Deposit of Radium in an Electric Field. 491 



this ratio was identical with the ratio of the percentage cathode 

 activities corresponding to these two potentials. 



As an example of the results obtained in this connection it 

 will suffice to compare the ratio 1*09 of the percentage cathode 

 activities obtained with potentials 975 and 160 volts respec- 

 tively with the corresponding ionization currents. From our 

 values for the ionization currents in air at 1 atmosphere 

 pressure obtained in three experiments when widely different 

 quantities of emanation were employed, we deduce the follow- 

 ing figures : 



Ratio of current with V volts to that with 160 volts : 

 = 1-10 when V=875, 

 = 1-10 when V=980, 

 = 1-07 when V=900. 



It would serve no useful purpose to reproduce in full any of 

 the ionization curves because, in the^ first instance, the early 

 slope of the curve depends markedly on the amount of emana- 

 tion employed, and, secondly, because the comparison could 

 only be made over the limited range from about 100 to 1000 

 volts, as the ionization current could not be accurately 

 measured when the larger potentials were employed. 



That the equality of the ionization and activity ratios still 

 holds approximately at low voltages when a constant amount 

 of emanation was employed was verified by measuring the per- 

 centage cathode activity with 18 volts applied, and the ioniza- 

 tion currents for 18 volts and higher potentials, it being known 

 that the percentage cathode activity at the higher potentials 

 was independent of the amount of emanation in the vessel. 

 The following results were obtained : 



Percentage cathode activity with 18 volts : 42'7 

 Ditto 160 volts : 79-1 



Ratio : *54 



Ionization current with 18 volts : 6*6 



Ditto 160 volts : 11*4 



Ratio : -58 



The agreement is only rough, and further experiments will 

 be necessary at these small potentials. 



The percentage cathode activity increases so slowly with the 

 higher potentials applied that it appeared as if some definite 

 fraction of the activity was always bound to be deposited on 

 the case. Subsequent experiments made with large potentials 

 obtained by using the Wimshurst machine showed, however, 

 that the percentage cathode activity continually increased with 

 the potential. It is not out of place to mention briefly here 

 two sets of experiments which were conducted prior to the use 

 of the Wimshurst machine. 



