THE CHEMISTRY AND PHYSICS
OF
DYEING
THE CHEMISTRY AND PHYSICS
OF
DYEING
BEING AN ACCOUNT OF THE;
RELATIONS BETWEEN FIBRES AND DYES,
THE FORMATION OF LAKES, AND THE
GENERAL REACTIONS OF COLLOIDS, AND
THEIR SOLUTION STATE
BY
W. P. DREAPER, F.I.C., F.C.S.
ILLUSTRATED BY CURVES AND NUMEROUS
TABULATED RESULTS
LONDON
J. & A. CHURCHILL
7 GREAT MARLBOROUGH STREET
1906
,
<K
PREFACE
IN the present volume an attempt is made to collect
and classify the work which has been brought for-
ward to explain the action of dyeing, mordanting
and lake formation.
The general text-books on dyeing devote little
space to this particular side of the question. They
deal with the operations of the dye-house, rather
than with the principles which seem to govern the
actual practice of this branch of industry.
It is advisable that the modern dyer should have
some knowledge of the general reactions, which give
rise to the results obtained in the many processes,
involved in the dyeing, and bleaching of textile fibres.
Without some such knowledge, it is difficult to
appreciate their nature ; or be in a position to control
their working in a systematic manner.
To obtain this under present conditions, it is
necessary to make a more, or less, tedious search
over the scientific and technical journals of the last
thirty years.
This same difficulty presents itself to the student,
who wishes to engage in research on this interesting,
but little understood subject.
It is, perhaps, equally difficult for the dyer to
obtain information of those branches of physical
science, which will possibly give an explanation
of many of the mordanting and dyeing operations
met with in daily practice.
With the extension of our knowledge of general
physics, and the breaking down of the artificial
vi PREFACE
barriers set up during the nineteenth century be-
tween the different branches of experimental science,
has come a wider outlook. The subject before us
forms an interesting chapter in the evolution of
theoretical speculation in its application to the
principles of a well-known, but little understood
industrial process.
From the very nature and complexity of the
subject, it is more than likely, that any further
advance in our knowledge will come from within
the industry itself. With the increasing number
of chemists who are devoting their time to this
subject, and gradually displacing the " rule of
thumb " methods of the past, this does not appear
to be improbable.
At the present time, the art of dyeing may be
said to be in advance of the science of the subject.
The first step towards restoring the balance, is
to take a general survey of the work done in
the past, by the many investigators who have given
this matter their attention. The foundation on
which we rest our present ideas of the nature of
the dyeing phenomena met with in our dye-houses,
and finishing factories, must be realised before any
further advance is possible. The subject has been
treated from this point of view. The object of this
book is to give the practical dyer, and student, a
collected record of the work done in the past, so
that it may be available for reference.
It is only by referring back the observed pheno-
mena in dyeing to the first principles of chemistry
and physics, that we can expect to advance beyond
the present /state of uncertainty as to the nature of
the actions involved.
The need for further research along systematic
lines is urgent. Much might be done in the dye-
ing departments of our technical institutions, if a
definite scheme of research could be devised, and
carried out.
PREFACE
vn
Then, perhaps, the process of dyeing with all
that it entails, will take its place in the general scheme
of physical science.
A study of the name index indicates how
little of this work has been done in England, and
the steps which are necessary in the future, if this
country is to hold its own in the dyeing industry.
The dyer must watch other things besides his
dye-pots, and his tinted yarns. He must know some-
thing of the general reactions of colloids, as typical
of those which may possibly take place in the sub-
stance of the materials he has to prepare, and dye.
It is important too, that he should have some know-
ledge of the general principles which seem to govern
solution, and the action of temperature, &c., on the
dye liquors, and fibres.
This book is therefore written to supply the
practical man with this knowledge. It is also hoped
that it may induce the student to embark on original
work, and by supplying him with an outline of what
has been already done on the subject, indicate new
lines on which further work may be undertaken
with advantage. A close study of this subject on
systematic lines, and in its wider aspect, cannot fail
to lead to important results.
It is difficult, under present conditions, to entirely
do away with the divisions, which still exist in con-
nection with the study of dyeing phenomena. While
sympathising with those who are ready to take
this step, the author feels that had this book been
written on these lines, it would have been less useful
to the majority of readers.
It is quite possible for the student to steer a
middle course, and, keeping for convenience the old
divisions before him, to remember that the general
scheme of research is an artificial one at best, and
that the recognised divisions are of an arbitrary
nature. This is being demonstrated daily. All that
the student in dyeing, or the practical dyer, needs to
viii PREFACE
remember is, that these divisions are upheld on the
grounds of general convenience.
To the general student of chemistry it is doubtful
whether there is at the present time a more fruitful
subject of research than that of dyeing. It is hoped
that the publication of the chief work which has been
done on the subject in the past in the present form
will tend to increase the interest taken in this
subject, and at the same time raise the standard of
the work done.
Wherever possible, references have been given
to the original communications in which the recorded
facts have first appeared, in order that fuller knowledge
may be obtained for special purposes.
The facts mentioned under their different head-
ings are also, as far as possible, put forward in their
historical sequence.
In this way the gradual development of the
subject under review may be followed from the
earliest investigations, and speculations, of Hellot
in the year 1734 to the present time ; and an insight
into the probable nature of dyeing obtained.
This can hardly fail to be of interest to the dyer,
whose aim should be, first of all, to understand the
principles which control the many and varied opera-
tions of dyeing, and by this means obtain [more
regular and satisfactory results in the practice of his
art.
The author wishes to express his thanks to Mr.
W. A. Davis, B.Sc., for his help in the revision of
proofs and for his valuable suggestions.
THE AUTHOR.
v
September 15, 1906.
CONTENTS
CHAP. PAGE
I. HISTORICAL INTRODUCTION . , . . . i
II. PROPERTIES OF FIBRES, AND THEIR REACTIONS . n
III. DYES AND LAKES, AND THEIR PROPERTIES . . 32
IV. ACTION, AND NATURE OF MORDANTS . . . 53
V. STATE OF FIBRES, AND ACTION OF ASSISTANTS . 72
VI. SOLUTION, AND THE PROPERTIES OF COLLOIDS . 102
VII. PHYSICAL ACTION, AND SOLID SOLUTION . . 140
VIII. EVIDENCE OF CHEMICAL ACTION IN DYEING. . 181
IX. EVIDENCE OF CHEMICAL ACTION IN DYEING
(continued) . . . . . . .208
X. PART PLAYED BY COLLOIDS IN DYEING, AND LAKE
FORMATION . . . . . . . 234
XL THE ACTION OF LIGHT ON DYEING OPERATIONS, AND
DYED FABRICS . . . ; . . 281
XII. METHODS OF RESEARCH . . . . 297
LIST OF ILLUSTRATIONS
CURVES
FIG. PAGE
1 . Formation of Lakes in Aqueous Solution . . 44
2. Absorption of Sulphuric Acid by Wool . . . 88
3. Influence of Time on Absorption of Acid . . . 89
4. Rosaniline Acetate on Wool . . 99
5. Absorption of Tannic and Gallic Acids in presence of
Acetic Acid . . . .. . . 162
6. Absorption of Gallic Acids by Colloids . . 164
7. Fastness of Ingrain Colours (phenolic) . . . . 202
8. Fastness of Ingrain Colours (amine) . . . 203
CHEMISTRY AND PHYSICS
OF DYEING
CHAPTER I
HISTORICAL INTRODUCTION
THE art of dyeing has been practised for long ages.
Its origin is lost in antiquity. There is distinct
evidence that operations of this nature were carried
on in Persia, Egypt, the East Indies, and Syria in
early days. The Tyrians excelled in the produc-
tion of the celebrated purple of Tyre, and seem to
have made its manufacture one of their chief occu-
pations. This colour was noted for its richness,
and durable qualities. It is believed that the
method of dyeing this colour was invented about the
year 1500 B.C. Wool dyed in this way sold in Rome
at a price equivalent to 30 per pound.
The purple of Tyre seemed to vary in its colour.
Pliny mentioned that the shade varied from a faint
scarlet to the red of coagulated bullock's blood.
The origin of the shell fish from which the colour
was developed seemed to determine the shade.
The Atlantic variety gave the darkest colours,
while those obtained off the Phoenician shore yielded
2 V :: CHEMISTRY AND PHYSICS OF DYEING
: ^ ^tfie' scarlet ^shades. The dye prepared from these
varieties of shell fish was probably developed by
some process of oxidation ; the exact nature of the
operation being unknown.
The secret of the production of this colour was
carefully guarded, and in this way a virtual mono-
poly was established.
i It was not until the fourteenth century that the
art of dyeing flourished in Europe. Florence was
one of the headquarters of this industry.
An inferior cochineal, or kermes, was collected
by the Arabs about this period.
This same product was known to the Greeks and
Romans under the name coccus. It is interesting
to note that between the ninth and fourteenth
centuries, the rural serfs were obliged to deliver to
the convents a certain quantity of this dye annually,
i A great deal of this German kermes was consumed
in Venice for the dyeing of scarlet.
Pliny ("Hist. Nat." lib. xxxv. cap. n) draws
attention also to the extraordinary method of dye-
ing linen in Egypt. They clearly developed the
colour on mordants in this case.
A great change came about in the dyeing in-
dustry with the discovery of America. With the
trading which sprung up between the two continents
many very valuable dyewoods were introduced to
Europe. Among these may be mentioned cochineal,
logwood and annotto.
/ About this time also Oricelli discovered the action
of ammoniacal liquors on certain lichens with the
HISTORICAL INTRODUCTION 3
production of coloured bodies which might be
used for dyeing organic fibres. These have only
given way before the aniline colours. A great
development took place about the year 1650, when
tin salts were introduced as a mordant in the place
of alum ; and with this introduction we have the
production of the first really brilliant colours on
fibres. As the result of the discovery, a large dye-
house was established at Bow. Cochineal was dyed
on this mordant with great success, and the colours
produced in this district were justly celebrated
for their purity and beauty.
In the year 1548 the first text-book on dyeing
appeared. The production and publication of this
book had a great effect on the art in Germany,
France and England. The dyeing operations in
these countries were greatly extended as a result ;
and the almost complete monopoly which had
existed for nearly a century or more in Italy was
gradually broken down by this natural extension
of the industry. The year 1667 was a most im-
portant one for England. A Fleming coming to
England brought with him the art of dyeing wool
in a state of great perfection. Since that date it
has been maintained at a high level in this country,
and sets a standard to the world.
With this increased activity came the publica-
tion of several works on the subject. This greatly
widened the interest taken in this important and
lucrative branch of industry.
The dyeing with woad was of importance in
4 CHEMISTRY AND PHYSICS OF DYEING
this country, and the introduction of indigo, with
its superior colours on wool, created a scare amongst
those interested in the woad industry. Severe
measures were taken by the government to keep
this product out of the country. It was not until
the reign of Charles II. that its use was permitted
in the English dyehouse.
As might be expected it gradually replaced the
native woad, until to-day the latter is only used
in limited quantities for the " indigo- woad " bath
in some special dyeing districts.
In the eighteenth century the art made great
progress. About this time madder was used in
large quantities and quercitron introduced. Mor-
dants were also manufactured in a purer state, with
the natural result that the colours were correspond-
ingly brighter in shade and of increased beauty.
Mineral colours were also introduced and used
in the colouring of fibres, being precipitated in their
substance. In the year 1734, Hellot published his
celebrated book on wool-dyeing, and this again led
to the natural extension of the industry. " L'art
de la teinture des laines et des etoffes de laine" was
a most important work, and its influence was great
on the industry.
About this time, also, the value of Turkey red
as dyed in India gradually impressed the European
dyers with its great and almost unique value. As a
result of this, the French government in 1765 caused
the details of this process of dyeing to be published.
To-day the seat of this industry is in Europe,
HISTORICAL INTRODUCTION 5
although it may possibly drift back to the East
again. Two other important books were published
in France during this century.
Le Pileur d'Apligny in 1776 published " L'art
de la teinture des fils et etoffes de coton/'
which has been generally recognised as marking a
stage in the development of this subject.
" Les elements de Fart de la teinture/' by
Berthollet, published in 1791, and " La chimie
appliquee aux arts/' by Chaptal, in 1807, greatly
added to the knowledge of dyeing.
These publications undoubtedly tended to give
to France that superior position which she has so
long held in the art of dyeing. Their influence is
difficult to over-estimate. The list of important
books published in France on this subject must also
include the following:
" Legons de chimie appliquees a la teinture/'
by Chevreul in 1828-1831 ; " Traite de chimie
appliquee aux arts/' in 1828-1846; " Legons de
chimie industrielle/' by de Girardin, published in
J 837 ; " Traite theorique et pratique de 1'impression
des tissus/' by Jean Persoz (1846) ; " Cours elemen-
taire de teinture/' de Vitalis (1823) ; " Manuel
complete de teinture/' Vergnaud (1832).
Another great step in dyeing as practised in
Europe was taken during the early part of the eight-
eenth century. Calico printing in its rudimentary
stage was introduced. This industry has grown to
enormous proportions. This very rough sketch of
the early days^of dyeing brings us up to the time
6 CHEMISTRY AND PHYSICS OF DYEING
when dyers began to study the theoretical basis of
their operations, and to trace the possible actions
of dyes and fibres ; and the part which they respec-
tively played in the process of dyeing.
From these early speculations by easy stages our
knowledge of this subject has gradually developed.
When we look back, remembering the elementary
state of scientific knowledge of those days, and the
admittedly complex nature of the processes of
dyeing, we cannot but give a full measure of praise
to the work of the early investigators, before whose
eyes the first opening out of this subject must have
been of great interest.
Even to-day, with our extended knowledge, we
are yet ignorant of the exact and complete causes
which bring about many of the complicated and
varied effects, which are classified under the com-
prehensive term, dyeing.
Much of the detail, at any rate, is little under-
stood. From the simpler speculations of these
investigators, and their rough experiments on pound-
samples of wool, the student of to-day may derive
valuable information and an insight into the early
methods of dyeing.
At the present time we are passing through a
transition state, and until the general ideas of
molecular physics and chemistry reach a more satis-
factory and sure basis, it is difficult to expect that
our knowledge of the operations of dyeing can rest
on a sure foundation.
It is, however, certain that if the study of
HISTORICAL INTRODUCTION 7
dyeing betaken up in the proper spirit, the results
obtained must influence on their side, either by
confirmation or otherwise, many of the most im-
portant speculations in the domain of solution, and
other equally important phenomena. The abnormal
nature of the reactions in dyeing, and the very
delicate nature of the available colour-tests, com-
bine to present us with an effective means for
further investigations into the state of matter, under
favourable conditions. This point is not so generally
recognised as it should be, owing, perhaps, to the
intimate knowledge of the practical part of the
question, which is necessary before the facts ob-
served in the dyehouse can be given their true signi-
ficance. This is only obtainable by direct contact
and continued observation of the dyehouse routine.
In this way, and this way only, will many abnormal
conditions, and results, yield to the investigator
their true significance.
In the earliest days there were the up-
holders of mechanical and chemical theories of
dyeing. Ever since the middle of the eighteenth
century, the conflict has raged round these two
hypotheses, greatly to the benefit of our knowledge
of dyeing. In the search after fresh evidence
many new and important facts have come to light.
The influence of this has been satisfactory, and has
led to improvements in the processes of dyeing, and
the gradual recognition of the fact that scientific
methods are necessary in the dyehouse. To-day we
have other possible explanations of the causes of
8 CHEMISTRY AND PHYSICS OF DYEING
dyeing, which, however, in their broadest terms, may
still be referred back to these early and rival ones.
There is a tendency at the present time to
discard such artificial barriers as divide the opera-
tions of nature into almost watertight compartments.
The terms mechanical, physical, and chemical, are
more and more regarded as mere phases, referring
phenomena back indirectly to a common origin of
matter and force.
It is not necessary for the dyer altogether to
discontinue those divisions of the past, which by
their very limitations have led to the necessary
concentration of ideas along certain lines. The
time is not yet come when we can do so with any
certainty or advantage. To the present system
we must at least ascribe our present position. It
is doubtful if, for some time to come, any advantage
would be gained by giving up these general divisions,
which have proved so useful in the past. At the same
time, the student must keep an open mind on this
subject. There is no indication that the problem
before us of indicating the true cause of dyeing is
becoming less complex in its nature. Some new
principle or factor in general physics may be applied
to dyeing operations, and in this way our knowledge
may be greatly extended. To-day, other theories
besides those already mentioned have their upholders.
Dyeing has been, for instance, associated with " solid
solution/' and an attempt has been made to
extend this state to cover the absorption results
when a dye is taken up by an organic fibre. From
HISTORICAL INTRODUCTION 9
another point of view the dyeing effect has been
ascribed to " dissociation effects."
Our increasing knowledge of the general reactions
of colloids, in which class we may include the textile
fibres, is modifying our views ; and the condition-
reactions of these complex bodies has given rise to
what is termed the " colloid " theory of dyeing.
The time has, perhaps, come when it is necessary
to classify the researches of the past in this and
kindred subjects, and formulate the general conclu-
sions which have been arrived at from time to time,
and examine them from the practical dyers* point of
view. It is unfortunate that the majority of in-
vestigators have contented themselves with working
on a qualitative rather than a quantitative basis.
Little care has been taken to work with pure materials
on the one hand, or under recorded conditions on
the other. It is, therefore, difficult to form an
estimate of the reliability of the recorded results in
many cases where accuracy of detail and conditions
are of the first importance.
