k l m are pieces of cast iron, for confining the fire in front, that is towards the side where the workman stands; o is the level of the floor of the works; p a copper tuyère; it is situated 41⁄2 inches above the bottom a, slopes 5 degrees towards it, and advances 4 inches into the hearth or fire-place, where it presents an orifice, one half inch in horizontal length, and one inch up and down; q the nose pipes of two bellows, like those represented in [fig. 602.], and under [Silver]; the round orifice of each of them within the tuyère being one inch in diameter. r is the lintel or top arch of the tuyère, beneath which is seen the cross section of the pig of cast iron under operation.
For the production of natural steel, a white cast iron is preferred, which contains little carbon, which does not flow thin, and which being cemented over or above the wind, falls down at once through the blast to the bottom of the hearth in the state of steel. With this view, a very flat fire is used; and should the metal run too fluid, some malleable lumps are introduced to give the mass a thicker pasty consistence.
If the natural steel be supposed to contain too little carbon, which is a very rare case, the metal bath covered with its cinder slag, is diligently stirred with a wooden pole, or it may receive a little of the more highly carburetted iron. If it contains the right dose of carbon, the earthy and other foreign matters are made progressively to sweat out, into the supernatant slag. When the mass is found by the trial of a sample to be completely converted, and has acquired the requisite stiffness, it is lifted out of the furnace, by the opening in front, subjected to the forge hammer, and drawn into bars. In Sweden, the cast-iron pigs are heated to a cherry-red, and in this state broken to pieces under the hammer, before they are exposed in the steel furnace. These natural steels are much employed on the Continent in making agricultural implements, on account of their cheapness. The natural steel of Styria is regarded as a very good article.
Wootz is a natural steel prepared from a black ore of iron in Hindostan, by a process analogous to that of the Catalan hearth, but still simpler. It seems to contain a minute portion of the combustible bases of alumina and silica, to which its peculiar hardness when tempered, may possibly be ascribed. It is remarkable for the property of assuming a damask surface, by the action of dilute sulphuric acid, after it has been forged and polished. See [Damascus] and [Steel].
[Fig. 605.] is the German forge-hammer; to the left of 1, is the axis of the rotatory cam, 2, 3, consisting of 8 sides, each formed of a strong broad bar of cast iron, which are joined together to make the octagon wheel. 4, 5, 6, are cast-iron binding rings or hoops; made fast by wooden wedges. b, b, are standards of the frame work e, l, m, in which the helve of the forge hammer has its fulcrum near u. h, the sole part of the frame. Another cast-iron base or sole is seen at m. n is a strong stay, to strengthen the frame-work. At r two parallel hammers are placed, with cast-iron heads and wooden helves. s is the anvil, a very massive piece of cast iron. t is the end of a vibrating beam, for throwing back the hammer from it forcibly by recoil. x y is the outline of the water-wheel which drives the whole. The cams or tappets are shown mounted upon the wheel 6, g, 6.
Analysis of Irons.—Oxidized substances cannot exist in metallic iron, and the foreign substances it does contain are present in such small quantities, that it is somewhat difficult to determine their amount. The most intricate point is, the proportion of carbon. The free carbon, which is present only in gray cast iron, may, indeed, be determined nearly, for most of it remains after solution of the metal in acids. The combined charcoal, however, changes by the action of muriatic acid into gas and oil; sulphuric acid also occasions a great loss of carbon, and nitric acid dissipates it almost entirely. Either nitre or chloride of silver may be employed to ascertain the amount of carbon; but when the iron contains chromium and much phosphorus, the determination of the carbon is attended with many difficulties.
The quantity of sulphur is always so small, that it can scarcely be ascertained by the weight of the precipitate of sulphate of barytes from the solution of the iron in nitro-muriatic acid. The iron should be dissolved in muriatic acid; and the hydrogen, as it escapes charged with the sulphur, should be passed through an acidulous solution of acetate of lead. The weight of the precipitated sulphuret shows the amount of sulphur, allowing 13·45 of the latter for 100 of the former. In this experiment the metal should be slowly acted upon by the acid. Cast iron takes from 10 to 15 days to dissolve, steel from 8 to 10, and malleable iron 4 days. The residuum of a black colour does not contain a trace of sulphur.
Phosphorus and chromium are determined in the following way. The iron must be dissolved in nitro-muriatic acid, to oxygenate those two bodies. The solution must be evaporated cautiously to dryness in porcelain capsules, and the saline residuum heated to redness. A little chloride of iron is volatilized, and the remainder resembles the red-brown oxide. This must be mixed with thrice its weight of carbonate of potash, and fused in a platinum crucible; the quantity of iron being from 40 to 50 grains at most.