The Redwood gazette. [volume] (Redwood Falls, Minn.) 1873-1940, 1879-01-02
Sympathetic Inks.

are designated certain liquids which,
being used for writing, leave no visible
trace on the paper, but which, through
the agency of heat, or by the action of
chemicals, are made to appear in va.
for secret correspondence is very an
cient. Ovid, Pliny and other Roman
writer's speak of ink of this kind,
which, however, was nothing more
than fresh milk. 1t merely sufficed to
dust powdered charcoal over the sur
face of the paper upon which charac-
tiers had been traced with the colorless
fluid, when the powder adhered only to
those places where the fatty matter of
the milk had spread. Such process.
however, was merely mechanical, and
the results very crude.
A great number of sympathetic inks
may be obtained by means of reactions
known to chemistry. For instance,
write on paper with a colorless solu-
ton Of sugar of lead; If the water that
is used for the solution be pure, no
trace of the writing will remain when
Fit becomes dry. Now hold The paper
over jet of sulphureted hydrogen,
and the characters will Immediately
appear on the paper, of an intense
black color. The following recipes for
inks of this kind are more simple: If
writing be executed with q dilute solu-
ton of sulphate of iron, the invisible
characters will appear of beautiful
blue. if the dry paper be brushed over
with pencil fullof solution of yellow
prussiate of potash; or they will be
black. if solution Of tannin be substitu-
ted for the prussiate. If the characters
be written with q solution of sulphate of
copper, they will at once turn blue on
exposing to the vapors Of ammonia.
Another sympathetic ink is afforded by
chloride OF gold, which becomes. red
dish purple, when acted upon by salt
of tin. j A red sympathetic ink may be
made in the following manner: Write
with very dilute solution of perchlo-
ride of iron-so dilute, indeed, that the
writing will be invisible when dry. BY
holding the paper in the vapor arising
from a long-necked glass flask contain
ing suIphuric acid and q few drops of a
solution Of sulpho-cyanideo of potassium,
the characters will appear of blood
red color, which will again disappear
on submitting them to the vapors of
caustic ammonia. This experiment
can be repeated ad in1snituns.
During the war in India, some years
ago, important correspondence was
carried on by the English by means of
tie use of rice water as writing fluid.
On the application of iodine, the dis
patches immediately appeared in blue
Characters.
Sympathetic inks which are devel-
oped under the influence of heat only
are much easier to use than the fore
going. The liquids which possess such
property are very numerous. Almost
everyone, perhaps, knows that if writ
ing be executed on paper with clean
quill pen dipped in onion or turnip
Juice, It becomes absolutely invisible
when dry; and that when the paper is
heated the writing at once makes its
appearance in characters OF brown
color. All albuminoid. mucilaginous
and saccharine vegetable juices make
excellent sympathetic INKS; we may
cite, a. among the best, the juices OF
lemon, orange, apple and pear. A
dilute solution of chloride OF copper
used for writing il invisible until the
paper IL heated, when the letters are
seen Of beautiful yellow. disappear
ing again when the heat that developed
them IL removed. The salts Of cobalt,
- tho acetate, nitrate, sulphate and