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AMALGAM l6l

edge strength. (5) Greater shrinkage, expansion and flow.

(6) Require less mercury to amalgamate.
Amalgam, on account of its inharmonious color, should be
confined to the posterior teeth.
Method of Mixing.—The proportion of mercury to the

alloy varies in different formulae and is obtained by testing
the batch, or from printed
directions on the package.
The average is about five
parts of alloy to seven
parts of mercury by

weight. Rapid-setting al-
loys usually require more
mercury. To prevent
change of form and to give

the greatest edge strength,
all excess of mercury must
be removed in mixing.
Directions.— (i) Place

the desired amount of al-
loy in a wedgewood or
glass mortar, preferably
the latter, and add the
necessary amount of mer-
Fig. 179.—Glass mortar and pestle.
cury by weight. (2) Mix
thoroughly with the pestle (Fig. 179) until the alloy and mer-
cury are completely incorporated. (3) Remove to the dry
and clean palm of the left hand and work vigorously, rapidly
and continuously with the fingers of the right hand for from

three to five minutes, squeezing frequently and removing ex-
cessive mercury until a characteristic cry of the mass is heard
when in close proximity to the ear. (4) With the thumb
and forefinger, forcibly squeeze out all remaining excess of
u