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Page:Popular Science Monthly Volume 19.djvu/832

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process had been a long time in use, however, before it occurred to any one to fuse the steel and make it homogeneous. This was done by Huntsman, about 1760.

By all the processes we have so far reviewed, good steel could be produced, but only in small quantity and at great expense. The applications of steel were, in consequence, very limited; in fact, practically, its use was confined to implements with a cutting edge.

In 1845 Heath patented a process which, had it been successful, would have given him the power of producing steel in quantity. He proposed to melt scrap-iron in a bath of molten pig iron in a reverberatory furnace heated by jets of gas. There were two conditions wanting in this method, which caused it to be a failure, viz., a sufficiently high temperature, and the power easily to regulate the character of the gases employed. Nevertheless, in this suggestion is to be found the germ of one of the two most important processes of the present day.

The dominant idea in treating cast-iron for steel had always been to refine the metal by the action of atmospheric air, and this was effected by causing a current of air to impinge upon the surface of the metal, by means either of a blowing apparatus or the drawing action of a chimney-stack. What more natural than that it should occur to some one to refine iron by blowing air into it, instead of merely on to its surface? We find that this idea did occur to several persons, widely separated, in the year 1855.

In this year a patent was taken out by John Gilbert Martien for refining iron, by forcing air through it as it flowed from the blast furnace, or cupola, along runners to the puddling-furnace. The process, as detailed in the patent, was impracticable, and showed internal evidence of not having been worked out on a manufacturing scale. Just after this patent was taken out, we find George Parry, of the Ebbw Yale Works, making the experiment of forcing air through molten cast-iron, on the bed of a reverberatory furnace, by means of perforated pipes imbedded in the fire-clay bottom. Vigorous action is said to have taken place; but the metal, through an accident, escaped from the furnace, and the further trial of the process was discouraged by the managing director. Two or three months after these experiments, Henry Bessemer took out his now celebrated patent for the production of cast-steel by blowing air through molten cast-iron; it should be clearly borne in mind that he had been, for a considerable time previously, engaged in experiments on the subject. He first carried out his process in crucibles, placed in furnaces, and so arranged that the contents could be tapped from the bottom into molds. Steam or air, either separately or together, and by preference raised to a high temperature, was forced down into the crucible through a pipe. The patent goes on to state that steam cools the metal, but air causes a rapid increase in its temperature, and it passes from a red to