up the bottle he carried the mercury in, he found it still filled,
and none in the bath, except only such particles as had adhered to the sides,
after dusting and being jolted for several miles over the rough road.
From this it will be seen that a very little mercury will suffice to
develop fine proofs. I saw some of the impressions referred to above,
and they were certainly well developed, and very superior specimens
of our art.

Removing the Coating.--After the impression has been developed over
the mercurial vapor, the next step is to remove the sensitive coating.
For this purpose the following solution is used:

Put about two ounces of hyposulphite of soda in a pint
of water, which should always be filtered before using.
A convenient way of doing this is to have two bottles,
and a large funnel with a sponge pressed into the neck
of it; or, what is better, some filtering paper folded in it.
The solution in one bottle, the funnel is placed in the other,
and the picture held over it; when the solution is poured
on the plate, it runs from it into the filter, and is always
ready for use.

It is best that the washing be done immediately on the plate coming
from the mercury bath. If allowed to stand long with the coating on,
it assumes a very dark tint--as the operation of the light continues,
though less active than while exposed in the camera, and destroys
that brightness which would otherwise have been obtained.
It is preferable to wash and gild a picture without it first
being dried; yet when there are doubts of its giving satisfaction,
there would sometimes be a saving by drying and getting the decision