1880.] On the Spectra of the Compounds of Carbon, Sfc, 495 



" On a review of the whole series of observations, certain points 

 stand out plainly. In the first place, the seven blue, the violet, and 

 ultra-violet bands, characteristic of the flame of cyanogen, are con- 

 spicuous in the arc taken in an atmosphere of nitrogen, air, nitric oxide, 

 or ammonia, and they disappear, almost, if not quite, when the arc is 

 taken in a non-nitrogenous atmosphere of hydrogen, carbonic oxide, 

 carbonic acid, or chlorine.* These same bands are seen brightly in the 

 flames of cyanogen and hydrocyanic acid, but are not seen in those of 

 hydrocarbons, carbonic oxide, or carbon disulphide. The conclusion 

 seems irresistible that they belong to cyanogen ; and this conclusion 

 does not seem to us at all invalidated by the fact that they are seen 

 weakly, or by flashes, in the arc or spark taken in gases supposed free 

 from nitrogen, by reason of the extreme difficulty of removing the last 

 traces of air. They are never, in such a case, the principal or pro- 

 minent part of the spectrum, and in a continuous experiment they are 

 seen to fade out in proportion as the nitrogen is removed. This con- 

 clusion is strengthened by the observations of one of us, that cyanogen 

 (or hydrocyanic acid) is generated in the arc in atmospheric air in 

 large quantity." 



The observations and experiments which we have since made all 

 tend to confirm the correctness of the foregoing induction, while they 

 help to remove the apparent inconsistency of some recorded observa- 

 tions with our conclusions. More particularly they explain the 



a 



appearance of the bands which we, in common with Angstrom and 

 Thalen, have ascribed to a compound of carbon with nitrogen, in some 

 cases in which nitrogen had been supposed to be absent, by showing 

 the sensibility of the spectroscopic test for nitrocarbon compounds 

 under varied circumstances, and the consequent necessity for some- 

 thing more than ordinary care in the preparation of materials and con- 

 duct of experiments, if inferences dependent on the presumed absence of 

 nitrogen (or hydrogen, as the case may be) are to be drawn from them. 



The Flame of Cyanogen. 



The accompanying diagram (fig. 1) shows approximately the 

 relative position of the bands in that part of the spectrum of the 

 flame of cyanogen fed with a jet of oxygen which is more refrangible 

 than the Fraunhofer line F. Only those bands which are less re- 

 frangible than the solar line L have been before described, but photo- 

 graphs show another set of two shaded bands slightly less refrangible 

 than the solar line IS" accompanied by a very broad diffuse band of less 

 intensity on the more refrangible side of 1ST ; also a strong shaded band, 

 which appears to be absolutely coincident with the remarkable shaded 



* We have repeated and confirmed the experiments with the De Meritens arc 

 in different gases. The arc examined in different fluids also supports the original 

 conclusions. 