No doubt, our further inquiries into this subject
will enable us to classify more correctly the recorded
results of the past than is possible at the present
time.
Space has been devoted to the consideration of
our present general knowledge of the properties
and nature of colloids, and a short resume of the
work done on this subject has been included in this
work. The abnormal actions of these substances in
a state of solution are of great interest to the dyer.
io CHEMISTRY AND PHYSICS OF DYEING
They seem to approximate to the results obtained
in the dyehouse.
For full details of the chemical constitution of
the dyes used to-day, the standard text-books on
this subject must be consulted. As regards the
possible actions in the operations of dyeing in rela-
tion to their constitution, the matter is dealt with
in this work in an elementary way.
CHAPTER II
PROPERTIES OF FIBRES AND THEIR REACTIONS
So much has been written on the properties of the
fibres themselves in their physical aspect, that no
great space will be devoted to this subject. This
matter should, however, receive careful attention,
and the standard works on the subject should be
consulted.
The most important properties of the leading
fibres are briefly reviewed here.
For our purpose we may fairly recognise the
accepted classification of the fibres into those of
animal and vegetable origin respectively.
From the present point of view, our knowledge is
mainly confined to the three important fibres, silk,
wool, and cotton. So far as the others are concerned,
with perhaps the possible exception of jute, little work
has been published. In these cases dyeing is of an
empirical nature, whatever may be said of our
knowledge in the first mentioned cases.
It is strange that more attention has not been
given to the reactions entailed in the dyeing and
mordanting of these other fibres. A systematic
and regular survey of the comparative reactions of
12 CHEMISTRY AND PHYSICS OF DYEING
these towards dyes, &c., in relation to their physical
nature, could not fail to give important results.
Cotton. This fibre may be regarded as a long
tubular compound vegetable cell. It is 1200-1500
times as long as it is broad. The outer sheath is
considered to be pure cellulose. The inner layers
are made up of secondary cellular deposits ; or are
formed of a gradual thickening of the outer layer.
The extreme end of the fibre is closed, that originally
attached to the seed is broken off irregularly.
We have here a fibre which from its natural
constitution may materially complicate the normal
action of dyeing. All the natural fibres are com-
plicated in their physical formation.
If all the fibres in a pound of cotton were placed
end on, they would extend to 2200 miles.
Within the limits of dyeing temperatures, a
dry heat has little, or no, influence on the fibre sub-
stance itself. The material which makes up the
purified cotton fibre is cellulose. This substance
has been the subject of a great deal of research.
Its ultimate composition is expressed by the formula :
C 6 H 10^5-
In its purest form, cellulose is regarded as an
inert substance, white in colour, insoluble in all
ordinary reagents, such as water, alcohol, &c. ;
and the action of these solvents on the fibre is said
to be a negative one. At a high temperature and
pressure, the fibre is, in some respects, altered by
water. Zinc chloride, phosphoric acid, and am-
moniacal copper solution dissolve this fibre. The
PROPERTIES OF FIBRES AND THEIR REACTIONS 13
precipitate from these solutions is called " regene-
rated " cellulose ; and it has been maintained that
the alteration in its substance is merely structural.
This is doubtful, however, for the capacity of fila-
ments prepared from these regenerated compounds
to absorb dyes is profoundly modified. The same
phenomenon is noticed with the regenerated cotton
from an alkaline thiocarbonate solution. The precipi-
tated substance is, in this case, a hydro-cellulose which
also has an increased affinity for certain dye-stuffs.
Some interesting speculations have been made by
A. G. Green (Rev. Gen. des Mat. Col. 1904, 130) on
the constitution of the cellulose molecule (compare
Green and A. G. Perkin, Proc. C.5., 1906, p. 136).
The empirical formula C 6 H 10 O 5 is not sufficiently
complex to explain the formation of tri- and penta-
nitro-compounds. This investigator considers the
existence of these derivatives doubtful. The fact
that cellulose can exist in the colloid state, and is
difficultly soluble is not considered to indicate, as
previously supposed, a high molecular weight. The
same argument is not used in the case of alumina
or silicic acid to explain their colloid state.
Many reasons are given to justify the simple
C 6 H 10 O 5 formula, and the original paper must be
consulted for the full details of this argument.
Faber and Tollens have obtained from oxycel-
lulose dihydroxybutyric acid and isosaccharic acid :
CH(OH).CH COOH
CH(OH).CH COOH.
14 CHEMISTRY AND PHYSICS OF DYEING
Green proposes the following formula for cellu-
lose :
CH(OH)-CH CH-OH
CH(OH)-CH CH 2 .
This formula brings forward the aldehyde nature
of cellulose as follows :
-CH-OH
-CH 2
which by fixation of water becomes :
-CH(OH) 2
-CH 2 (OH)
and then
-CHO
-CH 2 (OH).
When cotton is mercerised we get an action of
this order.
-ONa -OH
ONa a then, finally on washing _QJJ
This formula is also sufficiently complex to
explain the Fenton reaction, and the formation of
the intermediate hydration product.
CH = C
CH = C.
And then by addition of bromine
-CH.OH
-CH 2 Br.
And by elimination
CH=C-CHO
= C-CH 2 Br.
(w. brom methyl furfural.)
PROPERTIES OF FIBRES AND THEIR REACTIONS 15
From the ionic point of view, cellulose is regarded
as an aggregate of ions which take their origin
under special conditions present in the plant-cells
in which celluloses are present as mass aggregates.
The cellulose aggregate is, therefore, regarded as a
mixture of ions of varying dimensions. As a con-
sequence, cellulose as a typical colloid has no definite
reacting unit as a body which takes the crystalline
form, nor a fixed molecular constitution such as
could be represented by a constitutional formula,
the cellulose molecule not being regarded as a
static unit measurable in the ordinary physical units
so much as a dynamic equilibrium ; its reacting
unit at any moment being a function of the condi-
tions under which it is placed.
Such is, perhaps, the most recent definition of
the constitution of the celluloses from the ionic
point of view as advanced by C. F. Cross.
If this view is accepted as a working hypothesis,
and we regard the fibre colloids as solution aggre-
gates rather than fixed and definite units, it may be
taken for granted that the further study of the action
of dyeing will throw light on this subject generally.
The two extreme views of the constitution of
cellulose are expressed here, and will indicate to the
student the varied nature of the ideas on this sub-
ject to-day.
Action of reagents on cotton. Cellulose is unable
to resist entirely the action of reagents.
Acids, for instance, may modify its structure and
composition in a remarkable way.
16 CHEMISTRY AND PHYSICS OF DYEING
The ultimate action of sulphuric acid is the pro-
duction of grape sugar, but the action takes place in
stages which are more or less marked. Dextrin
is an intermediate compound of the same ultimate
composition as cellulose itself. The first action of
this acid is of a less destructive nature. The cotton
fibre swells up, gelatinising at the same time. By
a very rapid removal of the strong acid at this stage,
so-called " vegetable parchment " is produced.
This product finds important uses in the industrial
world. Its strength is greatly increased and its dye
affinity modified.
Nitric acid has a destructive action, if carried
to an extreme stage. At a high temperature the
acid breaks up the fibre and destroys it. The ultimate
products are different in this case, oxalic acid being
one of the final products of the reaction. The action
of this acid in the cold, either in the presence of
sulphuric acid or alone results in the production of
nitrates. The higher nitrates being used as explo-
sives (gun-cotton), the lower nitrates dissolve in
solvents such as ether-alcohol, and are then known
as collodion. They also enter into the composition of
xylonite, &c. The action of dyes on these nitrated
fibres is a more energetic one. A systematic exam-
ination of their relative actions on these different
nitro-products is greatly needed, and has never been
published. The solubility of these nitro-compounds
is entirely different to that of the original cotton.
As mentioned above it either swells up or dissolves in
alcohol-ether. On the other hand, it no longer
PROPERTIES OF FIBRES AND THEIR REACTIONS 17
dissolves in zinc chloride. It is practically insoluble
at low temperatures in this reagent.
The action of weak acids on cotton fibre is
roughly indicated in some experiments by A.
Scheurer. The fibre was subjected to a 20 grm.
solution of oxalic acid ; or its equivalent in other
acids. The results are expressed in percentages.
DIMINUTION IN STRENGTH OF FIBRE.
Acid.
After 4 hours
(cold).
After 3 days
in hot air.
After steaming
for i hour.
Oxalic
2-5
25.0
25.0
Tartaric . . .0
5-0
10.
o. -phosphoric . i.o
1-5
15.0
m. -phosphoric
2-5
31-5
35-o
p. -phosphoric
2-5
35-0
35-5
Phosphorous
1-5
27.0
28.0
The addition of such substances as glucose seems
to exert a protecting influence when present in the
above solutions.
For example, with oxalic acid and 50 grms.
glucose to the litre, a protection equivalent to
13 per cent, occurs in hot air, and 6 per cent, on
steaming, as compared with the above figures.
Mercer in his celebrated patent gives an account
of the action of such acid reagents on cotton, and
notices the increased effect of dyes on the same.
The action of hydrochloric acid is also a severe
one. The cotton fibre falls to powder, owing to a
partial, and uneven solution of the same. (Stern,
2
i8 CHEMISTRY AND PHYSICS OF DYEING
f.C.S.j 1904, 336.) In all these cases the acid must
be strong. Weak acids have little, or no effect, on
this fibre, so far as their subsequent reactions are
concerned.
Action of Acid Salts. Bisulphates, or salts which
are easily dissociated, such as aluminium chloride,
act on cotton, if their solutions are allowed to
concentrate by drying on the fibre. In such a way
cotton is separated from wool and silk, and the latter
recovered and used again. In the case of wool the
recovered fibre is known as shoddy. A few years
ago a lace effect was produced in Switzerland by
weaving silk designs on a cotton foundation and
subsequently " burning out " the latter in this way.
The other acid salts act in a milder way.
Action of Alkalies. A strong solution of caustic
alkali profoundly modifies the properties of the
cotton fibre. Here, as in the case of sulphuric acid,
a shrinking and gelatinising action takes place. A
sodium compound Na 2 O.C 12 H 20 O 10 . is said to be
formed. Washing in water decomposes this com-
pound, and a hydro-cellulose remains. Within the
last few years an enormous quantity of cotton has
been treated in this way. If a long staple cotton
be used, and the fibre " stretched," an increased
gloss is obtained ; in the case of artificial silk a similar
result is obtained (Dreaper and Tompkins). After
mercerising a greatly increased affinity for some dyes
is exhibited.
The action of oxidising agents produces oxy-
cellulose which also exhibits increased attraction
PROPERTIES OF FIBRES AND THEIR REACTIONS 19
for dyes. When treated with caustic soda solution
100 grammes of the fibre disengage heat as follows
(Vignon) :
Cellulose . . .74 cals.
Oxycellulose . . 1.30 cals.
This product also gives Schiffs' reaction for
aldehydes. It will, therefore, be seen that although
cellulose is a comparatively inert body, from the
dyer's point of view, yet it attracts dyes more
readily after being subjected to the action of strong
mineral acids, alkalies, or when dissolved and pre-
cipitated. Further particulars of the action of such
reagents may be found in the many papers written
on this subject, and in a monograph by P. Gardner,
from which the following details are taken.
The mercerising action of caustic alkali solu
tion begins at 10 B. and increases with the strength
of solution up to 35 B. The temperature should
not exceed 20 C. Gardner considers that to the
varying chemical action is due the different results
obtained with different cottons. 10 per cent, to
30 per cent, more dye is required to produce the
same shade after mercerising the fibre.
It is advantageous to mercerise at a low tem-
perature ; a weaker solution of caustic soda will
produce the same effect. Lefevre (Rev. Gen. des Mat.
Col., 1902, p. i) states that at the lower tem-
perature a 35 B. solution will give a result equal
to a 50 B. solution at ordinary temperatures ;
but with this stronger solution and refrigeration
no advantage is obtained.
20 CHEMISTRY AND PHYSICS OF DYEING
Kurz (ibid. p. i) considers that it is advanta-
geous to refrigerate with raw cotton, but that with
bleached cotton it is not so necessary.
The heat developed on mercerising the latter is
very small, but the temperature effect is more
evident in the case of raw cotton, a rise of 13 C.
to 21 C. being noticed in this case.
In the case of ramie and linen it is interesting
to note that the action of mercerising is a different
one. This is owing to the separate cells in these
fibres swelling up and ultimately bursting. The
surface of the fibre becomes correspondingly rough
and not smooth as in the case of cotton.
Interesting results will probably be obtained
by further research on this fibre and its relative
dyeing properties under these conditions.
If the cellulose aggregate or molecule is an
alcoholic anhydride, its chemical activity might be
due to the hydroxyl groups. Various acyl and alkyl
derivatives have been prepared and their relative
dyeing properties determined by W. Suida (Monatsh.
/. Chem., 1905, 26, 413). The results show that the
dyeing properties of the nucleus are not influenced
by the conversion of these OH groups into the acyl
or alkyl ones.
These results should be considered in conjunc-
tion with the results obtained with nitrocellulose
and hydrocellulose.
Nitration of the fibre, even to the extent of the
introduction of 80 per cent, of NO 2 groups, does not
appreciably alter the visible structure or breaking
PROPERTIES OF FIBRES AND THEIR REACTIONS 21
strain of the thread. (Bronnert, Rev. Gen. des
Mat. Col., 1900.)
It has also been stated that the introduction
of 80-90 per cent, of acetyl groups into the cellulose
molecule, does not alter the original properties of
the cellulose. (Cross, J .S.C.I., 23, p. 297.)
Cotton is stated to act energetically as a catalysing
agent (Suida, Monatsh. f. Chem., 1905, 26, 413).
In a mixture of benzoyl chloride and sodium hydrate
the former rapidly disappears on agitating the liquid
in the presence of cotton. In its absence this effect
is not noticed.
The action which magnesium and aluminium
chlorides exert on cotton and other vegetable fibres
is stated to be due to hydrolysis, owing to the hydro-
chloric acid set free on rapid drying.
Only the vegetable fibres dissociate these salts.
On wool magnesium chloride gives no trace of free
acid, even at a temperature of 140 C. That the
wool actually takes up the chloride is shown as follows.
Cotton cloth and cashmere were soaked in solu-
tions of magnesium chloride at 13 Tw.. and alu-
minium chloride at 10 Tw. The samples were
weighed after squeezing and the results would indi-
cate that the chlorine, magnesium and aluminium
taken up by the fibres were normal. An exception
was noted in the case of the aluminium salt and
wool ; more acid than base being absorbed in this
case. (Hanofsky, Chem. Zeit. y 56, 1897.)
The hydrolysing action of water is very marked
at high temperatures, and under pressure.
22 CHEMISTRY AND PHYSICS OF DYEING
The fibre may even be disintegrated with the
formation of soluble hydration products.
When cotton is wetted by water a certain rise
in temperature takes place. At first sight this
might be attributed to a hydrating action, but the
general results obtained on wetting inert substances
(finely divided solids) does not altogether support
this idea. It has long been known that a similar
action takes place when these powders are immersed
in inorganic or organic liquids (Pouillet). A careful
study of the conditions which give rise to these
phenomena has been made by Masson (Proc. Roy.
Soc., 74, 230). Unlike the ordinary disengagement
of heat which may take place in an exothermic reac-
tion, there is no definite limit either in time, or degree.
The action sometimes persists for hours, giving
an increased surface temperature of from 8 to 12
in the case of cotton. Similar temperature results
were obtained in the case of glass wool in the presence
of water vapour. The conclusion arrived at was
that the action is a distillation effect through a layer
of air ; and that this gives rise to the thermal pheno-
mena noticed in these cases. This investigator
recorded that if the solid is wetted, no temperature
effect is obtained ; and concluded, therefore, that
the action is not a chemical one.
The results obtained by Martini (Phil. Mag., (5) 47,
329) do not, however, seem to confirm these observa-
tions. With pure silica, in a finely divided state, a
great rise in temperature is recorded in such solutions
as distilled water (22.6), absolute alcohol (26), and
PROPERTIES OF FIBRES AND THEIR REACTIONS 23
sulphuric ether (31.5). Under exceptional circum-
stances the silica was raised from 17 to 80 C. There
can be little doubt, but that the alcohol and ether
actually wet the silica. Yet Masson distinctly states
that glass wool will not give the temperature effect
with water, but only with water vapour, on account
of the air film.
Martini considered that the liquids are absorbed
by the solids, and enter the solid state themselves
(ibid. (5) 50, 618). He subsequently modified this
idea, and considered the action a physico-chemical
one. Silica is said to abstract water from a mixture
of three parts of alcohol to one of water.
On the other hand, he notices a reverse action
in the case when mercury is the liquid. The whole
subject seems to be very involved in the present
stage of our knowledge. Three distinct theories
have been advanced to explain the action depending
on distillation effect ; transfer to the solid state,
or a physico-chemical cause respectively.
The matter must be allowed to rest here for the
present, but the ultimate solution of this problem
may possibly throw light on the subject of the
absorption of substances by fibres, &c., and is worthy
of further attention.
The idea that a liquid can enter a solid, and by
some influence be degraded to the solid state, under
conditions which would normally determine the
liquid one, is a far-reaching hypothesis. This
effect, if really present, must greatly modify our
ideas on the attractive value of fibres. Further
24 CHEMISTRY AND PHYSICS OF DYEING
work on this subject is urgently needed, to clear
up these points.
