IRON, NICKEL, COBALT 



489 



through a squeezer and then put through the rolls. The result- 

 ing bars are repeatedly cut, " piled " in a bundle, reheated, and 

 rolled. These treatments, and the presence of a little slag dis- 

 tributed through the mass, give wrought iron the valuable prop- 

 erties which distinguish it from all other iron products, namely 



FIG. 112 



its fibrous structure and its extreme toughness. On account of 

 these properties it is used for anchors, chains, and bolts. . It is 

 drawn into wire, and, when heated, can be cut, shaped, and 

 welded under the hammer. The impurities having been greatly 

 reduced (to 0.1 or 0.2 per cent), this iron is much less fusible than 

 cast iron, and is used for fire bars. 



Crucible Steel. Steel contains 0.75 to 1.5 per cent of carbon, 

 and is freed as far as possible from other impurities. Small lots, 

 for special purposes, are made in clay (or graphite and clay) 

 crucibles in melts of 60 to 100 pounds. The charge in Sheffield 

 consists of blister steel, i.e., carburized Swedish wrought iron of 

 varying carbon content. The modern method is to melt " melt- 

 ing bar," a very pure open hearth steel with charcoal, or even 

 pure pig iron. Crucible steel is used in making razors (1.5 per 

 cent C), tools (1 per cent C), dies (0.75 per cent C), pens, needles, 

 and cutlery. 



Electric heating (e.g. in the Heroult furnace), recently intro- 

 duced, permits the steel maker, first to wash the molten iron with 



