FUEL

(Norm. Fr. fuayl.) Any combustible substance which is used for the production of heat constitutes a species of fuel; and in this extended sense of the term, alcohol, wax, tallow, coal gas, oil, and other inflammable bodies which are occasionally used, especially in the chemical laboratory, 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 burned in grates, stoves, fireplaces, and furnaces of different descriptions. In this country coal, from its abundance and cheapne , is the commonly employed fuel; but where wood is abundant, or where its value is little more than that of felling it, it is used either in its original state or in the form of charcoal. But whatever substance is used, the ultimate elements of fuel are carbon and hydrogen; and the beat which is evolved by their combustion is derived from tlieir combination at high temperatures with the oxygen of the air: the results or products of this combustion are carbonic acid and water, these escaping into the atmosphere by the flue or chimney generally attached to furnaces and fireplaces. It is e ential to good and profitable fuel that it should be free from moisture; for unle it be dry, much of the heat which it generates is consumed in converting its moisture into vapour: hence the superior value of old, dense, and dry wood, to that which is porous and damp; hence also the greater quantity of heat evolved during the combustion of charcoal as compared with that of wood, for even the driest wood always retains a certain quantity of water; hence also coke gives out more heat than pit coal, partly because it is absolutely dry, and partly because during the combustion or heatmg of coal, tar, oil, water, and gas are evolved, all of which carry of if a certain proportion of the heat in a latent form. A pound of dry wood will, for instance, heat 35 pounds of water from 32° to 212°, and a pound of the same wood in a moist or fresh state will not heat more than 25 pounds from the same to the same temperature; the value, therefore, of different woods for fuel is nearly inversely as their moisture, and this may be roughly ascertained by finding how much a given weight of their shavings loses by drying them at 21 20. Charcoiil is itself very hygrometric, and when exposed to air increases in weight to the amount of 10 or 12 per cent, in consequence of the absorption of humidity: a pound of dr\' charcoal is capable of raising, when properly burned, 73 pounds of water from the freezing to the boiling point. 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 will heat from 64 to 66 pounds of water from 32° to 212''; its power, therefore, is about nine tenths that of wood charcoal. The value of turf and peat as fuel is liable to much variation, and depends partly upon their density, and partly upon their freedom from earthy impurities. 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 compre ing 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 Combustible. Pounds of Water which a Pound can raise from 32° toitl'^o. Dry wood Common wood Charcoal Pit coal t;oke Turf al gas Oil, wai, or tallow ^\ Icohol 5r,-oo 26-00 73-00. 60-00 65-00 3()-(J0 ■ 76-00 78-00 6^00 6-.T6 4.72 13-27 10-90 11-81 5-43 l.TSl 14-18 9-56 6-96 4-47 11-46 9-26 11-46 4-60 14-58 15-00 11-60 [s. 491]