COPPER 175 



There are different kinds of iron for different purposes. The 

 iron which forms the kitchen stove is different from that which 

 makes the horseshoe, and from the iron or steel which composes 



! the Pullman coach. The pig iron which comes from the blast 



1 furnace is not pure, but contains about 5 per cent of carbon, 

 and small quantities of phosphorus and sulphur. Pig iron which 

 contains so much carbon cannot be forged or hammered into 

 different shapes, but must be poured into molds. When it 



I solidifies, it expands and fills up the mold, and makes excellent 

 castings. The phosphorus and sulphur present in pig iron make 

 it brittle ; hence while cast iron is strong, it cannot be used 



I in places where it is subject to great shock. 



The forms of iron that can endure the greatest shock are 



1 wrought iron and steel, both of which are obtained from cast 



) iron. Wrought iron is made by heating cast iron in a furnace 

 until it has lost practically all of its impurities. It is tough 



i but soft, and is easily hammered or welded into any desired shape, 

 such as horseshoes and links of chains. It can be rolled into 

 sheets and plates and drawn out into wires. 



Steel is more important than either cast iron or wrought 

 iron. It contains practically no impurities except carbon ; and 

 it contains more carbon than wrought iron, but less than cast 

 iron. Steel is stronger and more durable than either of the 

 other forms of iron. It is so elastic that it forms the finest 

 springs in watches, and it is so resistant that it is used for the 

 cutting edge of tools and machines. 



Copper. The earliest implements and utensils used by man 

 were of stone, and the long years in which he depended solely 

 upon stone weapons and stone devices make up what is known 

 as the stone age. Gradually man learned to fashion crude 

 utensils from copper, a reddish metal which he found scattered 

 over the earth. The hard, tough, flexible copper was easily 

 softened by heat and fashioned into forms suitable for primi- 



