70 ACIDS AND BASES.
Test the conductivity of nitrobenzene after the same manner,
first alone, and then with the addition of a little anhydrous nitric
acid; the lamp does not glow in either case.- Hydrobromic Add. Hydriodic Acid.
(a) From the Elements. Connect in series, a Kipp hydrogen
generator, a wash bottle containing sulphuric acid, a wash bottle
containing 80 g. of bromine, and a glass tube about 25 cm. long
and 1 cm. wide which is rilled for a space of 8 to 12 cm. with
loosely-packed, platinized asbestos. (Cf. No. 28.) Place a
Bunsen lamp with a flame spreader under the tube. Connect the
farther end of the contact tube with a U-tube containing glass
beads and moist red phosphorus, then with a wash bottle made
from a test tube which contains 1 c.c. of water, and finally with
two wash bottles each containing 35 c.c. of water. Keep the
latter cooled during the experiment, first with ice-water and later
with a mixture of salt and ice.
At the beginning of the experiment, disconnect the train at a
point between the contact tube and the phosphorus tube. Fillthe apparatus up to this point with hydrogen, then heat the con-
tact layer to faint redness, and when the gas escaping from this
tube becomes colorless, reconnect the rest of the apparatus.
Regulate the amount of bromine vapor by pouring .warm (not
hot) water from time to time into the beaker which surrounds
the bromine bottle. The gases after passing the contact layer
must contain no uncombined bromine, and must therefore be
colorless.
From the first receiver fuming hydrobromic acid is obtained,
and the yield can be determined by weighing the flask before and
after the experiment.
Hydriodic Acid can be prepared from hydrogen and iodine in a
similar manner. Dry the hydrogen gas by passing it through three
wash bottles containing concentrated sulphuric acid and lead the
gas through glass tubing to the bottom of a small fractionating
flask which contains 50 g. of iodine and is being heated gently.
Insert the short arm of the distilling flask in a cork stopper which
fits into a wide glass tube, 70 cm. long, which is also kept warm.
Place a plug of platinized asbestos in the wide glass tube not far
from the place where the tubing from the flask enters the wider