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EFFECT OF METALS ON A^IALGAMS. 245

amalgam fillings in the month is largely clue to the forma-
tion of snlphicls. According to Essig,* the fluids of the
mouth, in every case where the most scrupulous cleanliness
is not ohserved, may be said to contain sulphur in combina-
tion with hydrogen, as dihydric sulphid (HoS), resulting
from decomposition of particles of food having a lodgment
between or adhering to the teeth. The affinity of sulphur
for both silver and mercury is so active that we may rea-
sonably assume that not only the discoloration of amalgam
fillings, but in many cases their failure to prevent a recur-
rence of decay, is due to the action of that element upon the
alloy.
Formation of Amalgam Alloys.—An alloy consisting of
silver, tin, gold, and platinum being a typical combination,
the method of producing the same will illustrate the process
sufficiently, there being little modification where other
metals are used.
The plumbago, or graphite, crucible is preferable; it
should be brought to a bright-red heat and a sufficient
quantity of borax dropped in and allowed to fuse to coat
the whole inner surface, after which the silver and gold,
with the platinum in small pieces, should be introduced and
thoroughly fused. The tin is then added and the fluid mass
poured into suitable molds. After it is thoroughly cooled
it may be brought into a suitable state for use, either with
a clean file or with a chisel in a lathe.

EFFECT OF CONSTITUENT METALS ON
AMALGAMS.

Silver.—The greater number of amalgams consists largely
of silver and tin, silver being the first and most important
metal for a good amalgam alloy. The union of silver with
* Essig's " Metallurgy."