\nrequired at some point near the lock to obtain the depth re-\nquisite.\nIt may be advisable in some cases, instead of placing the\nextreme locks at the outlets of the canal to the river, to form\na capacious basin at each extremity of the canal between the\nlock and river, where the boats can lie in safety. The outlets\nfrom the basins to the rivers may either be left open at all\ntimes, or else guard gates may be placed at them to shut off\nthe water during freshets.\nDigitized by Google\n504\nCIVIL ENGINEERING.\nCHAPTER X.\nSEACOAST IMPROVEMENTS.\n850. THE following subdivisions may be made of the works\nbelonging to this class of improvements: 1st. Artificial\nRoadsteads. 2d. The works required for natural and ar-\ntificial Harbors. 3d. The works for the protection of the\nseacoast against the action of the sea.\n851. Before adopting any definitive plan for the improve-\nment of the seacoast at any point, the action of the tides,\ncurrents, and waves at that point must be ascertained.\n852. The theory of tides is well understood; their rise and\nduration, caused by the attraction of the sun and moon, are\nalso dependent on the strength and direction of the wind,\nand the conformation of the shore. Along our own sea-\nboard, the highest tides vary greatly between the most\nsouthern and northern parts. At Eastport, Me., the highest\ntides, when not affected by the wind, vary between twenty-\nfive and thirty feet above the ordinary low water. At Bos-\nton they rise from eleven to twelve feet above the same\npoint, under similar circumstances; and from New York,\nfollowing the line of the seaboard to Florida, they seldom\nrise above five feet.\n853. Currents are principally caused by the tides, assisted,\nin some cases, by the wind. The theory of their action is\nsimple. From the main current, which sweeps along the\ncoast, secondary currents proceed into the bays, or indenta-\ntions, in a line more or less direct, until they strike some\npoint of the shore, from which they are deflected, and fre-\nquently separate into several others, the main branch follow-\ning the general direction which it had when it struck the\nshore, and the others not unfrequently taking an opposite\ndirection, forming what are termed counter currents, and, at\npoints where the opposite currents meet, that rotary motion\nof the water known as. whirlpools. The action of currents\non the coast is to wear it away at those points against which\nthey directly impinge, and to transport the débris to other,\npoints, thus forming, and sometimes removing, natural ob-\nstructions to navigation. These continual changes, caused\nby currents, make it extremely difficult to foresee their effects,\nDigitized by Google\nSEACOAST IMPROVEMENTS.\n505\nand to foretell the consequences which will arise from any\nchange in the direction, or the intensity of a current, occa-\nsioned by artificial obstacles.\n854. A good theory of waves, which shall satisfactorily\nexplain all their phenomena, is still a desideratum in science.\nIt is known that they are produced by winds acting on the\nsurface of the sea; but how far this action extends below\nthe surface and what are its effects at various depths, are\nquestions that remain to be answered. The most commonly\nreceived theory is, that a wave is a simple oscillation of the\nwater, in which each particle rises and falls, in a vertical\nline, a certain distance during each oscillation, without re-\nceiving any motion of translation in a horizontal direction.\nIt has been objected to this theory that it fails to explain\nmany phenomena observed in connection with waves.\nIn a recent French work on this subject, its author, Colonel\nEmy, an engineer of high standing, combats the received\ntheory; and contends that the particles of water receive also\na motion of translation horizontally, which, with that of as-\ncension, causes the particles to assume an orbicular motion,\neach particle describing an orbit, which he supposes to be\nelliptical. He farther contends, that in this manner the par-\nticles at the surface communicate their motion to those just\nbelow them, and these again to the next, and so on down-\nward, the intensity decreasing from the surface, without,\nhowever, becoming insensible at even very considerable\ndepths; and that, in this way, owing to the reaction from\nthe bottom, an immense volume of water is propelled along\nthe bottom itself, with a motion of translation SO powerful as\nto overthrow obstacles of the greatest strength if directly\nopposed to it. From this he argues that walls built to resist\nthe shock of the waves should receive a very great batir at\nthe base, and that this batir should be gradually decreased\nupward, until, towards the top, the wall should project over,\nthus presenting a concave surface at top to throw the water\nback. By adopting this form, he contends that the mass of\nwater, which is rolled forward, as it were, on the bottom,\nwhen it strikes the face of the wall, will ascend along it, and\nthus gradually lose its momentum. These views of Colonel\nEmy have been attacked by other engineers, who have had\nopportunities to observe the same phenomena, on the ground\nthat they are not supported by facts; and the question still\nremains undecided. It is certain, from experiments made\nby the author quoted upon walls of the form here described,\nthat they seem to answer fully their intended purpose.\nDigitized by Google\n506\nCIVIL ENGINEERING.\n855. Roadsteads. The term roadstead is applied to an\nindentation of the coast, where vessels may ride securely at\nanchor under all circumstances of weather. If the indenta-\ntion is covered by natural projections of the land, or capes,\nfrom the action of the winds and waves, it is said to be land-\nlocked; in the contrary case, it is termed an open roadstead.\nThe anchorage of open roadsteads is often insecure, owing\nto violent winds setting into them from the sea, and occasion-\ning high waves, which are very straining to the moorings.\nThe remedy applied in this case is to place an obstruction\nnear the entrance of the roadstead, to break the force of the\nwaves from the sea. These obstructions, termed breakwaters,\nare artificial islands of greater or less extent, and of variable\nform, according to the nature of the case, made by throwing\nheavy blocks of stone into the sea, and allowing them to take\ntheir own bed.\nThe first great work of this kind undertaken in modern\ntimes, was the one at Cherbourg in France, to cover the road-\nstead in front of that town. After some trials to break the\neffects of the waves on the roadstead by placing large conical-\nshaped structures of timber filled with stones across it, which\nresulted in failure, as these vessels were completely destroyed\nby subsequent storms, the plan was adopted of forming a\nbreakwater by throwing in loose blocks of stone, and allow-\ning the mass to assume the form produced by the action of\nthe waves upon its surface. The subsequent experience of\nmany years, during which this work has been exposed to the\nmost violent tempests, has shown that the action of the sea\non the exposed surface is not very sensible at this locality at\na depth of about 20 feet below the water level of the lowest\ntides, as the blocks of stone forming this part of the break-\nwater, some of which do not average over 40 lbs. in weight,\nhave not been displaced from the slope the mass first as-\nsumed, which was somewhat less than one perpendicular to\none base. From this point upwards, and particularly be-\ntween the levels of high and low water, the action of the\nwaves has been very powerful at times, during violent gales,\ndisplacing blocks of several tons weight, throwing them over\nthe top of the breakwater upon the slope towards the shore.\nWherever this part of the surface has been exposed the\nblocks of stone have been gradually worn down by the action\nof the waves, and the slope has become less and less steep,\nfrom year to year, until finally the surface assumed a slightly\nconcave slope, which, at some points, was as great as ten\nbase to one perpendicular.\nDigitized by Google\nSEACOAST IMPROVEMENTS.\n507\nThe experience acquired at this work has conclusively\nshown that breakwaters, formed of the heaviest blocks of\nloose stone, are always liable to damage in heavy gales when\nthe sea breaks over them, and that the only means of secur-\ning them is by covering the exposed surface with a facing of\nheavy blocks of hammered stone carefully set in hydraulic\ncement.