(From fero, to wound); iron; chalybs, Mars, aquarius, biladen, hadid. Its chemical character is
Iron is a bluish white metal, very hard, admitting of a brilliant polish, styptic to the taste, and emitting a smell when rubbed; the next in specific gravity to copper, between seven and eight times heavier than water; distinguishable from all other,bodies in its metallic state by its attracting, or being attracted by, the loadstone, but losing this peculiarity on being reduced by fire to a calx; and retaining it but a short time when perfectly pure. It is the hardest of all metals, not equally malleable with gold, silver, or copper; but more ductile and tenacious. It melts in the heat of 158 of Wedge-wood; but our powers of increasing temperature are here limited, and we know not at what degree it boils or evaporates. Its texture is fibrous. By the continuance of a weaker heat it calcines, and more easily, though it melts with more difficulty, than any other metal. If iron is long kept in fusion, it loses its sulphur, becomes more brittle, and at length is converted into a bluish glass; which, if exposed to the heat of a large burning glass, after placing it on a piece of charcoal, becomes iron again. Iron is corroded by a moist air into a reddish yellow rust, occasioned by the oxygen it absorbs, and is soluble in all acids, emitting a garlic odour. Acids precipitate from iron all the common metallic bodies, except zinc, forming with the marine acid a yellow, with the nitrous a dark red, and with the vitriolic a pale green, solution: all salts, except the alkaline, dissolve iron; and this metal by its strong affinity for oxygen decomposes water.
In medicine the distinction betwixt iron and steel, or carbonated iron, is not necessary; but as a medicine, as well as in chemical processes, the softest iron is preferred.
We omitted the chemical properties of iron in the article Chemia, because its medical were so intimately connected with them. We shall now previously explain the nature of iron in its different states.
Wrought iron is the metal in its purest form, though it is seldom perfectly pure. The malleability of the wrought iron is the best test of its freedom from any adventitious substance. Steel is carbonated iron. It usually contains about 1/60 of its weight of carbon; but it seems capable of combining with a larger quantity, and, in the same proportion, it becomes more brittle. A drop of nitric acid on a plate of steel leaves a black spot; but on a plate of iron, the mark left is a whitish green.
Cast iron contains a larger .proportion of carbon; sometimes 1/8, from whence its colour is blacker, and the metal more fusible; but it is always contaminated with oxide and phosphuret of iron, generally also with flint. This kind is reduced to the state of wrought iron, by exposing it with black oxide of iron to an intense heat. The oxygen and carbon escape in combination.
We have already pointed out the very great affinity of iron for oxygen. According to Mr. Proust there are, however, only two oxides of iron, the black or green, and the red or brown. The first, containing twenty seven parts of oxygen, and seventy-three of iron, is the least oxygenated of the two, and affords a white precipitate, with alkaline prussiats. It is the state of the martial ethiops, insoluble in alcohol, not affected by the gallic acid, and approaches so near that of the metal, as to be sometimes attracted by the magnet, and occasionally to crystallize in octoedral crystals.
The red oxide is composed of forty-eight parts of oxygen and fifty-two of iron. It is the common rust of iron, and, in the old pharmaceutical language,saffron of Mars. It is soluble in alcohol, and gives a blue precipitate with alkaline prussiats, and a black one with galls. With iron filings it is converted, as may be expected, into the black oxide. Sulphurated hydrogen gas, and many other substances, will also take away the superabundant oxygen, and reduce it to the state of the former. Hydrogen dissolves iron sparingly; azote refuses to combine with it; but with sulphur, phosphorus, and carbone, it unites readily. The phosphuret is what the workmen call the cold short (brittle when cold) iron; and was, for a time, supposed to be a new metal, to which the name of siderum was assigned. The carburet of iron is the plumbago, or black lead; the well known substance inclosed in pencils. A hypercarburet of iron is hard and unmalleable (Pearson, Philosophical Transactions): red short iron, which is brittle when hot, is supposed to owe this quality to arsenic or to carbon; most probably to the former.
Iron is dissolved in vitrolic acid, forming the green vitriol of commerce; and in the oxide, when combined with an acid, some of its properties just mentioned are only discoverable. Though green, it contains the most oxygenated calx. In the extemporaneous preparation the acid must be largely diluted. Nitric acid rather oxidates than dissolves it; and to obtain the nitrat of iron, the acid must be much diluted. Diluted muriatic acid dissolves iron with violence: the muriat forms in flat, deliquescent crystals. Vegetable acids have a considerable affinity with iron. In the acetic acid it is easily dissolved, and, by its means, iron is suspended in wine. With the tartarous, it forms the soluble martial tartar, or aperitive extract of Mars; and the oxalate of iron may be easily procured in astringent, deliquescent, effervescing, prismatic crystals of a greenish yellow colour, soluble in water. Soluble phosphats, added to the sulphats of iron, occasion two new compounds. The phosphat of iron, thus formed, becomes a phosphuret by fusion with powdered charcoal. Prussiats of iron are of a deep, beautiful blue colour: but if the oxide predominates, it is yellow; if defective, green. Carbonic acid unites with the metal, and by its means iron is suspended in the chalybeate waters.