226 Mr. Gr. A. Hemsalech on the Line Spectrum of 



temperature changes and we may therefore conclude that 

 their greater brightness in the cone envelope of the air- 

 hydrogen flame is indicative o£ a state of temperature in this 

 flame which is of a higher order than that prevailing in the 

 mantle of the air-coal gas flame. 



d. Air-acetylene and Oxy-acetylene Flames. 



Owing to the difficulty of securing the necessary appliances 

 for working these flames in conjunction with the electric 

 sprayer or spark methods, it has not been possible to investi- 

 gate, from the present point of view, the spectra of iron to 

 which they give rise. In the course of a previous research 

 conducted by the present author in conjunction with 

 Mons. de Watteville, it was, however, found that in neither 

 the air-acetylene nor the oxy-acetylene cone does iron vapour 

 emit a characteristic spectrum. This seems rather astonishing, 

 in view of the fact that chemical actions of a most violent 

 character take place in the explosion regions of these flames 

 and, in particular, in that of the oxy-acetylene flame. The 

 inner of the two cones of this latter flame is, indeed, so 

 brilliant as a consequence of the chemical reaction that it is 

 not possible to examine it with the unprotected eye. The 

 Swan spectrum given by this cone is extremely intense, as 

 are also the other carbon bands, all of which, in addition to 

 their great brightness, show an extraordinary development. 



By reason, perhaps, of the great velocity which it is neces- 

 sary to give to the gas mixture of the oxy-acetylene flame in 

 order to maintain its stability, the lower part of the cone is 

 enveloped by only a thin stratum of mantle, the full develop- 

 ment of the latter taking place some distance above the cone. 

 This may partly account for the fact that the greater number 

 of the metal lines given by this flame do not originate near 

 the base of the cone as in other flames, but in the region 

 above the cone, and only the very strongest are observed also 

 in the direction of the cone. Another explanation for the 

 absence of lines in the lower part of this flame may be that, 

 owing to the great velocity with which the material, mixed 

 with the gases, is carried through this part of the flame, it is 

 enabled to travel a certain distance before the effect on it by 

 the temperature has been fully developed *. 



The spectra given by both the air- and oxy-acetylene flames 

 present the same general characters as that emitted by the 



* Henisalech and de Watteville, Comptes Rendus de V Academie de s 

 Sciences, t. cl. p. 329 (1910). 



