Metallurgy of Iron. 15 



The interior of the blast furnace maybe divided into four dis- 

 tinct regions ; the first and uppermost is that in which the mix- 

 ture of ore and fuel is roasted ; the water and volatile matters are 

 there driven off, and the whole is gradually heated to redness. In 

 the second region, immediately below the last, the already ignited 

 ore is reduced to the metallic state by the ascending current of 

 carbonic oxyd gas; the metal thus produced is however in the 

 condition of malleable iron, nearly pure and very difficultly fusi- 

 ble ; but in the third region it combines with a portion of car- 

 bon, and is converted into the fusible compound known as cast 

 ^ron. In addition to this, small portions of manganese, alumi- 

 nium and silicium, whose combinations are always present in the 

 contents of the furnace, become reduced, and alloying with the 

 iron, affect very much its quality for better or worse. Cast iron 

 generally contains besides these, small portions of sulphur, phos- 

 phorus, and other impurities less important. 



In the fourth and lowest region of the furnace, which is near to 

 the blast, the heat becomes more intense, the carburetted metal 

 melts, together with the earthy matters, and both collect at the 

 bottom of the crucible upon what is called the hearth, from which 

 the two are drawn off from time to time. The cast iron thus ob- 

 tained is very fusible, but brittle, and is far from possessing those 

 precious qualities which belong to malleable iron or steel. 



To convert the cast metal into malleable iron, it is exposed to a 

 process which is called puddling, and consists essentially in fusing 

 it in a furnace of a peculiar kind, where the metal is exposed to 

 the action of the air. The carbon, manganese, silicium, and other 

 foreign matters, are thus burned away, and the once liquid metal 

 is converted into a pasty granular mass, which is then consolida- 

 ted . under hammers or rollers, and drawn out into bars of soft 

 malleable iron. 



To convert into steel the soft iron thus obtained, it is heated for 

 a long time in close vessels with powdered charcoal, a small quan- 

 tity of which is absorbed by the iron, and penetrating through the 

 mass changes it into steel. This process is known by the name of 

 cementation. The change is however irregular and imperfect ; it 

 is therefore necessary to break up these bars of cemented or blis- 

 tered steel, as it is called, and after assorting them according to 

 their quality, either to weld them together, or to melt down each 

 sort by itself in large crucibles. The metal is then made into in- 

 gots, and forms cast steel, which is afterwards wrought under th e 

 hammer and drawn out into bars. 



