Watson Smith - The Chemistry of Hat Manufacturing

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THE CHEMISTRY

OF

HAT MANUFACTURING

LECTURES DELIVERED BEFORE THE HAT MANUFACTURERS' ASSOCIATION

BY

WATSON SMITH, F.C.S., F.I.C.

THEN LECTURER IN CHEMICAL TECHNOLOGY IN THE OWENS COLLEGE, MANCHESTER
AND LECTURER OF THE VICTORIA UNIVERSITY

REVISED AND EDITED

BY

ALBERT SHONK

WITH SIXTEEN ILLUSTRATIONS

LONDON
SCOTT, GREENWOOD & SON
"THE HATTERS' GAZETTE" OFFICES
8 BROADWAY, LUDGATE HILL, E.C.

CANADA: THE COPP CLARK CO. LTD., TORONTO
UNITED STATES: D. VAN NOSTRAND CO., NEW YORK
1906

[_All rights remain with Scott, Greenwood & Son_]

Transcriber's Note: Underscores around words indicates italics while an
underscore and curly brackets in an equation indicates a subscript.

PREFACE

The subject-matter in this little book is the substance of a series of
Lectures delivered before the Hat Manufacturers' Association in the
years 1887 and 1888.

About this period, owing to the increasing difficulties of competition
with the products of the German Hat Manufacturers, a deputation of Hat
Manufacturers in and around Manchester consulted Sir Henry E. Roscoe,
F.R.S., then the Professor of Chemistry in the Owens College,
Manchester, and he advised the formation of an Association, and the
appointment of a Lecturer, who was to make a practical investigation of
the art of Hat Manufacturing, and then to deliver a series of lectures
on the applications of science to this industry. Sir Henry Roscoe
recommended the writer, then the Lecturer on Chemical Technology in the
Owens College, as lecturer, and he was accordingly appointed.

The lectures were delivered with copious experimental illustrations
through two sessions, and during the course a patent by one of the
younger members became due, which proved to contain the solution of the
chief difficulty of the British felt-hat manufacturer (see pages 66-68).
This remarkable coincidence served to give especial stress to the wisdom
of the counsel of Sir Henry Roscoe, whose response to the appeal of the
members of the deputation of 1887 was at once to point them to
scientific light and training as their only resource. In a letter
recently received from Sir Henry (1906), he writes: "I agree with you
that this is a good instance of the _direct money value_ of scientific
training, and in these days of 'protection' and similar subterfuges, it
is not amiss to emphasise the fact."

It is thus gratifying to the writer to think that the lectures have had
some influence on the remarkable progress which the British Hat Industry
has made in the twenty years that have elapsed since their delivery.

These lectures were in part printed and published in the _Hatters'
Gazette_, and in part in newspapers of Manchester and Stockport, and
they have here been compiled and edited, and the necessary illustrations
added, etc., by Mr. Albert Shonk, to whom I would express my best
thanks.

WATSON SMITH.

LONDON, _April_ 1906.

