420 



Profs. G. D. Liveing and J. Dewar. [Dec. 21, 



of aqueous vapour. Under these conditions acetylene is formed 

 synthetically during the electric discharge, the line spectrum of 

 hydrogen being absent; so that we were never convinced that the 

 spectrum was not due to the former substance. 



It is well to remark in passing, that our previous work on the 

 spectrum of the carbon compounds was mainly directed to that par- 

 ticular spectrum which is characteristic of the flame of cyanogen, and 

 only indirectly to the flame spectrum of hydrocarbon. We were 

 further supported in connecting the latter spectrum with acetylene, 

 by observing that cyanogen compounds are continuously formed when 

 the arc discharge takes place in gases containing nitrogen, and that in 

 all probability their formation is due, as Berthelot has shown, to a 

 reaction taking place between acetylene and nitrogen. Berthelot is 

 positive in his assertions that cyanogen is never formed by a direct 

 combination between carbon and nitrogen, and that any such apparent 

 combination is due to impure carbon, or to the presence of an imper- 

 fectly dried gas ; in other words, hydrogen is essential to the pro- 

 duction of cyanogen under such conditions according to the views of 

 Berthelot. Such considerations led us to suggest the following view, 

 expressed at the time the experiments were made, as to the origin of 

 the hydrocarbon flame spectrum. 



" The mere presence of the latter spectrum feebly developed in the 

 electric discharge in compounds of carbon supposed to contain no 

 hydrogen, appears to us to weigh very little against the series of 

 observations which connect this spectrum directly with hydrocarbons." 

 (" Proc. Hoy. Soc," vol. 30, p. 160.) 



" The arc in the middle of a magnesia crucible often shows no trace 

 of the hydrocarbon set, although the cyanogen are strong. If, how- 

 ever, puffs of air or carbonic acid are passed into the arc, the hydro- 

 carbon lines are produced." 



" When the hydrocarbon spectrum is strong the brilliancy and 

 number of the cyanogen groups that are visible are undoubtedly in- 

 creased, so that the one variety of vibrations seems to affect the other. 

 This is easily accounted for by the chemical interaction which takes 

 place between acetylene, nitrogen, and hydrocyanic acid. The hydro- 

 carbon spectrum is brought out at once in the magnesia crucibles by 

 moistening one of the poles. All such actions seem to show that 

 hydrogen is essentially connected with the production of this fluted 

 spectrum just as nitrogen is with the cyanogen series." (Ib., vol. 

 34, pp. 126, 127.) 



The fact that carbonic oxide, which is one of the most stable binary 

 compounds of carbon, forms a distinct spectrum of a character similar 

 to that of the flame spectrum, tended to support the view that the 

 flame spectrum might originate with acetylene. The similarity in the 

 character of the magnesium-hydrogen spectrum to that of the hydro- 



