228 HEAVY METALS OF GROUPS I AND IIby slow diffusion is to insure the formation of large, well-defined
crystals.
Materials: copper sulphate, CuSO4-5H 2 O, 25 grams = 0.1 F. W.
6.ZVNH4OH, 85 cc.
95% alcohol, 165 cc.
ether, 20 cc.
Apparatus: 125-cc. separatory funnel.
8-ounce common bottle.
two 300-cc. flasks.
400-cc. beaker.
4-inch porcelain dish.
Procedure: Pulverize the copper sulphate, place it in a flask and
dissolve it in the 85 cc. of cold 6 N NH 4 0H. (See Note 7, page 12.)
Pour the solution through a filter, catching the filtrate in another
flask. Place 125 cc. of alcohol in the bottle; fill the stem of the
dropping funnel with water; insert it to the bottom of the alcohol,
and run in 20 cc. of water to form a layer beneath the alcohol to
separate the latter from the ammoniacal copper solution, which
is next introduced through the funnel. Allow no bubbles of air
to be sucked with the liquid into the stem of the funnel and thus
avoid stirring up the solution and mixing the layers. Set the
bottle away for at least a week, at the end of which time crystals
2 or 3 cm. long will have formed. The alcoholic and aqueous
layers have not yet completely diffused into each other, and when
they are mixed, a meal of very small crystals is precipitated.
Therefore pour the liquid all at once out of the bottle into a clean
beaker. The large crystals adhere to the inside of the bottle.
Remove them to a small dish; add 10 cc. of alcohol to which 1 cc.
of ammonia has been added; stir thoroughly by rotating the dish,
and pour off the alcohol, allowing it to carry with it any of the
precipitate of small crystals. Repeat the washing with 10 cc. of
alcohol and then with 10 cc. of ether. Spread the crystals on
paper towels and leave them until they cease to smell of ether.
Then at once stopper them tightly in a 2-ounce cork-stoppered
bottle, since they give off their ammonia rather easily. Drain on
a suction filter the crystal meal formed in the beaker, and wash it
on the filter (Note 5 (a), page 9) with the same liquids as were
used for the larger crystals. Preserve the large crystals and the
crystal meal separately, each in a 2-ounce cork-stoppered bottle.