Lead solutions have been used for dyeing the hair black; not
caustic alkaline solutions like this, however. They would do something
more than turn the hair black--probably give rise to some vigorous
exercise of muscular power! Still it has been found that even the lead
solutions employed have, through gradual absorption into the system,
whilst dyeing the hair black, also caused colics and contractions of the
limbs.
Having now found means for proving the presence of the various elements
composing cotton, silk, and wool, fur or hair, we come to methods that
have been proposed for distinguishing these fibres more generally, and
for quantitatively determining them in mixtures. One of the best of the
reagents for this purpose is the basic zinc chloride already referred
to. This is made as follows: 100 parts of fused zinc chloride, 85 parts
of water, and 4 parts of zinc oxide are boiled together until a clear
solution is obtained. This solution dissolves silk slowly in the cold,
quickly if hot, and forms a thick gummy liquid.
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