390 On the Spectrum of Cyanogen. 



gases were removed from the cyanide of mercury and the 

 walls of the gasholder. The tap G was then closed, and the 

 cyanide in A strongly heated until sufficient cyanogen had 

 collected to fill the gasholder. The bulb C was then immersed 

 in liquid air, and all the cyanogen frozen therein ; the tap 

 G being then again opened, any gas left unliquefied was 

 pumped away, it being found that the exhaustion could be 

 carried very high, as the solid cyanogen has such an extremely 

 low vaponr-pressure at the temperature of boiling air. The 

 tap G was then again closed, and the cyanogen allowed to 

 boil back into the gasholder. 



The second stage was to exhaust the vacuum-tube as far as 

 possible, with the discharge passing during the whole time, in 

 order to remove every trace of gas from all parts of the tube. 

 When this process had been effectively carried out, small 

 quantities of cyanogen were admitted and pumped out again, 

 the spectrum being examined after each admission. At first 

 the carbon spectra were seen together with the nitrogen 

 spectra, showing undoubtedly that oxidation of the cyanogen 

 was taking place. This, however, became less and less 

 evident, and finally we were able to obtain a spectrum 

 absolutely free from the carbon and nitrogen spectra. The 

 spectrum obtained was extremely beautiful, and differs from 

 the flame-spectrum of cyanogen. It presents a series of 

 equidistant flutings through the whole of the red and yellow, 

 somewhat recalling those of the positive band-spectrum of 

 nitrogen. The cyanogen bands are, however, much wider 

 than the nitrogen bands, and do not show the characteristic 

 break in the orange seen in the nitrogen spectrum. The 

 flutings under higher dispersion are of course split into series 

 of very fine lines. 



The polymerization of the cyanogen was so rapid as only to 

 allow the observations to last a few seconds after the admission 

 of the gas. We succeeded, however, in overcoming this 

 difficulty by allowing a constant slow stream of cyanogen to 

 pass into the tube, and in this way were able to take careful 

 observations. That the brown deposit on the vacuum-tube 

 is paracyanogen, can easily be proved by its volatility at a 

 high temperature. 



It is worth while also to point out, that the admission of 

 oxygen or air into the vacuum-tube during the experiments 

 was at once attended by the appearance of the carbon spectra. 



In conclusion, these experiments tend to prove that 

 (Istj The Swan spectrum is not produced by a carbon 

 compound which does not contain oxygen ; whence 

 it follows that 



