Transformation of Thorium and Actinium Emanation. 727 



that time was taken as 100 per cent, and corrections made 

 corresponding to the time at which each deflexion was noted. 



Fiff. 3. 



100 

 .■80 



I 



^20 



































S 









16 



T/me //v Minutes 



24 



30 



Since the growth of the active deposit of thorium was very 

 much slower, the theoretical curve was plotted for a period 

 of 30 minutes and the corrections made using the activity 

 observed after 30 minutes as 100 per cent. 



When studying the decay of actinium emanation, deflexions 

 during 2 seconds were recorded. This time is rather long as 

 compared with the half-value period. It would therefore 

 appear that the average activity would not represent the true 

 activity at the mean time, i. <?., 1 second from the beginning 

 of deflexion. Calculation shows, however, that this correction 

 factor only amounts to '9936, and is absolutely negligible 

 for thorium emanation when deflexions extended over the 

 time used. 



The exact period of the pendulum, determined over a con- 

 siderable time by a stop watch, was 1*005 seconds. 



Data and Results, 



The complete data for an experiment with actinium 

 emanation are given in Table II. 



The natural leak without auxiliary capacity in parallel with 

 the electroscope was 5*1 divisions per minute. 



In order to obtain an idea of the value of each experiment 

 the log curves were plotted on a large scale. Points falling 

 on or near the log curve, separated as far as possible in time, 