Wool. The standard works must be referred
to for details as to the actual physical structure of
the many varieties which come upon the European
markets.
The fibre substance is called keratine. Its
chemical constitution is obscure. The published
analyses of wool vary greatly, and there is no direct
evidence that keratine is a definite substance. To
prove this, it is only necessary to state that the
sulphur varies from 2 to 4 per cent., and that this is
partly removed by dilute alkali. If strong alkali
is used the wool " dissolves," and if this solution be
acidified, the larger part of the sulphur passes off
as sulphuretted hydrogen.
The mineral matter present, probably in com-
bination, varies also in amount (J.S.D. and C., 1888,
104) and composition. It averages a little over
i per cent, on the weight of the wool.
The action of dilute acids seems to be more
specific than in the case of the vegetable fibres.
Wool treated with sulphuric acid (or hydrochloric)
and subsequently washed attracts colouring-matters
with increased avidity.
Nitric acid gives with wool a yellow coloura-
tion, due to the formation of xanthoproteic
acid.
Nitrous acid (Richard, J.S.D. and C., 1888,
154) " diazotises " part at least of the wool fibre.
Colours can be " dyed " on this by subsequent
PROPERTIES OF FIBRES AND THEIR REACTIONS 25
treatment with solutions of phenols and amines.
The writer attempted to prepare these substances
in a more or less pure state, but failed chiefly owing
to the small quantities present. These " dyes "
are not, as might be expected, " fast.'* They have
little resistance to the action of soap solutions at
the boil (J. S.C.I., 1894-95). It is claimed that the
substance in the wool fibre which acts in this way
is an amido acid, termed launginic acid, by the
discoverer (Champion, Compt. Rend., 72, 330). To
prepare this 500 grm. of carefully washed wool was
dissolved in baryta solution. The filtered solution
was precipitated by lead acetate. After washing
the lead salt was suspended in water and SH 2 passed
through the solution. The filtrate was evaporated
to dryness, yielding about 6 per cent, of a dirty
yellow powder. Champion gives the formula
C 19 H 30 N 5 O 10 for the acid, but Knecht and Apple-
yard (J.S.D. and C., 1889, 71) do not agree with
this, as they find that it contains 3 per cent, of
sulphur. The following reactions are given : sodium
acetate being present in the solution.
Alum = white precipitate.
Stannous chloride = white precipitate.
Copper sulphate = light green curdy precipitate.
Ferric chloride = light brown precipitate.
It shows the characteristic reaction with Millon's
reagent. A great number of lakes have been pre-
pared with this substance and the acid colouring-
matters. Schiitzenberger's formula for wool based
26 CHEMISTRY AND PHYSICS OF DYEING
on its hydrolysis indicates that the wool molecule
contains the groups
N = N
C < and the
but does not contain any NH 2 groups. Coloured
products would, however, be obtained as above by
the formation of nitrosamines from the NH group.
The compounds formed seem to withstand the action.
The formation of these compounds will be further
discussed in chap. vii. in the relation to the chemi-
cal theory of dyeing. It is considered by Knecht
(J.S.D. and C., 1889, 71) that the presence of this
amido acid in the wool fibre in an insoluble state
may be the cause of the action of dyeing. As pre-
pared, it precipitates acid and basic dyes, tannic
acid, and mordants.
Very strong mineral acids dissolve wool, and the
solution gives precipitates with the acid colours.
Alkalis affect the wool fibre more or less. Very
strong solutions may even dissolve it. It is stated
(" Manual of Dyeing," p. 43) that alkalis are not
retained so tenaciously as acids after absorption
by the fibres.
The action of certain metallic salts in solution on
wool is of the greatest importance from the practical
point of view.
Many salts of iron, chromium, copper, and other
metals seem to be decomposed in the presence of
the wool substance, and the oxide or basic salt is
precipitated on the wool out of the aqueous solution.
The whole subject of mordanting is a com-
PROPERTIES OF FIBRES AND THEIR REACTIONS 27
plicated one, and will be considered in chap, iv.,
where the probable nature of the reactions observed
will be discussed.
Silk. The silk fibre in its natural state con-
sists of an inner and insoluble fibre or filament, making
up about 70 to 76 per cent of the total weight of the
fibre, and an outer coating of silk gum, or sericine.
This material is soluble in caustic alkali solutions
in the cold, or soap solutions at the boil. The fibroin
or silk substance is then left in its final state.
The composition of the fibroin is, like that of all
albuminoids, uncertain. Richardson (J .S.C.I. , 1893,
426) considers the mass formula to be
C 14 H 16 (CO.OH) 3 .CO.OH(NH 2 ) 5
and considers that the graphic formula is of the fol-
lowing order :
NH.O
x representing a carbon residue.
There is, however, no satisfactory evidence that
this residual fibre is of a simple nature.
The ultimate analysis of mulberry leaves, silk-
worms sericine and fibroin are as follows :
Leaves.
Worms.
Sericine.
Fibroin.
C . . . - .
43-73
48.1
42.6
48.8
H .
5-9i
7.0
5-9
6.23
N . .
3-32
9 .6
16-5
19.00
. . . .
3544
26.3
35-0
25.00
Mineral matter
zx.6
9.0
It is possible that the sericine or silk gum is a
28 CHEMISTRY AND PHYSICS OF DYEING
more soluble oxidation product of the fibroin and
may possibly be formed in the following way :
C 15 .H 23 W 5 (5 + H 2 + O - C lft H, 5 N 4 8 .
Fibroin Sericine
Cramer by the action of dilute sulphuric acid on
silk gum obtained 5 per cent, of tyrosine (hydroxy-
phenyl-a-amido-propionic acid).
/OH /CO.OH
C 6 H 4 < /CH<r
X CH/ X NH,
and 10 per cent, of amido-glyceric acid,
COOH
This body like silk has a neutral reaction and
combines with both acids and bases.
This body which has been called serene (C 3 H 7 NO 3 )
is very similar to alanine (C 3 H 7 NO 2 ).
By the action of nitrous acid the former gives
glyceric acid, and the latter lactic acid.
TT COOH r /COOH
gives C a H 4 < QH
/COOH
C 2 H 3 ^NH 2 gives
\OH ,
glyceric acid.
Therefore, serene may be a mono-amido-glyceric
acid
Representing fibroin as
NH - CO
on saponification with KOH it would give :
^NH.,
2 *<CO.OK
PROPERTIES OF FIBRES AND THEIR REACTIONS 29
Some further work has been done on this sub-
ject by Fischer and Skita (Zeit. /. Phys.Chem., 1901,
177, and- 1902, 221).
By decomposing boiled off silk by hydrochloric
acid, the following substances were obtained (per
100 pts. of fibroin).
10 pts. . . /3-tyrosine
21 . "... 3-alanine
36 ' . . . glycocoll
i to 1.5 pts. . . /3-leucine
,, - . . /3-phenylalanine
Traces of diamino acids were discovered in the
products of hydrolysis, and arginine was recognised
among them. Serine is also one of the decompo-
sition products of fibroin as well as of sericine.
Sericine yields hydrolytic products from which a
considerable quantity of diamino-acids may be sepa-
rated by dialysis, arginine being among them.
These authors consider that the difference be-
tween fibroin and sericine is only a quantitative one.
The same mono-amino acids are obtained from both.
In addition to tyrosine and serine, they obtained
leucine and phenylalanine from them.
The well-known diazo reaction has been applied
to the animal fibres, and effect colours may be pro-
duced on silk, by subsequent development with
phenols, amines, &c. The colours do not seem, how-
ever, to be fast to either washing or light. The colours
produced on wool are duller than those from silk.
This matter is more fully entered into in chap. viii.
30 * [CHEMISTRY AND PHYSICS OF DYEING
One part of sodium nitrite was found to be suffi-
cient to " modify " fifteen parts of wool.
The resulting, and modified fibre is very sensitive
to light, and change of temperature, like many of the
diazo compounds. On boiling with water it takes
a brown colour. The same shade is produced by
the action of dilute sodium hydrate solution. The
alkaline carbonates act in the same way, but less
energetically. The treated wool is said to show an
increased affinity for basic colours and a decreased
one for acid ones. This property may even be made
use of in printing to obtain different shades with
the same dyes.
This special property is lost in sunlight. An
exposure of only a quarter of an hour to diffused
light will bring the wool back to its normal state so
far as this action is concerned.
Nitrite of soda itself, without the usual addition
of acid, will act on wool at ioo-no C. ; a charac-
teristic orange-rose colour being produced under
these conditions on the fibre.
Many aromatic oxy-derivatives will give colour
effects on the fibre, in the same way as phenols, and
amines, after treatment with nitrous acid.
Flick and Bourry (Bull, de Soc.de Mulh, 1889, 21)
consider that this action is rather due to the presence
of NH. than NH 2 groups in the fibre compounds.
The action of acids and alkalies on silk are
therefore in a way similar to those obtained with
wool.
The physical differences due to apparent solu-
PROPERTIES OF FIBRES AND THEIR REACTIONS 31
tion may be noticed when strong solutions of the
reagents are used. It is probable that hydrolysis
takes place, and that through this, the physical
structure is destroyed and the colloid enters the
pseudo solution state.
Owing to their complex nature our knowledge of
the composition of the fibre substances is very
limited, and, from our point of view, unsatisfactory.
It is, therefore, difficult to formulate the relations
of these bodies to the dyes and mordants during the
time of dyeing, with any certainty, by arguing from
their supposed chemical constitution. We must
rather look for evidence of a more indirect nature, to
determine the reactions between these animal fibres
and dyestuffs generally.
CHAPTER III
DYES AND LAKES, AND THEIR PROPERTIES
THE rough division of dyes into two groups, the one
containing the natural dyes, or those which are the
more or less direct products of organic life ; and the
other the artificial dyes, enables us to dispose of
the former group in a few words.
The nature of these dyes, and the state of impurity
in which they exist in the numerous extracts, which
serve in the ordinary dyeing operations, renders it
very difficult to discuss their action.
It may be stated that these vegetable dyes are
not present in the growing plant. They exist there
as chromogens, which are mostly colourless. These
yield their colouring-matters by subsequent oxida-
tion, fermentation, &c.
Some of the products like indigo, madder, orchil,
and logwood are, or have been, of great value in the
dyeing of woollen and other goods, but they are
being gradually replaced by new products.
Of recent years a good deal of work has been
done on the constitution of these dyes when pre-
pared in a state of purity. The results obtained are
hardly of sufficient interest, having little bearing
DYES AND LAKES, AND THEIR PROPERTIES 33
on the action of dyeing, to claim our attention in
the present work.
We may, therefore, pass on to the so-called
artificial dyes, the first of which was introduced by
Dr. Perkin in 1856.
This dye, mauveine, created a great sensation at
the time of its introduction. In 1859, Verquin in-
troduced fuchsine. Since that time the list has
increased by ever-varying shades and dyes of new
constitution, until, to-day, we have at our disposal
a range of colouring-matters, which will respond to
almost all the requirements of the dyer, as regards
fastness and application. It may be interesting
here to review the different ways under which these
dyes have been classified.
Bancroft's scheme, which in the past has received
general acceptance, divides the dyes into two classes.
(1) Subjective.
(2) Adjective.
The first class includes those colours which will
dye without a mordant. The second class includes
those which require one. In the present day it is
difficult to accept this simple classification. Some
dyes may even belong to both classes.
Von Prager used the terms dye and dye-stuff
respectively to describe the dye materials belonging
to these two great classes.
Hummel, on the other hand, taking note of the
many colours which may be produced by means of
different mordants, has called the two classes of
dyes monogenetic and poly genetic.
3
34 CHEMISTRY AND PHYSICS OF DYEING
With the great increase in number, and properties
of the dyes used in the present day, v. Georgievics
has fallen back on the divisions which are generally
accepted as representing their actions, viz. :
Acid dyes. Vat dyes.
Basic dyes. Mordant dyes.
Dye salts. Developing dyes.
Sulphur dyes. Albumin dyes.
Even this extended classification has obvious de-
fects.
With our increasing knowledge a modification
of O. N. Witt's classification, which is of a more
scientific nature, and depends on the constitution of
the dyes, may ultimately be accepted.
This method divides the dyes into classes depend-
ing on the presence of certain groups from which
there is evidence that their specific characters are
chiefly derived. These he calls the chromophorous
groups. These form the so-called chromogens, which
make up the root, or stock substance of the dye-
stuff.
These chromogens are converted into dyes by
the introduction of salt-forming substances.
For instance :
N = N is a chromophorous group.
C 6 H 5 N = N C 6 H 5 is a chromogen.
C 6 H 5 N = N C 6 H 4 .NH 9 is a basic dye.
C 6 H 5 N = N C 6 H 4 .OH~is an acid dye.
This classification does not indicate the action of
the dye in detail. In fact, it would be very difficult
to do this.
DYES AND LAKES, AND THEIR PROPERTIES 35
From the point of view of dyeing, it is possible that
some scheme of classification will be possible in the
future, which will include classes depending on their
physical state in solution, in conjunction with their
chemical properties (see chap. x.). It is at least a
fact that all the dyes are either acid, or basic in their
nature ; or contain both acid and basic groups at
the same time.
The OH and NH 2 groups which give to the dyes
the acid or basic properties, are naturally of the
greatest importance. In the above scheme, these
groups are called auxochromes. They also seem
to play a part which leads to the production of
coloured compounds.
Another group, which is so often present in the dye
molecule, is the sulphonic acid radical (HSO 3 ). The
introduction of this group into the molecule is gene-
rally brought about with the object of rendering
the dye more soluble in water, and not with the
object of producing colour. As a matter of fact,
the reverse action is generally noticed. The sul-
phonic acids of many dye-stuffs are deficient in
tinctorial power when compared with the non-sul-
phonated products.
This is by far the commonest way of bringing
the azo dyes within the range of practical solubility.
There are, however, other methods of arriving at the
same result. Geigy states that the introduction of a
trialkylammonium group has this effect.
All azo compounds are coloured, but all of them
are not dyes. Their chief value is in the fact that
36 CHEMISTRY AND PHYSICS OF DYEING
they are chromophores and can be converted into
dyes by Griess' reaction, which consists in diazotising
the amine and combining the product with phenols,
amines, &c.
This reaction is not, however, capable of universal
application. The constitution of the azo compound
may determine otherwise. The amidopyridines are
an example ; only the beta derivative can be readily
diazotised.
Also, if the amido groups are in the ortho position
as regards the azo group, the compound is incapable
of diazotisation.
As a general rule a phenol, or amine, will enter
the para position as compared with another OH,
or NH 2 group. If, however, the para position
is already occupied it will take up the ortho
position.
If both the ortho and para positions are filled it
will probably form no dye-stuff.
By double entrance of the diazo group the pro-
duction of tetrazo dyes is effected.
Generally speaking the simpler dyes are yellow
or greenish in yellow, but as the molecule increases
the colour changes to orange, then red, violet, or
blue. A simple example of this which is known to
all dyers is seen in the azo dyes produced from
primuline on the fibres. It will be remembered that
the following results are obtained :
With phenol, a golden yellow shade.
With resorcinol, an orange one.
With /3-naphthol, a red one.
DYES AND LAKES, AND THEIR PROPERTIES 37
Nietzki was the first to notice the general nature
of this action and Schultze to confirm it.
The actual cause of the production of colour is
not understood.
Armstrong favours the idea that the quinone
structure is directly connected with the produc-
tion of colour in this class of compounds. The
evidence, however, does not seem to be complete on
this point.
Discussing the question of constitution and
colour, Green (/.S.C.I., 1893, 12, 3) has pointed
out that the leuco- or reduction-compounds of various
dyes exhibit a striking difference of behaviour on
exposure to air.
Disregarding those colours which are entirely
split up by reduction, viz., the azo, nitro, and nitroso
colours, it is possible by this action to classify colours
into two groups.
(i) Colours whose leuco-compounds are not readily
oxidised on exposure to air.
(2) Colours whose leuco-compounds are rapidly
oxidised on exposure to air.
Group (i) consists of the triphenylmethane series,
the phthaleins or pyrone colours, the indophenols
and the indamines.
Group (2) contains the indigo class, azines,
azonium colours, oxazines, thiazines, acridine
colours, the thiazol, quinoline and oxyanthra-
quinone colours.
Accepting Armstrong's theory that colour is
due to the quinonoid structure of the molecule.
38 CHEMISTRY AND PHYSICS OF DYEING
The colouring-matters of the first group may be
regarded as paraquinonoid,
and those of the second group as ortho-quinonoid.
This view is confirmed (Proc. Chem. Soc., 1890,
222; Armstrong, Proc. Chem. Soc., 1888, 4, 27;
1892, 8, 101, 143, 189, 194).
The cause of some colours being mordant colours
seems to have been determined beyond dispute.
The presence of OH or CO.OH groups is essential
to the production of these colours. The position of
these groups is also a matter of importance. It is
necessary that the two hydroxyl groups shall be in
the ortho position. One carboxyl group may take
the place of one hydroxyl group.
The normal group may, therefore, be taken as
>M"
The introduction of a sulphonic acid group into
the dye molecule has a disturbing effect on the forma-
tion of metallic lakes.
For instance, Alizarine red S (powder) is
(i)
(2)
\S0 3 Na
The addition of copper sulphate to a solution
DYES AND LAKES, AND THEIR PROPERTIES 39
of this dye will not produce a lake or precipitate.
