1030 



by Gill and Pidduck ^). We found a lower value for the potential 

 at which the discharge occurs. (See fig. 4). The direction of our 

 curve is practically the same as Bouty's curve at high pressures. 

 As the direction of this curve according to Bouty is a test of the 

 purity of the argon, and the curve given in the figure corresponds 

 to Bouty's purest sample we may conclude that our argon satisfied 

 very high demands. Similarly to Bouty we found it exceedingly 

 difficult to obtain series of observations which give properly 

 corresponding results, as small quantities of gas — probably liberated 

 from the electrodes by the sparks — raised the sparking-potentials 

 considerably. We found it therefore neceSwSary to purify the argon 

 anew for the determination of each point. 



T A B L E 2. 



Sparking-potentials for argon, nitrogen and mixtures of argon and nitrogen. 



Pure nitrogen. 



Argon-nitrogen mixture 80.9 % N. 19.1 o/^ a. 



1) E. W. B. Gill and F. B. Pidduck, Phil. Mag. (6) 16, p. 280, 1908; 23, p. 837, 1912. 



