Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/883

F U R F U R 847 intervals by narrow slits a a a, which form the gas admission passages from the gas-producer flue/, the supply being regu lated by a valve v. These alternate with similar slits b b of less depth, communicating with a lateral flue, supplying FIG. 13. Gas-heated Retort Furnace (horizontal section on E F tig. 11). heated air ; the mixture being effected at a great number of points ensures uniformity of combustion along the whole length of the furnace. The flame, after heating the retorts, descends by passages under the ends of the side retorts in the lower series to a number of arched divisions in the sub structure containing the air-heating pipes, which are of cast iron in horse-shoe coils. By this means the temperature of the gases is considerably reduced by the time they reach the chimney flue, the heat intercepted being returned by the air to the combustion chamber. Laboratory and Portable Furnaces. Small air-furnaces with hot plates or sand bath flues were formerly much employed in chemical laboratories, as well as small blast furnaces for crucibles heated with charcoal or coke. The use of such furnaces has very considerably diminished, owing to the general introduction of coal gas for heat ing purposes in laboratories, which has been rendered possible by the invention of the Bunsen burner, in which the mixture of air and gas giving the least luminous but most powerfully heating flame is effected automatically by the effluent gas. These burners, or modifications of them, have also been applied to muffle furnaces, which are convenient when only a few assays have to be made the furnace being a mere clay shell and soon brought to a working temperature ; but the fuel is too expensive to allow of their being used habitually or on a large scale. Petroleum, or rather the heavy oils obtained in tar refineries, having an equal or superior heating power to coal gas, may also be used in laboratories for producing high temperatures. The oil is introduced in a thin stream upon a series of inclined and channelled bars, where it is almost im mediately volatilized and burnt by air flowing in through parallel orifices. Furnaces of this kind may be used for melting cast-iron or bronze in small quantities, and were employed by M. St Claire Deville in experiments in the metallurgy of the platinum group of metals. Sefstrom s blast furnace, used in Sweden for the assay of iron ores, is one of the most convenient forms of portable furnaces applied to melting in crucibles. It consists of a sheet-iron cylinder about 8 or 9 inches in diameter, within which is fixed one of smaller size lined with fire-clay, as shown in part section in fig. 1 4. The space between the two cylinders serves as a heater and distributor for the blast, which is introduced through the nozzle at the bottom, and enters the furnace through a series of several small tuyeres FIG. 14. - Sffstrom s Portable Blast Fur nace. arranged round the inner lining. Charcoal is the fuel used, and the crucibles stand upon the bottom of the clay lining. When a large body of fuel is required, the cylinder can be lengthened by an iron hoop which fits over the top ring. Deville s portable blast furnace is very similar in principle to the above, but the body of the furnace is formed of a single cast-iron cylinder lined with fire-clay, closed below by a cast-iron plate perforated by a ring of small holes a hemispherical basin below forming the air-heating chamber. The literature of furnaces is co-extensive with that of metallurgy. Most of the different patterns in use will be found described and fully illustrated in Percy s and Phillip s Metallurgy, Jordan s Album du Coursdc Httallurgic, &c. The atlas to Karsten s great work, and the plates in the Encyclopedic Methodiquc, are also of much interest, but the types of apparatus represented are chiefly antiquated and out of use. (H. B.) FURNITURE is the name, of obscure origin, used to describe the chattels and fittings required to adapt houses, churches, ships, &c., for use. The sculptures, paintings, and metal work of antiquity, of the Middle Ages, and of the Renaissance, now kept in museums and private collections, have, with few exceptions, formed part of decorations or of furniture made for temples, churches, or houses. Most of our ancient bronzes, if not images taken from ancient shrines, are pieces of mirrors, tripods, altar vessels, even the dishes and pans of the kitchen. Wood, ivory, precious stones, bronze, silver, and gold have been used from the most ancient times in the construction or for the decoration of seats, chests, tables, and other furni ture, and for the shrines and altars of sacred buildings. The kind of objects required for furniture have varied according to the changes of manners and customs, as well as with reference to the materials at the command of the workman, in different climates and countries. Of the furniture of the ancient Egyptians there remain several examples. The British Museum contains six chairs, about the same in height as those now used. One is of ebony, turned in the lathe and inlaid with collars and dies of ivory. It is low, with a back ; and both back and legs are strengthened with rails of cane. The seat is of plaited cane slightly hollowed. Another is shaped out of two frames of four pieces of wood each, hinged in the centres of the longer sides, the lower ends carved into the form of the heads of animals ; the seat has been made of skin or other flexible material so as to fold flat. Some Egyptian couches and seats had the legs carved like those of panthers; some had the arms or seat supported by figures representing slaves or captives taken in war. They were upholstered with rich stuffs and are accurately represented in wall paintings (see the great French work, Description de Vfigypte). Workmen s tables, massive blocks of wood with four plain legs, and head rests hollowed out, standing 9 or 10 inches high, are preserved in the British Museum, some being of alabaster, probably for the sake of coolness. Painted wooden chests, with convex lids (not hinged), and mummy cases can be seen both in the British Museum and in the Louvre in Paris. The excavations of;Nineveh have brought to light sculp tured representations of Assyrian seats. They were mas sive, the ends of the seat frame projected in the shape of rams heads ; in some instances figures of captives support the arms ; in one described by Sir H. A. Layard, two horses resting on the lower bars from front to back support the seat. The seats were cushioned or upholstered with rich materials. An elaborate piece of carved ivory, with depressions to hold coloured glass, agate, &c,, from Nineveh, now in the British Museum, has been inlaid into a throne,