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nued somewhat beyond the time requisite for the entire conversion. For there is less inconvenience attending a slight degree of excess in the cementation, than would result from a portion of iron remaining in the steel. The charcoal after cementation is as black, and apparently in the same state, as it was before. M. Duhamel moistened it, and applied it to the same use a second time: it answered the purpose, but so much more slowly that he objects to the use of it in manufactories. From this, as well as other circumstances attending the steel-making process, it seems advantageous, at least with regard to expedition, that the coals should contain volatile matter. And hence the superior advantages of animal coal, such as the coal of leather, or the hoofs and horns of animals, imperfectly burned, which are used in case-hardening, though they may be less applicable to the longer process of steelmaking for various reasons.
M. Duhamel advises to have two tilting hammers; one of the weight of one hun dred and fifty pounds, and the other half that weight; the first for the purpose of forging large works, and the latter small bars for cutlers. He recommends another small hammer of about twelve pounds for forging bars still smaller, to make gravers, small files, and the like. The steel must not be heated beyond the degree of cherry-red for forging. The tilting hammers should give at least three hundred strokes in a minute.
not affected by the different kinds of charcoal made use of. He remarks, nevertheless, that it may be advisable to add from one-fourth to one-third of wood ashes, especially where the iron is not of so good a quality as to afford steel possessing tenacity of body, as well as hardness. These ashes, which he used with success, prevent the steel-making process from being effected as rapidly as it would otherwise be, and give the steel pliability without diminishing its hardness. It is remarked, that in the case of this management, the blisters on the surface of the steel are smaller and more numerous. He likewise tried sea-salt. Fifty pounds of salt are sufficient for a furnace of steel of twelve thousand weight. The salt is pulverized, and sprinkled on the bars of iron when put into the furnace. He found that this ingredient likewise contributes to give body to the steel. In the arrangement of the bars in the furnace, the cement is laid one inch thick at the bottom, and half an inch thick between each layer of iron. Our author affirms, that the process would succeed equally well if the thickness were a little more than a quarter of an inch. The thickness of the bars of iron is indifferent, but there ought not to be a great difference in this respect between bars cemented at the same time. The common thickness is a little more than half an inch. It is not advisable that they should be very broad in proportion to the thickness, as this figure is found to produce flaws and cracks in the direction of the length of the bar. The À bars may be square, or their breadth may conveniently be somewhat more than twice their thickness. The fire for cementation must be of considerable intensity, and kept up until the conversion has perfectly taken place, which is ascertained by proof bars, so disposed as to be taken out from time to time. The cementation is finished on the sixth day; that is to say, it commonly lasts five times four-and-twenty hours. And ac cordingly, the workmen take one of the proofs out on the fifth day, which is forged, hardened,and examined by the fracture. If it break short, and show no indications of iron, the fire of the furnace is suffered to go out. But if it contain iron, the fire is kept up for twelve or twenty-four hours, accordingly as the quantity of fibrous irou may have prov. ed greater or less in the first proof. A second proof bar taken out at the proper time serves to direct them in the same manner with regard to their operations. By this management the cementation is conti.
The cast steel of England is made as follows; a crucible about ten inches high, and seven in diameter, is filled with ends and fragments of the crude steel of the manufactories, and the filings or fragments of steel works. They add a flux, the compc. nent parts of which are usually concealed. It is probable, however, that the success does not much depend upon this flux, which, from the quality of the cast steel itself, may be presumed to be of the nature of a steel cement. This crucible is placed in a wind furnace like that of the founders, but smaller, because intended to contain one pot only. It is likewise surmounted by a cover and chimney to increase the draught of air. The furnace is entirely filled with coke or charred pit-coal. Five hours are required for the perfect fusion of the steel. It is then poured into long square, or octagonal moulds, each composed of two pieces of cast iron fitted together. The ingots, when taken out of the moulds, have the appearance of cast iron. It is then forged in the same manner as other steel, but with less
heat and more precaution, because more liable to break.
This cast steel is almost twice as dear as other good steel. M. Duhamel says that it is not proper for all kinds of work, particularly those which require much tenacity, as well as hardness to resist violent blows and strains; but it is good for razors, knives, and all toys and small work which require an exquisite polish. It does not seem, however, that the tenacity of this steel is inferior to that of the best of the other kinds, and its uniformity of texture is for many works an invaluable advantange. It is daily more and more used in England, but must necessarily be excluded from many works of considerable size, on account of the facility with which it is degraded in the fire, and the difficulty of welding it, which cannot be done in the common way. We have been informed that the faces of anvils and broad hammers, for the use of silversmiths and other artists, have been made of cast steel, and welded to iron by a particular management, which consisted in substituting between the iron and the steel another kind of steel in the form of filings, or a thin plate. The steel plate intended for the face was made as hot as could be done with safety, and the iron being at the same time brought to the welding heat, was applied to the steel, and quickly united by hammering.
