1895.] in the Flame of Hydrocarbon Gases. 467 



25670+{25670-(21750x2)} , 

 25670 



>4 ' 



and the illuminating value, as determined by Mr. Lewis T. Wright, 

 is 5'2 ; but here, again, we know by experiment that methane requires 

 a very high temperature to bring about its conversion into acetylene 

 and decomposition into carbon and hydrogen, and that a large 

 portion of the gas must be burnt without decomposition to do 

 this. 



The facts which I have sought to establish in this paper 

 are : 



1. That the luminosity of hydrocarbon flames is principally due to 

 the localisation of the heat of formation of acetylene in the carbon 

 and hydrogen produced by its decomposition. 



2. That such localisation is produced by the rapidity of its decom- 

 position, which varies with the temperature of the flame and the 

 degree of dilution of the acetylene. 



3. That the average temperature of the flame due to combustion 

 would not be sufficient to produce the incandescence of the carbon 

 particles within the flame. 



In my paper on the action of heat upon ethylene, brought before 

 the Royal Society this spring, I showed that the decomposition of 

 ethylene into acetylene and simpler hydrocarbons was mainly due to 

 the action of radiant heat, and was but little retarded by dilution, 

 whilst I have shown in this paper that the acetylene so produced 

 requires a considerable increase in temperature to bring about its 

 decomposition when diluted, and it is possible with these data to 

 give a fairly complete description of the actions which endow hydro- 

 carbon flames with the power of emitting light. 



When the hydrocarbon gas leaves the jet at which it is being burnt, 

 those portions which come in contact with the air are consumed and 

 form a wall of flame which surrounds the issuing gas. The unburnt 

 gas in its passage through the lower heated area of the flame under- 

 goes a number of chemical changes, brought about by the action of 

 radiant heat emitted by the flame walls, the principal of which is the 

 conversion of the hydrocarbons into acetylene, methane, and hydro- 

 gen. The temperature of the flame quickly rises as the distance from 

 the jet increases, and a portion of the flame is soon reached at which 

 the heat is sufficiently intense to decompose the acetylene with a 

 rapidity almost akin to detonation, and the heat of its formation, 

 localised by the rapidity of its decomposition, raises the liberated 

 carbon particles to incandescence, this giving the principal part of 

 the luminosity to the flame ; whilst these particles, heated by the 

 combustion of the flame gases, still continue to glow, until finally 



2 L 2 



