144 METALS AND THEIR COMBINATIONS. 



others, and form a number of oxides, the higher of which show, 

 in some cases, decided acid properties, as, for instance, chromic 

 or manganic oxides. 



Occurrence in nature. Among all the heavy metals, iron is 

 both the most useful and the most widely and abundantly dif- 

 fused in nature. It is to be found, though usually in but 

 small quantities, in nearly all forms of rock, clay, sand, and 

 earth ; its presence in these being generally indicated by their 

 color (red, reddish-brown, or yellowish-red), as iron is the most 

 common of all natural, inorganic coloring agents. It is also 

 found, though in small quantities, in plants, and in somewhat 

 larger proportions in the animal system, chiefly in the blood. 

 In the metallic state iron is scarcely ever found, except in the 

 meteorites or metallic masses which occasionally fall upon our 

 earth from the universe. 



The chief compounds of iron found in nature are: 



Ked hematite, ferric oxide, Fe 2 O 3 . 

 Magnetic iron ore, ferrous- ferric oxide, FeO.Fe 2 3 . 

 Spathic iron ore, ferrous carbonate, FeCo 3 . 

 Iron pyrites, bisulphide of iron, FeS 2 . 



The carbonate and sulphate are sometimes found in spring 

 waters, which, when containing considerable quantities of iron, 

 are called chalybeate waters. Finally, iron is also a constituent 

 of some organic substances, which are of importance in the 

 animal system. 



Manufacture of iron. There is no other metal that is manu- 

 factured in such immense quantities as iron, the use of which 

 in thousands of different tools, machines, and appliances is 

 highly characteristic of our present age. Iron is manufactured 

 from the above-named oxides or the carbonate by heating with 

 coal, limestone, and sand in large blast furnaces, which have a 

 somewhat cylindrical shape, and are constantly fed from above 

 with a mixture of the substances named, while hot air is forced 

 into the furnace through suitable apertures from the side below. 

 The chemical change taking place in the upper and less heated 

 part of the furnace is a deoxidation of the ferric oxide or ferrous 

 carbonate by the carbon : 



Fe 2 O 3 + 3C = SCO + 2Fe ; 

 FeC0 3 + C = CO + C0 2 + Fe. 



