the Theory of Luminous Flames. 15 



non-luminosity brought about by nitrogen and carbon dioxide, 

 especially dilution and beat-absorption ; in the widening out 

 of the flame caused by a cold surface, absorption of heat and 

 more rapid oxidation of carbon; and in non-luminosity caused 

 by air, each of the three causes is at work. 



In the latter case the presence of the oxygen of the ad- 

 mitted air tends to cause a rise in the temperature and a 

 diminution in the size of the flame, circumstances which are 

 opposed to the absorption of heat and dilution of the flame. 



The flame of the Bunsen's burner appears to be the final 

 product of a whole series of causes acting some in one direc- 

 tion, some in another ; and it is not to be wondered at that 

 observers of luminous flames have arrived at such diverse and 

 contradictory conclusions, inasmuch as they have made the 

 study of this flame their principal object, overlooking the 

 great complexity of the conditions affecting it, instead of 

 preceding such a study by an investigation of more simple 

 instances of combustion. 



Effect of Withdrawal of Heat upon Flames. 

 On account of the simpler conditions affecting so-called 

 non-luminous flames I have considered these first, omitting all 

 mention of changes in the intensity of light, until a study of 

 the effect of the withdrawal of heat shall have given us some 

 exact knowledge concerning this cause of decreased luminosity. 



Distance between Flame and Burner. 



In a paper of Blochmann's* the fact is noticed that a gas- 

 flame does not touch the rim of the burner, nor a candle-flame 

 the wick. Blochmann says: ; — "If a gas-flame be closely ex- 

 amined it is seen not to rest immediately upon the opening 

 of the burner. In the case of a highly luminous flame the 

 luminous portion presents too great a contrast to enable one 

 to notice this fact with certainty ; but by decreasing the quan- 

 tity of gas the space between burner and flame becomes more 

 apparent in proportion as the intensity of the light diminishes. 

 The small semicircular non-luminous flame issuing from a 

 bat's-wing burner when the supply of gas is small, may be 

 arranged so that the space between the burner and the flame 

 shall appear as great as the height of the flame itself." 



This small intermediate space may be proportionately in- 

 creased by mixing an indifferent gas, such as nitrogen or 

 carbon dioxide, with the coal-gas before the latter is ignited. 

 Blochmann also noticed that the intermediate space was in- 

 creased by burning the diluted coal-gas under diminished 

 * Liebig 's Annalen, clxyiii. 345. 