\nAs the Cherbourg breakwater is intended also as a military\nconstruction, for the protection of the roadstead against an\nenemy's fleet, the cross section shown (in Fig. 248) has been\nadopted for it. Profiting by the experience of many years'\nobservation, it was decided to construct the work that forms\nthe cannon battery of solid masonry laid on a thick and broad\nbed of beton. The top surface of the breakwater is covered\nwith heavy loose blocks of stone, and the foot of the wall on\nthe face is protected by large blocks of artificial stone formed\nof beton. The top of the battery is about 12 feet above the\nhighest water level.\nB\nFig. 248-Represents a section of the Cherbourg breakwater.\nA, mass of stone.\nB, battery of masonry.\nThe next work of the kind was built to cover the roadstead\nof Plymouth in England. Its cross section was, at first, made\nwith an interior slope of one and a half base to one perpen-\ndicular, and an exterior slope of only three base to one per-\npendicular; but from the damage it sustained in the severe\ntempests in the winter of 1816-17, it is thought that its ex-\nterior slope was too abrupt.\nA work of the same kind is still in process of construction\non our coast, off the mouth of the Delaware. The same cross\nsection has been adopted for it as in the one at Cherbourg.\nAll of these works were made in the same way, discharg-\ning the stone on the spot, from vessels, and allowing it to\ntake its own bed, except for the facing, where, when practi-\ncable, the blocks were carefully laid, SO as to present a uni-\nform surface to the waves. The interior of the mass, in each\nDigitized by Google\n508\nCIVIL ENGINEERING.\ncase, has been formed of stone in small blocks, and the facing\nof very large blocks. It is thought, however, that it would\nbe more prudent to form the whole of large blocks, because,\nwere the exterior to suffer damage, and experience shows that\nthe heaviest blocks yet used have at times been displaced by\nthe shock of the waves, the interior would still present a great\nobstacle.\nFrom the foregoing details, respecting the cross sections of\nbreakwaters, which from experiment have been found to\nanswer, the proper form and dimensions of the cross section\nin similar cases may be arranged. As to the plan of such\nworks, it must depend on the locality. The position of the\nbreakwater should be chosen with regard to the direction of\nthe heaviest swells from the sea into the roadstead,-the\naction of the current and that of waves. The part of the\nroadstead which it covers should afford a proper depth of\nwater, and secure anchorage for vessels of the largest class,\nduring the most severe storms; and vessels should be able to\ndouble the breakwater under all circumstances of wind and\ntide. Such a position should, moreover, be chosen that there\nwill be no liability to obstructions being formed within the\nroadstead, or at any of its outlets, from the change in the\ncurrent which may be made by the breakwater.\n856. The difficulty of obtaining very heavy blocks of stone,\nas well as their great cost, has led to the suggestion of substi-\ntuting for them blocks of artificial stone, formed of concrete,\nwhich can be made of any shape and size desirable. This\nplan has been tried with success in several instances, particu-\nlarly in a jetty or mole, at Algiers, constructed by the French\ngovernment. The beton for a portion of this work was placed\nin large boxes, the sides of which were of wood, shaped at\nbottom to correspond to the irregularities of the bottom on\nwhich the beton was to be spread. The bottom of the box\nwas made of strong canvas tarred. These boxes were first\nsunk in the position for which they were constructed, and then\nfilled with the beton.\n857. Harbors. The term harbor is applied to a secure an-\nchorage of a more limited capacity than a roadstead, and\ntherefore offering a safer refuge during boisterous weather.\nHarbors are either natural or artificial.\n858. An artificial harbor is usually formed by enclosing a\nspace on the coast between two arms, or dikes of stone, or of\nwood, termed jetties, which project into the sea from the\nshore, in such a way as to cover the harbor from the action of\nthe wind and waves.\nDigitized by\nGoogle\nSEACOAST IMPROVEMENTS.\n509\n859. The plan of each jetty is curved, and the space enclosed\nby the two will depend on the number of vessels which it may\nbe supposed will be in the harbor at the same tinie. The dis-\ntance between the ends, or heads, of the jetties which forms\nthe mouth of the harbor, will also depend on local circum-\nstances; it should seldom be less than one hundred yards, and\ngenerally need not be more than five hundred. There are\ncertain winds at every point of a coast which are more un-\nfavorable than others to vessels entering and qutting the har-\nbor, and to the tranquillity of its water. One of the jetties\nshould, on this account, be longer than the other, and be so\nplaced that it will both break the force of the heaviest swells\nfrom the sea into the mouth of the harbor, and facilitate the\ningress and egress of vessels, by preventing them from being\ndriven by the winds on the other jetty, just as they are enter-\ning or quitting the mouth.\n860. The cross section and construction of a stone jetty\ndiffer in nothing from those of a breakwater, except that the\njetty is usually wider on top, thirty feet being allowed, as it\nserves for a wharf in unloading vessels. The head of the\njetty is usually made circular, and considerably broader than\nthe other parts, as it, in some instances, receives a lighthouse,\nand a battery of cannon. It should be made with great care,\nof large blocks of stone, well united by iron or copper cramps,\nand the exterior courses should moreover be protected by\nfender beams of heavy timber to receive the shock of floating\nbodies.\n861. Wooden jetties are formed of an open framework of\nheavy timber, the sides of which are covered on the interior\nby a strong sheeting of thick plank. Each rib of the frame\n(Fig. 249) consists of two inclined pieces, which form the\nsides-of an upright centre piece,-and of horizontal clamp-\ning pieces, which are notched and bolted in pairs on the\ninclined and upright pieces; the inclined pieces are farther\nstrengthened by struts, which abut against them and the up-\nright. The ribs are connected by large string-pieces, laid\nhorizontally, which are notched and bolted on the inclined\npieces, the uprights, and the clamping pieces, at their points\nof junction. The foundation, on which this framework rests,\nconsists usually of three rows of large piles driven under\nthe foot of the inclined pieces and the uprights. The rows\nof piles are firmly connected by cross and longitudinal beams\nnotched and bolted on them; and they are, moreover, firmly\nunited to the framework in a similar manner. The interior\nsheeting does not, in all cases, extend the entire length of\nDigitized by Google\n510\nCIVIL ENGINEERING.\nFig. 249-Represents a cross section of & wooden jetty. a, foundation piles. b, inclined\nside pieces. c, middle upright, d, cross pieces bolted in pairs. a struts, m, longitudinal\npieces bolted in pairs. o, parapet.\nthe sides, but open spaces, termed clear-ways, are often left,\nto give a free passage and spread to the waves confined be-\ntween the jetties, for the purpose of forming smooth water\nin the channel. If the jetties are covered at their back with\nearth, the clear-ways receive the form of inclined planes.\nThe foundation of the jetties requires particular care,\nespecially when the channel between them is very narrow.\nLoose stone thrown around the piles is the ordinary construc-\ntion used for this purpose; and, if it be deemed necessary,\nthe bottom of the entire channel may be protected by an\napron of brush and loose stone.\nThe top of the jetties is covered with a flooring of thick\nplank, which serves as a wharf. A strong hand-railing\nshould be placed on each side of the flooring as a protection\nagainst accidents. The sides of jetties have been variously\ninclined; the more usual inclination varies between three\nand four perpendicular to one base.