376 



TRANSACTIONS OF SECTION B. 



there may be an indefinite upward slow propagation of flame together with 

 incompleteness of combustion (much of the combustible mixture remaining 

 unburnt), and the question naturally arises as to how the term 'inflammability' 

 should be scientifically defined. Dr. Coward has argued with some force that 

 a gaseous mixture should not be termed ' inflammable ' at a given temperature 

 and pressure unless it will propagate flame indefinitely, the unburnt portion 

 being maintained at that temperature and pressure. Inflammability, thus 

 defined, would be a function of the temperature, pressure, and composition of 

 a particular mixture only and would be independent of the shape and size 

 of the containing vessel ; and, provided that it is kept in mind that for each 

 particular mixture at a given temperature and pressure a certain minimum 

 igniting energy and intensity is requisite, I am inclined to agree with the 

 definition. Also, there is the possibility that in a mixture just at or very near 

 one or other of the limits of inflammability flame may be propagated upwar^ds 

 but not downwards. 



From his experiments Dr. Coward has assigned the following as the lower 

 limits of inflammability of hydrogen, methane and carbon monoxide, respec- 

 tively, in air at atmospheric temperature and pressure : 



Per cent. 

 Hydrogen . . . . 4"1 



Methane 5-3^o 



Carbon monoxide . . . 12-0 



The Combustion of Hydrocarbons and the Relative Affinities of Methane, 

 Hydrogen, and Carbon Monoxide, respectively, for Oxygen in Flames. 



Under the title of ' Gaseous Combustion at High Pressure ' I have recently 

 published, in conjunction with various collaborators," a further instalment of 

 my researches upon the mechanism of hydrocarbon combustion,'- and I may 

 perhaps be allowed to draw your attention to certain new points which have 

 arisen in connection therewith. 



A detailed study of the behaviour of mixtures of methane and oxygen of 

 composition ranging between 2CH,-i-0, and CH^ +■ O., when exploded in steel 

 bombs at initial pressures of 12-7 atmospheres (see table, fig. 4), has shown 

 it to be consistent with the ' hydroxylation ' theory of hydrocarbon combustion 

 which I put forward some years ago as the result of my previous work. The 

 following scheme seems to interpret correctly the chemical and thermal changes 

 involved in the initial stages of the explosive combustion of methane : 



CH4 



oxidation 



o 



S 

 o 



u 



P 



+ 30 



B 



H, : C . OH^ 



22 7 



oxidation 



v ia Hg -.(y-. (OKh 



+ 59 



> Ha : C : + H2O 



22-8 



V 



C + 2H2 



Ai 



o 



a 



o 



o 



■ © 



O 



V 



CO + 2H2 

 Bi 



a 

 _2 



o 



a 



o 



o 



13-4 



V 



C0 + H2 



CI 



'" Too much stress need not be laid upon the difference between this number 

 and the 5'6 per cent, given by Dr. Wheeler (loc. cit.), because Dr. Coward 

 himself admits that the flames of mixtures containing from 5'3 to 5'6 per cent, 

 of methane are very sensitive to shock, whilst a 5'6 per cent, mixture will always 

 propagate flame indefinitely even when there is a moderate disturbance ; the 

 conditions must be exceedingly tranquil to prevent extinction in the other cases. 



" Messrs. Hamilton Davies, H. H. Crray. H. H. Henstock, and J. B. Dawson. 



'= Phtl. Trans. Roy. Soc., A., vol. 215 (1915), pp. 275 to 318. 



