820 PRINCIPLES OF CHEMISTRY 



often found in aqueous or stratified formations, and are knovrn as 

 brown hcematites ; they generally have a brown colour, form a yellowish- 

 brown powder, and have no metallic lustre but an earthy appearance. 

 They easily dissolve in acids and diffuse through other formations, espe- 

 cially clays (for instance, ochre) ; they sometimes occur in reniform and 

 similar masses,, evidently of aqueous origin. Such are, for instance, 

 the so-called bog or lake aiid v peat ores found at the bottom of marshes 

 and lakes, and also under and in peat beds. This ore is formed from 

 water' containing ferrous carbonate in solution, which, after absorbing 1 

 oxygen, deposits ferric hydroxide. In rivers and springs, iron is found 

 in solution as ferrous carbonate through the agency of carbonic 

 acid : hence the existence of chalybeate springs containing FeC0 3 . 

 This ferrous carbonate, or siderite, is either found as a non -crystalline 

 product of evidently aqueous origin, or as a crystalline spar called 

 spathic iron ore. The reniform deposits of the former are most re- 

 markable ; "they are called spherosiderites, and sometimes form whole 

 strata in the Jurassic and carboniferous formations. Magnetic 

 iron ore, Fe 3 O 4 = FeO,Fe 2 O 3 , in virtue of its purity and practical 

 uses, is a very important ore ; it is a compound of the ferrous and 

 ferric oxides, is naturally magnetic, has a specific gravity of 5-1, 

 .crystallises in well-formed crystals of the regular system, is with diffi- 

 culty soluble in acids, and sometimes forms enormous masses, as, for 

 instance, Mount Blagodat in the Ural.. However, in most cases for 

 instance, at Korsak-Mogila (to the north of Berdiansk and Nogaiska, 

 near the Sea of Azov), or at Krivoi Rog (to the west of Ekaterinoslav)-^. 

 the magnetic iron ore is mixed with other iron 'ores. In the Urals, the 

 Caucasus (without mentioning Siberia), and in the districts adjoining the 

 basin of the Don, Russia possesses the richest iron ores in the world. 

 To the south of Moscow, in the Governments of Toula and Nijni- 

 novgorod, in the Olonetz district, and in the Government of Orloffsky 

 (near Zinovieff in the district of Kromsky), and in many other places, 

 there are likewise abundant supplies of iron ores amongst the deposited 

 aqueous formations ; the siderite of Orloffsky, for instance, is dis- 

 tinguished by its great purity. 4 



and composition Fe^H 2 4 , or FeHO.j that is, one of oxide of iron to one of water, 

 Fe^Os,!!./); frequently found as brown ironstone, forming a dense mass of fibrous, 

 reniform deposits containing SFejO^SH^O that is, having a composition Fe 4 H 6 O 9 . In 

 bog ore and other similar ores we most often find a mixture of this hydrated ferric oxide 

 with clay and other impurities. The specific gravity of such formations is rarely as high 

 as 4-0. 



4 The ores of iron, similarly to all substances extracted from veins and deposits, are 

 worked according to mining practice by means of vertical, horizontal, or inclined 

 shafts which reach and penetrate the veins and strata containing the ore deposits. 

 The mass of ore excavated is raised to the surface, then sorted either by hand or else in 



