per with sulphur and moistened the
residue, and in 1648 by Glauber, who dissolved copper in strong
sulphuric acid. (For the mechanism of this reaction see C. H. Sluiter,
_Chem. Weekblad_, 1906, 3, p. 63, and C. M. van Deventer, ibid., 1906,
3, p. 515.) It crystallizes with five molecules of water as large blue
triclinic prisms. When heated to 100 deg., it loses four molecules of
water and forms the bluish-white monohydrate, which, on further
heating to 25O deg.-260 deg., is converted into the white CuSO4. The
anhydrous salt is very hygroscopic, and hence finds application as a
desiccating agent. It also absorbs gaseous hydrochloric acid. Copper
sulphate is readily soluble in water, but insoluble in alcohol; it
dissolves in hydrochloric acid with a considerable fall in
temperature, cupric chloride being formed. The copper is readily
replaced by iron, a knife-blade placed in an aqueous solution being
covered immediately with a bright red deposit of copper. At one time
this was regarded as a transmutation of iron into copper. Several
basic salts are known, some of which occur as minerals; of these, we
may mention brochantite (q.v.), CuSO4, 3Cu(OH2), langite, CuSO4,
3Cu(OH)2, H2O, lyellite (or devilline), warringtonite; woodwardite and
enysite are hydrated copper-aluminium sulphates, connellite is a basic
copper chlorosulphate, and spangolite is a basic copper aluminium
chlorosulphate. Copper sulphate finds application in calico printing
and in the preparation of the pigment Scheele's green.

A copper nitride, Cu3N, is obtained by heating precipitated cuprous
oxide in ammonia gas (A. Guntz and H. Bassett, _Bull. Soc. Chim._,
1906, 35, p. 201). A maroon-coloured powder, of composition CuNO2, is
formed when pure dry nitrogen dioxide is passed over finely-divided
copper at 25 deg.-30 deg.. It decomposes when heated to 90 deg.; with
water it gives nitric oxide and cupric nitrate and nitrite. Cupric
nitrate, Cu(NO3)2, is obtained by dissolving the metal or oxide in
nitric acid. It forms dark blue prismatic crystals containing 3, 4, or
6 molecules of water according to the temperature of crystallization.
The trihydrate melts at 114.5 deg., and boils at 170 deg., giving off
nitric acid, and leaving the basic salt Cu(NO3)2.3Cu(OH)2. The mineral
gerhardtite is the basic nitrate Cu2(OH)3NO3.

Copper combines directly with phosphorus to form several compounds.
Th