Free Electrons in Gases. 187 



owing mainly to the time involved in travelling, considerable 

 delay has arisen in publishing the new results. I think it 

 therefore advisable to make this brief communication, dwelling 

 especially on certain features of the subject which it appears 

 to me should be given prominence if satisfactory progress is 

 to be made. 



The free electrons were investigated for the gases carbon 

 monoxide, carbon dioxide, and hydrogen ; for the two latter 

 gases the electrons were considerably more numerous than 

 in air at the corresponding pressure, a fact which was con- 

 sistent with the result that the abnormal increase in the 

 ionic mobility set in for these gases at higher pressures than 

 for air. In hydrogen, the electrons appeared in considerable 

 numbers at atmospheric pressure. A number of vapours 

 were tried, but for the most part they showed no evidence of 

 free electrons ; however, in these cases there was always a 

 pressure of several mm., and it is quite possible that lower 

 pressures would bring them into evidence. An interesting 

 and remarkable exception is the vapour of petroleum ether 

 (a mixture of pentane and hexane); for this vapour, whose 

 molecules contain only atoms of carbon and hydrogen, the 

 negative carriers appeared to consist entirely of electrons, 

 the negative ions being absent : the vapour was, however, 

 particularly sensitive to impurities, and, after standing for a 

 few hours in a closed metallic vessel, would no longer contain 

 any considerable number of free electrons. 



I desire here to make some remarks with regard to the 

 effect of impurities on the relative number of free electrons 

 and negative ions in a gas ; this is a point on which there 

 exists considerable misapprehension. Franck found that the 

 free electrons in the inert gases were especially sensitive to 

 oxygen as an impurity. In the October number of the Philo- 

 sophical Magazine Mr. Haines has stated the existence of 

 free electrons in nitrogen and hydrogen at atmospheric 

 pressure, and has mentioned oxygen as one of the impurities 

 which if present in small amount would rob the former gas 

 of its free electrons. Mr. Haines does not enter into detail 

 with regard to the impurities in hydrogen, but I have myself 

 found that a small quantity of oxygen in hydrogen at atmo- 

 spheric pressure would deprive this gas of its electrons. It 

 has probably appeared to many to be extremely strange that 

 a trace of ox} T gen could have this effect and yet that free 

 electrons should exist in air at several cm. pressure. As a 

 matter of fact, the difficulty is more apparent than real. 

 Although the results to which reference has just been made 

 are perfectly correct, still, when the subject is viewed more 



