Produced by Audrey Longhurst, Labyrinths and the Online
Distributed Proofreading Team at https://www.pgdp.net
THE
DYEING OF COTTON FABRICS
_A PRACTICAL HANDBOOK FOR THE DYER AND STUDENT_
BY
FRANKLIN BEECH
PRACTICAL COLOURIST AND CHEMIST
_ILLUSTRATED BY FORTY-FOUR ENGRAVINGS_
LONDON SCOTT, GREENWOOD & CO. 19 LUDGATE HILL, E.C.
1901
[_All rights reserved_]
PREFACE.
In writing this little book the author believes he is supplying a want
which most Students and Dyers of Cotton Fabrics have felt--that of a
small handbook clearly describing the various processes and operations
of the great industry of dyeing Cotton.
The aim has not been to produce a very elaborate treatise but rather a
book of a convenient size, and in order to do so it has been necessary
to be brief and to omit many matters that would rightfully find a place
in a larger treatise, but the author hopes that nothing of importance
has been omitted. The most modern processes have been described in some
detail; care has been taken to select those which experience shows to be
thoroughly reliable and to give good results.
FRANKLIN BEECH.
_May, 1901._
CONTENTS.
CHAPTER I.
PAGE
STRUCTURE AND CHEMISTRY OF THE COTTON FIBRE 1
Action of Alkalies 6
Action of Acids on Cellulose 9
Action of Sulphuric Acid on Cotton 10
Action of Hydrochloric Acid 11
Action of Nitric Acid 12
Action of Oxidising Agents on Cellulose or Cotton 16
CHAPTER II.
SCOURING AND BLEACHING OF COTTON 23
Stains and Damages in Bleached Goods 50
CHAPTER III.
DYEING MACHINERY AND DYEING MANIPULATIONS 53
Hand Dyeing 53
Dyeing Machines 57
Dyeing, Slubbing, Sliver or Carded Cotton and Wool 58
Cop Dyeing 64
CHAPTER IV.
THE PRINCIPLES AND PRACTICE OF COTTON DYEING 82
(1) Direct Dyeing 85
(2) Direct Dyeing followed by Fixation with Metallic Salts 112
(3) Direct Dyeing followed by Fixation with Developers 128
(4) Direct Dyeing followed by Fixation with Couplers 139
(5) Dyeing on Tannic Mordant 147
(6) Dyeing on Metallic Mordants 156
(7) Production of Colour Direct upon Cotton Fibres 181
(8) Dyeing Cotton by Impregnation with Dye-stuff Solution 198
CHAPTER V.
DYEING UNION (MIXED COTTON AND WOOL) FABRICS 208
CHAPTER VI.
DYEING HALF SILK (COTTON-SILK, SATIN) FABRICS 225
Method of Dyeing 225
CHAPTER VII.
OPERATIONS FOLLOWING DYEING 239
Washing, Soaping, Drying 239
CHAPTER VIII.
TESTING OF THE COLOUR OF DYED FABRICS 257
CHAPTER IX.
EXPERIMENTAL DYEING AND COMPARATIVE DYE TESTING 262
LIST OF ILLUSTRATIONS
FIG. PAGE
1. Cotton Fibre 5
1A. Cross-section of Cotton Fibre 5
2. Mercerised Cotton Fibre 7
2A. Cross-section of Mercerised Cotton Fibre 7
3. Silkified Cotton Fibre 9
3A. Cross-section of Silkified Cotton Fibre 9
4. Mather & Platt's Low-pressure Bleaching Kier 31
5. Mather & Platt's Yarn-bleaching Kier 49
6. Rectangular Dye-tank 54
7. Round Dye-tub 54
8. Section of Dye-vat 56
9. Delahunty's Dyeing Machine 58
10. Obermaier Dyeing Machine 59
11. Holliday's Yarn-dyeing Machine 60
12. Klauder-Weldon Dyeing Machine 62
13. Graemiger Cop-dyeing Machine 65
14. Graemiger Cop-dyeing Machine 66
15. Beaumont's Cop-dyeing Machine 67
16. Warp-dyeing Machine 70
17. Warp-dyeing Machine 71
18. Dye-jiggers 72
19. Dye-jigger 73
20. Jig Wince 75
21. Cloth-dyeing Machine 76
22. Dye Beck 77
23. Holliday's Machine for Hawking Cloth 78
24. Continuous Dyeing Machine 79
25. Padding Machine 80
26. Padding Machine 81
27. Dye-tub for Paranitroaniline Red 191
28. Padding Machine for Paranitroaniline Red 192
29. Developing Machine for Paranitroaniline Red 194
30. Indigo Dye-vat for Cloth 199
31. Squeezing Rollers 240
32. Yarn-washing Machine 243
33. Dye-house Washing Machine 244
34. Cloth-washing Machine 245
35. Cloth-washing Machine 247
36. Washing and Soaping Vats 248
37. Steaming Cottage 249
38. Steaming and Ageing Chamber 250
39. Hydro-extractor 251
40. Hydro-extractor 252
41. Automatic Yarn-dryer 253
42. Truck Yarn-dryer 254
43. Drying Cylinders 255
44. Experimental Dye-bath 263
CHAPTER I.