If, however, the corresponding barium salt is produced
by adding barium chloride to the solution before the
addition of copper salt a precipitate is obtained
(Dreaper, /. S.C.I., 12, 272).
In the same way, Diamine Fast Red F. will also
give a lake with copper sulphate if the -SO 3 group is in
combination with barium . The action of the sulphonic
acid group is effective in preventing the lake for-
mation, even although it is far removed from the
lake-forming group, as will be seen in this particular
case.
/OH
CH-N - N CK-
TTT.M xr rw ^
C 6 H/N = N C 6 H 3 < OH (2
It is difficult to explain the cause of this action. It
may be found, perhaps, in the greater solubility of the
sulphonic acid, and the partial neutralisation of this
effect by formation of a barium salt.
The presence of an amido group may also materi-
ally interfere with the formation of lakes, even if
the OH groups are present in the ortho position.
It would almost seem that here the action is of a
different nature, the acid nature of the | _ QJJ
groups being in part neutralised by the proximity
of the NH 2 group.
The reason why certain colours are mordant
dyes is becoming increasingly involved.
The Liebermann and v. Kostanecki law is no
40 , CHEMISTRY AND PHYSICS OF DYEING
longer accepted, owing to our increased knowledge
on the subject since the year 1885.
Buntrock in 1901 was the first to throw doubt
on this law. He discovered that derivatives of
groups in the ortho position would dye on mordants.
(Rev. Gen. des Mat. Col. 1901, 99.)
In the same year, Noelting established the fact
that bodies like hystazarine and quinizarine (di-
hydroxyanthraquinones, 2. 3 and i. 4), also i. 3. 5. 7
tetrahydroxyanthraquinone, and i. 8 -hydrodioxy-
2. 4. 5. 7, tetranitrochrysazine were also capable
of being mordant colours.
V. Georgievics in 1902 pointed out that the hydro-
xyanthraquinones do not follow the above law.
In the years 1887 an d 1889, v. Kostanecki
extended and enlarged the original law which then
stood as follows :
(1) Nitroso-phenols are mordant colours when in
the ortho position.
(2) Phenolic colours dye on mordants when
they contain two OH groups in the ortho position.
(3) Orthoquinonedioximes are mordant colours.
(4) Ortho-oximes are mordant colours.
In the year 1904, Moehlau and Steimmig (Rev.
Gen. des Mat. Col. 1904, p. 360) return to this subject.
The following law is propounded. In an aromatic
hydroxyl derivative when an OH group is in a position
near to the chromophore, the body is a mordant dye.
Picric acid is not a mordant because the com-
pounds with metallic oxides are soluble.
But trinitro-resorcinol
DYES AND LAKES, AND THEIR PROPERTIES 41
OH
NO,
NO 2
OH
NO,
dyes wool on chromium or iron mordants, shades
which are very fast against the action of soap.
Nitro-amido-phenol-sulphonic acid
OH
NO, /\ NH,
S0 3 H
dyes wool, on chromium, iron, or aluminium mor-
dants and the shades also resist the action of soap.
Ortho-hydroxyazo-benzene-/>-sulphonic acid.
OH
N = N.C 6 H 5
SO 3 H
and nitro-phenol-sulpho-azo-/3-naphthol
OH
NO 2 /\ N = N
\) OH
S0 3 H
both dye on these same mordants.
Quinonoid Colours. From the point of view~of
NOH M . OH d\
colour the group
NQH
.
, is equivalent to
42 CHEMISTRY AND PHYSICS OF DYEING
~, OH (2)
ine group ^ analogous in grouping to
OH (2)
NOTT r V seems also to & lve colouring-matters the
property of dyeing on mordants.
Noelting and Trautmann have found that 8-
hydroxyquinoline and its derivatives
OH N.
are mordant colours.
6-Methyl-5-keto-8-isonitrosoquinoline
O
ca,
OH.N
is also a mordant colour.
In a further communication Prud'homme (Rev.
Gen. des Mat. Col., 1904, p. 365) doubts whether this
rule of Moehlau and Steimmig can always be applied ;
they having themselves pointed out that the chromo-
phores
CH == CH CO and CH = N-
are not powerful enough to transform ortho hy-
droxyls into mordant colours.
He also points out that Scheurer had previously
shown that dehydrated mordants will not combine
with mordant dyes.
Quite recently, further investigation tends to
DYES AND LAKES, AND THEIR PROPERTIES 43
show that in some cases alizarine lakes are
not chemical compounds. (W. Biltz, Ber. 1905,
P. 41430
From a study of their formation, alizarine iron
lakes are said to be of the nature of chemical com-
pounds ; but Alizarine Red S.W. lake on chromium
oxide is said to be formed by absorption.
It may be that these lakes resemble the tannic
acid ones, or are similar to Linder and Picton's dye
compounds (Trans. Chem. Soc. 1905, p. 1934),
where both actions seem to be involved.
The formation of alizarine lakes may be due to
solid solution, absorption, or they may be chemical
compounds.
Variations in the concentration of solutions of
alizarine dyes in contact with oxides of iron, or
chromium, in the hydrogel state, give interesting
results.
For instance, the following table, showing the
effect of hydroxide of iron on alizarine, is instruc-
tive.
Initial concent. End do. Col. abs. per grm.
of bath. of hydroxide.
.OOO5 . . .OOII4 . . .0677
.01 . . .00234 . . .134
.02 . . .00242 . . .308
.04 . . .00261 . . .655
.06 . . .0028 . . i.oi
.10 . . .00326 . . 1.695
.15 .. .00369 .. 2.57
In the case of Alizarine Red S.W. on chromium
hydroxide, the following results were obtained :
44
CHEMISTRY AND PHYSICS OF DYEING
Initial concentration.
.01
.02
.03
05
075
.IO
50
End do.
.00034
.0031
.00776
.01876
.0341
05
417
No. 2.
No. i.
Strength of solution,
FORMATION OF LAKES IN AQUEOUS SOLUTION.
The relative nature of the reactions indicating
chemical action, or absorption, respectively, is seen
in the above curves. No. i indicates chemical ac-
tion in the case of an alizarine iron lake, and No. 2
absorption in the case of alizarine on chromium
hydroxide. The decreased absorption of alizarine
dyes on a dehydrated mordant, as compared with the
same mordant in a highly gelatinised state, is shown
in the following ratios :
DYES AND LAKES, AND THEIR PROPERTIES 45
Alizarine 1/6
Gallein . . . . . i/n
Alizarine Yellow G.G.W. . 1/9-5
It is suggested that the reason why alizarine will
not dye in the absence of lime is that it is necessary
for the alizarine to be in the quinonoid state, and
that this state only occurs in the presence of alkali.
O
COH= { \ OH
-CO -
It must always be remembered, that the alizarin
aluminium lake may not be so insoluble as the double
calcium one.
To decide in practice whether a dye belongs to
the mordant class it should be sufficient to make
experiments with wool mordanted with the following
metals: aluminium, iron, chromium, copper, and
tin. The value of the mordant dye will, of
course, depend on the brilliancy and fastness of the
shades produced. These are most important factors,
especially from the wool-dyer's point of view.
In the case of the nitroso dye compounds the
ortho position between the O and NOH groups is
essential to a mordant dye.
In some cases dyes which possess an OH group
in the ortho position with regard to azo groups,
may possess the property of dyeing on mordants.
This action, in which closer grouping evidently
gives rise to what may be termed a more concen--
46 CHEMISTRY AND PHYSICS OF DYEING
trated effect, is an instructive one. It gives us an
insight into the structure of the molecule. Closer
grouping seems to be more favourable to combined
action. This is seen in the two nitro-salicylic acids,
and the relative acid nature of the i. 2. 3 and 1.2.5
compounds (/. C. 5., 88, 338) respectively.
The typical dye, Congo Red, which led to the
discovery of the series of dyes which dye vegetable
fibres directly, is produced from benzidine ; and hence
this series of dyes have sometimes been known as
the benzidine -colours. With the extension of this
class, and from their varied origin, they are now
known generally as " cotton dyes/' or sometimes
as " direct dyes."
Generally they are prepared by diazotising cer-
tain bases ; and combining the products with amines,
phenols, or their sulphonic acids.
Sometimes the dyes are mixed products. In
the preparation of these, advantage is taken of the
fact that the first molecule of the amine, &c., is
taken up at a greater rate than the second one.
In this way these mixed products are easily pre-
pared.
V. Georgievics, in discussing the possible cause
of the attraction of the cotton fibre for these dyes,
has pointed out that it cannot be due to the
presence of the diphenyl group, for certain dyes
only possessing one azo group are known to dye
cotton without a mordant.
The so-called sulphur dyes have recently become
of great importance in cotton-dyeing, on account of
DYES AND LAKES, AND THEIR PROPERTIES 47
their fastness and the ease with which they can be
applied.
The sulphur dyes originated with the researches
of Croissant and Bretonniere about thirty years ago.
Sawdust, horn, &c., were fused with alkali and
sulphur. As a result, products soluble in water
were obtained which were capable of dyeing yellow
brown shades. This substance was known in com-
merce as Cachou de Laval.
To-day, the class of sulphur dyes is an extensive
one, and they are classified by Pollak as follows :
(1) Dyes from simple benzene and naphthalene
derivatives.
(2) Dyes from diphenylamine derivatives.
(3) Dyes from anthraquinone derivatives.
(4) Dyes made by the help of sodium thio-
sulphate.
(5) Dyes made by the help of chloride of sulphur.
This classification is a rough and ready one, but
the chemistry of the subject is very involved. The
fact that it is almost impossible to isolate the inter-
mediate compounds, which are formed during the
manufacture of the dyes, renders it very difficult to
follow the change which take place. Vidal, Meyen-
berg, Green, and Perkin have attempted to throw
light on this most interesting subject. Vidal believes
that sulphide dyes produced from compounds of
simple structure, and at low temperatures, are pro-
bably thiazine derivatives.
These sulphur dyes are insoluble. They are
brought into solution by dissolving in sodium
4$ CHEMISTRY AND PHYSICS OF DYEING
sulphide. At the same time, they are reduced to their
leuco-compounds, so that subsequent oxidation is
necessary to reproduce the colours in situ. This
may be brought about in some cases by simple ex-
posure to the air ; or in others by the use of oxidising
materials, such as hydrogen peroxide.
Instead of sodium sulphide, neutral sodium sul-
phite has been recommended as a solvent, and is used
in conjunction with glucose and alkali, which serve
to reduce the dye to the leuco condition. The
addition of salt to the dye-bath greatly increases the
dye fixed. The other insoluble dyes which are pro-
duced in the fibres, such as indigo, or aniline black,
present interesting problems to the student.
From the fact that they are produced by oxida-
tion, the dyeing process is probably of a physical
nature.
The production of aniline black on the fibre is a
complicated process from the chemical point of
view.
Here again, the intermediate products are not
easily isolated, and this makes it difficult to follow
the reaction.
The basic dyes are usually hydrochlorides of
organic bases. The combination between the base
and acid is a weak one ; entirely different in its
nature from that of the sulphonic acid azo dyes,
are very stable compounds.
These bases form lakes with tannic acid, which
were at one time of great service in the dyeing of
cotton goods, and are still used for this purpose ;
DYES AND LAKES, AND THEIR PROPERTIES 49
and also in the production of lakes for pigment
colours.
Although at the point of saturation, these com-
pounds seem to combine in the ratio of their
chemical equivalents in the ordinary sense of the
word.
Pararosaniline hydrochloride
/C fi H 4 -NH 2
is a typical example of this class of dye.
It has also been more recently suggested that
in some cases the alizarine lakes are absorption com-
pounds (see page 43).
Identification of dyes. Of the many schemes
suggested, only that recently advanced by Prof.
Green in conjunction with Messrs. Yeoman and
Jones (J.S.D. and C. 1905, p. 236) is noticed here.
This scheme, like the earlier one proposed in
1893 by the first of these investigators, entails the
reduction of the dyes to their leuco-compounds.
Originally zinc dust was used as the reducing
agent, reoxidation being effected by exposure to
air, or else by chromic acid.
Nitro, nitroso, and azo compounds were com-
pletely destroyed on reduction. Dyestuifs having
an ortho-quinonoid structure gave leuco-compounds
which were readily reoxidised by air to their original
state. Para-quinonoid compounds giving leuco-
compounds required chromic acid for reoxidation,
4
50 CHEMISTRY AND PHYSICS OF DYEING
Sodium hydrosulphite is now recommended as a
reducing agent in place of zinc dust ; and the state-
ment is made, that the leuco-compounds formed
remain in great part attached to the fibre, while
washing will remove the fission products of the
azo dyestuffs.
A persulphate is used in place of the chromic acid.
The following general behaviour of the various
chemical groups of dyestuffs is noted.
Decolourised by hydrosulphite.
Not decolourised
Not altered by
but changed to
brown, original
Colour restored on
exposure to air.
Use of persulphate
required to restore.
Colour not re-
stored by air
or persulphate.
hydrosulphite.
colour restored
by air or persul-
phate.
Azines
Triphenyl
Nitro-,
Pyrone, acri-
Most dyestuffs
Oxazines
methane group.
Nitroso-,
dine, quino-
of the
Thiazines
and azo-
line, andthia-
anthracene
Indigo
groups.
zole groups.
group.
Some mem-
bers of anthra-
cene group.
Further tests with other reagents are given in the
original communication with a complete range of
colours dyed on wool and silk.
The point of interest is the way the leuco-com-
pounds are held by the fibres. Further details
should be of value. The action may be due to the
colloidal nature of these compounds.
The different rate of solubility of dyes in different
solutions is important, but before we consider this
point the relative solubilities of dyes in aqueous
solution at varying temperatures is given. The
results are stated in grammes per 100 cc. of solution
DYES AND LAKES, AND THEIR PROPERTIES 51
for some of the best known dyes. (Pawlewsky,
Chem. Zeit. 73, 773.)
Dye.
20 C.
60 C.
100 C.
Martius Yellow .
.002
.OI
13
Violet R. .
-03
.86
27.24
Cyanine
.04
.21
1. 21
Magenta
.22
1.28
12.23
Picric Acid .
I.I4
2.94
9.14
Erythrosine
4-56
12.7
24.58
The increase in solubility at high temperatures is
great in some cases.
The relative action of picric acid in solvents
has been studied with the following results. (Sisley,
Rev. Gen. des Mat. Col. 1902, 90.)
Water
H 2 S0 4 (.5% sol.)
Ether
Toluene
Amyl-alcohol
i.oo
43
3.56
8.60
1.49
In toluene
dichroism
The colour of the solution varies greatly,
it is almost colourless, and possesses a
not found in an aqueous solution.
This is attributed by Marckwald (Ber. 1900,
1128) to electrica] dissociation. At any rate a
difference in molecular state is indicated.
The following table shows the ratio of picric acid
taken up by toluene and water in mixtures of the
same at a temperature of 20 C.
CHEMISTRY AND PHYSICS OF DYEING
I
I
4.02
2.63
I
4.40
I
1.6
I
I
1.24
2.38
I
i-i5
I
1.63
I
0.72
All
in water
55
SOLUTION MIXTURE. RATIO TAKEN UP.
Solution 10 grms. per litre.
100 cc. OH, .25 cc. Tol.
100 cc. ,, .100 cc. ,,
50 cc. ,, .100 cc. ,,
Solution 3 grms. to litre.
100 cc. OH 2 .25 cc. Tol.
100 cc. ,, .100 cc.
50 cc. .100 cc.
Solution i grm. to litre.
100 cc. OHj .25 cc. Tol.
100 cc. .100 cc.
50 cc. .100 cc. ,,
Solution .1 grm. per litre.
100 cc. OH 3 .25 cc. Tol.
IOO CC. ,, .100 CC.
50 cc. .100 cc.
Sisley explains these abnormal results with dilute
solutions by assuming the dissociation of picric
acid in dilute solutions ; this being complete at .1 grm.
solution strength ; and that the toluene cannot ex-
tract the colour ion.
Similar results were obtained with ether and
amyl alcohol as follows :
Ratio of OH 2 to Ether or Amyl Alcohol 100 : 100.
10 grms. to litre sol. . I : 1.79 . . I : .209
I grm. . . I : 0.129 . . I : .071
.1 grm. . - > I : .01 . . I : .0101
.01 grm. . . All in water . . All in water
In these two cases we have dilution also interfering
with extraction from aqueous solution. It might
be pointed out that these results may be also
explained by accepting the association theory of
solution.
CHAPTER IV
ACTION AND NATURE OF MORDANTS
OUR knowledge of the action of fibres on certain
metallic salts in aqueous solutions is incomplete.
The subject is one of great interest to the dyer.
Many of the difficulties he has to contend with are
due to variations in the mordanting processes.
Aluminium mordants. There is a general im-
pression that these mordants act by producing a
basic salt on wool and silk fibres ; a corresponding
amount of acid remaining in solution.
This may, or may not, be the case according to
the varying condition of solution. Washing in water
after the mordanting process is said to render the
salt fixed more basic by the removal of acid, or an
acid salt. The rate of mordanting may, therefore,
increase with the basicity of the solution. This is
noticed in practice. Many neutral and stable salts
are said to be free from any action of this nature,
and will not act as mordants.
