Relative Activity of Radium and Uranium. 55 



mineral, so that the analytical determinations and radio- 

 active measurements are in direct accord with one another, 

 although it was assumed for purposes of calculation that 

 the uranoso-uranic oxide contained 84*8 per cent, of 

 uranium. 



It has been found by McCoy* that considerable absorption 

 of the radiation takes place in the film itself when its thick- 

 ness is appreciable. In earlier work by one of usf it was 

 shown that by the use of thin films any necessity for an 

 absorption correction could he avoided. To further demon- 

 strate this fact a series of films of uranoso-uranic oxide 

 weighing from 0*0019 g. to 0'04g. were prepared and their 

 activities were measured. The results are given in Table I. 

 and are shown graphically in fig. 1. In films weighing not 

 more than 10 milligrams the absorption of the a-radiation 

 was negligible. In all cases where values of importance 

 were to be derived the weight of the films used was less than 

 this maximum, so that no correction has to be made in the 

 results for absorption of the radiations. 



The average of the first eight values in the fourth column 

 of Table I. is 666, which denotes that the average activity 

 of the eight lighter films was 666 divisions per minute 

 per gram of uranium oxide. This corresponds to an activity 

 of 785 (viz. 666/0*848) divisions per minute per gram of 

 uranium. 



Table I. 



Film 



Weight of oxide 



Activity 



Activity 



Number. 



in grams. 



Div./Min. 



Weight. 



20 



•00187 



1-24 



663 



19 



•00432 



2-91 



673 



15 



•00566 



3-77 



666 



18 



•00653 



4-37 



669 



21 



•00740 



4-95 



668 



22 



•00832 



5-56 



5-95 



662 



14 



•00898 



662 



23 



•00653 



4-38 



670 



25A 



•01405 



8-89 



633 



8 



•01380 



8-94 



648 



25B 



•01440 



9-30 



645 



26 



•02150 



1345 



624 



24 



•04350 



25-96 



596 



* Journ. Am. Chem. Soc. xxvii. p. 391 (1905); Phys. Rev. i. p. 393 

 (1913). 



t Boltwood, Am. Journ. Sci. xxv. p. 176 (1908). 



