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



admitted until the pressure o£ the mixture was 38 mm., and 

 the readings were again taken. It was found that even in 

 the presence of 2 mm. o£ ether vapour a considerable number 

 of free electrons were able to traverse the distance between the 

 electrodes. The number was less than in the pure hydrogen, 

 but the EI curve for the mixture (fig. 7) was sufficiently 

 definite to justify the conclusion that the molecules of ether 

 vapour do not behave as electron sinks. 



The experiments with alcohol vapour were conducted in a 

 similar manner ; an EI curve was obtained for a mixture 

 consisting of hydrogen at 35 mm. and alcohol at a pressure 

 slightly less than 1 mm. The number of electrons was 

 again distinctly smaller than in the pure gas, but was suffi- 

 ciently great to make it evident that the molecules of alcohol 

 were unable to absorb the free electrons. 



In order to experiment with traces of water vapour present 

 in the gas, the tubes containing the drying agents were 

 removed so that the hydrogen passed into the measuring vessel 

 directly after generation in the Kipp's apparatus. The moist 

 hydrogen was introduced at a pressure of" 37 mm., and a 

 current-potential curve (v. fig. 7) was obtained in the usual 

 manner ; the presence of the moisture caused a reduction 

 in the number of free electrons, but these were in sufficient 

 evidence to show that the water molecules do not behave as 

 electron sinks. 



It is of course quite possible that in all these instances a 

 loose attachment may occasionally exist between the electron 

 and the vapour molecule ; the experimental results indicate, 

 however, that such an attachment, if it occur at all, persists 

 only for a time which is small in comparison with thnt during 

 which the electron remains free. 



Vapour of Petroleum Ether and the ageing effect. 



The previous experiments with C0 2 and H 2 suggested that 

 the atoms of carbon and hydrogen were in great measure 

 responsible for the relatively large number of free electrons 

 in these gases as compared with air. It became of interest 

 to make a special study of some member of the paraffin series 

 whose molecules contain only atoms of carbon and hydrogen, 

 or indeed of any vapour which does not contain electro- 

 negative atoms such as those of oxygen or iodine. It was 

 originally proposed to make the experiment with pentane, 

 but as this was not immediately available the vapour of 

 petroleum ether was employed instead. Petroleum ether 

 (sp. gr. ca. *67) consists of a mixture of pentane (C g H 12 ) 

 and hexane (C 6 H 14 ) ; its molecules contain, therefore, only 



