hese is thiosulphuric acid.

When sodium sulphite is boiled with sulphur the two substances
combine, forming a salt which has the composition represented
in the formula Na_{2}S_{2}O_{3}:

Na_{2}SO_{3} + S = Na_{2}S_{2}O_{3}.

The substance is called sodium thiosulphate, and is a salt of
the easily decomposed acid H_{2}S_{2}O_{3}, called
thiosulphuric acid. This reaction is quite similar to the
action of oxygen upon sulphites:

Na_{2}SO_{3} + O = Na_{2}SO_{4}.

More commonly the salt is called sodium hyposulphite, or merely
"hypo." It is a white solid and is extensively used in
photography, in the bleaching industry, and as a disinfectant.

~Monobasic and dibasic acids.~ Such acids as hydrochloric and nitric
acids, which have only one replaceable hydrogen atom in the molecule, or
in other words yield one hydrogen ion in solution, are called monobasic
acids. Acids yielding two hydrogen ions in solution are called dibasic
acids. Similarly, we may have tribasic and tetrabasic acids. The three
acids of sulphur are dibasic acids. It is therefore possible for each of
them to form both normal and acid salts. The acid salts can be made in
two ways: the acid may be treated with only half enough base to
neutralize it,--

NaOH + H_{2}SO_{4} = NaHSO_{4} + H_{2}O;

or a normal salt may be treated with the free acid,--

Na_{2}SO_{4} + H_{2}SO_{4} = 2NaHSO_{4}.

Acid sulphites and sulphides may be made in the same ways.

~Carbon disulphide~ (CS_{2}). When sulphur vapor is passed over highly
heated carbon the two elements combine, forming carbon disulphide
(CS_{2}), just as oxygen and carbon unite to form carbon dioxide
(CO_{2}). The substance is a heavy, colorless liquid, possessing, when
pure, a pleasant ethereal odor. On standing for some time, especially
when exposed to sunlight, it undergoes a slight decomposition and
acquires a most disagreeable, rancid odor. It has the property of
dissolving many substances, such as gums, resins, and waxes, which are
insoluble in most liquids, and it is extensively used as a solvent for
such substances. It is also used as an insecticide. It boils at a low
temperature (46 deg.), and its vapor is very inflammable, burning in the air
to form carbon dioxide and sulphur dioxide, according to the equation

CS_{2} + 6O = CO_{2} + 2SO_{2}.

[Illustration: Fig. 45]

~Commercial preparation of carbon disulphide.~