(^78) HALOGEN COMPOUNDS.
troduce a glass tube one-half meter long and about 1 cm. in diam-
eter, and make the joint tight with a piece of rubber tubing around
the glass. This long tube is to serve as a condenser, and to lead
the excess of bromine into the hood.
After starting the current of carbon dioxide, heat the bismuth
gently by means of a Bunsen burner with a flame spreader, and
warm the bromine by placing
the wash bottle in warm water
and renewing the latter as it
cools. Dark-red vapors of
bismuth bromide form and
condense as yellow flakes in
the bulb of the retort, and
to some extent in the glass
tube.
Break the retort, collect
the product, and let it stand
over night in a vacuum desic-
cator to remove any adhering
bromine; or, distil it from a
smaller plain retort. The
neck of the latter should be
about 8 cm. long and the whole should be suspended in a double
loop of wire (cf. No. 48). Yield, nearly theoretical.-
Boiling-point of Bismuth Bromide. Use a thermometer filled
under pressure, which measures temperatures as high as 540
0
.
1
Place the bismuth bromide in a Jena glass test-tube, 20 cm. long
and 2.5 cm. wide, and heat until the substance boils; suspend
the thermometer so that it reaches well into the vapor. When the
vapors first begin to reach the mercury bulb, lower or remove the
flame for a while so as to avoid heating the thermometer too
suddenly; then heat strongly again. Correct the boiling-point as
thus determined either as directed in No. 6, or by means of finding
the apparent boiling-point of pure sulphur under exactly the same
conditions. The difference between the latter observed reading
and 448° (the true boiling-point of sulphur) is to be applied as a
correction to the apparent boiling-point of the bismuth tribromide.
This very simple method of making the correction for stem expo-
FIG. 15.
(^1) Cf. No. 54 for the thermoelectric measurement of temperatures.