IRON 935 



The earthy and foreign substances, besides modifying the quality of the iron, by 

 their partial reduction play another and more important part in the economy of iron- 

 Bmelting in procuring the so-called slag, cinder, or scoriae, that is a fusible product usually 

 more or loss glassy, -which is formed by the addition of appropriate solvents or fluxes, 

 in order that the otherwise infusible earthy matters such as quartz, sand, clay, at 

 present in the ore, and the ash of the fuel may be separated and removed from 

 the reduced metal, which would otherwise be incapable of coalescing into a connected 

 mass, whether by fusion or otherwise. These fluxes, according to the nature of the 

 process, may be either lime, magnesia or other alkaline bases, alumina, or in some 

 cases the oxides of iron or manganese. The heat required for this operation is 

 very considerable, and requires a considerable consumption of fuel above that 

 necessary for the reduction and fusion of the metal. A further and still larger 

 source of expenditure of heat is due to the fact that when the carbonic acid produced 

 in the reduction of the ore is exposed to carbon at a high temperature it is partially 

 reduced with the production of carbonic oxide, which escapes, carrying a large propor- 

 tion of the total heating power of the fuel, unless special arrangements are adopted 

 for utilising it. 



Practically, therefore, the reactions of iron-smelting may be expressed synoptically 

 in the following manner : 



MATERIALS PRODUCTS 



Iron Ore . Oxides of iron .... _^ Iron : with some carbon, sili- 



Silica -^ ^-- "/ con, phosphorus. 



Alumina and other earthy matters- 

 Phosphate of Lime 

 Sulphides . , 



Flaxes . Carbonate of Lime 

 Aluminous minerals 

 Protoxide of Iron . 



Slag: silica, alumina, and 

 lime, protoxide of iron 

 and manganese, and sul- 

 phide of calcium. 



Protoxide of manganese 



Fuel . . Carbon *^ - ^^r Gases : carbonic acid, and 



Earthy matters of Ash . . ^^^"^ carbonic oxide, nitrogen, 



^^-^^ and water. 



Blast . . Air, with some water-vapour 



Production of malleable iron -directly from the ore. The simplest processes of iron- 

 smelting are those in which malleable iron is produced directly from the ore. They 

 are still practised to a considerable extent in India and other parts of the East, and 

 were formerly universally employed in Europe, but now they have become almost 

 extinct ; the latest representatives being the Catalan and Corsican forges, and the 

 Stiick-Ofen, or lump-furnace, which is to be found in one or two places in eastern 

 Europe. These processes consist essentially in the exposure of pure ore to the action 

 of heat in small blast-furnaces, which may be either open hearth-fires, like a smith's 

 forge, or have low shafts or stacks, a few feet high, in which the ore and fuel are 

 charged alternately, the combustion being urged by a blast of air introduced through 

 one or more nozzles below. The operation is continued until a lump of malleable iron 

 is formed in the bottom of the furnace from the reduction of the ore, or a portion of 

 the ore ; the remainder being employed in fluxing the silica and other earthy matters 

 both in the ore and the ash of the fuel. This is effected by a partial reduction of the 

 ore from peroxide of iron which is chemically indifferent to silica at a high tempera- 

 ture to the state of protoxide, which combines readily with it ; forming a fusible 

 slag or cinder at the welding temperature of iron. The spongy and slightly -alloyed 

 mass of iron so produced is then consolidated by hammering, which compacts it to a 

 solid mass, the liquid cinder being expelled by the blows of the hammer. The same 

 reaction takes place in all processes where no special fluxes are added for fluxing the 

 silica, the flux being essentially silicates of protoxide of iron, infusible at compara- 

 tively low temperatures ; and, under these conditions, only wrought iron can be 

 produced, the ore not being kept in contact with carbon for a sufficiently long time 

 to produce cast iron, except to a very small extent. 



The following are the principal processes in which malleable iron is produced 

 directly : 



1. The Catalan and Corsican forge. 



2. The German and American bloomary fires. 



3. The Stiick-Ofen or lump-furnace. 



4. The Chenot or retort-furnace. 



5. The Siemens' direct-furnace. 



Of these the first and second are conducted in open fires, and differ only in details of 

 manipulation ; the former using the ore partly in the state of lumps, which are reduced, 