STRUCTURE AND CHEMISTRY OF THE COTTON FIBRE.
There is scarcely any subject of so much importance to the bleacher,
textile colourist or textile manufacturer as the structure and chemistry
of the cotton fibre with which he has to deal. By the term chemistry we
mean not only the composition of the fibre substance itself, but also
the reactions it is capable of undergoing when brought into contact with
various chemical substances--acids, alkalies, salts, etc. These
reactions have a very important bearing on the operations of bleaching
and dyeing of cotton fabrics.
A few words on vegetable textile fibres in general may be of interest.
Fibres are met with in connection with plants in three ways.
First, as cuticle or ciliary fibres or hairs; these are of no practical
use, being much too short for preparing textile fabrics from, but they
play an important part in the physiology of the plant.
Second, as seed hairs; that is fibres that are attached to the seeds of
many plants, such, for instance, as the common thistle and dandelion;
the cotton fibre belongs to this group of seed hairs, while there are
others, kapok, etc., that have been tried from time to time in spinning
and weaving, but without much success. These seed hairs vary much in
length, from 1/4 inch to 1-1/2 inches or even 2 inches; each fibre
consists of a single unit. Whether it is serviceable as a textile fibre
depends upon its structure, which differs in different plants, and also
upon the quantity available.
The third class of fibre, which is by far the most numerous, consists of
those found lying between the bark or outer cuticle and the true woody
tissues of the plant. This portion is known as the bast, and hence these
fibres are known as "bast fibres". They are noticeable on account of the
great length of the fibres, in some cases upwards of 6 feet, which can
be obtained; but it should be pointed out that these long fibres are not
the unit fibres, but are really bundles of the ultimate fibres
aggregated together to form one long fibre, as found in and obtained
from the plant. Thus the ultimate fibres of jute are really very
short--from 1/10 to 1/8 of an inch in length; those of flax are somewhat
longer. Jute, flax, China grass and hemp are common fibres which are
derived from the bast of the plants.
There is an important point of difference between seed fibres and bast
fibres, that is in the degree of purity. While the seed fibres are
fairly free from impurities--cotton rarely containing more than 5 per
cent.--the bast fibres contain a large proportion of impurity, from 25
to 30 per cent. as they are first obtained from the plant, and this
large quantity has much influence on the extent and character of the
treatments to which they are subjected.
As regards the structure of the fibres, it will be sufficient to say
that while seed hairs are cylindrical and tubular and have thin walls,
bast fibres are more or less polygonal in form and are not essentially
tubular, having thick walls and small central canals.
=The Cotton Fibre.=--The seed hairs of the cotton plant are separated
from the seeds by the process of ginning, and they then pass into
commerce as raw cotton. In this condition the fibre is found to consist
of the actual fibrous substance itself, containing, however, about 8 per
cent. of hygroscopic or natural moisture, and 5 per cent. of impurities
of various kinds, which vary in amount and in kind in various
descriptions of cotton. In the process of manufacture into cotton
cloths, and as the material passes through the operations of bleaching,
dyeing or printing, the impurities are eliminated.
=Impurities of the Cotton Fibre.=--Dr. E. Schunck made an investigation
many years ago into the character of the impurities, and found them to
consist of the following substances:--
=Cotton Wax.=--This substance bears a close resemblance to carnauba wax.
It is lighter than water, has a waxy lustre, is somewhat translucent, is
easily powdered, and melts below the boiling point of water. It is
insoluble in water, but dissolves in alcohol and in ether. When boiled
with weak caustic soda it melts but is not dissolved by the alkali; it
can, however, be dissolved by boiling with alcoholic caustic potash.
This wax is found fairly uniformly distributed over the surface of the
cotton fibre, and it is due to this fact that raw cotton is wetted by
water only with difficulty.
=Fatty Acids.=--A solid, fatty acid, melting at 55° C. is also present
in cotton. Probably stearic acid is the main constituent of this fatty
acid.
=Colouring Matter.=--Two brown colouring matters, both containing
nitrogen, can be obtained from raw cotton. One of these is readily
soluble in alcohol, the other only sparingly so. The presence in
relatively large quantities of these bodies accounts for the brown
colour of Egyptian and some other dark-coloured varieties of cotton.
