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232 MECHANICAL nENTTSTRY AND METALLURGY.
ciiry, and scarcely at all with lead. It, however, forms a
variety of alloys with other metals. It seems to unite
readily with zinc, and these have been found to give the
best promise as solders for aluminum; but, unfortunately,
when melted, neither of them are sufficiently liquid and
do not run readily. A variety of alloys with nickel have
been made, and that consisting of 100 parts of aluminum
and 3 of nickel is found to work readily, and to have
gained harchiess and rigidity as compared with the pure
metal. The alloys, however, with copper are the most
striking; they are light and very hard, and capable of a
fine p(jlish. In the same degree that copper adds to the
hardness of aluminum, so does the latter, when used in
small quantities, give hardness to copper without injuring
its malleability.

ZINC.
Symbol, Zn (Zincum). Atomic zvcight, 65.
Occurrence.—The chief forms of zinc as found in nature
are the red oxid ; the sulphid, sinc-hlcnd ; and the hydrous
silicate. Calamine. These ores are roasted to expel car-
bonic acid, water, and sulphur, after which they are mixed
with small particles of powdered coke or charcoal and dis-
tilled at full red heat in earthen retort. Carbon monoxid
escapes, while the metallic zinc liberated distills over into
proper receivers.
General Properties. —Zinc is a bluish-white metal, the
fresh surface possessing considerable luster. It does not
easily tarnish in dry air, but soon becomes dull on exposure
to moisture. Under ordinary circumstances it is l)rittle,
but when heated to about 300° F. it becomes malleable and
ductile.
The fusing point of zinc is about 775° F., and when
heated to about 1800 V. it boils, volatilizes, and liurns, if