have been employed more and
more in writing fluids; not only in mixtures of which they are the
principal ingredients, but to a greater or less degree in all inks.
Their presence, even in small quantity, in the gallo-tannate of iron
and logwood inks can be generally detected by an iridescent and
semi-metallic luster.

To assist in determining the ages of writings by one and the same ink,
it is to be observed that the older the writing the less soluble it is
in dilute ammonia. If the writing be lightly touched with a brush
dipped in ten-per-cent ammonia, the later writing will always give up
more or less soluble matter to the ammonia before the earlier. In case
of inks of different kinds this test is not serviceable, for
characters written in logwood ink, for instance, will always give up
their soluble material sooner than nutgall inks, even if the last
named be later applied. To estimate the age of writing from the amount
of bleaching in a given time by hydrochloric or oxalic acid is very
precarious, because the thickness of the ink film in a written
character is not always the same, and the acid bleaches the thinner
layer sooner than the thicker.

The determination of the age of a written paper is a problem difficult
of solution. According to F. Carre the age can be approximately
determined if the characters written in iron ink are pressed in a
copying press and a commercial hydrochloric acid diluted with eleven
parts of water is substituted for water; or, if the written characters
are treated for some time with this diluted acid.

The explanation is that the ink changes in time, its organic substance
disappears little by little, and leaves behind an iron compound, which
in part is not attacked even by acids.

An unsized paper is impregnated with the described diluted acid,
copied with the press, and a copy from writing eight or ten years old
can be obtained as easily as one by means of water from a writing one
day old.

A writing thirty years old gives, by this method, a copy hardly
legible, and one over sixty years old, a copy hardly visible. In order
to protect the paper against the action of the acid, it should be
drawn through ammoniacal water.

To determine the exact age of writings by the ink is not easy. The
approximate age may be determined with some degree of certainty. If
ink-writings are but a few days old, it is easy to distinguish them
from other writing years old. But to tell by the ink which of t