58 Mr. E. M. Wellisch on the Motion of 



consist entirely of electrons even when the gas under con- 

 sideration is at atmospheric pressure. Chattock and Tyndall* 

 gave good reasons for believing that hydrogen possessed 

 similar characteristics ; more recently Haines | 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 

 possessing, by virtue of their inert character or otherwise, 

 the exceptional property of being able at high pressures to 

 contain electrons 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 considerable 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, no 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. 4 that the vapour of petroleum 

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

 maintain them in the free state provided we reduce the con- 

 tamination to a minimum. As the molecules of this vapour 

 contain only atoms of carbon and hydrogen, this result 

 suggests strongly that the negative ions in air, CO, C0 2 , &c, 

 are due almost entirely to the presence of the atoms of' 

 oxygen. Franck % has arranged gases in the following 

 order of increasing electron affinity: helium, argon, nitrogen, 

 hydrogen, oxygen, nitric oxide, chlorine. 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 



* Chattock and Tyndall, Phil. Mag. xxi. p. 585 (1911). 



t Haines, loc. cit. 

 X Franck, loc. cit. 



