The Chemistry of Hat Manufacturing | Page 6

of this curl is not known, there appears
to be a close relationship between the tendency to curl, the fineness of
the fibre, and the number of scales per linear inch upon the surface.
With regard to hair and fur, I have already shown that serrated fibres
are not specially peculiar to sheep, but are much more widely diffused.
Most of the higher members of the mammalia family possess a hairy
covering of some sort, and in by far the larger number is found a
tendency to produce an undergrowth of fine woolly fibre, especially in
the winter time. The differences of human hair and hairs generally,
from the higher to the lower forms of mammalia, consist only in
variations of size and arrangement as regards the cells composing the

different parts of the fibre, as well as in a greater or less development of
the scales on the covering or external hair surface. Thus, under the
microscope, the wool and hairs of various animals, as also even hairs
from different parts of the same animal, show a great variety of
structure, development, and appearance.
[Illustration: FIG. 5.]
[Illustration: FIG. 6.]
[Illustration: FIG. 7.]
[Illustration: FIG. 8.]
[Illustration: FIG. 9.]
[Illustration:
Finest merino wool fibre. Typical wool fibre. Fibre of wool from
Chinese sheep.
FIG. 10.]
[Illustration: FIG. 11.]
[Illustration: FIG. 12.]
We have already observed that hair, if needed for felting, is all the
better--provided, of course, no injury is done to the fibre itself--for
some treatment, by which the scales otherwise lying flatter on the
hair-shafts than in the case of the hairs of wool, are made to stand up
somewhat, extending outwards their free edges. This brings me to the
consideration of a practice pursued by furriers for this purpose, and
known as the sécretage or "carrotting" process; it consists in a
treatment with a solution of mercuric nitrate in nitric acid, in order to
improve the felting qualities of the fur. This acid mixture is brushed on
to the fur, which is cut from the skin by a suitable sharp cutting or
shearing machine. A Manchester furrier, who gave me specimens of
some fur untreated by the process, and also some of the same fur that

had been treated, informed me that others of his line of business use
more mercury than he does, i.e. leave less free nitric acid in their
mixture; but he prefers his own method, and thinks it answers best for
the promotion of felting. The treated fur he gave me was turned yellow
with the nitric acid, in parts brown, and here and there the hairs were
slightly matted with the acid. In my opinion the fur must suffer from
such unequal treatment with such strong acid, and in the final process
of finishing I should not be surprised if difficulty were found in getting
a high degree of lustre and finish upon hairs thus roughened or partially
disintegrated. Figs. 11 and 12 respectively illustrate fur fibres from
different parts of the same hare before and after the treatment. In
examining one of these fibres from the side of a hare, you see what the
cause of this roughness is, and what is also the cause of the difficulty in
giving a polish or finish. The free edges are partially disintegrated,
etched as it were, besides being caused to stand out. A weaker acid
ought to be used, or more mercury and less acid. As we shall afterwards
see, another dangerous agent, if not carefully used, is bichrome
(bichromate of potassium), which is also liable to roughen and injure
the fibre, and thus interfere with the final production of a good finish.

LECTURE II
TEXTILE FIBRES, PRINCIPALLY WOOL, FUR, AND
HAIR--Continued
With regard to the preparation of fur by acid mixtures for felting,
mentioned in the last lecture, I will tell you what I think I should
recommend. In all wool and fur there is a certain amount of grease, and
this may vary in different parts of the material. Where there is most,
however, the acid, nitric acid, or nitric acid solution of nitrate of
mercury, will wet, and so act on the fur, least. But the action ought to
be uniform, and I feel sure it cannot be until the grease is removed. I
should therefore first wash the felts on the fur side with a weak alkaline
solution, one of carbonate of soda, free from any caustic, to remove all
grease, then with water to remove alkali; and my belief is that a weaker
and less acid solution of nitric acid and nitrate of mercury, and a

smaller quantity of it, would then do the work required, and do it more
uniformly.
A question frequently asked is: "Why will dead wool not felt?" Answer:
If the animal become weak and