77C HALOGEN COMPOUNDS.
weighed quantity of potassium permanganate or of potassium
pyrochromate.2 KMnO, + 16 HC1 = 2 MnCl 2 + 2 KC1 + 8 H 2 O + 5 Cl 3 ,
K 2 Cr 207 + 14 HC1 = 2 CrCl 3 + 2 KC1 + 7 H 2 O + 3 C1 2.- Anhydrous Ferrous Chloride; Preparation of Hydrogen
Chloride.
On account of its higher melting-point it is more difficult to
prepare anhydrous ferrous chloride than the corresponding ferric
salt. Clamp a porcelain tube, 50 to 60 cm. long and 3 cm. in
inside diameter, in a horizontal position under the hood. Adjust
it at a suitable height above the blast lamp, and surround it with
an asbestos heating chamber (Fig. 4, p. 3). Introduce a loose
bundle of iron wires (0.1 cm. in diameter), weighing from
12 to 15 g., into the part of the tube which can be heated
hottest. Conduct into the tube a rapid current of hydrogen
chloride gas (see below) which is produced by the action of
concentrated, commercial sulphuric acid upon 750 c.c. of con-
centrated, commercial hydrochloric acid. Place a beaker in a
tilted position over the open end of the tube. Maintain the
temperature as high as possible during the experiment. The
product condenses in the cooler parts of the tube, and to some
extent in the beaker.
The yield is 15 to 20 g. of dirty-white, hygroscopic, leaf-like
crystals.
Small amounts of ferrous chloride can be prepared in a similar
way in a wide combustion tube which is heated in a furnace.
Aluminium chloride can be prepared in like manner from
aluminium and hydrogen chloride.Preparation of Hydrogen Chloride.Small amounts of hydrogen chloride are most conveniently
prepared in a Kipp generator containing large pieces of sal
ammoniac (ammonium chloride) upon which concentrated sul-
phuric acid is allowed to act. This method does not work as
well for preparing large quantities of the gas, because the foam-
ing which occurs becomes troublesome.