SODIUM CARBONATE 181Materials: sodium chloride, NaCl, 59 grams 1 F.W.
15 N ammonium hydroxide, 80 cc.
carbon dioxide, which can be drawn either from an
automatic gas generator (see Note 13 (c), page 20),
or from a gas holder which is filled as needed
from a steel cylinder of liquid carbon dioxide.
Apparatus: bubbling bottle, through which the carbon dioxide
is to pass to indicate its rate of flow.
suction filter and trap bottle.
2,000-cc. flask equipped with 1-hole rubber stopper,
a delivery tube with a short right-angle bend at
the top and reaching to within an inch of the
liquid in the flask, and 30 inches of rubber delivery
tube.
300-cc. flask with stopper.
funnel and filter.
4-inch porcelain dish.
iron ring and ring stand.
Bunsen burner.Procedure: Place the salt, the ammonium hydroxide, and 150 cc.
of water in the 300-cc. flask and shake vigorously until the salt
is nearly dissolved. Pour the solution through a filter into the
large flask. Use this flask as the absorption vessel and connect it
with the source of carbon dioxide. Loosen the stopper of the
flask and let the carbon dioxide expel the air. Then stopper the
flask and shake it as vigorously as possible until the absorption of
carbon dioxide has slackened. Loosen the stopper again to allow
any air that has accumulated in the flask to escape; then continue
the shaking until practically no more gas passes the bubbling
bottle even with vigorous shaking. If the shaking has been
continuous, this point will be reached within 30 minutes.
Pour the suspension of sodium bicarbonate into the suction
filter funnel (Notes 3 and 4 (6)) and allow it to drain until the
surface of the mass in the funnel is firm. Press the surface
gently with the blunt end of a test tube to close up any cracks or
channels that may have opened and to squeeze out the last possible
drops of chloride-containing solution. Stop the suction; pour
over the surface of the product 15 cc. of cold distilled water,
letting it penetrate uniformly into the mass for 3 minutes. Again