FURNACES bear various names, ac cording to their purpose. The object of all is to procure great heat, directly ap plicable to the purpose.
Iron furnaces consist of,a cone 20 or 30 feebdeep, to receive the ore, the flux, and the coke or fuel, in layers, with tin ash grate beneath, and blasting bellows to in crease the supply of oxygen. They are many weeks in preparation, so as to ae quire a high degree of heat, and then they are never suffered to cool, but constantly supplied with ore, flux, and fuel.
A gas furnace is so built that the fire and flame surround the retorts full of coal, and keep them at a. white heat.
A chemical furnace is more various in its uses, and should be built with a table top, and horizontal flue covered with plate iron, over which should be sand baths, and other receptacles, with hoods and covers.
The air furnace, for melting, has an ashes hole, and a lateral hole near the bottom of the grate. The fire-place is inclosed, and fuel put in at the top, so as to surround the covered crucibles or cucu bets placed in the fire. The exit of smoke, &e., is at the side, in a horizontal flue. A reverberatory furnace is one closed at the top, or with a reverberating dome with a fire beneath, and a perpendicular flue through the dome. At the side is an orifice for the neck of any retort placed in the body.
There are various patent and special varieties of furnaces, but the same gene ral forms pervade them. Charcoal, or coke, or ashes, produce the highest heat, but coals are used in glass-houses, distil leries, and breweries.
Accum's Lamp Furnace is very conve nient and powerful for operations in the small way. In the burning part it is Ar gand's lamp, but, on the upright stan dard, three or four arms slide with rings at their ends, to raise higher and lower, and fix with nuts and screws, adapted to receive retorts, alembics, flasks, &c., for distillations, digestions, &c. In some, a second cylinder and second flame is made, by which the heat is trebled, and most processes performed in a small way, with out a furnace.
The furnace of the Royal Institution is of brick-work, 52 inches by 30. The iron plate and sand-baths, 57 by 42. It is 84 inches high.
A very powerful furnace, equal to any purpose, has been made at the Royal In stitution, by cutting the bottom of a blue pot, and fixing it tight in a larger one, 18 by 13 inches ; then, through a single hole in the bottom of the outer pot, blowing with a pair of double bellows. It melts pure iron in a quarter of an hour, renders platinum soft, and fuses rhodium. The fuel is coke, and it disappears, leaving scarcely slag ; proving the superiority of the blast furnace over all others.
Faraday states, that a pint of water may be boiled in a cartridge-paper vessel, placed over a chemical lamp.
Mr. Nott has taken out a patent for a mode of giving to furnaces a circular or semicircular form, that the fresh coals, when the fire receives a supply of them, may be, by turtling the furnaces on pivots, by which it is supported, brought into a position with reference to the coals already ignited, that the gaseous products of the fresh coals shall pass through the ignited portion, that the combustible part may be consumed ; and thus effect a sav ing of fuel, and the prevention of much of the nuisance arising from the escape of uneonsumed smoke. This rotating, or rather vibrating furnace, is of course to be provided with an iron casing, to sur round the sides of the furnace not in tended to be exposed.
By Witty's improved furnace, fresh i coal is first carbonized, that is, the gas is separated from it and inflamed, leaving only coke, which, being slowly pushed forward, supplies the coke fire ; and the combusion or burning of the coke pro duces heat enough to carbonize the coal, and air enough to inflame the gas ; con sequently, coal, instead of being burned in its usual' crude state, is subjected to two distinct processes, viz. carbonization, and then combustion ; for, by this con trivance, he burns the gas and the coke together.