Separation of Spectra in Compound Gases. 727 



the line spectrum to the strongest, between them being the 

 negative band spectrum. 



The ring discharge would appear to be a somewhat powerful 

 method of examining the spectra of slightly impure, or of 

 mixed, gases ; as in several cases, particularly those of argon 

 and oxygen, the characteristic spectra of the elements have 

 appeared at stages of purity at which they would have been 

 quite absent in the ordinary vacuum-tube discharge. 



In view of the influence of electric intensity on spectra, it 

 would be interesting to study by this method the spectra 

 given by a gas having multiple spectra, when that gas is 

 mixed with traces of different impurities. 



In conclusion, I wish most heartily to thank Professor 

 Sir J. J. Thomson for the suggestion at which these experi- 

 ments were begun, and for his kindly interest and advice 

 throughout their progress. 



Cavendish Laboratory, Cambridge. 



May 8, 1911. N 



LXX. On the Separation of Spectra in Compound Gases. 

 By G. Stead, B.A., formerly Scholar of Clare College, 

 Cambridge* . 



IN a previous paper f I have described some experiments in 

 which evidence was obtained that a process somewhat 

 akin to electrolysis can occur in gases at low pressure. 

 Compound gases or vapours through which an electric dis- 

 charge is passed at a pressure of the order of a millimetre 

 usually show the spectra of certain constituents better deve- 

 loped at the anode, whilst the spectra of other components 

 appear more brightly at the cathode. Moreover elements 

 which show a preference for the anode are such as must be 

 supposed on chemical grounds to carry a negative charge, and 

 vice versa. Thus in the case of hydrogen chloride the hydrogen 

 spectrum is seen chiefly at the cathode and chlorine lines 

 mainly at the anode. This is partly analogous to what occurs 

 in the electrolysis of a solution of concentrated hydrochloric 

 acid. The present ] taper gives an account of further work 

 on the same subject, and for a description of the apparatus 

 and method of manipulation the former paper must be 

 consulted. 



(i.) Ethane. — The gas was prepared pure by the action of 

 distilled water on zinc ethyl. 



* Communicated bv the Author. 

 t Proc. Roy. Soc, August 1911. 



