a
quantity of flowers of sulphur, dissolve in caustic soda, and add to the
lead solution. It turns black at once, because the sulphur unites with
the lead to form black sulphide of lead. The nitroprusside, however,
gives a beautiful crimson-purple coloration. Now on taking a little
cotton and heating with the caustic alkaline lead solution, if sulphur
were present in that cotton, the fibre would turn black or brown, for
the lead would at once absorb such sulphur, and form in the fibre soaked
with it, black sulphide of lead. No such coloration is formed, so cotton
does not contain sulphur. Secondly, we must test silk. Silk contains
nitrogen, like wool, but does it contain sulphur? The answer furnished
by our tests is--no! since the fibre is not coloured brown or black on
heating with the alkaline lead solution. Thirdly, we try some white
Berlin wool, so that we can easily see the change of colour if it takes
place. In the hot lead solution the wool turns black, lead sulphide
being formed. On adding the nitroprusside solution to a fresh portion of
wool boiled with caustic soda, to dissolve out the sulphur, a splendid
purple coloration is produced. Fur and hair would, of course, do the
same thing. 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. Wool, fur, and vegetable
fibres are not affected by it. Hence if we had a mixture, and treated
with this solution, we could strain off the liquid containing the
dissolved silk, and would get cotton and wool left