\n862. Jetties are sometimes built out to form a passage to\na natural harbor, which is either very much exposed, or\nsubject to bars at its mouth. By narrowing the passage to\nthe harbor between the jetties, great velocity is given to the\ncurrent caused by the tide, and this alone will free the\ngreater part of the channel from deposites. But at the head\nof the jetties a bar will, in almost every case, be found to\naccumulate, from the current alongshore, which is broken\nDigitized by Google\nSEACOAST IMPROVEMENTS.\n511\nby the jetties, and from the diminished velocity of the ebbing\ntides at this point. To remove these bars resort may be had,\nin localities where they are left nearly dry at low water, to\nreservoirs, and sluices, arranged with turning gates, like those\nadverted to for river improvements. The reservoirs are\nformed by excavating a large basin inshore, at some suitable\npoint from which the collected water can be directed, with\nits full force, on the bar. The basin will be filled at flood-\ntide, and when the ebb commences the sluice gates will be\nkept closed until dead low water, when they should all be\nopened at once to give a strong water chase.\n863. In harbors where vessels cannot be safely and conve-\nniently moored alongside of the quays, large basins, termed\nwet-docks, are formed, in which the water can be kept at a\nconstant level. A wet-dock may be made either by an in-\nshore excavation, or by enclosing a part of the harbor with\nstrong water-tight walls; the first is the more usual plan.\nThe entrance to the basin may be by a simple sluice, closed\nby ordinary lock gates, or by means of an ordinary lock.\nWith the first method vessels can enter the basin only at\nhigh tide; by the last they may be entered or passed out at\nany period of the tide. The outlet of the lock should be\nprovided with a pair of guard gates, to be shut against very\nhigh tides, or in cases of danger from storms.\n864. The construction of the locks for basins differs in\nnothing, in principle, from that pursued in canal locks. The\ngreatest care will necessarily be taken to form a strong mass\nfree from all danger of accidents. The gates of a basin-lock\nare made convex towards the head of water, to give them\nmore strength to resist the great pressure upon them. They\nare hung and manœuvred differently from ordinary lock\ngates; the quoin-post is attached to the side walls in the usual\nway : but at the foot of the mitre-post an iron or brass roller\nis attached, which runs on an iron roller way, and thus sup-\nports that end of the leaf, relieving the collar of the quoin-\npost from the strain that would be otherwise thrown on it,\nbesides giving the leaf an easy play. Chains are attached to\neach mitre-post near the centre of pressure of the water, and\nthe gate is opened, or closed, by means of windlasses to which\nthe other ends of the chains are fastened.\n865. The quays of wet-docks are usually built of masonry.\nBoth brick and stone have been used; the facing at least\nshould be of dressed stone. Large fender-beams may be at-\ntached to the face of the wall, to prevent it from being\nbrought in contact with the sides of the vessels. The cross\nDigitized by Google\n512\nCIVIL ENGINEERING.\nsection of quay-walls should be fixed on the same principles\nas that of other sustaining walls. It might be prudent to add\nbuttresses to the back of the wall to strengthen it against the\nshocks of the vessels.\n866. Quay-walls with us are ordinarily made either by\nforming a facing of heavy round or square piles driven in\njuxtaposition, which are connected by horizontal pieces, and\nsecured from the pressure of the earth filled in behind them\nby land-ties; or, by placing the pieces horizontally upon each\nother, and securing them by iron bolts. Land-ties are used\nto counteract the pressure of the earth or rubbish which is\nthrown in behind them to form the surface of the quay.\nAnother mode of construction, which is found to be strong\nand durable, is in nse in our Eastern seaports. It consists in\nmaking a kind of crib-work of large blocks of granite, and\nfilling in with earth and stone rubbish. The bottom course\nof the crib may be laid on the bed of the river, if it is firm\nand horizontal; in the contrary case a strong grillage, termed\na cradle, must be made, and be sunk to receive the stone work.\nThe top of the cradle should be horizontal, and the bottom\nshould receive the same slope as that of the bed, in order that\nwhen the stones are laid they may settle horizontally.\n867. Dikes. To protect the lowlands bordering the ocean\nfrom inundations, dikes, constructed of ordinary earth, and\nfaced towards the sea with some material which will resist\nthe action of the current, are usually resorted to.\nThe Dutch dikes, by means of which a large extent of\ncountry has been reclaimed and protected from the sea, are\nthe most remarkable structures of this kind in existence. The\ncross section of those dikes is of a trapezoidal form, the width\nat top averaging from four to six feet, the interior slope being\nthe same as the natural slope of the earth, and the exterior\nslope varying, according to circumstances, between three and\ntwelve base to one perpendicular. The top of the dike, for\nperfect safety, should be about six feet above the level of the\nhighest spring tides, although, in many places, they are only\ntwo or three above this level.\nThe earth for these dikes is taken from a ditch inshore, be-\ntween which and the foot of the dike a space of about twenty\nfeet is left which answers for a road. The exterior slope is va-\nriously faced, according to the means at hand, and the charac-\nter of the current and waves at the point. In some cases, a\nstrong straw thatch is put on, and firmly secured by pickets,\nor other means; in others, a laver of fascines is spread over the\nthatch, and is strongly picketed to it the ends of the pickets\nDigitized by Google\nSEACOAST IMPROVEMENTS.\n513\nbeing allowed to project out about eighteen inches, so that\nthey can receive a wicker-work formed by interlacing them\nwith twigs, the spaces between this wicker-work being filled\nwith broken stone; this forms a very durable and strong facing,\nwhich resists not only the action of the current, but, by its\nelasticity, the shocks of the heaviest waves.\nThe foot of the exterior slope requires peculiar care for its\nprotection; the shore, for this purpose, is in some places cov-\nered with a thick apron of brush and gravel in alternate layers,\nto a distance of one hundred yards into the water from the foot\nof the slope.\nOn some parts of the coast of France, where it has been\nfound necessary. to protect it from encroachments of the sea,\na cross section has been given to the dikes towards the sea,\nof the same form as the one which the shore naturally takes\nfrom the action of the waves. The dikes in other respects\nare constructed and faced after the manner which has been\nso long in practice in Holland.\n868. Groins. Constructions, termed groins, are used when-\never it becomes necessary to check the effect of the current\nalong the shore, and cause deposites to be formed. These are\nartificial ridges which rise a few feet only above the surface\nof the beach, and are built out in a direction either perpen-\ndicular to that of the shore, or oblique to it. They are con-\nstructed either of clay, which is well rammed and protected\non the surface by a facing of fascines or stones; or of layers\nof fascines; or of one or two rows of short piles driven in\njuxtaposition; or any other means that the locality may fur-\nnish may be resorted to; the object being to interpose an\nobstacle, which, breaking the force of the current, will occa-\nsion a deposite near it, and thus gradually cause the shore to\ngain upon the sea.\n869. Sea-walls. When the sea encroaches upon the land,\nforming a steep bluff, the face of which is gradually worn\naway, a wall of masonry is the only means that will afford a\npermanent protection against this action of the waves. Walls\nmade for this object are termed sea-walls. The face of a sea-\nwall should be constructed of the most durable stone in large\nblocks. The backing may be of rubble or of beton. The\nwhole work should be laid with hydraulic mortar.\n22*\nEND.\nDigitized by Google\nDigitized by Google\nDigitized by Google\nDigitized by Google\nNew York, August, 1873.\nJOHN WILEY & SON'S\nLIST OF PUBLICATIONS,\n15 ASTOR PLACE,\nUnder the Mercantile Library and Trade Suberooms.\nAGRICULTURE.\nDOWNING.