124 NITRITE AND NITRATES.
be present, which will frequently be the case, evaporate the solu-
tion to dryness and heat the silver nitrate carefully until it just
begins to melt. In this way the remainder of the copper nitrate
is decomposed. Repeat the extraction with water.
The copper oxide residues should contain very little silver.- Bismuth Nitrate and Basic Bismuth Nitrate.
Bismuth nitrate may be obtained from the solution of the metal in nitric
acid in the form of large, colorless crystals with 5 molecules of water. The
salt is strongly hydrolyzed by water, and, according to the temperature and
the concentration of the acid, basic salts of various compositions are pro-
duced.^1 The following directions yield a precipitate of approximately the
composition, 4 Bi 2 O 3 • 3 N 2 O 6 • 9 H 2 O, which is not, however, to be regarded as
a homogeneous compound. This is the so-called bismuth subnitrate so much
used in medicine and often called bismuth by physicians.
Dissolve 100 g. of coarsely pulverized bismuth by heating it in
a flask with 500 g. of nitric acid (sp. gr. 1.2). Filter through a
hardened filter, using suction, and evaporate in a porcelain dish
until crystallization begins. Collect the crystals on a suction-
filter, wash with a little nitric acid (sp. gr. 1.2) and dry in a desic-
cator. Evaporate the mother-liquor to obtain more crystals.
To prepare the above mentioned basic salt, triturate one part of
the bismuth nitrate with four parts of water and stir this mixture
into 21 parts of boiling water. Allow the precipitate to settle,
wash by decantation, collect on a suction-filter and dry the prepa-
ration at a temperature not exceeding 30°.
(d) Manganates and Ferrates.
- Potassium Permanganate by the Fusion Method.
By fusing manganese compounds in an oxidizing-alkaline flux a man-
ganate is formed, and this, when it is dissolved in water and the free alkali
is neutralized, changes into permanganate and manganese dioxide:
MnO 2 + K 2 CO 3 + O = CO 2 + K 2 Mn0i,
3 K 2 Mn0 4 + 2 H 2 O = MnO 2 + 4 KOH + 2 KMnO 4.
Melt together 80 g. of potassium hydroxide and 40 g. of potas-
sium chlorate in a sheet iron crucible 6 to 8 cm. in diameter.
Remove the flame and while stirring with an iron spatula (a heavy
wire or an old file), add 80 g. of finely powdered pyrolusite, quite
rapidly but not all at once. The fusion effervesces somewhat.(^1) Cf. A. Findlay: The Phase Rule.