the Theory of Luminous Flames. 3 



not so convincing as might at first sight appear, inasmuch as 

 we know that the temperature of the flame is increased at 

 high pressures *, and also that at the temperature of the electric 

 spark many gases yield a continuous in place of a line spectrum. 

 The power of gases as regards emission of light also varies 

 considerably under these circumstances ; and it does not ap- 

 pear that we are absolutely necessitated, as Frankland has 

 supposed, to ascribe the increase in luminosity to the increased 

 density of the gas, although doubtless this circumstance is 

 not without considerable influence. 



The inquiry as to the nature of hydrocarbon-flames is quite 

 independent of the meaning which we may attach to these 

 appearances ; and if Frankland puts forward the above-cited 

 phenomena of combustion as analogies to guide him in views 

 concerning carbon-flames, no very forcible argument can be 

 really deduced from the examples, because, as W. Stein f has 

 pointed out, it cannot be shown that the reaction in luminous 

 carbonaceous flames must be an analogous one to that described 

 above. 



Frankland's declaration that the soot must be regarded as 

 an accumulation of heavy hydrocarbons whose vapours are 

 condensed on the cold body brought into the flame, may be 

 regarded as almost confuted by Stein's objection that in this 

 case the soot must become gaseous at higher temperatures 

 (which is not the case). 



New doubts arise concerning the prevailing theory when 

 we consider that the admixture not alone of air, but also of 

 nitrogen, carbon dioxide, or other completely indifferent gases, 

 with coal-gas causes a great decrease in the luminosity of the 

 flame of that gas. Hence we cannot trace the decrease in 

 luminosity solely to the more energetic oxidation of carbon 

 contained in the flame. 



The experiments of Stein % and R. Blochmann § allow us 

 to suppose that, the particles of carbon being more widely 

 separated by the admixed gases, the oxygen of the air is able 

 to oxidize them to carbon monoxide more quickly than under 

 the ordinary circumstances of combustion. 



To the theory of these authors, viz. that diminution of 

 luminosity is a consequence of dilution, Wibel || opposes the 

 view that the absorption of heat brought about by the admix- 

 ture of an indifferent gas is the sole cause of decrease in 



* Ste.-Claire Deyille, Compt. Rend, lxvii. 1089. 

 t J.pract. Cliem. [2] viii. 401. \ Ibid. 



§ Lieb. Ann. clxviii. 355. 

 I| JDeut. chem. Ges. Ber. viii. 226. 



B2 



