resinous matter used give to the paper a peculiar appearance. Sizing
takes away from the whiteness of the paper, and, thinned by the
scratching or washing, it absorbs much more quickly even when it has
been partially sized.

A simple mode of operation is to place a document or paper suspected
of being a forgery, on a sheet of paper or better still, on a piece of
glass; then moisten little by little with a paint brush all parts of
it, paying close attention to the behavior of the liquid as it comes
in contact with the paper.

By means of water one can discover what acids, alkalis, or salts the
parts of the paper with colored borders or white spots contain.

With the aid of a pipette cover these spots with water and let it
remain for ten or fifteen minutes; then with the pipette remove the
liquid and examine the products it holds in solution. Afterwards make
a comparative experiment on another part of the paper which is neither
spotted nor whitened.

If the original writing has been done with a very acid ink on a paper
containing a carbonate, such as calcium carbonate, the ink, in
attacking the calcareous salt, stains the paper, so that if the forger
has removed the ferruginous salts this removal is denoted by the
semi-transparence that water gives to the paper.

To study carefully the action of the water it is necessary to repeat
the experiment several times, allowing the paper to dry thoroughly
before recommencing it.