FUEL, any combustible substance which is used for the production of heat. In this extended sense of the term, alco hol, wax, tallow, coal-gas, oil, and other inflammable bodies which are occasionally used, especially in the chemical labora tory, as sources of heat as well as light, might be included under it. But the term fuel is more properly limited to coal, coke, charcoal, wood, and a few other substances, which are our common sources of heat, and as such are burnt in grates, stoves, fireplaces, and furnaces. In this country, as in England, coal, from its abundance and cheapness, is the fuel commonly employed; but in other coun tries, as France, Germany, etc., wood is chiefly used, either in its original state or in the form of charcoal. But what ever substance be used, the essential ulti mate elements of fuel are carbon and hydrogen; and the heat which is evolved by their combustion is derived from their combination at high temperatures with the oxygen of the air; the principal results or products of this combustion are carbonic acid and water, these escap ing into the atmosphere by the flue or chimney generally attached to furnaces and fireplaces. The different kinds of
pit-coal give out variable quantities of heat during their combustion; upon an average, one pound of coal should raise 60 pounds of water from the freezing to its boiling point. The heating power of coke as compared with coal is nearly in the ratio of 75 to 69: a pound of good coke, heating from 64 to 66 pounds of water from 32° to 212°. A pound of turf will heat about 26 pounds of water from 32° to 212°, and a pound of dense peat about 30 pounds; by compressing and drying peat, its value as a fuel is greatly increased. The following table, by Dr. Ure, shows the quantity of water raised from 32° to 212° by one pound weight of the different combustibles enumerated in the first column; it also shows the number of pounds of boiling water which the same weight of fuel will evaporate and the quantity of atmospheric air absolutely consumed during combustion: