the Theory of Luminous Flames. 21 



But besides this cooling action exercised by the gas itself, 

 the temperature of the flame suffers diminution by means of 

 the action of the cold air surrounding the stream of gas. The 

 air which the issuing gas carries along with it not only tends 

 to withdraw heat from the outer portions of the flame, but 

 penetrates also into the flame-mantle, the temperature of which 

 it therefore diminishes. 



Such withdrawal of heat by means of the cold gas, and by 

 means of admixed air, takes place in every flame, even when 

 burned under small pressure; but the action of these two 

 causes, especially of the latter, increases as the velocity of the 

 gas-stream increases ; and if this be great and the gas be also 

 under high pressure, the flame may be so cooled in the neigh- 

 bourhood of the burner as to be extinguished, and a mixture 

 of air and unburn ed gas may be formed and carried forward 

 on the surface of the issuing gas-stream. In this case the 

 existence of a flame will become possible only at a consider- 

 able distance from the burner, where the velocity of the gas 

 has diminished, and where therefore the ignited gas is not so 

 greatly cooled. 



By increasing greatly the velocity of the gas and by dimi- 

 nishing the orifice through which the gas issues, it may be 

 possible to prevent the stream of gas from becoming ignited 

 at all — as, for instance, it is possible to extinguish the flame of 

 a gas issuing from a burner with a small velocity, the stopcock 

 being partially closed, by fully opening the stopcock and so 

 increasing the rush of gas. 



The explanation of this extinction of the flame is to be found 

 in the fact that the space between burner and flame is increased 

 by cooling the gas, and that in this space an excess of air 

 finds its way into the gas-stream, which, as it increases its 

 distance from the burner, becomes more and more diluted with 

 air, until at last the mixture cannot be caused to ignite. If 

 the orifice be small this state of affairs is attained the sooner, 

 because under such conditions the diameter of the stream of 

 gas is small, and the gas therefore quickly becomes diluted 

 with air. If the explanation which has been given of the fact 

 that a rapid stream of gas burns only at some distance from 

 the orifice whence it issues be true, it follows that the distance 

 between burner and flame must be decreased by raising the 

 temperature of the gas previously to its leaving the burner. 

 I have been able to prove that this is the case by making use 

 of the flame of alcohol- vapour already described. 



A thin platinum tube, the length of one's finger, was attached 

 to the glass exit-tube at which the alcohol vapour was burned. 

 The alcohol was boiled, so that a space of 2 or 3 centims. in- 

 tervened between the flame and the orifice of the tube. The 



