76 Professor WiUiam Arthur Bone [Feb. 28, 



Who was the author of this view, or whaL was oiigLiially its ex- 

 perimental basis, is not quite clear, but it received the active support 

 of two such eminent authorities as Thomas Graham and Micliael 

 Faraday, and for fifty years it was regarded as one of the most cei'- 

 tain articles of chemical faith. Its final overthrow 1)y Dixon and 

 Smithells in the year 1892, caused no small stir in chemical circles. 



2. The second theory originated with Kersten in 1861, who as 

 the outcome of experiments on the explosion of a mixture of ethylene 

 and electrolytic gas, asserted that " before any portion of the hy- 

 drogen is burnt, all the carbon is burnt to carbonic oxide, and 

 that the excess of oxygen then divides itself between the carbonic 

 oxide and the hydrogen." In other words, Kersten attempted to sub- 

 stitute the idea of the preferential burning of carbon for that of the 

 preferential burning of hydrogen. His views, however, received no 

 serious attention until they were revived and endorsed by Dixon and 

 Smithells in 1892. 



The chief experimental basis for this theory is the behaviour of 

 ethylene and acetylene when exploded with their own volume of 

 oxygen. More than a century ago, Dalton found that a mixture of 

 equal volumes of ethylene and oxygen yields mainly carbonic oxide 

 and hydrogen on explosion, without any separation of carbon, in 

 conformity with the equation : — 



C2H4 + O2 = 200 + 2H2 

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This fact, after being overlooked for nearly eighty years, was 

 rediscovered by Dixon in 1891 ; moreover, a few years later, when 

 it was proved that acetylene behaves in a precisely similar manner- — 



C2H2 + O2 = 2C0 + H.,, 

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the advocates of the theory were able to claim a strong body of evi- 

 dence in support of their case. 



3. But the idea of a '''preferential " combustion, whether of carbon 

 or of hydrogen, seemed repugnant to well-established principles con- 

 cerning the nature and conditions of chemical interactions in gaseous 

 systems. Moreover, whilst the assumption of a direct passage from 

 an initial system of ethylene and oxygen, C^H^ + O2, to the system 

 carbonic oxide and hydrogen, 200 + 2H2, implied a simple trans- 

 action from the kinetic standpoint, an extension of the idea to the 

 case of such a hydrocarbon as propylene — 



203H,3 + 302 = ^>^^ + ^H-i, 



would at once raise serious difficulties. 



It therefore remained to consider whether the solution of the 



