(p. 006)
globular cells is entirely absent. Also the serrated character of the
outermost layer of cells reaches a much higher state of development in
some samples of wool than in others.

Wool is a much more hygroscopic fibre than cotton or any of the other
vegetable fibres, usually it contains about 18 per cent. of water, but
much depends upon the atmospheric conditions that prevail. This water
is contained in the wool in two forms: (1) as water of hydration
amounting to about 81 per cent., and (2) as hygroscopic water.

Experiments have shown that when a piece of dried wool is exposed to
an atmosphere saturated with water vapour it will absorb 50 per cent.
of its weight; cotton under the same conditions will take up 23 per
cent.; flax, 27.5 per cent.; jute, 28.5 per cent., and silk, 36.5 per
cent.

Heated to about 100 deg. C. it parts with nearly the whole of its water
and becomes hard, horny and brittle, exposed to the air, the dry wool
again absorbs water and is restored to its former condition. When
heated to 100 deg. C. wool becomes somewhat plastic, so that whatever
form is then imparted to it it will retain when it becomes cold, this
property is very useful in certain processes of finishing wool
fabrics, making hats, etc.

#Chemical Composition.#--In the natural or raw state each wool fibre is
surrounded by a considerable amount of foreign matter, so that in
treating of its chemical constitution it is necessary to distinguish
between pure wool and the raw fibre. The incrusting substance is
technically known as "Yolk," or "Suint," and is principally composed
of a kind of natural soap, consisting of the potash salts of certain
fatty acids, together with some fats which are incapable of
saponification.

The amount of yolk present upon different samples of wool varies
greatly, the finer varieties containing, as a rule, a larger
proportion than the coarser, and less valuable sorts.

The variation in the relative amount of pure fibres and yolk is (p. 007)
well shown in the following analyses which, however, do not by any
means represent extreme cases.

ANALYSES OF RAW MERINO WOOL. DRIED AT 100 deg. C.

No. 1. No. 2.
Moisture 6.26 10.4
Yolk 47.30 27.0
Pure Wool 30.31 59.5
Dirt 11.13 3.1
------ ------
100.00 100.00

Yolk consists very largely of two complex substances which have been
termed wool perspiration and woo