Wellisch — Motion of Ions and Electrons through Gases. 15 



vapor 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 mix- 

 ture (fig. 7) was sufficiently definite to justify the conclusion 

 that the molecules of ether vapor do not behave as electron 

 sinks. 



The experiments with alcohol vapor were conducted in a 

 similar manner ; an EI curve was obtained for a mixture con- 

 sisting of hydrogen at SS""'" and alcohol at a pressure slightly 

 less than 1™"". The number of electrons was again distinctly 

 smaller than in the pure gas, but was sufficiently 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 vapor 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°'"" 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 elec- 

 trons, 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 vapor 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 that during 

 which the electron remains free. 



Vapor of Petroleum Ether and the ageing effect. 



The previous experiments with CO, and H^ suggested that the 

 atoms of carbon and hydrogen were in great measure responsi- 

 ble 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 vapor 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 vapor of petroleum ether was em- 

 ployed instead. Petroleum ether (sp. gr. ca. '67) consists of a 

 mixture of pentane (C^Hj^) and hexane (CgH^J; its molecules 

 contain, therefore, only atoms of carbon and hydrogen. A 

 number of determinations of ionic mobilities were also made 

 for this vapor ; reference is, however, made to these only as far 

 as they concern the motion of electrons, the actual values 

 obtained for the mobilities of the ions being deferred to a later 

 section (4D). 



