SULPHATE OF IRON. Green vi triol, copperas. Names given to the com bination of sulphuric acid with protoxido of iron. It is made up 1 Equivalent sulphuric acid 40 1 Equivalent protoxide iron 28 7 Equivalents of water 63 It is generally made from the bitumin. oils shales of or near the coal beds. The shales of the midland counties of New York afford the materials for making sul phate of iron ; and in the coal regions along the slope of the Alleghanies it is found abundantly, and is found crystal lized in eastern Tenessee.
Sulphate of iron is generally made from combinations of iron with brimstone, called iron pyrites, or, in common lan guage, copperas stones, gold stones, or horse gold. These stones being collected in great quantity, are laid in heaps about two feet thick, upon a clay floor, sur rounded by boards, that direct the rain water that falls upon them, to flow into a cistern. The copperas-stones are five or six years before they yield any consider-. able quantity of strong liquor. In time, the stones turn to a vitriolic earth, which swells and ferments like leavened dough. When a bed is come to perfection, it is refreshed every four years, by laying fresh copperas-stones on the top. When a new bed is made, the work is hastened by mixing a good quantity of the old fer mented earth with the new stones.
When the copperas-liquor is 14 penny weights strong it is esteemed rich. It will dissolve the shell off an egg in three minutes, and produce holes in any clothes on which it may fall.
The liquor is boiled in leaden vessels, old iron is put in at first, and more added as fast as it dissolves. The boiling is esteemed finished when a little of the li quor, put into an earthen-ware dish, and cooled, deposits crystals on the sides. In some works, iron is added to the liquor in the cistern • and of course, less , is required in the boiling. is ano ther kind of pyrites, which contains a double proportion of sulphur ; this sort does not alter by exposure to the weather, until the extra proportion of sulphur is removed, either by roasting in piles, or by distilling in close vessels. There is
also a kind of bituminous earth, that pro duces copperas by exposure to the air, and from which it may be obtained by washing with water in the usual manner. Copperas is also manufactured by dis solving old iron in weak sulphuric acid, at 35° Beaume, and crystallizing the solu tion.
Its color is a bright green, and its taste very astringent. A solution in water, dropped on oak bark, instantly produces a black spot. It is in request with dyers, tanners, and the manufacturers of ink., and, for their use, is artificially prepared from pyrites, which being moistened and exposed to the air a crust is formed upon it, to be dissolved in water, and, from this, crystals of vitriol are obtained by evaporation. Green vitriol is used in dying woollen articles, hats, &a., black, and it is the basis of ink, and used in the manufacture of Prussian blue. Reduced to powder, dried, and mixed with pow der of galls, it forms the dry, portable ink cakes and powders.
When the green sulphate is exposed to the air it is decomposed, and gradually converted into red oxide of iron and per sulphate of iron. When copperas is heated in a crucible, or over a lamp, it is converted into the red oxide or peroxide of iron.
An excellent powder for applying to razor-strops, is made by igniting together in a crucible equal parts of well-dried copperas and sea salt. The heat must be slowly raised and well regulated, other wise the materials will boil over in a pasty state, and the product will be in a great measure lost. When well made, out of contact of air, it has the brilliant aspect of plumbago. It has a satiny feel, and is a true fer olegiste, similar in composition to the Elba iron ore. It requires to be ground and elutriated ; after which it affords, on an impalpable pow der, that may be either rubbed on a strop of smooth buff leather, or mixed up with hog's-lard or tallow into a stiff cerate.