Wellisch — Motion of Ions and Electrons through Gases. 13 



and that the critical potential is really smaller than the value 

 (Yo=4-5) apparently obtained. 



In this connection it is a significant fact that several of the 

 E curves, especially those obtained at the highest pressures, 

 showed a distinct curvature in the neighborhood of the poten- 

 tial axis, the tendency being to shift the point of intersection 

 tov^^ards the origin. This shape of the current-potential curves 

 in the vicinity of the origin suggests accelerated motion of the 

 electron or a slow acquisition of a terminal velocity. 



Further experimental data are of course necessary before the 

 nature of the motion of the electron is definitely ascertained ; 

 the suggestion here given is that the electron may traverse a 

 considerable distance with accelerated motion before its ter- 

 minal velocity is acquired. It should be remembered that 

 Franck and Hertz* have already shown that the collisions of 

 electrons with the molecules of the inert gases are practically 

 perfectly elastic so that the drift motion of the electron would 

 under these circumstances be accelerated. The experiments 

 with regard to the effect of impurities upon the number of 

 free electrons in CO^ or H, strongly suggest that the collisions 

 of electrons with the molecules of these gases have a high 

 degree of elasticity, although naturally not so high as with the 

 inert gases. The effect of this high but imperfect elasticity 

 would be to cause the electrons when moving under an electric 

 field in CO^ or H^ to move with an accelerated motion until 

 their terminal velocity is acquired. 



On this view the effect of traces of impurities in the gas in 

 diminishing the velocity of the electron is readily explained ;: 

 the impact of the electron with the molecule of the impurity is 

 in all probability either inelastic or considerably less elastic 

 than the collision with the gas molecule, and, in consequence,, 

 the electron is unable to acquire as great a velocity as in the 

 pure gas. 



(C) Electrons in 'Vapors. 



The demonstration of the existence of free electrons in air, 

 CO2 and H^, at relatively high pressures rendered it fairly 

 obvious that all permanent gases were able to contain electrons 

 in the free state. Franck's experiments had shown previously 

 that the inert gases were especially conspicuous in this respect, 

 the negative carriers appearing to consist entirely of free elec- 

 trons. It became of interest to extend the investigation to the 

 case of vapors, especially as these are liable to occur as impuri- 

 ties in gases. It was thought extremely improbable that the 

 electrons, if they were present in the free state, would occur 

 in large numbers except at very low pressures ; preliminary 



* Franck and Hertz, Verb. Deutscli. Phys. Ges., xv, pp. 873, 613, 1918. 



