ndle is made of ebony, and has a
silver ferrule, from which the ivory extends to the end and completes
the instrument.

"The metal pin in the end of the handle is for picking up and carrying
the gold."

[Illustration: FIG. 8.]

Tin has been used successfully for completely lining cavities, filling
the remainder with gold; it is also useful for repairing gold fillings.

Two or three thicknesses of tin foil may be pressed into a cavity with a
rubber point or hard piece of spunk, allowing it to come well out to the
margin; filling the rest with amalgam.

"As a lining it presents to dentin an amalgam of tin and mercury which
does not discolor the dentin like ordinary amalgam, and helps do away
with local currents on the filling, which is one cause of amalgam
shrinkage in the mouth." (Dr. S. B. Palmer.)

When caries extends to the bifurcation of roots, make a mat of two or
three layers of tin, place it in the bifurcation and use it as a base in
filling the rest of the cavity with amalgam.

Tin is second in importance in alloys for amalgam, as it increases
plasticity, prevents discoloration, reduces conductivity and edge
strength, retards setting, favors spheroiding, therefore should not be
the controlling metal.

It will be noticed that when cavities are lined with tin foil, it only
constitutes a small part of the filling, and that it has not been melted
with the other metals in the alloy before being amalgamated.

A thick mat of tin has been recommended as a partial non-conductor under
amalgam fillings.

Plastic tin can be made by pouring mercury into melted tin, or by mixing
the fillings with mercury at ordinary temperatures; it has a whitish
color, and if there is not too much mercury it occurs in the form of a
brittle granular mass of cubical crystals. Generally amalgams of tin and
mercury do not harden sufficiently, but forty-eight parts of mercury and
one hundred of tin make a fairly good filling, said to have a
therapeutical value; it should not be washed or squeezed before using,
and "is not a chemical combination."

"Tin unites with mercury in atomic proportions, forming a weak
crystalline compound." (Dr. E. C. Kirk.)

Mercury and tin readily unite as an amalgam under ordinary
circumstances, and form a definite chemical compound having the formula
Sn_{2}Hg. (Hodgen.)

Another preparation of tin is known as stannous gold; it is manufactured
in heavy sheets and used the same as cohesive gold foil, and