The influence of the basicity of aluminium salts
on the actual absorption results is indicated in the
following table. Aluminium sulphates were pre-
pared, and solutions containing 200 grms. per litre
54 CHEMISTRY AND PHYSICS OF DYEING
of the respective salts were taken. The fibre was
cotton. (Liechti and Suida, J.S.C.I. 1883, 537.)
Composition of sulphate used. % A1 2 O 3 taken up.
A1 2 (SO 4 ) 3 + i8H v O (normal) . . 12.9
A1 : (S0 4 )-(OH) 6 .. 51.0
A1 4 -(S0 4 ) 3 -(OH) 4 . . 58.7
A1 2 -S0 4 -(OH) 4
The last and most basic salt dissociated so rapidly,
that the experiment could not be completed.
It will be seen that a slight increase in basicity
over the last salt mentioned would produce an in-
soluble compound on the cotton fibre irrespective
of any combination with the cotton fibre itself.
Some of these salts have been prepared, and are in-
soluble. These experiments are not so complete as
they might be. The composition of the salts pre-
cipitated on the fibre has not been ascertained.
They have only been expressed in terms of the
hydrate.
The fact that these basic salts cannot be obtained
directly by the addition of alumina to the normal
sulphate is important. There does not seem to be
any tendency for the solution to redissolve any
alumina actually precipitated in the fibre.
The fact that a salt is a basic one is not, however,
any indication that it will act as a mordant. Basic
chlorides and oxychlorides of alumina can be pre-
pared, yet they are very indifferent mordants. Very
little of the metal can be fixed on the cotton fibre by
solutions of these salts.
ACTION AND NATURE OF MORDANTS 55
On the other hand, the sulphites and thiosulphates
of alumina are available as mordants.
The basic thiocyanates, and the acetates and
sulphacetates are of great value.
In practice, it is advisable to supplement the
direct fixing action of the fibre, by some secondary
reaction. For instance, suitable substances may
be present, which in themselves form insoluble com-
pounds by loose combination with the alumina. As
an alternative process the mordanted fibre may
be passed through a suitable alkaline bath. Such
materials as oil mordants, or tannic acid, are used
as a preliminary treatment. Their action is suf-
ficiently clear. The alumina is sometimes fixed as
arsenate, phosphate, or silicate. It is worthy of note
that all these precipitates are of a colloidal
nature.
Turkey red mordanting. The process of fixing
alumina on the cotton fibre assumes fresh importance
from the fact, that the mordant must contain fatty
acids in some shape, or form.
The modern method of dyeing Turkey red,
differs materially from the older processes of dyeing
which originated in the East, many years ago.
Le Pileur d'Alpigny published an account of
these older processes in 1765.
The original process took between three and five
weeks to complete, and it is quite unnecessary to
try and follow the many operations entailed. To-day
Turkey red may be dyed in three days, or even less,
using artificial alizarine in the place of madder, and
56 CHEMISTRY AND PHYSICS OF DYEING
soluble oils in the place of olive oil, or other fatty
matters of a more or less obscure nature.
Alizarine (dihydroxyanthraguinone), C 14 H 8 O 4 ,
may be regarded as a weak dibasic acid. It is even
capable of decomposing sodium acetate. It contains
two OH groups in the ortho position.
It combines with most of the metallic oxides
forming insoluble lakes. A serious study of these
compounds has been undertaken by Liechti and
Suida (J.S.D. and C. 1885, 271; 1886, 102, 120, 131,
146) and the chief results obtained are as follows :
Alizarine combines with calcium to form normal
or basic alizarates as the case may be. At a high
temperature, or if a solution of the basic alizarates
be heated, the normal salt, C 14 H 6 O 4 -Ca, is always
formed.
On the other hand, the aluminium lakes are
formed with great difficulty in the absence of calcium
salts. The presence of ammonia helps the reaction.
Basic aluminium alizarates are formed, and are more
insoluble than the normal salt.
In the production of a Turkey red on cotton, it is
essential that a compound lake of aluminium be
formed. A great many of these have been prepared,
varying in their properties and reactions. The
normal lake is (C I4 H 6 O 4 ) 3 Al 2 -(CaO)-H 2 O/ and is
readily soluble in ammonia.
In practice the alizarine lake is a compound of
alizarine, calcium, aluminium, and fatty acids
and therefore little can be said of the actual com-
position of these lakes as present on the fibre.
ACTION AND NATURE OF MORDANTS 57
The actual operations entailed in the produc-
tion of this colour are said to be as follows
(" Manual of Dyeing/' p. 558) :
(1) Oiling.
(2) Sumacing.
(3) Mordanting.
(4) Dyeing.
(5) Clearing.
(1) To-day, little seems to be used for oiling but
the so-called sulphated oils. These are probably
sulphonic acids. At any rate, their usefulness lies
first in their solubility in water, and, secondly, in
the fact that they are readily decomposed by steam,
&c. Bodies similar to the oxidation products pro-
duced from olive and castor oils in the older pro-
cesses are said to be formed at the same time. This
has, however, been denied.
(2) The object of sumacing is to introduce tannic
acid into the fibre in order that it may subsequently
precipitate and hold a larger proportion of alumina.
(3) The mordanting operations consist of treating
the fibre with aluminium salts ; and subsequently
completing the fixation of the alumina on the fibre.
(4) The dyeing which follows these operations sup-
plies the alizarine, and lime necessary. A minimum
temperature of 70 C. is necessary to complete the
formation of the lake.
(5) The clearing operations are generally two
soapings. These remove any impurities, and here
the formation of the lake is also modified.
At this stage stannous chloride is sometimes
58 CHEMISTRY AND PHYSICS OF DYEING
added to give " fire " to the colour. It is generally
supposed that this does not enter the lake, but
simply acts physically. Tin oleate is formed which
acts as a varnish on the fibre. A certain propor-
tion of the fatty acids in the soaping solution is fixed
on the fibre.
This roughly represents the action and process
of dyeing Turkey red.
Further light has been thrown on these reactions
by Persoz (Bull. Soc. Ind. de Mulh. 1903, 193).
When mordanted cotton is dyed with 2 grms. of 10
per cent, alizarine, and an equivalent quantity of lime
per litre, a deep red colour is produced in a few
minutes. If at this stage the fibre be washed and
dried, the shade produced is a dull yellowish brown.
If this be treated with a fatty acid and steamed, a
bright red colour is produced.
If, on the other hand, the dyeing is prolonged to
say one hour, this brightening action will not take
place. These experiments indicate that there are
two possible modifications of the compound lake of
alizarine, alumina, and lime. The former can be
transformed into the latter by steaming, and will not
then develop ; nor can it be reconverted into its
first form by any known means. It is, of course,
just as easy to argue that when the final and satu-
rated lake is formed it will not combine with the
fatty acids. The first " modification " may simply
be a compound still containing aluminium in a
state capable of combining with the fatty acids.
This explains the object of having the fatty acid
ACTION AND NATURE OF MORDANTS 59
present before the mordanted fibre enters the dye
bath. It is well known that the so-called alizarine
reds, which are dyed with subsequent oiling, are
inferior to Turkey reds in fastness, and colour effect.
The chief constituent of the modern soluble oils
is said to be ricinoleic acid, free or combined with
alkalies. Boiling the oil with dilute hydrochloric
acid decomposes the sulphonic acid compound liber-
ating this acid. (Noelting and Binder, Bull. Soc.
Ind. de Mulh. 1888, 730.)
On the other hand, the superiority of soluble oil
prepared from castor oil over that from olive oil is
stated to be due to the fact that in the former case
an acid sulphonic ether of an unsaturated acid is
present. In the latter case we have the corresponding
derivative of a saturated acid. This is held to in-
dicate that the former product will have a higher
oxidising power and consequently be a better
mordant for this purpose. (Benedikt and Ulyer,
Monat. Chem. 8, 208.) Further research must decide
which of these views is the correct one.
Prepared in the pure state the above ricinoleic
acid gives lakes, as bright as those prepared with the
oleins.
Purified aluminium ricinoleate after drying is
pulverulent. Its formula is A1 2 O(OH) 2 (C 18 H 33 O 3 ) 2 .
This compound heated with water and alizarine
begins to attract the colouring-matter at 40 C.,
It then melts and gradually assumes a bright red
colour, while the temperature is being carried up to
105 C.
60 CHEMISTRY AND PHYSICS OF DYEING
This would seem to indicate that it is necessary
for the fatty acid to melt before it can enter into
combination. This lake is unaltered by boiling soap
solution. Alcohol and ether dissolve this lake with
difficulty, and then cotton may be " dyed " with
this solution. It would be interesting to know
something of the fastness of the colour, dyed in this
very mechanical way. Fischli (ibid.) also denies
that oxidation takes place in the fixing of ricinoleic
acid on the fibre. This he confirms by analysis.
He also shows that mere heating in dry air will not
" develop " the colour of the lake, but if steam is
present, the colour develops instantly. Micro-
scopical examination shows that steam favours the
formation of the alizarine-lime-alumina-fatty-acid
lake. Immediately after the steaming, the cloth
has a sticky feel partly due to the melting of this
lake. In this way it penetrates the fibre. It is
also contended that tin, if present in the soap liquor,
actually enters into combination with the mordant.
One of the most extraordinary statements made
in connection with the formation of these lakes is
that light is an important factor in the formation of
the fatty mordants. (Storck and Coninck, Bull.
Soc. Ind. de Rouen, 1887, 44.) Much work remains
to be done on this subject.
Iron mordants. The lakes formed with alizarines
are quite fast, and not dependent on either the pre-
sence of lime or fatty acids for their colour, although
the latter greatly aids in the fixing of the iron, and
lime is distinctly beneficial.
ACTION AND NATURE OF MORDANTS 61
It is stated that the iron must be introduced into
the cotton fibre in the ferrous state and oxidised in
situ. If not, the colour is not fast. It is known that
many dyes are much faster if produced in situ, but
this is the only known case where a mordant acts in
the same way.* A ferric ferrous compound may be
produced in the case of alizarine, and is said to have
the following constitution (C 14 H 6 O 4 ) 3 Fe 2 'FeO.
The fact that mordants are for the most part
of a basic nature was noticed as early as the year
1849 by Gonfreville. When cream of tartar was used
he considered that it entered into the composition of
the lake, and in some way, or other, prevented the
" rubbing off." Acids were considered to lessen the
affinity of the wool for the mordant, and at the same
time to increase the power of diffusion.
Rouard and Thenard {Ann. de Chimie, 74, 267)
held the idea that wool could not decompose alum,
but simply absorbed it. It could all be removed by
boiling water. The fibre would decompose cream
of tartar on boiling, acid being taken up and neu-
tral tartrate left in the solution. He considered that
wool boiled with tartar and alum might contain alum,
tartrates of alumina, potash, and free tartaric acid.
Later on, Chevreul denied that the alum could be
washed out by water, and Bolby stated that actual
decomposition took place ; a basic salt being depo-
sited on the fibre leaving the solution more acid.
Schiitzenberger considered that wool exerted some
special attractive force retaining the alum in this
* If the mineral colours are excepted.
62 CHEMISTRY AND PHYSICS OF DYEING
way. The idea that the wool precipitates the basic
alum by removing the acid from the solution was
first put forward by Liechti and Hummel. (J. S.C.I.
T 3> 357-) The addition of organic acids, or acid
salts, was said to prevent the too rapid precipitation
of the resulting basic salt on the fibre.
They considered also that the appearance of a
well mordanted wool points to the presence of a salt,
and not a hydrate.
These authors also support the idea that a salt
is precipitated, by pointing out that in "single bath"
dyeing the liquid is always acid. It is difficult,
however, to see the connection between these two
operations . In the latter case the already formed lake
is present, the acid playing the part of a more or less
active solvent, as in the case of a logwood-iron lake ;
or else by directly influencing the fibre state.
Harvey pointed out in 1872 (Monit. Sclent. 1872,
598) that in the case of very concentrated solutions
of alum, more sulphuric acid than alumina is ab-
sorbed. This has been recently confirmed by v.
Georgievics. It appears that with a 24 per cent,
solution of alum, and a proportion of water to fibre
of 30 : i, alumina and sulphuric acid are taken up in
their normal proportions. The affinity of wool for
acid is stronger in dilute solutions, and stronger for
the alumina in strong solutions. The relative
curves cross each other at 24 per cent.
Although wool will take up large quantities of
sulphuric acid from concentrated solutions of this
acid, yet in dilute solutions water plays the part of
ACTION AND NATURE OF MORDANTS 63
a base just as it precipitates basic salts from
solutions of the heavy metals.
Alum is said to be so far dissociated in solution
that the whole of the SO 3 can be titrated with
sodium hydroxide using phenol-phthalein as indicator
(Carey Lea). It is also noticed that wool mordanted
with alum reacts acid ; the indication is that the
acid is present in the free state.
Chromium salts. The mordanting of wool by
bichromate was at one time simply regarded as a
case of absorption, the bichromate being taken up
by the fibre. The idea that the bichromate splits
up into a chromate which remains in solution, and
chromic acid which is absorbed by the fibre is put
forward by E. Knecht. (J.S.D. and C. 1889, 186.)
It is assumed that the chromic acid combines with
one of the fibre constituents to form an insoluble
chromate. This has been disputed, it being held
that the dissociation of the salt is due to the presence
of ammonia, due to the decomposition of the fibre
material on boiling.
Knecht found that the ammonia given off is not
sufficient to account for more than a thousandth part
of the change. He also denies that the presence of
alkaline salts in the wool bring about the action.
Taking a sample of wool and mordanting it after
treatment with hydrochloric acid, he found the
chromium distributed as follows :
Total bichromate in solution . . .030 grm.
Total chromate . . . . .112 ,,
Chromic acid on wool '.-. , . . .057
64 CHEMISTRY AND PHYSICS OF DYEING
He does not uphold Nietzki's assertion that a
chromate of chromium is formed in the fibre. It is
held that if this action, which is represented by the
following equation, took place serious damage to the
fibre must result.
5Krp 7 + 5H,0 = 2 Cr,(CrO 4 ) 3 + icKOH + 30,
He agrees that a certain amount of oxidation goes
on, but that it is not of this order.
Whatever the state of the chromium, it is
capable of easy reduction. This is practised by
immersing the mordanted wool in sulphurous acid.
The action of assistants in chromium mordanting
such as tartaric, oxalic, or sulphuric acids is said to
be primarily that of the liberation of chromic
acid .Tartar, lactic acid, and oxalic acid also act
as reducers.
It is necessary that the mordants shall be pro-
perly fixed on the fibres, and shall not be merely
precipitated on the surface.
The presence of sulphates, chlorides and other
salts in the mordanting bath prevents the dissocia-
tion of the mordant salt.
The state in which dichromate of potash is pre-
sent in aqueous solutions has been studied by
Abegg and Cox (Nature, vol. 71, 281). They deter-
mined the proportion of free chromic acid present in
solutions of different strengths, the presence of
chromic acid being indicated by the following reac-
tion :
ACTION AND NATURE OF MORDANTS 65
Complete dissociation is calculated to take place at
a dilution of 1000 litres. At greater concentra-
tions the following results were obtained
At 100 litres . . 99%
At 10 litres . 91%
At i litre . . .- 62%
These figures indicate, that the greater part of the
salt is decomposed into chromic acid, in solutions
corresponding in strength to those used in mor-
danting wool.
In the mordanting of cotton, for alizarine, it has
been shown that the presence of calcium salts as
well as aluminium salts is necessary.
It is also found necessary to have a metallic
monoxide present in the case of wool-dyeing (Mohlau
and Steimmig). With pure alumina mordant on
wool, no lake formation seems to take place in the
absence of calcium, barium, strontium, or magne-
sium compounds. The same effect is noticed with
iron mordants. In this case magnesium gives the
best results. It is said that the same effect may be
noticed with chromed wool.
Chromium chloride, and chromium fluoride, are
both used for mordanting wool. Little is known
about the nature of the reactions in these cases.
Iron mordants on cotton and wool have received
little attention from the theoretical point of view.
The probable nature of the reactions may be taken
to be of a simpler nature than in chromium mor-
danting.
Copper mordants. The results obtained by these
5
66 CHEMISTRY AND PHYSICS OF DYEING
mordants in practice is satisfactory, but little is
known of the actions which take place. Copper
finds little use except in the case of wool-dyeing.
No figures are available which indicate in any way
the course of the reaction in this case. It may
simply be a case of absorption. On the other hand,
basic compounds may be fixed in the fibre ; or some
chemical action may even take place, which leads
to the same result.
Other metallic mordants. Little is known as to the
actions involved in the use of these compounds.
Some of them give satisfactory shades, and leave
little to be desired on the score of fastness, but beyond
this our knowledge does not extend.
The salts of nickel and titanium are of interest
in this connection.
Tannic Acid. This substance is of the greatest
value to the dyer of cotton and some other vegetable
fibres.
The well-known property of tannic acid of form-
ing lakes with basic dyes is taken advantage of. The
vegetable fibres also seem to have an attractive
power for this acid, perhaps because of its colloid
properties. The fact that antimony tannate gives
faster lakes with the basic dyes, is perhaps against any
theory of direct chemical combination between the
acid and the fibre.
O. N. Witt holds (Chem. Zeit., 12, 1885) that
in these lakes there is no distinct molecular ratio
between the colour base, and the tannic acid. There
seems to be a definite saturation point, however,
ACTION AND NATURE OF MORDANTS 67
for a solution of night blue has been used volu-
metrically for the estimation of tannic acid by direct
precipitation.
