which rapidly forms the green
hydrated salt CuCl2, 2H2O on exposure. The oxychloride Cu3O2Cl2.4H2O
is obtained as a pale blue precipitate when potash is added to an
excess of cupric chloride. The oxychloride Cu4O3Cl2, 4H2O occurs in
nature as the mineral atacamite. It may be artificially prepared by
heating salt with ammonium copper sulphate to 100 deg.. Other
naturally occurring oxychlorides are botallackite and tallingite.
"Brunswick green," a light green pigment, is obtained from copper
sulphate and bleaching powder.

The bromides closely resemble the chlorides and fluorides.

Cuprous iodide, Cu2I2, is obtained as a white powder, which suffers
little alteration on exposure, by the direct union of its components
or by mixing solutions of cuprous chloride in hydrochloric acid and
potassium iodide; or, with liberation of iodine, by adding potassium
iodide to a cupric salt. It absorbs ammonia, forming the compound
Cu2I2, 4NH3. Cupric iodide is only known in combination, as in CuI2,
4NH3, H2O, which is obtained by exposing Cu2I2, 4NH3 to moist air.

Cuprous sulphide, Cu2S, occurs in nature as the mineral chalcocite or
copper-glance (q.v.), and may be obtained as a black brittle mass by
the direct combination of its constituents. (See above, METALLURGY.)
Cupric sulphide, CuS, occurs in nature as the mineral covellite. It
may be prepared by heating cuprous sulphide with sulphur, or
triturating cuprous sulphide with cold strong nitric acid, or as a
dark brown precipitate by treating a copper solution with sulphuretted
hydrogen. Several polysulphides, e.g. Cu2S5, Cu2S6, Cu4S6, Cu2S3, have
been described; they are all unstable, decomposing into cupric
sulphide and sulphur. Cuprous sulphite, CuSO3.H2O, is obtained as a
brownish-red crystalline powder by treating cuprous hydrate with
sulphurous acid. A cuproso-cupric sulphite, Cu2SO3, CuSO3,2H2O, is
obtained by mixing solutions of cupric sulphate and acid sodium
sulphite.

Cupric sulphate or "Blue Vitriol," CuSO4, is one of the most important
salts of copper. It occurs in cupriferous mine waters and as the
minerals chalcanthite or cyanosite, CuSO4.5H2O, and boothite,
CuSO4.7H2O. Cupric sulphate is obtained commercially by the oxidation
of sulphuretted copper ores (see above, METALLURGY; wet methods), or
by dissolving cupric oxide in sulphuric acid. It was obtained in 1644
by Van Helmont, who heated cop