IONIZATION POTENTIALS IN DISSOCIATED GASES. 223 



critical potentials reported is probably due to (i) the fact that the 

 velocity distribution correction is likely to be exaggerated for the 

 stronger effects, unless a systematic method such as was suggested by 

 Smyth or its graphical equivalent is used, (2) two effects occurring 

 close together are likely to be reported as one, (3) the form of 

 apparatus may be such as to enhance ionization effects relatively to 

 radiation effects, or vice-versa. 



Nitrogen. 

 This gas has been studied by Dr. Duffendack, using the low volt- 

 age arc method as in the case of hydrogen. It was found that the 

 gas could not be appreciably dissociated into atomic nitrogen by any 

 attainable temperature of the tungsten tube furnace, although it was 

 possible to produce atomic nitrogen (Strett's "active" nitrogen) ^^ by 

 electronic bombardment at lower current densities and voltages when 

 the tube was very hot than when it was cooler. 



Lozv Voltage Arc in Nitrogen. 

 Typical current-voltage curves are shown in Fig. 7. In curve 



Volts 



Fig. 7. 



(b) the filament was hotter and the gas pressure lower than in curve 

 (a), both conditions favoring the production of the arc. The 

 "break" point of the arc was found to be 16.15 volts as an average 

 of a large number of closely agreeing observations made under vari- 

 ous experimental conditions. Under no conditions- could the arc be 

 ^^ Roy. Soc. Proc, A, 85, p. 219, 191 1, et seq. 



