254 OXY-ACIDS AND SALTS OF THE NON-METALSinto the solutions. After a short time a marked frothing occurs
in the first flask, due to the escape of carbon dioxide, and after
this frothing ceases a similar frothing soon commences in the
second flask. When the latter ceases, pass the gas a little while
longer until sulphur dioxide escapes freely from the second bottle.
Then place the solution of sodium bisulphite in a 600-cc. beaker,
and cautiously add the remaining 53 grams of sodium carbonate.
Boil the solution uncovered for 15 minutes, replacing water lost
by evaporation; weigh and record the weight of the sulphur in the
note book; then add the sulphur, cover the beaker with a watch
glass, and keep the mixture gently boiling for an hour and a half
or longer, again replacing all the water boiled off. Filter the
solution without suction. Rinse the residual sulphur onto the
filter with 15 cc. of water, catching the drainings with the filtrate.
Then wash the sulphur, dry it, and weigh it to find whether the
calculated quantity has reacted. Evaporate the filtrate in a
porcelain dish to 200 cc, let it cool to 30°; if any unchanged sodium
sulphite is left it will separate as a crystal meal which is to be
filtered off. Leave the solution uncovered at room temperature
in an 8-inch crystallizing dish until an abundant crop of crystals is
obtained; discard the final 30 cc. of mother liquor. Sodium thio-
sulphate can remain in highly supersaturated solution; it is best
therefore to add some seed crystals to the solution set to crystal-
lize. Wrap the product in paper towels and leave it over night to
dry. Preserve it in an 8-ounce cork-stoppered bottle.
QUESTIONS- Dissolve 0.5 gram of the product in 5 cc. of water and add
2 cc. of hydrochloric acid. Observe the odor and the precipitate.
What is the free acid corresponding to the salt, sodium thio-
sulphate? What can be said regarding the stability of this
acid? - What is the valence of sulphur in each of the salts: sodium
sulphide, sodium sulphite, and sodium sulphate? State in each
case whether the sulphur plays the part of a positive or negative
element. - Distinguish between the parts played by the two atoms of
sulphur in sodium thiosulphate. - When sulphur dioxide was passed into the sodium carbonate