﻿116 M. H. St. -Claire Deville on the Temperature of Flames. 



where all the manipulation necessary for determining the tem- 

 perature produced by flames and solid combustibles may be 

 effected without danger. 



if, as is almost already demonstrated by what I have said and 

 by almost all the observations made by engineers and by physi- 

 cists in chambers containing compressed air, the temperature 

 of combustion rises at the same time as the pressure increases, 

 that would be one analogy more to be added to the number of 

 those I have indicated between the phenomena of combination 

 and of decomposition on the one hand, and the phenomena of the 

 condensation of vapours and of volatilization on the other hand. 



We may in fact give the name greatest temperature of conden- 

 sation of vapour to what is improperly known as the boiling- 

 point of a liquid. This temperature is no other than that com- 

 mencing from which a vapour no longer condenses on the surface 

 of a cold thermometer, which is merely heated by means of the 

 latent heat yielded to it by the vapour in which it is immersed. 

 The boiling-point, or temperature of condensation, rises, as we 

 know, when the pressure above the liquid which produces the va- 

 pour is increased. 



The combination of bodies, and particularly that of oxygen 

 and hydrogen in the oxyhydrogen blowpipe, is apparently a more 

 complex phenomenon, but corresponds perfectly to the act of the 

 condensation of vapours. 



Assuming that the temperature of the combination of hydro- 

 gen and oxygen is 2800°, the quantity of water formed under 

 a pressure of 760 millims. will be in the flame, at the hottest 

 part *, 



637 + (2800-100)0-475 _ 



3833 --O-oj 



that is to say, only half the oxygen and hydrogen will be com- 

 bined under a pressure of 760 millims. 



But if we increase the pressure, the temperature of the flame 

 increasing also, it will be seen from the preceding formula that 

 the proportion of substance combined or of aqueous vapour 

 formed will increase as the pressure increases — just as the tension 

 of a saturated vapour increases in proportion as the temperature 

 increases. Lastly, the temperature of combination of a gaseous 

 mixture, like the greatest temperature of condensation (or boil- 

 ing-point) of a vapour, increases with the pressure. 



The substance combined in a flame plays the same part as the 

 substance condensed in a space full of vapour the temperature 

 and pressure of which are varied so that the vapour is always 

 saturated. 



* Vide Legonsde Ckimie, given in 1864 and 1865,p.290(Hachette,1866). 