=Pectic Acid.=--This is the chief impurity found in raw cotton. It can
be obtained in the form of an amorphous substance of a light yellow
colour, not unlike gum in appearance. It is soluble in boiling water,
and the solution has a faint acid reaction. Acids and many metallic
salts, such as mercury, chloride and lead acetate, precipitate pectic
acid from its solutions. Alkalies combine with it, and these compounds
form brown substances, are but sparingly soluble in water, and many of
them can be precipitated out by addition of neutral salts, like sodium
and ammonium chlorides.
=Albumens.=--A small quantity of albuminous matter is found among the
impurities of cotton.
=Structure of the Cotton Fibre.=--The cotton fibre varies in length from
1 to 2 inches, not only in fibres of the same class but also in fibres
from different localities--Indian fibres varying from 0.8 in the
shortest to 1.4 in the longest stapled varieties; Egyptian cotton fibres
range from 1.1 to 1.6 inches long; American cotton ranges from 0.8 in
the shortest to 2 inches in the longest fibres. The diameter is about
1/1260 of an inch. When seen under the microscope fully ripe cotton
presents the appearance of irregularly twisted ribbons, with thick
rounded edges. The thickest part is the root end, or point of attachment
to the seed. The free end terminates in a point. The diameter is fairly
uniform through 3/4 to 7/8 of its length, the rest is taper. In Fig. 1
is given some illustrations of the cotton fibre, showing this twisted
and ribbon-like structure, while in Fig. 1A is given some transverse
sections of the fibre. These show that it is a collapsed cylinder, the
walls being of considerable thickness when compared with the internal
bore or canal.
Perfectly developed, well-formed cotton fibres always present this
appearance. But all commercial cottons contain more or less of fibres
which are not perfectly developed or are unripe. These are known as
"dead fibres"; they do not spin well and they do not dye well. On
examination under the microscope it is seen that these fibres have not
the flattened, twisted appearance of the ripe fibres, but are flatter,
and the central canal is almost obliterated and the fibres are but
little twisted. Dead fibres are thin, brittle and weak.
=Composition of the Cotton Fibres.=--Of all the vegetable textile fibres
cotton is found to have the simplest chemical composition and to be, as
it were, the type substance of all such fibres, the others differing
from it in several respects. When stripped of the comparatively small
quantities of impurities, cotton is found to consist of a substance to
which the name of cellulose has been given.
[Illustration: FIG. 1.--Cotton Fibre.]
[Illustration: FIG. 1A.]
Cellulose is a compound of the three elements, carbon, hydrogen and
oxygen, in the proportions shown in the following analysis:--
Carbon, 44.2 per cent.,
Hydrogen, 6.3 per cent.,
Oxygen, 49.5 per cent.,
which corresponds to the empirical formula C{6}H{10}O{5}, which shows
it to belong to the group of carbo-hydrates, that is, bodies which
contain the hydrogen and oxygen present in them in the proportion in
which they are present in water, namely H{2}O.
Cellulose may be obtained in a pure condition from cotton by treatment
with alkalies, followed by washing, and by treatment with alkaline
hypochlorites, acids, washing and, finally, drying. As thus obtained it
is a white substance having the form of the fibre from which it is
procured, showing a slight lustre, and is slightly translucent. The
specific gravity is 1.5, it being heavier than water. It is
characterised by being very inert, a property of considerable value from
a technical point of view, as enabling the fibres to stand the various
operations of bleaching, dyeing, printing, finishing, etc. Nevertheless,
by suitable means, cellulose can be made to undergo various chemical
decompositions which will be noted in some detail.
Cellulose on exposure to the air will absorb moisture or water. This is
known as hygroscopic moisture, or "water of condition". The amount in
cotton is about 8 per cent., and it has a very important bearing on the
spinning properties of the fibre, as it makes the fibre soft and
elastic, while absolutely dry cotton fibre is stiff, brittle and
non-elastic; hence it is easier to spin and weave cotton in moist
climates or weather than in dry climates or weather. Cotton cellulose is
insoluble in all ordinary solvents, such as water, ether, alcohol,
chloroform, benzene, etc., and these agents have no influence in any way
on the material, but it is soluble in some special solvents that will be
noted later on.
ACTION OF ALKALIES.
The action of alkalies on cellulose or cotton is one of great importance
in view of the universal use of alkaline liquors made from soda or
caustic soda in the scouring, bleaching and dyeing of cotton, while
great interest attaches to the use of caustic soda in the "mercerising"
of cotton.
Dilute solutions of the caustic alkalies, caustic soda or caustic
potash, of from 2 to 7 per cent. strength, have no action on cellulose
or cotton, in the cold, even when a prolonged digestion of the fibre
with the alkaline solution takes place. Caustic alkali solutions of from
1 to 2 per cent. strength have little or no action even when used at
high temperatures and under considerable pressure--a fact of very great
importance from a bleacher's point of view, as it enables him to subject
cotton to a boil in kiers, with such alkaline solutions at high
pressures, for the purpose of scouring the cotton, without damaging the
fibre itself.
