chloride of barium to a small quantity of the washings, and when
there is no white precipitate formed by the test, the precipitate is
sufficiently washed. A solution of cyanide of potassium is now added
to this precipitate until it is dissolved, during which process the
solution becomes warm by the chemical re-action which takes place.
The solution is filtered, and allowed to repose all night. If
the solution of cyanide of potassium that is used is strong, the
greater portion of the ferrocyanide of potassium crystalises in the
solution, and may be collected and preserved for use again. If the
solution of cyanide of potassium used to dissolve the precipitate is
dilute, it will be necessary to condense the liquor by evaporation
to obtain the yellow prussiate in crystals. The remaining solution
is the coppering solution; should it not be convenient to separate
the yellow prussiate by crystallization, the presence of that salt
in the solution does not deteriorate it nor interfere with its power
of depositing copper.


19. PECULIARITIES IN WORKING CYANIDE OF COPPER SOLUTION

The true composition of the salts thus formed by copper and cyanide
of potassium has not yet been determined, but their relations to
the battery and electrolyzation are peculiar. The solution must
be worked at a heat not less than from 150 to 200 degrees Farenheit
(that is not quite as hot a boiling water, which is 212 degrees
Farenheit.) All other solutions we have tried follow the laws, that
if the electricity is so strong as to cause gas to be evolved at
the electrode, the metal will be deposited in a sandy or powdered
state, but the solution of cyanide of copper and potassium is an
exception to these laws, as there is no reguline deposit obtained