Laboratory Methods of Inorganic Chemistry, 2nd English Ed. 1928

186 METAL^AMMONIA COMPOUNDS.

The preparation of these two isomeric compounds is described in Preparations

142 and 143. Both of these can be obtained from hexamminecobaltous

chloride, which, as described here, is prepared in much the same way as the

analogous nickel salt (No. 128).

Before beginning the experiment proper, prepare some air-free

alcoholic ammonia solution. Boil 200 c.c. of alcohol, in a flask

connected with a reflux condenser, for half an hour, then remove

the condenser and pass a current of dry ammonia into the alcohol

while it is cooling. Take the ammonia from a bomb or generate

it as in Preparation No. 140.

Dissolve 15 g. of cobaltous chloride crystals, CoCU-GH^O, in

15 c.c. of water and boil the solution to expel all air. While still

hot, pour this solution into 40 c.c. of hot, concentrated ammonia

solution. Filter immediately into a 150 c.c. Erlenmeyer flask

using a 12 cm. filter which has been moistened with concentrated

ammonia solution and letting the funnel hang in the neck of the

flask to avoid contact of air with the filtrate. Keep the filtrate

hot, over a burner, and add enough of the alcoholic ammonia

solution to form a slight permanent turbidity. The flask will now

be practically full of liquid; close it loosely with a cork stopper

and cool under running water; tiny, pink, octahedral crystals of
hexamminecobaltous chloride will form. To collect the precipi-

tate, it is best to use a small filter tube containing a perforated

porcelain plate covered with a flat piece of filter paper. A large

Gooch crucible and paper filter can be used if preferred but a
Btichner filtering funnel is less satisfactory because there is too

much exposure to the air. Wash the precipitate once with con-

centrated, aqueous ammonia solution, three times with alcoholic

ammonia solution and finally with ether, keeping the crystals
covered with liquid throughout the washing operations. Finally,

apply strong suction for a moment, remove the crystals to a vacuum

desiccator and dry over soda lime to which a little powdered

ammonium chloride has been added. The color of the crystals
should be a pale, yellowish-pink. A deeper yellow or brown color

shows that oxidation has taken place.

Yield, 7 g. A better yield can be obtained if the ammoniacal

cobalt solution is completely precipitated with the alcoholic

ammonia, but the crystals are then so small that they are very

susceptible to atmospheric oxidation and are hard to wash
thoroughly.