[Illustration: FIG. 2.--Mercerised Cotton Fibre.]
[Illustration: FIG. 2A.]
Solutions of caustic soda of greater strength than 3 per cent. tend,
when boiled under pressure, to convert the cellulose into soluble
bodies, and as much as 20 per cent. of the fibre may become dissolved
under such treatment. The action of strong solutions of caustic soda or
caustic potash upon cellulose or cotton is somewhat different. Mercer
found that solutions containing 10 per cent. of alkali had a very
considerable effect upon the fibre, causing it to swell up and become
gelatinous and transparent in its structure, each individual cotton
fibre losing its ribbon-like appearance, and assuming a rod-like form,
the central canal being more or less obliterated. This is shown in Fig.
2 and 2A, where the fibre is shown as a rod and the cross section in
Fig. 2A has no central canal. The action which takes place is as
follows: The cellulose enters into a combination with the alkali and
there is formed a sodium cellulose, which has the formula
C{6}H{10}O{5}2NaOH. This alkali cellulose, however, is not a stable
body; by washing with water the alkali is removed, and hydrated
cellulose is obtained, which has the formula C{6}H{10}O{5}H{2}O.
Water removes the whole of the alkali, but alcohol only removes one
half. It has been observed that during the process of washing with water
the fibre shrinks very much. This shrinkage is more particularly to be
observed in the case of cotton. As John Mercer was the first to point
out the action of the alkaline solutions on cotton, the process has
become known as "mercerisation".
Solutions of caustic soda of 1.000 or 20° Tw. in strength have very
little mercerising action, and it is only by prolonged treatment that
mercerisation can be effected. It is interesting to observe that the
addition of zinc oxide to the caustic solution increases its mercerising
powers. Solutions of 1.225 to 1.275 (that is from 45° to 55° Tw. in
strength) effect the mercerisation almost immediately in the cold, and
this is the best strength at which to use caustic soda solutions for
this purpose. In addition to the change brought about by the shrinking
and thickening of the material, the mercerised fibres are stronger than
the untreated fibres, and at the same time they have a stronger affinity
for dyes, a piece of cloth mercerised taking up three times as much
colouring matter as a piece of unmercerised cloth from the same
dye-bath.
The shrinkage of the cotton, which takes place during the operation of
washing with water, was for a long time a bar to any practical
application of the "mercerising" process, but some years ago Lowe
ascertained that by conducting the operation while the cotton was
stretched or in a state of tension this shrinkage did not take place;
further, Thomas and Prevost found that the cotton so treated gained a
silky lustre, and it has since been ascertained that this lustre is
most highly developed with the long-stapled Egyptian and Sea Island
cottons. This mercerising under tension is now applied on a large scale
to produce silkified cotton. When viewed under the microscope, the
silkified cotton fibres have the appearance shown in Fig. 3, long
rod-like fibres nearly if not quite cylindrical; the cross section of
those fibres has the appearance shown in Fig. 3A. This structure fully
accounts for the silky lustre possessed by the mercerised fibres. Silky
mercerised cotton has very considerable affinity for dye-stuffs, taking
them up much more readily from dye-baths, and it is dyed in very
brilliant shades.
[Illustration: FIG. 3.--Silkified Cotton Fibre.]
[Illustration: FIG 3A.]
In the chapter on Scouring and Bleaching of Cotton, some reference will
be made to the action of alkalies on cotton.
ACTION OF ACIDS ON CELLULOSE.
The action of acids on cellulose is a very varied one, being dependent
upon several factors, such as the particular acid used, the strength of
the acid, duration of action, temperature, etc. As a rule, organic
acids--for example acetic, oxalic, citric, tartaric--have no action on
cellulose or cotton. Solutions of sulphuric acid or hydrochloric acid of
2 per cent. strength have practically no action in the cold, and if
after immersion the cotton or cellulose be well washed there is no
change of any kind. This is important, as in certain operations of
bleaching cotton and other vegetable fibres it is necessary to sour
them, which could not be done if acids acted on them, but it is
important to thoroughly wash the goods afterwards. When the acid
solutions are used at the boil they have a disintegrating effect on the
cellulose, the latter being converted into hydrocellulose. When dried,
the cellulose is very brittle and powdery, which in the case of cotton
yarn being so treated would show itself by the yarn becoming tender and
rotten. The degree of action varies with the temperature (the higher
this is the stronger the action), and also according to the strength of
the acid solution. Thus a 10 per cent. solution of sulphuric acid used
at a temperature of 80° C. begins to act on cotton after about five
minutes' immersion, in half an hour there is a perceptible amount of
disintegration, but the complete conversion of the cotton into
hydrocellulose requires one hour's immersion. A dilute acid with 8
volumes of water, used in the cold, takes three hours' immersion before
any action on the cotton becomes evident.
