Deposit of Radium in an Electric Field. 



489 



Table I. 



Emanation in Air at 1 Atmosphere. 



Potential in 



Percentage cathode 



volts 



activity 



18 



42-7 



160 



79-1 



900 



85-9 



975 



86-6 



2250 



86-9 



2800 



88-5 



3250 



89-0 



4000 



91*3 



be in the ratio 1 : 50, and assuming that the uncharged restatoms 

 were distributed in this proportion. The true percentage 

 cathode activity, that is, the number of positive carriers 

 expressed as a percentage of the total number of carriers, is 

 obtained from the percentage cathode activity (p), as deter- 



51p 



50 



- 2. 



mined experimentally, by evaluating the expression 



All values given in this paper for the percentage cathode activ- 

 ity denote the true percentage obtained by correcting in this 

 manner. 



A typical set of measurements is given below : 



Emanation passed through P 2 5 and glass-wool into 

 vessel containing air at 1 atmosphere. +975 volts 

 on case. Exposure about 2 hours. 



Equilibrium rate with added capacity : 6*17. 



Activity on case measured at 10 and 15 minutes after 

 removal of emanation ; rates with added capacity : '19 

 and *17 respectively. 



Activity on cathode measured at 20 and 25 minutes 

 after removal of emanation ; rates with added capac- 

 ity : 1*05 and *98 respectively. 



Calculated maximum activity on case : '38. 



Ditto cathode : 2*53. 



Ratio of max. cathode to max. case activity : 6-66 : 1. 



Percentage cathode activity : 86*9. 



True percentage cathode activity as corrected for dif- 

 fusion of uncharged carriers to cathode : 86"6. 



It is difficult to estimate with precision the experimental 

 error in the determination of the percentage cathode activity. 

 A slight error probably arises from the fact that the cathode 



