MANGANESE, IKON, COBALT, NICKEL, CHROMIU3I. 245 



used. Ore and fuel are dumped in at the top, the material 

 gets hotter and hotter as it descends, reduction of the ore 

 takes place, and the melted iron settles down into the lower 

 part of the tall furnace, whence it is run off from time to 

 time on the inclined plane to the left. The arrangement 

 for the blast of air, by means of which the combustion is 

 accelerated, is seen at the right hand in the lower portion 

 of the picture. 



341. Cast Iron. This pig-iron is used for making castings. 

 It is fit for this purpose from having had combined with it 

 in the process above described about five per cent, of car- 

 bon. It is from this addition that the metal runs so readily 

 into the moulds. If it were pure iron, or if it contained 

 much less carbon, it would not do this. Besides, this com- 

 bination of carbon and iron, as it passes from the liquid to 

 the solid state in cooling, increases a little in bulk, and so 

 fills out the mould in every line. This is owing to the crys- 

 tallization which takes place every where in it. Cast iron 

 is very brittle, and is not in the least malleable or ductile. 

 Its hardness and its capability of being cast in moulds fit it 

 for a great variety of uses, while its brittleness unfits it for 

 many uses to which other modifications of this metal are 

 especially adapted. 



342. 'Wrought Iron. This is obtained from cast iron by 

 taking advantage of the fact that carbon is more combusti- 

 ble than iron. The carbon is mostly burned out of the cast 

 iron. It is done by exposing the iron to a current of air 

 when it is strongly heated in what is called a reverberatory 

 furnace. The result is that the oxygen of the air unites 

 with the carbon of the cast iron, and passes off as carbonic 

 oxide. Fig. 96 (p. 246) will give you an idea of the con- 

 struction of the furnace. The upper figure is a vertical, and 

 the lower a horizontal section. At a is the fire, and b is the 

 ash-pit ; at c is a wall called the bridge, which serves to direct 



