Furnace
2 of the 6 encyclopedias on this shelf carry an entry for Furnace. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
a place where a vehement fire and heat may be made and maintained, as for melting ores or metals, heating the boiler of a steam engine, of warming a house, baking pottery or bread, and other purposes. Furnaces are constructed in a great variety of ways, according to the different purposes to which they are applied. In constructing furnaces the following objects are kept in view: (1) To obtain the greatest quantity of heat from a given quantity of fuel. (2) To prevent the dissipation of the heat after it is produced. (3) To concentrate the heat and direct it as much as possible to the substances to be acted on. (4) To be able to regulate at pleasure the necessary degree of heat 's and have it wholly under the operator's management. An air furnace is one in which the flames are urged only by the natural draught; a blast furnace, one in which the heat is intensified by the injection of a strong current of air by artificial means; a reverberatory furnace, one in which the flames in passing to the chimney are thrown down by a low-arched roof on the objects which it is intended to expose to their action. See BLAST FURNACE.
The Encyclopedia of Founding (1892)
A suitably provided chamber where fire is produced by the use of fuel, as for melting metals, smelting ores, etc., the former being a cupola, the latter a smelting furnace. When the fire receives no other support than a natural draught, it is termed a wind or air furnace; when a forcible current of air is injected by means of a fan, blower, or engine, it is a blast-furnace; and a reverberatory furnace when the flame in passing through towards the chimney is thrown down by a low arched roof upon the materials to be operated upon. See CUPOLA; REVERBERATORY FURNACE; BLAST-FURNACE; BRASS-FURNACE; also many other furnaces, in their respective order.
What Has Changed in the Last Century
The classification Collier's gave in 1921 — air furnace, blast furnace, reverberatory furnace, all judged by how the draught is supplied — still describes fuel-fired practice, and the blast furnace remains the world's main route from iron ore to iron. What both accounts omit is heating without a fire at all: the electric arc furnace, then a novelty, now melts the majority of steel made in the United States, mostly from scrap, and induction furnaces have largely replaced the coke-fired cupola in foundries. The reverberatory furnace has mostly disappeared from copper and steel work. In the house, the coal-fired hot-air furnace of 1921 has given way to sealed gas units whose condensing designs recover well over 90 percent of the fuel's heat, and steelmakers are now piloting hydrogen-based direct reduction to get away from coke entirely.
Written for this edition, 2026.