﻿emitted Of/ Thorium and Actinium. 183 



found necessary to remove these residues by successive pre- 

 cipitations before it was possible to drive off most of the 

 active deposit by heat. 



The results are shown graphically in fig. 2, the prdinates 



100 



80 









Fig. 



2. 













^S 









B 6 







60 



^ & 



















"> 



-t-i 

 o 



< 40 



A 



1 £ 

 9 ^ 















°0 





<y 



< 



















1 



















Time in hours. 



giving the activities, and the abscissa} the time in hours 

 measured from the end of the heating. 



The initial decrease of the a. and /3 activities found in some 

 experiments with thorium X was not observed with actinium 

 X. The curves in some experiments were nearly horizontal 

 for the first few minutes, indicating that the active deposit 

 had not been completely removed. The activities rose rapidly 

 to a maximum in the course of about three hours in conse- 

 quence of the formation of the active deposit by the emanation. 

 By producing the rise curve backwards in order to obtain 

 the activity at the moment the heating ceased, it was found 

 that the initial /3 activity in different experiments was 2'5, 

 3*5, and 5"0 per cent, of the maximum (3 activity. The 

 initial a. ray activity, on the other hand, was betwen 12 and 

 76 per cent, of the maximum. These values would be only 

 slightly lowered by taking into account, as in the case of the 

 experiments with thorium X, the fact that the equilibrium 

 activity in the beginning should be higher than the maximum 



