MEECUEY, SILVEE, GOLD, AND PLATINUM. 267 



metals from substances with which they happen to be min- 

 gled. Silver and gold are often obtained by this process, 

 which is called amalgamation. Suppose, for example, that 

 we have some quartz with gold finely scattered through it. 

 The quartz is first powdered, and then the powder is agi- 

 tated with mercury, which seeks out, as we may say, all 

 the gold, and unites with it to form an amalgam. Suf- 

 ficient mercury is used to have the amalgam liquid, so that 

 it may be readily separated from the powder. This liquid 

 amalgam, which is really a solution of gold in mercury, is 

 poured upon buckskin or a closely woven cloth, which al- 

 lows most of the mercury to run through, leaving the gold 

 alloyed with a small part of the mercury. The remaining 

 mercury is driven off by heat, and the gold is obtained 

 pure. The dust of jeweler-shops is often treated in this 

 way to save the gold which has been scattered by filing 

 and other processes. 



378. Silver. This metal stands in regard to hardness be- 

 tween gold and copper, and requires to be alloyed with 

 copper to make it wear well In the coinage of the United 

 States the proportion of copper is one tenth. Silver is very 

 ductile and malleable. Its polished surface reflects both 

 light and heat better than any other metal, and accordingly 

 it is used for reflectors. The tarnishing which gradually 

 occurs is not from oxidation, but from the formation of a 

 sulphide of silver by the sulphuretted hydrogen which is 

 generally in the air in small quantity. When this gas is 

 present in the air in considerable amount, as in the neigh- 

 borhood of some sulphur springs, silver tarnishes rapidly. 

 It is the sulphur in the egg that discolors the spoon with 

 which you eat it, forming a sulphide. Silver is sometimes 

 found native, but is usually obtained from ores. The most 

 common of its ores is the sulphide called argentite. This 

 occurs abundantly in Nevada. It is sometimes combined 



