=336. Steel, character and utility.=—While the limits of our space will not permit us to trace further the development of machine tools, which have been made marvelously efficient in recent years, and while we must also forego a study of the details of iron production, the topic of steel manufacture certainly deserves some consideration. Ordinary cast iron, while strong and hard enough for many purposes, still is brittle by reason of the large proportion of carbon and other impurities which it contains. These impurities may be burned out in the puddling process, and the nearly pure iron thus obtained, called malleable or wrought iron, has a toughness enabling it to resist far greater strains than cast iron can stand. Intermediate between the two irons, and containing one per cent of carbon, more or less, is still another product, steel, which may be made even more tenacious than wrought iron, or even harder than cast iron. Its peculiar property of “taking a temper” is probably known to most readers. The valuable properties of steel have been known and prized for ages, but till well into the nineteenth century it could be used only sparingly; it was commonly manufactured by first making wrought iron, by the tedious process of puddling, and then heating the iron bars in contact with charcoal until they had absorbed the proper amount of carbon. The expense of this process prohibited the use of steel for most purposes; the wrought iron cost $75 a ton and the finished steel $250 or more; and the output would seem to-day inconsiderable. =337. Recent improvements in the manufacture of steel; the Bessemer process.=—Many men have contributed to bring the manufacture of steel to its present efficiency, and we may notice only the names associated with the greatest improvements. An Englishman, Bessemer, patented in 1855 the idea, as simple as it is ingenious, of turning cast iron directly into steel by blowing air through it when melted, and so consuming the excess of carbon. It has not proved possible to make good steel according to Bessemer’s original idea, but with a slight modification his process has been wonderfully successful; in present practice all the carbon is burned out by the air current, and then the requisite amount is added before the metal is poured out. Ore containing a large amount of phosphorus is treated by melting it in a converter lined with lime, which removes this dangerous impurity (“basic process”).