ay be smelted with
carbon (coal). The reactions are strictly analogous to those which
occur in the smelting of galena (see LEAD), the carbon reducing any
oxide, either present originally in the ore or produced in the
calcination and the iron combining with the sulphur of the bismuthite.
A certain amount of bismuth sulphate is always formed during the
calcination; this is subsequently reduced to the sulphide and
ultimately to the metal in the fusion. Calcination in reverberatory
furnaces and a subsequent smelting in the same type of furnace with
the addition of about 3% of coal, lime, soda and fluorspar, has been
adopted for treating the Bolivian ores, which generally contain the
sulphides of bismuth, copper, iron, antimony, lead and a little
silver. The lowest layer of the molten mass is principally metallic
bismuth, the succeeding layers are a bismuth copper matte, which is
subsequently worked up, and a slag. Ores containing the oxide and
carbonate are treated either by smelting with carbon or by a wet
process.

In the wet process the ores, in which the bismuth is present as oxide
or carbonate, are dissolved out with hydrochloric acid, or, if the
bismuth is to be extracted from a matte or alloy, the solvent employed
is _aqua regia_ or strong sulphuric acid. The solution of metallic
chlorides or sulphates so obtained is precipitated by iron, the
metallic bismuth filtered, washed with water, pressed in canvas bags,
and finally fused in graphite crucibles, the surface being protected
by a layer of charcoal. Another process consists in adding water to
the solution and so precipitating the bismuth as oxychloride, which is
then converted into the metal.

The crude metal obtained by the preceding processes is generally
contaminated by arsenic, sulphur, iron, nickel, cobalt and antimony,
and sometimes with silver or gold. A dry method of purification
consists in a liquation on a hearth of peculiar construction, which
occasions the separation of the unreduced bismuth sulphide and the
bulk of the other impurities. A better process is to remelt the metal
in crucibles with the addition of certain refining agents. The details
of this process vary very considerably, being conditioned by the
composition of the impure metal and the practice of particular works.
The wet refining process is more tedious and expensive, and is only
exceptionally employed, as in th