Deposit of Radium in an Electric Field. 



495 



Table III : they were obtained in the early stages of the 

 research when little information was at hand concerning the 

 distribution of the activity for various potentials. For this 

 reason the experiments appear very unsystematic ; however, 

 the results will serve to convey a good idea of the difficulty of 

 obtaining approximate saturation of the activity, even with 

 large applied potentials. 



Table III. 



Pressure, 



Potential in 



Percentage cathode 



atm. 



volts 



activity 



1-6 



+ 700 



68-8 



2-0 



650 



64-1 



2-5 



160 



55-2 



2 '5 



750 



60*1 



3-13 



880 



57-5 



3*33 



3750 



80-6 



3-53 



750 



53*8 



The difficulty of saturating the ionization current through 

 the gas likewise made itself manifest at these pressures ; as an 

 example it may be mentioned that with an applied potential 

 of 1100 volts the ionization current due to a constant source 

 of radiation increased as the pressure was increased from 1 to 

 2^ atmospheres, and then continually decreased with any 

 further increase in the pressure. 



These considerations afford an explanation for the maximum 

 of cathode activity which has been found by several experi- 

 menters to set in at certain pressures when a constant potential 

 is employed. 



No indication of any decided effect upon the distribution of 

 the activity was obtained by subjecting the gas throughout the 

 exposure to the influence of a strong source of Rontgen rays. 

 In this experiment the vessel contained emanation in air at a 

 pressure of 3-J- atmospheres ; the applied positive potential was 

 1100 volts ; the equilibrium rate with added capacity was 5 mm 

 per sec, and with the Rontgen rays acting was 25 mm per sec. 

 The percentage cathode activity was 56*2, which is of the order 

 that might have been expected from the previous results. 



7. Discussion of Experimental Results. 



In the interpretation of the experimental results which have 

 been obtained in connection with the distribution of activity 

 the question arises immediately : what is the reason for the 



