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INTRODUCTION OF THE GOLD. 275

carbon or sulfur deposits upon the surface of the gold. All or any
of these accidents would impair the working qualities of the gold.
The most satisfactory method of annealing gold is by the use of the
Electric Annealing Tray. Such a device has been invented by Dr. L.
E. Custer, and is shown in Fig. 22(3. By this method the gold can be
Fig. 226.

Custer's electric annealing tray.
heated to anv desired decree and with a uniformitv not easilv attained
by the methods generally used. The working qualities of foil whether
non-coliesive or cohesive are greatly enhanced by the application of
heat at the time of using. Gold that is absolutely non-cohesive is made
tougher by annealing and yet its softness is not impaired, while cohesive
gold may be made either slightly or decidedly cohesive according as
much or little heat may be applied to it. It is the practice of many
operators to use the gold but slightly cohesive when filling cavities sur-
rounded by strong walls, and the gold known as semi-cohesive, in the
form of loosely rolled cylinders, is much used. As the filling approaches
completion the cylinders are heated and additional cohesive property
imparted to them. But when the object is the restoration of contour or
building up of teeth Avhich have been broken, the gold should be heated
but little short of redness in order that the greatest cohesive property-
may be realized.
Introduction of the Gold, and Manner of Adapting It to
THE Walls op the Cavity.
It has been shown in C'liai)ter VIII. that few cavities are of proper
shape for retaining the filling when the decay alone has been removed.
Most cavities require to be given a retentive shape so that the filling'
shall not be dislodged during: its introduction or bv mastication or
otherwise after its completion. In former times, when the operator was
restricted to one form of gold and that the non-cohesive variety, he was
compelled to prepare his cavities accordingly ; but at the present time,
when the variety is almost endless, he can shape his cavity with a view