Mackintosh's Patent.— A few years ago Mr. Mackintosh, of Crossbaskets, in Lanarkshire, took out a patent for converting malleable iron into steel, by sub jecting it to a stream of carburetted hydrogen gas, evolved from coal under dis tillation. The iron is inclosed in a pot or crucible in the furnace, and when arrived at a proper heat, a stream of gas is directed by a pipe into the crucible, which has another aperture to allow that part of the gas to escape which has not been taken up by the metal. The apparatus for conducting this process will of course admit of various modifications. This invention appears to have reason for its basis ; for it must be evident that in the process of cementation before described, the carbon must have entered into combination in a gaseous state with the iron : the steel made by it was reported to be excellent. Whether experience has proved it to be an economical process, is a point upon which we are not informed.
Mushat's Patent Steel.—The preceding articles are descriptive of three dis tinct modes of preparing steel. First, by the careful refinement of cast-iron ; second, by the stratification of malleable iron with charcoal; and third, by the application of gaseous carbon to the metal. A fourth process, materially dif fering from those, but producing very similar results, and attended with some peculiar advantages, was patented in the year 1800 by Mr. Mushat, the gen tleman whose metallurgical labours we have before noticed. The specification of the patent directs that malleable iron (in scraps or bars) is to be put into a crucible, together with a due proportion of powdered charcoal, or pit coal, plumbago, or any other substance containing the carbonaceous principle, and subjected to an intense heat in an air or blast furnace until the metal is reduced to a fluid state, when it is to be poured out into moulds to form ingots, or any other article that may be required ; which castings will be of a similar nature to the steel produced by cementation. But in those cases when iron ore can be obtained sufficiently rich and free from foreign admixtures, the patentee pro poses to save all the tune and expense attending the tedious operations neces sary for the conversion of such ore, first into cast-iron, and afterwards into bar iron ; for such ore, he observes, being previously roasted or torrified, may be substituted for the malleable iron, and the result will be cast-steel, provided the proper quantity of carbonaceous matter be used, as for the common and ordinary qualities of cast steel. The quantity of carbonaceous matter required, is much less than had been previously supposed to be necessary. In employing wood charcoal, from a seventieth to a ninetieth of the weight of the iron being sufficient ; and when the quantity is increased beyond a seventieth to a sixtieth, or a fortieth of the weight of the iron, the steel becomes so fusible that it may be run into moulds of any shape, and afterwards be capable of being filed and polished. Hence, by casting, may be constructed stoves, grates, kitchen utensils, wheels, mill-work, and a great variety of things which could not be so made by the processes previously in use. By varying the proportions of
the carbonaceous matter, he can make as great a variety in the qualities of the steel, as the various kinds of pig-metal differ from each other. Cast-steel, made in the ordinary way, Mr. Mushat observes, is so volatile when in fusion as not to admit of being run into any shape except straight moulds of considerable diameter; but that steel of such density as to admit of being cast into any form may be produced by his process, by increasing the quantity of charcoal, and fusing the matter as before directed. To produce qualities of steel softer than is usually manufactured by the common processes, he uses a very small propor tion of charcoal, sometimes so little as a two-hundredth part of the weight of the iron ; and he states that steel produced with any proportion of charcoal not exceeding the one-hundredth part, will generally be found to possess every property requisite to its being cast into those shapes which require great elas ticity, strength, and solidity ; and will also be generally found capable of sus tainmg a white heat, and of being welded together like malleable iron.
Tilted Steel.—As blistered steel in its crude state is applicable to but few purposes, it is moderately heated in a furnace, and subjected to the action of a tilt hammer, which strikes about 700 blows per minute : this operation increases its tenacity and solidity, and adapts it to numerous uses.
Shear SteeL—This name was given to a steel that was first made by Crowley, of Newcastle, about sixty years ago, in imitation of a peculiar kind of bar steel that we formerly imported from Germany. Crowley, however, stamped his production with the figure of a pair of shears, to indicate its suitable application. The process of making it at Sheffield, where the manufacture of this and all other kinds of British steel is conducted on an immense scale, is as follows :—The bars of blistered steel are broken into pieces of from one to two feet in length, which are then piled up into bundles or faggots of a size and weight adapted to their subsequent applications. The faggots are then taken up by means of a long bar having a ring at the end, into which one extremity of the faggot is inserted; and by means of the bar as a handle, a workman puts it into a reverberatory furnace, whence, after it is brought to a welding heat, it is taken out and placed under a heavy hammer, by which it is drawn out into a bar ; this bar is then divided, the pieces laid together, brought again to a welding in the furnace, and then under the hammer, or by rolling, reduced to the size required. By this process the steel bus lost much of its previous brit tleness, and has acquired a uniform texture, which adapts it to the manufacture of a great variety of edge tools and other purposes to which it was before unsuited. Various qualities of shear steel are made, distinguished by the terms half-shear, single-shear, and double-shear, according to the number of times it has been cut, piled, welded, and drawn out.