sulphocyanogen, C_{2}NS_{2}, which is expressed by the symbol Csy. The
sulphocyanide of potassium, KCsy, is prepared by fusing ferrocyanide of
potassium, deprived of its water of crystallization, intimately mixed
with half its weight of sulphur and 17 parts of carbonate of potassa. The
molten mass, after having cooled, is exhausted with water, the solution
evaporated to dryness, and extracted with alcohol, from which the
crystals of the salt are separated by evaporation.

It is also made by melting the ferrocyanide of potassium with sulphide of
potassium. It is a white, crystallizable salt of a taste resembling that
of niter, soluble in water and alcohol, and extremely poisonous. It
dissolves the chlorides, iodides, and bromides of silver, is, therefore,
a fixing agent, but has not come in general use as such. Vogel speaks
highly of it as an addition to the positive toning bath, although he
prefers the analogous ammonium salt in the following formula:

Chloride of gold solution.... (1:50) 3 c. cm. (46-1/5 grains).
Sulphocyanide of ammonium ... 20 grammes (308 grains).
Water........100 c. cm. (3 ounces 5 drachms 40 grains).

_Ferrocyanide of Potassium_--K_{2}Cfy+3HO, or K_{2}C_{8}N_{3}Fe+3HO, is
generally known 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