230 On the Flame and Furnace Spectra of Iron. 



furnace temperatures the component atoms of a molecule 

 become more firmly united, which, as has been shown, is 

 accompanied by further restrictions in the line emission, and 

 it is reasonable to conclude that the final extinction of the 

 luminous vibrations would coincide with the completion of 

 the chemical union of the atoms concerned. Thus the 

 extinction of light which I observed* on passing a stream 

 of oxygen or nitrogen through a coloured flame given by a 

 weak gas mixture, receives a satisfactory explanation by 

 supposing that the relaxed atoms of the heated salt molecule 

 had completely recombined as a result of the cooling effected 

 by the stream of gas. Moreover, the supposition that 

 chemical union arrests the luminous vibrations of the atoms 

 would at once enable us to account in a most plausible 

 manner for the abrupt extinction of the cone emission as 

 observed in the air- coal gas flame: namely, the emission 

 of this spectrum would, in conformity with this view, stop 

 instantly on the completion of the chemical union between 

 the atoms of iron and nitrogen. 



The hypothesis here developed is in short as follows: — 

 The iron atom is never completely liberated by the action of 

 heat either in flame or furnace, but remains always more 

 or less chemically associated with the other atoms in the 

 compound molecule ; the light radiations which the atomic 

 system of iron is capable of emitting under these conditions 

 of restraint are always appreciably curtailed in development. 

 On the other hand, in the explosion region of the air-coal 

 gas flame the iron atom, thanks to its strong affinity for 

 nitrogen, is severed from its partner in the original compound 

 and the luminous vibrations, which are emitted whilst the 

 atomic system is in the free state, show a high degree of 

 development comparable to that observed in the arc and 

 spark. Completion of chemical union is accompanied by 

 the instant extinction of the line emission, as is shown 

 by the abrupt cessation of the cone spectrum as the 

 formation of the nitride is accomplished. 



In conclusion I have great pleasure in placing on record 

 my high appreciation of Dr. Kino's pioneering work on 

 furnace spectra. It is mainly to the inspirations received 

 through the medium of his important publications that the 

 present research owes its origin. 



Manchester, May 16th, 1918. 



* Hemsalech, Phil. Mag. vol. xxxv. p. 387 (1918). 



