1914] Surface Combustion 41 



WEEKLY EVENIXa MEETING, 



Friday, February 27, 1914. 



Sir James Crichton-Browxe, J.P. M.D. LL.D. F.E,.S., 



Treasurer and Yice-President, in the Chair. 



Professor W. A. Boxe, D.Sc. Ph.D. F.R.S. 



Surface Combustion. 



During- his researches upon Flame,* Sir Humphry Davy discovered, 

 in 1817, that the constituents of a combustible mixture will com- 

 bine slowly below the ignition temperature ; this led him to enquire 

 whether, seeing that the temperatures of flames far exceed those at 

 which solids become incandescent, a metallic wire can be maintained 

 at incandescence by the combination of gases at its surface, without 

 actual flame. He thereupon tried the effect of introducing a warm 

 platinum wire into a jar containing a mixture of coal-gas and air 

 rendered non-explosive by an excess of the combustible constituents ; 

 the wire immediately became red hot, and continued so until nearly 

 the whole of the oxygen had disappeared. 



We will repeat the experiment, in a modified form, with the aid 

 of a platinum crucible and a Bunsen burner. If the platinum 

 crucible be warmed by the flame, and the flow of the explosive 

 mixture through the burner be momentarily arrested, and then 

 immediately renewed, the gases, instead of burning with flame at the 

 burner head, will immediately combine without flame over the 

 platinum surface, causing it to glow. 



During the twenty yeai's which followed Davy's discovery, several 

 distinguished chemists (William Henry and Thomas Graham in this 

 country, but more particularly Dulong and Thenard, and independ- 

 ently Dobereiner in France) experimented upon the slow combination 

 of gases at temperatures below the ignition point, in contact with hot 

 solids, whereby it was established (1) that hot solids, and pre- 

 eminently metals of the platinum group, have the power of inducing 

 gaseous combustion at relatively low temperatures ; and (2) that 

 hydrogen is of all combustible gases, the most susceptible to this 

 action. 



The mechanism of this induced slow surface combustion formed 

 the subject of a celebrated controversy between Faraday and De la 

 Rive in 1834-5. De la Rive held the view that it consists essentially 

 in a series of rapidly alternating oxidations and reductions of the 



* Collected Works, vol. vi. p. 8. 



