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AMALGAM. 311

shrinkage — of the alloys from 40 silver and 60 tin on to those
containing equal parts of the metals.*
No attempt was made, when this table was first published,
to represent the variation of shrinkage that might occur from
different samples of alloy made from the same formula. Varia-
tions must be expected. The amendment made is on account of
the constant variation (which is not the same in each sample of
metals obtained from the dealer) of alloys made in hydrogen
gas in the closed electric crucible, an arrangement that gives
the greatest facility in accurate alloy making.
Will alloys prepared for use by annealing to the normal
for room temperature maintain these properties permanently?
(1) as to shrinkage or expansion; (2) as to working properties;
(3) as to amount of mercury required. These questions required
time for their full determination, but something could be learned
at once.
(1.) Annealing longer continued at the temperature of boil-
ing water did not effect further changes in shrinkage or expan-
sion. This gave the presumption that time would not.
(2.) Additional annealing does continue to aiTect the work-
ing properties in such a way as to render the amalgamation
easier, reduce the amount of mercury required, and it also slows
the setting. This is not very great, but it is quite marked.
Tubes of alloy were put up for time tests, some of which
yet remain after twelve years, and frequent tests have been
made. Shrinkage and expansion remain imaffected. The amount
of mercury required diminishes, the amalgamation becomes
easier, the setting becomes slower, and the strength of the amal-
gam is gradually reduced. An alloy that makes a crisp amalgam
which sets quickly, such as should always be used in practice,
will, if kept two to three years at ordinary room temperatures,
come to make rather a sloppy, slow-setting mass. If the alloy is
exposed to the heat of the sun or otherwise to unusually high
temperatures, these changes will be rapid in proportion. If the
alloy is much of the time exposed to cold, as in cold rooms in
winter in northern localities, these changes will be slower.

Note.— In the expansions recordeJ, which occurred at the beginning of the set-
ting, the amalgam, being firmly held by the walls of the steel tube, was caused to flow
upward in the tube. Therefore, the expansion recorded represents more nearly the
cubical expansion. All of the shrinkages recorded, however, represent purely lineal
contraction. The record of shrinkage recorded is that below the measurement at the
beginning of the experiment.