The most usual misnaming of manufactured furs is as follow:—Musquash, pulled and dyedSold as seal.Nutria, pulled and dyedSold as seal.Nutria, pulled and naturalSold as beaver.Rabbit, sheared and dyedSold as seal or electric seal.Otter, pulled and dyedSold as seal.Marmot, dyedSold as mink or sable.Fitch, dyedSold as sable.Rabbit, dyedSold as sable or French sable.Hare, dyedSold as sable, or fox, or lynx.Musquash, dyedSold as mink or sable.Wallaby, dyedSold as skunk.White RabbitSold as ermine.White Rabbit, dyedSold as chinchilla.White Hare, dyed or naturalSold as fox, foxaline, and other similar names.Goat, dyedSold as bear, leopard, &c.Dyed manufactured articles of all kindsSold as “natural.”White hairs inserted in foxes and sablesSold as real or natural furs.KidsSold as lamb or broadtails.American sableSold as real Russian sable.MinkSold as sable.
The most usual misnaming of manufactured furs is as follow:—
The Preservation of Furs.—For many years raw sealskinshave been preserved in cold storage, but it is only within a recent period, owing to the difficulty there was in obtaining the necessary perfectly dry atmosphere, that dressed and made-up furs have been preserved by freezing. Furs kept in such a condition are not only immune from the ravages of the larvae of moth, but all the natural oils in the pelt and fur are conserved, so that its colour and life are prolonged, and the natural deterioration is arrested. Sunlight has a tendency to bleach furs and to encourage the development of moth eggs, therefore continued exposure is to be avoided. When furs are wetted by rain they should be well shaken and allowed to dry in a current of air without exposure to sun or open fire.
Where a freezing store for furs is not accessible, furs should be well shaken and afterwards packed in linen and kept in a perfectly cool dry place, and examined in the summer at periods of not less than five weeks. Naphthalene and the usual malodorous powders are not only very disagreeable, but quite useless. Any chemical that is strong enough to destroy the life in a moth egg would also be sufficiently potent to injure the fur itself. In England moth life is practically continuous all the year round, that is, as regards those moths that attack furs, though the destructive element exists to a far greater extent during spring and summer.
Comparative Durability of Various Furs and Weight of Unlined Skins per Square Foot.The following estimates of durability refer to the use of fur when made up “hair outside” in garments or stoles, not as a lining. The durability of fur used as linings, which is affected by other conditions, is set forth separately. Otter, with its water hairs removed, the strongest of furs for external use, is, in this table, taken as the standard at 100 and other furs marked accordingly:—The Precious Furs.Points ofDurability.2Weightin oz. persq. ft.Sable602½Sea753Fox, Silver or Black403Fox, White203Ermine251¼Chinchilla151½Sea-otter (for stoles or collars)1004¼The Less Valuable Furs.Points ofDurability.Weightin oz. persq. ft.Sable “topped,”i.e.top hairs coloured552½Sable tinted,i.e.fur all coloured.502½Baum Marten, natural652¾Baum Marten, tinted452¾Stone Marten402¾Nutria273¼Musquash, natural373¼Musquash, water hairs removed, sheared and seal finished.333¼Skunk702¾Mink703¼Lynx, natural252¾Lynx, tinted black202¾Marmot, tinted103Fox, tinted black253Fox, tinted blue203Opossum373Otter (with water hairs)1004Otter (water hairs removed)95315⁄16Beaver (water hairs cut level with fur)904Beaver (water hairs removed)85315⁄16Moleskin71¾Persian Lamb653¼Grey Lamb303¼Broadtail152¼Caracul Kid103¼Caracul Lamb153¼Squirrel251¾Hare51¾Rabbit52¼Quantities of Fur needed, in Square Feet.The “Paris Model” figure is the basis of these estimates for ladies’ garments, the standard measurements being height 5 ft. 6 in., waist 23 in., bust 38 in.Sq. Ft.(approximate).Straight stole ½ length (just below the waist line)2¾Straight stole ¾ length (just below the knee)3¾Stole, broad enough at the neck to cover the top of arm ¾ length5The same, full length (to hem of skirt)6Eton jacket, without collar13Plain cape, 15 in. long6½Deep cape, 30 in. long15Full cape with broad stole front, ¾ length15Inverness cape (to knee)25Double-breasted, straight, semi-fitting coat, covering hips16Double-breasted sacque jacket, 36 in. long, full sleeves20Same, 30 in. long18Same, 22 in. long15Long, full, shawl cape with points at back and front, well below knee15Shorter shawl cape16Motoring or driving coat, ¾ length22Motoring or driving coat, full length27Weight and Durability of Furs for Men’s Coat Linings.Otter with the water hairs removed, the strongest fur suited for linings, is here taken as the standard.Points ofDurability.Weightin oz. persq. ft.Otter (the water hairs removed)100315⁄16Beaver (the water hairs removed)90315⁄16Mink903¼Sealskin753Raccoon754½Persian lamb or astrachan703¼Sable652½Musquash553½Nutria403¼Grey