212 IRON 



to keep the fire in their furnaces alight, and from the earliest 

 time some sort of bellows was used. To-day the blast furnace 

 has taken the place of the ancient bellows. 



A modern blast furnace is a great hollow iron tower (some- 

 times as high as 100 feet) lined with firebrick. Near the 

 bottom of this tower are pipes called tuyeres (French tuyau, 

 a pipe), through which a blast of hot air is driven at a pressure 

 varying from 8 to 20 Ib. per square inch, and at a temperature 

 of 800 to 1,100 C. (In the Black Country they call these 

 tuyeres, twyers, or two irons.) 



Into the furnace are put iron ore, or ' mine V coke, and 

 limestone. As before explained, the oxygen of the iron ore 

 unites with the carbon, and the iron is set free, though some 

 of the carbon unites with the iron. The lime mixes with 

 some of the various other impurities and form slag or cinder, 

 which being lighter than the molten iron, floats on top of it. 

 This slag is let out from a hole in the furnace, and lower down 

 the iron is run off from another hole into moulds made of 

 sand. The pieces of new cast-iron in the moulds are called 

 pigs, and the iron is called pig-iron. Each pig weighs about 

 one hundredweight. The iron still contains a good deal of 

 carbon and other impurities and is very brittle. 



Cast-iron articles are obtained by melting together various 

 qualities of pig-iron, mixed with some scrap iron, and then 

 casting it into sand-moulds of the shape of the article required. 

 It can stand great heat, but is still rather brittle. 



Wrought Iron. Pig-iron is put into a reverberatory furnace, 

 i.e. a furnace in which the fuel is in a separate compartment 

 from the iron. The flame from the coal passes through the 

 compartment containing the iron. The roof of this compart- 

 ment slopes downwards and the flame is beaten down on to 



1 Often the ironstone or ore is heaped up in beds or ' rucks ' about 

 4 feet high, 20 to 50 feet wide, and 100 or more feet long, and is burned or 

 calcined in the open air, the carbon, hydrogen, and sulphur contained in 

 the ore in some cases contains sufficient fuel to burn the whole bed ; these 

 and other impurities are thus separated from the mass, the residue being 

 the ' mine ' or iron in its first stage of manufacture, and a varying percentage 

 of ashes containing silica, &c. 