ACTION OF SULPHURIC ACID ON COTTON.
When cellulose (cotton) is immersed in strong sulphuric acid the cotton
becomes gradually dissolved; as the action progresses cellulose
sulphates are formed, and some hydrolytic action takes place, with the
formation of sugar. This fact has long been known, but only recently has
it been shown that dextrose was the variety of sugar which was formed.
On diluting the strong acid solution with water there is precipitated
out the hydro or oxycelluloses that have been formed, while the
cellulose sulphates are retained in solution.
By suitable means the calcium, barium, or lead salts of these
cellulose-sulphuric acids can be prepared. Analysis of them shows that
these salts undergo hydrolysis, and lose half their sulphuric acid.
The action of strong sulphuric acid has a practical application in the
production of parchment paper; unsized paper is immersed in strong acid
of the proper strength for about a minute, and then immediately rinsed
in water. The acid acts upon the surface of the paper and forms the
cellulose-sulphuric acid which remains attached to the surface. On
passing into the water this is decomposed, the acid is washed away, and
the cellulose is deposited in an amorphous form on the paper, filling up
its pores and rendering it waterproof and grease-proof. Such papers are
now largely used for packing purposes.
ACTION OF HYDROCHLORIC ACID.
Dilute hydrochloric acid of from 1° to 2° Tw. in strength, used in the
cold, has no action on cellulose. Cotton immersed in acids of the
strength named and then well washed in water is not materially affected
in any way, which is a feature of some value in connection with the
bleaching of cotton, where the material has to be treated at two points
in the process with weak acids. Boiling dilute hydrochloric acid of 10°
Tw. disintegrates cellulose very rapidly. The product is a white very
friable powder, which if viewed under the microscope appears to be
fragments of the fibre that has been used to prepare it. The product has
the composition C{12}H{22}O{11}, and is therefore a hydrate of
cellulose, the latter having undergone hydrolysis by taking up the
elements of water according to the equation 2C{6}H{10}O{5} + H{2}O
= C{12}H{22}O{11}. By further digestion with the acid, the
hydrocellulose, as it is called, undergoes molecular change, and is
converted into dextrine. In composition hydrocellulose resembles the
product formed by the addition of sulphuric acid which has received the
name of amyloid. It differs from cellulose in containing free carboxyl,
CO, groups, while its hydroxyl groups, HO, are much more active in their
chemical reactions.
Hydrocellulose is soluble in nitric acid, 1.5 specific gravity, without
undergoing oxidation. Nitrates are formed varying in composition.
The formation of hydrocellulose has a very important bearing in woollen
manufacture. It is practically impossible to obtain wool free from
vegetable fibres, and it is often desirable to separate these vegetable
fibres. For this purpose the goods are passed into a bath of
hydrochloric acid or of weak sulphuric acid. On drying the acid converts
the cotton or vegetable fibre into hydrocellulose which, being friable
or powdery, can be easily removed, while the wool not having been acted
on by the acid remains quite intact. The process is known as
"carbonising". It may not only be done by means of the acids named but
also by the use of acid salts, such as aluminium chloride, which on
being heated are decomposed into free acid and basic oxide. For the same
reason it is important to avoid the use of these bodies, aluminium
chloride and sulphate, zinc and magnesium chlorides, etc., in the
treatment of cotton fabrics; as in finishing processes, where the goods
are dried afterwards, there is a great liability to form hydrocellulose
with the accompaniment of the tendering of the goods.
ACTION OF NITRIC ACID.
The action of nitric acid on cellulose is a variable one, depending on
many factors, strength of acid, duration of action and temperature.
Naturally as nitric acid is a strong oxidising agent the action of
nitric acid on cellulose is essentially in all cases that of an oxidant,
but the character of the product which is obtained varies very much
according to the conditions just noted. When cellulose or cotton in any
form is immersed in nitric acid of 1.4 to 1.5 specific gravity for a
moment, and the fibre be well washed, there is a formation of hydrate of
cellulose which has a gelatinous nature. This is deposited on the rest
of the material, which is not materially affected so far as regards
strength and appearance, but its power of affinity for dyes is
materially increased. There is some shrinkage in the size of the cotton
or paper acted upon.
Nitric acid changes all kinds of cellulose into nitro products, the
composition of which depends upon the strength of the acid, the duration
of treatment, and one or two other factors. The nitrocelluloses are all
highly inflammable bodies, the more highly nitrated burning with
explosive force. They are produced commercially and are known as "gun
cotton" or "pyroxyline". The most highly nitrated body forms the basis
of the explosive variety; the least highly nitrated forms that of the
soluble gun cotton used for making collodion for photographic and other
purposes.