Opossum403Wallaby303¾Squirrel301¾Hamster151¼Rabbit102¼Durability and Weight of Linings for Ladies’ Coats or Wraps.Sable gills, the strongest fur suited for ladies’ linings, is taken as the standard.Points ofDurability.Weightin oz. persq. ft.Sable gills10027⁄8Sable852½Sable paws6415⁄8Ermine571¼Squirrel back501¾Squirrel heads362½Squirrel lock2113⁄16Hamster101¼Rabbit72¼Durability and Weight of Motoring Furs made up with Fur outside.Otter with the water hairs, the strongest fur suited for motoring garments, is taken as the standard.Points ofDurability.Weightin oz. persq. ft.Otter (with water hairs)1004Sealskin, marble803”Hair Sealskin” (tinted) with water hairs (a special variety of seal)753¼Raccoon654½Russian Pony3525⁄8Durability and Weight of Furs for Rugs and Foot-sacks.Points ofDurability.Weightin oz. persq. ft.Wolverine1006Bear (black or brown natural)947Bear (tinted black)887½Beaver884Raccoon774½Opossum613Wolf506½Jackal274½Australian Bear166Goat1141⁄6Wolverine, the strongest fur suited for rugs and foot-sacks, is taken as the standard.For a rug about 20 to 25 sq. ft. of fur are needed, for a foot-sack 14½.
Comparative Durability of Various Furs and Weight of Unlined Skins per Square Foot.
The following estimates of durability refer to the use of fur when made up “hair outside” in garments or stoles, not as a lining. The durability of fur used as linings, which is affected by other conditions, is set forth separately. Otter, with its water hairs removed, the strongest of furs for external use, is, in this table, taken as the standard at 100 and other furs marked accordingly:—
The Precious Furs.
The Less Valuable Furs.
Quantities of Fur needed, in Square Feet.
The “Paris Model” figure is the basis of these estimates for ladies’ garments, the standard measurements being height 5 ft. 6 in., waist 23 in., bust 38 in.
Weight and Durability of Furs for Men’s Coat Linings.
Otter with the water hairs removed, the strongest fur suited for linings, is here taken as the standard.
Durability and Weight of Linings for Ladies’ Coats or Wraps.
Sable gills, the strongest fur suited for ladies’ linings, is taken as the standard.
Durability and Weight of Motoring Furs made up with Fur outside.
Otter with the water hairs, the strongest fur suited for motoring garments, is taken as the standard.
Durability and Weight of Furs for Rugs and Foot-sacks.
Wolverine, the strongest fur suited for rugs and foot-sacks, is taken as the standard.
For a rug about 20 to 25 sq. ft. of fur are needed, for a foot-sack 14½.
(W. S. P.)
1The measurements given are from nose to root of tail of average large sizes after the dressing process, which has a shrinking tendency. The depths of fur quoted are the greatest, but there are plenty of good useful skins possessing a lesser depth.2Stout, old-fashioned boxcloth is almost the only cloth that (after a soft, heavy lining has been added to it) affords even two-thirds as much protection against cold as does fur. It weighs 4.273 oz. per sq. ft. more than the heaviest of coat-furs, and is so rigid as to be uncomfortable, while the subtileness of fur makes it “kind” to the body.
1The measurements given are from nose to root of tail of average large sizes after the dressing process, which has a shrinking tendency. The depths of fur quoted are the greatest, but there are plenty of good useful skins possessing a lesser depth.
2Stout, old-fashioned boxcloth is almost the only cloth that (after a soft, heavy lining has been added to it) affords even two-thirds as much protection against cold as does fur. It weighs 4.273 oz. per sq. ft. more than the heaviest of coat-furs, and is so rigid as to be uncomfortable, while the subtileness of fur makes it “kind” to the body.
FURAZANES(furo—a.a′—diazoles), organic compounds obtained by heating the glyoximes (dioximes of ortho-diketones) with alkalis or ammonia. Dimethylfurazane is prepared by heating dimethylglyoxime with excess of ammonia for six hours at 165° C. (L. Wolff,Ber., 1895, 28, p. 70). It is a liquid (at ordinary temperature) which boils at 156° C. (744 mm.). Potassium permanganate oxidizes it first to methylfurazane-carboxylic acid and then to furazanedicarboxylic acid. Methyl-ethylfurazane and diphenylfurazane are also known. By warming oxyfurazane acetic acid with excess of potassium permanganate to 100° C. oxyfurazanecarboxylic acid is obtained (A. Hantzsch and J. Urbahn,Ber., 1895, 28, p. 764). It crystallizes in prisms, which melt at 175° C. Furazanecarboxylic acid is prepared by the action of a large excess of potassium permanganate on a hot solution of furazanepropionic acid. It melts at 107º C, and dissolves in caustic soda, with a deep yellow colour and formation of nitrosocyanacetic acid (L. Wolff and P.F. Ganz,Ber., 1891, 24, p. 1167). Furoxane is an oxide of furazane, considered by H. Wieland to be identical with glyoxime peroxide; Kekulés dibromnitroacetonitrile is dibromfuroxane.
