aceto-nitrate
of silver and the saturated solution of gallic acid, which are to be mixed
and immediately applied to the exposed surface. This may be done several
hours after the pictures have been removed from the camera. Care should be
taken that the back of the picture does not become wetted, as this is apt
to produce a stain which may spoil the printing of the positive.

If upon the removal of the paper from the dark frame, the picture is very
apparent, by first applying little gallic acid, and immediately afterwards
the _mixed_ solutions, less likelihood is incurred of staining the
negative, which will be more evenly and intensely developed. If a browning
take place, a few drops of strong acetic acid will generally check it.

Should the picture be very tardy, either from an insufficient exposure,
want of light, or other cause, a few drops of a solution of pyrogallic
acid, made with 3 grains to the ounce of water, and a drachm of acetic
acid, will act very beneficially. It sometimes gives an unpleasant redness
upon the surface, but produces great intensity upon looking through it.
Until the pyrogallic solution was added, there was scarcely anything
visible upon the specimen exhibited, the failure having in the _first_
instance happened from the badness of the iodized paper.

As soon as the picture is sufficiently developed it should be placed in
water, which should be changed once or twice; after soaking for a short
time, say half an hour, it may be pinned up and dried, or it may at once be
placed in a solution almost saturated, or quite so, of hyposulphite of
soda, remaining there no longer than is needful for the entire removal of
the iodide, which is known by the disappearance of the yellow colour.

When travelling it is often desirable to avoid using the hyposulphite, for
many reasons (besides that of getting rid of extra chemicals), and it may
be relied on that negatives will keep even under exposure to light for a
very long time. I have kept some for several weeks, and I believe Mr.
Rosling has kept them for some months.

The hyposulphite, lastly, should be effectually removed from the negative
by soaking in water, which should be frequently changed.

Some prefer to use the hypo, quite hot, or even boiling, as thereby the
size of the paper is removed, allowing of its being afterwards readily
waxed.[9] I have always found that pouring a little boiling water upon the
paper effectually accomplishes the object;