The products formed by the action of nitric acid are usually considered
to be nitrocelluloses. It would appear that they are more correctly
described as cellulose-nitrates, for analysis indicates the presence of
the NO{3} group, which is characteristic of nitrates, and not of the
NO{2} group, which is the feature of nitro bodies in general. Further,
nitro compounds, when subject to the action of reducing agents, are
converted into amido compounds, as is the case, for instance, with
nitro-benzene, C{6}H{5}NO{2}, into aniline, C{6}H{5}NH{2}, or with
nitro-naphthalene, C{10}H{7}NO{2}, which changes into naphthylamine,
C{10}H{7}NH{2}.
But the nitric acid derivatives of cellulose are not capable of
conversion by reducing agents into similar amido compounds. They have
the following properties, which accord more closely with nitrates than
with nitric bodies: alkalies remove the nitric acid; cold sulphuric acid
expels the nitric acid, cellulose sulphates being formed; boiling with
ferrous sulphate and hydrochloric acid causes the elimination of the
nitric acid as nitric oxide (on which reaction a method for determining
the degree of nitration of gun cotton is based). It is best therefore to
consider them as cellulose nitrates. Several well-characterised
cellulose nitrates have been prepared, but is an exceedingly difficult
matter to obtain any one in a state of purity, the commercial articles
being always mixtures of two or three. Those that are best known and of
the most importance are the following:--
Cellulose Hexa-nitrate, C{6}H{4}O{5}(NO{3}){6}. This forms the
principal portion of the commercial explosive gun cotton, and is made
when a mixture of strong nitric acid and strong sulphuric acid is
allowed to act on cotton at from 50 to 55° F. for twenty-four hours. The
longer the action is prolonged, the more completely is the cotton
converted into the nitrate, with a short duration the finished product
contains lower nitrates. This hexa-nitrate is insoluble in ether,
alcohol, or in a mixture of those solvents, likewise in glacial acetic
acid or in methyl alcohol.
Cellulose Penta-nitrate, C{6}H{5}O{5}(NO{3}){5}, is found in
explosive gun cotton to a small extent. When gun cotton is dissolved in
nitric acid and sulphuric acid is added, the penta-nitrate is thrown
down as a precipitate. It is not soluble in alcohol, but is so in a
mixture of ether and alcohol, it is also slightly soluble in acetic
acid. Solutions of caustic potash convert it into the di-nitrate.
Cellulose Tetra-nitrate, C{6}H{6}O{5}(NO{3}){4}, and Cellulose
Tri-nitrate, C{6}H{7}O{5},(NO{3}){3}, form the basis of the
pyroxyline or soluble gun cotton of commerce. It has not been found
possible to separate them owing to their behaviour to solvents being
very similar. These nitrates are obtained by treating cotton with nitric
acid for twenty or thirty minutes. They are characterised by being more
soluble than the higher nitrates and less inflammable. They are freely
soluble in a mixture of ether and alcohol, from which solutions they are
precipitated in a gelatinous form on adding chloroform. Acetic ether,
methyl alcohol, acetone and glacial acetic acid, will also dissolve
these nitrates.
Cellulose Di-nitrate, C{6}H{8}O{5}(NO{3}){2}, is obtained when
cellulose is treated with hot dilute nitric acid, or when the high
nitrates are boiled with solutions of caustic soda or caustic potash.
Like the last-mentioned nitrates it is soluble in a mixture of alcohol
and ether, in acetic ether, and in absolute alcohol. The solution of the
pyroxyline nitrates in ether and alcohol is known as collodion, and is
used in photography and in medical and surgical work.
One of the most interesting applications of the cellulose nitrates is in
the production of artificial silk. Several processes, the differences
between which are partly chemical and partly mechanical, have been
patented for the production of artificial silk, those of Lehner and of
Chardonnet being of most importance. They all depend upon the fact that
when a solution of cellulose nitrate is forced through a fine aperture
or tube, the solvent evaporates almost immediately, leaving a gelatinous
thread of the cellulose nitrate which is very tough and elastic, and
possesses a brilliant lustre. Chardonnet dissolves the cellulose nitrate
in a mixture of alcohol and ether, and the solution is forced through
fine capillary tubes into hot water, when the solvents immediately
evaporate, leaving the cellulose nitrate in the form of very fine fibre,
which by suitable machinery is drawn away as fast as it is formed.
Lehner's process is very similar to that of Chardonnet. Lehner uses a
solution of cellulose nitrate in ether and alcohol, and adds a small
quantity of sulphuric acid; by the adoption of the latter ingredient he
is able to use a stronger solution of cellulose nitrate, 10 to 15 per
cent., than would otherwise be possible, and thereby obtains a stronger
thread which resists the process of drawing much better than is the case
when only a weak solution in alcohol and ether is employed. By
subsequent treatment the fibre can be denitrated and so rendered less
inflammable.
The denitrated fibres thus prepared very closely resemble silk in their
lustre; they are not quite so soft and supple, nor are they in any way
so strong as ordinary silk fibre of the same diameter.
