Fuel

(fā'cl.) [O. Fr. fuayl.] Any material which serves to maintain fire; as alcohol, tallow, coal, .; but the torm is more properly limited to coal, coke, charcoal, wood, and a few other common sources of heat. Whatever the substance used as fuel, its ultimate elements are carbon, hydrogen, or both; and the heat is derived from their combination with the oxygen of the air. Unle F. is free from moisture, much of the heat which would be otherwise available is lost in converting the water into vapor. Hence the superiority of dry over green wood, and of charcoal over wood; hence also coke gives a greater heat than coal, which contains vaporizable bodies which must be driven off at an expense of heat. [s. 388]