Pbofbssor Thomab Thomson on Coal Gas. 169 



senting the atoms of each constituent, the quantity of azote being 

 reckoned 1 atom. We leave out the ashes, because they have nothing 

 to do with the production of the gas, excepting that they materially 

 influence its quantity. 



It appears from this table, that Newcastle coal contains the most 

 carbon, and cannel coal the least ; while cannel coal contains the 

 most oxygen, and Newcastle coal the least. Newcastle coal con- 

 tains the least hydrogen, and cannel coal the most Now cannel 

 coal yields the best, and Newcastle coal the worst gas. This need 

 excite no surprise. Carbon not being volatile, it is obvious that if 

 coal contained nothing but carbon, it would yield no gas at all. Coal 

 gas is a mixture of four different gases, most of which are compounds. 

 Two are compounds of carbon and hydrogen, one of carbon and oxy- 

 gen, and the fourth is pure hydrogen. There is no difficulty in 

 conceiving the formation of the gaseous compounds of carbon and 

 hydrogen ; but it is not so easy to explain the formation of carbonic 

 oxide and hydrogen. These two gases are never entirely wanting ; at 

 least, I have analysed above forty specimens of coal gas from different 

 kinds of coal, and from different gas works, without ever failing to 

 find them. I think it probable that they make their appearance 

 towards the end of the process of heating the coaL It is well known, 

 that the longer the process of gas making is continued, and the higher 

 the temperature at which the gas is produced, the worse is the gas, 

 and, of course, the more hydrogen it contains. Is it not possible that 

 coal may contain water — that this water can only be extricated at a 

 high temperature — that its oxygen combines with carbon and forms 

 carbonic oxide, while the liydrogen makes its escape in the gaseous 

 state? If this supposition were true, there ought to be a constant 

 ratio between the volume of carbonic oxide and hydrogen in the coal 

 gas. But this not being the case, it is obvious that the supposition 

 cannot be well founded. 



A ton of Lesmahagow coal, when distilled at the usual temperature, 

 yields about 10080 cubic feet. One-fifth of the weiglit of coal is gas, 

 two-fifths coke, and two-fifths tar, water, &c. 



The gas contains about one-fifth of the carbon in the raw coal, two- 

 elevenths of the hydrogen, and two-ninths of the oxygen. About one- 

 half of the carbon remains in the state of coke, so that about two-fifths 

 go to the formation of the naphthalin, naphtha, naphthene, naphthol, 

 &c., which are formed during the distillation. 



