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HISTOKY OF DENTAL SURGERY 277

twenty parts, gold, one part, silver, two part?, melted into an ingot for cast
work.
Dr. Hayford designed a dental mold for use in manipulating his own and
other cast metals. All of the foregoing methods contemplate casting the base
plate and attaching the teeth at the same time.
In many cases a plate of sufficient thickness may be cast, and the teeth
subsequently attached with vulcanite or celluloid, or the base-plate may be
cast in the form of the rubber base and faced with celluloid. Others wlio ex-
perimented with cast tin bases were. Dr. Edward Hudson (1820), Dr. William
A. Royce (1836), Dr. George E. Hawes (18.50). W. G. Oliver and Thomas
Harrison (1856), who patented a tooth without pins to be used for cast bases.
About 1870 Dr. J. B. Bean made numerous e.xperiments in casting alum-
inum plates, but his process was difficult and rather uncertain in results.
Dr. C. 0. C'arroll used a prepared form of aluminum which he describes
as first being made pure to prevent disintegration, and then alloyed with
a small per cent of noble metals that expand in cooling and thus compensate
for the contraction of the aluminum, "tluis enabling us to cast directly upon
the teeth without a fracture, making the base plate and attaching tlie teeth
at the same time. The difficulty of casting aluminum is overcome by the wse
of our pneumatic crucil>le, .which enables us to force the molten metal into
every part of the matrix."
x\nother method was to cast a base plate and attach the teeth, either plain
or gum, with pink rubber or celluloid. The Zeller cast aluminum apparatus
resemljles the Carroll, but varies in some important features. The first method
tried was to blow the metal into the mold; the second was to introduce the
metal by suction. Dr. R. C. Brophy says : "In my alloy of aluminum I use
five per cent of silver, and after the case is dried out and heated red-hot I
place tlie ingot of metal in the crucible which is attached to the flask, similar
to Carroll's, and when the metal fuses I jar the flask on the bench, and this
injects the metal into the matrix.'' He has a special flask and crucible, and
uses his gasoline furnace for heat.
About 18!»1 A\'ai'd introduced a process of depositing, by the action of a
battery, gold and silver directly upon the surface of the cast obtained from the
impression, thus securing perfect adaptation. The surface of the plaster cast
is prepared for the deposit of gold liy coating it with plumbago. A defijiite
thickness of gold is first deposited and upon this a deposit of silver is made,
which is then covered with another deposit of gold. Sometimes a thin silver
plate is swaged, and the gold deposited upon it to any desired thickness. In
a set of full metal the teeth are attached by depositing gold about and around