the Theory of Luminous Flames. 369 



the separated carbon in such a condition as that it shall emit 

 light. Such flames (the flame of turpentine for instance) 

 become luminous when their temperature is increased ; this 

 may be done by admitting air or oxygen. The admission of 

 chlorine to such flames may be shown experimentally to have 

 no effect in increasing luminosity. 



Frankland has put forward the suggestion that the soot de- 

 posited from luminous flames does not consist of carbon, but 

 of a mixture of heavy hydrocarbons whose vapours have been 

 condensed upon the cold body introduced within the flame. 

 Stein * has pointed out that in this case increase of tempera- 

 ture should cause the soot to again assume the gaseous form ; 

 experiment proves that this is not so. The absorptive power 

 of carbon for gases seems to me to explain the fact that the 

 soot deposited from luminous flames does not consist of pure 

 carbon. Stein's analyses show 99'1 per cent, of carbon and 

 0'9 per cent, of hydrogen. I have shown that admission of 

 chlorine to flames containing decomposable hydrocarbons 

 causes an increase in the luminosity of these flames, and that 

 this increase is attended with deposition of soot. Can it be 

 supposed that this soot consists of condensed heavy hydrocar- 

 bons ? Frankland has himself told us that to obtain pure 

 carbon from the soot deposited from luminous flames it is ne- 

 cessary to heat the deposit in chlorine. If chlorine be then 

 capable of decomposing hydrocarbons at a red heat with pro- 

 duction of pure carbon, it can scarcely be the means of bring- 

 ing about the formation of heavy hydrocarbons in the flame 

 itself. In the case of flames rendered luminous by admission of 

 chlorine, free carbon is evidently separated ; and as the pheno- 

 mena attending the luminosity of flames of high temperature 

 present no points of difference from the same phenomena in 

 the case of flames containing chlorine, the conclusion is that 

 in the high-temperature flames free carbon is also separated. 



It has been already shown that when a porcelain rod is held 

 in a gas-flame, the lower surface (that is, the surface opposed 

 to the stream of burning gas) is alone at first covered with 

 soot, and that a thin film of soot is formed on the upper sur- 

 face only after the expiry of a considerable time. 



This experiment affords direct proof of the presence of solid 

 carbon particles in the luminous flame. If tue action of the 

 cold object were to condense the vapours of hydrocarbons, 

 such condensation would of course take place equally around 

 the cold object ; but the facts of the experiment show that the 

 deposition is a purely mechanical operation exactly compa- 

 rable with the deposition of dust upon the walls of a room. 

 * Journ. Tract. Chem. (N. S.) vol. viii. p. 402. 



Phil Mag. S. 5. Vol. 3. JS T o. 19. May 1877. 2 B 



