ISOMERIC CHROMIC CHLORIDE HYDRATES. 199
- Isomeric Chromic Chloride Hydrates, CrCls.6H 2 O.
Hydrated chromic salts possess both violet and green modifications.
Although solutions of most of the green chromic compounds cannot be made
to yield the crystallized salts, the chloride, on the other hand, can be crystal-
lized in both forms, each having the same composition CrCl 3 .6H 2 O. The
violet salt is normal in its behavior, inasmuch as when it is dissolved in
water the entire chlorine is ionizable, and the solution thus contains three
chlorine ions to one hydrated chromic ion. The formula of the violet modi-
fication is therefore [Cr(H 2 O) 6 ]Cl 3. On the other hand, the solution of the
green salt contains chlorine in a non-ionic condition — according to Werner
and Gubser,^1 two of the chlorine atoms are attached in the complex. Since,
furthermore, two of the six molecules of water are less firmly bound in the
salt than the other four, the green chloride may be formulated:
[Cr(H 2 O) 4 Cl 2 ]C1.2H 2 O.
For further details, consult the original article cited in which the above ex-
planation is deduced from conductivity measurements. It has been shown
by Weinland and Koch^2 that precipitations with silver salts serve qualita-
tively but not quantitatively to explain the relations.
Preparation of the Crude Chloride. Warm 100 g. of chromic
acid anhydride (under the hood in the hydrogen sulphide room)
in a flask, with 400 g. of concentrated hydrochloric acid. Red
vapors are first evolved. Boil the solution until it becomes pure
green and no more chlorine is evolved. About three hours are
required, and during the boiling more hydrochloric acid is added
if necessary. Concentrate the solution in an evaporating dish
until it has the consistency of sirup, allow it to cool, spread the
thick mass of crystals on a porous plate, and finally dry the pro-
duct in a desiccator over lime. - Crystallized Green Chromic Chloride. Dissolve 50 g. of the
impure chloride in 40 c.c. of water, filter, and while keeping cold
with a mixture of ice and salt, saturate the solution with gaseous
hydrogen chloride. After standing several hours, drain the
crystalline paste in a funnel containing a marble around which
a thin cord of asbestos is laid. Without washing, dry the crys-
tals one to two days in a desiccator; then stir them up with
acetone, which does not dissolve the dry salt, drain the product
on a hardened filter, and wash it with acetone until the latter runs
through colorless. Yield, 10 to 20 grams.
(^1) Ber. 34, 1591 (1901).
(^1) Z. anorg. Chem. 39, 296, 320 (1904).