. No matter how
much salt is used, provided enough be added to throw down all the
chloride of silver. This solution should be well agitated and then
allowed to stand for a few minutes; thus the white precipitate is in
the bottom of the bottle. When the water has become clear, pour it off
with care, leaving the sediment behind, then add a fresh quantity of
clean water, shake, let settle, and pour off as before. Repeat the
same for several times, and the excess of salt will disappear, leaving
the white precipitate, which may be drained of the water and dried in
the dark, and kept free from light and air.

CYANIDE OF POTASSIUM.

Cyanide of Potassium.--This important article is worthy the undivided
attention of every Daguerreotypist. I here give Mr. Smee's process for
its preparation. This is from that author's work entitled, "Electro
Metallurgy," American edition:

"The cyanide of potassium, so often alluded to while treating of the
metallo-cyanides, may be formed in several ways. It may be obtained by
heating to a dull redness the yellow ferrocyanate of potash, in a
covered vessel, filtering and rapidly evaporating it. The objection to
this method, however, is that without great care the whole of the
ferrocyanate is not decomposed, a circumstance which much reduces its
value for electro-metallurgy. By boiling, however, the ignited residue
with spirits of wine this difficulty is said to be overcome, as the
ferrocyanate is absolutely insoluble in that menstruum, while the
cyanuret, at that heat, freely dissolves, and is as easily re-deposited
on cooling.

"There is, however, a much better process by which this salt may be
formed, viz. by simply transmitting hydrocyanic acid through
potassium. Although the modes of making this acid are very numerous,
there is but one which is likely to be employed on a very large scale,
and that is its formation from the yellow ferrocyanate by means of
sulphuric acid. This process is performed as follows: any given
weight of the yellow salt is taken and dissolved in about five times
its weight of water; this is placed in a retort, or some such analogous
vessel, to which is then added a quantity of strong sulphuric acid,
twice the weight of the salt, and diluted with three or four times its
quantity of water. A pipe is carried from the neck of the retort to
the receiving bottle, which should be kept as cool as possible.

"For small operations, those invaluable vessels, Fl