﻿484 Prof. C. A. Skinner on the Evolution of Gas 



the values m helium and argon practically identical during 

 the first seven minutes, and for the same period they coincide 

 within the errors of observation with the line F. After that 

 time the evoultion of gas falls gradually below the calculated 

 rate, as indicated by the direction of the points dropping 

 below that of the line. It may be noted that the values for 

 argon are slightly nearer F throughout than those for helium. 

 Fig. 2, representing the observations obtained under a current 



Tiff. 2. 



to 75 



Duration of Current (Minutes) 



of two milliamperes, shows a marked divergence in the results 

 from the two gases during the first minute after starting the 

 current, but agreement in rate during the next few minutes, 

 after which helium falls below argon and both as before 

 below F. Here again the results in argon are very near the 

 calculated values until such a time is reached when we must 

 conclude that the metal has been relieved largely of its 

 available gas, namely, that in its surface-layer. After the 

 first minute helium gives equally satisfactory results until a 

 similar condition is reached. The results obtained with a 

 current of three milliamperes (fig. 3) are practically identical 

 in direction with F in the two gases between the first and third 

 minutes, both, however, giving excessive values on starting 

 the current. Contrary to the results in foregoing tests, the 

 sample of aluminium used in this case in argon became 

 depleted before that used in helium. 



We may conclude from these experiments that Faraday's 

 law is the controlling factor in the evolution of gas from the 

 cathode, though as the current-density increases there is an 



