Free Electrons in Gases. 189 



electronic effect to traces of oxygen increases, therefore, 

 over a wide range with the pressure of the hydrogen. 



An interesting question arises as to whether in the case of 

 certain vapours the electron has sufficient energy at ordinary 

 temperatures to form with a molecule a negative ion : in such 

 cases permanently free electrons would not be possible except 

 with field strengths high enough to effect ionization by 

 collision. I was not able to make a systematic study of 

 vapours at low pressures to ascertain whether free electrons 

 did really exist, but an examination of the decay of the free 

 electrons in petroleum ether vapour as ageing occurred, 

 indicated the appearance in the vapour of another constituent 

 capable of absorbing electrons at ordinary temperatures. 

 This arose probably from the walls of the containing vessel, 

 although the possibility of a formation of aggregates by the 

 vapour molecules themselves has to be considered. In any 

 event these " electron sinks " undoubtedly exist, and should 

 be carefully distinguished as regards their effect upon 

 electrons from impurities such as oxygen. 



The study of tbe free electrons in various gases is one of 

 great importance and should repay careful investigation. 

 They are really observable in practice, especially if a high- 

 frequency commutator be employed ; elaborate precautions 

 are not necessary if it be merely required to bring the 

 electrons into evidence — e.g., in my preliminary experiments 

 I was able to observe the electrons in considerable numbers 

 at atmospheric pressure, in hydrogen which was prepared 

 from commercial acid and zinc in a Kipp's generator and 

 dried in the usual way before passing into the apparatus. 



What is urgently needed is a determination of the pro- 

 portion of ions and electrons in a pure gas at a specified 

 pressure; to say that the electrons occur in air at 8 cm. or in 

 hydrogen at 1 atmosphere provides little information, because 

 the sensitivity of the measuring apparatus is involved. A 

 case of particular interest would be to ascertain whether any 

 negative ions are present in pure inert gases, as a small 

 proportion of ions might not unreasonably be expected. 



I hope within a few months to be able to publish the full 

 account of my work. 



Yours very truly. 



The University, E. M. WELLISCH. 



Sydney, 

 December 22nd, 1915. 



