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iron, at the same time that a large quantity of hydrogen is disengaged, and the mixture becomes hot. In this, as well as in the sulphuric solution of iron, the same quantity of alkali is said to be required to saturate the acid as before the solution; whence it is inferred, that the acid is not decomposed, but that the oxidation is effected by the oxygen of the water ; whence also it appears to follow, that the hydrogen must be afforded from the decomposed water, and not from the metal. Carbonic acid, dissolved in water, combines with a considerable quantity of iron, in proportion to its mass. Vinegar scarcely dissolves it, unless by the assistance of the air. Phosphoric acid unites with iron, but very slowly. The union is best, effected by adding an alkaline phosphate to a solution of one of the salts of iron, when it will fall down in a white precipitate. A saturated phosphate of iron has been found native in France, semi-transparent, of a red brown colour, and foliated texture. A deep blue phosphate of iron, lamellated, and fragile, of the specific gravity of 2.6, brought from the isle of France, and analysed by Laugier, Fourcroy, and Vauquelin, gave iron 41.25, phosphoric acid 19.25, water 31.25, alu. mina, 5, and ferruginous silex 1.25, in 100 parts. A similar phosphate has been found in Brazil. This acid is found combined with iron in the bog ores, and, being at first taken for a peculiar metal, was called siderite by Bergman. Liquid fluoric acid attacks iron with violence; the solution is not crystallizable, but thickens to a jelly, which may be rendered solid by continuing the heat. The acid may be expelled by heating it strongly, leaving a fine red oxide. Borate of iron may be obtained by precipitating a solution of the sulphate with neutral borate of soda. Arsenic acid likewise unites with iron. This arseniate is found native in Cornwall, in pretty large cubic crystals, tolerably transparent, of a dark green colour, with a brownish tinge; sometimes yellowish, or of a brown yellow, like resin. The Count de Bournon found likewise a cupreous arseniate of iron, in minute rhomboidal crystals, of a faint sky blue colour and uncommon brilliancy. Specifig gravity 3.4. The green and red sulphates of iron may be decomposed by arseniate of ammonia, and afford arseniate of iron in the two different states. Chromate of iron is said to have been found abundantly in the department of War in France, and to form a beautiful
green for enamelling or colouring pastes. Its analysis by Vauquelin and Tassaert gave chromic acid 43, oxide of iron 34.7, alumina 20.3, silex 2, in 100 parts. In the dry way, this metal does not combine with earths, unless it be previously oxided; in which case it assists their fusion, and imparts a green colour to the glass. It appears to combine with alkalies by fusion. Nitre detonates strongly with it, and becomes alkalized. Sulphur combines very readily with iron in the dry, and even in the humid way, though neither of these substances is scarcely at all soluble in water. A mixture of iron filings and flowers of sulphur being moistened, or made into a paste, with water, becomes hot, swells, adheres together, breaks, and emits watery vapours of an hepatic smell. If the mixture be considerable in quantity, as for example, one hundred pounds, it takes fire in twenty or thirty hours, as soon as the aqueous vapours cease. By fusion with iron, sulphur produces a compound of the same nature as the pyrites, and exhibiting the same radiated structure when broken. If a bar of iron be heated to whiteness, and then touched with a roll of sulphur, the two substances combine, and drop down together in a fluid state. It is necessary that this experiment should be made in a place where there is a current of air to carry off the fumes; and the melted matter, which may be received in a vessel of water, is of the same nature as that produced by fusion in the common way, excepting that a greater quantity of sulphur is fused by the contact of the bar of iron. According to Proust, the native sulphuret, or pyrites, contains 47.36 per cent. of sulphur, the artificial sulphuret but 37.5. Mr. Hatchett however has found, that the magnetical pyrites contains the same proportion as the artificial sulphuret. Phosphorus may be combined with iron, by adding it cut into small pieces to fine iron wire, heated moderately red in a crucible; or by fusing six parts of iron clippings, with six of glacial phosphoric acid, and one of charcoal powder. This phosphuretis magnetic; and Mr. Hatchett remarks that iron, which in its soft or pure state cannot retain magnetism, is enabled to do so, when hardened by carbon, sulphur, or phosphorus, unless the dose be so great as to destroy the magnetic property, as in most of the natural pyrites and plumbago. The combination of