Page 128 - My FlipBook

124 OPERATIVE DENTISTRY

// tlie Surface of Foil Becomes contaminated with a non-evapor-
able substance the injury is permanent.
To Protect tlie Surface of Gold. Place in the drawer where the
gold is kept a small pledget of cotton or spunk saturated with am-
monia.
Ammonium salts Avill form on the surface of the gold, which are
easily volatilized by heat, leaving the gold clean. Before anneal-
ing such gold Avill be found thoroughly non-cohesive. This meth-
od of treating the gold to the fumes of ammonia will obviate the
necessity of keeping more than one kind of gold on hand, as all
will be non-cohesive till annealed and can be used in either form.
Annealing' Gold is for the sole purpose of cleaning the surface
of the gold by volatilizing any film that may have collected.
The Degree of Heat is about 1100°F., or just below red heat.
In the daylight this color is not apparent, but on a dark day
the dull red color should show. The gold is not materially injured
if carried to the full red of 1200 or 1300 degrees, but in no case
should the melting point be reached, as it destroys the possibility
of adaptation to the walls of the cavity, or the surface of the gold
already in place.
Methods of Annealing. The electric annealer is by far the most
satisfactory means, as it is possible to always obtain the same de-
gree of heat for a continued period.
The Next Best Means is to place the gold on a tray above a flame,
thus separating the flame from the gold, preventing contamination
of the gold with carbon, and various gases which are frequently met
with in combustion.
Gold SJiould Not Be Annealed hy Passing It TlirougJi tlie Open
Flame of either gas or alcohol, holding the gold either on a plug-
ger point or the foil carriers. This is quite a common practice,
which should be discontinued. In the first place, heating the gold
with the open flame frequently contaminates its surface, to the
injury of its welding properties.
Also that portion of the gold next to the carrier is not sufficient-
ly heated and remains non-cohesive, a fact which is shown by the
subsequent pitting of the surface of the filling during service by
the flecking off of these non-cohesive particles.
Specific Gravity. The specific gravity of the cast gold inlay is
about 19, varying the fraction of a point.
It is possible to condense a cohesive gold filling when confined
between the walls of elastic dentine so as to obtain a slightly
greater specific gravity than the cast inlay. However, this degree