The Chemistry of Hat Manufacturing | Page 8

the warm dilute acid, are extended
and project more, and stand out from the shafts of the hairs. On the
whole, were I a hat manufacturer, I should prefer to buy my fur
untreated by that nitric acid and mercury process previously referred to,
and promote its felting properties myself by the less severe and more
rational course of proceeding, such, for example, as treatment with
warm dilute acid. We have referred to two enemies standing in the way
to the obtainment of a final lustre and finish on felted wool or fur, now
let us expose a third. In the black dyeing of the hat-forms a boiling
process is used. Let us hear what Dr. Bowman, in his work on the wool
fibre, says with regard to boiling with water. "Wool which looked quite
bright when well washed with tepid water, was decidedly duller when
kept for some time in water at a temperature of 160° F., and the same
wool, when subjected to boiling water at 212° F., became quite dull and
lustreless. When tested for strength, the same fibres which carried on
the average 500 grains without breaking before boiling, after boiling
would not bear more than 480 grains." Hence this third enemy is a
boiling process, especially a long-continued one if only 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° C., it
begins to decompose, and to give off ammonia; if still further heated to
from 140° to 150° 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
colour of wool and woollen goods already dyed, in order that they may
be re-dyed. Listen, however, to the important precautions followed: A
nitric acid not stronger than from 3° to 4° Twaddell is used, and care is
taken not to prolong the action more than three or four minutes.
Action of Alkalis.--Alkalis have a very considerable action on fur and
wool, but the effects vary a good deal according to the kind of alkali
used, the strength and the temperature of the solution, as also, of course,
the length of period of contact. The caustic alkalis, potash and soda,
under all conditions affect wool and fur injuriously. In fact, we have a
method of recovering indigo from indigo-dyed woollen rags, based on
the solubility of the wool in hot caustic soda. The wool dissolves, and
the indigo, being insoluble, remains, and can be recovered. Alkaline
carbonates and soap in solution have little or no injurious action if not
too strong, and if the temperature be not over 50° C. (106°