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into wires. It is attracted by the magnet, and, like iron, may be rendered magnetic. It is very infusible. It is not altered by exposure to the air at common temperatures, but at a red heat it is oxidated, and at the same temperature decomposes water. Its specific gravity, after being melted, is 8.279, and after being hammered, 8.932. Its combining weight has been computed to be 29.62. All the characters of this metal connect it with iron; and if our hypothesis be correct, it only differs from iron in containing 2 more equivalents of hydrogen; and this, it will be admitted, is a more probable hypothesis than that it is a distinct substance, formed of simple particles proper to itself.
Iron is, of all the metals which have been referred to, that which is the most generally diffused, and the most important in its uses. It forms a part of all the great masses of rocks and mineral deposites which form the solid crust of the globe. It is found in the water of rivers and the ocean, and it forms a constituent part of most animal and vegetable substances. It is found in small quantities native, but it is almost always in combination with oxygen, sulphur, silica, and other substances. The minerals which yield it in such quantity as to be termed ores of iron, are very numerous ; but those from which the greater part of the iron consumed in the arts is derived, are two,—black magnetic iron ore, and clay iron-stone. The former, a combination of the protoxide and peroxide of iron, occurs in beds, or single crystals, in the oldest rock formations, and it is from it that the purest of the iron of commerce is derived. Clay ironstone is essentially a carbonate of the protoxide, and occurs in veins in the primary formations, frequently along with ores of lead and copper, and very largely in the deposites of the coal formation, from which source the greater part of the immense consumption of Europe is supplied. The general method of smelting iron consists in exposing the ore to a powerful heat, along with carbonaceous matter and lime, in a large furnace. The carbonaceous matter, usually coke or charcoal, but now frequently common coal, acts by depriving the iron, brought to the state of an oxide by heat, of its oxygen, while the lime combines with the foreign matters of the ore, and forms a fusible compound termed slag. The particles of melted metal descend by their greater density to the bottom of the furnace, while the slag floats
upon the surface, and protects the metal from the action of the air. The slag runs out at an aperture in the side of the furnace, while the melted iron is let off by a hole at the bottom, plugged with sand or clay. Fresh matter being constantly supplied to the furnace, the process of fusion goes on continually. The liquid metal is received from the furnace in moulds of sand, and then forms the cast-iron of commerce. The substance thus obtained is an impure iron, but largely used, and of vast importance in the arts. It contains carbon, oxygen, and other foreign bodies. It is to free it from these, and convert it into what is termed soft or malleable iron, that it is subjected to a further process of purification. This consists in again fusing it in a peculiar kind of furnace, in contact with carbonaceous matter. The melted metal thus obtained, technically termed fine metal, is broken in pieces, and placed in a reverberatory furnace, where it undergoes the operation of puddling, which consists in stirring the metal, while semi-liquid, in the furnace, by which means a large disengagement takes place of carbonic oxide, which burns with a blue flame. The metal is next formed into balls and forged, which may be done by heavy hammers, but which, on the great scale, is effected by passing the metal, while hot, through a series of grooved rollers. The metal in this state, is termed mill-bar iron. It is then subjected to a further operation, which consists in welding pieces of it together, from which it derives its properties of more perfect malleability, ductility, and cohesiveness. It is now the bar-iron of commerce.
The iron thus procured contains a small proportion of carbon, and traces of silica and other substances. It may be rendered pure by bringing it to the state of an oxide, and then exposing it, at a red heat, in a tube of porcelain, to a current of hydrogen gas, by which means the oxide is
reduced, and the metal obtained in the form of a porous spongy mass.
Iron in its compact state, has a peculiar gray colour, known familiarly as iron-gray. It possesses the metallic lustre, and when polished exhibits considerable brilliancy. It has a styptic taste, and when rubbed emits a peculiar odour. It is malleable at every temperature, and its malleability increases with the degree of heat, and when heated to redness, it is so soft and pliable that it may be hammered into any form. It then, too, acquires the property of becoming so soft, without being fused, that it can be welded, that is, pieces of it may be united together by hammering or pressure. This property, so valuable in the arts, is possessed likewise, it has been seen, by platinum, though in a far inferior degree. Iron, although malleable, is less so than gold, silver, or copper. It is very ductile, and may be drawn into wires as fine as a human hair. In tenacity it exceeds all the metals, a wire of .078 of an inch supporting a weight of 449.34 lb. avoirdupois.
Pure iron is exceedingly infusible. The melting point of cast-iron is 3479° F., but that of malleable iron is much higher. In cooling it expands, and like the other metals tends to crystallize. When kept for a time at a red heat, it often forms large cubical or octahedral crystals, and the metal becomes brittle. When exposed to the air in which any moisture exists, its surface is speedily covered with the brown powder known by the name of rust; but if the air be perfectly dry, the iron is not acted upon. It is believed that in the rusting of iron, carbonate of the protoxide is first formed, and that this gradually passes into hydrate of the peroxide, the carbonic acid being evolved. It is remarkable that this rust of iron always contains ammonia, and that the native oxides likewise contain the same substance. When iron is heated to redness in the open air, it
is oxidated, and when inflamed in oxygen gas, it burns with brilliant sparks, the oxide in either case being fused. If the vapour of water be passed over it in a heated state, it decomposes the water by the abstraction of its oxygen. When in the state of minute division in which it is obtained by reduction of its oxide, it takes fire spontaneously in the open air.
Iron possesses the property of being attracted by the magnet, and it then becomes itself magnetic by induction, but if perfectly pure it instantly loses its polarity when the magnet is withdrawn. If it contains carbon, as in the case of steel or cast iron, it may become permanently magnetic. This property may be communicated by friction with the native loadstone, or with a bar of steel already magnetic, or by percussion, or by the electric shock, nay, by the body being placed for a sufficient time in a given position inclining to the horizon. The magnetic property is possessed by the black oxide, popularly termed the loadstone, and by the corresponding sulphuret.
The specific gravity of iron is about 7.7, with a slight variation dependent on the degree in which it has been hammered or compressed. By fusion its density is increased to 7.8439. Its combining weight is usually calculated at 27.18.
Iron forms with oxygen two well known compounds :
1. Protoxide, or ferrous oxide,
2. Peroxide, or sesqui-oxide,
The black oxide or magnetic iron ore being
Fe 0+Fe2 03.
The peroxide and its compounds are isomorphous with alumina and its compounds, and in other respects are very analogous to the aluminous compounds in their properties.
Iron, with respect to its abundance in the mineral king