1895.] in the Flames of Hydrocarbon Gases. 451 



took place, bnt the acetylene formed from the ethylene decomposed 

 at once into carbon and hydrogen, whilst the methane, which up to 

 this temperature had been but little affected, decomposed into 



^V_/JbL4 ^^ O2-*-J-2 "T" -"2j 



and this fresh supply of acetylene at once broke up to carbon and 

 hydrogen, so that at temperatures above 1200 0. the complete 

 action might be looked upon as being 



C 2 H 4 = C 2 + 2H 2 . 



These results have an important bearing upon the cause of the 

 luminosity in the name, as it is manifest that if the temperature 

 of the luminous zone is above 1200 C., the light emitted must be 

 due to incandescent particles of carbon, and not to incandescent 

 hydrocarbon vapours. 



On determining the temperature of an ethylene flame whilst burn- 

 ing from a small fish-tail burner by means of the Le Chatelier thermo- 

 couple, used in the way described in my paper* on the luminosity of 

 coal-gas flames, I found that the temperatures were as follows : 



Height above 

 Portion of flame. burner. Temperature. 



Non-luminous zone -J inch. 952 C. 



Commencement of luminosity ... 1 ,, 1340 



Top of luminous zone 2 1865 



Sides of 1875 



showing that luminosity commenced at 1340 C., and continued even 

 at 1875 C., temperatures at which the incandescent vapour theory 

 becomes untenable. 



It might be urged that the heavy hydrocarbons already produced 

 at a lower temperature in the non-luminous zone are not so easily 

 decomposed by heat as acetylene, and that these may be causing the 

 luminosity, even though carbon particles be present from the decom- 

 posed acetylene ; but this would hardly be possible, as so little besides 

 acetylene is to be found at the top of the non-luminous zone of an 

 ethylene flame, and it can be experimentally shown that even when 

 benzene vapour is formed and is largely diluted it begins to break up 

 and deposit carbon at 1200 C. 



The supporters of the " solid particle " theory of luminosity agree 

 in concluding that the liberated carbon, existing as it does in a con- 

 dition of molecular division, is heated to incandescence partly by its 

 own combustion, and partly by the combustion of the hydrogen and 

 carbon monoxide going on around the finely-divided carbon particles. 



* ' Chem. Soc. Journal,' 1893. 



2 K 2 



