Volatility of Thorium T). 



817 



that of Th C. The presence of a small percentage of Th B 

 with the Th C in no way affects the point to be discussed, as 

 the soft /3 rays from Th B are completely absorbed by the 

 bottom of the electroscope. Fig. 3 B represents the " log 

 curve " for the exponential portion of curve A, whence we 

 can at once obtain the whole curve of /3 activity in the case 

 where no Th D has been volatilized; this is represented by the 

 dotted portion (6) of curve A fig. 3. It is obvious that the 

 difference between the portions (a) and (b) of curve A repre- 

 sents the decay of activity of the Th I) which has been 



Fier. 4. 



//y Mirw re. 



removed in the furnace. This is shown in fig, 4 A, curve B 

 representing the corresponding " log curve/' showing that 

 decay is exponential with a period of 3*1 min. Figs. 3 & 4 

 at once give the relative initial ionizations due to Th C and 

 Th J) — i n this case 2:1. Using the values given by Marsden 



