as produced and modified by Spark Discharges. 217 



nitrogen, elementary carbon does not yield the same spectrum, no 

 matter what the temperature may be ; and lastly, that cyanogen gas 

 burns with a flame of which the banded spectrum is known as that 

 uf cyanogen by reason of the foregoing facts. Furthermore, I have 

 found by recent experiments that when a condensed spark is passed 

 between electrodes of gold in an atmosphere of cyanogen, the same 

 spectrum is photographed. 



If we admit that under conditions favourable to synthesis from its 

 elements, cyanogen is capable of emitting a spectrum of its own, this 

 emission should occur only at the moment of its formation, but while 

 giving consideration to this view we are met by the difficulty that 

 the flame of cyanogen burning in oxygen would less probably emit 

 a spectrum of the compound substance itself, which is being burnt, 

 than a spectrum of the products of its combustion, or of the 

 separated elements of which it is composed, which are nitrogen and 

 carbon ; and for this reason, that the process it is passing through is 

 not a synthetical but an analytical one. Indeed it has been shown 

 by Liveing and Dewar* that when cyanogen is exploded with oxygen 

 it gives a bright continuous spectrum, but no cyanogen spectrum, or 

 carbon bands, or carbon lines. 



I shall have to refer to these facts and adduce later evidence of the 

 existence of the cyanogen spectrum in the latter part of this paper. 



Evidence derived from their Spectra, of the progress of Chemical 

 Changes in Flames. In support of the view that the flame of burning 

 cyanogen ought to exhibit the spectrum of carbon, I may mention 

 the following facts which have been recorded during a very careful 

 examination of a number of photographs of the spectra of flames 

 which were obtained by burning gases under normal atmospheric 

 conditions. 



The majority of these photographs were taken in 1882. 





The Combustion of Compound Sub- Components of the Spectra photo- 



stances, graphed. 



Hydrocarbons in oxygen. Carbon bands, cyanogen bands, water- 



vapour lines.*!" 



Sulphuretted hydrogen in air and in Sulphur bands and water-vapour lines, 

 oxygen. 



Ammonia in air. Water-vapour lines. 



Carbon disulphide in air. Sulphur bands only. 



Carbon disulphide and nitric oxide. Sulphur bands only. 



Carbon monoxide and oxygen. Continuous spectrum of carbon mon- 



oxide. Faint lines due to carbon, 

 very few in number. 



* l Roy. Soc. Proc.,' vol. 49, p. 222. " On the Influence of Pressure on Flames." 

 f When nitrogen is present, Liveing and Dewar have observed the formation of 

 N0 2 (loc. cit.). 



