anged into oxides and the
silver remains behind unaltered.

~Amalgamation process.~ In some localities the old amalgamation
process is used. The silver ore is treated with common salt and
ferrous compounds, which process converts the silver first into
chloride and then into metallic silver. Mercury is then added
and thoroughly mixed with the mass, forming an amalgam with the
silver. After some days the earthy materials are washed away
and the heavier amalgam is recovered. The mercury is distilled
off and the silver left in impure form.

~Refining silver.~ The silver obtained by either of the above processes
may still contain copper, gold, and iron, and is refined by "parting"
with sulphuric acid. The metal is heated with strong sulphuric acid
which dissolves the silver, copper, and iron present, but not the gold.
In the solution of silver sulphate so obtained copper plates are
suspended, upon which the pure silver precipitates, the copper going
into solution as sulphate, as shown in the equation

Ag_{2}SO_{4} + Cu = 2Ag + CuSO_{4}.

The solution obtained as a by-product in this process furnishes most of
the blue vitriol of commerce. Silver is also refined by electrolytic
methods similar to those used in refining copper.

~Properties of silver.~ Silver is a heavy, rather soft, white metal, very
ductile and malleable and capable of taking a high polish. It surpasses
all other metals as a conductor of heat and electricity, but is too
costly to find extensive use for such purposes. It melts at a little
lower temperature than copper (961 deg.). It alloys readily with other heavy
metals, and when it is to be used for coinage a small amount of
copper--from 8 to 10%--is nearly always melted with it to give it
hardness.

It is not acted upon by water or air, but is quickly tarnished when in
contact with sulphur compounds, turning quite black in time.
Hydrochloric acid and fused alkalis do not act upon it, but nitric acid
and hot, concentrated sulphuric acid dissolve it with ease.

[Illustration: Fig. 88]

~Electroplating.~ Since silver is not acted upon by water or air,
and has a pleasing appearance, it is used to coat various
articles made of cheaper metals. Such articles are said to be
silver plated. The process by which this is done is called
electroplating. It is carried on as follows: The object to be
plated (such as a spoon) is attached to