POTASSIUM PERMANGANATE 339manganate decomposes spontaneously, two-thirds being oxidized
to permanganate at the expense of the other one-third, which is
reduced again to manganese dioxide:
3K 2 Mn0 4 + 4H 2 CO 3 -»• 2KMnO 4 + MnO 2 + 2H 2 O + 4KHCO 3The permanganate (or permanganic acid) corresponds to the
heptoxide of manganese, Mn 2 O7, which is the most strongly acid-
forming of the oxides of manganese. Permanganic acid is a strong
and very soluble acid, being of approximately the same acid
strength as nitric or hydrochloric acids. It is in addition a very
powerful oxidizing agent.
Materials: powdered pyrolusite, MnO 2 , 50 grams,
potassium hydroxide, 60 grams,
potassium chlorate, 25 grams,
carbon dioxide,
shredded asbestos for filter.
Apparatus: 4-inch sheet-iron crucible,
tongs.
8-inch porcelain dish.
4-inch porcelain dish.
5-inch watch glass,
porous plate.
suction filter and glass marble.
2-liter common bottle,
iron ring and ring stand.
Bunsen burner.
Procedure: Grind 50 grams of pyrolusite to as fine a powder as
possible (the finer it is ground, the more successful the preparation).
Place 60 grams of potassium hydroxide and 25 grams of potassium
chlorate in a 4-inch sheet-iron crucible. Heat the mixture care-
fully until it is just melted. Remove the flame from under the
crucible and add the pyrolusite, a little at a time, stirring vigor-
ously all the while. Since the charge in the crucible effervesces and
spatters particles of melted salt, great care should be taken to keep
the eyes at a safe distance. The hand holding the stirrer should
be protected, and with the other [hand the crucible should be
held firmly by means of iron tongs. After all the pyrolusite is
added, place a small flame below the crucible, and keep stirring
the charge. Gradually increase the strength of the flame, and