POTASSIUM CYAN ATE. 113tear it into several small pieces. After drying in the air the
small amounts of the preparation adhering to the bits of paper will
explode violently when heated or struck. It is very dangerous to
prepare any larger amount of silver hydrazoate than that indicated.
Another simple method for obtaining silver hydrazoate is given
by Sabanejeff. Heat gently 1.5 g. of hydrazine sulphate (No. 122)
with 4 c.c. of nitric acid, d. 1.3, in a test-tube which isprovided
with a gas exit tube bent at right angles. Pass the escaping gas
into a little silver nitrate solution in a second test-tube; silver
hydrazoate is obtained in the form of a white, curdy precipitate.
Filter and test the salt as before, but do not preserve it.OXYACIDS AND THEIR SALTS.
(a) Cyanates.- Potassium Cyanate; Urea from Ammonium Cyanate.
The cyanates, i.e. the salts of cyanic acid, are produced by the addition
of oxygen to the cyanides:
KCN + O - KCNO.
With regard to the constitution of cyanic acid there are two possible for-
mulas:
I. C* II. C
^O ^OH
but which of these correctly shows the structure of the free acid and of its
salts has not been definitely determined; it is quite possible that both forms
exist iii the presence of one another.
Similarly two possible formulas may be written for hypochlorous acid:I. C1^
H
II. Cl
%
O \0Hbut the second is undoubtedly the correct one for free hypochlorous acid in
aqueous solution.
The potassium cyanide required for the production of the cyanate is formed,
together with some cyanate, by heating potassium ferrocyanide with an alkali:
K 4 [Fe(CN) 6 ] + K 2 O = Fe + KCNO + 5 KCN.
In the presence of an oxidizing agent (CrO 3 ) the cyanide is oxidized to cyanate.
Dehydrate 130 g. of coarsely broken potassium ferrocyanide by
stirring it in a shallow iron dish over a rather low Fletcher burner
flame. When no more dark yellow particles can be detected in
the lumps, grind the mass to a fine powder and remove the last
traces of moisture by reheating. While still warm, triturate 100 g.