on.

It is necessary that pure water should be used for the fixing, as the
presence of any muriate damages the picture, and here arises another
pleasing variation of the Chromatype. If the positive picture be
placed in a very weak solution of common salt the image slowly fades
out, leaving a faint negative outline. If it now be removed from the
saline solution, dried, and again exposed to sunshine, a positive
picture of a lilac color will be produced by a few minutes exposure.
Several other of the chromates may be used in this process, but none is
so successful as the chromate of copper.

IV. ANTHOTYPE.

The expressed juice, alcoholic, or watery infusion of flowers, or
vegetable substances, may be made the media of photogenic action. This
fact was first discovered by Sir John Herschel. We have already given
a few examples of this in the third chapter.

Certain precautions are necessary in extracting the coloring matter of
flowers. The petals of fresh flowers are carefully selected, and
crushed to a pulp in a marble mortar, either alone or with the addition
of a little alcohol, and the juice expressed by squeezing the pulp in a
clean linen or cotton cloth. It is then to be spread upon paper with a
flat brush, and dried in the air without artificial heat. If alcohol
be not added, the application on paper must be performed immediately,
as the air (even in a few minutes), irrecoverably changes or destroys
their color. If alcohol be present this change is much retarded, and
in some cases is entirely prevented.

Most flowers give out their coloring matter to alcohol or water. Some,
however, refuse to do so, and require the addition of alkalies, others
of acid, &c. Alcohol has, however, been found to enfeeble, and in many
cases to discharge altogether these colors; but they are, in most
cases, restored upon drying, when spread over paper. Papers tinged
with vegetable colors must always be kept in the dark, and perfectly
dry.

The color of a flower is by no means always, or usually, that which its
expressed juice imparts to white paper. Sir John Herschel attributes
these changes to the escape of carbonic acid in some cases; to a
chemical alteration, depending upon the absorption of oxygen, in
others; and again in others, especially where the expressed juice
coagulates on standing, to a loss of vitality, or disorganization of
the molecules. To secure an eveness of tint on paper, the following
manipulation i