Contributions to the Theory of Luminous Flames. 98 



a very desultory manner. I earnestly commend it to the 

 attention of those interested in an examination of the chemical 

 action of radiations, as one of the most important and pro- 

 mising topics. 



John W. Draper. 



University, New York, 

 December 13, 1876. 



XIV. Contributions to the Theory of Luminous Flames. — 

 Part II. By Dr. KarlHeumann*. 



Influence of Withdrawal of Heat from , anal Addition of Heat to 

 Luminous Flames. 



ALTHOUGH the phenomenon of a small distance existing 

 between flame and burner, or flame and a cold substance 

 placed therein, is most apparent in the case of non-luminous 

 flames, or of those flames which have been diluted by indifferent 

 gases, nevertheless this appearance is also noticeable in the 

 case of luminous flames. In the latter flames the eye is some- 

 what overpowered by the light, and hence has difficulty in ob- 

 serving the vacant space ; the recognition of this space is made 

 easier by placing a screen in such a position as to cover the 

 luminous part of the flame as completely as possible. 



Mention has already been made of the fact that a flame loses 

 luminosity by being pressed down or widened out by the in- 

 troduction of a cold substance ; and by properly regulating 

 the experiment, it has been shown that the withdrawal of heat 

 is of itself sufficient to account for the observed diminution in 

 luminosity. By combining the results so obtained with those 

 which we have gained concerning the distance between flame 

 and burner, or flame and cold object placed therein, we are led 

 to deductions of great practical interest. 



If a cold metallic wire be placed in a luminous gas- or candle- 

 flame, the flame is totally extinguished in the immediate neigh- 

 bourhood of the wire, and the luminosity of the flame is dimi- 

 nished throughout a very considerable area. 



In this experiment the low conductivity for heat of gases 

 comes into play, aided by the great freedom of motion and dif- 

 fusibility of the particles, whereby highly heated particles are 

 continually brought into fresh contact with the cold wire. 

 The cooling action of the wire is therefore the greater, and 

 extends throughout a larger space, the lower the temperature 

 of the wire itself. The wire is therefore also more potent in 



* Translated from Liebig's A?malen, vol. clxxxiii. part 1, pp. 102-141, 

 by M. M. Pattison Muir, the Owens College, Manchester. 



