iron is mixed in the smelting furnace with combustible matter and glass, it will either be completely 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 crude 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 suffiVOL. VI.

ciently refined; and the residue offusible 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 afterwards 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

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quantity of water being thrown upon the surface of the metal cause 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 matter 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 exhibited 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 disengaged: 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 sixtytwo, 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 plumba. go afforded by the several kinds of iron. For the plumbago, as it becomes disen gaged, 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 af forded by the fuel. It appears also, that the reduction of the metallic oxide takes place first at a lower temperature; and that the combination 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 crystallize in water, always take up part of the solvent in the formation of their crystals.

It would require many volumes to enumerate 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 dyeing black. The stuff is first prepared with a bath of galls and logwood,

then with a similar bath to which verdigris 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: other wise 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 hours in a mixture of water made grass green with sheep's dung and a solution of white soap; twice more, an hour each time, with half the quantity of soap; and a fourth time, in ley of pot or pearl ashes, one pound to twenty of yarn, another hour. He then passes it through iron liquor, to every gallon of which half a pound of red chalk, or ruddle, in powder, is added; the liquor being poured off clear, after it has stood four hours to settle; and immerses it in an alkaline lixivium. When of the proper colour, for which this operation may be repeated, if necessary, he dries it, as after each of the former processes; and then puts it into a warm lixivium, in which it is brought to a scald. It is afterwards to be soaked an hour in water made almost as sour as lemon juice with sulphuric acid, and then washed and wrung twice.Lastly, it is to be boiled slowly an hour in a solution of white soap, one pound to ten of yarn.

The ancients appear to have had the art of preparing a blue enamel from iron. glass of a sapphire blue colour, transpaM. Klaproth analysed a piece of antique grains of which gave the following prorent only on the edges, two hundred alumina 3; oxide of copper 1 ; lime 0.5.— ducts: silex 163 grains; oxide of iron 19;

The loss was 13.5

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 four-fifths 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 wash ing 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 remov ed 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 sulphuret may be applied, and, after this has been well washed off, the acid will remove the stain.