Phosphoric acid unites with iron, but very slowly. The union is best effected by adding an alkaline phosphate to a so lution 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 tex ture. 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, Four croy, 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 com bined 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 crystalliza ble, 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 pre cipitating a solution of the sulphate with neutral borate of soda.
Arsenic acid likewise unites with iron. This arseniate is found native in Corn wall, in pretty large cubic crystals, toler ably transparent, of a dark green colour, with a brownish tinge ; sometimes yel lowish, 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. Speci fic gravity 3.4. The green and red sul phates of iron may be decomposed by arseniate of ammonia, and afford arse niate of iron in the two different states.
Chromate of iron is said to have been found abundantly in the department of Far in France, and to form a beautiful green for enamelling or colouring pastes. Its analysis by Vauquelin and 'l assaert. 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 pre viously 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 strong ly 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 sul phur 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 thesame 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 ex periment 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 pro duced by fusion in the common way, ex cepting 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 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 car lifon, sulphur, or phosphorus, unless dose be so great as to destroy the mag netic 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 exten sively in the large way, soft cast steel, capable of welding, contains 1 one-hun dred 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 one twentieth, 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 car bon, it becomes what is commonly called plumbago.