of this metal, that all substances which exhibit magnetism do contain iron; but it must be confessed, that there remain many experiments to be made among the earths and powders which exhibit magnetical properties, before this negative proposition, which contines magnetism to iron, can be admitted as proved. When iron is exposed to the action of pure water, it acquires weight by gradual oxydation, and hydrogen gas escapes: this is a very slow operation. But if the steam of water be made to pass through a red hot gun-barrel, or through an ignited copper or glass tube, containing iron wire, the iron becomes converted into an oxide, while hy drogen gas passes out at the other end of the barrel. The action of air, assisted by heat, converts iron into a black oxide, containing twenty-five of oxygen. By the action of stronger heat this becomes a reddish brown oxide, containing forty-eight of oxygen. The yellow rust, formed when iron is long exposed to damp air, is not a simple oxide, as it contains a portion of carbonic acid. According to M. Chenevix, there are four stages of oxydation of iron: the first, or minimum, white; the second, green; the third, black; the fourth, or maximum, red. Thenard admits only three, the white, green, and red. The concentrated sulphuric acid scarcely acts on iron, unless it is boiling. If the sulphuric acid be diluted with two or three parts of water, it dissolves iron readily, without the assistance of any other heat than what is produced by the act of combination. During this solution, hydrogen gas escapes in large quantities. Sulphate of iron is not made in the direct way, because it can be obtained at less charge from the decomposition of martial pyrites. It exists in two states, one containing oxide of iron, with .27 of oxygen, which is of a pale green, not altered by gallic acid, and giving a white precipitate with prussiate of potash. The other, in which the iron is combined with .48 of oxygen, is red, not crystallizable, and gives a black precipitate with gallic acid, and a blue with prussiate of potash. In the common sulphate these two are mixed in various proportions. Distillation separates the acid from sulphate of iron, and leaves the brown oxide of iron, called colcothar. Vegetable astringent matters, such as nut-galls, the husks of nuts, logwood, tea, &c. which contain the gallic acid, precipi tate a fine black fecula from sulphate of iron, which remains suspended for a considerable time in the fluid, by the addition of gum arabic. This fluid is well known by the name of ink. See INK. The beautiful pigment, well known in the arts by the name of Prussian blue, is likewise a precipitate afforded by sulphate of iron. If two parts of alum, and one of sulphate of iron, be dissolved in eight or ten parts of boiling water, and a solution of prussiate of potash be added as long as any effervescence and precipitation are produced, the precipitate, thoroughly washed by affusion of boiling water, will have a green colour. This is owing to the yellow oxide of iron thrown down with the prussiate, which must be dissolved by adding muriatic acid. The deep blue powder, insoluble in this acid, is then to be washed and dried for use. According to Professor Proust, the iron in Prussian blue contains .48 of oxygen, and is obtained only from a super-oxygenated sulphate; the precipitate from a pure alkaline prussiate and sulphate of iron with a minimum of oxygen being white, and containing only .27 of oxy. gen. This may explain a fact observed by a French colourman, who, having mixed some Prussian blue and white lead with nut oil, and set it by for some time covered with water, found the surface, only blue, and all the rest white. On pouring it out on his stone, and beginning to grind it afresh, with intention to add more Prussian blue, he found the colour gradually returning of itself. Here it might be supposed that the oxide of the prussiate had parted with oxygen to the oil, or the oxide of lead, or both, thus becoming white; except that on the surface, which was supplied with oxygen from the superincumbent water; and that it recovered its colour by attracting oxygen from the air. But on this supposition it would seem, that light must contain oxygen, since the colour of this paint, spread on wood or paper, returned by exposure to light in vacuo as well as in the open air. The colour of Prussian blue is affected by the contact of iron. Mr. Gill, finding a knife with which he was mixing some Chinese blue acquire a green tinge, spread a little of it, and afterward a little Prussian blue, sufficiently diluted on the blade of a knife, and with a camel hair pencil took off enough to form a tint on paper, and thus continued, till he had taken off in the first instance thirty-six, and in the second eighty six, without adding any fresh colour. These tints differed in regular gradation from greenish blue to green, olive green, yellowish green, yellow, and so on to a buff. Concentrated nitric acid acts very strongly upon iron filings, much nitrous gas being disengaged at the same time. The solution is of a reddish brown, and deposits the oxide of iron after a certain time; more especially if the vessel be left exposed to the air. A diluted nitric acid affords a more permanent solution of iron, of a greenish colour, or sometimes of a yellow colour. Neither of the solutions affords crystals; but both deposit the oxide of iron by boiling, at the same time that the fluid assumes a gelatinous appearance. Diluted muriatic acid rapidly dissolves 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 sa turated 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 Langier, Fourcroy, and Vauquelin, gave iron 41.25, phosphoric acid 19.25, water 31.25, alumina 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 preci pitating 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. Specific 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 Var 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, unls 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 S7.5. Mr. Hatchett however has found, that the magnetica! pyrites contains the same proportion as the artificial sulphuret. Phosphorns 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 phosphuret is 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 investi. gated the subject very extensively in the large way, soft cast steel capable of welding contains of carbon, common cast steel To, cast steel of a harder kind, steel too hard for drawing, white cast iron, melted cast iron, black cast iron. He conceives, however, that in steel the carbon is more intimately united with the iron. When iron is saturated with carbon it be comes 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 plunged 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 as suming 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 fabrica. tion 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 oxida tion by the access of air. After the iron plates are scraped, or rendered very clean by 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 disposed to alter, by the united action of air and moisture. The process for tinning iron vessels does not essentially differ from that which has already been described 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 bismuth. As nickel caunot be purified from iron without the greatest difficulty, it may be presumed that these substances would 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 bro ken. 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 metal 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 scoria. After the mass is cooled, the antimony is found separate at the bottom of the crucible, while the iron remains in combination with the sulphur and alkali. If the proportion of the iron be considerably greater than five ounces to the pound of ore, the antimony will be alloyed with jron. 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 other 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 ores of iron, which are either nearly pure, or else mixed with earths, as in spars, jasper, boles, basaltes, &c., iron is mineralized with sulphur, as in the pyrites; or with arsenic. The coally iron ores contain bitumen. The magnet, or loadstone, 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 sul phate. To analize 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 ziuc or manganese, the Prussian blue must be calcined to redness, 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 afford 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 frag. ments 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 scoriæ 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 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 dis-, tinguished 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 grey 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 fused 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 repeated 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, 's 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 |