MANUFACTURE OF IRON AND STEEL 187 



tion, but this is costly, as the yield is low. Commercially, it 

 is produced by indirect methods, by purification of pig iron, 

 removing impurities by oxidation. This can be done in an 

 open hearth or reverberating furnace, the methods being 

 known as the open-hearth and Bessemer processes, respec- 

 tivglv. 



163. The Open-Hearth Process oxidizes the impurities 

 of the pig iron by means of adding iron ore to a bath of molten 

 pig iron. The fuel is, therefore, in contact with the metal, 

 and the oxygen of the blast combined with the impurities are 

 eliminated as oxides. This is a comparatively slow process of 

 refinement, taking from seven to twelve hours to complete. 

 Its advantages are a fine quality of iron produced and a large 

 amount of material which can be handled at one time. 



164. The Bessemer Process also is an oxidizing one, but 

 the metal and fuel are not in contact. The oxygen is fur- 

 nished by means of a large volume of compressed air blown 

 thru a bath of molten pig iron. The oxygen combines with 

 the carbon to evolve as gases while it combines with other im- 

 purities to form slag. The process requires but a few min^ 

 utes from twelve to twenty. 



165. Steel. It is practically impossible to define steel 

 accurately. It is an alloy of iron and carbon, but as alloys of 

 iron and carbon include cast iron^ this definition is not a 

 technical one. Ordinary steel may be said to be iron con- 

 taining from 0.1 to 2.0 per cent of carbon in combined form 

 which has been subjected to complete fusion and poured into 

 an ingot or mold for the production of forgeable metal. Such 

 a metal steel has the composition of wrought iron, but it 

 has been produced in a steel-melting furnace. 



