FURNACE (from OF. fornais, Fr. fournaise, It. fornace, from Lat. fornax, furnace, from for nus, oven; connected with Lat. form us, Gk. &p ubs, thermos, Skt. gharma, hot, Eng. warm). A structure in which to make and maintain a fire, the heat of which is used for heating, generating steam, smelting ores, melting metals and glass, baking pottery, and for a: great variety of other purposes in science and the arts. Furnaces may be divided into the following classes: (1) Fur naces in which the fire and the material to be heated are placed in contact. To this class belong the open blacksmith fire (see FoRGE), blast-fur nace, cupola or foundry furnace, etc. (See FOUND ING and IRON AND STEEL for descriptions of blast furnaces and converters and foundry furnaces.) (2) Furnaces in which the fuel is in one compart ment and the material to be heated in another, the material being heated by the flame and hot gases from the burning fuel. The most familiar
form of this class of furnace is the reverberatory, employed in heating and melting iron and steel. (See IRON AND STEEL.) (3) Furnaces in which the material to be heated is within a close cham ber or retort which is heated externally by the fire or by flame and gases from the fire. Pot furnaces for making glass (see GLAss), and cru cible furnaces for making crucible steel (see IRON AND STEEL) are examples. Furnaces may employ gas, powdered coal, and oil as fuel. The Siemens gas furnace is used in steel manufacture. (See Inox AND STEEL.) Furnaces for generating steam and those for heating form in a measure classes in themselves. See BOILERS; FUEL; HEAT ING AND VENTILATION; KILNS.