272 MR. JOHN LEIGH ON THE CHEMICAL CHANGES 



is now in excess, the gas is poor and gives little light ; the 

 heat still increasing, the affinity between the hydrogen and 

 carbon is altogether disrupted, the remaining carbon is de- 

 posited, and pure hydrogen given off? Certainly all this 

 can be effected artificially; and that, to a large extent, it is 

 so in gas-making, is evident from the thick lining of almost 

 pure carbon which soon forms in the interior of gas retorts, 

 and which must proceed from the decomposition of the gas 

 by the red-hot surface — must be deposited from it, in fact. 

 Still it is not simply and entirely thus; there are probably 

 three products, at least, of the decomposition of a liquid 

 carbo-hydrogen, solid carbon, a gaseous product containing 

 much hydrogen, and a solid hydro-carbon containing much 

 carbon, the elements being divided amongst each other. When 

 naphtha vapour is passed over red-hot crystal, it deposits 

 carbon, gives off olefiant gas and light carburetted hydrogen, 

 and forms a crystalline compound, naphthaline, composed of 

 C. 20, H. 8* With these facts before us, is it not reasonable 

 to conclude, that there is a temperature, a point at which, 

 in the process of decomposition, olefiant gas and volatile 

 hydro-carbon (which I would call trito or tetarto carburet 

 of hydrogen) should be formed, and which yet should be 

 unable to decompose these into compounds poorer in car- 

 bon? for we have seen that the intensity of decomposition 

 is proportionate to the intensity of heat. I think there 

 cannot be a doubt that there is such a tejnperature ; but it 

 must be far below that at present employed for the manu- 

 facture of gas. Let us now examine the present system of 

 gas-making, and I thiiik we shall soon see the true source 

 of the hydrogen and carbonic oxide, so invariably found in 

 gas, and constituting so large a portion of its bulk. I may 

 premise, that when carbonic acid is passed over red-hot 

 coke it is resolved into carbonic oxide, by taking up an 

 additional atom of carbon. 



When compact masses of coal are thrown in heaps of a 



