SPONTANEOUS IGNITION. 307 



In the economic production of heat and light, we 

 have the combination of hydrogen and carbon with the 

 oxygen of common air, forming water and carbonic 

 acid. In our domestic fires we employ coal, which is 

 essentially a compound of carbon and hydrogen contain- 

 ing a little oxygen and some nitrogen, with some earthy 

 matters which must be regarded as impurities ; the 

 taper, whether of wax or tallow, is made up of the same 

 bodies, differing only in their combining proportions, 

 and, like coal gas, these burji as carburetted hydrogen. 

 All these bodies are very inflammable, having a tendency 

 to combine energetically with oxygen at a certain 

 elevation of temperature. 



We are at a loss to know how heat can cause the 

 combination of those bodies. Sir Humphry Davy has 

 shown that hydrogen will not burn, nor a mixture of it 

 with oxygen explode, unless directly influenced by a 

 body heated so as to emit light* May we not, there- 

 fore, conclude that the chemical action exhibited in a 

 burning body is a development of some latent force, 

 with which we are unacquainted, produced by the absorp- 

 tion of light; that a repulsive action at first takes 

 place, by which the hydrogen and carbon are separated 

 from each other ; and that in the nascent state they 

 are seized by the oxygen, and again compelled, though 

 in the new forms of water and carbonic acid, to resume 

 their chains of combining affinity ? 



Every equivalent of carbon and of hydr-ogen in the 

 burning body unites with two equivalents of oxygen, in 

 strict conformity with the laws of combination. The 

 flame of hydrogen, if pure, gives scarcely any light, but 

 combined with the solid particles of carbon, it increases 

 in brightness. The most brilliant of the illuminating 

 gases is the olefiant gas, produced by the decomposition 

 of alcohol, and it is only hydrogen charged with carbon 



* Researches on Flame : Sir H. Davy's Collected Works. 



