with a little water, and a small
piece of the nitroprusside of sodium is added, there will be produced
a splendid purple color. This color, or reaction, will be produced
from any substance containing sulphur, such as the parings of the
nails, hair, albumen, etc. In regard to these latter substances, the
carbonate of soda should be mixed with a little starch, which will
prevent the loss of any of the sulphur by oxidation. Coil a piece of
hair around a platinum wire, moisten it, and dip it into a mixture of
carbonate of soda, to which a little starch has been added, and then
heat it with the blowpipe, when the fused mass will give with the
nitroprusside of sodium the characteristic purple reaction, indicative
of the presence of sulphur. With the proper delicacy of manipulation,
a piece of hair, half an inch in length, will give distinct
indications of sulphur.

_Preparation._--The nitroprussides of sodium and potassium (for either
salt will give the above reactions), are prepared as follows: One atom
(422 grains) of pulverized ferrocyanide of potassium is mixed with
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 cont