988 



IRON 



than whon it contains about ^ of one per cent, carbon. It has also boon proved that 

 a furnace making steel that never runs lower in carbon than of one per cent, 

 lasts from three to four times as long as one that runs the steel down to wrought 

 iron. Therefore it is cheaper to use manganese or ferro-manganoso than spiogel- 

 eisen. 



The Conversion of Crude or Carburiscd Iron into Malleable Iron. This is effected 

 by one or more .operations, which are necessarily of an oxidising nature, the object 

 being to eliminate from the cast iron the carbon in the form of carbonic oxide gas, 

 and the silicon, sulphur, phosphorus, and other foreign bodies in the form of oxidised 

 products, which pass either partially or wholly into the scorise or cinders. The pig- 

 iron is either subjected to a preliminary docarburation in the oxidising blast lH-ar;!i, 

 or 'refinery,' and the operation thus commenced afterwards completed in tho oxi- 

 dising air furnace, or ' puddling furnace ;' or the complete conversion of the mule 

 iron is effected by one operation in the puddling furnace, by tho process called ' boiling.' 

 It is said (Blackwcll) that, at several works abroad, tho attempt to arrest tho progress 

 of decarburation in the puddling or boiling furnace at that point in which the con- 

 version has proceeded only so far as to leave the iron in tho state of steel, or sub- 

 carburet, has been successful, and that a valuable natural or puddled steel, not requiring 

 cementation before conversion into refined or cast steel, has been the result. 



English Method of Refining. The finery furnace is composed of a body of brick- 

 work, about 9 feet square, rising but little above the surface of the ground. Tho 

 hearth, the bottom of which is of millstone grit, placed in the middle, is 2 feet deep; 

 it is rectangular, being in general 3 feet by 2, with its greatest side parallel to tho face 

 of the tuyeres, and it is made of cast iron in four plates. On the side of tho tuyeres 

 there is a single brick wall, on the three sides sheet-iron doors are placed, to prevent 

 the external air from cooling the metal, which is almost always worked under an 

 open shed or in the open air, but never in a space surrounded by walls. The chimney, 

 from 15 to 18 feet high, is supported upon four columns of cast iron ; its lintel is 4 feet 

 above the level of the hearth, in order that the labourers may work without restraint. 

 The air is supplied by the blowing cylinders which supply the blast-furnace, and enter 

 the hearth through 6 tuyeres, so arranged that the current issuing from those on the 

 opposite sides of the crucible are not disposed in the same plane. These tuyeres, like 

 those in the furnaces in which cast iron is made, are provided with double casings, 

 through which a current of cold water is constantly flowing, and each pipe is furnished 

 with a suitable stop valve for regulating the volume of the blast. The tuyeres are 

 placed at the height of the lip of the crucible or hearth, and are inclined towards the 

 bottom, at an angle of from 25 to 30, so as to point upon the bath of melted metal 



as it flows. The quantity of air blown into 

 the fineries is considerable, being nearly 400 

 cubic feet per minute for each finery. The 

 ground plan of a finery is shown in fig. 

 1245, A being the hearth, b the tapping-hole, 

 B the chill mould, and a a a a a a the nozzles 

 of the tuyeres. The operation of refining 

 crude iron is conducted as follows : A fire is 

 lit in the centre of the hearth, which is first 

 urged by a gentle blast; a charge of pig, 

 about 2 tons, is then laid on, and the whole 

 is covered up dome-form with a heap of coke ; 

 the full power of the blast is now turned on, 

 the cast iron melts, and flowing down gradu- 

 ally collects in the crucible, more coke being 

 added as the first quantity burns away. Tho 

 operation proceeds by itself, the melted metal 

 is not stirred about as in some modes of 

 refinery, and tho temperature is always kept 

 high enough to preserve the motel liquid. 

 During this stage the coals are observed con- 

 tinually heaving up: a movement duo in part 

 to the action of tho blast, but in part to 

 an expansion caused in the metal by the discharge of carbonic oxide gas. When all 

 the pig-iron is collected at the bottom of tho hearth, which happens in about two 

 hours, it is blown vigorously for some time longer, tlm tap-hole is opened, and tho 

 fine metal runs out with tho slag into the chili Ti.oulil, <>r pit. as it is called, which has 

 been previously washed with a thin clay liquid, to prevent the refined metal from 

 adhering to its surface. The chill mould is in a prolongation of the tapping-hole ; it 

 is a heavy cast-iron trough, about 10 foot long, 3 feet broad, and 2 to 2 inches deep. 



