IRON 989 



The slag, from its inferior specific gravity, forms a crust on the surface on the metal : 

 its separation is facilitated by throwing cold water in large quantities on the fluid 

 mass immediately that the entire charge has left the refinery. This sudden chilling 

 of the metal makes it exceedingly brittle, so that it can be broken into smaller pieces 

 by heavy hammers, for the subsequent operation of puddling, The refined metal is 

 very white, hard, and brittle, and possesses in general a fibrous radiated texture ; or 

 sometimes a cellular, including a considerable number of small spherical cavities, like 

 a decomposed amygdaloid rock. The loss of iron in the refinery process is very large, 

 varying from 10 to 20 per cent. In the Welsh iron works, 1 ton of white iron takes 

 from if to 2 hours to refine, the consumption of coke being from 6 to 8 cwts., and the 

 loss about 3 cwts. Grey iron takes from 7 to 9 cwts. of coke per ton, the time required 

 to refine being from 2 to 3 hours, and the loss of iron per ton 4 cwts. The pig-iron to 

 be decarburised in the refinery is frequently mixed with rich silicates (forge cinders), 

 and occasionally with oxides of iron, the object being to protect the melted metal in 

 some degree from the oxidising effects of the blast, and to react on the carbon which 

 it contains. The quantity employed depends on the degree to which the pig-iron is 

 carburised. The crude iron, from which wrought iron of the best quality is produced, 

 is that possessing a medium degree of carburation, or what is generally termed grey 

 pig-iron. White iron, which possesses an inferior degree of fluidity to grey pig-iron, 

 and which comes as it is termed more rapidly to nature, is that quality which is most 

 generally employed in the manufacture of wrought iron, especially when the conversion 

 is effected in the single operation of boiling in the puddling furnace ; but this species 

 of pig-iron being the result of imperfect re-actions in smelting, is always more impure 

 than grey iron obtained from the same materials, and does not produce wrought iron 

 of the best quality. 



The coke employed in the refinery should be as free as possible from shale, and 

 should contain only a low percentage of ash ; it should especially be free from sul- 

 phuret of iron, which it often contains in considerable quantity, as it is found that 

 nearly the whole of this sulphuret enters into combination with the metal, and does 

 not pass off in the slags. 



Kefineries are sometimes worked on hot fluid iron, run direct from the hearth of 

 the blast-fur nace % a considerable saving, both of time and fuel, being hereby effected. 

 Various proposals have been patented for the employment of fluxes to assist in the re- 

 moval of the impurities of cast iron, both in the refining and puddling furnaces. Thus Mr. 

 Hampton patented, in 1855, a flux, prepared by slaking quicklime with the solution of 

 an alkali, or alkaline salt. MM. Du Motay and Fontaine propose, in a patent secured in 

 1856, to purify and decarbonise iron in the refining and puddling furnace, by the em- 

 ployment of fluxes prepared from the scoriae of the puddling furnace, from oxides of iron 

 and silicates or carbonates of alkalis, or other bases. Mr. Pope (1856) proposes to add 

 the residue obtained by the distillation of Boghead or Torbane mineral to such fuel as is 

 employed in the refining of iron. Mr. Sanderson, of Sheffield (1855), employed for the 

 refining of iron such substances as sulphate of iron, capable of disengaging oxygen 

 or other elements, which will act upon the silicium, aluminium, &c., contained in the 

 metal. These and various other schemes have been suggested with the object of lessening 

 the enormous waste which pig-iron undergoes on its passage through the refinery ; for as 

 the process is at present conducted, the partial elimination of the carbon, sulphur, phos- 

 phorus, &c., is only effected at the expense of a large quantity of iron, which is oxidised 

 by the blast, and passes in the form of silicate into the slag ; the desideratum is the dis- 

 covery of some method of reducing the oxide of iron, and substituting for it some other 

 base, which will form with silica a sufficiently fusible silicate. Mr. Blackwell suggests 

 that the decarburation of pig-iron might be effected by remelting it in a cupola-furnace, 

 either alone, or with minerals containing nearly pure oxides of iron ; the oxide of iron 

 would be reduced by the carbon of the pig-iron, while the silicates of the fuel, with 

 the silica, alumina, and other easily oxidisable alloys eliminated from the crude 

 iron, would be separated in the form of fusible earthy glass. The employment- of 

 steam as a purifying agent for crude iron has been patented by several persons. Mr. 

 Nasmyth in 1854 obtained a patent for the treatment of iron in the puddling furnace 

 with a current of steam, which being introduced into the lower part of the iron, passes 

 upwards, and meeting with the highly heated metal, undergoes decomposition, both 

 elements acting as purifying agents. The steam employed is at a pressure of about 5 

 pounds per square inch, and passes into the metal through a species of hollow rabble, 

 the workman moving this about in the fused metal until the mass begins to thicken, 

 which occurs in from five to eight minutes after the introduction of the steam ; the 

 steam-pipe is then removed and the puddling finished as usual. 



The advantages are said to consist in the time saved at each heat or puddling 

 operation f from ten to fifteen minutes) ; the very effective purification of the metal ; 

 and the possibility of treating highly carbonised pig-iron at once in the puddling 



