Spectra of Carbon Compounds. 481 



The hypothesis attributing the Swan spectrum to carbon 

 monoxide thus receives additional support. The increased 

 development of this spectrum when cyanogen is burnt in 

 oxygen instead of in air is consistent with the increased con- 

 centration of carbon monoxide that would ensue. . 



That two distinct spectral components are contained in 

 the spectrum of burning cyanogen is generally acknowledgedj 

 and one of these is usually considered to be incandescent 

 cyanogen itself. The spectrum due to the undecomposed 

 cyanogen, which includes a good deal of continuous light, no 

 doubt exercises a considerable masking effect upon the Swan 

 spectrum, which is the other component. When oxygen is 

 used a higher general temperature reigns in the flame, and 

 both components of the spectra are intensified, but as this 

 effect is mainly towards the violet the Swan spectrum is 

 relatively less masked by the other component than when air 

 is used. 



The Spectrum of the Carbon Disulphide Flame. 



The flame of carbon disulphide gives a continuous spectrum 

 with no sign of the Swan bands. When carbon disulphide 

 vapour mixed with air is burned in a Bunsen burner, carbon 

 monoxide may be detected as a partial product, but no Swan 

 spectrum is observed, even when a dispersion of six prisms is 

 used to weaken the continuous light. 



I performed an experiment to discover whether if the Swan 

 spectrum were potentially present it would be obliterated by 

 the continuous spectrum of the burning sulphur. For this 

 purpose a mixture of ethylene and hydrogen sulphide was 

 made so as to have the same proportion of carbon and sulphur 

 burning as in the case of carbon disulphide. No Swan spec- 

 trum was observed in the flame of this mixture. It appears 

 that the Swan spectrum is easily suppressed by that of 

 simultaneously burning sulphur, so that its nonappearance 

 in the flame of carbon disulphide is of no unfavourable 

 significance to the hypothesis. Besides this it has been shown 

 that carbon-oxysulphide COS is a partial product of a 

 carbon-disulphide flame (Julius, Die Licht and Warmextrah- 

 lung verbrannter Gase, p. 53, Berlin, Simion, 1890, also Dixon 

 and Russell, Journ. Chem. Soc. lxxv. p. 600, 1899), so that 

 the amount of carbon monoxide formed may be small. 



I know of no other carbon compounds which yield flames 

 specially suited to test the question of the origin of the Swan 

 spectrum. 



