and Electrons through Gases. 



47 



very low pressures ; preliminary trials with a few vapours 

 justified this conclusion. With the high-frequency com- 

 mutator there was not the slightest indication of the presence 

 of free electrons either in dry S0 2 at a pressure of 7 mm. or 

 in CH 3 I at a pressure of 28 mm. It was, however, quite 

 possible that lower pressures would bring the electrons into 

 evidence; but as the apparatus did not readily lend itself to 

 securing low vapour pressures, the investigation was resumed 

 in a slightly different manner. A small quantity of the 

 vapour under consideration was mixed with a permanent 

 gas, and experiments were made to ascertain whether free 

 electrons cbuld continue to exist in this mixture; if the 

 vapour molecules behaved as electron sinks and were present 

 in appreciable amount, then the number of collisions and 

 subsequent attachments between electrons and vapour mole- 

 cules would be sufficiently great to prevent the existence of 



Fig. 7. 



140 !6Q 

 Volts. 



free electrons. This information was of importance in view 

 of the experimental results with regard to the effect of im- 

 purities on the number of free electrons in a gas. Three 

 vapours were tried in this connexion, viz.: ether, alcohol, 

 and water ; these were chosen because they were deemed to 

 be the most probable absorbers of electrons. In each of 

 these instances hydrogen at a reduced pressure was chosen 

 as the gas with which the vapour was mixed because of the 

 copious supply of free electrons which it affords. 



An EI curve was first obtained for dry hydrogen at 

 a pressure of 36 mm. (fig. 7); ether vapour was then 