\nFRUITS AND FRUIT-TREES OF AMERICA; or the\nCulture, Propagation, and Management in the Garden and\nOrchard, of Fruit-trees generally, with descriptions of all the\nfinest varieties of Fruit, Native and Foreign, cultivated in this\ncountry. By A. J. Downing. Second revision and correction,\nwith large additions. By Chas. Downing. 1 vol. 8To, over\n1100 pages, with several hundred outline engravings. Price,\nwith Supplement for 1872\n$5 00\nAs a work of reference it has no equal in this country, and deserves a place in\nthe Library of every Pomologist in America.\"-Marshall P. Wilder.\n64\nENOYCLOPEDIA OF FRUITS; or, Fruits and Fruit-\nTrees of America. Part 1.-APPLES. With an Appendix\ncontaining many new varieties, and brought down to 1872.\nBy Chas: Downing. With numerous outline engravings. 8vo,\nfull cloth\n$2 50\n\"\nENCYCLOPEDIA OF FRUITS; or, Fruits and Fruit-\nTrees of America. Part .-CHERRIES, GRAPES, PEACHES,\nPEARS, &c. With an Appendix containing many new varie-\nties, and brought down to 1872. By Chas. Downing. With\nnumerous outline engravings. 8vo, full cloth\n$2 50\n\"\nFRUITS AND FRUIT-TREES OF AMERICA. By A. J.\nDowning. First revised edition. By Chas. Downing 12ino,\ncloth\n$2 00\n\"\nSELECTED FRUITS. From Downing's Fruits and Fruit-\nTrees of America. With some new varieties, including their\nCulture. Propagation, and Management in the Garden and\nOrchard, with a Guide to the selection of Fruits, with refer-\nence to the Time of Ripening. By Chas. Downing. Illus-\ntrated with upwards of four hundred outlines of Apples,\nCherries, Grapes, Plums, Pears, &o. 1 vol, 12mo\n$2 50\n\"\nLOUDON'S GARDENING FOR LADIES, AND COM-\nPANION TO THE FLOWER-GARDEN. Second\nAmerican from third London edition. Edited by A. J.\nDowning. 1 vol., 12mo\n$2 00\nDOWNING & THE THEORY OF HORTICULTURE. By J. Lindley.\nLINDLEY.\nWith additions by A. J. Downing. 12mo, cloth\n$2 00\nDOWNING.\nCOTTAGE RESIDENCES. A Series of Designs for Rural\nCottages and Cottage Villas, with Garden Grounds. By A.\nJ. Downing. Containing a revised List of Trees, Shrubs,\nand Plants, and the most recent and best selected Fruit, with\nsome account of the newer soyle of Gardens. By Henry\nWinthrop Sargent and Charles Downing. With many new\ndesigns in Rural Architecture. By George E Harney,\nArchitect. 1 vol. 4to\n$6 00\nDigitized by Google\n92\nJOHN WILEY & SON'S LIST OF PUBLICATIONS.\nDOWNING & HINTS TO PERSONS ABOUT BUILDING IN THE\nWIGHTWICK.\nCOUNTRY. By A. J. Downing. And HINTS TO\nYOUNG ARCHITECTS, calculated to facilitate their\npractical operations. By George Wightwick, Architect.\nWood engravings. 8vo, cloth\n$2 00\nKEMP.\nLANDSCAPE GARDENING; or, How to Lay Out a Gar-\nden. Intended as a general guide in choosing, forming,\nor improving an estate (from a quarter of an acre to a hun-\ndred acres in extent), with reference to both design and exe-\ncution. With numerous fine wood engravinga. By Edward\nKemp. 1 vol. 12mo, cloth.\n$3 50\nLIEBIG.\nCHEMISTRY IN ITS APPLICATION TO AGRICUL-\nTURE, &c. By Justus Von Liebig. 12mo, cloth $1 00\n\"\nLETTERS ON MODERN AGRICULTURE. By Baron\nVon Liebig. Edited by John Blyth, M.D. With addenda\nby a practical Agriculturist, embracing valuable suggestions,\nadapted to the wants of American Farmers. 1 vol. 12mo,\ncloth\n$1 00\n64\nPRINCIPLES OF AGRICULTURAL CHEMISTRY, with\nspecial reference to the late researches made in Eng'and. By\nJustus Von Liebig. 1 vol. 12mo\n75 cents.\nPARSONS.\nHISTORY AND CULTURE OF THE ROSE. By S. B.\nParsons. 1 vol. 12mo\n$1 25\nARCHITECTURE.\nDOWNING.\nCOTTAGE RESIDENCES; or, a Series of Designs for Rural\nCottages and Cottage Villas and their Gardens and Grounds,\nadapted to North America. By A. J: Downing. Containing\na revised List of Trees, Shrubs, Plants, and the most recent\nand best selected Fruits. With some account of the newer\nstyle of Gardens, by Henry Wentworth Sargent and Charles\nDowning. With many new designs in Rural Architecture by\nGeorge E. Harney, Architect\n$6 00\nDOWNING &\nHINTS TO PERSONS ABOUT BUILDING IN THE\nWIGHTWICK.\nCOUNTRY. By A. J. Downing. And HINTS TO\nYOUNG ARCHITECTS, calculated to facilitate their\npractical operations. By George Wightwick, Architect\nWith many wood-cuts. 8vo, cloth\n$2 00\nHATFIELD.\nTHE AMERICAN HOUSE CARPENTER. A Treatise\nupon Architecture, Cornices, and Mouldings, Framing, Doors,\nWindows, and Stairs together with the most important\nprinciples of Practical Geometry. New, thoroughly revised,\nand improved edition, with about 150 additional pages, and\nnumerous additional plates. By R. G. Hatfield. 1 vol\n8vo\n$3 50\nNOTICES OF THE WORK.\nThe clearest and most thoroughly practical work on the subject.\"\nThis work is & most excellent one, very comprehensive, and lucidly arranged.\"\nThis work commends itself by its practical excellence.\"\nIt is a valuable addition to the library of the architect, and almost indispensable\nto every scientific master-mechanic.' R. Journal.\nHOLLY\nCARPENTERS' AND JOINERS' HAND-BOOK, contain-\ning a Treatise on Framing, Roofs, etc., and useful Rules and\nTables. By H. W. Holly. 1 vol. 18mo, cloth\n$0 75\n\"\nTHE ART OF SAW-FILING SCIENTIFICALLY\nTREATED AND EXPLAINED. With Directions for\nputting in order all kinds of Saws. By H. W. Holly. 18mo,\ncloth\n$0 75\nRUSKIN\nSEVEN LAMPS OF ARCHITECTURE 1 vol. 12mo,\ncloth, plates.\n$1 75\nDigitized\nby\nGoogle\nJOHN WILEY & SON'S LIST OF PUBLICATIONS.\n93\nRUSKIN.\nLECTURES ON ARCHITEOTURE AND PAINTING.\n1 vol. 12mo, cloth, plates\n$1 50\n\"\nLECTURE BEFORE SOCIETY OF ARCHITECTS. 0 15\nWOOD.\nA TREATISE ON THE RESISTANCE OF MA-\nTERIALS, and an Appendix on the Preservation of Timber.\nBy De Volson Wood, Prof. of Engineering, University of\nMichigan. 1 vol. 8vo, cloth\n$2 50\nThis work is used as a Text-Book in Iowa University, Iowa Agricultural College,\nIllinois Industrial University, Sheffield Scientific School, New Haven, Cooper\nInstitute, New York, Polytechnic College, Brooklyn, University of Michigan,\nand other institutions.\n\"\nA TREATISE ON BRIDGES. Designed as a Text-book and\nfor Practical Use. By De Volson Wood. 1 vol. 8vo, nu-\nmerous illustrations,\n$3 00\nASSAYING-ASTRONOMY.\nBODEMANN.\nA TREATISE ON THE ASSAYING OF LEAD, SILVER,\nCOPPER, GOLD, AND MERCURY. By Bodemann\nand Kerl. Translated by W. A. Goodyear. 1 vol. 12mo,\ncloth\n$2 50\nMITCHELL.\nA MANUAL OF PRACTICAL ASSAYING. By John\nMitchell Third edition, edited by William Crookes. 1 vol.\nthick 8vo, cloth\n$10 00\nNORTON.\nA TREATISE ON ASTRONOMY, SPHERICAL AND\nPHYSICAL, with Astronomical Problems and Solar, Lunar,\nand other Astronomical Tables for the use of Colleges and\nScientific Schools. By William A. Norton. Fourth edition,\nrevised, remodelled, and enlarged. Numerous plates. 8vo,\ncloth\n$8 50\nBIBLES, &c.\nBACSTER.\nTHE COMMENTARY WHOLLY BIBLICAL Contents:\n-The Commentary: an Exposition of the Old and New Tes-\ntaments in the very words of Scripture. 2264 pp. II. An\noutline of the Geography and History of the Nations men-\ntioned in Scripture. III. Tables of Measures, Weights, and\nCoins. IV. An Itinerary of the Children of Israel from\nEgypt to the Promised Land. V. A Chronological compara-\ntive Table of the Kings and Prophets of Israel and Judah.\nVI. A Chart of the World's History from Adam to the Third\nCentury, A. D. VII. A complete Series of Illustrative Maps.\nIX. A Chronological Arrangement of the Old and New Tes-\ntaments. X. An Index to Doctrines and Subjects, with\nnumerous Selected Passages, quoted in full. XL An Index\nto the Names of Persons mentioned in Scripture. XII. An\nIndex to the Names of Places found in Scripture. XIII.\nThe Names, Titles, and Characters of Jesus Christ our Lord,\nas revealed in the Scriptures, methodically arranged.\n2 volumes 4to, cloth\n$19 50\n2 volumes 4to, half morocco, gilt edges\n26 00\n2 volumes 4to, morocco, gilt edges\n35 00\n3 volumes 4to, cloth\n20 00\n8 volumes 4to, half morocco, gilt edges\n33 00\n8 volumes 4to, morocco, gilt edges.\n40 00\nBLANK-PAGED THE HOLY SCRIPTURES OF THE OLD AND NEW\nBIBLE.\nTESTAMENTS; with copious references to parallel and\nillustrative passages, and the alternate pages ruled for MS.\nnotes.\nThis edition of the Scriptures contains the Authorized Version, illustrated by the\nreferences of Bagster's Polyglot Bible,\" and enriched with accurate maps,\n1\nuseful tables, and an Index of Subjects.\n1 vol. 8vo, half morocco\n$8 50\n1 vol. 8vo, morocco.\n10 50.\nDigitized by\nGoogle\n94\nJOHN WILEY & SON'S LIST OF PUBLICATIONS.