Relative Activity of Radium and, Uranium. 57 



2606 divisions per minute per gram of mineral for the 

 uranium series of products which it contains and a value 

 of 3570 divisions per minute per gram of uranium present 

 (2606/-73). 



The uraninite, however, contained less than the full equi- 

 librium amounts of the uranium- radium products because of 

 the fact that in the finely divided form in which it was used 

 it spontaneously lost a small proportion of its radium emana- 

 tion. The loss of this and the absence of the proportionate 

 amounts of radium A and radium C would cause a deficiency 

 which must be corrected for. 



The relative proportion of radium emanation lost by the 

 films of uraninite was determined by the method described 

 by McCoy and Leman*. It w r as found to be 9'1 per cent. 

 In applying the correction, the value for the ratio of tne 

 activity of the radium products (radium emanation, radium A 

 and radium C) to the activity of the radium with which 

 they are in equilibrium, as found by McCoy and Leman, 

 namely 4*11, was made use of, as was also the ratio of the 

 activity of radium to the activity of the uranium with which 

 it is in equilibrium (0*49) which was derived in the course 

 of the present investigation (see p. GO). 



The correction has the following form, 



3570 + (785 x 4-11 x 0-49x0-091) = 3715, 



which gives an activity of 3715 divisions per minute per 

 gram of uranium as the activity of the mineral due to 

 uranium and its products in a complete state of equilibrium. 



From this final result w^e are able to calculate the value 

 sought, namely, the ratio of the activity of the uranium with 

 its equilibrium amounts of disintegration products to the 

 activity of the uranium (uranium 1. 4- uranium II.) alone. 



This is 3715/785 = 4*73, which is in good agreement with 

 the value 4'69 found earlier by Boltwood. 



Ratio of the Activity of Radium to the Activity of the Uranium 

 ivitli which it is associated. 



If the transformation of the atoms of uranium I. into 

 atoms of uranium II. takes place directly without the pro- 

 duction of any side products, and the transformations 

 uranium IL — ionium — radium proceed in the same direct 

 manner, then the relative activities of the three members — 

 uranium I., uranium II., radium — should be proportional to 



* Phys. Rev. vi. p. 185 (1915). 



