[KENNEDY] 



ACTIVE DEPOSIT FROM ACTINIUM 



6S 



than that of the positive. For potential differences from 200 to 450 

 volts the activities were practically independent of the potential differ- 

 ence applied. From 460 volts upward, however, the activities of both 

 electrodes increased and finally at about 600 volts again became inde- 

 pendent of the applied potential. 



From Carr's results i it is known that 460 volts is the spark po- 

 tential for a pressure of 9 mms. with the plates 2 mm. apart, conse- 

 quently for all voltages above 460 the exposures were made witli a cur- 

 rent passing between the plates. This would mean that a large number 

 of ions were present between the terminals under the circumstances dur- 

 ing the exposure and it is interesting to note that the presence of these 

 ions resulted in a considerable increase in the activity of the two plates. 

 But just how this result is brought about is difficult to explain as the 

 exact relation which exists between the niunber of ions present in a gas 

 and the active deposit particles is still obscure, and it will be necessary 

 to make additional experiments before the question can be cleared up. 



Pressure 9 mm. 



TABLE IX 

 Electrodes 2 cm apart. 



Distance of salt 1 . 3 cm. 



iPhll. Trans., Vol. 201, pp. 403-43n. 



Sec. III., Ifl09. 5. 



