plate. I prepare this salt as follows:

Dissolve one part chloride of gold and four parts hyposulphite of soda
in equal quantities of distilled water: pour the gold into the
hyposulphite solution, in the same manner as in mixing the gilding
solution; let it stand until it becomes limpid; filter and evaporate to
dryness. Re-dissolve and add a few grains of burnt alum.

After standing a few hours, filter and evaporate again. If not
sufficiently pure, repeat the crystallization until it is so. For
gilding, dissolve in water and use in the same manner as the common
gilding solution.

N.B.--The four following mixtures were employed in Neipce's process in
his earliest experiments:

Aqueous Solution of Bichloride of Mercury.--Eight grains of bichloride
of mercury in 10,000 grains of distilled water.

Solution of Cyanide of Mercury.--A flask of distilled water is
saturated with cyanide of mercury, and a certain quantity is decanted,
which is diluted with an equal quantity of distilled water.

Acidulated White Oil of Petroleum.--This oil is acidulated by mixing
with it one tenth of pure nitric acid, leaving it for at least 48
hours, occasionally agitating the flask. The oil, which is acidulated,
and which then powerfully reddens litmus paper, is decanted. It is
also a little colored, but remains very limpid.

Solution of Chloride of Gold and Platinum.--In order not to multiply
the solutions, take the ordinary chloride of gold, used for fixing the
impressions, and which is composed of 1 gramme of chloride of gold and
50 grains of hyposulphate of soda, to a quart of distilled water.

With respect to chloride of platinum, 4 grains must be dissolved in 3
quarts of distilled water; these two solutions are mixed in equal
quantities.

Acids.--I shall not go into the preparations of the various acids
employed in the Daguerreotype. This would be useless to the operator,
as there are few, if any, that it would be advisable to prepare. It is
only necessary for the experimenter to be made acquainted with their
properties, and this in order to prevent any haphazard experiments,
which are too common among operators. Any person who may be desirous
to try an experiment, should first study the agents he wishes to
employ. By so doing much time and money will be saved; while the
searcher after new discoveries would rarely become vexed on account of
his own ignorance, or be obliged to avail himself of the experience of
others in