Letters Received to H.H. Barker, October 5, 1928

UNIVERSITY OF MISSOURI COLUMBIA RECEING OCT 8 DEPARTMENT OF CHEMISTRY October 5, 1928 Mr. H. H. Barker, 535 Pearl Street, RADI* United States Radium Corporation, New York, N. Y. My dear Barker: We have not yet shipped you the spinthar- iscopes and the reason for our delay is the fact that our screens all appear to be somewhat radioactive. Ve have had several of them made by different persons but all from the same stock sample of zinc sulfide. We believed up to this time that this sample was practically free from radioactive substances because we had tested it with the high power microscopes and found only accasion- al scintillations, but now when the area of the field is greatly increased we find scintillations to be too numerous for compara- tive counting when the number of scintillations to be counted is rather small. We shall, however, send on one of these instruments and in the meantime we shall try to secure samples of luminous zinc sulfide from other sources and we hope that we may acciden- tally get hold of a sample which is free from this residual acti- vity. I wish to thank you for your suggestions on the section of the report which has gone out to you. That is just exactly the kind of criticism we welcome and I hope that Dr. Flinn will make equally constructive suggestions. I am now pre- paring the theoretical part of our report. Sincerely yours Herman Schlundt Herman Schlundt. HS c b