carbon with iron is of all the most important, under the names of cast iron and steel. We shall just observe here, that, according to Mr. Mushet, of the Calder iron-works, who has investigated the subject very extensively in the large way, soft cast steel, capable of welding, contains 1 one-hundred and twentieth of carbon, common cast steel 1 one-hundreth, cast steel of a harder kind 1 ninety-sixth, steel too hard for drawing one-fiftieth, white cast iron one-twenty-fifth, melted cast iron onetwentieth, black cast iron one-fifteenth. He conceives, however, that in steel the carbon is more intimately united with the iron. When iron is saturated with carbon, it becomes what is commonly called plumbago. Iron unites with gold, silver, and platina. When heated to a white heat, and plunged in mercury, it becomes covered with a coating of that metal. Long trituration of mercurial amalgams likewise causes a coating to adhere to the ends of iron pestles; small steel springs, kept lunged beneath the surface of mercury in certain barometers, become brittle in process of time; and the direct combination of iron and mercury in the form of an amalgam may be obtained, according to Vogel, by triturating the filings with twice their weight of alum, then adding an equal weight or more of mercury, and continuing the friction, with a very small quantity of water, till the union is completed. Mr. A. Aikin unites an amalgam of zinc and mercury with iron filings, and then adds muriate of iron, when a decomposition takes place, the muriatic acid combining with the zinc, and the amalgam of iron and mercury assuming the metallic lustre by kneading, assisted with heat. Iron and tin very readily unite together, as is seen in the art of tinning iron vessels, and in the fabrication of those useful plates of iron, coated with tin, which are generally distinguished by the simple name of tin alone. The chief art of applying these coatings of tin consists in defending the metals from oxidation by the excess of air. After the iron Fo are scraped, or rendered very clean y scouring with an acid, they are wetted with a solution of sal ammoniac, and plunged into a vessel containing melted tin, the surface of which is covered with pitch or tallow, to preserve it from oxydation. The tin adheres to, and intimately combines with, the iron to a certain depth, which renders the tinned plates less disposed to harden by hammering than before ; as well as much less dis. posed to alter by the united action of air and moisture. The process for tinning
tion with the sulphur and alkali.
iron vessels does not essentially differ
from that which has already been de
scribed for copper vessels. Iron does not unite easily with bismuth, at least in the direct way. This alloy is brittle, and attractable by the magnet, even with three fourths of bismuh. As nickel cannot be purified from iron without the greatest difficulty, it may be presumed that these substances weuld readily unite, if the extreme infusibility of both did not present an obstacle to the chemical operator. Arsenic forms a brittle substance in its combination with iron. Cobalt forms a hard mixture with iron, which is not easily broken. The inflammability and volatility of zinc present an obstacle to its combination with iron. It is not improbable, however, but that clean iron filings would unite with zinc, if that netal were kept in contact with them for a certain time, in a heat not sufficient to cause it to rise ; for it has been found, that zinc may be used in the operation of coating iron in the same manner as tin. Antimony unites with iron, and forms a hard brittle combination, which yields in a slight degree to the hammer. The sulphuret of antimony is decomposed by vir. tue of the greater affinity of the iron to the sulphur. For this purpose, five ounces of the points of nails from the farriers may be made red hot in a crucible, one pound of pulverized ore of antimony must then be thrown into the crucible, and the heat quickly raised to fuse the whole. When the fusion is perfect, an ounce of nitre in powder may be thrown in, to facilitate the separation of the scorize. After the mass is cooled, the antimony is found separate at the bottom of the crucible, while the iron remains in combinaIf the proportion of the iron be considerably greater than five ounces to the pound of ore, the antimony will be alloyed with iron. Manganese is almost always united with iron in the native state. Tungsten forms a brittle,whitish-brown, hard alloy, of a compact texture, when fused with white crude iron. The habitudes of iron with molybdena are not known. Iron is the most diffused, and the most abundant, of metallic substances. Few mineral bodies or stones are without an admixture of this metal. Sands, clays, and the waters of rivers, springs, rain, or snow, are scarcely ever perfectly free from it. The