Sodium hypochlorite can be prepared by the electrolysis of brine
solution in the presence of carbon electrodes, having no diaphragm in
the electrolytic cell, and mixing the anode and cathode products by
agitating the liquid. The temperature should be kept at about 15 deg. C.,
and the concentration of the hypochlorite produced must not be allowed
to become too great, in order to prevent reduction taking place at the
cathode.

Chlorous acid is not known in the pure condition; but its sodium salt
is prepared by the action of sodium peroxide on a solution of chlorine
peroxide: 2ClO2 + Na2O2 = 2NaClO2 + O2. The silver and lead salts are
unstable, being decomposed with explosive violence at 100 deg. C. On
adding a caustic alkali solution to one of chlorine peroxide, a
mixture of a chlorite and a chlorate is obtained.

Chloric acid was discovered in 1786 by C.L. Berthollet, and is best
prepared by decomposing barium chlorate with the calculated amount of
dilute sulphuric acid. The aqueous solution can be concentrated _in
vacuo_ over sulphuric acid until it contains 40% of chloric acid.
Further concentration leads to decomposition, with evolution of oxygen
and formation of perchloric acid. The concentrated solution is a
powerful oxidizing agent; organic matter being oxidized so rapidly
that it frequently inflames. Hydrochloric acid, sulphuretted hydrogen
and sulphurous acid are rapidly oxidized by chloric acid. J.S. Stas
determined its composition by the analysis of pure silver chlorate.
The salts of this acid are known as chlorates (q.v.).

Perchloric acid is best prepared by distilling potassium perchlorate
with concentrated sulphuric acid. According to Sir H. Roscoe, pure
perchloric acid distils over at first, but if the distillation be
continued a white crystalline mass of hydrated perchloric acid,
HClO4.H2O, passes over; this is due to the decomposition of some of
the acid into water and lower oxides of chlorine, the water produced
then combining with the pure acid to produce the hydrated form. This
solid, on redistillation, gives the pure acid, which is a liquid
boiling at 39 deg. C. (under a pressure of 56 mm.) and of specific
gravity 1.764 (22/4) deg.. The crystalline hydrate melts at 50 deg. C.
The pure acid decomposes slowly on standing, but is stable in dilute
aqueous solution. It is a very powerful oxidizing agent; wood and paper
in contact