1908] on ETplosivp, Gomlustlon. 79 



does not justify the assertion that it cannot be formed at that tem- 

 perature by the operation of factors which are not concerned in its 

 decomposition. Therefore, I am not prepared to admit that because 

 the acetaldehyde molecule does not long rcjmain intact at high tem- 

 peratures, it necessarily follows that it cannot be brought into 

 actual existence as the result of the interaction of ethane and oxygen 

 in flames. 



Professor Smithells, in his recent presidential address to the 

 chemical section at the British Association (1907), expressed his 

 dissent from my views, as applied to flames, on the ground that 

 " The isolation of an intermediate product under one set of circum- 

 stances is in itself no proof that this product is transitorily formed 

 when the reaction is proceeding under another set of circumstances. 

 ..." To this I would reply, that whilst the isolation of (say) 

 acetaldehyde in the slow oxidation of ethane is not hy itself sufficient 

 proof of its transitory formation in the explosive combustion of the 

 hydrocarbon, yet if it can be demonstrated, not only that the facts 

 of explosive combustion can be best interpreted on the assumption 

 of its formation, but that, so far as can be judged at present, no 

 other interpretation can be advanced, and, moreover, that aldehydes 

 are actually produced in flames, then it may be justly claimed 

 that the assumption is well founded, and that the onus of its experi-. 

 mental disproof rests with the sceptics. 



Having thus, I hope, explained the main issues involved in the 

 controversy, I shall now proceed to perform a series of experiments 

 on the explosive combustion of acetylene, ethylene, and ethane, some 

 of wln'ch are crucial as regards the rival theories under discussion. 



Experiment II. — I have here three cyUndrical bulbs of stout boro- 

 silicate glass (capacity = about 60 c.c), fitted with firing wires, her- 

 metically sealed, and containing respectively equimolecular mixtures 

 of each of the three hydrocarbons with oxygen, that is to say, mix- 

 tures corresponding to C2H2 -f- Oo, C2H4 + Oo, and CoHg + 0.,, 

 respectively. 



Now, according to the theory of the preferential combustion of 

 carbon, these mixtures should on explosion, yield nothing but car- 

 bonic oxide and hydrogen, without any separation of carbon, or 

 formation of steam, as follows : — 



(a) C..H., + O., = 2C0 + H2 1-5 



(6) dn; + 0: = 2C0 + 2H. 2-0 



(c) G^He + Ol = 2G0 + SKl 2-5 



* The symbols p^ and p.,, used in this and subsequent tables, denote the 

 initial and final pressures of the cold original mixture and gaseous products 

 (dry) at constant volume and at the same temperature, 



