106 IRON. 



FerrO'prussiale qfirorij called prussian blue, used 

 as a pigment. 



Iron also combines with sulphur, phosphorus, 

 carbon, chlorine, and iodine. 



Sulphuret of iron, composed of sulphur and iron, 

 is called also pyrites. Iron with carbon forms plum- 

 hago, commonly called blach-lead, used for making 

 pencils. Steel is another compound of iron with 

 carbon. 



The ores of iron consist either of the black ox- 

 ide, which is called the magnetic iron oi^e, the red 

 oxide or the i^ed iro7i ot^e, carbonate of iron, and 

 clay ironstone. 



The iron is separated from these ores by smelting 

 in furnaces, where it is made to flow out into va- 

 rious moulds made in a kind of loam. The first pro- 

 duct is called cast iro7i. It contains some carbon 

 and oxygen ; and, it is thought, also silicium, besides 

 casual impurities. Of this, cannon, pipes, grates, 

 and other articles of cast iron are made. It is of 

 two kinds : "white cast-iron is very brittle ; grey cast 

 iron is less brittle, though not malleable, but may 

 be bored and turned in the lathe. 



To render iron malleable it must be freed from 

 those substances with which it is combined in the 

 crude state. To effect this, it is kept in fusion in 

 a furnace exposed to air and flame, and well stired. 

 The oxygen combines with the carbon, and escapes 

 in the form of carbonic acid gas ; and the earthy 

 matter is vitrified, and rises to the surface as slag. 

 It is then subjected to the action of large hammers 

 and rollers, by which the remainder of the impuri- 

 ties is forced out. It then constitutes bar iron, 

 also called 'wrought iron, fit for manufacturing. 



AVr.ought iron is of a fibrous structure, and is the 

 metal in a pure slate. It is now extremely malle- 



