It occurs native in sufficient quantity to constitute one of the chief
ores of the metal. It also occurs combined with sulphur (as in
argentite), with sulphur and antimony (as in stephanite or brittle
silver ore, and in pyrargyrite or ruby silver), and with copper,
sulphur, antimony, and arsenic, as in polybasite. Chloride of silver
occurs native as horn silver or kerargyrite. Silver is found in the ores
of other metals, such as fahlerz, which sometimes contains from two to
ten per cent. of the metal, and galena, which is an important source of
it; in fact, galena is never found entirely free from silver. It is
present also in greater or less quantity in the ores of copper and zinc.
Silver dissolves readily in nitric acid, forming silver nitrate. It only
forms one family of salts, and of these the chloride and nitrate are of
chief importance to the assayer. The formation of the chloride of silver
on the addition of hydrochloric acid or a soluble chloride to the nitric
acid solution, serves for the recognition and separation of silver. The
precipitated chloride is white (becoming violet on exposure to light),
insoluble in nitric acid, soluble in ammonia, hyposulphite of soda, or
concentrated solutions of chlorides. The best confirmatory test is made
by wrapping the precipitate in a little sheet lead, and cupelling, when
the silver will be left in the metallic state, and is easily recognized.
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