Artificial silk can be dyed in the same manner as ordinary silk.
ACTION OF OXIDISING AGENTS ON CELLULOSE OR COTTON
Cellulose resists fairly well the action of weak oxidising agents; still
too prolonged an action of weak oxidising agents has some influence upon
the cotton fibre, and it may be worth while to point out the action of
some bodies having an oxidising effect.
Nitric acid of about 1.15 specific gravity has little action in the
cold, and only slowly on it when heated. The action is one of oxidation,
the cellulose being transformed into a substance known as oxycellulose.
This oxycellulose is white and flocculent. It tends to form gelatinous
hydrates with water, and has a composition corresponding to the formula
C{6}H{10}O{6}. It is soluble in a mixture of nitric and sulphuric
acids, and on diluting this solution with water a tri-nitrate
precipitates out. A weak solution of soda dissolves this oxycellulose
with a yellow colour, while strong sulphuric acid forms a pink
colouration. It is important to note that nitric acid of the strength
given does not convert all the cellulose into oxycellulose, but there
are formed also carbonic and oxalic acids. When cotton is passed into
strong solutions of bleaching powder and of alkaline hypochlorites and
then dried, it is found to be tendered very considerably. This effect of
bleaching powder was first observed some thirteen years ago by George
Witz, who ascribed the tendering of the cotton to the formation of an
oxycellulose. Although the composition of this particular oxycellulose
so formed has not yet been ascertained, there is reason to think that it
differs somewhat from the oxycellulose formed by the action of the weak
nitric acid. A notable property of the oxycellulose now under
consideration is its affinity for the basic coal-tar dyes, which it will
absorb directly. The oxycellulose is soluble in alkaline solutions.
In the ordinary bleaching process there is considerable risk of the
formation of oxycellulose by the employment of the bleaching solutions
of too great a strength, or in allowing the goods to lie too long before
the final washing off. The presence of any oxycellulose in bleached
cotton may be readily determined by immersing it in a weak solution of
Methylene blue, when, if there be any oxycellulose present, the fibre
will take up some of the dye-stuff.
Permanganate of potash is a very powerful oxidising agent. On cellulose
neutral solutions have but little action, either in the cold or when
heated. They may, therefore, be used for the bleaching of cotton or
other cellulose fibres.
Alkaline solutions of permanganate convert the cellulose into
oxycellulose, which resembles the oxycellulose obtained by the action of
the nitric acid.
Chromic acid, when used in the form of a solution, has but little action
on cellulose. In the presence of mineral acids, and used warm or
boiling, chromic acid oxidises cellulose into oxycellulose and other
products.
It is therefore always advisable in carrying out any technical process
connected with cotton which involves its treatment with oxidising agents
of any kind, and where it is desired not to alter the cotton, to allow
these actions to be as short as possible.
=Dyes and Cotton Dyeing.=--An account of the chemistry of the cotton
fibre would not be complete unless something is said about the reactions
involved in the processes of dyeing and printing cotton. This is a most
interesting subject and opens up quite a number of problems relating to
the combination of the fibre with colouring matter of various kinds, but
here only a brief outline of the principles that present themselves in
considering the behaviour of the cotton fibre as regards colouring
matter will be given.
When the question is considered from a broad point of view, and having
regard to the various affinities of the dyes for cotton; we notice (1)
that there is a large number of dye-stuffs--the Benzo, Congo, Diamine,
Titan, Mikado, etc., dyes--that will dye the cotton from a plain bath or
from a bath containing salt, sodium sulphate, borax or similar salts;
(2) that there are dyes which, like Magenta, Safranine, Auramine and
Methyl violet, will not dye the cotton fibre direct, but require it to
be mordanted or prepared with tannic acid; (3) that there are some dyes
or rather colouring matters which, like Alizarine, Nitroso-resorcine,
barwood, logwood, etc., require alumina, chrome and iron mordants; (4)
that there are some dyes which, like the azo scarlet and azo colours in
general, cannot be used in cotton dyeing; (5) that there are a few dyes,
_i.e._, indigo, which do not come under this grouping.
From the results of recent investigations into the chemistry of dyeing
it is now considered that for perfect dyeing to take place there must be
formed on the fibre a combination which is called a "colour lake," which
consists of at least two constituents; one of these is the dye-stuff or
the colouring matter itself, the other being either the fibre or a
mordant, if such has to be used. The question of the formation of colour
lakes is one connected with the molecular constitution of the colouring
matter, but much yet remains to be done before the proper functions and
mode of action of the various groups or radicles in the dye-stuffs can
be definitely stated. While the constitution of the dye-stuff is of
importance, that of the substance being dyed is also a factor in the
question of the conditions under which it is applied.
