ATTENDING THE FORMATION OF COAL, See. 269 



moisture. The water, in its decomposition in the retorts, 

 furnishes oxygen to the carbon of the coal, impoverishing 

 the gas, whilst the hydrogen of the water does not combine 

 with the carbon of the coal, but is liberated in the simple 

 state. 



When the vapour of water is passed over red-hot coke 

 and coal, and analysed, the resulting gas is found to consist 

 in 100 volumes, of hydrogen 56, of carbonic oxide 29, car- 

 bonic acid 1 5*8, and of light carburetted hydrogen only two- 

 hundredths of 1 per cent 



It contains no olefiant gas whatever; this experiment is 

 quite conclusive against the use of water or steam. It is 

 evident that there are no products of the decomposition of 

 water by red-hot coal or coke that possess any illuminating 

 power. It has often been proposed to pass steam into the 

 retorts during the distillation of coal, but such a proceeding 

 could have no good effect, but the contrary. When it is 

 considered that 50 per cent, of the whole of the gases pro- 

 ceeding from the decomposition of water by red-hot car- 

 bonaceous matter is hydrogen, another very formidable 

 objection arises to its use ; viz., that it would not only 

 diminish the light of gas with which it was mixed, but 

 would give out such an amount of heat during the burning 

 of it, as would render the use of such gas almost insupport- 

 able. The coal then should be dry ; but we have also seen 

 that air, passed between seams of coal, has been deprived 

 of a portion of its oxygen, which must have combined with 

 the carbon and hydrogen of the coal, and by as much have 

 impaired its quality. We have seen that coal and cannel 

 are continually giving off gas (fire-damp), and this teaches 

 us that the coal should be dried quickly and then used. 



Let us now consider what takes place during the manu- 

 facture of gas by the distillation of coal in red-hot retorts. 

 The nitrogen in gas is entirely derived from atmospheric 

 air, admitted into the retorts during the charges, and by 



