186 BLACKSMITHING 



drates or carbonates of iron. Ores appearing as siil 



poor, as it is difficult to remove the sulphur. However, 



weathering ore allowing it to stand in the open will change 



sulphides to sulphates, which are largely dissolved out by 



rain. 



One of the richest ores is magnetite, or black oj^e, which, 

 when pure, contains 72.4 per cent iron jind 27.6 per cent oxy- 

 gen. Hematite, or red ore, when pure, contains 70 per cent 

 iron^and 30 per cent oxygen. 



161. Pig Iron is made bv crushing ore^to uniform size and 

 legating it in a blast furnace until it can be drawn off at the 

 bottom in a molten condition. The blast furnace is a long, 

 vertical cylindrical shaft which is fed from the top with ore, 

 fuel or flux. Air under pressure is introduced at the bottom 

 for purposes of combustion. The metal when molten is 

 drawn off at the bottom, usually twice during twenty-four 

 hours, and run into sand molds or iron chilled molds, 

 "pigs" of cast iron. Cast 11011 lias 4 01 irfrer cent of impuri- 

 ties such as carbon, sulphur, phosphorus, manganese and sui- 

 con.. The amount of carbon present determines whether the 

 iron is gray or white. If the greater part of the carbon is free 

 as graphite, the iron is known as gray. If the greater amount 

 of carbon present is combined, the iron is known as white. 

 White iron, or iron with low combined carbon, is soft_ 



162. Wrought Iron is pure carbonless iron produced in jt 

 pasty condition. It is the converse of cast iron, as it is fairly 

 tenacious and extremely ductile. When heated, it can be 

 welded better than any other iron or steel. When heated to 

 full red and quenched in water, it will not harden. 



Wrought iron may be produced from iron ore in one opera- 