CONTENTS

LECTURE PAGE

I. TEXTILE FIBRES, PRINCIPALLY WOOL, FUR, AND HAIR 1

II. TEXTILE FIBRES, PRINCIPALLY WOOL, FUR,
AND HAIR--_continued_ 18

III. WATER: ITS CHEMISTRY AND PROPERTIES;
IMPURITIES AND THEIR ACTION; TESTS OF PURITY 29

IV. WATER: ITS CHEMISTRY AND PROPERTIES; IMPURITIES AND
THEIR ACTION; TESTS OF PURITY--_continued_ 38

V. ACIDS AND ALKALIS 49

VI. BORIC ACID, BORAX, SOAP 57

VII. SHELLAC, WOOD SPIRIT, AND THE STIFFENING AND
PROOFING PROCESS 62

VIII. MORDANTS: THEIR NATURE AND USE 69

IX. DYESTUFFS AND COLOURS 79

X. DYESTUFFS AND COLORS--_continued_ 89

XI. DYEING OF WOOL AND FUR; AND OPTICAL PROPERTIES
OF COLOURS 100

INDEX 117

THE CHEMISTRY OF HAT MANUFACTURING

LECTURE I

TEXTILE FIBRES, PRINCIPALLY WOOL, FUR, AND HAIR

_Vegetable Fibres._--Textile fibres may be broadly distinguished as
vegetable and animal fibres. It is absolutely necessary, in order to
obtain a useful knowledge of the peculiarities and properties of animal
fibres generally, or even specially, that we should be, at least to some
extent, familiar with those of the vegetable fibres. I shall therefore
have, in the first place, something to tell you of certain principal
vegetable fibres before we commence the more special study of the animal
fibres most interesting to you as hat manufacturers, namely, wool, fur,
and hair. What cotton is as a vegetable product I shall not in detail
describe, but I will refer you to the interesting and complete work of
Dr. Bowman, _On the Structure of the Cotton Fibre_. Suffice it to say
that in certain plants and trees the seeds or fruit are surrounded, in
the pods in which they develop, with a downy substance, and that the
cotton shrub belongs to this class of plants. A fibre picked out from
the mass of the downy substance referred to, and examined under the
microscope, is found to be a spirally twisted band; or better, an
irregular, more or less flattened and twisted tube (see Fig. 1). We know
it is a tube, because on taking a thin, narrow slice across a fibre and
examining the slice under the microscope, we can see the hole or
perforation up the centre, forming the axis of the tube (see Fig. 2).
Mr. H. de Mosenthal, in an extremely interesting and valuable paper (see
_J.S.C.I._,[1] 1904, vol. xxiii. p. 292), has recently shown that the
cuticle of the cotton fibre is extremely porous, having, in addition to
pores, what appear to be minute stomata, the latter being frequently
arranged in oblique rows, as if they led into oblique lateral channels.
A cotton fibre varies from 2.5 to 6 centimetres in length, and in
breadth from 0.017 to 0.05 millimetre. The characteristics mentioned
make it very easy to distinguish cotton from other vegetable or animal
fibres. For example, another vegetable fibre is flax, or linen, and this
has a very different appearance under the microscope (_see_ Fig. 3). It
has a bamboo-like, or jointed appearance; its tubes are not flattened,
nor are they twisted. Flax belongs to a class called the bast fibres, a
name given to certain fibres obtained from the inner bark of different
plants. Jute also is a bast fibre. The finer qualities of it look like
flax, but, as we shall see, it is not chemically identical with cotton,
as linen or flax is. Another vegetable fibre, termed "cotton-silk," from
its beautiful, lustrous, silky appearance, has excited some attention,
because it grows freely in the German colony called the Camaroons, and
also on the Gold Coast. This fibre, under the microscope, differs
entirely in appearance from both cotton and flax fibres. Its fibres
resemble straight and thin, smooth, transparent, almost glassy tubes,
with large axial bores; in fact, if wetted in water you can see the
water and air bubbles in the tubes under the microscope. A more detailed
account of "cotton-silk" appears in a paper read by me before the
Society of Chemical Industry in 1886 (see _J.S.C.I._, 1886, vol. v. p.
642). Now the substance of the cotton, linen or flax, as well as that of
the cotton-silk fibres, is termed, chemically, cellulose. Raw cotton
consists of cellulose with about 5 per cent. of impurities. This
cellulose is a chemical compound of carbon, hydrogen, and oxygen, and,
according to the relative proportions of these constituents, it has had
