CHAPTER XX 

 Iron, Aluminum, and Their Compounds 



178. Occurrence of Iron. Iron is found in nature 

 mainly in the form of its oxids, hematite, Fe 2 O 3 , and 

 magnetite, Fe 3 O 4 . It also occurs in the form of carbonate, 

 FeCO 3 , pyrite, FeS 2 , and brown iron ore or basic hydroxid. 

 It is found in the soil in combination with silicon and 

 other elements, forming double silicates. It enters into 

 the composition of all plant and animal bodies and takes 

 an essential part in plant growth and animal life. Some 

 waters contain carbonate of iron which, like calcium 

 carbonate, is soluble in the presence of carbon dioxid ; 

 upon exposure to the air, the iron is precipitated as hy- 

 droxid, forming a brown deposit. Iron takes an im- 

 portant part in industrial operations and its chemistry 

 has been more extensively studied than that of any other 

 element. 



179. Reduction of Iron Ores. Only iron ores of a high 

 degree of purity are ready, as mined, for the blast-furnace. 

 Magnetic iron ore is concentrated and separated from its 

 impurities by magnetic concentrators. The blast-fur- 

 nace used for the production of cast iron is constructed 

 of brick and is shown in Fig. 59. Ore, coke, and flux, 

 usually limestone, are mixed in the right proportion and 

 introduced into the top of the furnace. The flux is used 

 to separate the impurities, forming a fusible slag which 

 is largely calcium silicate. Hot air is forced into the 

 furnace by means of blowing engines, through tuyeres. 



