FUR′NACE

An enclosed fireplace for obtaining a high degree of heat. Furnaces vary much in construction and size, according to the particular manufacture in which they are employed. They may be broadly divided into two cla es— WIND-FURNACES and BLAST FURNACES . In the former a high temperature is produced without the aid of bellows by means of a powerful draught. In the latter heated air is blown in through a pipe or pipes at the bottom. For many metallurgic and large chemical operations REVERBERATORY FURNACES are employed. A furnace of this kind is usually long, with a low roof to keep down the flame and hot air upon the ‘hearth’ or space between the fireplace and the flue. [322] For the smaller operations in chemistry, a variety of furnaces have been invented, and the introduction of coal-gas as a fuel by Develle, Griffin, Gore, Fletcher, and others, has wrought a complete change in the arrangements of the laboratory. The GAS-FURNACES of Mr J. J. Griffin are adapted for almost every operation performed by the aid of heat. Those more recently introduced by Mr W. Gore are very compact and portable, and will rapidly produce a ‘white heat,’ without the help of bellows or high chimney, by means of ordinary coal-gas and atmospheric air. The first and smallest size consumes 33 cubic feet of gas (value seven farthings) per hour, and is suitable for a ayers, jewellers, analytical chemists, experimentalists, dentists, and others. It is capable of fusing eight ounces of copper or six ounces of cast iron, copper begins to melt in it in about twelve minutes from the time of lighting. The second-sized one consumes about twice that quantity of gas, is suitable for manufacturing jewellers generally, and for a great variety of practical persons who require to melt small quantities of gold, silver, copper, german silver, bra , cast iron, gla , and other substances, or require a small crucible heated to high temperatures. It is capable of melting 45 ounces of copper, or 40 ounces of cast iron, and with its heat up it melts one pound of copper in eight minutes; copper begins to melt in about twenty minutes from the time of lighting. [322] For an illustration of this kind of furnace, see Sodium , Carbonate of. Fletcher’s [323] Universal Furnaces for high temperatures, which are said to require neither blast nor attention, are intended for laboratory purposes, enamel burning, heating soldering irons, and for jewellers’ and dentists’ work. These furnaces are made in two distinct types; one with a perforated cover to the crucibles and muffles to attain the maximum heat; the other with a slide chimney and a double lid over the crucible. [323] Manufactured by Thos. Fletcher, Museum Street, Warring ton. The power and rapidity of working depend in each case on the length of the chimney used. A furnace with a four-feet chimney will melt a crucible of cast-iron in thirty-five minutes; a furnace with an eight-feet chimney will melt the same quantity of iron in about twenty minutes, starting with the furnace cold. The stove with the side chimney, although more convenient in use, is slower in working, taking about twice as long to obtain the same temperature. The following are varieties of Fletcher’s Universal Furnace :— 1. Small Laboratory Furnace for crucibles, with nickel-plated burner tubes. This takes crucibles up to 2 1 ⁄ 2 by 2 1 ⁄ 4 inches outside, and with a three-feet chimney, as supplied with the furnace, will, it is stated, melt copper, gold, silver, ., in about ten minutes, or cast-iron in thirty-five minutes from the time the gas is lighted. Small muffle fittings, with muffles 2 1 ⁄ 4 by 3 by 2 1 ⁄ 2 inches inside, can be supplied with this furnace. 2. Small Crucible Furnace , with fixed chimney. This furnace is more especially designed for gold, silver, copper, ., and, as sent out with a four-feet chimney and a single lid, is amply powerful, and practically of a very convenient form. 3. Small Muffle Furnace , with three feet chimney. This requires about eighteen inches longer chimney than the small crucible furnace to obtain the same temperature in the same time, owing to a slight lo of heat by radiation from the stoppers. 4. a. Large Muffle Furnace. This is identical in design and construction with the smaller one. The clear working space inside the muzzle is 3 7 ⁄ 8 by 5 inches, by about 3 inches deep. This is recommended as a useful furnace for watch dial enamellers, a ayers, photo-enamel burning, and for all purposes where exact temperatures are required not exceeding the fusing point of cast iron. The burner of this furnace is twice the size of the small laboratory furnace, and requires a gas supply from a pipe and tap of half-an-inch bore. The burner is the same shape as the muffle, and is unfit for crucible work. b. Extra Large Muffle Furnace 4 1 ⁄ 2 by 3 3 ⁄ 4 by 7 inches clear inside working space. This will take a No. 3 plumbago pot, and with half an inch gas pipe, giving a supply of about 35 feet per hour, will, it is affirmed, melt 3 or 4 lbs. of bra in about 25 minutes, and the same quantity of cast iron in 60 or 70 minutes from the time the gas is first lighted, without the slightest trouble or attention. 5. Ladle Furnace . This takes ladles up to 6 1 ⁄ 2 inches diameter, and will melt 6 or 8 lbs. of zinc in about 15 minutes, or the same quantity of lead, tin, ., in about half the time. It is said to be a convenient and powerful arrangement for dentists, heating soldering-irons, making granulated zinc, sand baths, . 6. Small Laboratory Furnace , complete for crucibles, muffles, ladles, and sand baths. 7. Fletcher’s Injector Gas Furnace (with Blast). This furnace is intended for general purposes, and for the treatment of refractory substances at high temperatures. The patentee states “that it will burn perfectly in the same space any available gas supply from 10 to 50 feet per hour, or more, if required, giving temperatures in exact proportion; and any operation may be repeated at any time by taking a note of the position of the air slide which governs the combustion of the gas.” Mr Fletcher gives the power of the small furnace as follows:—With an 1 ⁄ 2 inch gas supply-pipe, day pre ure, starting with the furnace cold, it will melt silver in 3 minutes, cast iron in 8 minutes, cast steel in 25 minutes. With a supply of 50 feet per hour, the same results are stated to be obtained in a little over half the time, and so on in proportion with a greater or le gas supply. It is also said to work satisfactorily for gold, ., melting it with a supply of gas too small for any other furnace, and the maximum temperatures obtained are limited, only by the available gas supply and the fusibility of the casing. The highest temperature as obtained by measuring by Wedgwoods’ Pyrometer, is said to be 9000 Fahrenheit. This furnace is stated to be particularly suited for gold and silver melting, and refining, iron a ays, and general crucible work, and safe in the hands of the most carele workman. It is adapted for crucibles not exceeding 4 inches by 2 1 ⁄ 4 , 5 inches by 3 1 ⁄ 2 , 7 1 ⁄ 2 inches by 5. For further information respecting furnaces intended for use in the laboratory and a ay office, the reader is referred to ‘Watt’s Dictionary of Chemistry,’ also to ‘Ure’s Dictionary of Arts, Manufactures, and Mines,’ for description of the furnaces employed in the different metallurgical operations; and to the ‘Chemical News’ (June 30th, 1876, and February 2nd, 1877), for a description of a new decomposing furnace. See A aying , Chimneys , Copper , Crucible , Fuel , .