342 HEAVY METALS OF GEOUPS VI, VII, AND VIII
cannot ignite the next addition instantly. On the other hand, if
another portion is added before the previous one has acted, both
may start together with explosive effect. When the crucible has
cooled, break it, and separate the regulus of metallic manganese
from the slag of fused aluminum oxide.
QUESTIONS- If pyrolusite containing water were used without previous
heating, what disadvantage would result during the process? - What economy of materials is effected by converting the man-
ganese dioxide into the lower oxide?
PREPARATION 73
FERROUS AMMONIUM SULPHATE, FeSO 4 -(NH 4 ) 2 SO4-6H 2 O, AND
FERRIC AMMONIUM ALUM, Fe 2 (SO4)3-(NH 4 ) 2 SO4-24H 2 O, FROM IRON
Corresponding to the two most important oxides of iron, FeO
and Fe 2 O 3 , the two sulphates, FeSC>4 and Fe 2 (SO4)3, can be pre-
pared. By dissolving iron in sulphuric acid a solution of ferrous
sulphate is obtained. This, however, is readily oxidizable, slowly
even by the oxygen of the air, to the higher sulphate, and ferrous
sulphate can be preserved free from ferric salt only when all oxygen
is excluded, or when it is kept in contact with an excess of metallic
iron in an acidified solution. Dry, crystallized ferrous sulphate,
or green vitriol, FeSO4-7H 2 O, can be preserved fairly well without
becoming oxidized; but the double salt, ferrous ammonium sul-
phate, not only is more easily prepared on account of the readiness
with which it crystallizes, but also is less easily oxidized by con-
tact with the air.Materials: 6N H 2 SO 4 , 222 cc. + 61 cc.
iron filings, 40 grams,
ferrous carbonate, 10 grams,
ammonium sulphate, 45 grams + 25 grams.
16 N HN0 3 , 14 cc.
Apparatus: 500-cc. flask.
500-cc. graduated cylinder,
two 8-inch crystallizing dishes.
8-inch porcelain dish.