In dealing with the first of the above groups of dyes, the direct dyes,
the colourist is somewhat at a loss to explain in what manner the
combination with the cotton fibre is brought about. The affinity of
cellulose for dyes appears to be so small and its chemical activities so
weak, that to assume the existence of a reaction between the dye-stuff
and the fibre, tending to the formation of a colour lake, seems to be
untenable. Then, again, the chemical composition and constitution of the
dyes of this group are so varied that an explanation which would hold
good for one might not do so for another. The relative fastness of the
dyes against washing and soaping precludes the idea of a merely
mechanical absorption of the dye by the fibre; on the other hand the
great difference in the fastness to soaping and light between the same
dyes on cotton and wool would show that there has not been a true
formation of colour lake.
The dyeing of cotton with the second group of dyes is more easily
explained. The cotton fibre has some affinity for the tannic acid used
in preparing it and absorbs it from the mordanting bath. The tannic acid
has the property of combining with the basic constituents of these dyes
and forms a true colour lake, which is firmly fixed on the fibre. The
colour lake can be formed independently of the fibre by bringing the
tannic acid and the dye into contact with one another.
In the case of the dyes of the third group, the formation of a colour
lake between the metallic oxide and the colouring matter can be readily
demonstrated. In dyeing with these colours the cotton is first of all
impregnated with the mordanting oxide, and afterwards placed in the
dye-bath, the mordant already fixed on the fibre then reacts with the
dye, and absorbs it, thus dyeing the cotton. To some extent the dyeing
of cotton with the basic dyes of the second group and the mordant dyes
of the third group is almost a mechanical one, the cotton fibre taking
no part in it from a chemical point of view, but simply playing the part
of a base or foundation on which the colour lake may be formed. In the
case of the dyes of the fourth group, there being no chemical affinity
of the cotton known for them, these dyes cannot be used in a successful
manner; cotton will, if immersed in a bath containing them, more or less
mechanically take up some of the colour from the liquor, but such colour
can be almost completely washed out again, hence these dyes are not used
in cotton dyeing, although many attempts have been made to render them
available.
Indigo is a dye-stuff that stands by itself. Its combination with the
cotton fibre is chiefly of a physical rather than a chemical nature; it
does not form colour lakes in the same way as Alizarine and Magenta do.
Cellulose can be dissolved by certain metallic solutions and
preparations:--
(1) =Zinc Chloride.=--When cotton or other form of cellulose is heated
with a strong solution, 40 to 50 per cent., it slowly dissolves to a
syrupy liquid. On diluting this liquid with water the cellulose is
thrown down in a gelatinous form, but more or less hydrated, and
containing some zinc oxide, 18 to 25 per cent., in combination.
(2) =Zinc Chloride and Hydrochloric Acid.=--When zinc chloride is
dissolved in hydrochloric acid a liquid is obtained which dissolves
cellulose; on dilution the cellulose is re-precipitated in a hydrated
form. It is worth noting that the solution is not a stable one: on
keeping, the cellulose changes its character and undergoes hydrolysis to
a greater or less extent.
(3) =Ammoniacal Copper.=--When ammonia is added to a solution of copper
sulphate, there is formed at first a pale blue precipitate of copper
hydroxide, which on adding excess of ammonia dissolves to a deep blue
solution--a reaction highly characteristic of copper. The ammoniacal
copper solution thus prepared has, as was first observed by John Mercer,
the property of dissolving cellulose fairly rapidly, even in the cold.
If instead of preparing the ammoniacal copper solution in the manner
indicated above, which results in its containing a neutral ammonium
salt, the copper hydroxide be prepared separately and then dissolved in
ammonia a solution is obtained which is stronger in its action.
The cupra-ammonium solutions of cellulose are by no means stable but
change on keeping. When freshly prepared, the cellulose may be
precipitated from them almost unchanged by the addition of such bodies
as alcohol, sugar and solutions of neutral alkaline salts. On keeping
the cellulose undergoes more or less hydrolysis or even oxidation, for
it has been observed that oxycellulose is formed on prolonged digestion
of cellulose with cupra-ammonium solutions, while there is formed a
fairly large proportion of a nitrite.
On adding lead acetate to the cupra-ammonium solution of cellulose, a
compound of lead oxide and cellulose of somewhat variable composition is
precipitated. It is of interest also to note that on adding metallic
zinc to the cupra-ammonium solution the copper is thrown out and a
solution containing zinc is obtained.
This action of cupra-ammonium solutions on cellulose has been made the
basis for the production of the "Willesden" waterproof cloths. Cotton
cloths or paper are passed through these solutions of various degrees of
strength according to requirements, they are then passed through rollers
which causes the surface to become more compact. There is formed on the
surface of the goods a deposit of a gelatinous nature which makes the
surface more compact, and the fabric becomes waterproof in character
while the copper imparts to them a green colour and acts as a
preservative. The "Willesden" fabrics have been found very useful for a
variety of purposes.