32 Wellisch — Motion of Ions and Electrons through Gases. 



the view that the electron is able to unite with a molecule 

 during its drift motion so as to form a nes^ative ion; before 

 such an attachment occurs the electron in general traverses dis- 

 tances through the gas which are large compared with its free 

 path. The distinct separation between the ions and the free 

 electrons which is shown in a whole series of EI curves lends, 

 however, strong support to the view that the electron traverses 

 the whole distance between the electrodes without effecting any 

 permanent union with a gas molecule ; a well-defined bend in 

 the experimental curve could not have been obtained if any 

 considerable fraction of the electrons had become attached ta 

 molecules during their passage through the gas, 



6. Summary. 



1. The separation previously effected between the electrons 

 and the negative ions in dry air at the lower pressures has in 

 the present investigation been extended to other gases, notably 

 CO^ and Hg ; for these two gases the electrons are relatively 

 more numerous than in air at the corresponding pressure. 



2. A trace of impurity is especially effective in reducing the 

 number of free electrons when the gas is at a relatively high 

 pressure ; at low pressures the effect of the impurity is often 

 inconsiderable. 



In most cases a velocit}^ greater than that arising from ther- 

 mal agitation at ordinary temperatures appears to be necessary 

 to enable the electron to effect a permanent union with an 

 uncharged molecule of the gas or impurity. 



3. For the vapor of petroleum ether, whose molecules con- 

 tain only atoms of carbon and hydrogen, the negative carriers 

 appear to consist practically entirely of free electrons ; a trace 

 of impurity, however, is sufficient to effect the production of a 

 considerable number of negative ions. 



4. A brief investigation has been made of the motion of free 

 electrons through CO^ ; the results do not indicate that the 

 velocity of the electron is proportional to the applied field 

 but suggest that the electron may traverse a considerable dis- 

 tance with accelerated motion before its terminal velocity is 

 acquired. 



5. In no instance was any evidence obtained of a change in 

 the nature of either the positive or the negative ion as the pres- 

 sure of the gas was reduced. 



6. The present method was employed to determine the 

 values of the ionic mobilities for a few vapors ; the results 

 have been compared with previous determinations. 



7. A discussion is given with regard to the bearing of the 

 results on certain outstanding problems of ionic theory. 



The University of Sydney, December, 1916. 



