IRON, COBALT, AND NICKEL 827 



Cast iron is a material which is either suitable for direct application 

 for casting in moulds or else for working up into wrought iron and 

 eteel. The latter principally differ from cast iron in their containing 

 less carbon thus, steel contains from 1 p.c. to 0*5 p.c. of carbon and 

 far less silicon and manganese than cast iron ; wrought iron does 

 not generally contain more than 0'25 p.c. of carbon and not more than 

 0-25 p.c. of the other impurities. Thus the essence of the working up 

 of cast iron into steel and wrought iron consists in the removal of the 

 greater part of the carbon and other elements, S, P, Mu, Si, &c. This 

 is effected by means of oxidation, because the oxygen of the atmosphere, 

 oxidising the iron at a high temperature, forms solid oxides with it ; 

 and the latter, coming into contact with the carbon contained in the 

 cast iron, are deoxidised, forming wrought iron and carbonic oxide, 

 which is evolved from the mass in a gaseous form. It is evident that 

 the oxidation must be carried on with a molten mass in a state of 

 agitation, so that the oxygen of the air may be brought into contact 

 with the whole mass of carbon contained in the cast iron, or else the 

 operation is effected by means of the addition of oxygen compounds 

 of iron (oxides, ores, as in Martin's process). Cast iron melts much 

 more easily .than wrought iron and steel, and, therefore, as the carbon 

 separates, the mass in the furnace (in puddling) or hearth (in the 

 bloomery process) becomes more and more solid ; .moreover the degree of 

 hardness forms, to a certain extent, a measure of the amount of carbon 

 separated, and the operation may terminate either in the formation of 

 steel or wrought iron. 10 In any case, the iron used for industrial pur- 

 yields a portion of the substance dissolved. The separation of carbon in the form of 

 graphite on the conversion of white cast iron into grey is never complete, however slowly 

 the separation be carried on; part of the carbon remains in combination with the 

 iron in the same state in which it exists in white cast iron. Hence when grey cast iron is 

 treated with acids, the whole of the carbon does not remain in the form of graphite, but a 

 part of it is separated as hydrocarbons, which proves the existence of chemically-combined 

 carbon in grey cast iron. It is sufficient to re-melt grey cast iron and to cool it quickly to 

 transform it into white cast iron. It is not carbon alone that influences the properties of 

 cast iron ; when it contains a considerable amount of sulphur, cast iron remains white 

 even after having been slowly cooled. The same is observed in cast iron very rich in 

 manganese (5 to 7 p.c.), and in this latter case the fracture is very distinctly crystalline 

 and brilliant. When cast iron contains a large amount of manganese, the quantity of 

 carbon may also be increased. Crystalline varieties of cast iron rich in manganese are in 

 practice called ferro-manganese (p. 810), and are prepared for the Bessemer process. 

 Grey cast iron not having an uniform structure is much more liable to various changes 

 than dense and thoroughly uniform white cast iron, and the latter oxidises much more 

 slowly in air than the former. White cast iron is not only used for conversion into wrought 

 iron and steel, but also in those cases where great hardness is required, although it be ac- 

 companied by a certain brittleness , for instance, for making rollers, plough- shares, &c. 



10 This direct process of separating the carbon from cast iron is termed puddling. It 

 is conducted in reverberatory furnaces. The cast iron is placed on the bed of the 

 furnace and melted ; through a special aperture, the puddler stirs up the oxidising raasa 



