Letters Received to H.H. Barker, December 10, 1928

UNIVERSITY OF MISSOURI COLUMBIA DEPARTMENT OF CHEMISTRY December 10, 1928 Mr. H. H. Barker United States Radium Corporation 535 Pearl Street New York, New York My dear Howard: Your letter of December 8 has just come to hand and I shall take just a moment to tell you about the différence between your value and my value in the amount of radium required to liberate the radon which we reported for Dr. Flinn's subject. In explanation of the discrepancy, let me quote the paragraph from the letter to Dr. Flinn which will, I think, clear up the matter. "Your letter of the 27th giving experimental data obtained on the girl which you tested for radioactivity has just come to hand. I note that the girl is rather low in activity by the gamma ray method, and your test on Nov- ember 27 is lover than the one made in June. I have made some approximate cal- culations of the radium content of the subject of November 27. The value is ap- proximately four micrograms by the gamma ray test. The expired air test seems to be perfectly definite also. Assuming a constant for the instrument of 7.3 X 10-9 and assuming further that the volume of air contained in the chamber is 2.7 liters, I find that the expired air from this subject contains about 15. x 10-12 curies per liter, and if we assume that it takes 15 seconds to blow a liter of air through the instrument, then it follows that non emanation continuously expired corresponds to about half a microgram of radium." Please note that I have assumed that it takes 15 seconds to blow a liter of air through the instrument while you are assuming that the air in the chamberwould be expired in 18 seconds. I am assuming that it would be expired in 45 seconds. Your assumption is based upon the relations which we have assumed up to this time but in the experiments which I have conducted here recently, I have always timed myself and I find that in blowing air through the chamber in series with a drying train that one does not breathe as fast as in normal breathing. I found that it takes about 15 seconds to expire a liter of air in the set=up which I make use of. I determined this by finding the time required to expire six liters of air which I caught in a 6 liter flask filled with water inverted in a pneumatic trough. I found it took a minute and a half to displace the water and I tried to duplicate the rate of blowing just as I did in blowing the expired air through the drying train and the chamber of the electroscope. I therefore feel that your point about using the Douglass bag is a very good one and that we should use the Doublass bag in making tests upon expired air. I may add, too, that our Douglass bag outfit has come to hand fully equipped with valves and stopcocks.