208 ANNUAL OP SCIENTIFIC DISCOVERY. 



The first and most important of these objects is effected by bringing a cer- 

 tain measured quantity of oxygen, in the shape of oxides of iron, in contact 

 with the cast iron, so that Avhile the iron is hot the oxygen combines with 

 the carbon, and passes off in the form of carbonic acid gas. The purifica- 

 tion of the cast iron from silica, sulphur, magnesia, etc., is effected by 

 bringing the iron, when it is in a melted state, into contact with the alkaline 

 earths, so that the impurities combine with them, and remain floating on the 

 top of the melted metal. 



In order to effect these two operations at the same time, the pig iron is 

 first melted in a furnace, or ordinary foundry cupola, and then run into a 

 cold water tank, where it is reduced into small granules. The mode in 

 which the granulation is performed is stated to be as follows: The cold 

 water tank has a horizontal wheel placed in it at one end, provided with 

 wooden floats dipping below the surface of the water, and driven at consid- 

 erable speed; the melted metal running into the tank from the furnace, falls 

 on the wheel, which scatters it in a finely divided state towards the deep 

 end of the tank, and it falls to the bottom in the form of small granules. 

 This granulated cast iron is mixed with pulverized oxide of iron and some 

 alkaline earths, and the whole put into the ordinary steel-melting crucibles, 

 and placed in the furnaces, and brought into a fluid state. The degree of 

 hardness of the steel is thus capable of being regulated by the size of the 

 granules, and by the quantity of oxides used. 



The chemical change which takes place in the crucible is as follows: 

 Each granule being surrounded by the pulverized oxides, etc., the dccarbon- 

 i/ation takes place first on the outside of each granule, and so progresses 

 towards the centre as the heat increases, the oxygen in the ores combining 

 with the carbon in the granules and passing off as carbonic acid gas; if, 

 therefore, during the process, the granule could be examined, it would be 

 found that the outside of each is entirely deprived of its carbon, the next 

 portion partially decarbonized, and the centre not decarbonized at all; so 

 that each granule would be composed of pure wrought iron, steel, and cast 

 iron. By increasing the heat, the cast iron centre portion of the granule 

 first becomes fluid, and the granule bursts, and falls by its own weight to 

 the bottom of the crucible. At the same time, the earths mixed with the 

 ores melt and rise to the top, forming a layer of scoria or dross floating on 

 the surface of the melted iron. Each granule of melted metal has therefore 

 in falling to pass through the rising scoria; and it is in the passing through 

 that the combination of the impurities of the metal with the alkaline earths 

 takes place, so that the decarbonized iron, on reaching the bottom of the 

 crucible, is cleansed from all impurities. The heat continuing to increase, 

 melts the outside portions of the granules, and the whole is reduced to one 

 homogeneous fluid mass in the crucible, which is then ready for being poured 

 into the ingot mould. The iron contained in the oxides mixes at the same 

 time with the fluid mass, and yields about six per cent, more of east steel 

 than the weight of granules put into the crucible. 



The oxides employed in this process are iron ores of the finest quality, 

 such as spathose and hematite, which arc previously calcined and pulver- 

 ized. The proportion of the oxide to the granulated iron is according to 

 the hardness of steel required, say from twenty to thirty per cent. ; the 

 greater the quantity of the oxide employed, the greater the decarbonization, 

 and consequently the softer will be the steel produced. 



The process is attended with the following advantages : A rapid manu- 



