PROPERTIES OF CAST Inox. The product of the blast-furnace. as already said, is cast iron. As this is the preliminary form of practically all iron for making, both wrought iron and steel, its prop erties require a brief description. Cast iron consists of metallic iron combined with at least per cent. of carbon and smaller percentages of silicon, sulphur, phosphorus. and manganese; the elements other than metallic iron being about per cent. of the whole, though this percentage may vary considerably. Cast iron melts at about I 200' C., and when cold is hard and brittle. It is not malleable or ductile, and cannot be tempered. Of the several elements named, carbon and sili con are of value in steel-making, which is the chief purpose for which cast is produced at the present time; but sulphur and phosphorus are generally highly objectionable. In using the term cast iron here, the chemical' nomenela tore has been retained. The foundryman gener ally gives the name pig iron to the direct prod uct of tile blast-furnace. rind the term cast iron
to the form which pig iron assumes after re melting. For commercial purposes pig iron is graded into several classes. according to the ap pearance of the fracture. This is an unscientific and unsatisfactory method of grading. but it is the one almost always adopted. The different grades are given different names. and these Lames vary in character and significance in dif ferent countries. In the United States the more common grades are: No. I Foundry. No. 2 Foundry, No. 3 Foundry, No. I Soft, No. 2 Soft, Silver Gray, Gray Forge, Mottled, and White. These grades vary in chemical composition, and it is tieing urged by many prominent metal lurgists that chemical composition lie substituted for the appearance of the fracture in distinguish ing between different grades of iron.