MANGANESE, IRON, COBALT, NICKEL, CHROMIUM. 241 



titles, and by the chemist in his laboratory. The most 

 striking property of iron is its magnetic power. 



337. Importance and Abundance of Iron. As iron can be 

 applied to a greater variety of uses than any other metal, 

 it is very abundant. Stockhardt says of it, " If gold is 

 called the king of metals, iron must be deemed by far the 

 most important and useful subject in the metallic realm. It 

 is not only converted into swords and cannons, but into 

 plowshares and chisels, and into a thousand other imple- 

 ments and machines, from the simple coffee-mill to the won- 

 derful steam-engine. It is the ladder upon which the arts 

 and trades have mounted to such an extraordinary height. 

 It is the bridge upon which we now glide over mountains 

 and valleys with the rapidity almost of magic." Besides 

 all this, it is present in all soils and in almost all plants, and 

 is an ingredient of the blood in a large portion of the ani- 

 mal world. Although we understand but little in regard 

 to its influence upon plants and animals, we have sufficient 

 facts to show that, small as its amount is, it is as essential 

 in the chemical operations of the living world as are com- 

 mon salt, lime, and some other substances. 



338. Oxides of Iron. There are three oxides of iron : the 

 monoxide, FeO ; the sesquioxide, Fe 2 O 3 ; and the so-called 

 magnetic oxide, Fe 3 O 4 . The first named has not been pre- 

 pared in a pure state owing to the rapidity with which it 

 takes up oxygen and passes to the sesquioxide. It occurs 

 in nature in combination with acids, forming important 

 minerals. Ferrous sulphate, or green vitriol ; ferrous car- 

 bonate, or spathic iron ore ; ferrous sulphide, FeS 2 , also 

 called iron pyrites, are the most abundant. On adding am- 

 monium hydrate to a solution of a ferrous salt, a white pre- 

 cipitate forms consisting of ferrous hydrate, but this imme- 

 diately begins to change in color, passing through green 

 to brownish red by absorption of oxygen from the air, and 



L 