the chemical formula C_{6}H_{10}O_{5} assigned to it. Each letter
stands for an atom of each constituent named, and the numerals tell us
the number of the constituent atoms in the whole compound atom of
cellulose. This cellulose is closely allied in composition to starch,
dextrin, and a form of sugar called glucose. It is possible to convert
cotton rags into this form of sugar--glucose--by treating first with
strong vitriol or sulphuric acid, and then boiling with dilute acid for
a long time. Before we leave these vegetable or cellulose fibres, I will
give you a means of testing them, so as to enable you to distinguish
them broadly from the animal fibres, amongst which are silk, wool, fur,
and hair. A good general test to distinguish a vegetable and an animal
fibre is the following, which is known as Molisch's test: To a very
small quantity, about 0.01 gram, of the well-washed cotton fibre, 1 c.c.
of water is added, then two to three drops of a 15 to 20 per cent.
solution of alpha-naphthol in alcohol, and finally an excess of
concentrated sulphuric acid; on agitating, a deep violet colour is
developed. By using thymol in place of the alpha-naphthol, a
red or scarlet colour is produced. If the fibre were one of an animal
nature, merely a yellow or greenish-yellow coloured solution would
result. I told you, however, that jute is not chemically identical with
cotton and linen. The substance of its fibre has been termed "bastose"
by Cross and Bevan, who have investigated it. It is not identical with
ordinary cellulose, for if we take a little of the jute, soak it in
dilute acid, then in chloride of lime or hypochlorite of soda, and
finally pass it through a bath of sulphite of soda, a beautiful crimson
colour develops upon it, not developed in the case of cellulose (cotton,
linen, etc.). It is certain that it is a kind of cellulose, but still
not identical with true cellulose. All animal fibres, when burnt, emit a
peculiar empyreumatic odour resembling that from burnt feathers, an
odour which no vegetable fibre under like circumstances emits. Hence a
good test is to burn a piece of the fibre in a lamp flame, and notice
the odour. All vegetable fibres are easily tendered, or rendered rotten,
by the action of even dilute mineral acids; with the additional action
of steam, the effect is much more rapid, as also if the fibre is allowed
to dry with the acid upon or in it. Animal fibres are not nearly so
sensitive under these conditions. But whereas caustic alkalis have not
much effect on vegetable fibres, if kept out of contact with the air,
the animal fibres are very quickly attacked. Superheated steam alone has
but little effect on cotton or vegetable fibres, but it would fuse or
melt wool. Based on these differences, methods have been devised and
patented for treating mixed woollen and cotton tissues--(1) with
hydrochloric acid gas, or moistening with dilute hydrochloric acid and
steaming, to remove all the cotton fibre; or (2) with a jet of
superheated steam, under a pressure of 5 atmospheres (75 lb. per square
inch), when the woollen fibre is simply melted out of the tissue, and
sinks to the bottom of the vessel, a vegetable tissue remaining
(Heddebault). If we write on paper with dilute sulphuric acid, and dry
and then heat the place written upon, the cellulose is destroyed and
charred, and we get black writing produced. The principle involved is
the same as in the separation of cotton from mixed woollen and cotton
goods by means of sulphuric acid or vitriol. The fabric containing
cotton, or let us say cellulose particles, is treated with dilute
vitriol, pressed or squeezed, and then roughly dried. That cellulose
then becomes mere dust, and is simply beaten out of the intact woollen
texture. The cellulose is, in a pure state, a white powder, of specific
gravity 1.5, _i.e._ one and a half times as heavy as water, and is quite
insoluble in such solvents as water, alcohol, ether; but it does
dissolve in a solution of hydrated oxide of copper in ammonia. On adding
acids to the cupric-ammonium solution, the cellulose is reprecipitated
in the form of a gelatinous mass. Cotton and linen are scarcely
dissolved at all by a solution of basic zinc chloride.

