nown by the name of yellow prussiate of potassa. It contains
ferrocyanogen, a compound radical, consisting of 1 eq. of metallic iron
and 3 eq. of the elements of cyanogen, and is designated by the symbol
Cfy.

The potassium salt is manufactured on a large scale from refuse animal
matter, as old leather, chips of horn, woolen rags, hoofs, blood (hence
its German name, "Blutlaugen salz"), greaves, and other substances rich
in nitrogen, by fusing them with crude carbonate of potassa and iron
scraps or filings to a red heat, the operation to go on in an iron pot or
shell, with the exclusion of all air. Cyanide of potassium is generated
in large quantities. The melted mass is afterward treated with hot water,
which dissolves the cyanide and other salts, the cyanide being then
quickly converted by the action of oxide of iron, formed during the
operation of fusing, into ferrocyanide. The filtered solution is
evaporated, crystallized, and recrystallized. The best temperature for
making the solution is between 158 and 176 deg. F. The conversion of the
cyanide into the ferrocyanide is greatly facilitated by the presence of
finely divided sulphuret of iron and caustic potash. Some years ago this
salt was manufactured by a process which dispensed with the use of animal
matter, the necessary nitrogen being obtained by a current of atmospheric
air. Fragments of charcoal, impregnated with carbonate of potassa, were
exposed to a white heat in a clay cylinder, through which a current of
air was drawn by a suction pump. The process succeeded in a chemical
sense, but failed on the score of economy.

Richard Brunquell passes ammonia through tubes filled with charcoal, and
heated to redness so as to form cyanide of ammonium, which is converted
into the ferrocyanide of potassium by contact with potash solution and
suitable iron compounds. Ferrocyanide of potassium is in large beautiful
transparent four-sided tabular crystals, of a lemon-yellow color, soluble
in four parts of cold and two of boiling water, insoluble in alcohol.
Exposed to heat it loses three eq. of water, and becomes anhydrous; at a
high temperature it yields cyanide of potassium, carbide of iron, and
various gases. This salt is said to have no poisonous properties,
although the dangerous hydrocyanic acid is made from it. In large doses
it occasions, however, vertigo, numbness, and coldness. It is used in
various photographic processes. Newton employs it in combination with