132 



METALS AND THEIR COMBINATIONS. 



H. Davy discovered methods for the 

 separation of these metals from 

 their oxides. 



Valence of metals. 



Univalent. 



Lithium, 



Potassium, 



Sodium, 



Silver. 



Bivalent. 



Barium, 



Calcium, 



Strontium, 



Magnesium, 



Cadmium, 



Zinc, 



Copper, 



Mercury. 



Trivalent. 

 Aluminum, 

 Bismuth, 

 Gold. 



Sexivalent. 

 Molybdenum. 



Bi- and sexivalent. 

 Chromium, 

 Cobalt, 

 Iron, 



Nickel. 



Bi- and quadrivalent 

 Lead, 

 Platinum, 

 Tin. 



Tri- and quinquivalent. 

 Antimony, 

 Arsenic. 



Occurrence in nature. 



a. In a free or combined state. 



| Almost exclusively in the metallic state. 

 Platinum, 



Silver, I Ag metalg Qr gulphides . 



Mercury, 



Bismuth, generally metallic, also as oxide and sulphide. 



Copper, rarely metallic ; chiefly as sulphide, oxide, and carbonate. 



6. In combination only. 



Potassium, 



Sodium, \ Chiefly as chlorides or silicates. 



Lithium, 



