5//? WILLIAM S/KMEXS, F.K.S. 245 



In the ordinary coke oven the whole of the volatile constituents 

 are lost, and each 100 Ibs. of coal yield only C6 Ibs. of coke, 

 including the earthy constituents which on a large average may 

 be taken at 6 Ibs., leaving a balance of GO Ibs. of solid carbon. 

 In burning these 60 Ibs. of pure carbon, 220 Ibs. of carbonic 

 anhydride (C0 2 ) are produced, and in this combination 60 x 14,500 

 = 870,000 heat units (according to accurate determinations by 

 Favre and Silbermann, Dulong, and Andrews) are produced. 



The 84 per cent, of volatile matter driven off yield, when the 

 condensible vapours of water, ammonia, and tar, are separated, 

 about 16 Ibs. of pure combustible gas (being equal to about 

 10,000 cubic feet per ton of coal), which in combustion produce 

 about 16x22,000 = 352,000 heat units. The escape of these 

 gases from the coke-oven constitutes a very serious loss, which 

 may be prevented, to a great' extent at least, if the decarburiza- 

 tion is effected in retorts. The total heat producible from each 

 100 Ibs. of coal is in that case 870,000 + 352,000 = 1,222,000, or 

 12,220 units per Ib. of coal. Deduction must, however, be made 

 from this, for the heat required to volatilize 34 Ibs. of volatile 

 matter in every 100 Ibs. of coal used, and also to heat the coke to 

 redness, or to say 1000 Fahr. Considering the multiplicity of 

 gases and vapours produced, it would be tedious to give the details 

 of this calculation, the result of which would approximate to 

 60,000 heat units, or 600 units per Ib. of coal treated. We thus 

 arrive at 12,200 - 600 = 11,600 heat units as the maximum result 

 to be obtained from 1 Ib. of best coal. Considering, however, that 

 the coal commonly used for industrial purposes contains a larger 

 quantity of ashes and water than has been here assumed, a reduc- 

 tion of say 10 per cent, is necessary, and the calorific power of 

 ordinary coal may fairly be taken at 10,500 units per Ib. 



In comparing these figures with those obtained in actual practice, 

 it will be found that the margin for improvement is large indeed. 

 Thus in our best steam engines we obtain one actual HP. with an 

 expenditure of 2 Ibs. of coal per hour (the best results on record 

 being 1*5 Ib. of coal per indicated HP.). A HP. represents 



33,000x60 = 1,980,000 foot-lbs. per hour, which is 1 > 98 Q> 000 = 



ft 



990,000 foot-lbs., or units of force, per Ib. of fuel. Dr. Joule 

 has shown us that 772 foot-lls. represent one unit of heat, and 