The formulae of the compounds above mentioned are:
FURETIÈRE, ANTOINE(1619-1688), French scholar and miscellaneous writer, was born in Paris on the 28th of December 1619. He first studied law, and practised for a time as an advocate, but eventually took orders and after various preferments became abbé of Chalivoy in the diocese of Bourges in 1662. In his leisure moments he devoted himself to letters, and in virtue of his satires—Nouvelle Allégorique, ou histoire des derniers troubles arrivés au royaume d’éloquence(1658);Voyage de Mercure(1653)—he was admitted a member of the French Academy in 1662. That learned body had long promised a complete dictionary of the French tongue; and when they heard that Furetière was on the point of issuing a work of a similar nature, they interfered, alleging that he had purloined from their stores, and that they possessed the exclusive privilege of publishing such a book. After much bitter recrimination on both sides the offender was expelled in 1685; but for this act of injustice he took a severe revenge in his satire,Couches de l’académie(Amsterdam, 1687). HisDictionnaire universelwas posthumously published in 1690 (Rotterdam, 2 vols.). It was afterwards revised and improved by the Protestant jurist, Henri Basnage de Beauval (1656-1710), who published his edition (3 vols.) in 1701; and it was only superseded by the compilation known as theDictionnaire de Trévoux(Paris, 3 vols., 1704; 7th ed., 8 vols., 1771), which was in fact little more than a reimpression of Basnage’s edition. Furetière is perhaps even better known as the author ofLe Roman bourgeois(1666). It cast ridicule on the fashionable romances of Mlle de Scudéry and of La Calprenède, and is of interest as descriptive of the everyday life of his times. There is no element of burlesque, as in Scarron’sRoman comique, but the author contents himself with stringing together a number of episodes and portraits, obviously drawn from life, without much attempt at sequence. The book was edited in 1854 by Edward Fournier and Charles Asselineau and by P. Jannet.
TheFureteriana, which appeared in Paris eight years after Furetière’s death, which took place on the 14th of May 1688, is a collection of but little value.
TheFureteriana, which appeared in Paris eight years after Furetière’s death, which took place on the 14th of May 1688, is a collection of but little value.
FURFOOZ, a village some 10 m. from Dinant in the Ardennes, Belgium. Three caves containing prehistoric remains were here excavated in 1872. Of these theTrou de Frontalis the most famous. In it were found human skeletons with brachycephalic skulls, associated with animal bones, those of the reindeer being particularly plentiful. Among the skeletons was discovered an oval vase of pottery. The Furfooz type of mankind is believed to date from the close of the Quaternary age. G. de Mortillet dates the type in the Robenhausen epoch of the Neolithic period. His theory is that the bones are those of men of that period buried in what had been a cave-dwelling of the Madelenian epoch.
FURFURANE, orFurane, C4H4O, a colourless liquid boiling at 32° C., found in the distillation products of pine wood. It was first synthetically prepared by H. Limpricht (Ann., 1873, 165, p. 281) by distilling barium mucate with soda lime, pyromucic acid C4H3O·CO2H being formed, which, on further loss of carbon dioxide, yielded furfurane. A. Henniger (Ann. chim. phys., 1886 [2], 7, p. 220), by distilling erthyrite with formic acid, obtained a dihydrofurfurane
C4H6(OH)4+ 2H2CO2= C4H6O + CO + CO2+ 4H2O,
which, on treatment with phosphorus pentachloride, yielded furfurane. Furfurane is insoluble in water and possesses a characteristic smell. It does not react with sodium or with phenylhydrazine, but yields dye-stuffs with isatin and phenanthrenequinone. It reacts violently with hydrochloric acid, producing a brown amorphous substance. Methyl and phenyl derivatives have been prepared by C. Paal (Ber., 1884, 17, p. 915). Paal prepared acetonyl acetophenone by condensing sodium acetoacetate with phenacylbromide, and this substance on dehydration yields αα′-phenylmethylfurfurane, the acetonyl acetophenone probably reacting in the tautomeric “enolic” form,
This ester readily hydrolyses, and the acid formed yields acetonyl acetophenone (by loss of carbon dioxide), which then on dehydration yields the furfurane derivative, thus
L. Knorr (Ber., 1889, 22, p. 158) obtained diacetosuccinic ester by condensing sodium acetoacetate with iodine, and by dehydrating the ester he prepared αα′-dimethylfurfurane ββ′-dicarboxylic acid (carbopyrotritaric acid), which on distillation yields αα′-dimethylfurfurane as a liquid boiling at 94° C. Paal also obtained this compound by using monochloracetone in the place of phenacylbromide. By the distillation of mucic acid or isosaccharic acid, furfurane-α-carboxylic acid (pyromucic acid), C4H3O·CO2H, is obtained; it crystallizes in needles or leaflets, and melts at 134° C.
