IRON is a metal of a bluish white co lour, of considerable hardness and elasti city ; very malleable, exceedingly cious and ductile, and of a moderate spe cific gravity among metallic substances. It is much disposed to rust by the access of air, or the action of water, in the com mon temperature of the atmosphere.— The appearance of prismatic colours on its polished surface takes place long be fore ignition ; and at so low a tempera ture, that the slightest coating of grease is sufficient to prevent their appearance, by defending it from the contact of air. It may be ignited, or at least rendered sufficiently hot to set fire to brimstone, by a quick succession of blows with a hammer. When struck with a flint, or other hard stone, it emits decrepitating ignited particles, such as can be obtained from no other metal by the same means. These particles are seldom larger than the two hundreth part of an inch in dia meter; and, when examined by a magni fier, are found to be hollow, brittle, and of a greyish colour, resembling the scales of burned iron. This metal is easily ox ided by fire. A piece of iron wire, im mersed in a jar of oxygen gas, being ig nited at one end, will be entirelyconsum ed by the successive combustion of its parts. It requires a very intense heat to fuse it ; on which account, it can only be brought into the shape of tools and uten sils by hammering. This high degree of infusibility would deprive it of the most valuable property of metals, namely, the uniting of smaller masses into one, if it did not possess another singular and ad vantageous property, which is found in no other platina ; namely, that of welding. In a white beat, iron ap pears as if covered with a kind of tarnish; and in this state, if two pieces be applied together, they will adhere, and may be perfectly united by forging. Iron is thought to be the only substance in na ture, which has the property of becom ing magnetical. It is highly probable, from the great abundance 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, be fore this negative proposition, which con fines magnetism to iron, can be admitted as proved.
When iron is exposed to the action of pure water, it acquires weight by gradual oxplation, and hydrogen gas escapes: this is a very slow operation. But if the steam water be made to pass through a red hot gun-barrel, or through an ig sited copper or glass tube, containing iron wire, the iron becomes converted into an oxide, while hydrogen gas passes out at the other end of the barrel. The action of air, assisted by heat, converts iron into a black wade, containing twen ty-five of oxygen. By the action of strong er heat this becomes a reddish brown ox ide, containing forty-eight of oxygen. The yellow rust, formed when iron is long ex posed 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 thir, black ; the fourth, or maxi mum, red. Thenard admits only three, the white, green, and red.
The concentrated sulphuric acid scarce ly 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 di rect 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, wifh .27 of oxygen, which is of a pale green, not al tered 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.