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242 MECHANICAL DENTISTRY AND METALLURGY.

water. One part of bismuth with 24 of tin is malleable,
but the alloy of these metals becomes brittle by the addition
of more bismuth. Bismuth unites readily with antimony,
and, in the proportion of one part or more of the former
to two of the latter, it expands in the act of cooling.
Dental Uses.—The principal use of bismuth in the dental
laboratory is as a constituent of certain alloys, known as
fusible metals.
MERCURY.
Symbol, Hg (Hydrargyrum). Atomic weigJit, 200.
Occurrence.—Mercury is frequently found in nature in
the metallic state. It is sometimes found disseminated
through the vein-stone in mines of this metal, and trickling
from crevices in the ores. It is also found in globules
disseminated through its most important ore, its sulphid,
or cuuiabar, HgS, wdiich is the principal source of its supply.
The principal mines are in Spain, Austria, China, Aus-
tralia, and California. It has been found in great abundance
and of remarkable purity in the California and Australian
mines.
Extraction.—Two general methods for extracting mer-
cury from its ore are in use. The first is to simply roast
the cinnabar, wnth access of air, which converts the sulphur
into sulphurous anhydrid and pure mercury, liberated in
the form of vapor, wdiich is condensed in suitable receivers.
The second is to mix the sulphid with lime or oxid of iron
and distil the mixture. The sulphur combines with flux to
form calcium or iron sulphid as the case may be. The
mercurial vapors are condensed as before, in receivers.
General Properties.—Mercury, in the solidified condi-
tion, is malleable and ductile. It is silvery-white in color,
and has a strong metallic luster. It is readily distinguished
from other metals by its liquidity, which it maintains at