These lakes are soluble in excess of tannic acid,
and also in acetic acid. The latter reaction is some-
times made use of in printing, the acetic acid being
subsequently driven off by heat.
The lakes containing antimony are more resistant
to the action of alkali.
The tannic acids are little used on wool, and on
silk they play the part of a dye, rather than a mor-
dant. The bleached acid has a use in the weighting
of light colours on this fibre, and in blacks the
amount of tannin lake held by the silk fibre is of
an extraordinary nature in some cases.
The action of tannic and gallic acid on fibres
generally is entered into more fully elsewhere.
A series of results obtained by observing the
action of different mordants on silk both in the
"raw" and " boiled off " state are given byP.Heer-
mann (Farb. Zeit. 3, 1903). The mordants chosen
were basic ferric sulphate, basic chromium chloride,
acetate of alumina, and stannic chloride. The in-
fluence of time on the mordanting process is indi-
cated in the table on p. 68. The figures given
indicate the increase of weight of 100 parts of fibre.
It is unfortunate that these experiments were
not conducted on such lines that the composition
of the precipitated mordants could be given.
The decrease in the weight of mordant fixed
during the period of seven, and fourteen days, may
68
CHEMISTRY AND PHYSICS OF DYEING
Q
O
g
H
Q
w
o
K
CTxCOO
H
H ro in <M
O"^ O t^s t^
M CO T}-
ro H csi
lOCOHtO
H H H H H
rj-Hoo csi N O C^oororo
oo o Hcoc^Ho co c
O O
mo
.
e
1
ff
ACTION AND NATURE OF MORDANTS
69
be due not so much to a decrease in the percentage
of metal deposited, as to the same being in a more
basic state.
The influence of temperature on the mordanting
process is indicated in the following table (Farb.
Zeit. 8 and 9, 1903) :
COMPARATIVE AMOUNTS TAKEN UP AT DIFFERENT
TEMPERATURES.
Per cent, increase of maximum increase.
Actual
increase.
oC.
5
10
15
20
25
30
per cent.
Tin
Raw Silk .
74-5
83-5
86.5
89.4
93-3
97-5
IOO
18.93
Boiled off .
100
100
100
100
100
100
IOO
1 6.0-
Iron
Raw Silk .
62.6
68.1
77-8
84.3
90.3
95-3
IOO
7.85
Boiled off .
100
100
100
100
100
100
IOO
4-95
Chrome
Raw Silk .
100
100
100
100
100
IOO
IOO
11.38
Boiled off .
69.1
72.9
78.4
86.8
92.6
97.2
IOO
5.83
Al.
Raw Silk .
39.1
54-5
66.4
84.7
100
IOO
IOO
1-43
Boiled off .
81.4
85.6
92.0
95-5
100
IOO
IOO
3.12
(Tin and iron solutions 52Tw.
Cr. 32Tw. Al. i5Tw.;
The effect of the condition of the mordanting
bath as regards its basicity is important. Heermann
defines the " basicity number " of a mordant as the
ratio of absolute acid content to the absolute metal
content ; e.g., the number for stannic chloride is
4x36.45-118.5 = 1.23.
The influence of additions of acid and alkali to
the normal mordants, star.nic chloride, chromium
chloride (basic), Cr 2 Cl 3 (OH) 3 , basic ferric sulphate,
and aluminium acetate is as follows: the addition
of alkali in all cases resulted in considerably more
mordant being absorbed, but the addition of acid
did not always produce the opposite effect. With tin
70 CHEMISTRY AND PHYSICS OF DYEING
and aluminium a very slight decrease was noted ;
iron, on the other hand, showed a rapid decline, 5 per
cent, of acid decreasing the absorption value to one-
half. In the case of chromium also a rapid drop
was noticed. That is to say, the influence of acid
on normal salts is small, but its influence on basic
salts great.
In concluding this work, Heermann examined
the five theories which have been put forward to
explain the mordanting process, in the light of the
following facts (Farb. Zeit. 1904, 15, 165) :
(1) Nature of fibre has a great influence on the
result.
(2) Mordants cannot be rubbed, or boiled off.
(3) Duration of treatment, temperature, and
state of solutions, have great influence on ultimate
result.
(4) Efficiency of mordant not proportional to its
ionisation.
(5) Temperature of bath increases during mor-
danting action.
(6) Chemically indifferent compounds take part
in the process.
(7) Fibre not altered structurally, or chemically
by the process.
(8) The basicity of mordant remains constant
during the process.
(9) Mordant base on the fibre is capable of further
combination and reaction.
(10) Ratio between weight of mordant and fibre,
influences the result of operations.
ACTION AND NATURE OF MORDANTS 71
Of the theories put forward to explain the action
of mordanting Heermann prefers the ionic one to the
impregnation, solution, " organo-metallic " or the
catalytic ones which are considered less satisfactory.
Light may be thrown on this subject by the further
study of the reactions of substances in the colloidal
state.
CHAPTER V
STATE OF FIBRES AND ACTION OF ASSISTANTS
THE condition of the fibres at the time of dyeing is
a most important factor in the production of satis-
factory results, especially where even dyeing and
fast colours are required.
It matters little whether the action of dyeing is
of a physical or chemical nature. In either case the
fibre must be presented to the dye solution in such a
condition, that an even and equal absorption of the
dye-stuff will result. All parts of the skein, or piece
of woven material, must be equally acted upon by
the assistants present in the dye-bath, when these
tend to influence the fibre state.
The problem of equal dyeing seems to entail
three essential factors : (i) The state or condition of
the fibre ; (2) The conditions of dyeing ; (3) The con-
dition of the dye solution. It is therefore essential
that the fibre substance shall be free from all im-
purities, natural, or acquired during the preliminary
processes of manufacture.
Fibres are subjected to the action of many sub-
stances, or solutions, with the object of attaining this
end.
STATE OF FIBRES AND ACTION OF ASSISTANTS 73
It is advisable to consider the action of these
different reagents on the impurities known to
be present in the natural fibres ; and to allow for
any possible action of these reagents themselves,
on the purified fibre substances met with in com-
merce.
In any specific case, those reagents which remove
the impurities, and leave the fibre in a homogeneous
state, of good colour and lustre, will be most suitable
for that special material, and lead to satisfactory
dyeing results.
It is hardly necessary to state that these condi-
tions are never entirely satisfied in practice. The
processes in vogue at the present time which make
up this preliminary treatment, are briefly considered
under the headings of the respective fibres.
Silk. This fibre comes into the markets in what
is called the " gum " or raw state.
The silk fibre or " boiled off " silk is obtained in
a pure state by treating the raw silk with a hot solu-
tion of some alkali or soap.
In practice this is brought about by boiling the
silk in one or more soap solutions, with subsequent
thorough washing with soft water.
The soap solution should be carefully made up
with a neutral soap. A soap made from olive oil is
generally considered to be a satisfactory one. If any
free alkali be present it must be in small quantities,
or the gloss of the fibre will suffer.
In these hot baths, the silk gum is rapidly re-
moved, and leaves the fibroin in a suitable condition
74 CHEMISTRY AND PHYSICS OF DYEING
for the subsequent operations of mordanting and
dyeing.
The original harshness of the raw silk disappears,
and the surface of the fibroin is shown in all its
beauty.
In the dyeing operations which follow, it is im-
portant that the fibre shall be free from insoluble
soaps.
Great care is therefore taken to remove all soap
from the fibre, and to protect the silk against any
surfaces which might introduce dirt, or oil.
Owing to the absorptive power of silk, iron is
easily taken up by the fibre, and this action must be
particularly guarded against in the choice of dye-
vessels, &c.
Although many substitutes for soap have been
suggested for " boiling out " the silk, yet in this
country, at least, it is almost universally used.
Such materials as borax, sodium carbonate,
sodium sulphide, and other weak alkalies, are possible
substitutes for soap in the boiling-off process, but
they do not leave the silk in such a satisfactory state,
the strength and brightness of the fibre not being
so good.
The following figures indicate the relative boiling-
out action of sodium carbonate in distilled water and
soap solution (5 per cent. sol.).
The time of boiling-out was a quarter of an hour,
and the temperature 95 C.
STATE OF FIBRES AND ACTION OF ASSISTANTS 75
Sam-
ple I.
Per cent, of sodium
carbonate.
Per cent, of Gum removed.
In water.
In soap sol.
I
.02
7.2
2
05
13-0
3
.07
19.1
4
.11
19-3
5
.15
19.6
6
.0
22 j
7
.01
22.2
8
.04
22-9
9
.07
23.2
10
15
234
The use that the " boiled off " liquor is put to in
the subsequent process of dyeing is also an important
factor in favour of the use of soap. In the presence
of the silk gum the soap solution may be acidified
without any separation of fatty acids. This emul-
sion has a " levelling up " action, and tends to pre-
vent uneven dyeing when it is added to the dye
liquor. The only other preliminary treatment wh'ch
" boiled off" silk may be subjected to is a bleaching
process. Where the yellow raw silk is used this is
necessary for light colours.
The operations entailed are not of a complicated
nature, but the action of the bleaching reagents on
the composition of the silk itself has not been deter-
mined.
Hydrogen peroxide and sulphurous acid are the
more commonly used agents. Permanganates are
occasionally used, as also is nitrous acid.
The silk fibre is therefore usually presented to the
76 CHEMISTRY AND PHYSICS OF DYEING
dye bath in a hydrated, and slightly alkaline state.
It is free from grease or wax. The efficiency of soap
for boiling out is probably due^ to the presence of
free alkali in small quantity in the liquor. Lime, or
magnesium salts, in the water may lead to the forma-
tion of insoluble soaps, and uneven dyeing.
The silk itself may contain these substances. A
preliminary acid bath will remove them.
We know that alkalies are held by silk against the
action of water in common with many other sub-
stances.
This makes it difficult to obtain the boiled-out
silk fibre, in a uniform condition, for purposes of
investigation and until further work has been done
it is impossible to suggest a standard method of
boiling out silk for this purpose.
It is clear that experiments in the past have been
performed on the fibre, which has been treated in
different ways.
It is suggested that silk skeins for special work
should be first treated at 95 C. with a i per cent,
solution of olive oil soap, followed by a further treat-
ment with \ per cent, solution for half an hour, with
subsequent washings in very weak ammonia (i c.c.
to 1000 c.c.), and three or four washings in distilled
water at 40 C. This will give a fairly pure sample of
boiled-off silk. The temperature of the boiling- off
solution should not be above that indicated.
The action of excess of free alkali, if present in any
quantity, on silk or wool, is decidedly harmful. The
silk itself is attacked with loss of strength and lustre.
STATE OF FIBRES AND ACTION OF ASSISTANTS 77
The action of alkali on wool at high temperatures is
of a similar nature.
The effect of boiling wool for one hour in a solu-
tion of alum, acidified with sulphuric acid, causes
considerable hydrolysis (Gelmo and Suida, Monatsh.
/. Chem. 26, 855). There is considerable loss in
weight and formation of soluble amino -acids. Some
of the decomposition products resemble peptones
in their action. These are -said to interfere with
the fastness of the colours, in the absence of mineral
acids.
This breaking down of the fibre substance is
accelerated in the presence of mineral acids. This
is noticed also in alkaline solutions, as might be
expected, with products of animal origin.
The action of caustic soda on wool is specific
(Washburn, /. 5. D. and C., 1901, 261). At ordinary
temperatures wool is increased in strength in the
ratio of 55 to 41 when soaked in an 82 Tw. solution.
At the same time 84 per cent, of the sulphur present
is removed. The lustre and feel are said to be im-
proved, and the affinity for dyestuffs increased.
Treatment with alcoholic potash, with subsequent
slight acidification and washing is said also to give
a similar result, on dyeing with direct and azo dyes.
(Gelmo and Suida, ibid.}
It will therefore be realised that these preliminary
processes may materially modify the subsequent
operations of dyeing, &c., by direct action on the
fibre substances themselves.
The processes used in preparing vegetable fibres,
78 CHEMISTRY AND PHYSICS OF DYEING
by reason of their more inert nature, may be
correspondingly drastic.
Of the preliminary operations in the treatment
of wool fibre the objects to be attained seem to be
fairly simple. In the unwashed state wool consists
of the fibre proper, which is protected by wool fat
and the suint, or yoke.
I Thoroughly cleaned wool seems to have the same
composition as horn, or feathers. This substance
has been named keratin. It is a proteid.
The wool fat is peculiar in its way. It contains
no glycerides. It is chiefly made up of cholesterin,
isocholesterin, oleic, stearic, and other fatty acids.
The suint contains about 40 per cent, of inorganic
matter. It chiefly consists of potash salts of stearic
and oleic acids, besides phosphates, silicates, &c., in
smaller quantities. The object of the preliminary
operations is clearly to remove these from the fibre.
The fatty and wax-like bodies may be removed
by light spirits, such as petroleum ether. The potash
salts may, of course, be removed by water.
Soap and soda are chiefly used to wash wool. The
temperature should not be above 40 C.
The operation of bleaching wool may modify its
composition, or may merely change the colouring-
matter. The figures given elsewhere indicate that
the latter is quite possible.
Sulphurous acid and peroxide of hydrogen are the
two substances used for bleaching wool.
The former may be used in the form of the gas
(stoving), or else in aqueous solution.
STATE OF FIBRES AND ACTION OF ASSISTANTS 79
The basis of hemp, flax, jute, ramie, &c., is
cellulose more or less ligaified. Oils, resins, and
colouring-matters have to be removed. Cellulose,
although a carbohydrate, like starch, is very resistant
to the action of ordinary solvents, which may, there-
fore, be used in the preparation of these fibres.
Dilute acids, and alkalies, are used for this purpose.
In the absence of air the action of the latter solutions
is reduced to a minimum.
In the preliminary preparation of these fibres they
are submitted to a retting process. A series of
changes brought about chiefly by bacterial action
takes place. As a result the fibre is freed from certain
binding substances.
The purified flax is pure cellulose. Bleaching is
difficult with this fibre, and dyes are not so readily
taken up as by cotton.
Ramie (china grass) in a purified state is cellulose,
and is easily bleached to a beautiful white shade.
The general action of bleaching vegetable fibres
is an obscure one, and demands farther attention.
Sodium hypochlorite is superior in many ways to
the calcium compound. No tendering of the fibre
is noticed with it. This is probably due to the pre-
sence of a smaller quantity of free hypochlorous acid.
The attraction of cellulose for water is of a definite
nature. It is a property of the cellulose substance
itself, and is independent of structure. Dissolved
and reprecipitated cellulose exhibits the same
phenomenon. (Cross and Be van.)
The hydrating action seems to be a function of
8o CHEMISTRY AND PHYSICS OF DYEING
the OH groups in the cellulose molecule. As they
are suppressed by combination, so this property is
said to decrease.
A study of the conditions of hydration indicate
that the process is a continuous, and reversible one.
Cellulose in the state of hydration is more readily
attacked by reagents, and absorbs larger quantities
of certain dyes.
Cross and Bevan have stated that cellulose which
has been artificially dehydrated by alcohol shows a
greater resistance to reagents.
This hydrating action may be carried so far that
actual solution seems to take place. The cellulose is
said to be present in a gelatinised form. (Erdmann,
/. Pr. Chem. 76, 385.) Cramer has, however, shown
that this conclusion does not agree with the osmotic
pressure of the solution. This is not, however, a
fatal objection to this view.
The action of alkalies on cellulose at high tem-
peratures has been examined by H. Tauss (J. S.C.I.,
1889, 913 ; 1890, 883). Cross and Bevan group the
celluloses in their action as follows :
(a) Those of maximum resistance to hydrolytic
action, and containing no directly active groups.
(6) Those of lesser resistance, and containing
active CO groups.
(c) Those of low resistance, i.e., more or less
soluble in alkalies, &c.
To the first class belongs the typical cellulose, such
as flax, hemp, ramie, &c. The second class contains
STATE OFj FIBRES AND ACTION OF ASSISTANTS 81
the oxycelluloses, and the last class the non-fibrous
celluloses.
The lignocelluloses (jute) are unsaturated com-
pounds. They form definite compounds with
chlorine. The action of jute in dyeing is noticed
elsewhere.
The many operations which cotton has to go
through in these processes are partly due to original
defects, and partly due to those acquired in the manu-
facture (oil, grease, &c.). They include : boiling in
water, boiling in lime-water under pressure, treatment
with dilute acid, boiling with resin soap, bleaching,
treatment with weak acid, thorough washing, and
drying.
The lime is said to form compounds with the fatty
acids ; to remove certain substances ; and to act on the
natural impurities, so that they are more easily
removed by subsequent operations.
The object of the next acid bath will be obvious.
The effect of the following bath, soda lye, is to remove
fatty acids.
Boiling with this reagent is said to be the essential
process to render cotton wool absorbent (Kilmer,
/.S.C.7., 1904, 967).
The loss of weight on boiling cotton with
caustic soda solution is indicated in the following
table.
Loss on boiling for
Strength of solution. ,
Half-hour. One hour.
I per cent. 4.41 per cent. 5.71 per cent.
2-5 5-08 7.33
6
82 CHEMISTRY AND PHYSICS OF DYEING
Resin soap is added to the lye-bath when the cotton
is to be printed.
The action of bleaching with bleaching powder,
and subsequent acid bath, are processes which bring
about changes in the colour of the impurities, and
to a certain extent an oxidation of the cellulose
itself.
The importance of equal bleaching is evident from
this point of view. The theory of bleaching has been
considered by A. Scheurer in more or less detail.
