1 98 



GENERAL SCIENCE 



when present in sufficient quantity to warrant profitable 

 extraction of the metal the mixture is called an ore. Com- 

 pounds of iron are widely distributed in soils often giving 

 them a yellow, brown, or reddish appearance. The charac- 

 teristic red of brick and tile is due to oxides of iron. Bricks 

 made from clays free of iron compounds are light yellow in 

 color. 



MILLION TONS 

 65 



IG7O 1875 IBQO 1865 1390 1895 I9OO /905 I9IO 1 

 FIG. 64. Production of iron ore in the United States 1870 to 1914. 



The sulphides are perhaps the most abundant of the iron 

 compounds but are nearly worthless as ores owing to the 

 difficulty in completely ridding the iron from them of all 

 sulphur, a small amount of which makes the iron brittle. 

 Coal mined in certain districts contains iron sulphide, and 

 when burned it gives off very offensive gases as sulphur com- 

 pounds. Iron disulphide (FeS 2 ) as glittering yellow particles 