\nTHE TREASURY Containing the authorized English version of the Holy Scriptures,\nBIBLE.\ninterleaved with a Treasury of more than 500,000 Parallel\nPassages from Canne, Brown, Blayney, Scott, and others.\nWith numerous illustrative notes.\n1 vol., half bound\n$7 50\n1 vol., morocco\n10 00\nCOMMON PRAYER, 48mo Size.\n(Done in London expressly for us.)\nCOMMON\nNo. 1. Gilt and red edges, imitation morooco\n$0 621\nPRAYER. No. 2. Gilt and red edges, rims\n87#\nNo. 3. Gilt and red edges, best morocco and calf\n1 25\nNo. 4. Gilt and red edges, best morocco and calf, rims. 1 50\nBOOK-KEEPING.\nJONES.\nBOOKKEEPING AND ACCOUNTANTSHIP. Elementary\nand Practical. In two parts, with a Key for Teachers By\nThomas Jones, Accountant and Teacher. 1 volume 8vo.\ncloth\n$2 50\n\"\nBOOKKEEPING AND ACCOUNTANTSHIP. School Edi-\ntion. By Thomas Jones. 1 vol. 8vo, half roan\n$1 50\n\"\nBOOKKEEPING AND ACCOUNTANTSHIP. Set of\nBlanks. In 6 parts. By Thomas Jones\n$1 50\n\"\nBOOKKEEPING AND ACCOUNTANTSHIP. Double\nEntry; Results obtained from Single Entry; Equation of\nPayments, etc. By Thomas Jones. 1 vol. thin 8vo $0 75\nCHEMISTRY.\nCRAFTS.\nA SHORT COURSE IN QUALITATIVE ANALYSIS;\nwith the new notation. By Prof. J. M. Crafts. Second\nedition. 1 vol. 12mo, cloth\n$1 50\nJOHNSON'S\nA MANUAL OF QUALITATIVE CHEMICAL ANALY-\nFRESENIUS.\nSIS. By C. R. Fresenius. Edited by S. W. Johnson, Pro-\nfessor in Sheffield Scientific School, Yale College. With\nChemical Notation and Nomenclature. old and new. 1 vol.\n8vo, cloth\n$4 50\n\"\nA SYSTEM OF INSTRUCTION IN QUANTITATIVE\nCHEMICAL ANALYSIS. By C. R. Fresenius. From\nlatest editions, edited, with additions, by Prof. S. W. John-\nson. With Chemical Notation and Nomenclature, old and\nnew\n$6 00\nKIRKWOOD\nCOLLECTION OF REPORTS (CONDENSED) AND\nOPINIONS OF CHEMISTS IN REGARD TO THE\nUSE OF LEAD PIPE FOR SERVICE PIPE, in the\nDistribution of Water for the Supply of Cities. By Jas. P.\nKirkwood. 8vo, cloth\n$1 50\nMILLER.\nELEMENTS OF CHEMISTRY, THEORETICAL AND\nPRACTICAL By Wm. Allen Miller. 3 vols. 8vo $18 00\n\"\nPart I-CHEMICAL PHYSICS. 1 vol. 8vo.\n$4 00\n\"\nPart IL.-INORGANIC CHEMISTRY. 1 vol. 8vo\n6 00\n06\nPart III-ORGANIC CHEMISTRY. 1 vol. 8vo\n10 00\n\"Dr. Miller's Chemistry is a work of which the author has every reason to feel\nproud. It is now by far the largest and most accurately written Treatise on\nChemistry in the English language,\" etc.-Dublin Med. Journal.\n$\nMAGNETISM AND ELECTRICITY. By Wm. Allen Miller.\n1 vol. 8vo\n$8 50\nDigitized by\nGoogle\nJOHN WILEY & SON'S LIST OF PUBLICATIONS.\n95\nMUSPRATT.\nCHEMISTRY THEORETICAL, PRACTICAL, AND\nANALYTICAL-as applied and relating to the Arts and\nManufactures. By Dr. Sheridan Muspratt. 2 vols. 8vo,\ncloth, $18.00; half russia\n$24 00\nNOAD.\nA MANUAL OF QUALITATIVE AND QUANTITATIVE\nCHEMICAL ANALYSIS. For the use of Students. By\nH. M. Noad, author of Manual of Electricity.\" 1 vol.\n12mo. (London.) Complete.\n$6 00\n\"\nQUANTITATIVE ANALYSIS. 1 vol. cloth\n4 00\nPERKINS.\nAN ELEMENTARY MANUAL OF QUALITATIVE\nCHEMICAL ANALYSIS. By Maurice Perkins. 12mo,\ncloth\n$1 00\nDRAWING AND PAINTING.\nBOUVIER\nHANDBOOK ON OIL PAINTING. Handbook of Young\nAND OTHERS.\nArtists and Amateurs in Oil Painting; being chiefly a con-\ndensed compilation from the celebrated Manual of Bouvier,\nwith additional matter selected from the labors of Merriwell,\nDe Montalbert, and other distinguished Continental writers\non the art. In 7 parts. Adapted for a Text-Book in\nAcademies of both sexes, as well as for self-instruction.\nAppended, a new Explanatory and Critical Vocabulary. By\nan American Artist. 12mo, cloth\n$2 00\nCOE.\nPROGRESSIVE DRAWING BOOK. By Benj. H. Coe.\nOne vol., cloth\n$3 50\n\"\nDRAWING FOR LITTLE FOLKS or, First Lessons for\nthe Nursery. 30 drawings. Neat cover\n$0 20\n\"\nFIRST STUDIES IN DRAWING. Containing Elementary\nExercises, Drawings from Objects, Animals, and Rustic\nFigures. Complete in three numbers of 18 studies each, in\nneat covers. Each\n$0.20\n\"\nCOTTAGES. An Introduction to Landscape Drawing. Con-\ntaining 72 Studies. Complete in four numbers of 18 studies\neach, in neat covers. Each\n$0.20\n\"\nEASY LESSONS IN LANDSCAPE. Complete in four\nnumbers of 10 Studies each. In neat 8vo cover. Each, $0 20\n\"\nHEADS, ANIMALS, AND FIGURES. Adapted to Pencil\nDrawing. Complete in three numbers of 10 Studies each.\nIn neat 8vo covers. Each\n$0 20\n\"\nCOPY BOOK, WITH INSTRUCTIONS\n$0 371\nRUSKIN.\nTHE ELEMENTS OF DRAWING. In Three Letters to\nBeginners. By John Ruskin. 1 vol. 12mo\n$1 00\n\"\nTHE ELEMENTS OF PERSPECTIVE. Arranged for the\nuse of Schools. By John Ruskin\n$1 00\nSMITH.\nA MANUAL OF TOPOGRAPHICAL DRAWING. By\nProf. R. S. Smith. Second edition. 1 vol. 8vo, cloth,\nplates\n$2 00\n\"\nMANUAL OF LINEAR PERSPECTIVE. Form, Shade,\nShadow, and Reflection. By Prof. R. S. Smith. 1 vol. 8vo,\nplates, cloth\n$2 00\nWARREN.\nCONSTRUCTIVE GEOMETRY AND INDUSTRIAL\nDRAWING. By S. Edward Warren, Professor in the Mas-\nsachusetts Institute of Technology, Boston:-\nL ELEMENTARY WORKS.\n1. ELEMENTARY FREE-HAND GEOMETRICAL DRAWING.\nA series of progressive exercises on regular lines and forms,\nincluding systematic instruction in lettering; a training of\nthe eye and hand for all who are learning to draw. 12mo,\ncloth, many cuts\n75 cts.\nVols. 1 and 8, bound in 1 vol.\n$1 75\nDigitized by Google\n96\nJOHN WILEY & SON'S LIST OF PUBLICATIONS.\nELEMENTARY WORKS.-Continned.\nWARREN\n2. PLANE PROBLEMS IN ELEMENTARY GEOMETRY. With\nnumerous wood-cuts. 12mo, cloth\n$1 25\n3. DRAFTING INSTRUMENTS AND OPERATIONS. Con-\ntaining full information about all the instruments and\nmaterials used by the draftsmen, with full directions for their\nuse. With plates and wood-cuts. One vol. 12mo, cloth, $1 25\n4. ELEMENTARY PROJECTION DRAWING. Revised and en-\nlarged edition. In five divisions. This and the last volume\nare favorite text-books, especially valuable to all Mechanical\nArtisans, and are particularly recommended for the use of all\nhigher public and private schools. New revised and enlarged\nedition, with numerous wood-cuts and plates. (1872.) 12mo,\ncloth\n$1 50\n5. ELEMENTARY LINEAR PERSPECTIVE OF FORMS AND\nSHADOWS. Part I.-Primitive Methods, with an Introduc-\ntion. Part II-Derivative Methods, with Notes on Aerial\nPerspective. and many Practical Examples. Numerous wood-\ncuts. 1 vol. 12mo, cloth\n$1 00\nII. HIGHER WORKS.\nThese are designed principally for Schools of Engineering and\nArchitecture. and for the members generally of those professions;\nand the first three are also designed for use in those colleges which\nprovide courses of study adapted to the preliminary general\ntraining of candidates for the scientific professions, as well as for\nthose technical schools which undertake that training themselves.\n1. GENERAL PROBLEMS OF ORTHOGRAPHIC PROJEC-\nTIONS. The foundation course for the subsequent theo-\nretical and practical works. A new edition of this work will\nsoon appear.\n2. GENERAL PROBLEMS OF SHADES AND SHADOWS. A\nwider range of problems than can elsewhere be found in\nEnglish, and the principles of shading. 1 vol 8vo, with\nnumerous plates. Cloth\n$3 50\n8. HIGHER LINEAR PERSPECTIVE. Distinguished by its con-\ncise summary of various methods of perspective construction;\na full set of standard problems, and a careful discussion of\nspecial higher ones. With numerous large platea 8vo,\ncloth\n$4 00\n4. ELEMENTS OF MACHINE CONSTRUCTION AND DRAW-\nING; or, Machine Drawings. With some elements of descrip-\ntive and rational cinematics. A Text-Book for Schools of\nCivil and Mechanical Engineering, and for the use of Me-\nchanical Establishments, Artisans, and Inventors. Containing\nthe principles of gearings, screw propellers, valve motions, and\ngovernors, and many standard and novel examples, mostly from\npresent American practice. By S. Edward Warren. 2 vols.\n8vo. 1 vol. text and cuts, and 1 vol. large plates\n50\nA FEW FROM MANY TESTIMONIALS\n\"It seems to me that your Works only need a thorough examination to be intro-\nduced and permanently used in all the Scientific and Engineering Schools.\"\n-Prof. J. G. FOX, Collegiate and Engineering Institute, New York City.\n\"I have used several of your Elementary Works, and believe them to be better\nadapted to the purposes of instruction than any others with which I am\nacquainted.\"-H. F. WALLING, Prof. of Civil and Topographical Engt\nneering, Lafayette College, Easton, Pa.