Furfurol(furol), C4H3O·CHO, is the aldehyde of pyromucic acid, and is formed on distilling bran, sugar, wood and most carbohydrates with dilute sulphuric acid, or by distilling the pentoses with hydrochloric acid. It is a colourless liquid which boils at 162° C., and is moderately soluble in water; it turns brown on exposure to air and has a characteristic aromatic smell. It shows all the usual properties of an aldehyde, forming a bisulphite compound, an oxime and a hydrazone; whilst it can be reduced to the corresponding furfuryl alcohol by means of sodium amalgam, and oxidized to pyromucic acid by means of silver oxide. It also shows all the condensation reactions of benzaldehyde (q.v.); condensing with aldehydes and ketones in the presence of caustic soda to form more complex aldehydes and ketones with unsaturated side chains,such as furfuracrolein, C4H3O·CH:CH·CHO, and furfuracetone, C4H3O·CH:CH·CO·CH3. With alcoholic potassium cyanide It changes to furoin, C4H3O·CHOH·CO·C4H3O, which can be oxidized to furil, C4H3O·CO·CO·C4H3O, whilst alcoholic potash converts it into furfuryl alcohol. With fatty acids and acid anhydrides it gives the “Perkin” reaction (seeCinnamic Acid). Furfurol is shown to have its aldehydic group in theaposition, by conversion into furfurpropionic acid, C4H3O·CH2·CH2·CO2H, which on oxidation by bromine water and subsequent reduction of the oxidized product is converted inton-pimelic acid, HO2C(CH2)5CO2H. Furfurol in minute quantities can be detected by the red colour it forms with a solution of aniline acetate.
Furfurane—αα′-dicarboxylic acid or dehydromucic acid, C4H2O(CO2H)2, is formed when mucic acid is heated with hydrochloric acid at 100° C. On being heated, it loses carbon dioxide and gives pyromucic acid. By digesting acetoacetic ester with sodium succinate and acetic anhydride, methronic acid, C8H8O5, is obtained; for the constitution of this acid, see L. Knorr,Ber., 1889, 22, p. 152, and R. Fittig,Ann., 1889, 259, p. 166.Di- and tetrahydrofurfurane compounds are also known (see A. Lipp,Ber., 1889, 22, p. 1196; W.H. Perkin, junr.Journ. Chem. Soc., 1899, 57, p. 944; and S. Ruhemann,ibid., 1896, 69, p. 1383).
Furfurane—αα′-dicarboxylic acid or dehydromucic acid, C4H2O(CO2H)2, is formed when mucic acid is heated with hydrochloric acid at 100° C. On being heated, it loses carbon dioxide and gives pyromucic acid. By digesting acetoacetic ester with sodium succinate and acetic anhydride, methronic acid, C8H8O5, is obtained; for the constitution of this acid, see L. Knorr,Ber., 1889, 22, p. 152, and R. Fittig,Ann., 1889, 259, p. 166.
Di- and tetrahydrofurfurane compounds are also known (see A. Lipp,Ber., 1889, 22, p. 1196; W.H. Perkin, junr.Journ. Chem. Soc., 1899, 57, p. 944; and S. Ruhemann,ibid., 1896, 69, p. 1383).
FURIES(Lat.Furiae, also calledDirae), in Roman mythology an adaptation of the Greek Erinyes (q.v.), with whom they are generally identical. A special aspect of them in Virgil is that of agents employed by the higher gods to stir up mischief, strife and hatred upon earth. Mention may here be made of an old Italian deity Furina (or Furrina), whose worship fell early into disuse, and who was almost forgotten in the time of Varro. By the mythologists of Cicero’s time the name was connected with the verbfurereand the nounfuria, which in the plural (not being used in the singular in this sense) was accepted as the equivalent of the Greek Erinyes. But it is more probably related tofurvus,fuscus, and signifies one of the spirits of darkness, who watched over men’s lives and haunted their abodes. This goddess had her own special priest, a grove across the Tiber where Gaius Gracchus was slain, and a festival on the 25th of July. Authorities differ as to the existence of more than one goddess called Furina, and their identity with the Forinae mentioned in two inscriptions found at Rome (C.I.L.vi. 422 and 10,200).
