HEXAMMINENICKELOUS BROMIDE. 171'
The mixture becomes heated to boiling as a result of the reaction,
and it should therefore be cooled somewhat to prevent too much
evaporation. When a clear, deep-blue solution is obtained add
8 c.c. of alcohol and again saturate the liquid with ammonia, this
time cooling it with ice. Drain the deposited salt on a hardened
filter, wash it with alcohol to which a little concentrated ammonia
has been added, then with pure alcohol and finally with ether,
and suck it as dry as possible. Yield, 15 to 18 grams. The
preparation must be placed immediately in a stoppered bottle,
as it loses ammonia on standing in the open air. The addition
of the alcoholic washings to the mother-liquor causes the pre-
cipitation of a few grams more of finely-divided and consequently
lighter-colored product.- Hexaniminenickelous Bromide, [Ni(NH 3 )c]Br 2.
Hexamminenickelous bromide can be used in making cobalt-free prepa-
rations of nickel such as are required for atomic weight determinations.
The corresponding cobalt salt is far more soluble. The raw material used
and the final product obtained should be tested qualitatively for cobalt.
Pour a solution of 141 g. crystallized nickel sulphate in 4 liters
of water into a large flask and add a solution of 41 g. sodium
hydroxide in 200 c.c. of water. Wash the resulting, voluminous,
light-green precipitate by decantation; let it settle as much as
possible, then siphon off the supernatant liquid and fill the flask
again with distilled water; repeat this process from time to time
for from three to five days. Collect the washed precipitate upon
a large plaited filter and dissolve it in an aqueous solution of hydro-
bromic acid containing about 82 grams of the acid.
1
Evaporate
the filtered solution to dryness on the water-bath, take up the
residue in as little water as possible, cool the solution to 0° with
a mixture of ice and salt and then treat it with concentrated
ammonia; an abundant precipitate of violet, micro-crystalline
flakes is obtained and the liquid becomes colorless. After stand-
ing for a short time at 0°, collect the crystalline mass on a suction-
filter, wash it carefully with ice-cold ammonia (to remove any
cobalt present), and dry it in a desiccator over lime which is
mixed with a little solid ammonium chloride. The yield is almost
> Cf. No. 35.