Disappearance of Gas in the Electric Discharge. 585 



(2) The relation can probably be extended to fche pre- 

 cipitation of positively and negatively charged colloids by 

 anions and cations respectively of any valence. 



(3) It' the above is true, it follows that Whetbam's law- 

 requires modification, probably by comparing the precipitating 

 power of only those ions for which the values of N", as given 

 above, are approximately equal. 



Christ Church, Oxford. 

 April, 1920. 



LXIX. The Disappearance of Gas in the Electric Discharge. 

 By The Research Staff of the General Electric Company, 

 Ltd., London *. ( Work conducted by N. R. Campbell and 

 J. W. H. Ryde.) 



Introduction, 



1. VTTHEN an electric discharge is passed through a gas- 

 T T at low pressure, the pressure often decreases and 

 the gas seems to disappear. In spite of the considerable 

 investigation to which the matter has been subjected, a 

 complete understanding of it has not been reached. It is 

 not known precisely what is the relation between the 

 disappearance and the electrical conditions of the discharge, 

 and it is not known precisely what becomes of the gas that 

 has disappeared. The following pages describe some ex- 

 periments designed to elucidate further the fundamental 

 principles concerned in the process. It is not certain, of 

 course, that there are any fundamental principles ; there 

 may be many totally distinct actions possible, each of which 

 happens to have as one of its consequences the disappearance 

 of gas ; any attempt to explain them all by the same theory 

 would then be misleading. Accordingly it may be well to 

 state at the outset that no attempt will be made to cover the 

 whole field, either in experiment or in theory. We shall 

 merely point out certain features of the process which can 

 be traced in certain cases, and must not bo left out of 

 consideration in the elaboration of any theory that is pro- 

 posed to account for it. 



2. First some of the main results established by earlier 

 work may be recalled. It seems that by the passage of a 

 current at a sufficiently low pressure, as in an X-ray tube 

 of the old type, any gas whatever, including the inactive 



* Communicated by the Director. 

 Phil. Maq. S. 6. Vol. 40. No. 239. Nov. 1920. 2 Q 



