5-16 IRON ORES. 



greatly affect the methods of reducing it. Its particles agglu- 

 tinate at a full red heat, although the pure metal is nearly in- 

 fusible. The oxides of iron, which are easily reduced by com- 

 bustible matter, thus yield in the furnace a spongy metallic 

 mass, which may admit of being compacted by subsequent 

 heating and hammering, if the oxide has originally been free 

 from earthy and other foreign matter. Such probably was 

 everywhere the earliest mode of treating the ores of iron, and 

 we find it still followed among rude nations. But iron is also 

 singular in forming, at an elevated, temperature, a fusible com- 

 pound with carbon (cast iron), the production of which facili- 

 tates the separation of the metal from every thing extraneous in 

 the ore, and is the basis of the only method of extracting iron, 

 extensively practised. 



The ore of iron most abundant in the primary formations, 

 is the black oxide or magnetic ore, which affords the most 

 celebrated and valuable irons of Sweden and the north of Eu- 

 rope ; but of which the application is greatly circumscribed from 

 its not being associated with coal. In the secondary and ter- 

 tiary formations, the anhydrous and hydrated peroxide of iron, 

 red and brown hematite, occur occasionally in considerable 

 quantity, often massive, reniform, and quite pure, at other 

 times pulverulent and mixt with clay. It is employed to some 

 extent in England, in the last condition, but only for the pur- 

 pose of mixing with the more common ore. The crystallized 

 carbonate of iron, or spathic iron, is smelted in some parts of 

 the continent, and gives an iron often remarkable for a large 

 proportion of manganese. The celebrated iron of Elba is de- 

 rived from specular or oligistic iron, a crystallized peroxide. 

 But the consumption of all these ores is inconsiderable, compared 

 with that of the clay iron-stone of the coal measures. This is 

 the carbonate of the protoxide of iron mixt with variable quan- 

 tities of clay and carbonates of lime, magnesia, etc. ; it is often 

 called the argillaceous carbonate of iron. It is a sedimentary 

 rock wholly without crystallization, resembling a dark coloured 

 limestone, but of higher density, from 2.936* to 3.471, and not 

 effervescing so strongly in an acid. It occurs in strata, beds 

 or bands, as they are also named, from 2 to 10 or 14 inches in 

 thickness, alternating with beds of coal, clay, bituminous schist, 

 and often limestone. The proportion of iron in this ore, varies 

 considerably, but averages about 30 per. cent, and after it has 



