108 Prof. Draper on the Production of Light 



represents the spectium of carbonic oxide burning in the air. 

 It begins in the red region short of tlie fixed line C, and termi- 

 nates between the lines G and H. It yields therefore rays of 

 every colour; and this is in accordance with the principles I 

 have laid down ; but when the relative quantity' and force of the 

 rays are estimated, in comparison with the sunlight spectrum, 

 the red and orange are deficient, and the more refrangible 

 colours predominate, and indeed it is the excess of these that 

 gives the flame its characteristic blue tint. This agrees with 

 what has been observed as to anthracite and charcoal; for 

 with carbonic oxide a very limited supply of oxygen can bring 

 about the maximum chemical action, and therefore liberate in 

 abundance rays of maximum refrangibility. 



This condition of things is inverted in the case of cyanogen 

 gas. It is the nature of its flame to be enveloped, as it were, 

 in a sheet of nitrogen arising from its own burning ; and this 

 necessarily impedes the access of air, and checks the intensity 

 of the chemical change; a check which is at once betokened 

 by the emission of a predominant number of rays of low re- 

 frangibility, or of a red colour. 



But there is a striking difference in the chemical conditions 

 under which carbonic oxide and cyanogen burn. In the case 

 of the former the whole gas is combustible, in the latter the 

 carbon alone; and we have in reality introduced an incom- 

 bustible element into the flame; for as iht carbon burns, the 

 incombustible nitrogen is set free. It occurred to me, in se- 

 lecting this gas for experiment, that this condition should im- 

 press a physical characteristic on the flame. I thought it was 

 not impossible that dark lines in its spectrum might be the 

 result; because there must be a peculiar arrangement of the 

 burning strata, which together make up the shell of the flame, 

 every two atoms of carbon setting free one of nitrogen. I did 

 not know until subsequently that this flame had already been 

 examined by Mr. Faraday. Having therefore confineil some 

 cyanogen, made from the cyanide of mercury, in a glass gas- 

 holder, which was filled with a saturated solution of common 

 salt, 1 burnt it from the jet-pipe, and found that what I had 

 surmised was actually the fact. There was a spectrum so 

 beautiful, that it is impossible to describe it by words or depict 

 it in colours. It was crossed throughout its extent by black 

 lines, separating it into well-marked divisions. I could plainly 

 count four great red rays of definite refrangibility, followed 

 by one orange, one yellow, and seven green ; whilst in the 

 more refrangible spaces were two extensive groups of black 

 lines, recalling somewhat from their position, but greatly ex- 

 ceeding in extent, Fraunhofer's lines marked G and H in the 



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