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NATURE AND PROPERTIES OF AMALGA3I. 313
pared by the ordinary processes. This method was suggested to the
writer by Dr. E. C. Kirk.
In its tj-pical form and condition, copper amalgam, when made
plastic by heat, may be packed into matrices, such as cavities in
teeth, where it sets quickly, undergoes no change of volume or form,
and is devoid of flow. Therefore a cavity which has been sealed by
it remains sealed. Upon its outer surface a coating of black sulfid
quickly forms, which remains but does not penetrate the tooth struc-
ture. The dentinal walls are commonly stained green through the
absorption of the metallic salts.
In improperly prepared specimens there is not a perfect chemical
union between the metallic mercury and the copper. The presence in a
filling mass of oxids of either of these metals establishes local electrolytic
conditions which prevent the formation of the black sulfid coating and
bring about the gradual dissolution of the amalgam mass. To recapitu-
late : Copper amalgam is physically unchangeable as a filling material
it brings about very offensive discoloration both of the dentin and of
its own surface ; it is antiseptic.
The second binary amalgam is that of palladium. Palladium is
precipitated from a solution of its chlorid by iron or zinc, washed in
nitric acid, and dried. To the precipitated metal, mercury is added,
the combination being attended by the evolution of much heat (/. e. is
an active chemical union). If an excess of mercury has not been used
the amalgam sets quickly, does not alter in form,' and becomes black
upon the surface,'^ but does not discolor the dentin. The addition of
an excess of mercury retards the setting, and produces an inferior filling.
Ternary Amalgams.—The base of all ternary amalgams is the
alloy of silver and tin. The first of these was the alloy of ToAvnsend,
44^ per cent, silver, 55^ per cent. tin. From this point the investi-
gations and experiments radiated—it being found after many years of
clinical testing that those alloys containing more than 50 per cent, of
silyer gave the best results.
The formula given by Dr. J. Foster Flagg as affording the most
stable alloy for amalgam—60 silver, 35 tin, and 5 copper—was found
by Dr. Black to be that giving the highest degrees of resistance to
change of form, to flo^y, and to crushing. In view of Dr. Black's
researches into the effects of annealing alloys it is evident that the
ternary amalgam of the future will have a composition closely approxi-
mating 72.5 per cent, silver, 27.5 per cent. tin.
The binary alloys of tin and silver form the basis of all of the
quaternary amalgams used in dentistry.
^ Tomes, Trans. Odontoloqkal Society of Great Britain, 1872.
" Bogue, Dental Cosmos, 1884.
NATURE AND PROPERTIES OF AMALGA3I. 313
pared by the ordinary processes. This method was suggested to the
writer by Dr. E. C. Kirk.
In its tj-pical form and condition, copper amalgam, when made
plastic by heat, may be packed into matrices, such as cavities in
teeth, where it sets quickly, undergoes no change of volume or form,
and is devoid of flow. Therefore a cavity which has been sealed by
it remains sealed. Upon its outer surface a coating of black sulfid
quickly forms, which remains but does not penetrate the tooth struc-
ture. The dentinal walls are commonly stained green through the
absorption of the metallic salts.
In improperly prepared specimens there is not a perfect chemical
union between the metallic mercury and the copper. The presence in a
filling mass of oxids of either of these metals establishes local electrolytic
conditions which prevent the formation of the black sulfid coating and
bring about the gradual dissolution of the amalgam mass. To recapitu-
late : Copper amalgam is physically unchangeable as a filling material
it brings about very offensive discoloration both of the dentin and of
its own surface ; it is antiseptic.
The second binary amalgam is that of palladium. Palladium is
precipitated from a solution of its chlorid by iron or zinc, washed in
nitric acid, and dried. To the precipitated metal, mercury is added,
the combination being attended by the evolution of much heat (/. e. is
an active chemical union). If an excess of mercury has not been used
the amalgam sets quickly, does not alter in form,' and becomes black
upon the surface,'^ but does not discolor the dentin. The addition of
an excess of mercury retards the setting, and produces an inferior filling.
Ternary Amalgams.—The base of all ternary amalgams is the
alloy of silver and tin. The first of these was the alloy of ToAvnsend,
44^ per cent, silver, 55^ per cent. tin. From this point the investi-
gations and experiments radiated—it being found after many years of
clinical testing that those alloys containing more than 50 per cent, of
silyer gave the best results.
The formula given by Dr. J. Foster Flagg as affording the most
stable alloy for amalgam—60 silver, 35 tin, and 5 copper—was found
by Dr. Black to be that giving the highest degrees of resistance to
change of form, to flo^y, and to crushing. In view of Dr. Black's
researches into the effects of annealing alloys it is evident that the
ternary amalgam of the future will have a composition closely approxi-
mating 72.5 per cent, silver, 27.5 per cent. tin.
The binary alloys of tin and silver form the basis of all of the
quaternary amalgams used in dentistry.
^ Tomes, Trans. Odontoloqkal Society of Great Britain, 1872.
" Bogue, Dental Cosmos, 1884.
