The Chemistry of Hat Manufacturing | Page 4

clear solution is obtained, and then on adding tannic acid the fibroïn is
precipitated. Strong caustic potash or soda dissolves silk; more easily if
warm. Dilute caustic alkalis, if sufficiently dilute, will dissolve off the
sericin and leave the inner fibre of fibroïn; but they are not so good for
ungumming silk as soap solutions are, as the fibre after treatment with
them is deficient in whiteness and brilliancy. Silk dissolves completely
in hot basic zinc chloride solution, and also in an alkaline solution of
copper and glycerin, which solutions do not dissolve vegetable fibres or
wool. Chlorine and bleaching-powder solutions soon attack and destroy
silk, and so another and milder agent, namely, sulphurous acid, is used
to bleach this fibre. Silk is easily dyed by the aniline and coal-tar
colours, and with beautiful effect, but it has little attraction for the
mineral colours.
Wool.--Next to silk as an animal fibre we come to wool and different
varieties of fur and hair covering certain classes of animals, such as
sheep, goats, rabbits, and hares. Generally, and without going at all
deeply into the subject, we may say that wool differs from fur and hair,
of which we may regard it as a variety, by being usually more elastic,
flexible, and curly, and because it possesses certain features of surface
structure which confer upon it the property of being more easily matted
together than fur and hair are. We must first shortly consider the
manner of growth of hair without spending too much time on this part
of the subject. The accompanying figure (see Fig. 5) shows a section of
the skin with a hair or wool fibre rooted in it. Here we may see that the
ground work, if we may so term it, is four-fold in structure. Proceeding
downwards, we have--(first) the outer skin, scarf-skin or cuticle;
(second) a second layer or skin called the rete mucosum, forming the
epidermis; (third) papillary layer; (fourth) the corium layer, forming the

dermis. The peculiar, globular, cellular masses below in the corium are
called adipose cells, and these throw off perspiration or moisture,
which is carried away to the surface by the glands shown (called
sudoriparous glands), which, as is seen, pass independently off to the
surface. Other glands terminate under the skin in the hair follicles,
which follicles or hair sockets contain or enclose the hair roots. These
glands terminating in the hair follicles secrete an oily substance, which
bathes and lubricates as well as nourishes the hair. With respect to the
origin of the hair or wool fibre, this is formed inside the follicle by the
exuding therefrom of a plastic liquid or lymph; this latter gradually
becomes granular, and is then formed into cells, which, as the growth
proceeds, are elongated into fibres, which form the central portion of
the hair. Just as with the trunk of a tree, we have an outer dense portion,
the bark, an inner less dense and more cellular layer, and an inmost
portion which is most cellular and porous; so with a hair, the central
portion is loose and porous, the outer more and more dense. On
glancing at the figure (Fig. 6) of the longitudinal section of a human
hair, we see first the outer portion, like the bark of a tree, consisting of
a dense sheath of flattened scales, then comes an inner lining of
closely-packed fibrous cells, and frequently an inner well-marked
central bundle of larger and rounder cells, forming a medullary axis.
The transverse section (Fig. 7) shows this exceedingly well. The end of
a hair is generally pointed, sometimes filamentous. The lower
extremity is larger than the shaft, and terminates in a conical bulb, or
mass of cells, which forms the root of the hair. In the next figure (Fig. 8)
we are supposed to have separated these cells, and above, (a), we see
some of the cells from the central pith or medulla, and fat globules;
between, (b), some of the intermediate elongated or angular cells; and
below, (c), two flattened, compressed, structureless, and horny scales
from the outer portion of the hair. Now these latter flattened scales are
of great importance. Their character and mode of connection with the
stratum, or cortical substance, below, not only make all the difference
between wool and hair, but also determine the extent and degree of that
peculiar property of interlocking of the hairs known as felting. Let us
now again look at a human hair. The light was reflected from this hair
as it lay under the microscope, and now we see the reason of the
saw-like edge in the longitudinal section, for just as the tiles lie on the

roof of a house, or the scales on the back of a fish, so the whole surface
of the hair is