Letters Sent to Dr. James E. Ives, June 11, 1929

June 11th,1929. Dr. James E. Ives, Room 1-123 "C" Bldg., 16 Seventh St. S.W. Tashington, D. C. Dear Dr. Ives: The matter of determining the quantity of radium in unknown preparations by the film method may be accomplished with a fair degree of accuracy, provided the physical conditions are well stendardized and, held within certain limits. However, my experience has been that it is difficult to prepare a standard which will sarve satisfactorily for measur- ing unknown preparations unless such preparations are prepard in a manner identical with that utilized in preparing a standard. At one time in the refining of radium we used to separate a product which we termed "slimes", such products being a concentration of radium in the fines of the ore and, one would assume that these products could be compared successfully by the film method, but such was not the case - by attempting such a practice we often had variations of 100% or more. If you elect to follow this course, I would suggest that you have at least one of your samples so collected, analysed so that you actu- ally know the radium content and then use such a preparations as a standard. The amount of material placed in the electroscope for measure- ment must be the same and, the physical conditions identical. Any varia- tion in the amount of material, the distance from the electrode,the physical characteristics of the incinerated residue, etc., will obviously introduce errors. It is difficult for me to advise you definitely on such a subject, as this, for after all one can arrive at definite conclusions based upon experimental data only. I would consider it rather hazardous to prepare a preparation containing a known amount of radium and use that as a standard for computing the quantities of radium in unknown proparations by the film method. If it is at all possible I would suggest that you have the preparations collected and analyzed for the radium and mesothorium content, for after all that is the only sure way of knowing what you have present. The film method is more or less qualitätive at the best. Sincerely yours, Vice President. HHBarker RH