\n\"Your Works appear to me to fill a very important gap in the literature of the\nsubjects treated. Any effort to draw Artisans, etc., away from the 'rule of\nthumb,' and give them an insight into principles, is in the right direction,\nand meets my heartiest approval. This is the distinguishing feature of your\nElementary Works.\"-Prof. H. L. EUSTIS, Lawrence Scientific School,\nCambridge, Mass.\n\"The anthor has happily divided the subjects into two great portions: the former\nembracing those processes and problems proper to be taught to all students in\nInstitutions of Elementary Instruction; the latter, those suited to advanced\nstudents preparing for technical purposes. The Elementary Books ought to\nbe used in all High Schools and Academies; the Higher ones in Schools of\nTechnology.\"-WM. W. FOLWELL, President of University of Minnerota,\nDigitized\nby\nGoogle\nJOHN WILEY & SON'S LIST OF PUBLICATIONS.\n97\nDYEING, &c.\nMACFARLANE. A PRACTICAL TREATISE ON DYEING AND CALICO-\nPRINTING. Including the latest Inventions and Improve-\nments. With an Appendix, comprising definitions of chemical\nterms, with tables of Weights, Measures, &c. By an expe-\nrienced Dyer. With a supplement, containing the most\nrecent discoveries in color chemistry. By Robert Macfarlane.\n1 vol. 8vo\n$5 00\nREIMANN.\nA TREATISE ON THE MANUFACTURE OF ANILINE\nAND ANILINE COLORS. By M. Reimann. To which\nis added the Report on the Coloring Matters derived from\nCoal Tar, as shown at the French Exhibition, 1867. By Dr.\nHofmann Edited by Wm. Crookes. 1 8vo, cloth, $2 50\n\"Dr. Reimann's portion of the Treatise, written in concise language, is profoundly\npractical, giving the minutest details of the processes for obtaining all the\nmore important colors, with woodcuts of apparatus. Taken in conjunction\nwith Hofmann's Report, we have now a complete history of Coal Tar Dyes,\nboth theoretical and practical.\"-Chemist and Druggist.\nENGINEERING.\nAUSTIN.\nA PRACTICAL TREATISE ON THE PREPARATION,\nCOMBINATION, AND APPLICATION OF CALCA-\nREOUS AND HYDRAULIC LIMES AND CEMENTS.\nTo which is added many useful recipes for various scientific,\nmercantile, and domestic purposes. By James G. Austin.\n1 vol. 12mo\n$3 00\nCOLBURN\nLOCOMOTIVE ENGINEERING AND THE MECHAN-\nISM OF RAILWAYS. A Treatise on the Principles and\nConstruction of the Locomotive Engine, Railway Carriages,\nand Railway Plant, with examples. Illustrated by Sixty-four\nlarge engravings and two hundred and forty woodcuts. By\nZerah Colburn. Complete, 20 parts, $15.00; or 2 vols.\ncloth\n$16 00\nOr, half morocco, gilt top.\n$20 00\nKNIGHT.\nTHE MECHANICIAN AND CONSTRUCTOR FOR EN-\nGINEERS. Comprising Forging, Planing, Lining, Slotting,\nShaping, Turning, Screw-cutting, &o. Illustrated with\nninety-six plates. By Cameron Knight. 1 vol. 4to, half\nmorocco.\n$15 00\nMAHAN.\nAN ELEMENTARY COURSE OF CIVIL ENGINEER-\nING, for the use of the Cadets of the U. S. Military Academy.\nBy D. H. Mahan. 1 vol. 8vo, with numerous woodcuts.\nNew edition. Edited by Prof. De Volson Wood. Full\ncloth\n$5 00\n\"\nDESCRIPTIVE GEOMETRY, as applied to the Drawing of\nFortifications and Stone-Cutting. For the use of the Cadeta\nof the U. S. Military Academy. By Prof. D. H. Mahan.\n1 vol. 8vo. Plates\n$1 50\nINDUSTRIAL DRAWING. Comprising the Description and\nUses of Drawing Instruments, the Construction of Plane\nFigures, the Projections and Sections of Geometrical Solids,\nArchitectural Elements, Mechanism, and Topographical\nDrawing. With remarks on the method of Teaching the\nsubject. For the use of Academies and Common Schools.\nBy Prof. D. H. Mahan. 1 vol. 8vo. Twenty steel plates.\nFull cloth\n$3 00\nA TREATISE ON FIELD FORTIFICATIONS. Contain-\ning instructions on the Methods of Laying Out, Constructing,\nDefending, and Attacking Entrenchments. With the General\nOutlines, also, of the Arrangement, the Attack, and Defence\nof Permanent Fortifications. By Prof. D. H. Mahan. New\nedition, revised and enlarged. 1 vol. 8vo, full cloth, with\nplates\n$3 50\nELEMENTS OF PERMANENT FORTIFICATIONS. By\nProf. D. H. Mahan. 1 vol. 8vo, with numerous large plates.\nCloth\n$6 50\nDigitized by Google\n98\nJOHN WILEY & SON'S LIST OF PUBLICATIONS.\nMAHAN.\nADVANCED GUARD, OUT-POST. and Detachment Service\nof Troops, with the Essential Principles of Strategy and\nGrand Tactics. For the use of Officers of the Militia and\nVolunteers. By Prof. D. H. Mahan. New edition, with\nlarge additions and 12 plates. 1 vol. 18mo, cloth\n$1 50\n.MAHAN\nMECHANICAL PRINCIPLES OF ENGINEERING\n& MOSELY.\nAND ARCHITEOTURE. By Henry Mosely, M.A., F.R.S.\nFrom last London edition, with considerable additions, by\nProf. D. H. Mahan, LL.D., of the U. S. Military Academy.\n1 vol. 8vo, 700 pages. With numerous cuts. Cloth $5 06\nMAHAN\nHYDRAULIC MOTORS. Translated from the French Cours\n& BRESSE.\nde Mecanique, appliquée par M. Bresse. By Lieut. F. A.\nMahan, and revised by Prof. D. H. Mahan 1 vol. 8vo.\nplates\n$2 50\nWOOD.\nA TREATISE ON THE RESISTANCE OF MATE-\nRIALS, and an Appendix on the Preservation of Timber.\nBy De Volson Wood, Professor of Engineering, University of\nMichigan. 1 vol. 8vo. cloth\n$2 50\nA TREATISE ON BRIDGES. Designed as a Text-book and\nfor Practical Use. By De Volson Wood. 1 vol. 8vo, nume-\nrous illustrations, cloth\n$3 00\nGREEK.\nBACSTER.\nGREEK TESTAMENT, ETC. The Critical Greek and\nEnglish New Testament in Parallel Columns, consisting of\nthe Greek Text of Scholz, readings of Griesbach, etc., etc.\n1 vol. 18mo, half morocco\n$3 00\n\"\ndo.\nFull morocco, gilt edges\n4 50\n\"\nWith Lexicon, by T S. Green. Half-bound\n4 50\n\"\ndo. Full morocco, gilt edges\n6 00\n\"\ndo. With Concordance and Lexicon. Half mor., 6 00\n\"\ndo. Limp morocco\n7 50\n\"\nTHE ANALYTICAL GREEK LEXICON TO THE NEW\nTESTAMENT. In which, by an alphabetical arrangement,\nis found every word in the Greek text in every form in which\nit appears-that is to say, every occurrent person, number,\ntense or mood of verbs. every case and number of nouns, pro-\nnouns, &c., is placed in its alphabetical order, fully explained\nby a careful grammatical analysis and referred to its root, so\nthat no uncertainty as to the grammatical structure of any\nword can perplex the beginner, but, assured of the precise\ngrammatical force of any word he may desire to interpret, he\nis able immediately to apply his knowledge of the English\nmeaning of the root with accuracy and satisfaction. 1 vol.\nsmall 4to, half bound\n$6 50\nGREEK-ENGLISH LEXICON TO TESTAMENT. By\nT. S. Green. Half morocco\n$1 50\nHEBREW.\nCREEN.\nA GRAMMAR OF THE HEBREW LANGUAGE. With\ncopious Appendixes. By W. H. Green, D.D., Professor in\nPrinceton Theological Seminary. 1 vol. 8vo, cloth\n$3 50\n\"\nAN ELEMENTARY HEBREW GRAMMAR. With\nTables, Reading Exercises, and Vocabulary. By Prof. W. IL\nGreen, D.D. 1 vol. 12mo, cloth\n$1 50\n\"\nHEBREW CHRESTOMATHY; or, Lessons in Reading and\nWriting Hebrew. By Prof. W.H. Green, D.D. 1 vol. Svo,\ncloth\n$2 00\nLETTERIS.\nA NEW AND BEAUTIFUL EDITION OF THE HE-\nBREW BIBLE. Revised and carefully examined by Myer\nLevi Letteris. 1 vol. 8vo, with key, marble edges\n$2 50\nThis edition has a large and much more legible type than the known one volume\neditions, and the print is excellent, while the name of LETTERIS is a sufficient\nguarantee for correctness.\" -Rev. Dr. J. M. WISE, Editor of the ISRABLITE.\nDigitized\nby\nGoogle\nJOHN WILEY & SON'S LIST OF PUBLICATIONS.\n99\nBAGSTER'S\nBAGSTER'S COMPLETE EDITION OF GESENTUS\nCESENIUS.\nHEBREW AND CHALDEE LEXICON. In large\nclear, and perfect type. Translated and edited with addi-\ntions and corrections, by S. P. Tregelles, LL.D.\nIn this edition great care has been taken to guard the student from Neologian\ntendencies by suitable remarks whenever needed.\n\"The careful revisal to which the Lexicon has been subjected by a faithful and\nOrthodox translator exceedingly enhances the practical value of this edition.\"\n-Edinburgh Ecclemantical Journal.\nSmall 4to, half bound\n$7 50\nBACSTER'S\nNEW POCKET HEBREW AND ENGLISH LEXICON.\nThe arrangement of this Manual Lexicon combines two\nthings-the etymological order of roots and the alphabetical\norder of words. This arrangement tends to lead the learner\nonward; for, as he becomes more at home with roots and\nderivatives, he learns to turn at once to the root, without first\nsearching for the particular word in its alphabetic order. 