Collier's New Encyclopedia (1921)/Bleaching

BLEACHING, the art of rendering materials colorless. This is done by exposing them to the actinic rays of the sun, or by the action of bleaching agents. The chief of these is called bleaching powder. It is chloride of lime, and is prepared by exposing moistened quick-lime to the action of chlorine, when hypochlorite and chloride of calcium are formed, the former being the bleaching agent. By the action of an acid on good bleaching powder 30 per cent. of chlorine is liberated. Substances are bleached by alternately dipping them in dilute solutions of bleaching powder and of dilute sulphuric acid. Bleaching powder is also used to purify an offensive or infectious atmosphere.