ly with water itself. If we could use coal-tar colours and dye in only
a warm weak acid bath, not boil, we could get better lustre and finish.

We will now turn our attention to the chemical composition of wool and
fur fibres. On chemical analysis still another element is found over and
above those mentioned as the constituents of silk fibre. In silk, you
will recollect, we observed the presence of carbon, hydrogen, oxygen,
and nitrogen. In wool, fur, etc., we must add a fifth constituent,
namely, sulphur. Here is an analysis of pure German wool--Carbon, 49.25
per cent.; hydrogen, 7.57; oxygen, 23.66; nitrogen, 15.86; sulphur,
3.66--total, 100.00. If you heat either wool, fur, or hair to 130 deg. C.,
it begins to decompose, and to give off ammonia; if still further heated
to from 140 deg. to 150 deg. C., vapours containing sulphur are evolved. If some
wool be placed in a dry glass tube, and heated strongly so as to cause
destructive distillation, products containing much carbonate of ammonium
are given off. The ammonia is easily detected by its smell of hartshorn
and the blue colour produced on a piece of reddened litmus paper, the
latter being a general test to distinguish alkalis, like ammonia, soda,
and potash, from acids. No vegetable fibres will, under any
circumstances, give off ammonia. It may be asked, "But what does the
production of ammonia prove?" I reply, the "backbone," chemically
speaking, of ammonia is nitrogen. Ammonia is a compound of nitrogen and
hydrogen, and is formulated NH_{3}, and hence to discover ammonia in the
products as mentioned is to prove the prior existence of its nitrogen in
the wool, fur, and hair fibres.

_Action of Acids on Wool, etc._--Dilute solutions of vitriol (sulphuric
acid) or hydrochloric acid (muriatic acid, spirits of salt) have little
effect on wool, whether warm or cold, except to open out the scales and
confer roughness on the fibre. Used in the concentrated state, however,
the wool or fur would soon be disintegrated and ruined. But under all
circumstances the action is far less than on cotton, which is destroyed
at once and completely. Nitric acid acts like sulphuric and hydrochloric
acids, but it gives a yellow colour to the fibre. You see this clearly
enough in the fur that comes from your furriers after the treatment they
subject it to with nitric acid and nitrate of mercury. There is a
process known called the stripping of wool, and it consists in
destroying the colo