The additional attractive power of hydrated
cellulose (hydrocellulose) for dyes, must also be
considered. This action has been noticed by many
observers, including Schaposchnikoff and Minajeff
(Zeit. /. Farb. und Text. Ch., 1903, 13 ; 1904, 163),
and Hiibner and Pope (J. S.C.I., 1904, 404). The
iodides seem to be capable of replacing caustic soda in
mercerising. If the fibre be soaked in a strong solu-
tion of potassium iodide, and subsequently washed
with alcohol, 15 per cent, of the salt is retained.
After removing this with water the fibre shows in-
creased affinity for Benzopurpurine 4 B; but no
increased effect for basic dyes.
Twelve hours treatment with boiling water will
also greatly increase the dyeing effect of cotton for
4B and decrease it for methylene blue (ibid.}.
It will therefore be seen that the fibres are very
sensitive to changes in either composition, or nature,
when they are subjected to the action of solutions.
Even in the case of water itself this action is very
evident. Mere handling will at once show that the
STATE OF FIBRES AND ACTION OF ASSISTANTS 83
physical conditions have greatly altered. The dyer
is most concerned with the action of aqueous solu-
tions, but the action of other solutions is of great
interest from a general point of view.
When considering the action of different solutions
on animal fibres during the process of dyeing, espe-
cially at high temperatures, it is instructive to note
their effect on solutions of albuminoid bodies.
Some albumins may be salted out of their solu-
tions by sodium chloride, or sulphate. Others are
not acted on by these reagents.
Ammonium sulphate will, however, precipitate or
salt out nearly all the proteins.
Hollmann considers that the point of concentra-
tion at which a salt begins to precipitate an albumin,
is just as characteristic for these substances, as is the
point of saturation in a crystalloid.
Prolonged boiling with dilute acids, or alkalies
decomposes the albumins, forming among other
substances a series of amino acids, including tyrosine
and leucine, and diami.no acids such as ornithine and
arginine.
So far as their reactions with salts of the heavy
metals go, they act like acids, and form precipitates.
Some albumins are said to yield insoluble com-
pounds with weak acids, and may therefore be said
to behave like a base.
They absorb tannic, picric, and phosphotungstic
acids in this way.
The acidic and basic properties of these albumins,
are said to recall those of the pseudo acids and bases.
S4 CHEMISTRY AND PHYSICS OF DYEING
These reactions are of interest to the dyer.
Fibres of animal origin undoubtedly assume the
hydrogel condition on boiling with water.
From a study of the general reactions we
may obtain an insight into the possible results of
treating these fibres in a similar way, and of
varying the conditions of the liquors at the time
of dyeing.
Very little real work has been done on the subject
of the action of assistants in dyeing operations.
This subject embraces what may be termed the
action of such reagents as acids, alkalies, neutral and
acid salts, &c., on the absorption of the dyes by the
fibres, and on the fibres themselves.
The nature of these actions is in many cases
obscure, and it can hardly be said that in any case
it is fully understood.
From the practical point of view, this study is of
the greatest importance. It is only necessary to
instance the action of the addition of acid to the bath
in the case of dyeing silk, or wool, with acid colours ;
or the addition of salt to the bath in the direct dyeing
of cotton with the direct cotton dyes to obtain darker
shades.
The first attempt to determine the relation
between acids and fibres was undertaken by Mills
and Takamine (/.C.5., 1883, 144).
Their research on this subject was divided into
two parts. The rate and amount of absorption of
individual acids by silk, wool, and cotton, was first
determined ; and then the relative absorption of the
STATE OF FIBRES AND ACTION OF ASSISTANTS 85
acids by the fibres, when more than one acid was
present.
In the case where more than one acid was used,
the results obtained were of special interest.
For instance the following table shows the results
obtained with mixtures of sulphuric and hydro-
chloric acids with wool and silk fibres, the ratio of
absorption being shown.
Proportion of
Wool.
'Silk.
H 2 SO 4 to HCL
H 2 S0 4 .
HCL
H 2 S0 4 .
HCl.
I to I
5-o
32-5
6.63
.87
I to 2
11.3
25-5
5-0
2-5
I to 4
16.56
18.4
4.0
3-5
These figures at once show that the addition of
the second acid influences the absorption figure of
the first one.
The writer of this book has made an extended
series of trials with acids of varying nature. If
mixtures of hydrochloric acid and, say, tartaric acid
are used, the estimation of the relative absorption
of the two acids is an easy one. The former acid can
be estimated in two ways, viz., by n / IO sodium car-
bonate solution, and by W / IO silver nitrate.
After allowing for a certain amount of hydro-
chloric acid, which blank experiments indicate is
present in the combined state in the solution, the
writer could not trace any selective action of the fibre
for the stronger acid, as might be expected if the
general action was equivalent to any chemical action
86 CHEMISTRY AND PHYSICS OF DYEING
of an ordinary nature, such as might be anticipated if
the amino acids in the fibres entered into the reaction.
These figures are not completed at the present time.
Mills and Takamine found that the rate of
absorption of the acids when present in the ratio of
H 2 SO 4 : 4HC1 by wool and silk is expressed by the
following figures :
RATE OF ABSORPTION
Fibre. H 2 SO 4 . HC1.
Wool . . . 100 x 79-6
Silk - . 100 175.0
The maximum absorption ratio for silk and cotton,
on the other hand, is given as follows :
Acid. Cotton. Silk.
H 2 S0 4 .! . i 2.6
HC1 . . I 2.2
NaHO- . . i 2.2
In the case of wool and silk the former takes up
much more acid, but they both absorb about the
same quantity of sodium hydrate.
When wool is treated with weak reagents
separately in the proportion of HC1 : NaHO, the
absorption is in the ratio of 2HC1 : 3NaHO.
In the case of silk and cotton the absorptions are
in each case sHCl : loNaHO.
It is argued from this that there is some intimate
relation between cotton and silk. It would be more
accurate, however, to assume that the action as
represented by absorption of acids is a similar one
in both cases.
It would be of value to find out whether the.
relative absorption of acid and basic dyes, follows
STATE OF FIBRES AND ACTION OF ASSISTANTS 87
these figures. They should clearly do so if the
actions are identical ones.
The figures for wool, silk and cotton, therefore,
stand as follows :
Wool . ' ' .- HC1. 1.5 NaHO
Silk . ' . . HC1. 3.3 NaHO
Cotton . . HC1. 3.3 NaHO
The writer found when repeating some of these
results that in the case of silk the absorption of acid
reaches the maximum very rapidly. It is complete
in a few minutes. After this no further alteration
in the ratio between acid in solution to acid in
fibre, took place.
So far as the experiments went, temperature had
little effect on the action, but these matters are
under investigation.
If the action of acid, and alkali, is a specific one,
depending on the presence of ami do acids in the fibre,
it must follow the laws of ordinary chemical action.
It is perfectly legitimate to argue from this action
to that of dyes, when comparing their action on
fibres.
The methods of estimating the absorption are
definite, and, so far as can be seen, beyond question.
The following results obtained with sulphuric acid
solutions and wool are of interest.
% Acid employed. % Left in solution. % Taken up by wool.
2j .38 2.12
5 2.17 2.83
10 6.37 3.63
20 15.87 4.13
40 35.18 4.82
88
CHEMISTRY AND PHYSICS OF DYEING
These figures should be extended ; several results
should be shown between o and 2.5 per cent, acid
and the amount extended to, say, 200 per cent.
There is a certain amount of evidence that there may
be two causes of absorption, but nothing is definite.
Up to 40 per cent, the maximum effect is not
reached.
Repeated extraction does not remove all the acid,
but there are no reliable figures on this subject.
The general effect will be better seen in the
following curve which is plotted from the above
numbers.
20 30
Acid in solution.
40%
ABSORPTION OF SULPHURIC ACID BY WOOL.
STATE OF FIBRES AND ACTION OF ASSISTANTS 89
The influence of time on the absorption of
sulphuric acid in the cold (4C.) is shown in the follow-
ing curve. (Mills and Takamine.)
20 40 60 80
Time of immersion.
INFLUENCE OF TIME ON ABSORPTION OF ACID.
[OH 2 . 250 cc. : Wool 2.61 grms. : H 2 SO 4 .6625 grms. Time unit hour.]
Action of Acids in Dyeing. Acid colours. The
generally accepted theory here is that the sodium
salts of the sulphonic acids are decomposed, and
the dye acids set free. This action certainly takes
place, and is an important one, but from the
chemical point of view has not been satisfactorily
settled. From a practical point of view the excess
of acid over and above the amount required to set all
the dye acid free, seems to be of even greater import-
ance. All silk dyers know that an excess of acid in
90 CHEMISTRY AND PHYSICS OF DYEING
the dye-bath has a pronounced effect on the rate
of absorption, and the amount of dye absorbed.
A great deal of work has yet to be done on this
subject. For instance, starting with silk, and a pure
salt of an acid dye, the absorption results obtained
by the addition of known amounts of acid should be
carefully noted.
If the additional effect is due to the greater
affinity of the fibre for the free colour acid, a sudden
difference in the result would be expected at the
point when the acid present is all set free. Care
would have to be taken to see that the added acid
was not neutralised by some fibre substance. To do
this, it would be necessary to check the amount of
free acid in the dye solution.
It must be acknowledged that the effect of the
addition of excess of acid in dyeing is obscure.
If we assume that the excess of acid in the solu-
tion is taken up by the fibre substance chemically,
we should expect a decreased affinity for the dye
acid. The effect of the addition of a second acid in
the experiments of Mills and Takamine shows that
this is the result produced in practice. Increasing
the ratio of the one acid to the other decreases the
amount of the second acid absorbed.
The result obtained with the colour acids in the
presence of excess of a mineral acid is of the opposite
nature. The amount of the dye absorbed is increased.
It is possible that the acid modifies the state of the
fibre either chemically or otherwise, and that this
STATE OF FIBRES AND ACTION OF ASSISTANTS 91
must be taken into account, as well as possible changes
in the solution state of the dye.
Quite recently some work has been done on this
subject by Gelmo and Suida (Monatsh. f. Chem. 26,
855), which seems directly to contradict some of the
previously recorded results.
Using purified wool, and dyeing with free colour
acids of Crystal Ponceau, Lithol Red, Fast Red R.,
and Alizarine Yellow G.G.W., the intensity of the re-
sulting shade is said to be independent of the presence,
or absence, of free mineral acid in the dye bath.
The authors consider that the role played by the
excess of acid is that of neutralising the lime, com-
bined with the acid groups of the wool.
The writer has observed that with silk this action
can be directly seen, by allowing this fibre to remain
in contact with deci-normal hydrochloric acid solu-
tion, and subsequently titrating with both M / IO alkali
and n / IO silver nitrate solutions. The results indicate
that all the hydrochloric acid remaining in the solu-
tion is not in the free state. This complicates the
estimation of the absorption of acids by fibres, and
must be allowed for.
It has been noticed that wool treated with
sulphuric acid and subsequently washed has a con-
siderably decreased affinity for basic dyes, but its
affinity for acid dyes is increased.
If the wool is washed with hot water, and trials
are made with alcoholic solution of sulphuric acid it is
found that the subsequent absorption of basic dyes
92 CHEMISTRY AND PHYSICS OF DYEING
is slightly more in the case of hot water washing
than when cold water was used. In the case of
aqueous sulphuric acid the reverse action is noticed.
On the other hand, the affinity for acid colours
is considerably increased after washing with hot
water, in the treatment with sulphuric acid, in either
aqueous, or alcoholic solution.
Very similar results are obtained with hydro-
chloric acid. On the other hand, treatment with
acetic acid under these conditions has little effect.
The wool after washing behaves like the untreated
samples.
On boiling wool with a sulphuric acid solution of
alum, considerable hydrolysis takes place, with loss in
weight, and the formation of soluble amino acids is
said to be the final result of the reaction.
Wool treated with alcoholic zinc chloride (.1 per
cent, sol.) and washed shows a decided loss in affinity
for basic dyestuffs, and a greater affinity for Azo-
fuchsine G. (acid colours). This effect is more
pronounced than when an aqueous solution is used.
The effect of a preliminary treatment with either
alcoholic, or aqueous, sulphuric acid before mordant-
ing is said to be as follows. With chromium
sulphate no appreciable difference is recorded, but
with aluminum sulphate stronger dyeings are ob-
tained. On the other hand, weaker shades are pro-
duced with sulphate of iron on subsequent dyeing.
Wool mordanted in this way also shows a reduced
affinity for basic dye-stuffs, and an increased affinity
for acid ones.
STATE OF FIBRES AND ACTION OF ASSISTANTS 93
Treatment with ammonium carbonate solution
is said to reverse the action of the mordanted fibre.
This secondary effect of acids is clearly seen in
some experiments on the absorption of fl naphthol
sulphonic acid R. The amount absorbed by wool
is greatly increased by the presence of sulphuric acid.
(Hirsch, Chem. Zeit. 13, 432.)
The action here, if a chemical one, must be on the
wool, and here again we might look for the opposite
result to that which actually takes place. A careful
study of this phenomenon is greatly needed.
The action of acids in dyeing with basic colours is
even more complicated than in the case of acid dyes.
Sulphuric acid is said to impede the dyeing of
wool with strongly basic dyes (magenta, methylene
blue, &c.), but to promote the action of slightly basic
dyes like Light Green SF, and Acid Magenta. Hydro-
chloric acid acts in the same way (Gillet, Rev. Gen.
des Mat. Co/., 1900, 4, 327). The fixing action of
acids seems to be inversely proportional to the
basicity of the dye-stuff.
The action here from a chemical point of view is
very obscure. There seem to be two possible
explanations of this action.
(1) That a more stable salt is produced with the
more strongly basic dyes, and that consequently the
amount of base absorbed will be less.
(2) That the formation of basic salts, which are
insoluble, in the fibre, is prevented ; or even that if
the base itself is precipitated, or fixed, in the fibre it is
redissolved in the presence of excess of a strong acid.
94 CHEMISTRY AND PHYSICS OF DYEING
A weaker acid like sulphurous acid is said to have no
action on the dyeing of wool.
On the other hand Prud'homme (Rev. Gen. des
Mat. Col. y 1898, 2, p. 209) gives the following table
which indicates that the opposite is the effect pro-
duced in practice. The table shows the altered
attraction of wool for dyes after treatment with
sulphur dioxide and hydrogen peroxide. Typical
acid and basic dyes were taken, and the maximum
dyeing effect taken as=ioo.
Experi-
ments.
Treatment.
Intensity of colour.
Basic colours.
Acid colours.
I
S0 2 . . ... .
50
40
2
SO f andH 9 0, .
100
50
3
SO 2 and Na 2 CO 3 . -
30
IOO
4
S0 2 and H 9 2 and Na 2 CO 3
80
9
5
Water only
20
70
These figures indicate a possible cause for the
results of uneven bleaching or dyeing in practice.
Assuming that the wool molecule has in its
constitution the group
N-C n H 2n -CO
it is claimed that the above results are explained.
The treatment would probably lead to the formation
of
.OH.
N-C n H 2n CO
Our knowledge of the action of acids is in a very
elementary state. The results recorded are very
STATE OF FIBRES AND ACTION OF ASSISTANTS 95
contradictory, and indefinite in their nature. This is
specially the case with the sulphonic acids, be they
dyes, or otherwise. Green, on the one hand, states
that with the exception of dehydrothiotoluidine
sulphonic acid he could not find any colourless
sulphonic acids of phenols, or amines, which had
any attraction for fibres. On the other hand, the
results recorded by Hirsch and Vignon would indicate
that they may be absorbed.
It is probable that the study of the action of
assistants will do more than anything else to throw
light on the general nature of dyeing.
Action of alkalies. Beyond a general indication
as to the action of these bodies on dyeing, we have
little knowledge.
In silk dyeing, for instance, it might be thought
that they remove the dye from the fibre by forming
an alkaline, and soluble salt. The fact that they will
almost equally well remove basic dyes is against this
theory ; and indicates that the general action is not a
chemical one. They may act by increasing the
solubility of the dye in the solution, or by counter-
acting the attraction of the fibre colloid.
The action seems to be a specific one ; soap,
borax, the soluble alkaline carbonates, ammonia, act
in the same way, although they vary in degree. For
instance, the relative action of soap and sodium
carbonate on ingrain colours and direct dyes on
silk is given elsewhere ; also the relative amounts,
of a series of primuline dyes taken up by silk in
soap solution under standard conditions where it
g6 CHEMISTRY AND PHYSICS OF DYEING
seems almost impossible for the sodium salt to be
decomposed. The action of these substances is an
important one, but its study has been neglected. The
use of these compounds in the bath itself is chiefly
restricted to the dyeing of cotton with the direct
dyes, and the dyeing of alkaline blue on wool or
silk.
The latter example is an interesting one from the
theoretical point of view, and one which seems to have
been overlooked. In order to prevent the too rapid
dyeing of this colour, and also to obtain even results,
the dye is applied in an alkaline solution. It is,
therefore, fairly certain that it is absorbed as an
alkaline salt, and consequently without combination
with the fibre substance. A weak acid will sub-
sequently set the colour acid free.
Action of neutral salts. It is generally agreed that
the action of these compounds in the dye-bath is of a
physical nature. It is assumed that the decreased
solubility of the direct dyes in saline solutions is the
chief cause of their action. This may be so, but
little work has been done on this subject to prove it.
