the Theory of Luminous Flames. 7 



" 1. Decrease in luminosity cannot be due to dilution of 

 the gases, whether understood in Frankland or Blochmann's 

 meaning of the term, inasmuch as' in the above mentioned re- 

 searches such dilution was at any rate increased by heating, 

 yet the flame became luminous." 



" 2. Decrease in luminosity, in Knapp's experiments, as 

 also in the case of the ordinary Bunsen's flame, is much more 

 to be traced to the cooling effect, on the interior of the flame, of 

 the entering gas. By heating the latter the flame becomes 

 luminous." 



Wibel finds " a most noteworthy argument " in favour of 

 these two points in the peculiar behaviour of the flame of 

 coal-gas and oxygen. 



On the one hand, this flame becomes non- luminous only 

 when the current of oxygen is rapid, and when the flame is 

 cooled by metallic gauze ; on the other hand, by proper treat- 

 ment the flame may be made a source of intense light. These 

 circumstances show, according to Wibel, that neither dilution 

 nor oxidation is a cause of decrease of luminosity. By similar 

 reasoning it might be shown that Wibel's theory is itself 

 erroneous. Everyday experience tells us that the blue flame 

 of Bunsen's burner, as well as that of the blowpipe, possesses 

 a much higher temperature than the ordinary luminous flame ; 

 but if Wibel be correct in saying that decrease of luminosity 

 is a consequence of cooling only, then, logically, the tempe- 

 rature of the luminous flame ought to be higher than that of 

 the non-luminous flame. 



Those flames whose luminosity is decreased by means of 

 air might perhaps not be classed with those in which a similar 

 result is brought about by means of indifferent gas ; but little 

 would thus be gained, for the Bunsen's flame behaves, so far 

 as its power of becoming luminous is concerned, similarly 

 to Knapp's flame, the only distinctive point (the higher 

 flame-temperature consequent upon the entrance of oxygen 

 in the admitted air) not being proportionately altered by 

 heating the tube of the burner, the flame nevertheless 

 becoming luminous. 



But while, in the case of flames rendered non-luminous 

 by indifferent gases, it might be supposed that the heat gained 

 when the tube of the burner is warmed merely serves to re- 

 place that lost by absorption into the entering inert gas (which 

 heat had formerly caused luminosity), this supposition is con- 

 tradicted by the already cited analogous case of decrease of 

 luminosity by means of air, inasmuch as it cannot be supposed 

 that there is a withdrawal of heat from the luminous material 

 in the flame, the temperature of which is greatly increased. 



