] either in
the solid state or as a liquid extract. The essential constituent of
bleaching-powder from the present aspect is calcium hypochlorite, which
readily oxidises sulphuretted hydrogen, and more particularly phosphine,
converting them into sulphuric and phosphoric acids, while the acetylene
is practically unattacked. In simple purifying action the material proved
satisfactory; but since high-grade commercial bleaching-powder contains
some free chlorine, or some is set free from it in the purifier under the
influence of the passing gas, the issuing acetylene was found to contain
chlorine, free or combined; and this, burning eventually to hydrochloric
acid, is hardly less harmful than the original sulphur compounds.
Moreover, a mixture of acetylene, chlorine, and air is liable to catch
fire of itself when exposed to bright sunlight; and therefore the use of
a bleaching-powder purifier, or rather the recharging thereof, was not
unattended by danger in the early days. To overcome these defects, the
very natural process was adopted of diluting the bleaching-powder, such
diluent also serving to increase the porosity of the material. A very
unsuitable substance, however, was selected for the purpose, viz.
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