parts of animal and vegetable substances likewise afford iron in the residues they leave after incineration. It has been found native, in large masses, in Siberia, and in the internal parts of South America. This metal, however, in its native state is scarce: most iron is found in the state of oxide, in ochres, bog ores, and 9ther friable earthy substances, of a red, brown, yellow, or black colour. The hematites, or blood stones, are likewise ores with oxide of iron : these are either of a red colour, or blue, yellow, or brown. An iron ore is likewise found, of a blue colour, and powdery appearance. This useful metal is so abundant, that whole mountains are composed of iron stone; whereas other metals usually run in small veins. Besides these eres of iron, which are either nearly pure, or else mixed with earths, as in spars, jaspers, boles, basaltes, &c. iron is mineralized with sulphur, as in the pyrites, or with arsenic. The coally iron ores contain bitumen. The magnet, or load stone, is an iron ore, the constitution of which has not yet been accurately examined. Iron is also found in combination with the sulphuric acid, either dissolved in water, or in the form of sulphate. To analyse the ores of iron in the humid way, they must be reduced to a very subtle powder, and repeatedly boiled in muriatic acid. If the sulphureous ores should prove slow of solution, a small quantity of nitric acid must be added to accelerate the operation. The iron being thus extracted, the insoluble part of the matrix only will remain. Prussiate of potash being added to the decanted solution, will precipitate the iron in the form of Prussian blue. This precipitate, when washed and dried, will be equal in weight to six times the quantity of metallic iron it contains; and from this iron four parts in the hundred must be deducted, to allow for the iron which is contained in the prussiate of potash itself. But as this alkali, and every other preparation containing the prussic acid, does not constantly afford the same quantity of iron, the most exact way, in the use of such preparations, consists in previously dissolving a known quantity of iron in sulphuric acid, and precipitating the whole by the addition of the prussiate of potash. This result will afford a rule for the use of the same alkali in other solutions. For as the weight of the precipitate obtained in the trial experiment is to the quantity of iron which was dissolved and precipitated, so is the weight of the precipitate obtained from any other solution to the quantity of iron sought. If the iron be united to any considerable proportion of zinc or manganese, the WOL. VI.
Prussian blue must be calcined to red. ness, and treated with strong nitric acid, which will take up the oxide of zinc. The manganese may then be dissolved by nitric acid with the addition of sugar, and the remaining iron being dissolved by muriatic acid, and precipitated by subcarbonate of soda, will .. 225 grains of precipitate for every 100 grains of metallic iron. To examine the ores of iron in the dry way, the only requisite is fusion, in contact with charcoal. For this purpose eight parts of pulverized glass, one of calcined borax, and half a part of charcoal, are to be well mixed together. Two or three parts of this flux being mixed with one of the pounded ore, and placed in a crucible, lined with a mixture of a little clay, and pounded charcoal, with a cover luted on, is to be urged with the strong heat of a smith’s forge for half an hour. The weight of the ore, in this experiment, should not exceed sixty grains. Other processes for determining the contents, or metallic product, of iron ores, are instituted, by performing the same operations in the small, as are intended to be used in the large way. In the large iron works, it is usual to roast or calcine the ores of iron, previously to their fusion; as well for the purpose of expelling sulphureous or arsenical parts, as to render them more easily broken into fragments of a convenient size for melting. The mineral is melted or run down in large furnaces, from sixteen to thirty feet high; and variously shaped, either conical or elliptical, according to the opinion of the iron-master. Near the bottom of the furnace is an aperture for the insertion of the pipe of large bellows, worked by water or steam, or of other machines for producing a current of air; and there are also holes at proper parts of the edifice, to be occasionally opened, to permit the scoriae and the metal to flow out, as the process may require. Charcoal, or coke, with lighted brushwood, is first thrown in ; and when the whole inside of the furnace has acquired a strong ignition, the ore is thrown in by small quantities at a time, with more of the fuel, and commonly a portion of limestone, as a flux: the ore gradually subsides into the hottest part of the furnace, where it becomes fused; the earthy part being converted into a kind of glass, while the metallic part is reduced by the coal, and falls through the vitreous matter to the lowest place. . The quantity of fuel, the additions, and the heat, must be S 5
