[Illustration: FIG. 158.--Preparing chlorine from hydrochloric acid
and manganese dioxide.]
218. An Artificial Bleaching Agent. While the sun's rays are
effective as a bleaching agent, the process is slow; moreover, it
would be impossible to expose to the sun's rays the vast quantity of
fabrics used in the civilized world of to-day, and the huge and
numerous bolts of material which daily come from our looms and
factories must therefore be whitened by artificial means. The
substance almost universally used as a rapid artificial bleaching
agent is chlorine, best known to us as a constituent of common salt.
Chlorine is never free in nature, but is found in combination with
other substances, as, for example, in combination with sodium in salt,
or with hydrogen in hydrochloric acid.
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