Iron Vapour in Air-Coal Gas Flame. 229 



In short, the admixture of oxygen to the gases feeding an 

 air-coal gas flame reduces the effect of the special 

 chemical actions in the explosion region and intensifies 

 the thermal actions in the mantle. 



§ 5. A Possible Cause of the Cone Emission. 



The foregoing results supply sufficient data for suggesting 

 a preliminary hypothesis as to the nature of the chemical 

 actions to which may be ascribed the emission of the cone 

 lines. The particular reaction involved attains its full 

 development in the air-coal gas flame and, as has been 

 shown, the presence of nitrogen is one of the determining- 

 conditions. Further, it would appear that a favourable in- 

 fluence is exercised by one of the constituents of coal gas, 

 perhaps methane, but probably not hydrogen. The con- 

 ditions for the reaction may then be summarized thus : — 



Favourable to reaction. Opposed to reaction. 



nitrogen. oxygen, 



methane. hydrogen, 



acetylene. 



Of the two gases favourable to the reaction methane is 

 decomposed in the cone, the carbon burning to its monoxide 

 and part of the hydrogen to water. The former reaction is 

 accompanied by the emission of the Swan spectrum and the 

 latter by the so-called water-vapour bands. These two 

 spectra are emitted whether the flame contains metal vapour 

 or not. Hence the two elements, carbon and hydrogen, do 

 not seem to participate, at least not to any appreciable 

 extent, in any further reactions which might be caused by 

 the presence of metal vapours. From this consideration 

 we are led to conclude that nitrogen must play a paramount 

 part in the reaction which gives rise to the cone lines. What 

 could be the nature of this reaction ? A possible answer to 

 this question appears to be pointed out by the very inte- 

 resting observations on the formation of metallic nitrides by 

 Messrs. Beilby and Henderson *. These chemists have shown 

 that many metals, when exposed to the action of ammonia 

 at high temperatures (varying between about 400 and 

 800° C), are either converted into nitrides or else pro- 

 foundly changed in their physical properties. These latter 

 changes are being caused by the continuous formation and 

 decomposition of unstable nitrides. When hydrogen is 

 present in excess, decomposition of the nitrides takes place. 



* G. T. Beilby and G. G. Henderson, Journ. Chem. Soc. vol. lxxiv. 

 p. 1245 (1901). 