1\nvol. 18mo, cloth\n$2 00\n\"This is the most beautiful, and at the same time the most correct and per fect\nManual Hebrew Lexicon we have ever \"-Eclectic Review.\nIRON, METALLURGY, &c.\nBODEMANN.\nA TREATISE ON THE ASSAYING OF LEAD, SILVER,\nCOPPER, GOLD, AND MERCURY. By Bodemann &\nKerl. Translated by W. A. Goodyear. 1 vol. 12mo, $2 50\nCROOKES.\nA PRACTICAL TREATISE ON METALLURGY. Adap-\nted from the last German edition of Prof. Kerl's Metallurgy.\nBy William Crookes and Ernst Rohrig. In three vols. thick\n8vo. Price.\n$30 00\nSeparately. Vol. 1. Lead, Silver, Zinc, Cadmium, Tin, Mer-\ncury, Bismuth, Antimony, Nickel, Arsenic, Gold, Platinum,\nand Sulphur\n$10 00\nVol. 2. Copper and Iron\n10 00\nVol. 3. Steel, Fnel, and Supplement\n10 00\nFAIRBAIRN.\nCAST AND WROUGHT IRON FOR BUILDING. By\nWm. Fairbairn. 8vo, cloth\n$2 00\nFRENCH.\nHISTORY OF IRON TRADE, FROM 1621 TO 1857. By\nB. F. French. 8vo, cloth\n$2 00\nKIRKWOOD\nCOLLECTION OF REPORTS (CONDENSED) AND\nOPINIONS OF CHEMISTS IN REGARD TO THE\nUSE OF LEAD PIPE FOR SERVICE PIPE, in the\nDistribution of Water for the Supply of Cities. By I. P.\nKirkwood, C.E. 8vo, cloth\n$1 50\nLESLEY.\nTHE IRON MANUFACTURER'S GUIDE TO THE\nFURNACES, FORGES, AND ROLLING-MILLS OF\nTHE UNITED STATES. By J. P. Lesley. With maps\nand plates. 1 vol. 8vo, cloth\n$8 00\nMACHINISTS-MECHANICS.\nFITZCERALD.\nTHE BOSTON MACHINIST. A complete School for the\nApprentice and Advanced Machinist. By W. Fitzgerald. 1\nvol. 18mo, cloth\n$0 75\nHOLLY.\nSAW FILING. The Art of Saw Filing Scientifically Treated\nand Explained. With Directions for putting in order all kinds\nof Saws, from a Jeweller's Saw to a Steam Saw-mill. Illus-\ntrated by forty-four engravings. Third edition. By H. W.\nHolly. 1 vol. 18mo, cloth\n$0 75\nKNIGHT.\nTHE MECHANISM AND ENGINEER INSTRUCTOR.\nComprising Forging. Planing, Lining, Slotting, Shaping,\nTurning, Screw-Cutting, etc., etc. By Cameron Knight. 1\nvol. 4to, half morocco.\n$15 00\nDigitized\nby\nGoogle\n100\nJOHN WILEY & SON'S LIST OF PUBLICATIONS.\nTURNING, &c.\nLATHE, THE, AND ITS USES, ETC.; or, Instruction in\nthe Art of Turning Wood and Metal. Including a descrip-\ntion of the most modern appliances for the ornamentation of\nplane and curved surfaces, with a description also of an\nentirely novel form of Lathe for Eccentric and Rose Engine\nTurning, a Lathe and Turning Machine combined, and other\nvaluable matter relating to the Art. 1 vol. 8vo, copiously\nillustrated. Including Supplement. 8vo, cloth\n$7 00\nThe most complete work on the subject ever published.\"-Amerscan Artisan.\nHere is an invaluable book to the practical workman and amateur.\"-Londom\nWeekly Times.\nTURNING, &c.\nSUPPLEMENT AND INDEX TO LATHE AND ITS\nUSES. Large type. Paper, 8vo\n$0 90\nWILLIS.\nPRINCIPLES OF MECHANISM. Designed for the use of\nStudents in the Universities and for Engineering Students\ngenerally. By Robert Willis, M.D., F.R.S., President of the\nBritish Association for the Advancement of Science, &c., &c.\nSecond edition, enlarged. 1 vol. 8vo, cloth\n$7 50\nIt ought to be in every large Machine Workshop Office. in every School of\nMechanical Engineering at least, and in the hands of every Professor of\nMechanica, &c.-Prof. B. EDWARD WARREN.\nMANUFACTURES.\nBOOTH.\nNEW AND COMPLETE CLOCK AND WATCH\nMAKERS' MANUAL. Comprising descriptions of the\nvarious gearings, escapements, and Compensations now in\nuse in French, Swiss, and English clocks and watches, Patents,\nTools. etc., with directions for cleaning and repairing. With\nnumerous engravings. Compiled from the French, with an\nAppendix containing a History of Clock and Watch Making in\nAmerica. By Mary L. Booth. With numerous plates. 1\nvol. 12mo, cloth\n$3 00\nGELDARD.\nHANDBOOK ON COTTON MANUFACTURE; or, A\nGuide to Machine-Building, Spinning, and Weaving.\nWith practical examples. all needful calculations, and many\nuseful and important tables. The whole intended to be a\ncomplete yet compact authority for the manufacture of\ncotton. By James Geldard. With steel engravings. 1 vol.\n12mo, cloth\n$2 50\nMEDICAL, &c.\nBULL\nHINTS TO MOTHERS FOR THE MANAGEMENT OF\nHEALTH DURING THE PERIOD OF PREG-\nNANCY, AND IN THE LYING-IN ROOM. With an\nexposure of popular errors in connection with those subjects.\nBy Thomas Bull, M.D. 1 vol. 12mo, cloth\n$1 00\nFRANCKE\nOUTLINES OF A NEW THEORY OF DISEASE, applied\nto Hydropathy, showing that water is the only true remedy.\nWith observations on the errors committed in the practice of\nHydropathy, notes on the cure of cholera by cold water, and\na critique on Priessnitz's mode of treatment. Intended for\npopular use. By the late H. Francke. Translated from the\nGerman by Robert Blakie, M.D. 1 vol. 12mo, cloth\n$1 50\nGREEN.\nA TREATISE ON DISEASES OF THE AIR PASSAGES.\nComprising an inquiry into the History, Pathology, Causes,\nand Treatment of those Affections of the Throat called Bron-\nchitis, Chronic Laryngitis, Clergyman's Sore Throat, etc., eta\nBy Horace Green, M.D. Fourth edition, revised and enlarged.\n1 vol. 8vo, cloth.\n$3 06\n\"\nA P? CTICAL TREATISE ON PULMONARY TUBER-\nCULOSIS, embracing its History, Pathology, and Treat-\nment. By Horace Green, M.D. Colored plates 1 vol. 8vo,\ncloth\n$5 06\nDigitized\nby\nGoogle\nJOHN WILEY & SON'S LIST OF PUBLICATIONS.\n101\nGREEN.\nOBSERVATIONS ON THE PATHOLOGY OF CROUP\nWith Remarks on its Treatment by Topical Medications By\nHorace Green, M.D. 1 vol. 8vo, cloth\n$1 25\n\"\nON THE SURGICAL TREATMENT OF POLYPI OF\nTHE LARYNX, AND CEDEMA OF THE GLOTTES.\nBy Horace Green, M.D. 1 vol 8vo\n$1 25\n66\nFAVORITE PRESCRIPTIONS OF LIVING PRACTI-\nTIONERS. With a Toxicological Table, exhibiting the\nSymptoms of Poisoning, the Antidotes for each Poison, and\nthe Test proper for their detection. By Horace Green. 1\nvol. 8vo, cloth\n$2 50\nTILT.\nON THE PRESERVATION OF THE HEALTH OF\nWOMEN AT THE CRITICAL PERIODS OF LIFE.\nBy E. G. Tilt, M.D. 1 vol. 18mo, cloth.\n$0 50\nVON DUBEN.\nGUSTAF VON DUBEN'S TREATISE ON MICRO-\nSCOPICAL DIAGNOSIS. With 71 engravings. Trans-\nlated, with additions, by Prof. Louis Bauer, M.D. 1 vol. 8vo,\ncloth\n$1 00\nMINERALOGY.\nBRUSH.\nON BLOW-PIPE ANALYSIS. By Prof. Geo. J. Brush. (In\npreparation.)\nDANA.\nDESCRIPTIVE MINERALOGY. Comprising the most re-\ncent Discoveries. Fifth edition. Almost entirely re-written\nand greatly enlarged. Containing nearly 900 pages 8vo, and\nupwards of 600 wood engravings. By Prof. J. Dana.\nCloth\n$10 00\n\"We have used a good many works on Mineralogy, but have met with none that\nbegin to compare with this in fulness of plan, detail, and execution.\"-\nAmerican Journal of Mining.\nDANA & BRUSH. APPENDIX TO DANA'S MINERALOGY, bringing the\nwork down to 1872. By Prof. G. J. Brush. Svo\n$0 50\nDANA.\nDETERMINATIVE MINERALOGY. 1 vol. (In prepa-\nration.)\n\"\nA TEXT-BOOK OF MINERALOGY. 1 vol. (In prepa-\nration.)\nMISCELLANEOUS.\nBAILEY.\nTHE NEW TALE OF A TUB. An adventure in verse. By\nF. W. N. Bailey. With illustrations. 1 vol. 8vo\n$0 75\nCARLYLE.\nON HEROES, HERO-WORSHIP, AND THE HEROIC IN\nHISTORY. Six Lectures. Reported, with emendations and\nadditions. By Thomas Carlyle. 1 vol. 12mo, cloth $0 75\nCATLIN.\nTHE BREATH OF LIFE; or, Mal-Respiration and its\nEffects upon the Enjoyments and Life of Man. By Geo.\nCatlin. With numerous wood engravings. 1 vol. 8vo, $0 75\nCHEEVER.\nCAPITAL PUNISHMENT. A Defence of. By Rev. George\nB. Cheever, D.D. Cloth\n$0 50\n\"\nHILL DIFFICULTY, and other Miscellanies. By Rev.\nGeorge B. Cheever, D.D. 1 vol. 12mo, cloth\n$1 00\n\"\nJOURNAL OF THE PILGRIMS AT PLYMOUTH ROCK.\nBy Geo. B. Cheever, D.D. 1 vol. 12mo, cloth\n$1 00\n6\nWANDERINGS OF A PILGRIM IN THE ALPS. By\nGeorge B. Cheever, D.D. 1 vol. 12mo, cloth\n$1 00\n\"\nWANDERINGS OF THE RIVER OF THE WATER OF\nLIFE. By Rev. Dr. George B. Cheever. 1 vol. 12mo,\ncloth\n$1 00\nCONYBEARE.\nON INFIDELITY. 12mo, cloth\n1 00\nCHILD'S BOOK OF FAVORITE STORIES. Large colored plates. 4to.\ncloth\n$1 50\nDigitized by\nGoogle\n102\nJOHN WILEY & SON'S LIST OF PUBLICATIONS.\nEDWARDS.\nFREE TOWN LIBRARIES. The Formation, Management\nand History in Britain, France, Germany, and America.\nTogether with brief notices of book-collectors, and of the\nrespective places of deposit of their surviving collections.\nBy Edward Edwards. 1 vol. thick 8vo\n$4 00\nGREEN.\nTHE PENTATEUCH VINDICATED FROM THE AS\nPERSIONS OF BISHOP COLENSO. By Wm. Henry\nGreen, Prof. Theological Seminary, Princeton, N. J. 1 vol.\n12mo, cloth\n$1 25\nCOURAUD.