When we consider the operations by which crude iron is brought into the malleable state, then converted into steel, and afterward into a fusible metal, which is not malleable; we may perceive that steelmaking is a kind of inversion of the process of refining iron, as practised in the first instance. When the oxide of iron is mixed in the smelting furnace with combustible matter and glass, it will either be complete ly or partially revived, according to the management of the process. Much of the coal will however be so enveloped with the vitreous matter as to remain unburned: and the reduced iron, with which it may be in contact, will be in the same situation as forged iron in the cementing pot; that is to say, it will be in contact with coal at a very elevated temperature, and defended from the air. From the great infusibility of iron, it may reasonably be concluded, that the reduced metal does not flow into the bottom of the furnace, until the charcoal has converted it into a fusible matter similar to steel, by the same action which takes place in cementation, whatever that
action may be. Hence it must follow, that the various specimens of crude or cast iron will differ in their qualities, as well on account of the degree of cementation they have undergone, as the degree of reduction which has taken place among the metallic parts, which are carried down, and form the whole mass. Since the coal, in the process of cementation, communicates or adds weight to the iron; and since crude iron, as well as steel, exhibits sparkles, and is more easily burned than other iron; it may therefore be concluded, that in the process of refining, that part of the inflammable substance which had united with the metal is burned, and leaves the iron much less fusible than before. Stirring the mass multiplies the contacts of the air with the burned substances; these surfaces of contact will therefore successively afford thin coats of infusible metal. In this manner it is found, that, if a large piece of erode iron be exposed to heat in a wind furnace, the external part will be deprived of its fusibility during the time required to produce a strong heat in the whole mass; and the internal part will be melted, and run out, leaving the shell behind. Iron, which is of the consistence of paste, may therefore be considered, like any other paste, as a mixture of a fluid with a solid. It will be easily understood, that the forging will bring the parts of difficult fusion together, and extrude the less refined and fluid parts: it will also be evident, that this operation is not likely to drive out the whole of the fusible matter. When the iron has arrived at that state, wherein the quantity of fibre or tough iron is sufficient to answer the mechanical purposes to which it is intended to be applied, the artist will consider it as sufficiently refined; and the residue of fu sible iron contained in the bar, answers, in all probability, the valuable purpose of connecting these infusible masses together. Thus we find that forged iron appears as if covered with a varnish, when urged to a white heat; we find that this varnish is more abundant in steel; and that iron and steel may be respectively welded together by application in this state; an effect which it would be very difficult to account for, in this most infusible of metals, if it were not for such an admixture. But cast steel, steel over cemented, and crude iron, appear to be in the state of all other metals, platina excepted. They cannot be welded, because welding implies a partial fusion: or an effect similar to the gluing or uniting of
solids by the application of a fluid, which afterward becomes consistent. And as platina possesses this valuable property, it seems reasonable to infer, that it must also consist of two metallic substances of different degrees of fusibility; a supposition that appears to be confirmed by the discoveries of Dr. Wollaston and Mr. Tennant.
Crude iron, and steel of a uniform texture, consist therefore of a fusible combination of iron with the combustible substance of the coal, or something which is imparted from it; the crude iron differing from the steel simply in being overdosed with carbon, and less pure, on account of the admixture of metallic oxide, which can scarcely, perhaps, be avoided in the large process. It appears therefore, that crude iron must pass through the state of steel, before it can become forged iron; and consequently, that 'the fabrication of steel from this last is a circuitous process, which can only be repaid by the absence of those unreduced parts, which may exist in the crude iron. At some forges, however, where the ore, the flux, the fuel, and the management, are adapted to each other, the produce affords steel, when duly refined. At other manufactories, the crude iron is either refined, or converted into steel, by running it into thin plates, which are stratified with charcoal, and burned in a close furnace. In this way the metal is refined by degrees, without undergoing fusion; and if the heat be raised to that of cementation, the iron will not only be reduced, but converted into steel. In the forges of Carinthia the grey crude iron is also converted either into soft iron, or steel, according to the management of a somewhat similar process. The iron is fused in a large melting-pot; and a small quantity of water, being thrown upon the surface of the metal, causes a thin plate to congeal, which is taken off; and by continuing the operation, the greatest part of the fused iron becomes converted into plates. To produce steel, these plates are again fused, and kept a long time in an elevated heat; at the same time that the metal is defended from the contact of the air by a sufficient quantity of the vitreous slag. To produce soft iron, the plates are exposed to a continued roasting, while the air is constantly renewed by means of two pair of bellows. The extensive surface of the plates renders it unnecessary to use that agitation, or stirring, which is required when fused crude iron is refined. In these processes it is evident, that the same matVOL. II.
ter in the crude iron, which it obtained in the smelting furnace, is employed, and supplies the place of the charcoal used in forming steel by cementation; and on the other hand, that this substance, which prevented the crude iron from being soft, tough, and infusible, is burned away, together with a portion of the iron itself, while the remainder is left in a much purer state.
