530 McCoy and Ashman — TJrano- Uranic Oxide. 



Summary. 



1. Uranium is easily freed from all other radio-active sub- 

 stances. 



2. Pure TTg0 8 of perfectly definite composition is readily 

 obtained by heating any lower or higher oxide of uranium in 

 air at 700° 



3. Uniform films of U 3 8 , 7 cm in diameter, weighing 0*6 to 

 0*8 g., have definite and constant a-ray activity and are there- 

 fore recommended as standards of radio-activity. 



4. The a-ray saturation current for such a standard film 

 was measured in absolute units and from the results the total 

 ionization current for 1 g. of uranium, in an infinitely thin film, 

 was calculated. 



Kent Chemical Laboratory, University of Chicago, Sept., 1908. 



