30 DEPARTMENT OF AGRICULTURE GEORGIA. ]316] 



purest natural form is in meteorites, in which it is alloyed 

 with nickel. 



The ores from which iron is chiefly obtained are the 

 magnetic oxide, and red and brown hematites (oxides), 

 which, in some localities, are found in great masses. The 

 iron is easily reduced from these, by heating, at a very 

 high temperature, with coal and limestone, in furnaces 

 made for the purpose, The impurities of the iron remain 

 in the slag, the oxygen is driven off, and the melted iron, 

 containing carbon, collects at the bottom of the furnace, 

 and is run off in the form of pig iron. 



The usual forms of iron in use are cast, wrought, and 

 steel. 



Cast Iron contains much carbon, and is merely pig iron 

 remelted and run into moulds made in the desired form. 

 These moulds are made of a mixture of sand and other 

 material. 



Wrought Iron is made from cast, or pig, iron by burning 

 out some of the carbon, and drawing out the iron between 

 huge rollers, into rods, bars, or plates. Thus treated, it 

 becomes fibrous in structure, and will not break so easily 

 as the cast iron. It is hardened by cooling rapidly, and 

 softened by cooling slowly. 



Steel contains more carbon than wrought iron, and has 

 less than cast, and is more difficult to manufacture. Its 

 value depends upon its tempering qnality. 



Case-hardened is a term applied to those articles, such as 

 cheap knives, whose surface only is steel, while the inte- 

 rior of the blade is soft iron. As soon as the steel surface 

 is worn off, the soft iron is exposed, and will take no edge. 



Welding. Wrought iron and steel become soft without 

 melting, at certain temperatures, and two pieces may, by 

 hammering, be united together. That they may unite per- 

 fectly, it is necessary that their surfaces be free from iron 

 rust, or oxide of iron, which is formed in heating, and 

 hence some substance is used to protect them. Borax 