FURLONG(from the O. Eng.furlang,i.e.“furrow-long”), a measure of length, originally the length of a furrow in the “common field” system. As the field in this system was generally taken to be a square, 10 acres in extent, and as the acre varied in different districts and at different times, the “furlong” also varied. The side of a square containing 10 statute acres is 220 yds. or 40 poles, which was the usually accepted length of the furlong. This is also the length of1⁄8th of the statute mile. “Furlong” was as early as the 9th century used to translate the Latinstadium,1⁄8th of the Roman mile.
FURNACE, a contrivance for the production and utilization of heat by the combustion of fuel. The word is common to all the Romance tongues, appearing in more or less modified forms of the Latinfornax. But in all those languages the word has a more extended meaning than in English, as it covers every variety of heating apparatus; while here, in addition to furnaces proper, we distinguish other varieties asovens,stovesandkilns. The first of these, in the formOfen, is used in German as a general term like the Frenchfour; but in English it has been restricted to those apparatus in which only a moderate temperature, usually below a red heat, is produced in a close chamber. Our bakers’ ovens, hot-air ovens or stoves, annealing ovens for glass or metal, &c., would all be calledfoursin French andÖfenin German, in common with furnaces of all kinds. Stove, an equivalent of oven, is from the GermanStube,i.e.a heated room, and is commonly so understood; but is also applied to open fire-places, which appears to be somewhat of a departure from the original signification.
Furnaces are constructed according to many different patterns with varying degrees of complexity in arrangement; but all may be considered as combining three essential parts, namely, the fire-place in which the fuel is consumed, the heated chamber, laboratory, hearth or working bed, as it is variously called, where the heat is applied to the special work for which the furnace is designed, and the apparatus for producing rapid combustion by the supply of air under pressure to the fire. In the simplest cases the functions of two or more of these parts may be combined into one, as in the smith’s forge, where the fire-place and heating chamber are united, the iron being placed among the coals, only the air for burning being supplied under pressure from a blowing engine by a second special contrivance, the tuyere, tuiron, twyer or blast-pipe; but in the more refined modern furnaces, where great economy of fuel is an object, the different functions are distributed over separate and distinct apparatus, the fuel being converted into gas in one, dried in another, and heated in a third, before arriving at the point of combustion in the working chamber of the furnace proper.
Furnaces may be classified according as the products of combustion are employed (1) only for heating purposes, or (2) both for heating and bringing about some chemical change. The furnaces employed for steam-raising or for heating buildings are invariably of the first type (seeBoilerandHeating), while those employed in metallurgy are generally of the second. The essential difference in construction is that in the first class the substances heated do not come into contact with either the fuel or the furnace gases, whereas in the second they do. Metallurgical furnaces of the first class are termed crucible, muffle or retort furnaces, and of the second shaft and reverberatory furnaces. The following is a detailed subdivision:—(1) Fuel and substance in contact.(a) Height of furnace greater than diameter = shaft furnaces.(α) No blast = kilns.(β) With blast = blast furnaces.(b) Height not much greater than diameter = hearth furnaces.(2) Substance heated by products of combustion = reverberatory furnaces.(a) Charge not melted = roasting or calcining furnaces.(b) Charge melted = melting furnaces.(3) Substance is not directly heated by the fuel or by the products of combustion.(a) Heating chamber fixed and forming part of furnace = muffle furnaces.(b) Crucible furnaces.(c) Retort furnaces.Another classification may be based upon the nature of the heating agent, according as it is coal (or some similar combustible) oil, gas or electricity. In this article the general principles of metallurgical furnaces will be treated; the subject of gas- and oil-heated furnaces is treated in the article Fuel, and of the electric furnace in the article Electrometallurgy. For special furnaces reference should be made to the articles on the industry concerned,e.g.Glass,Gas, §Manufacture, &c.
Furnaces may be classified according as the products of combustion are employed (1) only for heating purposes, or (2) both for heating and bringing about some chemical change. The furnaces employed for steam-raising or for heating buildings are invariably of the first type (seeBoilerandHeating), while those employed in metallurgy are generally of the second. The essential difference in construction is that in the first class the substances heated do not come into contact with either the fuel or the furnace gases, whereas in the second they do. Metallurgical furnaces of the first class are termed crucible, muffle or retort furnaces, and of the second shaft and reverberatory furnaces. The following is a detailed subdivision:—
(1) Fuel and substance in contact.
(a) Height of furnace greater than diameter = shaft furnaces.
(a) Height of furnace greater than diameter = shaft furnaces.
(α) No blast = kilns.(β) With blast = blast furnaces.
(α) No blast = kilns.
(β) With blast = blast furnaces.
(b) Height not much greater than diameter = hearth furnaces.
(b) Height not much greater than diameter = hearth furnaces.
(2) Substance heated by products of combustion = reverberatory furnaces.
(a) Charge not melted = roasting or calcining furnaces.(b) Charge melted = melting furnaces.