These are facts observed at the furnaces. But the observations and inquiries of the chemist must be carried further, in order to determine what it is that iron gains or loses at the time of its conversion into its various states. It is found, that crude iron approaches towards the soft state, not only by heating with exposure to the air, which burns the combustible addition, but likewise by fusion, without the free access of air. In this case, when the fusion has been complete, and the cooling gradual, it is found that a black substance is thrown up to its surface, which is more abundant the greyer or blacker the iron; and the same black substance is observed to coat the ladles of forged iron, which are used to take out the metal, and pour it into moulds for casting shot, and other articles. It appears, therefore, that the heated iron, like other heated fluids, is capable of holding a larger quantity of matter in solution than when cold; and that a portion of this black substance separates during the cooling, whether by the gradual effect of surrounding bodies, or by the contact of the ladle, in the same manner as various salts are separated, in part, from water, by a diminution of temperature. From chemical analysis, as well as from its obvious characters, this black substance is found to be plumbago, or the materials used to make pencils, and commonly known by the name of black lead, which is nothing but a carburet of iron.
The presence of this black matter is likewise exlubited by dissolving steel, or crude iron, in acids, in which plumbago is insoluble, and therefore remains behind in the form of a powder. Hence likewise is deduced the cause of the black spot which remains upon steel, or crude iron, after its surface has been corroded by acids; for this spot consists of the plumbago, which remains after the iron has disappeared by solution.
Solution in the sulphuric or muriatic acid not only exhibits the plumbago contained in iron, but likewise possesses the advantage of showing the state of its reduction by the quantity of hydrogen gas which is disen
gaged: for the quantity of this gas, in like circumstances, is proportional to that of the iron which is converted into oxide. There are considerable differences between the various products of the smelting furnace in these respects; but it is found, that the white crude iron affords the least quantity of hydrogen in proportion to its bulk, and leaves a moderate portion of plumbago; the grey crude iron affords more hydrogen, and more plumbago than the white; and the softest bar iron affords most hydrogen of any, and little or no plumbago. The quantities of hydrogen gas, at a medium, by ounce measures, were sixty-two, afforded by one hundred grains of the white crude iron: seventy-one by the grey crude iron; and seventy-seven by the malleable iron.
Hence it may be inferred, that, in the white crude iron, the processes of reduction and cementation are both carried to a less extent than in the grey crude iron, which is produced by means of a stronger heat, excited with a larger quantity of fuel: and that the reduction of grey crude iron is still less perfect than that of the soft bar iron; though this last, by the refining in an open vessel, is so far from being more cemented, that it scarcely contains any plumbago at all.
It must be admitted, however, that the solution in acids serves only to support these general conclusions, in conjunction with the facts observed in the dry processes; but cannot accurately show the quantities either of hydrogen or plumbago afforded by the several kinds of iron. For the plumbago, as it becomes disengaged, floats on the top of the sulphuric acid; where it gradually disappears, though insoluble in that acid. It must therefore be taken up by the hydrogen gas, and it is found that the volume of this air is diminished by the absorption. Hence there is a double source of inaccuracy from the loss of plumbago, and the contraction of the hydrogen gas.
On the whole then, since iron contains carburet in a state of combination, of which it may be deprived by heat with access of oxygen, which converts its carbon into the carbonic acid; and since it recovers the plumbago by cementation with charcoal; there can be no question, but that this substance is originally afforded by the fuel. It appears also, that the reduction of the metallic oxide takes place first at a lower temperature; and that the combina
tion of the carbon follows at a greater heat. Whence, in the refining of iron, the carbon is first burned, and the iron remains reduced; and in the cementation of bar iron, the metal is converted into steel, with blisters on its surface; which most probably arise from carbonic acid, formed by the oxygen of some portions of unreduced oxide uniting with the acidifiable base from the charcoal. And lastly, as iron holds this acidifiable base, or carbon, in solution, so likewise it may not be separable from this metallic solvent, without carrying a portion with it; in the same manner as salts, which erystallize in water, always take up part of the solvent in the formation of their crystals.
