IRON 



87 



out, the lime combines with the clay-like impurities of 

 the ore to form a slag, and the molten iron sinks to 

 the bottom of the furnace where it is drawn off through 

 holes into molds. These molds are called ' ' pigs, ' ' from 

 which the iron gets its name of pig iron. 



Courtesy of American Steel <C- Wire Co. 



Fig. 37. Bessemer converters In which pig iron is made into 

 steel. The view on the right shows the inside of a converter ; the 

 middle one shows a converter in action throwing sparks of burning 

 steel particles into the air. The converter on the left is discharging 

 the finished steel. 



Three forms of iron. The three forms of iron known 

 to commerce are cast iron, wrought iron, and steel. 

 Each kind is truly iron, though having very widely 

 differing physical properties. Pure iron is practically 

 unknown. The different kinds contain carbon and 

 small amounts of other substances in composition. 