(a) Charge not melted = roasting or calcining furnaces.
(b) Charge melted = melting furnaces.
(3) Substance is not directly heated by the fuel or by the products of combustion.
(a) Heating chamber fixed and forming part of furnace = muffle furnaces.(b) Crucible furnaces.(c) Retort furnaces.
(a) Heating chamber fixed and forming part of furnace = muffle furnaces.
(b) Crucible furnaces.
(c) Retort furnaces.
Another classification may be based upon the nature of the heating agent, according as it is coal (or some similar combustible) oil, gas or electricity. In this article the general principles of metallurgical furnaces will be treated; the subject of gas- and oil-heated furnaces is treated in the article Fuel, and of the electric furnace in the article Electrometallurgy. For special furnaces reference should be made to the articles on the industry concerned,e.g.Glass,Gas, §Manufacture, &c.
Shaft, Blast and Hearth Furnaces.—The blast furnace in its simplest form is among the oldest, if not the oldest, of metallurgical contrivances. In the old copper-smelting district of Arabia Petraea, clay blast-pipes dating back to the earlier dynasties of ancient Egypt have been found buried in slag heaps; and in India the native smiths and iron-workers continue to use furnaces of similar types. These, when reduced to their most simple expression, are mere basin-shaped hollows in the ground, containing ignited charcoal and the substances to be heated, the fire being urged by a blast of air blown in through one or more nozzles from a bellows at or near the top. They are essentially the same as the smith’s forge. This class of furnace is usually known as an open fire or hearth, and is represented in a more advanced stage of development by the Catalan, German and Walloon forges formerly used in the production of malleable iron.
Fig. 1 represents a Catalan forge. The cavity in the ground is represented by a pit of square or rectangular section lined with brick or stone of a kind not readily acted on by heat, about 1½ or 2 ft. deep, usually somewhat larger above than below, with a tuyere or blast-pipe of copper penetrating one of the walls near the top, with a considerable downward inclination, so that the air meets the fuel some way down. In iron-smelting the ore is laid in a heap upon the fuel (charcoal) filling up the hearth, and is gradually brought to the metallic state by the reducing action of the carbon monoxide formed at the tuyere. The metal sinks through the ignited fuel, forming, in the hearth, a spongy mass or ball, which is lifted out by the smelters at the end of each operation, and carried to the forge hammer. The earthy matters form a fusible glass or slag melt, andcollect at the lowest point of the hearth, whence they are removed by opening a hole pierced through the front wall at the bottom. The active portion of such a furnace is essentially that above the blast-pipe, the function of the lower part being merely the collection of the reduced metal; the fire may therefore be regarded as burning in an unconfined space, with the waste of a large amount of its heating power. By continuing the walls of the hearth above the tuyere, into a shaft or stack either of the same or some other section, we obtain a furnace of increased capacity, but with no greater power of consuming fuel, in which the material to be treated can be heated up gradually by loading it into the stack, alternately with layers of fuel, the charge descending regularly to the point of combustion, and absorbing a proportion of the heat of the flame that went to waste in the open fire. This principle is capable of very wide extension, the blast furnace being mainly limited in height by the strength the column of materials or “burden” has to resist crushing, under the weight due to the head adopted, and the power of the blowing engine to supply blast of sufficient density to overcome the resistance of the closely packed materials to the free passage of the spent gases. The consuming power of the furnace or the rate at which it can burn the fuel supplied is measured by the number of tuyeres and their section.
Fig. 1 represents a Catalan forge. The cavity in the ground is represented by a pit of square or rectangular section lined with brick or stone of a kind not readily acted on by heat, about 1½ or 2 ft. deep, usually somewhat larger above than below, with a tuyere or blast-pipe of copper penetrating one of the walls near the top, with a considerable downward inclination, so that the air meets the fuel some way down. In iron-smelting the ore is laid in a heap upon the fuel (charcoal) filling up the hearth, and is gradually brought to the metallic state by the reducing action of the carbon monoxide formed at the tuyere. The metal sinks through the ignited fuel, forming, in the hearth, a spongy mass or ball, which is lifted out by the smelters at the end of each operation, and carried to the forge hammer. The earthy matters form a fusible glass or slag melt, andcollect at the lowest point of the hearth, whence they are removed by opening a hole pierced through the front wall at the bottom. The active portion of such a furnace is essentially that above the blast-pipe, the function of the lower part being merely the collection of the reduced metal; the fire may therefore be regarded as burning in an unconfined space, with the waste of a large amount of its heating power. By continuing the walls of the hearth above the tuyere, into a shaft or stack either of the same or some other section, we obtain a furnace of increased capacity, but with no greater power of consuming fuel, in which the material to be treated can be heated up gradually by loading it into the stack, alternately with layers of fuel, the charge descending regularly to the point of combustion, and absorbing a proportion of the heat of the flame that went to waste in the open fire. This principle is capable of very wide extension, the blast furnace being mainly limited in height by the strength the column of materials or “burden” has to resist crushing, under the weight due to the head adopted, and the power of the blowing engine to supply blast of sufficient density to overcome the resistance of the closely packed materials to the free passage of the spent gases. The consuming power of the furnace or the rate at which it can burn the fuel supplied is measured by the number of tuyeres and their section.
