1880.] 



Note on the Spectrum of Carbon. 



337 



that, if so, they must be absent from flames in which carbon is absent, 

 -and present in flames in which carbon is present ; that they must be 

 observable equally in the flames of the oxide, sulphide, and nitride as 

 in that of the hydride of carbon ; and, finally, that they must be 

 present whether the incandescence be produced by the chemical force, 

 as in burning jets of the gases in the open air, or by the electric force, 

 as when hermetically sealed tubes of the gases are exposed to the dis- 

 charge of a powerful induction coil. 



" To establish the absolute identity of the hydro- and nitro- carbon 

 spectra, excluding of course the lines due to nitrogen, they were 

 simultaneously brought into the field of the spectroscope : one occupy- 

 ing the upper, and the other the lower half of the field. 



" This was readily effected after fixing the small prism, usually sup- 

 plied with spectroscopes, over half of the narrow slit at the further 

 end of the object-tube of the instrument. The light from the 

 oxyhydrocarbon flame was now directed up the axis of the tube by 

 reflection from the little prism, while that from the oxynitrocarbon 

 flame passed directly through the uncovered half of the slit. A glance 

 through the eye- tube was sufficient to show that the characteristic 

 lines of the hydrocarbon spectrum were perfectly continued in the 

 nitrocarbon spectrum. A similar arrangement of apparatus, in which 

 the hydrocarbon light was replaced by that of pure nitrogen, showed 

 that the remaining lines of the nitrocarbon spectrum were identical 

 with those of the nitrogen spectrum. In this last experiment the 

 source of the pure nitrogen light was the electric discharge through 

 the rarefied gas. 



" The above experiment certainly seemed to go far towards proving 

 tJie spectrum in question to be that of the element carbon. Never- 

 theless, the ignition of the gases having been effected in air, it was 

 conceivable that hydrogen, nitrogen, or oxygen had influenced the 

 phenomena. To eliminate this possible source of error, the experiments 

 were repeated out of contact with air. A thin glass tube 1 inch in 

 diameter and 3 inches long, with platinum wires fused into its sides, 

 &nd its ends prolonged by glass quills having a capillary bore, was 

 filled with pure dry cyanogen, and the greater portion of this gas then 

 removed by a good air-pump. Another tube was similarly prepared 

 with olefiant gas. The platinum wires in these tubes were then so 

 connected with each other that the electric discharge from a power- 

 ful induction-coil could pass through both at the same time. On now 

 observing the spectra of these two lights in the simultaneous manner 

 previously described, the characteristic lines of the hydrocarbon 

 spectrum were found to be rigidly continued in that of the nitro- 

 carbon. Moreover, by the same method of simultaneous observation, 

 the spectrum of each of these electric flames, as they may be termed, 

 was compared with the corresponding chemical flames, that is, with 



