200 HYDRATES.
The preparation dissolves in water to an emerald-green solu-
tion. If this solution is precipitated with ammonia, and the
chromic hydroxide is redissolved in hydrochloric acid while cool-
ing, a violet solution of the other modification of the chloride is
obtained. The violet modification is the more stable in solutions
that are free from acid.
- Crystallized Violet Chromic Chloride. Dissolve 40 grams of
commercial chromic nitrate, Cr(NO3)3-9H2O in 40 c.c. of water,
add 20 c.c. of concentrated hydrochloric acid, cool with ice and
saturate with hydrogen chloride at ice temperature. Collect the
precipitate on a double layer of hardened filter paper in a 5 cm.
Biichner funnel and wash it with ice-cold concentrated HC1.
Dissolve this product in 40 c.c. water, filter if necessary, add
20 c.c. of concentrated HC1 and again saturate at the ice tempera-
ture with hydrogen chloride. Pour the now almost colorless
mother-liquor off and drain the crystal mass on a double layer of
hardened filter paper in the Buchner funnel; wash several times
with acetone, and lastly with anhydrous ether. Dry the product
in a vacuum desiccator over sulphuric acid. The violet chromic
chloride can only be kept unchanged when it is completely dry;
otherwise it turns green.