Steel is manufactured from pure malleable iron by the process called cementation; the Swedish iron from the Dannemora mines marked with the letter L in the center of a circle, and called "Hoop L," is almost exclusively used; irons of a few other marks are also used for second-rate kinds of steel. The bars are arranged in a furnace that consists of two troughs, about fourteen feet long, and two feet square; a layer of charcoal powder is spread over the bottom, then a layer of bars, and so on alternately; the full charge is about ten tons, the top is covered over first with charcoal, then sand, and lastly with the waste or slush from the grind-stone trough, applied wet, so as to cement the whole closely down, for the entire exclusion of the air.

A coal fire is now lighted below and between the troughs; and at the end of about seven days, the bars are found to have increased in weight the one hundred and fiftieth part, by an absorption of carbon, and to present when broken, a fracture more crystalline, although less shining than before. The bars, when thus converted, arc also covered with blisters, apparently from the expansion of the minute bubbles of air within them; this gives rise to the appellation blistered-steel.

The continuance of the process of cementation introduces more and more carbon, and renders the bars more fusible, and would ultimately cause them to run into a mass, if the heat were not checked; to avoid this mischief a bar is occasionally withdrawn and broken to watch the progress; and the work is complete when the cementation has extended to the center of the bars; the conversion occupies, with the time for charging and emptying the furnace about fourteen days.

A very small quantity of steel is employed in the blistered state, for welding to iron for certain parts of mechanism, but not for edge tools; the bulk of the blistered steel is passed through one of the two following processes, by which it is made either into shear-steel, or cast-steel.

Shear-steel is produced by piling together six or eight pieces of blistered-steel, about thirty inches long, and securing the ends within an iron ring, terminating in a bar about five feet long by way of a handle. They are then brought to a welding heat in a furnace, and submitted to the helve or tilt hammer, which unites and extends them into a bar called shear-steel, from its ha ring been much used in the manufacture of shears for cloth mills and also German steel, from having been in former years procured from that country. Sometimes the bars are again cut and welded, and called double-shear steel, from the repetition.

This process of working, as in the manufacture of iron, restores the fibrous character, and retains the property of welding: the shear steel is close, hard, and elastic; it is much used for tools, composed jointly of steel and iron; its superior elasticity also adapts it to the formation of springs, and some kinds are prepared expressly for the same under the name of spring-steel.

We are indebted to Mr. Huntsman for the process of manufacturing the cast-steel, for which he took out a patent: he justly attained a celebrated name for its manufacture, and his process is still followed almost without change. In making cast-steel, about twenty-six or twenty-eight pounds of fragments of blistered-steel selected from different varieties, are placed in a crucible made of Stourbridge clay, shaped like a barrel, and fitted with a cover, which is cemented down with a fusible lute that melts after a time the better to secure the joining. Either one or two pots are exposed to a vivid heat, in a furnace like the brass-founders' air-furnace, in which the blistered-steel is thoroughly melted in the course of three or four hours; it is then removed by the workman in a glowing state, and poured into a mould of iron, either two inches square for bars, or about six by eighteen inches, for rolling into sheet steel For large ingots the contents of two or more pots are run together in the same mould, but it requires extremely great care in managing the very intense temperature, that it shall he alike in both or all the pots.