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DENTAL METALLURGY.

Metallurgy may l^e defined as the operation of obtaining
metals from their ores, or combinations with non-metalhc
elements, their physical properties or special characteristics,
and the methods of manipulation.
Metals are elementary substances, and with the exception
of mercury, are solid at ordinary temperatures. They have
many physical properties which are so pronounced as to
place them in a class by themselves.
Physical Properties of Metals.—Some of the most im-
portant characteristics are their molecular structure, density,
malleability, ductility, tenacity, toughness, hardness, brittle-
ness, elasticity, conductivity, and fusibility.
Molecular Structure.—Like all other elements, metals are
composed of atoms grouped in molecules, and the presence
of any other element or extraneous force altering the rela-
tion of the atoms in the molecules modifies the physical
properties of the metal.
Density.—The density of a metal is dependent upon the
intimacy of the contact between the molecules. This prop-
erty is therefore influenced by the temperature of casting,
the rate of cooling, the mechanical treatment, and the purity
of the metal.
Malleability. —The malleability of metals is the property
in virtue of which their form may be changed by ham-
mering or by rolling.
Ductility.—This is the property in virtue of which metals
may be dra^^•n into wire.
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