A Manual of the Chemistry of the Carbon Compounds

THE CARBON COMPOUNDS. 59
an ammoniaoal solution of copper sulphate to an aqueous solution
of cyanuric acid, a crystalline violet precipitate is fowned, having the
formula:—
SULPHOCYANIC ACID AND SULPHOCYANATES.
Potamnm Snlphocyanatc ^ U S.—To prepare this salt, anhydrous
potassium ferrooyanide, potassium carbonate, and sulphur are fused
together, and the melt exhausted -with spirits of wine, On evaporating
this solution the salt crystallizes in large colourless prisms. It
is very readily soluble in watev, the temperature being at the same
time so much lowered that it is sometimes used as a freezing mixture.
On mixing 500 grams with 400 grams of cold water the ternperatnre
goes down to - 20°.
CN1
Amnumuni Sulphoeyaiwie yra f S, is formed by lieating pmssic
acid with yellow ammoninm sulphide:—
CN > , NH4> „ CN > „ . NH
H | + NH;} & 2 =
S
N H ;
+
The best method to prepare it in quantity is to mix carbon disulphide
with alcohol and strong aqueous ammonium, and distil the
alcohol off after some time. On evaporating the residue on a water
bath the ammonium snlphocyanate crystallizes out. The reaction
which takes place will be explained under sulphocarbonic acid.
Ammonium sulphocyanate crystallizes in colourless deliquescent
plates, which melt at 147°, and readily dissolve in water, with the
production of cold. When heated for some time to 170° it is transformed
into the isomeric sulphocarbamide.
Sit&phocyanates of Mercury.—The two nitrates of mercury are precipitated
by soluble sulphocyanates. The mercuric sulphocyanate is
decomposed by heat, the mass swelling up and leaving a very voluminous
residue behind. It is used for the preparation of the so-called
Pharaoh's Serpents.
CN1
Sulphocyanic Acid „ \ S.—To obtain the anhydrous acid, snlphu-
retted hydrogen is passed over heated mercuric snlphocyanate. It is
a colourless, oily liquid, having a pungent odour, like acetic acid, and
solidifying at -12-5". It readily undergoes decomposition, prussic
acid Being given off, and a yellow crystalline residue left behind,
which has been called persulphoci/anic add HaC2N4Sj. Aqueous
sulphocyanic acid can be obtained by distilling potassium sulpho-