The development of blast furnaces is practically the development of iron-smelting. The profile has been very much varied at different times. The earliest examples were square or rectangular in horizontal section, but the general tendency of modern practice is to substitute round sections, their construction being facilitated by the use of specially moulded bricks which have entirely superseded the sandstone blocks formerly used. The vertical section, on the other hand, is subject to considerable variation according to the work to which the furnace is applied. Where the operation is simply one of fusion, as in the iron-founder’s cupola, in which there is no very great change in volume in the materials on their descent to the tuyeres, the stack is nearly or quite straight-sided; but when, as is the case with the smelting of iron ores with limestone flux, a large proportion of volatile matter has to be removed in the process, a wall of varying inclination is used, so that the body of the furnace is formed of two dissimilar truncated cones, joined by their bases, the lower one passing downwards into a short, nearly cylindrical, position. For further consideration of this subject seeIron and Steel.
Hearth furnacesare employed in certain metallurgical operations,e.g.in the air-reduction process for smelting lead ores. The principle is essentially that of the Catalan forge. Such furnaces are very wasteful, and have little to recommend them (see Schnabel, Metallurgy, 1905, vol. 1. p. 409).
Reverberatory Furnaces.—Blast furnaces are, from the intimate contact between the burden to be smelted and the fuel, the least wasteful of heat; but their use supposes the possibility of obtaining fuel of good quality and free from sulphur or other substances likely to deteriorate the metal produced. In all cases, therefore, where it is desired to do the work out of contact with the solid fuel, the operation of burning or heat-producing must be performed in a special fire-place or combustion chamber, the body of flame and heated gas being afterwards made to act upon the surface of the material exposed in a broad thin layer in the working bed or laboratory of the furnace by reverberation from the low vaulted roof covering the bed. Such furnaces are known by the general name of reverberatory or reverbatory furnaces, also as air or wind furnaces, to distinguish them from those worked with compressed air or blast.
Originally the term cupola was used for the reverberatory furnace, but in the course of time it has changed its meaning, and is now given to a small blast furnace such as that used by iron-founders—reverberatory smelting furnaces in the same trade being called air furnaces.
Figs. 2, 3 and 4 represent a reverberatory furnace such as is used for the fusion of copper ores for regulus, and may be taken as generally representing its class. The fire-place A is divided from the working bed B by a low wall C known as the fire bridge, and at the opposite end there is sometimes, though not invariably, a second bridge of less height called the flue bridge D. A short diagonal flue or up-take E conveys the current of spent flame to the chimney F, which is of square section, diminishing by steps at two or three different heights, and provided at the top with a covering plate or damper G, which may be raised or lowered by a chain reaching to the ground, and serves for regulating the speed of the exhaust gases, and thereby the draught of air through the fire. Where several furnaces are connected with the same chimney stack, the damper takes the form of a sliding plate in the mouth of the connecting flue, so that the draught in one may be modified without affecting the others. The fire bridge is partially protected against the intenseheat of the body of flame issuing through the fire arch by a passage to which the air has free access. The material to be melted is introduced into the furnace from the hoppers HH through the charging holes in the roof. When melted the products separate on the bed (which is made of closely packed sand or other infusible substances), according to their density; the lighter earthy matters forming an upper layer of slag are drawn out by the slag hole K at the flue end into an iron wagon or bogie, while the metal subsides to the bottom of the bed, and at the termination of the operation is run out by the tap hole L into moulds or granulated into water. The opposite opening M is the working door, through which the tool for stirring the charge is introduced. It is covered by a plate suspended to a lever, similar to that seen in the end elevation (fig. 4) in front of the slag hole.
Figs. 2, 3 and 4 represent a reverberatory furnace such as is used for the fusion of copper ores for regulus, and may be taken as generally representing its class. The fire-place A is divided from the working bed B by a low wall C known as the fire bridge, and at the opposite end there is sometimes, though not invariably, a second bridge of less height called the flue bridge D. A short diagonal flue or up-take E conveys the current of spent flame to the chimney F, which is of square section, diminishing by steps at two or three different heights, and provided at the top with a covering plate or damper G, which may be raised or lowered by a chain reaching to the ground, and serves for regulating the speed of the exhaust gases, and thereby the draught of air through the fire. Where several furnaces are connected with the same chimney stack, the damper takes the form of a sliding plate in the mouth of the connecting flue, so that the draught in one may be modified without affecting the others. The fire bridge is partially protected against the intenseheat of the body of flame issuing through the fire arch by a passage to which the air has free access. The material to be melted is introduced into the furnace from the hoppers HH through the charging holes in the roof. When melted the products separate on the bed (which is made of closely packed sand or other infusible substances), according to their density; the lighter earthy matters forming an upper layer of slag are drawn out by the slag hole K at the flue end into an iron wagon or bogie, while the metal subsides to the bottom of the bed, and at the termination of the operation is run out by the tap hole L into moulds or granulated into water. The opposite opening M is the working door, through which the tool for stirring the charge is introduced. It is covered by a plate suspended to a lever, similar to that seen in the end elevation (fig. 4) in front of the slag hole.
