five atoms of commercial nitric acid, diluted with an equal quantity
of water. One-fifth of this quantity (one atom) of the acid is
sufficient to transfer the ferrocyanide into nitroprusside; but the
use of a larger quantity is found to give the best results. The acid
is poured all at once upon the ferrocyanide, the cold produced by the
mixing being sufficient to moderate the action. The mixture first
assumes a milky appearance, but after a little while, the salt
dissolves, forming a coffee-colored solution, and gases are disengaged
in abundance. When the salt is completely dissolved, the solution is
found to contain ferrocyanide (red prussiate) of potassium, mixed with
nitroprusside and nitrate of the same base. It is then immediately
decanted into a large flask, and heated over the water-bath. It
continues to evolve gas, and after awhile, no longer yields a dark
blue precipitate with ferrous salts, but a dark green or slate-colored
precipitate. It is then removed from the fire, and left to
crystallize, whereupon it yields a large quantity of crystals of
nitre, and more or less oxamide. The strongly-colored mother liquid is
then neutralized with carbonate of potash or soda, according to the
salt to be prepared, and the solution is boiled, whereupon it
generally deposits a green or brown precipitate, which must be
separated by filtration. The liquid then contains nothing but
nitroprusside and nitrate of potash or soda. The nitrates being the
least soluble, are first crystallized, and the remaining liquid, on
farther evaporation, yields crystals of the nitroprusside. The sodium
salt crystallizes most easily.--(PLAYFAIR.)

As some substances, particularly in complicated compounds, are not
detected with sufficient nicety in the dry way of analysis, it will
often be necessary to resort to the wet way. It is therefore necessary
to have prepared the reagents required for such testing, as every