regulated, in order to obtain iron of any desired quality; and this quality must likewise, in the first product, be necessarily different, according to the nature of the parts which compose the ore. The iron which is obtained from the smelting furnaces is not pure, and may be distinguished into three states: white crude iron, which is brilliant in its fracture, and exhibits a crystallized texture, more brittle than the other kinds, not at all malleable, and so hard as perfectly to withstand the file: j crude iron, which exhibits a granulated and dull texture when broken; this substance is not so hard and brittle as the former, and is used in the fabrication of artillery, and other articles which require to be bored, turned, or repaired: and black cast iron, which is still rougher in its fracture; its parts adhere together less perfectly than those of the grey crude iron; this is usually fused again with the white crude iron. Whenever crude iron,especially the grey sort, is used again in contact with air, it emits sparkles, loses weight, and becomes less brittle. In order to convert it into malleable iron it is placed on a hearth, in the midst of charcoal, urged by the wind of two pair of bellows. As soon as it becomes fused, a workman continually stirs it with a long iron instrument. During the course of several hours it becomes gradually less fusible, and assumes the consistence of paste. In this state it is carried to a large hammer, the repeatcd blows of which drive out all the parts that still partake of the nature of crude iron so much as to retain the fluid state. By repeated heating and hammering, more of the fusible iron is forced out; and the remainder, being malleable, is formed into a bar or other form for sale. Crude iron loses upwards of one fourth of its weight in the process of refining; sometimes, indeed, one half. Purified, or bar iron, is soft, ductile, flexible, malleable, and possesses all the qualities, which have been enumerated under this article as belonging exclusively to iron. When a bar of iron is broken, its texture appears fibrous; a property which depends upon the mechanical action of the hammer while the metal is cold. Ignition destroys this fibrous texture, and renders the iron more uniform throughout; but hammering restores it. If the purest malleable iron be bedded in pounded charcoal, in a covered crucible, and kept for a certain number of hours in a strong red heat, (which time must be longer or shorter, according to
the greater or less thickness of the bars
of iron) it is found that by this operation, which is called cementation, the iron has gained a small addition of weight, amounting to about the hundred and fiftieth, or the two hundredth part, and is remarkably changed in its properties. It is much more brittle and fusible than before. Its surface is commonly blistered when it comes out of the crucible; and it requires to be forged to bring its parts together into a firm and continuous state. This cemented iron is called steel. It may be welded like bar iron, if it have not been fused or over-cemented ; but its most useful and advantageous property is that of becoming extremely hard when ignited and plunged into cold water. The hardness produced is greater in proportion as the steel is hotter, and the water colder. The colours which appear on the surface of steel slowly heated are yellowish-white, yellow, gold colour, purple, violet, deep blue; after which the ignition takes place. These signs direct the artist in tempering or reducing the hardness of steel to any determinate standard. If steel be too hard, it will not be proper for tools which are intended to have a fine edge, because it will be so brittle that the edge will soon become notched; if it be too soft, it is evident that the edge will bend or turn. Some artists ignite their tools, and plunge them into cold water; after which they brighten the surface of the steel upon a stone: the tool being then laid upon charcoal, or upon the surface of melted lead, or placed in the flame of a candle, gradually acquires the desired colour; at which instant they plunge it into water. If a hard temper be desired, the piece is dipped again, and stirred about in the cold water as soon as the yellow tinge appears. If the purple appear before the dipping, the temper will be fit for gravers, and tools used in working upon metals; if dipped while blue, it will be proper for springs, and for instruments used in the cutting of soft substances, such as cork. leather, and the like , but if the last pale colour be waited for, the hardness of the
steel will scarcely exceed that of iron.
