1914] on Surface Combustion 43 



(1) that the power of accelerating gaseous combustion is possessed 

 by all surfaces at temperatures below the ignition point in varying 

 degrees, dependent upon their chemical characters and physical tex- 

 ture ; (2) that such an accelerated surface combustion is dependent 

 upon an absorption of the combustible gas, and probably also of the 

 oxygen, by the surface, whereby it becomes "activated" (probably 

 ionized) by association with the surface ; and (3) that the surface 

 itself becomes electrically charged during the process. Finally, 

 certain important differences between homogeneous combustion in 

 ordinary flames and heterogeneous combustion in contact with a hot 

 surface from a chemical point of view were established, so that there 

 can be no longer any doubt as to the reality of the phenomenon.* 



The fact that such catalytic combustion depends upon an inti- 

 mate association of the surface with the combining gases is beau- 

 tifully illustrated by two photomicrographs of the surface of a silver 

 gauze taken before and after a long series of experiments in which it 

 was employed as the catalysing medium for the com1)ination of hydro- 

 gen and oxygen at 400° C. (848° F.). Fig. 1 show^s the original 

 smooth condition of the surface, and Fig. 2 shows the " frosted " 

 effect produced by the deep "pitting" action of the reacting gases 

 during their absorption and "activation" by the surface. 



My next contention is that if hot surfaces possess the power of 

 accelerating gaseous combustion at temperatures below, or in the 

 neighbourhood of, the ignition point, the same power must also be 

 manifested in even a greater degree at higher temperatures, and 

 especially so when the surface itself becomes incandescent. Indeed, 

 there are experimental grounds for the belief that not only does the 

 accelerating influence of the surface rapidly increase with the tem- 

 perature, but also that the differences between the catalysing powers 

 of various surfaces, which at low^ temperatures are often considerable, 

 diminish with ascending temperatures until at bright incandescence 

 they practically disappear. 



Such considerations as I have thus briefly explained convinced me 

 some years ago that if an explosive, gaseous mixture be either injected 

 on to or forced through the interstices of a porous refractory incan- 

 descent solid under certain conditions, w^hich wdll be hereafter ex- 

 plained, a greatly accelerated combustion would take place within the 

 interstices or pores, or, in other words, within the boundary layers 

 between the gaseous and solid phases wherever these may be in con- 

 tact — and the heat developed by this intensified combustion would 

 maintain the surface in a state of incandescence without any develop- 

 ment of flame, thus realizing the conception of flameless incandescent 



* Bone and Wheeler, Phil. Trans. Roy. Soc, 1906 (A. 206, pp. 1-67), also 

 further (unpublished) results (1905-12) in collaboration with Messrs. G. W. 

 Andrew, A. Forshaw, and H. Hartley, which are summarized in Berichte der 

 Deutschen Chem. Ges., 1913. 



