340 HEAVY METALS OF GROUPS VI, VII, AND VIII
stir continuously until the mass stiffens completely. Then cover
the crucible and heat it 5 minutes longer at a dull red heat.
When the mass has cooled, place crucible and all in 1 liter of
water in an 8-inch porcelain dish. After the solid has entirely
disintegrated, remove the crucible and rinse it off with a little
water from the wash bottle. Transfer the mixture to a 2-liter
bottle and pass carbon dioxide into the cold solution until the green
color of the manganate has entirely changed to the violet red of
the permanganate. Test the color by touching a drop of the
solution to a piece of filter paper. Examine the spot on the reverse
side. If it is purple with no trace of green the change to perman-
ganate is complete. Let the sludge of manganese dioxide settle
in the bottle for 10 minutes; then syphon the liquid on to an as-
bestos filter. Lastly, with the aid of a jet of water from the wash
bottle, transfer all the sludge to the filter and drain it free from
liquid. Evaporate the solution in a clean dish to a volume of
300 cc. Let it settle a moment and filter it through asbestos as
before. Pour the nitrate into the 8-inch porcelain dish, and allow
it to cool slowly in a place protected from dust. When cold,
collect the crystals of potassium permanganate in a filter funnel in
which a marble is placed. Evaporate the mother liquor to 100 cc,
filter it hot through asbestos, and obtain a second crop of crystals
on cooling the nitrate. Discard the remaining liquid, since it
cannot contain more than about 6 grams of potassium permanga-
nate and to evaporate it further would cause potassium chloride
also to crystallize out. Weigh all the crystals, dissolve them in
eight times their weight of water (to give a saturated solution at
about 40°), filter the solution through asbestos at near the boiling
temperature, and let it cool slowly and crystallize in a small por-
celain dish covered with a watch glass. Recover another crop of
crystals in the same way from the mother liquor, after evaporating
it to a volume of 60 cc. Allow the crystals to dry on a clean un-
glazed plate, and preserve them in a 2-ounce, cork-stoppered bottle.
QUESTIONS- Name and give the formulas of all the oxides of manganese.
- From which oxide is K 2 Mn04 derived? KMnO 4?
- Write the reactions involved in the above preparation.
- How could KMnO 4 be converted back into K2M11O4? Equa-
tion?