When soft steel is heated to any one of these colours, and then plunged into water, it does not acquire nearly so great a
degree of hardness as if previously made
quite hard, and then reduced by tem
pering. The degree of ignition required
to harden steel is different in the dif
ferent kinds. The best kinds require only a low red heat. The harder the
steel, the more coarse and granulated its fracture will be; and as this is not completely remedied by the subsequent tem|..."; it is advisable to employ the least leat capable of affording the requisite hardness. It is a circumstance worthy of remark, that steel has a less specific gravity when hardened than when soft; but there are no circumstances upon which a probable connection between these two properties, namely, the increased hardness and the diminished specific gravity, can be made out. If the cementation be continued too long, the steel becomes porous, brittle, of a darker fracture, more fusible, and incapable of being forged or welded. On the contrary, steel cemented with earthy infusible powders is gradually reduced to the state of forged iron again. Simple ignition produces the same effect; but is attended with oxidation of the surface. The texture of steel is rendered more uniform by fusing it before it is made into bars; this is called cast steel, and is rather more difficultly wrought than common steel, because it is more fusible, and is dispersed under the hammer if heated to a white heat. The conversion of iron into steel, either by fusion, viz. the direct change of crude iron into steel, or by cementation of bariron, presents many objects of interesting inquiry. From various experiments of Bergman, it appeared that good crude iron, kept for a certain time in a state of fusion, with such additions as appeared calculated to produce little other effect than that of defending the metal from oxidation, became converted into steel with loss of weight. These facts are conformable to the general theory of Vandermonde, Monge, and Berthollet: for, according to their researches, it should follow, that part of the carbon in the crude iron was dissipated, and the remainder proved to be such in proportion as constitutes steel. The same chemist cemented crude iron with plumbago, or carbonate of iron, and found that the metal had lost no weight. Morveau repeated the experiment with grey crude iron. The loss of weight was little, if any. The metal exhibitcd the black spot by the application of nitric acid, as steel usually does, but it did not harden by ignition and plunging in water. Hence it is conclud: ed, that it was scarcely altered: for crude iron also exhibits the black spot, and cannot by common management acquire the hardness of steel. From the experiments of the three excellent chemists last mentioned, it appears that the grey crude iron consists
principally of iron, with as much carbon as it can dissolve in the strong heat of the smelting furnace. They have shown also, that it deposits part of this addition, when cooled in contact with an iron bar immersed in the bath. This separation must be general in the erdinary or gradual way of cooling, whence the grey colour must arise from the blue white colour of the iron mixed with the black of the carbon. And this grey colour is also in a degree perceived, when soft closegrained steel is broken. These circumstances lead to an inference, that hard steel may in a certain respect differ from that which is softer by the intimate combination of a larger proportion of carburet. This accounts for the whiter and more metallic aspect of hardened steel, than of such as is soft. For the former contains less of disengaged carburet. Hence also we may account for the greater hardness of steel, which has been made quite hard, and then let down by tempering to a certain colour, than of steel merely heated to that colour, and pluuged in water. For, in the first method of hardening, a sufficient degree of heat is given to produce combination between part of the disengaged carburet and the iron, which in the latter does not take place. If the carburet be merely sufficient to saturate all the ironata moderate degree of §o the hardness will be considerable; but the steel will be easily degraded to the state of iron by frequent ignition. Such steel, in its hard state, will be very uniform in its texture, not excessively hard in its temper, but disposed to take a very fine firm edge, which will not easily be broken or injured by violence. These are accurately the properties of the English cast steel, which is of so uniform a nature, as to be distinguished by its conchoidal or glassy fractire. When the dose of carbon in steel is greater, it will bear a greater heat without o insomuch that it may be welded like iron. Its hardness will also be capable of a higher degree; and if this degree, produced by a strongerignition, be not given, the edge of the tool will never, become fine and smooth; and even at this higher degree, with all the advantage of subsequén: tempering, it will be less smooth than that of the cast steel, and more disposed to break. Steel of this kind is better adapted for the construction of hammers, vices, hatchets, leather-cutters’ knives, and other instruments, wherein the edge is either stout, or sudden blows unnecessary, or the construction demands frequent heating and welding.