i88 



GENERAL SCIENCE 



in the present-day production of aluminum metal by elec- 

 trolysis. Bauxite, an ore of aluminum, contains 50 per cent 

 or more of alumina (A^Os) . This is separated from the other 

 material in the ore by a series of chemical changes relatively 

 inexpensive. Alumina is insoluble in water, and its melting 

 point is too high for practical purposes. However, a mineral 

 known as cryolite and imported in large quantities from 



FIG. 60. Manufacture of aluminum. A, A', a lining of carbon which 

 serves as the cathode in the electrolytic action. B, melted cryolite which 

 dissolves the oxide of aluminum as it is added from time to time. The tem- 

 perature of the "bath" is kept so high by the passage of the electric current 

 that the aluminum metal as liberated collects in a molten state. 



Greenland not only melts at a relatively low temperature, 

 but when in a molten state it readily dissolves alumina. 

 When a powerful electric current is sent through such a 

 solution, the alumina is decomposed. Oxygen is given off 

 at the anode and pure aluminum metal at the cathode. 

 The heat developed in the passage of the current through the 

 electrolyte keeps the material in the bath molten, and the 

 aluminum metal is drawn off from time to time in a liquid 

 form. 



