any of the same elements with
which chlorine unites, but with less energy. It combines with hydrogen
and takes away the latter element from some of its compounds, but not
so readily as does chlorine. Its bleaching properties are also less
marked.

Bromine finds many uses in the manufacture of organic drugs and
dyestuffs and in the preparation of bromides.

~Hydrobromic acid (HBr).~ When sulphuric acid acts upon a bromide
hydrobromic acid is set free:

2NaBr + H_{2}SO_{4} = Na_{2}SO_{4} + 2HBr.

At the same time some bromine is set free, as may be seen from the red
fumes which appear, and from the odor. The explanation of this is found
in the fact that hydrobromic acid is much less stable than hydrochloric
acid, and is therefore more easily oxidized. Concentrated sulphuric acid
is a good oxidizing agent, and oxidizes a part of the hydrobromic acid,
liberating bromine:

H_{2}SO_{4} + 2HBr = 2H_{2}O + SO_{2} + 2Br.

~Preparation of pure hydrobromic acid.~ A convenient way to make
pure hydrobromic acid is by the action of bromine upon moist
red phosphorus. This can be done with the apparatus shown in
Fig. 56. Bromine is put into the dropping funnel A, and red
phosphorus, together with enough water to cover it, is placed
in the flask B. By means of the stopcock the bromine is
allowed to flow drop by drop into the flask, the reaction
taking place without the application of heat. The equations are

(1) P + 3Br = PBr_{3},

(2) PBr_{3} + 3H_{2}O = P(OH)_{3} + 3HBr.

[Illustration Fig. 56]

The U-tube C contains glass beads which have been moistened
with water and rubbed in red phosphorus. Any bromine escaping
action in the flask acts upon the phosphorus in the U-tube. The
hydrobromic acid is collected in the same way as hydrochloric
acid.

~Properties.~ Hydrobromic acid very strikingly resembles hydrochloric acid
in physical and chemical properties. It is a colorless, strongly fuming
gas, heavier than hydrochloric acid and, like it, is very soluble in
water. Under standard conditions 1 volume of water dissolves 610 volumes
of the gas. Chemically, the chief point in which it differs from
hydrochloric acid is in the fact that it is much more easily oxidized,
so that bromine is more readily set free from it than chlorine is from
hydrochloric acid.

~Salts of hydrobromic acid,--bromides.~ The bromides are very similar to
the chlorides i