102 



Mr. A. S. Eve on the Radioactive 



contained air by means o£ convection currents caused by 

 heating the outside of the cylinder. After charging for 

 three hours the wire was removed and wound on the reel, 



Fig. 2. 



and then placed as before in the zinc cylinder above the 

 electroscope. The activity, ten minutes after the charge 

 stopped, caused a fall of potential of 7*8 scale-divisions per 

 minute. The solution of radium bromide, initially freed 

 from emanation by passing a current of air through it, had 

 been allowed to stand for fifteen hours in a closed vessel 

 before introducing it into the zinc cylinder. Since the 

 constant of change, A, for radium emanation is about '18, it 

 can readily be shown that only one-tenth of the full supply 

 of the emanation had been obtained from the radium bromide. 

 Thus the total active deposit, which could be obtained from 

 2 x 10~ 4 mgs. of radium bromide in radioactive equilibrium, 