It would require many volumes to enmerate the leading uses of iron. This most valuable of metals is applied to so many, and such important uses, that we cannot look round us without seeing its effects. When we contemplate the innumerable effects of human industry, and ask ourselves the simple question, Could this have been done without iron? There is not a single instance, which will not immediately show its value.
Iron is one of the principal ingredients for dying black. The stuff is first prepared with a bath of galls and logwood, then with a similar bath to which verdegris is added, and lastly dyed in a similar bath with the addition of sulphate of iron. If it be wished, that the colour should be particularly fine, the stuff should previously be dyed of a deep blue: otherwise a brown may be first given with the green husks of walnuts. Silk however must not be previously blued with indigo, and sumach may be substituted instead of galls. Leather, prepared by tanning with oak bark, is blackened by a solution of sulphate of iron.
Cotton has a very strong affinity for oxide of iron, so that, if it be immersed in a solution of any salt of iron, it assumes a chamois colour, more or less deep, according to the strength of the solution. The action of the air on the oxide of iron deepens the colour; and if the shade were at first deep, the texture of the stuff is liable to be corroded by it. To prevent this, the cotton should be immersed in the solution cold, carefully wrung, and immediately plunged into a ley of potash mixed with a solution of alum. After having lain in this four or five hours, it is to be wrung, washed, and dried.
Mr. Brewer, to give a nankeen colour,
prepares his cotton yarn by boiling it five
The ancients appear to have had the art
ret may be applied, and, after this has been well washed off, the acid will remove the stain.
IRON-FOUNDRY, the art of casting iron, and forming moulds, into which it is poured when in a fluid state.
The moulds are commonly made in sand, held in wooden frames, (fig. 3 and 4, Plate Iron-foundry.) Two of these frames, A B, (fig. 4.) are called a pair of flasks, and fit together by pins, a a, in one flask, entering eyes, bb, in the other. A wooden pattern of whatever is to be cast must first be made, exactly of the same dimensions as the article required. For an example, we have chosen to describe the manner of casting a roller, such as is used for the wheels of small wag. gons, the rolls of windmill heads, &c. The pattern is shown in fig. 5, 6, and 7: fig. 5 is a plan, fig. 6 a section, and in fig. 7 it is shewn edgeways. This pattern is exactly similar to the wheel which is to be cast, except that in place of the hole through the centre of the wheel: a pin, m, is stuck on, projecting from each side in the same place that the holes will be: the use of these pins will be shown hereafter. The lower flask, A, (fig. 4.) is placed on a board laid on the ground: it is then filled with sand, and rammed down, first with the rammer, (fig. 9) and afterwards with fig. 10,which is broader, and smooths the work. The workman then with the trowel, (fig. 8) digs out a hole in the sand, and presses the pattern into it, the flat surface horizontal, and fills the sand in round the pattern, until it is exactly half buried, he then takes out the pattern, and if there are any holes in the under part, where the sand is not filled round close to the pat. tern, he puts in a small quantity of sand, and presses the pattern down again, until a perfect impression of it is left in the sand, as in fig. 1. He now returns the pattern, and sprinkles some dry sand, which has been burnt in the furnace, over the pattern and flask, and then places the upper flask, B, (fig. 4) upon it: two small sticks are placed upon the pattern, and the sand filled in round them; the sand is rammed down by the rammers (fig. 9 and 10), and the two sticks drawn out, leaving holes, 11, (fig. 2) through the sand in the upper flask. The workman now takes off the upper flask, B, by its two handles, leaving the pattern in the lower flask; the burnt sand causes the two flasks to separate exactly at the joining of the flasks: the upper flask is now completely finished, the holes, 7 l, made by drawing out the sticks, being left to pour in the metal, and the pattern leaving a perfect print of
Iron is very liable to be oxided, or contract rust. Conté informs us, that if fat oil varnish be mixed with half, or at most fourfifths of its weight of oil of turpentine, and this be applied lightly and evenly with a sponge to iron or steel, and left to dry where it is not exposed to dust, the metal will retain its lustre, without any danger of rusting. In order to prevent gun-barrels from rusting they are frequently browned. This is done by rubbing it over, when finished, with aquafortis, or spirit of salt diluted with water, and laying it by for a week or two till a complete coat of rust is formed. A little oil is then applied, and the surface, being rubbed dry, is polished by means of a hard brush and a little bees-wax.
The yellow spots, called iron moulds, which are frequently occasioned by washing ink spots with soap, may in general be removed by lemon juice, or the oxalic or tartarous acids; or by muriatic acid diluted with five or six parts of water, but this must be washed off in a minute or two. Ink spots may readily be removed by the same means. If the iron mould have remained so long, that the iron is very highly oxided, so as to be insoluble in the acid, a solution of an alkaline sulphu