bbed
dry. The object of using the acid is to remove stains and whiten the
tin, and the ammonia is used to neutralize the effect of the acid.

The strips are then cut into pieces one and a half inch square, filled
into a cutch and beaten to about three inches square. It is then removed
from the cutch and filled into a mold, and further beaten to the desired
size. When the ragged edges are trimmed off, the foil is ready for
booking.

It takes skill and experience to beat tin foil, for it is not nearly as
malleable as gold; up to No. 20 it is usually beaten, but higher numbers
are prepared by rolling. In each case the process is similar to that
employed in preparing gold foil. The number on the book is supposed to
indicate the weight or thickness of the leaf. On the lower numbers the
paper of the book leaves its impression.

On weighing sheets of tin foil from different manufacturers a remarkable
discrepancy was found between the number on the book and the number of
grains in a sheet, viz: Nos. 3, 4, 5, weighed 7 gr. each; No. 6, 9 gr.;
No. 8, from 9 to 18 gr.; No. 10, from 14 to 15 gr.; No. 20, 18 gr. In
some instances the sheets in the same book varied three grains. We
submit that it would be largely to the advantage of both manufacturer
and dentist to have the number and the grains correspond. No dentist
wishes to purchase No. 8 and find that he has No. 18; no one could sell
gold foil under like circumstances. Of the different makes tested,
White's came the nearest to being correct. The extra tough foil which
can now be obtained is chemically pure, and with it we can begin at the
base of any cavity, and with mallet or hand force produce a filling
which will be one compact mass, so that it can be cut and filed; yet in
finishing, it will not bear so severe treatment as cohesive gold. Always
handle tin foil with clean pliers, never with the fingers; and prepare
only what is needed for each case, keeping the remainder in the book
placed in the envelope in which it is sold, otherwise extraneous matter
collects upon it, and it will oxidize _slightly_ when exposed to the air
for a _great_ length of time.

Before using tin foil, a few prefer to thoroughly crumple it in the
hands or napkin, under the impression that they thus make it more
pliable and easier to manipulate.

A piece of blue litmus paper moistened and moved over a sheet of tin
foil will occasionally give an acid reaction, probably owing to the acid
with which