mainly of Cu4Si, is obtained (Lebeau, C.R., 1906; Vigouroux,
ibid.).

Copper silicates occur in the mineral kingdom, many minerals owing
their colour to the presence of a cupriferous element. Dioptase (q.v.)
and chrysocolla (q.v.) are the most important forms.

_Detection._--Compounds of copper impart a bright green coloration to
the flame of a Bunsen burner. Ammonia gives a characteristic blue
coloration when added to a solution of a copper salt; potassium
ferrocyanide gives a brown precipitate, and, if the solution be very
dilute, a brown colour is produced. This latter reaction will detect
one part of copper in 500,000 of water. For the borax beads and the
qualitative separation of copper from other metals, see CHEMISTRY:
ANALYTICAL. For the quantitative estimation, see ASSAYING: COPPER.

_Medicine._--In medicine copper sulphate was employed as an emetic,
but its employment for this purpose is now very rare, as it is
exceedingly depressant, and if it fails to act, may seriously damage
the gastric mucous membrane. It is, however, a useful superficial
caustic and antiseptic. All copper compounds are poisonous, but not so
harmful as the copper arsenical pigments.

REFERENCES.--See generally H. J. Steven's _Copper Handbook_ (annual),
W. H. Weld, _The Copper Mines of the World_ (1907), _The Mineral
Industry_ (annual), and _Mineral Resources of the United States_
(annual). For the dry metallurgy, see E. D. Peters, _Principles of
Copper Smelting_ (New York, 1907); for pyritic smelting, see T. A.
Rickard, _Pyrite Smelting_ (1905); for wet methods, see Eissler,
_Hydrometallurgy of Copper_ (London, 1902); and for electrolytic
methods, see T. Ulke, _Die electrolytische Raffination des Kupfers_
(Halle, 1904). Reference should also be made to the articles
METALLURGY and ELECTRO-METALLURGY. For the chemistry of copper and its
compounds see the references in the article CHEMISTRY: Inorganic.
Toxicologic and hygienic aspects are treated in Tschirsch's _Das
Kupfer vom Standpunkt der gerichtlichen Chemie, Toxikologie und
Hygiene_ (Stuttgart, 1893).

COPPERAS (Fr. _couperose_; Lat. _cupri rosa_. the flower of copper),
green vitriol, or ferrous sulphate, FeSO4.7H2O, having a
bluish-green colour and an astringent, inky and somewhat sweetish taste.
It is used in dyeing and tanning, and in the manufacture of ink and of
Nordhausen sulphuric acid or fuming oil of v