Boiler

—A ve el in which water is evaporated into steam for the generation of power, for heating purposes, ete. The various types may be cla ified under two heads: shell boilers, in which the water is contained within more or le cylindrical ve els traversed by tubes, through which the flame and heated gases of combustion pa to impart their heat to the water; tubulous or water tube boilers, in which the water is contained within the tubes, the products of combustion circulating around them on courses determined by suitable bafies. The shell boiler is self-contained, or else mounted on brickwork, which contains various flue pa ages, etc.; the water tube boiler is contained within a suitable casing of brickwork or metal, or both. The chief varieties are the Belleville, Cornish, Lancashire, Locomotive, Multi tubular, Return tube, Water tube, ete.