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202 MECHANICAL DENTISTRY AND METALLURGY.
impairing its malleability; it gives a deeper color and
renders it capable of receiving a richer polish.
Silver renders gold more fusible, increases hardness, does
not materially affect mallealjility, and gives a lighter color.
Platinum in small proportions renders gold harder and
more elastic without impairing malleability. Makes color
pale and dull. Excess of platinum renders the alloy in-
fusible in the blast furnace.
Mercury dissolves gold and combines with it at all tem-
peratures.

PREPARING ALLOYS OF GOLD FOR DENTAL PURPOSES.
Gold in its pure state is rarely employed by the dentist
in laboratory processes on account of its softness and flexi-
bility; it is, therefore, usually alloyed with such metals as
impart to it—without practically impairing its malleability,
pliancy or purity—the degree of hardness, strength, and
elasticity necessary to resist the wear and strain to which
an artificial piece constructed from it is unavoidably ex-
posed in the mouth.
Reducing Metals.—The metals with which gold is usually
combined are copper and silver. It is sometimes reduced
with silver alone, many regarding the introduction of copper
into the alloy as objectionable' as plate derived from it is
supposed to be more readily tarnished and to communicate
to the mouth a disagreeable metallic taste. The small pro-
portion of copper usually employed in forming gold plate,
however, is not likely to produce in any objectionable degree
the consequences complained of, unless the fluids of the
mouth are greatly perverted. If gold coin is used in the
formation of plate, it may be sufficient to add silver alone,
inasmuch as copper is already present ; though, usually,
additional quantities of the latter metal are added.