\nPHRENO-MNEMOTECHNY; or, The Art of Memory.\nThe series of Lectures explanatory of the principles of the\nsystem. By Francis Fauvel-Gouraud. 1 vol. 8vo, cloth, $2 00\n\"\nPHRENO-MNEMOTECHNIC DICTIONARY. Being a\nPhilosophical Classification of all the Homophonic Words of\nthe English Language. To be used in the application of the\nPhreno-Mnemotechnic Principles. By Francis Fauvel-Gou-\nraud. 1 vol. 8vo, cloth\n$2 00\nHEIGHWAY.\nLEILA ADA. 12mo, cloth\n1 00\n6:\nLEILA ADA'S RELATIVES. 12mo, cloth\n1 00\nKELLY.\nCATALOGUE OF AMERICAN BOOKS. The American\nCatalogue of Books, from January, 1861, to January, 1866.\nCompiled by James Kelly. 1 vol. 8vo, net cash\n$5 00\n\"\nCATALOGUE OF AMERICAN BOOKS. The American\nCatalogue of Books from January, 1866, to January, 1871.\nCompiled by James Kelly. 1 vol. 8vo, net\n$7 50\nMAVER'S\nCOLLECTION OF GENUINE SCOTTISH MELODIES.\nFor the Piano-Forte or Harmonium, in keys suitable for the\nvoice. Harmonized by C. H. Morine. Edited by Geo. Alex-\nander. 1 vol. 4to, half calf\n$10 00\nNOTLEY.\nA COMPARATIVE GRAMMAR OF THE FRENCH,\nITALIAN, SPANISH, AND PORTUGUESE LAN-\nGUAGES. By Edwin A. Notley. 1 vol., cloth\n$5 00\nPARKER.\nPOLAR MAGNETISM. First and Second Lectures. By John\nA. Parker. Each\n$0 25\n\"\nNON-EXISTENCE OF PROJECTILE FORCES IN\nNATURE. By John A. Parker\n$0 25\nSTORY OF\nA POCKET BIBLE. Illustrated. 12mo, cloth\n$1 00\nTUPPER\nPROVERBIAL PHILOSOPHY. 12mo\n1 00\nWALTON\nTHE COMPLETE ANGLER; or, The Contemplative Man's\n& COTTON.\nRecreation, by Isaac Walton, and Instructions how to Angle\nfor a Trout or Grayling in a Clear Stream, by Charles\nCotton, with copious notes, for the most part original. A\nbibliographical preface, giving an account of fishing and\nFishing Books, from the earliest antiquity to the time of\nWalton, and a notice of Cotton and his writings, by Rev.\nDr. Bethune. To which is added an appendix, including\nthe most complete catalogue of books in angling ever printed,\n&c. Also a general index to the whole work. 1 vol. 12mo,\ncloth\n$3 00\nWARREN.\nNOTES ON POLYTECHNIC OR SCIENTIFIC SCHOOLS\nIN THE UNITED STATES. Their Nature. Position,\nAims, and Wants. By S. Edward Warren. Paper $0 40\nWILLIAMS.\nTHE MIDDLE KINGDOM. A Survey of the Geography,\nGovernment, Education. Social Life, Arts, Religion, &a, of\nthe Chinese Empire and its Inhabitanta. With a new map of\nthe Empire. By S. Wells Williams. Fourth edition, in\n2 vols\n00\nDigitized by Google\nJOHN WILEY & SON'S LIST OF PUBLICATIONS.\n103\nRUSKIN'S WORKS.\nUniform in size and style.\nRUSKIN.\nMODERN PAINTERS. 5 vols. tinted paper, bevelled toards,\nplates, in box\n$18 00\n\"\nMODERN PAINTERS. 5 vols. half calf\n27 00\n\"\n\"\n\"\n\"\nwithout plates\n12 00\n\"\n..\n\"\n\"\n\"\nhalf calf, 20 00\nVol. 1.-Part 1. General Principles. Part 2. Truth.\nVol. 2.-Part 8. Of Ideas of Beauty.\nVol. 3.-Part 4. Of Many Things.\nVol. 4.-Part 5. Of Mountain Beauty.\nVol. 5.-Part 6. Leaf Beauty. Part 7. Of Cloud Beauty. Part\n8. Ideas of Relation of Invention. Formal. Part 9. Ideas of\nRelation of Invention, Spiritual.\n66\nSTONES OF VENICE. 3 vols., on tinted paper, bevelled\nboards, in box\n$7 00\n\"\nSTONES OF VENICE. 8 vols., on tinted paper, half\ncalf.\n$12 00\n\"\nSTONES OF VENICE. 8 vols., cloth\n6 00\nVol. 1.-The Foundations.\nVol. 2.-The Sea Stories.\nVol. 3.-The Fall.\n\"\nSEVEN LAMPS OF ARCHITEOTURE. With illustrations,\ndrawn and etched by the authors. 1 vol. 12mo, cloth, $1 75\n\"\nLECTURES ON ARCHITECTURE AND PAINTING.\nWith illustrations drawn by the author. 1 vol. 12mo,\ncloth\n$1 50\nof\nTHE TWO PATHS. Being Lectures on Art, and its Appli-\ncation to Decoration and Manufacture. With plates and\ncuts. 1 vol. 12mo, cloth\n$1 25\nis\nTHE ELEMENTS OF DRAWING. In Three Lettars to\nBeginners. With illustrations drawn by the author. 1 vol.\n12mo, cloth.\n$1 00\n1\nTHE ELEMENTS OF PERSPECTIVE. Arranged for the\nuse of Schools. 1 vol. 12mo, cloth\n$1 00\n\"\nTHE POLITICAL ECONOMY OF ART. 1 vol. 12mo,\ncloth\n$1 00\n\"\nPRE-RAPHABLITISM.\nNOTES ON THE CONSTRUCTION OF\nSHEEPFOLDS.\nKING OF THE GOLDEN RIVER; or, The\n}\n1 vol. 12mo,\ncloth, $1 00\nBlack Brothers. A Legend of Stiria.\nRUSKIN.\nSESAME AND LILIES. Three Lectures on Books, Women,\n&c. 1. Of Kings' Treasuries. 2. Of Queens' Gardens. 3.\nOf the Mystery of Life. 1 vol. 12mo, cloth\n$1 50\n\"\nAN INQUIRY INTO SOME OF THE CONDITIONS AT\nPRESENT AFFECTING \"THE STUDY OF AR-\nOHITHOTURE\" IN OUR SCHOOLS. 1 vol. 12mo,\npaper.\n$0 15\nof\nTHE ETHICS OF THE DUST. Ten Lectures to Little\nHousewives, on the Elements of Crystallization. 1 vol.\n12mo, cloth.\n$1 25\n&\n\" UNTO THIS LAST.\" Four Essays on the First Principles of\nPolitical Economy. 1 vol. 12mo, cloth\n$1 00\nDigitized by Google\n104\nJOHN WILEY & SON'S LIST OF PUBLICATIONS.\nRUSKIN.\nTHE CROWN OF WILD OLIVE. Three Lectures OR Work,\nTraffic, and War. 1 vol. 12mo. cloth\n$1 00\n\"\nTIME AND TIDE BY WEARE AND TYNE. Twenty-\nfive Letters to a Workingman on the Laws of Work. 1 rol.\n12mo, cloth\n$1 00\n\"\nTHE QUEEN OF THE AIR. Being a Study of the Greek\nMyths of Cloud and Storm. 1 vol. 12mo, cloth\n$1 00\n6\nLECTURES ON ART. 1 vol. 12mo, cloth\n1 00\n\"\nFORS CLAVIGERA. Letters to the Workmen and Labourers\nof Great Britain. Part 1. 1 vol. 12mo, cloth, plates, $1 00\n\"\nFORS CLAVIGERA. Letters to the Workmen and Labourers\nof Great Britain. Part 2. 1 vol 12mo, cloth, plates, $1 00\n\"\nMUNERA PULVERIS. Six Essays on the Elements of\nPolitical Economy. 1 vol. 12mo, cloth\n$1 00\n\"\nARATRA PENTELICL Six Lectures on the Elements of\nSculpture, given before the University of Oxford. By John\nRuskin. 12mo, cloth, $1 50, or with plates.\n$3 00\n\"\nTHE EAGLE'S NEST. 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Extra cloth,\ngilt head.\n$2 00\n\"\nSELECTIONS FROM THE WRITINGS OF JOHN\nRUSKIN. 1 vol. 12mo, cloth extra, gilt head\n$2 50\n\"\nSELECTIONS FROM THE WRITINGS OF JOHN\nRUSKIN. 1 vol. 12mo, plain cloth\n$2 00\n\"\nSESAME AND LILIES. 1 vol. 12mo\n$1 75\n\"\nETHICS OF THE DUST. 12mo.\n1 75\n\"\nCROWN OF WILD OLIVE. 12mo\n1 50\nRUSKIN'S BEAUTIES.\n\"\nTHE TRUE AND BEAUTIFUL\nPRECIOUS THOUGHTS.\n8 vols., in box, cloth extra,\ngilt head.\n$6 00\nCHOICE SELECTIONS.\ndo,, half calf 10 00\nRUSKIN'S POPULAR VOLUMES.\nCROWN OF WILD OLIVE. SESAME AND LILIES.\nQUEEN OF THE AIR. ETHICS OF THE DUST.\n4 vols. in box, cloth extra, gilt head.\n$6 00\nRUSKIN'S WORKS.\nRevised edition.\nRUSKIN.\nVol. 1.-SESAME AND LILIES. Three Lectures. By John\nRuskin, LL.D. 1. Of King's Treasuries. 2. of Queens'\nGardens. 3. Of the Mystery of Life. 1 vol. 8vo, cloth.\n$2.00. Large paper.\n$2 50\nDigitized by\nGoogle\nJOHN WILEY & SON'S LIST OF PUBLICATIONS.\n105\nRUSKIN'S WORKS.\nRevised edition.\n\"\nVol. 9.-MUNERA PULVERIS. Six Essays on the Elements\nof Political Economy. By John Ruskin. 1 volume 8vo,\ncloth.\n$2 00\nLarge paper\n2 50\n$\nVol. 8.-ARATRA PENTELICL Six Lectures on the Fle.\nments of Sculpture, given before the University of On for\nBy John Ruskin. 1 vol. 8vo\n$4 00\nLarge paper\n4 50\n\"\nTHE POETRY OF ARCHITECTURE: Villa and Cottage.\nWith numerous plates. By Kata Phusin. 1 vol. 12mo,\ncloth\n$1 50\nKata Phusin is the supposed Nom de Plume of John Ruskin.\n\"\nFORS CLAVIGERA. Letters to the Workmen and Laborers\nof great Britain. Part 3. 1 vol. 12mo, cloth\n$1 50\nRUSKIN-COMPLETE WORKS.\nTHE COMPLETE WORKS OF JOHN RUSKIN. 27 vols, extra cloth, in a box $40 00\nDitto\n27 vols., extra cloth. 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Comprising Seven Lec-\ntures delivered before the Franklin Institute, showing the\ngreat want of improved methods of Ventilation in our build-\nings, giving the chemical and physiological process of res-\npiration, comparing the effects of the various methods of\nheating and lighting upon the ventilation, &c. Illustrated\nby many plans of all classes of public and private buildings,\nshowing their present defects, and the best means of im-\nproving them. By Lewis W. Leeds. 1 vol. 8vo, with nu-\nmerous wood-cuts and colored plates. Cloth\n$2 50\n\"It ought to be in the hands of every family in the country.\"-Technologist.\n\"Nothing could be clearer than the author's exposition of the principles of the\nprinciples and practice of both good and bad ventilation.\"-Van Nostrand's\nEngineering Magazine.\n\"The work is every way worthy of the widest circulation. \"-Scientific American.\nREID.\nVENTILATION IN AMERICAN DWELLINGS. 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