82 Professor WiUiam Arthur Bone [Feb. 28, 



C„H9„ + " Oo = nCO + nE,, 



a diminution of the oxygen below this Hmit at once gives rise to 

 steam formation. 



Experiment /F. — The next experiment is designed to ihustrate the 

 infinitely greater affinity of acetylene and ethylene as compared with 

 that of hydrogen for oxygen at the high temperatures of flames. I 

 have here two bulbs containing mixtures of each of these hydrocarbons 

 with hydrogen and oxygen corresponding to C2H2 + 2H2 + O2 and 

 C2H4 + Ho + O2, respectively, and I will ask you to contrast the be- 

 haviour of these with that of the equimolecular mixture of ethane and 

 oxygen, C2H6 + O2, which was exploded a few^ minutes ago. It should 

 be noted that whilst all three mixtures contain the same relative pro- 

 portions of carbon, hydrogen and oxygen, they differ in respect of the 

 proportions between the combined carbon and hydrogen. Asking you 

 to bear in mind how the equimolecular mixture of ethane and oxygen 

 on explosion gave rise to a black cloud of carbon and a considerable 

 formation of water, I will now fire the other two mixtures. You will 

 observe that in neither case has there been any deposition of carbon, 

 and an inspection of the cold bulbs will show that little or no steam 

 formation has occurred. In fact, the hydrocarbon has been burnt 

 to carbonic oxide and hydrogen, leaving the hydrogen absolutely 

 untouched by the oxygen, as the following detailed results show 

 (Table II.). 



These experiments have an important bearing on the chemistry of 

 flames. Hydrogen is usually considered as one of the most com- 

 bustible of gases, but here we see it pushed to one side by the all- 

 powerful hydrocarbon, as though it were so much inert nitrogen. 

 This at once raises another question which has lately been occupying 

 my attention. Ever since Davy's experiments on flame, the com- 

 bustibility of hydrogen has been considered to be superior to that of 

 methane ; this, however, cannot be true in regard to slow combustion, 

 since it can be easily proved that between ^00° and 400° C. methane is 

 oxidised at a far faster rate than hydrogen. Nevertheless, I have 

 recently observed facts which incline me to think that possibly it may 

 be true in regard to flames. If further investigation confirms this 

 opinion, it will be necessary to enquire into tlie cause of the peculiar 

 relative inertness and stability of methane as compared with other 

 gaseous hydrocarbons when subjected to the action of oxygen at 

 high temperatures. 



It does not I think impose too great a strain on the imagination 

 to picture the probable mechanism of combustion in hydrocarbon 

 flames, and for this purpose ethylene and ethane may be taken as 

 typical examples. It may be assumed that, with the possible excep- 

 tion of methane, the affinity of a hydrocarbon for oxygen is so great 

 at high temperatures that the initial stage of its combustion takes 



