244 THE ADDRESSES, LECTURES, ETC., OF 



tible and the air necessary to sustain combustion to the tempera- 

 ture of ignition, but in dealing with the combustible called coal 

 other preparatory work has to be accomplished besides mere heat- 

 ing in order to sustain combustion. The following is an analysis 

 taken from Dr. Percy's work on " Fuel " of a coal from the 

 Newcastle district : 



Carbon . . 81'41 Nitrogen . . 2'05 



Hydrogen . . 5'83 Sulphur . . 0'74 



Oxygen . . 7'90 Ash . . . 2 '07 



which shows at a glance that nearly 16 per cent, of the total 

 weight of the fuel consists of such permanent gases as hydrogen, 

 oxygen, and nitrogen. These gases are partly occluded or absorbed 

 within the coal, and are partly combined with carbon, forming 

 such volatile compounds as the hydrocarbons and ammonia, so 

 that when coal is subjected to heat in a closed retort, as much as 

 34 per cent, in weight passes away from the retort in a gaseous 

 condition ; a portion of this condenses again in the form of water, 

 tar, and ammoniacal liquor, and the rest passes into the gas mains 

 as illuminating gas, a mixture mainly of marsh gas (CH 4 ), olefiant 

 gas (C 2 H 4 ), and acetylene (C 2 H 2 ). The result of the distillation 

 of a ton of coal will be as follows, from data with which Mr. Alfred 

 Upward has kindly supplied me : 



Cwt. 



Coke. . 13-60 



Tar T20 



Ammoniacal liquor T45 



Gas 3-15 



Carbonic acid 0'18 



Sulphur removed by purifying . . . 0*30 

 Loss 0-12 



So great is the loss of heat sustained in an ordinary coal fire, in 

 consequence of this internal work of volatilization, that such a fire 

 is scarcely applicable for the production of intense temperature 

 effects ; and it has been found necessary to deprive the coal in the 

 first place of its volatile constituents (to convert it into coke) in 

 order to make it suitable for the blast furnace, for steel melting, 

 and for many other purposes where a clear intense heat is required. 