According to the purposes to which they are applied, reverberatory furnaces may be classed into two groups, namely, fusion or melting furnaces, and calcining or wasting furnaces, also called calciners. The former have a very extended application in many branches of industry, being used by both founders and smelters in the fusion of metals; in the concentration of poor metallic compounds by fusion into regulus; in the reduction of lead and tin ores; for refining copper and silver; and for making malleable iron by the puddling processes and welding. Calcining furnaces have a less extended application, being chiefly employed in the conversion of metallic sulphides into oxides by continued exposure to the action of air at a temperature far below that of fusion, or into chlorides by roasting with common salt. As some of these substances (for example, lead sulphide and copper pyrites) are readily fusible when first heated, but become more refractory as part of the sulphur is dissipated and oxygen takes its place, it is important that the heat should be very carefully regulated at first, otherwise the mass may become clotted or fritted together, and the oxidizing effect of the air soon ceases unless the fritted masses be broken small again. This is generally done by making the bed of the furnace very long in proportion to its breadth and to the fire-grate area, which may be the more easily done as a not inconsiderable amount of heat is given out during the oxidation of the ore—such increased length being often obtained by placing two or even three working beds one above the other, and allowing the flame to pass over them in order from below upwards. Such calciners are used especially in roasting zinc blende into zinc oxide, and in the conversion of copper sulphides into chlorides in the wet extraction process. In some processes of lead-smelting, where the minerals treated contain sand, the long calciner is provided with a melting bottom close to the fire-place, so that the desulphurized ore leaves the furnace as a glassy slag or silicate, which is subsequently reduced to the metallic state by fusion with fluxes in blast furnaces. Reverberatory furnaces play an important part in the manufacture of sodium carbonate; descriptions and illustrations are given in the articleAlkali Manufacture.
Muffle, Crucible and Retort Furnaces.—A third class of furnaces is so arranged that the work is done by indirect heating; that is, the material under treatment, whether subjected to calcination, fusion or any other process, is not brought in contact either with fuel or flame, but is raised to the proper temperature by exposure in a chamber heated externally by the products of combustion. These are known as muffle or chamber furnaces; and by supposing the crucibles or retorts to represent similar chambers of only temporary duration, the ordinary pot melting air furnaces, and those for the reduction of zinc ores or the manufacture of coal gas, may be included in the same category. These are almost invariably air furnaces, though sometimes air under pressure is used, as, for example, in the combustion of small anthracitic coal, where a current of air from a fan-blower is sometimes blown under the grate to promote combustion. Types of muffle furnaces are figured in the articleAnnealing, Hardening and Tempering.
Furnace Materials.—The materials used in the construction of furnaces are divisible into two classes, namely, ordinary and refractory or fire-resisting. The former are used principally as casing, walls, pillars or other supporting parts of the structure, and includes ordinary red or yellow bricks, clay-slate, granite and most building stones; the latter are reserved for the parts immediately in contact with the fuel and flame, such as the lining of the fire-place, the arches, roof and flues, the lower part if not the whole of the chimney lining in reverberatory furnaces, and the whole of the internal walls of blast furnaces. Among such substances are fireclay and firebricks, certain sandstones, silica in the form of ganister, and Dinas stone and bricks, ferric oxide and alumina, carbon (as coke and graphite), magnesia, lime and chromium oxide—their relative importance being indicated by their order, the last two or three indeed being only of limited use.
The most essential point in good fireclays, or in the bricks or other objects made from them, is the power of resisting fusion at the highest heat to which they may be exposed. This supposes them to be free from metallic oxides forming easily fusible compounds with silica, such as lime or iron, the presence of the former even in comparatively small proportion being very detrimental. As clays they must be sufficiently plastic to be readily moulded, but at the same time possess sufficient stiffness not to contract too strongly in drying, whereby the objects produced would be liable to be warped or cracked before firing. In most cases, however, the latter tendency is guarded against, in making up the paste for moulding, by adding to the fresh clay a certain proportion of burnt material of the same kind, such as old bricks or potsherds, ground to a coarse powder. Coke dust or graphite is used for the same purpose in crucible making (seeFirebrick).