The Romance of Modern Chemistry

METALS, COMMON AND UNCOMMON The oxide is mixed with coke, which contains a high proportion of carbon and the mixture is heated in a furnace, a flux, such as lime, being added to remove the earthy matter from the ore in a fluid form. At the high temperature of the furnace the carbon in the coke depiives the metal of its oxygen and carries it off in the form of carbon monoxide or carbon dioxide. The metal is thus obtained in the free state, and is generally run out of the furnace in a molten condition, while the earthy material that was in the ore is separated along with the flux as slag. 1 'erhaps the commonest example of such a metallurgical operation is iron-smelting, a process which may be seen at work in many parts of Great Britain. In the case of iron it is desirable to inform ourselves a little more about what is done with the crude metal obtained from the blast furnace, and it is well that we should understand the chemical differences between the various kinds of iron which are of technical importance, namely, cast-iron, wiought-iron, and steel. The different properties which characterise these varieties of the metal show in a very interesting manner how the behaviour of a pure substance is modified by the presence of small quantities of foreign matter. In a description, given in an earlier chapter, of the attempts which have been made to manufacture diamonds it was said that molten iron dissolves carbon. Since now in the process of iron-smelting the fused metal has been in contact with coke in the furnace, it is not surprising that the crude metal which is taken out of the furnace contains an appreciable amount of carbon, as much as 3 to 5 per cent. ; it is run into moulds, and is then known as cast or pig-iron. Careful examination has shown that 68