174 METAL-AMMONIA COMPOUNDS.hour, a separation of chloropentamminecobaltic chloride takes
place. After cooling, filter off the crystals and wash them with
dilute hydrochloric acid.
For purification, dissolve the crude product in 300 c.c. of twoper cent ammonia solution, whereby aquopentamminecobaltic
chloride is formed (cf. No. 134), extract the residue twice with
50 c.c. of the same ammonia solution, and precipitate the filtrate
by adding 300 c.c. of concentrated hydrochloric acid and heat-
ing the mixture for three-quarters of an hour on the water-bath.
After it has become perfectly cold, filter off the salt, and wash it
with dilute hydrochloric acid and alcohol. Yield, 30 to 34 grams,
which is nearly the theoretical quantity.
Since nickel does not form any similar salt, this gives a means of preparing
a nickel-free product from impure cobalt preparations.
Reactions. A cold, concentrated, aqueous solution of the above
salt when treated with hydrochloric acid yields short, red crystals
after standing some time. Mercuric chloride causes the imme-
diate precipitation of long, rose-red needles of the composition
[Co(NH 3 ) 5 Cl]Cl2-3 HgCl 2. Potassium chromate gives brick-brown
crystals. Potassium dichromate causes the slow formation of
clusters of fine, orange needles, or of large, flat prisms; ammonium
oxalate slowly yields well-formed, red prisms which can be seen
under the microscope.
- Sulphate and Nitrate of the Chloropentammine Series.
Acid Chloropentamminecobaltic Sulphate, [CoiNHshClhiHSO^ySO^
Triturate 5 g. of chloropentamminecobaltic chloride with 12 g.
of concentrated sulphuric acid in a mortar, whereby hydrogen
chloride is evolved. Dissolve the mass in 40 c.c. of water at
70° and filter. On cooling the solution, long, thin, fuchsine-red
prisms are deposited. The crystals become larger if they are
allowed to stand for several days in contact with the mother-
liquor, because smaller crystal grains are slightly more soluble
than larger ones and therefore dissolve slowly, while the larger
crystals grow still larger. Wash the crystals with absolute alcohol
and dry them in the hot closet. Yield, 3 grams.
When the alcoholic washings are added to the mother-liquor
a fine, dull-red, crystalline meal of the same salt is precipitated.