. Introduction to inorganic chemistry . e surviving sulphide of iron makes it brittle when hot ( red-short )r and unsuitable for forging. Wrought iron should containonly per cent of carbon. The above operations are now largelyperformed by machinery. Steel. — This is a variety of iron almost free from phosphorus,sulphur, and silicon. Tool steel contains per cent of carbon,structural steel per cent, and mild steel per cent or evenless. Steel combines the properties of cast and wrought iron, beinghard and elastic, and at the same time available for forging and weld-ing
. Introduction to inorganic chemistry . e surviving sulphide of iron makes it brittle when hot ( red-short )r and unsuitable for forging. Wrought iron should containonly per cent of carbon. The above operations are now largelyperformed by machinery. Steel. — This is a variety of iron almost free from phosphorus,sulphur, and silicon. Tool steel contains per cent of carbon,structural steel per cent, and mild steel per cent or evenless. Steel combines the properties of cast and wrought iron, beinghard and elastic, and at the same time available for forging and weld-ing when the proportion of carbon is low. Steel is made largely by the Bessemer process. The molten castiron is poured into a converter (Fig. 106) and a blast of air (A) Isblown through it. The oxidation of the manganese, carbon, silicon,and perhaps a little of the iron gives out sufficient heat to raise thetemperature of the mass above the melting-point of wrought required proportion of carbon is then introduced by adding pure. 760 INORGANIC CHEMISTRY cast iron, spiegel iron, or coke, and the contents, first the slag, andthen the molten steel, are finally poured into molds by turning theconverter. When the cast iron contains much phosphorus, the oxideof this element is reduced again by the iron as fast as it is formed bythe blast. In such cases a basic lining containing lime and magnesiatakes the place of the sand and clay lining of the ordinary Bessemerconverter, and a slag containing a basic phosphate of calcium is pro-duced. This modification constitutes what is known as the Thomas-Gilchrist process. The slag ( Thomas-slag ) when pulverized formsa valuable fertilizer (cf. p. 605). In the Siemens-Martin, or open hearth process, the cast iron ismelted in a saucer-shaped depression lined with sand, and scraps ofiron plate (for dilution) and haematite, or some other oxide ore, arethen added in proper proportions. The materials are heated with gasfuel for 8-10 hours unti
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