230 Mr. G. A. Hemsalech on the Line Spectrum of 



Let us now examine whether the conditions prevailing in 

 the explosion region of the air-coal gas flame are favourable 

 to the formation of nitrides. The gas mixture, containing 

 hydrogen and nitrogen (the constituents of ammonia) in the 

 free state, enters the explosion region at about room-tempera- 

 ture — say, 15° C. On passing through the thin wall of the 

 cone its temperature is raised considerably and near the tip 

 of the cone it reaches over 1000° C. Thus during one stage 

 of its passage through the explosion region the gas mixture 

 has passed through that range of temperature recognized as 

 essential for the formation of nitrides, viz. 400-800° G. 

 Hence the temperature conditions in the Bunsen cone are 

 favourable to the formation of metallic nitrides. 



We know, however, very little about the changes in 

 the state of the metal as it passes through the explosion 

 region. The material enters this region generally as a 

 minute globule of a salt solution of the metal, or as an 

 ultra-microscopic particle of the oxide. In either case the 

 reaction takes place with the emission of cone lines, 

 although with the oxide, to judge by the relative faint- 

 ness of the resulting iron spectrum, the reaction is not so 

 intense. Is the temperature of the explosion region alone 

 sufficient to dissociate these minute quantities of the com- 

 pound and thus to set free the metal prior to its combination 

 with the nitrogen, or, if not, is the chemical affinity of 

 nitrogen for the metal so great as to liberate the metal atoms 

 at a lower temperature than they would be set free at under 

 the influence of thermal actions alone? To these and many 

 similar questions which naturally arise, no satisfactory answer 

 can as yet be given. 



But let us suppose that the cone lines are caused by the 

 successive formation and decomposition of a nitride of the 

 metal, how is it then that this reaction does not take place 

 also in the cones of the air-hydrogen and air-acetylene 

 flames ? Several reasons can be advanced in explanation 

 of this discrepancy : — 



Firstly ■, it may be that the temperatures prevailing in the 

 explosion regions of these two flames are too high for 

 the formation of the nitrides, i. e. above 800° C. As we have 

 seen (§ 2, c & d), the spectroscopic evidence seems to point 

 to the existence in the air-hydrogen cone of a temperature 

 higher than that prevailing in the mantle of the Bunsen flame, 

 namely, above 1700° C. We know nothing about the tem- 

 perature of* the air-acetylene cone, but to judge by its great 

 luminosity it must be considerably higher than that of the 

 Bunsen cone. 



