Welliseh — Motion of Ions and Electrons through Gases. IT 



Subsequent experiments were made with freshly introduced 

 vapor at a pressure of 20'°"' and gave evidence of a very large 

 percentage of electrons; however, the ageing effect was very 

 pronounced, the free electrons decreasing in number so rapidly 

 that no regular curve was obtained. 



The general indications seem to be that in the pure vapor of 

 petroleum ether a large fraction of the negative carriers are 

 free electrons, the negative ions if present at all appearing only 

 in small numbers; the free electrons are, however, extremely 

 sensitive to the presence of some constituent which arises 

 gradually in the vapor, with the result that at the expiration of 

 a few hours the electrons have disappeared and the current of 

 negative electricity is due entirely to ions. 



The nature of the constituent which occasions the ageing 

 effect in the vapor can at present only be conjectured ; system- 

 atic experiments are necessary before a definite conclusion can 

 be reached. There is distinct evidence, however, that we are 

 dealing here with a true electron sink ; in other words, this 

 constituent, whatever be its nature, is capable of absorbing an 

 electron during its drift motion through the vapor and in this 

 respect must be carefully distinguished from impurities such as 

 oxygen, which seem to require for the absorption of electrons 

 velocities considerably higher than those which are afforded by 

 thermal agitation at ordinary temperatures. The effect of the 

 latter type of impurity is to reduce the number of free elec- 

 trons in a gas and at the same time to diminish appreciably the 

 velocity of the electron through the gas ; this diminution in 

 velocity has been ascribed {y. sec. 4B) to the comparatively 

 inelastic impact between the electron and the molecule of the 

 impurity. 



In the experiments with the vapor of petroleum ether the 

 effect of the impurity is to cause likewise a reduction in the 

 number of free electrons and a diminution in the electron 

 velocity ; the electron, however, appears now to be capable of 

 acquiring all velocities intermediate between that of a free 

 electron in the pure vapor and that of a negative ion. We 

 seem, therefore, to be dealing with a carrier which changes 

 continuously and progressively from a free electron to a nega- 

 tive ion ; the most feasible hypothesis is that the electron as it 

 drifts through the vapor is for part of the time in the free 

 state and for the remainder in attachment with the molecule 

 of the impurity. It is highly probable that this attachment, 

 occurring as it does as a result of ordinary thermal motion, is of 

 a very loose nature and is liable to be broken at molecular 

 encounters; we would thus expect continual alternations of the 

 electron between the free and combined states. 



Am. Jour. Sci.— Fourth Series, Vol. XLIV, No. 259— July, 1917. 



