SUCCESSION OF CHAM IKS IN RADIOACTTVK RODIKS. 



199 



ami, in consequence, the amount of B present after A is transformed should be 

 somewhat greater than if B were produced in<lr|'iidently. Since the change of A is 

 fairly rapid, the effect should be most marked in the early part of the curve. 



In order to examine this point experimentally, the curve of rise of activity, 

 measured by the /? rays, was determined immediately after the introduction of a 

 large quantity of the radium emanation into a closed vessel. The curve of decay of 

 activity on a body after removal of the emanation, and the rise of activity after the 

 introduction of the emanation, are in all cases complementary to one another. While, 

 however, it is difficult to measure with certainty whether the activity has fallen in a 

 given time, for example, from 100 to 99 or 98*5, it is easy to be sure whether the 

 corresponding rise of activity in the converse experiment is 1 or 1 '5 per cent, of the 

 final amount. Fig. 14, curve I., shows the rise of activity (measured by the /8 rays) 



IO 15 ao 



Time in MinuCes. 



Fig. 14. 



obtained for an interval of 20 minutes after the introduction of the emanation. The 

 ordinates represent the percentage amount of the final activity regained at any time. 



Curve III. shows the theoretical curve obtained on the assumption that A is a 

 parent of B. This curve is calculated from equation (9) discussed in section 11, and 

 X,, X,j, Xg are the values previously found. 



Curve IL gives the theoretical activity at any time on the assumption that the 

 sukstances A and B arise independently. This is calculated from an equation of the 

 same form as (8). 



It is seen that the experimental results agree best with the view that A and B 

 arise independently. Such a conclusion, however, is of too great importance to be 

 accepted before examining closely whether the theoretical conditions are fulfilled in 



