242 



METALS. 



of a light green color. But it may be otherwise col- 

 ored to suit the taste, and cast into slabs, columns, ar- 

 chitectural and parlor ornaments of great beauty. 

 The process by which its brittleness is removed, and 

 the slag adapted to the above uses, has not been made 

 public. 



599. CAST IRON The pig or cast iron, 



Give the com- . . 



position and as it is called, which is thus obtained from 



P c r aTiron f the furnace > is not P ure iron > but a con > 



pound of iron with carbon. It has ob- 

 tained four or five per cent, of this element from the 

 coal with which it was reduced. The addition of 

 carbon to its composition causes iron to melt more 

 readily. But for its absorption, the metal would not 

 have become sufficiently soft to flow from the fur- 

 nace. Carbon has also the opposite property of mak- 

 ing iron harder and more brittle when cold. Castings 

 of agricultural implements and other objects, are made 

 by remelting the pig iron, and pouring it into moulds 

 of the required shape. 



600. WROUGHT IRON. Wrought iron is 



How is 



wrought iron made from cast iron, by burning out its 

 made? carbon. This done in what is called a 



reverberatory furnace, such 

 as is represented in the fig- 

 ure. The carbon is burned 

 out by the surplus air of the 

 flame, which is made to play 

 upon the molten iron. Prom 

 the constant stirring which is essential, such a furnace 

 for refining iron is called a puddling furnace. The 



