SODIUM COBALTINITRITE. 149cadmium iodide solution is very small, treat the last mother-
liquor with hydrogen sulphide. A slight separation of cadmium
sulphide takes place after some time, but the precipitation is
incomplete.
NITRITO ACIDS AND THEIR SALTS.- Potassium Mercurinitrite, K 3 [Hg(NO 2 ) 5 ]. H 2 O.
Treat 43 g. of yellow mercuric oxide in a 500 c.c. flask with 71 g.
of potassium nitrite and 240 g. of 10% acetic acid, and shake
frequently until all is dissolved. Filter and concentrate the
solution to crystallization on the water bath. The separation of
crystals is much aided by the cautious addition of some alcohol.
Collect the crystals and work up the mother-liquor. Recrys-
tallize the combined crude product from a little water to which a
few drops of potassium nitrite solution have been added. Pale-
yellow, lustrous prisms, or plates, are obtained which are easily
soluble in water; by slow evaporation, crystal aggregates are
sometimes obtained of finger length.
The small content of mercuric ions in the solution of this salt is
shown by its indifference toward a solution of urea, or toward a
cold sodium bicarbonate solution that is saturated with carbon
dioxide; on the other hand, precipitates are produced by sodium
carbonate and by sodium hydroxide. From this it follows that
a potassium mercurinitrite solution contains mercuric ions in
about the same concentration as a solution of mercuric chloride.- Sodium Cobaltinitrite; Potassium Cobaltinitrite.
Sodium Cobaltinitrite. Dissolve 50 g. of cobaltous nitrate and
150 g. of sodium nitrite in 150 c.c. of water. Cool the solution
to 40° and, while shaking frequently, add 50 c.c. of 50% acetic
acid, a little at a time. Then oxidize the cobaltous salt by draw-
ing air through the liquid for half an hour (see No. 107). After
some time filter off the precipitate, which consists of sodium cobalti-
nitrite and perhaps a little of the corresponding potassium salt.
Stir this precipitate with 50 c.c. of water at 70°-80° and after
10 minutes filter off the solution. Combine the two filtrates, and
by introducing 350 c.c. of 96% alcohol from the jet of the wash-
bottle while stirring, throw down the sodium cobaltinitrite from