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30 THE TREATMENT OF TEETH
described as either soft gold or soft cohesive
gold.
There is so much confusion of terms and mis-
understanding of the properties of gold in its various
states or conditions that an attempt at explanation
may not be out of place. It has been stated that
the softest gold in itself is the cohesive variety.
It is also well known that annealinof a bar of gold
brings it to the softest possible condition, just as it is
well kno\yn that it can be hardened by hammering.
In speaking of soft and hard golds, so far as filling
teeth is concerned, we mean the softness or hardness
of the metal during its manipulation, and the com-
parative hardness of the filling when it is completed.
There is no doubt that fully annealed gold becomes
harder during its manipulation in a tooth, and the
resulting filling is harder when completed than one
that is made in exactly the same way with slightly
annealed gold, and the less the gold is annealed the
softer it will work and the softer will be the filling.
It is presumed that the gold in these cases is welded
into a coherent mass. All this is difficult to account
for. The fact that the layers of fully annealed gold
in a pellet, cylinder, or strip stick together very
quickly during the process of packing, and that
consequently a more resistant pellet is produced,
does not account for the greater hardness of the