Chlorine has no effect on dry material, as may be seen if we put dry
gingham into the jar; in this case there is no water to furnish
hydrogen for combination with the chlorine, and no oxygen to be set
free.
219. Bleaching Powder. Chlorine gas has a very injurious effect on
the human body, and hence cannot be used directly as a bleaching
agent. It attacks the mucous membrane of the nose and lungs, and
produces the effect of a severe cold or catarrh, and when inhaled,
causes death. But certain compounds of chlorine are harmless, and can
be used instead of chlorine for destroying either natural or
artificial dyes. One of these compounds, namely, chloride of lime, is
the almost universal bleaching agent of commerce. It comes in the form
of powder, which can be dissolved in water to form the bleaching
solution in which the colored fabrics are immersed. But fabrics
immersed in a bleaching powder solution do not lose their color as
would naturally be expected. The reason for this is that the chlorine
gas is not free to do its work, but is restricted by its combination
with the other substances. By experiment it has been found that the
addition to the bleaching solution of an acid, such as vinegar or
lemon juice or sulphuric acid, causes the liberation of the chlorine.
The chlorine thus set free reacts with the water and liberates oxygen;
this in turn destroys the coloring matter in the fibers, and
transforms the material into a bleached product.
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