e phosphide obtained by heating cupric phosphate, Cu2H2P2O8, in
hydrogen, when mixed with potassium and cuprous sulphides or levigated
coke, constitutes "Abel's fuse," which is used as a primer. A
phosphide, Cu3P2, is formed by passing phosphoretted hydrogen over
heated cuprous chloride. (For other phosphides see E. Heyn and O.
Bauer, _Rep. Chem. Soc._, 1906, 3, p. 39.) Cupric phosphate,
Cu3(PO4)2, may be obtained by precipitating a copper solution with
sodium phosphate. Basic copper phosphates are of frequent occurrence
in the mineral kingdom. Of these we may notice libethenite,
Cu2(OH)PO4; chalcosiderite, a basic copper iron phosphate; torbernite,
a copper uranyl phosphate; andrewsite, a hydrated copper iron
phosphate; and henwoodite, a hydrated copper aluminium phosphate.

Copper combines directly with arsenic to form several arsenides, some
of which occur in the mineral kingdom. Of these we may mention
whitneyite, Cu9As, algodonite, Cu6As, and domeykite, Cu3As. Copper
arsenate is similar to cupric phosphate, and the resemblance is to be
observed in the naturally occurring copper arsenates, which are
generally isomorphous with the corresponding phosphates. Olivenite
corresponds to libethenite; clinoclase, euchroite, cornwallite and
tyrolite are basic arsenates; zeunerite corresponds to torbernite;
chalcophyllite (tamarite or "copper-mica") is a basic copper aluminium
sulphato-arsenate, and bayldonite is a similar compound containing
lead instead of aluminium. Copper arsenite forms the basis of a number
of once valuable, but very poisonous, pigments. Scheele's green is a
basic copper arsenite; Schweinfurt green, an aceto-arsenite; and
Casselmann's green a compound of cupric sulphate with potassium or
sodium acetate.

Normal cupric carbonate, CuCO3, has not been definitely obtained,
basic hydrated forms being formed when an alkaline carbonate is added
to a cupric salt. Copper carbonates are of wide occurrence in the
mineral kingdom, and constitute the valuable ores malachite and
azurite. Copper rust has the same composition as malachite; it results
from the action of carbon dioxide and water on the metal. Copper
carbonate is also the basis of the valuable blue to green pigments
verditer, Bremen blue and Bremen green. Mountain or mineral green is a
naturally occurring carbonate.

By the direct union of copper and silicon, cuprosilicon, consisting