146 NON-METALLIC ELEMENTS IN BINARY COMPOUNDSThe phosphorus will not stick to the glass. Add water one drop
at a time, shaking after each addition until the phosphorus adheres
to the glass, but avoid using enough water to give any appearance
of wetness. Place the uncoated broken glass in the bend of each
small U-tube and fill the vertical arms nearly up to the side arm
with the glass coated with phosphorus. Pack a little glass wool
on top of the broken glass. Pour 25 cc. of distilled water, or enough
to close the bend, into the large U-tube. Caution: Use extreme
care in handling bromine. The liquid produces severe burns on the
skin and the vapor is very irritating to the eyes and throat. Make
sure that the stop cock of the separatory funnel is tight, properly
lubricated, and turns easily. When manipulating it after the
bromine has been added, hold the bulb with one hand, and exert
a slight inward pressure on the stop cock while turning it with the
other hand. Be very careful that the cock does not slip out of the
socket letting the bromine leak out over the fingers.
After making sure that the apparatus is tight, measure the bro-
mine and pour it into the funnel. Then let a single drop of bro-
mine fall into the flask, watching its effect. Add the rest of the
bromine a drop at a time as rapidly as proves safe. After the gas
ceases to be absorbed in the large U-tube disconnect the apparatus.
When the hydrobromic acid has cooled to room temperature deter-
mine its volume and specific gravity. Use either a hydrometer or
the apparatus shown in Fig. 19. Consult the table on page 371
and determine the percentage composition of your solution.
Calculate the weight of hydrogen bromide obtained, the normality
of the solution, and the percentage yield. Preserve your prepara-
tion in a 2-ounce glass-stoppered bottle. Wash out the apparatus
at the sink under the hood.
QUESTIONS- Why would not a metal like zinc, which will combine vig-
orously with bromine, serve instead of phosphorus? - Explain why phosphorus is placed in the small U-tubes.
- Explain why at the outset of the process bubbles pass out-
ward through the large U-tube, and later they pass in the op-
posite direction. - What are the products of the reaction of concentrated
sulphuric acid with potassium bromide? (See Experiment 13,
page 167.) Write the equations. What property possessed by
hydrogen bromide, but not by hydrogen chloride, is shown?