Iron Vapour in Air-Coal Gas Flame. 



227 



oxy-hydrogen flame, but they are much more intense. Espe- 

 cially with the oxygen-£ed flame the iron spectrum is so 

 luminous that an exposure of only ten minutes gives a con- 

 siderably brighter and better developed spectrum than an 

 exposure of two hours under otherwise identical conditions 

 with the oxy-hydrogen flame. 



With the oxy-acetylene flame the necessary minimum 

 temperature seems to have been reached which is required 

 for the excitation, by purely thermal actions, of those vibra- 

 tions which in most other light sources are brought about 

 by chemical or electrical actions only. Thus we found in 

 this flame traces of a number of Class III. lines, amongst 

 which the group at 4957 and the enhanced line X 3936. 

 Although in the air-coal gas cone these lines are relatively 

 prominent, the very high temperature of the oxy-acetylene 

 flame (nearly 3000° C.) has only been able to excite them 

 very feebly indeed, as compared with Class I. and II. 

 lines. As already stated, Class III. lines have not been 

 observed in the hottest parts of the oxy-coal gas and oxy- 

 hydrogen flames, the temperatures of which, 2400 and 

 2600° C. respectively according to E. Bauer, are probably 

 not sufficient for their thermal excitation. 



The results obtained with the air-hydrogen and air-acety- 

 lene flames show clearly that nitrogen is not the only factor 

 in bringing about the special chemical actions to which is 

 due the emission of the characteristic cone spectrum observed 

 in the Bun sen flame. 



The observations recorded in this paragraph are sum- 

 marized in the following table, which shows at a glance 

 the absence or presence of any one of the three types of 

 iron lines in the various flames examined : — 



Nature of 

 Flame. 



Class I. 



Class II 



Class II 



Air- f cone 

 coal gas \ mantle 



present 

 present 



present 

 traces 



present 

 absent. 



Oxygen- f cone 

 coal gas \ mantle 



absent 

 present 



traces 

 present 



traces, 

 absent. 



Air- f cone 

 hydrogen [ mantle 



present 

 present 



present 

 present 



absent, 

 absent. 



Oxygen- J* cone 

 hydrogen \ mantle 



absent 

 present 



absent 

 present 



absent, 

 absent. 



Air- f cone 



acetylene \ mantle 



absent 

 present 



absent 

 present 



absent. 

 ? 



Oxygen- f cone 

 acetylene \ mantle 



absent 

 present 



absent 

 present 



absent, 

 traces. 



