Wellisch — Motion of Ions and Electrons through Gases. 25 



for certain gases, viz. the inert gases and nitrogen (which 

 l>ehaves often as an inert gas), the negative carriers consist 

 entirely of electrons even when the gas under consideration is 

 at atmosplieric pressure. Chattock and TjndalF gave good 

 reasons for believing that hydrogen possessed similar character- 

 istics ; more recently Hainesf has shown independently that 

 the negative carriers in hydrogen consist practically entirely 

 of electrons. In all these instances a slight trace of impurity 

 (especially oxygen) was sufficient to convert the carriers into 

 ions. 



The older point of view was to regard these gases as possess- 

 ing, by virtue of their inert character or otherwise, the excep- 

 tional property of being able at high pressures to contain elec- 

 trons in the free state : on this account they had to be clearly 

 distinguished from gases, such as oxygen, chlorine, &c., which 

 were regarded as being unable to contain free electrons except 

 at very low pressures. The present experiments indicate that 

 the difference is merely one of degree inasmuch as the electrons 

 are capable of existing in the free state even in air at consider- 

 able pressure. We may now regard at any rate the so-called 

 permanent gases as being able to contain both negative ions 

 and free electrons, each kind of carrier maintaining its identity 

 throughout its motion. The inert gases and hydrogen are now^ 

 regarded as being exceptional not in their power of containing 

 free electrons but rather by reason of their great reluctance to 

 form negative ions, i. e. by reason of the exceptionally large 

 proportion of electrons to ions. 



It was shown in sec. 4C that the vapor of petroleum ether 

 is able to afford a copious supply of electrons and to maintain 

 them in the free state provided we reduce the contamination to 

 a minimum. As the molecules of this vapor contain only 

 atoms of carbon and hydrogen this result suggests strongly that 

 the negative ions in air, CO, CO^, etc., are due almost entirely 

 to the presence of the atoms of oxygen. Franckij: has arranged 

 gases in the following order of increasing electron affinity : 

 helium, argon, nitrogen, hydrogen, oxygen, nitric oxide, chlor- 

 ine. This list was obtained by considering the relative power 

 of the different gases, when present as impurities, to deprive 

 helium of its free electrons. If, in accordance with the views 

 embodied in this section, we regard this series of gases as 

 affording a relative idea of the proportion of electrons and 

 ions which results from the process of ionization, it would seem 

 probable that in order to supply an appreciable number of 

 negative ions the molecules of a gas must contain atoms either 

 of oxygen or chlorine ; we may by analogy include other elec- 



* Chattock aud Tyndall, Phil. Mag., xxi, p 585. 1911. 

 f Haines, loc. cit. X Fraiick, loc. cit. 



