142 



IRON. 



crystals are in the form of right oblique-anglei 

 prisms, considerably modified by replacements ; frac- 

 ture, conchoidal ; lustre, vitreous ; colour, severa 

 shades of green passing into white ; streak, white ; 

 semitransparent and translucent ; brittle ; hardness, 

 that of gypsum ; specific gravity, 1-83 ; taste, sweet- 

 ish-astringent and metallic. It consists of 



Oxide of iron, 

 Sulphuric acid. 

 Water, 



25 T 

 28-0 

 43-4 



It is easily soluble in water, and the solution becomes 

 black on being mixed with tincture of galls. II 

 exposed to the open air, it soon becomes covered 

 with a yellow powder, which is persulphate of iron. 

 Before the blowpipe, it becomes magnetic, and col- 

 ours glass of borax green. In most instances, it is 

 produced by the decomposition of other minerals, 

 particularly of iron pyrites and magnetic iron pyrites; 

 and the crystallized varieties are rarely found, except 

 in those places where artificial heaps of these sub- 

 stances have been formed. It is also found incrusting 

 slate rocks, and dissolved in the waters of certain 

 mines. 



Treatment of the Ores. Of the fifteen species of 

 iron ore just described, but four are employed for 

 obtaining metallic iron and steel, viz., magnetic 

 iron ore, specular iron ore, brown iron ore, and car- 

 bonate of iron. The metallurgical details belonging 

 to the treatment of these ores, cannot be described 

 within the limits of the present work. 



When the iron stone lies in a stratum or vein 

 between two strata of clay, not more than thirty 

 feet below the surface of the earth, it is obtained 

 by sinking a pit, at first, of a diameter of eight feet, 

 and deepened until the ore is reached where the 

 pit is undermined, until the diameter at the bottom 

 becomes twice that at the top. When all the ore is 

 taken out of this pit, another is dug similar to the first, 

 and near it ; so that when the second pit is exca- 

 vated, the bottom of the two will meet. In digging 

 the second pit the earth is thrown into the first, and 

 thus one pit is made and another filled, until the 

 whole vein is exhausted. When the iron stone lies 

 deeper it is extracted in the same way as coal, and 

 as they frequently occur in the same district, one 

 engine serves to drain and draw for both ore and coal. 



The first step after the ore has been taken from 

 the vein, is to calcine the stones ; a process techni- 

 cally called roasting. This consists in the applica- 

 tion of a moderate heat, whereby the more volatile 

 components of the ore, such as sulphur, arsenic, &c. 

 are expelled. This is effected by spreading upon 

 the ground a stratum of coals to a depth of about 

 eight inches, ten feet long, and eight broad ; over 

 which is laid a layer of iron stone, to a depth of 

 about six feet, interspersed with small cinders and coke 

 dust, and covered with small coals. The coals being 

 set fire to, combustion will go on for nearly a month, 

 when the cementation is completed. It is not uncom- 

 mon to perform the roasting process in a kiln, the 

 coal and iron stone being put in at the top, and the 

 roasted ore taken out at the bottom. Care is 

 requisite in conducting the process of roasting, for if 

 the heat be too intense, or too long applied, then will 

 the metal partially melt and the pieces cake together, 

 and if on the other hand the heat be too little, all 

 the extraneous matter, such as the water, sulphur, &c., 

 will not be expelled, when the iron stones must be 

 thrown aside, as unfit for the future processes in the 

 manufacture. The iron stone of this country usually 

 contains a sufficiency of carbonaceous matter to 

 carry on the roasting after the fuel has been ignited ; 

 but the ores of the continent contain less carbon, and 

 therefore require proportionally more fuel for their 



((mentation. On the continent and in America, iron 

 ore is most commonly roasted with wood and char- 

 coal. When the roasting is performed with charcoal 

 alone, a layer of the ore is laid on the ground, then 

 a layer of charcoal, and so on alternately, the iron 

 stone layers being each about nine inches, and the 

 charcoal about six, until the height of the bed be seven 

 feet. It is better, however, to lay a stratum of wood 

 below the ironstone. When the roasting is complet- 

 ed, the ore becomes friable, rough to the touch, not 

 at all vitreous, but full of fissures. The ore by the 

 power of cementation, sustains a loss of weight of 

 from twenty to fifty per cent. ; according to the 

 quality of the ore. The iron stones thus prepared 

 are called by the workmen mine. 



The next operation is the conversion of the roasted 

 ore into metal, by the application of strong heat in a 

 furnace; which process is called smelting. As will be 

 readily understood after what we have said on the 

 ores of iron, they commonly consist of an oxide of 

 the metal combined with some earthy matter, in very 

 various proportions. If these ores were fused alone, 

 the chemical student will at once perceive, that they 

 would be formed into glasses, the properties of which 

 will vary with the composition of the ore, but 

 retain no metallic character. The method of pro- 

 ceeding, therefore, must be to intermix the iron stones 

 with such substances as during the process of fusion, 

 will combine with the oxygen and earthy matter of 

 the ore, and leave the metal free. From the great 

 affinity of carbon for oxygen, forming carbonic acid 

 gas, charcoal, or some other carbonaceous substance, 

 is selected as the proper substance for separating 

 the metallic base from the oxygen ; and the nature of 

 the other substances to be employed in separating 

 the earthy matter of the ore, will be determined by 

 the species to which that earthy matter belongs. 

 The earths mixed with the iron, may be either 

 calcarious, silicious, or aluminous : these exist in 

 different proportions, in different ores, and it should 

 be the first object of the iron manufacturer, to select 

 such earthy matter as a flux, that when combined with 

 the earthy matter of the iron stone, a glass will be 

 formed, and the metallic base of the ore left free. 

 Sometimes the combination of several kinds of ore, 

 will produce a congeries of earths that of themselves 

 will form an excellent flux but this, in the ordinary 

 course of manufacture, never occurs, so that some 

 flux, such as lime, is always employed. 



The strong affinity of carbon for oxygen, as before 

 remarked, points it out as the best substance for 

 separating the oxygen from the iron. In Russia and 

 Sweden, and even in some parts of England, char- 

 coal is employed, and it undoubtedly is best for 

 making that kind of iron that is to be formed into steel. 

 For many years past, almost the only ore in Britain 

 that has been smelted with charcoal, has been the 

 red ore of Lancashire, which being extremely rich, the 

 product of smelting can be calculated upon with 

 certainty. The abundance of coal in this country, in 

 those districts where iron stone is found, determines 

 our iron makers to employ coke from its cheapness; 

 coal when properly coked, yields a very considerable 

 proportion of carbonaceous matter, and bears a 

 strong resemblance to charcoal. When coke was 

 first introduced instead of charred wood, it was 

 made, by merely piling the coals in a heap, which 

 being ignited, were allowed to burn until sufficiently 

 coked, when they were covered with ashes and sand 

 to prevent any further combustion. In many places 

 in Wales, this plan is still pursued. From thirty to 

 forty tons of coals, are piled in a heap, as loose and 

 open as possible. Small coals being spread on the 

 surface to give a level appearance. It is then ignited 



