Letters Received to H.H. Barker, May 23, 1930

TREASURY DEPARTMENT UNITED STATES PUBLIC HEALTH SERVICE OFFICE OF INDUSTRIAL HYGIENE WASHINGTON, D. C. AND SANITATION Room 1-123, "C" Bldg. 16 Seventh St., S. W. May 23, 1930 Mr. H. H. Barker, U. S. Radium Corporation, 535 Pearl St., New York, N. Y. Dear Mr. Barker: You were kind enough to send Dr. Schwartz one gram of luminous paint. I note that this paint is marked Grade L, and I also understand through Mr. knowles that the paint supplied by your company and used in the various factories where he has been making surveys is of different grades, identified by different letters. I should be very much obliged if you would tell me what the different letters signify. Do they signify different compositions or simply different degrees of strength of the radium salt used in making them up? I suppose that the luminous material is made up by mixing a certain amount of radium bromide or radium chloride with zinc sulphide and some other substances. The point we are particularly interested in at the present timeisto know how the various grades manufactured by your company differ from each other. Yours sincerely, James E was (James E. Ives) Physicist, U.S.P.H.S.