1895.] in the Flames of Hydrocarbon Gases. 461 



On plotting out these results, they certainly seem to point to 

 the fact that, with flames of the same size burning from the same 

 burner, the light emitted by the flame is directly proportional to the 

 percentage of acetylene present at the top of the non-luminous zone 

 of the flame, provided always that the temperature is sufficiently 

 high to complete its decomposition. 



FIG. 2. 



It is perfectly possible for the temperature of a flame to be so little 

 above the point necessary to decompose the diluted acetylene that, 

 whilst some decomposes and renders the flame faintly luminous, the 

 larger portion burns without decompositioa. A good example of this 

 is to be found in the combustion of alcohol, the flame of which con- 

 tains as much acetylene as is to be found in a good coal-gas flame, 

 but which is practically almost non-luminous. If alcohol in a small 

 dish be ignited, it burns with a faintly luminous flame, and if a bell- 

 jar is placed over it, some of the products of combustion mingling 

 with the flame still further co6l it and render it non -luminous ; but 

 if now a stream of oxygen be introduced under the bell-jar the 

 temperature of the flame is at once increased and becomes highly 

 luminous, whilst a cold porcelain vessel held in the flame is coated 

 with soot. 



In all the experiments in which light was developed in heated 

 tubes by the decomposition of acetylene, the glow of the carbon was 

 red and lurid, the light emitted being of the same character and 

 appearance as that developed by the combustion of potassium in 

 carbon dioxide, and entirely lacking the pure white incandescence of 

 the acetylene flame as burnt from a flat- flame burner. 



This may be due to the fact that in the open flame the tempera- 

 ture of the carbon particles is presumably due to three sources of 

 heat : 



