77A HALOGEN COMPOUNDS.
dish over the free flame in order to expel the excess of hydro-
chloric acid. Dissolve the residue, which solidifies on cooling, in
3 to 4 liters of water. Dilute one-tenth of this solution in a flask
with a large amount of water, and add caustic soda, avoiding an
excess, in order to precipitate manganese hydroxide. After
settling, siphon off the clear solution, shake up the precipitate
with pure water, and wash it repeatedly by decantation until, at
the end of three or four days, all of the sodium salt has been
removed. Add the manganese slime thus obtained to the remain-
ing nine-tenths of the first solution, and allow the mixture to stand
for several days in a thick-walled, five-liter flask which is placed
in a warm place. Shake the mixture frequently until all of the
iron has been precipitated by means of the manganese hydroxide.
This usually requires about two days, and at the end a little of
the filtered solution should give no test with potassium thiocya-
nate. Filter the solution through a plaited filter and evaporate it
until crystals begin to separate. Then transfer it to a flask and
cool rapidly while rotating under the water tap. Drain the crystal
meal in a suction-funnel and wash it first with 50%, and then with
pure alcohol. By evaporating the mother liquor a further yield
is obtained. Allow the light pink crystals, which are still moist
with alcohol, to dry in contact with the air.
- Anhydrous Ferric Chloride; Preparation of Chlorine.
Clamp a tubulated retort (cf. Fig. 15, p. 78), of about 250 c.c.
capacity so that its neck (which is 1 to 2 centimeters wide) is in a
horizontal position. Insert a bundle of iron wires (about 0.1 cm.
in diameter), weighing 10 to 25 g., to about the middle of the neck,
and connect the end of the latter, through two sulphuric acid wash-
bottles, with a chlorine generator. Into the tubulus of the retort
insert a vertical tube, about 50 cm. long and 1 cm. wide, making
the joint tight by means of a short piece of rubber tube. Place
the whole apparatus under the hood.
Conduct a fairly rapid stream of chlorine into the retort, and
heat gently, with a small flame that does not touch the glass, that
part of the neck which contains the iron wire. Very soon a reac-
tion begins to take place with the emission of light, and a shower of