Chloride of lime or “bleaching-powder” is made for the purposes of
bleaching calicoes, linens, &c., and also for purifying foul air,
which it does by giving out chlorine, a gas capable of uniting with
and changing the injurious properties of foul air (which generally
contains some combination of sulphur and hydrogen). Chloride of lime
is made on the large scale by mixing hydrochloric acid with black
oxide of manganese. This mixture gives off chlorine. This is made
to pass over a layer of slaked lime, which absorbs it greedily, and
becomes converted into the bleaching powder. The hydrochloric acid
used is a product resulting from the manufacture of soda, and was
formerly wasted; it is now used in large quantities for the process
above described. “Burnett’s Disinfecting Fluid” is a solution
of chloride of zinc. It is made by dissolving scraps of zinc in
hydrochloric acid; hydrogen gas is given off, with effervescence, and
the liquid remaining is the solution of chloride of zinc, which acts
like chloride of lime, by giving off chlorine; for the chloride is
slowly decomposed by the air, the oxygen of which takes the place of
the chlorine, uniting with the zinc to form oxide of zinc, while the
chlorine is set free.