[Footnote 1: _J.S.C.I. = Journal of the Society of Chemical Industry._]

[Illustration: FIG. 1.]

[Illustration: FIG. 2.]

[Illustration: FIG. 3.]

[Illustration: FIG. 4.]

_Silk._--We now pass on to the animal fibres, and of these we must first
consider silk. This is one of the most perfect substances for use in the
textile arts. A silk fibre may be considered as a kind of rod of
solidified flexible gum, secreted in and exuded from glands placed on
the side of the body of the silk-worm. In Fig. 4 are shown the forms of
the silk fibre, in which there are no central cavities or axial bores as
in cotton and flax, and no signs of any cellular structure or external
markings, but a comparatively smooth, glassy surface. There is, however,
a longitudinal groove of more or less depth. The fibre is
semi-transparent, the beautiful pearly lustre being due to the
smoothness of the outer layer and its reflection of the light. In the
silk fibre there are two distinct parts: first, the central portion, or,
as we may regard it, the true fibre, chemically termed _fibroin_; and
secondly, an envelope composed of a substance or substances, chemically
termed _sericin_, and often "silk-glue" or "silk-gum." Both the latter
and _fibroin_ are composed of carbon, hydrogen, nitrogen, and oxygen.
Here there is thus one element more than in the vegetable fibres
previously referred to, namely, nitrogen; and this nitrogen is contained
in all the animal fibres. The outer envelope of silk-glue or sericin can
be dissolved off the inner fibroin fibre by means of hot water, or warm
water with a little soap. Warm dilute (that is, weak) acids, such as
sulphuric acid, etc., also dissolve this silk-glue, and can be used like
soap solutions for ungumming silk. Dilute nitric acid only slightly
attacks silk, and colours it yellow; it would not so colour vegetable
fibres, and this forms a good test to distinguish silk from a vegetable
fibre. Cold strong acetic acid, so-called glacial acetic acid, removes
the yellowish colouring matter from raw silk without dissolving the
sericin or silk-gum. By heating under pressure with acetic acid,
however, silk is completely dissolved. Silk is also dissolved by strong
sulphuric acid, forming a brown thick liquid. If we add water to this
thick liquid, a clear solution is obtained, and then on adding tannic
acid the fibroin 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 fibroin; 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 externally coated with a firmly adhering layer of flat overlying
scales, with not very even upper edges, as you see. The upper or free
edges of these scales are all directed towards the end of the hair, and
away from the root. But when you look at a hair in its natural state you
cannot see these scales, so flat do they lie on the hair-shaft. What you
see are only irregular transverse lines across it. Now I come to a
matter of great importance, as will later on appear in connection with
means for promoting felting properties. If a hair such as described,
with the scales lying flat on the shaft, be treated with certain
substances or reagents which act upon and dissolve, or decompose or
disintegrate its parts, then the free edges of these scales rise up,
they "set their backs up," so to say. They, in fact, stand off like the
scales of a fir-cone, and at length act like the fir-cone in ripening,
at last becoming entirely loose. As regards wool and fur, these scales
are of the utmost importance, for very marked differences exist even in
the wool of a single sheep, or the fur of a single hare. It is the duty
of the wool-sorter to distinguish and separate the various qualities in
each fleece, and of the furrier to do the same in the case of each fur.
In short, upon the nature and arrangement and conformation of the scales
on the hair-shafts, especially as regards those free upper edges,
depends the distinction of the value of many classes of wool and fur.
These scales vary both as to nature and arrangement in the case of the
hairs of different animals, so that by the aid of the microscope we have
often a means of determining from what kind of animal the hair has been
derived. It is on the nature of this outside scaly covering of the
shaft, and in the manner of attachment of these scaly plates, that the
true distinction between wool and hair rests. The principal epidermal
characteristic of a true wool is the capacity of its fibres to felt or
mat together. This arises from the greater looseness of the scaly
covering of the hair, so that when opposing hairs come into contact, the
scales interlock (see Fig. 9), and thus the fibres are held together.
Just as with hair, the scales of which have their free edges pointing
upwards away from the root, and towards the extremity of the hair, so
with wool. When the wool is on the back of the sheep, the scales of the
woolly hair all point in the same direction, so that while maintained in
that attitude the individual hairs slide over one another, and do not
tend to felt or mat; if they did, woe betide the animal. The fact of the
peculiar serrated, scaly structure of hair and wool is easily proved by
working a hair between the fingers. If, for instance, a human hair be
placed between finger and thumb, and gently rubbed by the alternate
motion of finger and thumb together, it will then invariably move in the
direction of the root, quite independently of the will of the person
performing the test. A glance at the form of the typical wool fibres
shown (see Fig. 10), will show the considerable difference between a
wool and a hair fibre. You will observe that the scales of the wool
fibre are rather pointed than rounded at their free edges, and that at
intervals we have a kind of composite and jagged-edged funnels, fitting
into each other, and thus making up the covering of the cylindrical
portion of the fibre. The sharpened, jagged edges enable these scales
more easily to get under the opposing scales, and to penetrate inwards
and downwards according to the pressure exerted. The free edges of the
scales of wool are much longer and deeper than in the case of hair. In
hair the overlapping scales are attached to the under layer up to the
edges of those scales, and at this extremity can only be detached by
the use of certain reagents. But this is not so with wool, for here the
ends of the scales are, for nearly two-thirds of their length, free, and
are, moreover, partially turned outwards. One of the fibres shown in
Fig. 10 is that of the merino sheep, and is one of the most valuable and
beautiful wools grown. There you have the type of a fibre best suited
for textile purposes, and the more closely different hairs approach
this, the more suitable and valuable they become for those purposes, and
_vice versa_. With regard to the curly structure of wool, which
increases the matting tendency, though the true cause 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 _secretage_ 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.

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