THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XL VII. — The Preparation oflTrano-uranic Oxide, U 3 8 , 

 and a Standard ofltadio-activity; by H. N. McCoy and 

 G. C. Ashman. 



It is obvious that for the comparison of the activities of 

 radio-active substances a standard or unit of activity is of 

 prime importance. One of us* has proposed to take as this unit 

 the activity due to one square centimeter of a thick film of 

 U 3 8 , of sufficient thickness to have maximum a-ray activity. 

 It was shown that such a standard could be reproduced easily 

 and apparently with quite definite activity. We have now 

 studied the problem of the preparation of a standard of activity 

 more fully, with the results recorded below. 



The chief points of importance are : 



First, The complete removal from uranium of radium and 

 other active as well as inactive impurities ; 



Second, The preparation of an oxide of perfectly definite 

 composition ; 



Third, The preparation of uniform films of the oxide. 



Fourth, The activity due to the /3 rays. 



Material from three distinct sources was used : 



(A) So-called chemically pure uranyl nitrate from the firm 

 of. C. A. F. Kahlbaum. This was practically free from all 

 ordinary impurities. The radium content, which was deter- 

 mined by means of the emanation, amounted to 2*5 X *0~ 5 of 

 the equilibrium quantity. A portion of this nitrate, recrystal- 

 lized from water twice, constituted sample A. It was not 

 tested for radium again, as the original amount would increase 

 the activity less than 0*01 per cent. 



(B) An old sample of uranyl acetate, which contained a con- 

 siderable amount of sodium as the chief impurity. The amount 



* McCoy, Phil. Mag., xi, 177, 1906. 



Am. Jour Sci. — Fourth Series, Vol. XXVI, No. 156. — December, 1908. 

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