If this were the only action, it is clear that in any
solution the cotton fibre should dry a darker colour
in the cold, for the dye would be still more insoluble
under these conditions.
In practice the reverse is the case. The fibre
state is clearly an important factor, and here
temperature is possibly more important than the
decreased solubility of the dye under any working
conditions.
STATE OF FIBRES AND ACTION OF ASSISTANTS 97
Under constant conditions of temperature, &c.,
a carefully conducted series of experiments, dealing
with the relative solubilities of these direct dyes
and their dyeing actions in, say, solutions of sodium
sulphate of different strengths is required; also
the relative actions of the different assistants of
this nature, as compared with their influence on the
solubilities of the dyes, the solubility tests to be made
at the temperature of dyeing.
A series of figures (W. M. Gardner, Text, Manuf.,
1890, 345) has been given indicating the best pro-
portions of salt to add to the bath to get the maxi-
mum effect. The conditions of the trials are of too
indefinite a nature to be of much value from a theo-
retical point of view.
The experiments suggested above might be
extended. Skeins dyed with colour should be boiled
with white skeins in different saline solutions and
the relative rates of diffusion compared, the relative
solubilities under the conditions of the experiments
being carefully noted. The writer hopes to give
this subject attention.
There is nothing which more clearly indicates
the indefinite nature of our present knowledge of
the subject of dyeing, than the absence of reliable
information on the action of these bodies, especially
when we consider their great value, and general use
in dyeing.
It is hoped that before long these interesting
problems will be cleared up.
Reference may be made to the experiments
7
98 CHEMISTRY AND PHYSICS OF DYEING
of Hallitt on the action of sodium sulphate in the
dyeing of wool, which, for convenience, is noticed
elsewhere.
The action of formaldehyde on the fibre sub-
stances, and the influence of this body on the general
process of dyeing are characteristic, and a further
examination in this direction is needed.
The coagulating action of the substance on
albumin and gelatin is well known. In a similar
way, wool, and silk fibres are influenced by this
reagent.
The keratin of the wool fibre is rendered less
soluble. Beyond becoming harder the wool suffers
little from this treatment. It is much more resistant
to change in the presence of alkaline liquors, and
steaming, or boiling in water, has less disturbing
influence on the fibre.
The treatment is, therefore, of advantage where
wool is dyed with the sulphide dyes.
In the same way the silk gum present in raw silk
may be rendered less soluble under the action of
alkaline liquids, and soap solution.
This reagent is used to fix direct blacks on
cotton. In this case the application follows the
actual dyeing, and takes place at a temperature of
about i6oF.
J. Collingwood (f.S.D. and C., 1905, 243) shows
that with Diamine, Columbia and Zambezi Blacks
the effect of treating in this way is to increase the
fastness to acids and washing. The fastness to light
is not appreciably altered.
STATE OF FIBRES AND ACTION OF ASSISTANTS 99
The dyeing of basic colours on cotton treated
with casein followed by formaldehyde is of interest.
The baths are said to be exhausted, and the
shades bright and good.
The Influence of Temperature on Dye Absorption
is indicated in the following curves.
3 3
No. 2.
No. i
20 40 60 8oC.
Temperature of 'Solution, 'jj
ROSANILINE ACETATE ON WOOL.
(OH 2 '200 cc. : Dye solution -i grm. per litre ^
The reversal in the absorption of the dye as
indicated in the curve is attributed to dissociation
stress, which is said to take place at high tempera-
tures with this dye.
Assuming Hood's law, and considering the absorp-
tion as due to chemical effect, as well as the dissocia-
tion of the rosaniline acetate, the combined effect
should be proportional to the fourth power of the
temperature.
ioo CHEMISTRY AND PHYSICS OF DYEING
The sum of the fifth differences being only .07,
or very nearly zero, and this being also a criterion of
a quadratic curve, the equation of the curve is
y = b (t + 1.46) - c (t + 1.46)- - d (^ + 1.46)" -r ^+1.46)'
when y is amount of colour absorbed, t = tem-
perature, and b, c, d constants of condition.
A further set of experiments similar to the above
(see curve 2) with a constant quantity (.0005 grm.) in
excess of dye shows a double reversal as indicated.
The results from this set of figures indicate that
at no practically attainable temperature, near to
oC. does colour cease to be deposited. At about
39C. the maximum colour is deposited (.09 per cent.).
At 82 the curve falls lowest to the axis of no colour.
The general effect of using an excess of colour is
to widen the range of temperature, within which
colour is deposited; to increase the general dyeing
effects; and shift the point of greatest deposition
about 8 upwards, and to doubly reverse it hereafter.
With mauveine the calculated point at which no
colour would be taken up is - 23.8C. At 49 there
is greatest deposition of colour (.08 per cent.). Then
there ensues a single inflexion in the curve, and
lastly, the curve descends rapidly to the axis of no
colour, although at 8sC. it is still remote therefrom.
The positive disadvantage of dyeing with these
basic colours at high temperatures is therefore
apparent, so far as colour absorption is concerned.
The absorption of dyes by wool has also been
studied by Brown (J.S.D. and C., 17, 92).
STATE OF FIBRES AND ACTION OE ASSISTANTS icfi
The dye left in the solution on 00 parts ^taikeri is
shown for varying temperatures.
Dye.
20
40
60
80
100
Acid Magenta .
79
14
4
4-3
5-6
Tartrazine
46
3
i
i
97
Indigo Carmine
46
3
3-4
3-5
6.2
Acid Green
79
18
4
3-6
5-2
Acid Violet 4 BW. .
44
26
20.8
20.8
28.7
These variations are of interest to the dyer.
They indicate the possibility of different shades being
produced by a dye solution containing mixtures of
these dyes at different temperatures, irrespective of
depth of shade.
They explain also why in wool dyeing the fibre
will often absorb a further amount of dye, if left to
cool in the dye solution.
CHAPTER VI
SOLUTION AND THE PROPERTIES OF COLLOIDS
AT every turn the dyer is brought in contact with
solutions of dyes, mordants, and other substances ;
and it is therefore necessary for him to have some idea
as to the physical state of substances in solution.
Many of the difficulties met with in the dyehouse
are intimately connected with the solution state of
these materials.
In cases where the remedies take the form of
alteration in the strength, or temperature of the dye
liquors ; or the addition of third substances to the
same, the changes brought about in the dyeing
processes are clearly due to corresponding variations
in the solutions themselves. Through these the
absorption of the dyes may be modified, and different
dyeing effects produced.
This subject, generally, is a complicated and
involved one, and has given rise to much controversy.
A general clearing up of our ideas on the subject
is urgently needed, in view of the importance of its
influence on many branches of physical chemistry.
The solution state of a dissolved substance may,
if the ideas of to-day are correct, be ascribed to one
SOLUTION AND THE PROPERTIES OF COLLOIDS 103
of two actions. It may be that both are involved in
the production of solutions.
Stated briefly, the molecules of the dissolved
substance (solute) are either in association with the
solvent molecules ; or else they simply migrate in an
inert solvent , or medium.
The issue is therefore clear and defined.
In the latter case the solute is considered to be
more or less in a state of dissociation, being split up
into ions which also have the power of independent
migration in the solvents, the cause of this action
being unknown.
The two theories may be termed the association,
and dissociation ones respectively. They may be
said to include all the possible explanations of these
phenomena known to us at the present time.
The association theory was primarily based on
the work done by Mendeleef on the isolation of
definite hydrates in solutions. The work of Cromp-
ton and Pickering supported this view. Prof.
Armstrong in this country, and H. C. Jones in
America, have advocated this conception of solu-
tion.
The original idea of Mendeleef supposes, that a
series of hydrates are formed in the aqueous solution ;
and that these hydrates are in equilibrium with the
solvent and with one another. It must be remem-
bered that the presence of such compounds has not
been recognised in the case of many other solvents,
but a number of hydrates have been isolated by
crystallisation from aqueous solutions by the above
104 CHEMISTRY AND PHYSICS OF DYEING
investigators ; and many others have been indicated
by the alteration in the physical constants of the
solutions.
Armstrong suggested that the association was
only between the solvent molecules and the negative
radicle of the solute only.
In dealing with the phenomena of pseudo solution
and de-solution in dye solutions (J.S.C.I., 1905,
228), I ventured to suggest that the action might be
of an intermediate nature, it being assumed that the
so-called secondary attraction of the solvent mole-
cules for those of the solute correspondingly reduces
the primary attraction between the positive and
negative radicles thus :
(OH,), . . . H-C1 . . . (OH,),
As a result the hydrogen and chlorine atoms are
never entirely beyond the influence of their primary
attraction for one another. Their mutual influence
is lessened, but not entirely replaced by the secondary
attraction.
On the other hand, Dr. Lowry has more recently
advanced the hypothesis that actual dissociation
may occur owing to the formation of " hydrated "
ions. For instance, he represents the solution of
potassium chloride as follows :
The solution state, so far as the solute is ionised,
is represented as split up into ionic hydrates. The
full argument in favour of this theory is set
SOLUTION AND THE PROPERTIES OF COLLOIDS 105
forth in a recent paper read before the Faraday
Society.
So that we have the three possible states of solu-
tion, the ionic, the associated, and the intermediate
one, which assumes that the primary and second-
ary attraction are interchangeable and of the same
order.
There is a further and alternative hypothesis,
which associates the action in the case of aqueous
solution with the presence of an unsaturated tervalent
oxygen atom.
The subject is, therefore, narrowed down, so far
as our ideas extend at the present time, as indicated.
Enough is already known to enable us to judge the
importance of the whole subject. It is impossible,
however, at the present time to indicate the hypo-
thesis which will be ultimately accepted as most
truly representing the solution state. In the mean-
time the dyer cannot fail to gain information on the
condition of his solutions, and their possible actions,
by keeping in touch with the general principles laid
down from time to time in connection with this
subject.
It may be generally stated that all substances are
soluble in water. There is apparently no exception
to this rule. Even such substances as quartz,
platinum, and gold, are soluble. It may be accepted
as a fact, therefore, that no known substance is able
to withstand the solvent action of water. The
degree of solution varies ; sodium sulphate is very
soluble, barium sulphate is relatively very insoluble.
io6 CHEMISTRY AND PHYSICS OF DYEING
Yet the solvent action is there ; the general action is
the same in both cases.
When, therefore, water is brought into contact
with any substance, fibres, dyes, salts, copper vessels,
&c., solution takes place in every case. Although
this action may in some cases be neglected, yet,
under certain favourable conditions it may adversely
influence the dyeing results. This solvent action
may be greatly modified by the presence of third
substances, such as acids, or alkalies, and must be
carefully considered.
As previously stated, the dissociation theory
assumes that salts, acids, and bases are more or
less split up into electrically charged ions on
dissolving in water.
According to Faraday's law, hydrogen and the
metallic radicles are positively charged, while
hydroxyl and radicles are negatively charged.
Acids in aqueous solutions are supposed to act as
such by virtue of the free hydrogen ions present.
Consequently the hydrogen ions in a given equiva-
lent of acid are said to determine its strength as
an acid.
These H ions are also supposed to have the power
of carrying electricity, and consequently the more
free ions present the greater will be the carrying
power, or conductivity of the solution.
Beyond a certain stage of aqueous dilution
Kohlrausch found that the molecular conductivity
of these substances reached a maximum value.
The dissociation theory implies that at this point
SOLUTION AND THE PROPERTIES OF COLLOIDS 107
the substance is entirely split up into ions, or, in
other words, completely dissociated.
Having therefore determined the molecular con-
ductivity of an acid at infinite dilution (that is to say,
at the point of maximum dissociation), its molecular
conductivity at any other dilution greater than that
will vary as the number of ions present.
So that the ratio of the molecular conductivity at
any dilution v to the molecular conductivity at
infinite dilution will give the degree of dissociation at
any other dilution thus :
Uoo
The future investigations on the action of dyeing
will certainly be closely connected with the abnormal
actions of substances in the colloid state. When the
nature of the fibres and dyes is considered, it will be
seen that every dyer should have at least an elemen-
tary knowledge of the properties and actions of these
bodies.
The further study of this subject must un-
doubtedly lead to important results. Whether the
advanced views held by some investigators will be
ultimately accepted, or not, is hardly a fit subject for
speculation. The study of these substances, their
properties, and their relations to other materials
with which they may be brought into contact, is a
wide one ; and many years will probably elapse
before our knowledge is brought down to anything
like a firm or satisfactory basis.
Be this as it may, sufficient facts have already
io8 CHEMISTRY AND PHYSICS OF DYEING
come to light to lead us greatly to modify our views
and theories, and undoubtedly this disturbing influ-
ence will tend to become greater rather than to
decrease.
Not the least important result of these investiga-
tions will certainly be directly to influence our
ideas on the so-called ionic theory of solution. It
may be that they will lead to its destruction or they
may possibly add additional, and perhaps it may
be said, much- wanted confirmation of the general
principles laid down by those who support, and up-
hold it against an increasing number of opposing
facts. At any rate, the study of colloids when in
a state of pseudo-solution cannot fail to indicate
fresh lines of research, which may, in their general
effect, help us to understand many points which
are at present beyond our range of thought, and
experience.
It is here also, that the true relations between
dyeing and physical chemistry will become evident.
There is little doubt but that many actions which
are of but everyday interest to the dyer, and at
present almost beneath the consideration of the
physicist, will be ultimately recognised as of prime
importance, and lead to a general extension of
knowledge.
A rapid survey of the actions which make up this
most useful art will make this at once evident. The
extreme delicacy of the colour reactions, the nature
of the dyes, the extreme complexity of the problem,
which deals with the ultimate determination of the
SOLUTION AND THE PROPERTIES OF COLLOIDS 109
fibre-state, and all that this entails, indicate that
the future study of this subject cannot but have its
direct influence on the general considerations upon
which we shall ultimately base our knowledge and
theoretical speculations on the state of matter,
and the forces which influence it.
Graham divided all substances into two
classes, viz., crystalloids and amorphous substances
(colloids). We already know that this division is of
an arbitrary nature ; but in the absence of a direct
method of accurately determining the condition of
the state taken up by these units in solution, as
regards the exact condition of the dissolved sub-
stance, we are unable at present to do much more
than indicate that this division, like so many others
which were set up during the nineteenth century, is
not altogether a satisfactory one.
Crystalloids undoubtedly, when dissolved in, say,
water, change its physical properties to a marked
degree. They diminish the vapour tension, lower the
freezing-point, and raise the boiling-point. In fact,
they act as if there exists a more or less close relation-
ship between the molecules of the solution and the
solute, which modifies the normal properties of the
solvent liquid.
On the other hand, the so-called colloids do not
seem to enter into so close a relationship with the
solution system, and this seems to be confirmed by
the fact that the molecules of the latter seem to be
present in a state of higher aggregation.
Correspondingly, they exert little influence on the.
no CHEMISTRY AND PHYSICS OF DYEING
state of the solvent, for they do not materially alter
its freezing- or boiling-point or the vapour tension.
These bodies are therefore regarded more in the
light of mixtures, or suspensions than true solutions.
But all these divisions are of an arbitrary nature,
and only serve as stepping-stones on our way to a
serviceable appreciation of the true facts of the case.
They are crude, and must never be accepted as any-
thing more than the scaffolding, which will ultimately
be removed when our knowledge is more complete.
Although in some ways the relationship between
the solution and solute seems to indicate that colloids
do not enter into such close relationship with the
solution, yet it must not be lost sight of that they
persistently retain what we call " water of hydra-
tion." This, taken in conjunction with the above
facts, will indicate the extreme complexity of the
reactions which govern the relative relations between
the two systems,
(Solution + crystalloid) and (solution + colloid),
and the impossibility of our natural division being
anything more than a very incomplete and un-
satisfactory one.
Colloids when mixed with water will generally
form jellies when the proportion of colloid to
water is within certain limits. In certain cases, the
structure of these is so coarse that it maybe visible
to the eye under a low power objective. It is then
seen to consist of a more or less solid framework
through which the liquid is dispersed.
The two states in which a colloid can exist in a
SOLUTION AND THE PROPERTIES OF COLLOIDS in
solution state, using this term in its widest sense, are
termed the hydrosol state and hydrogel state respec-
tively.
In its outward condition, the former resembles
a true solution, such as a solution of sugar in water.
The latter is of the nature of a jelly, and may be
regarded as a two-phase state.
The dividing line between these two states is, in a
way, a sharp one. It has been said that the critical
point between them is as sharp as the crystallising
point of an ordinary salt, but our knowledge of this
alteration in the solution state when the one passes
into the other is very indefinite. It is difficult to
form anything like a mental picture of what goes on
during the transition stage.
This idea of the solid framework through which
the liquid is dispersed is perhaps the best, and only
one, we have before us, which may indicate the fibre
state of a silk filament at the time of dyeing. A
similar state probably exists in the case of artificial
silk under similar conditions.
In the case of other fibres our ideas of their con-
struction will be modified from time to time, as our
knowledge of their physical structure increases.
The crystalloids are capable of forming solutions
which are perfect enough to pass through the inter-
stices of these colloid jellies with considerable
freedom. This very interesting fact must be care-
fully considered in its relation to the presence of
these bodies in the dye solution, and their possible
action in dyeing. As a rn.atter of fact, the rate of
112
CHEMISTRY AND PHYSICS OF DYEING
diffusion of these bodies through gelatine or agar-
agar is practically the same as that through pure
water.
This was clearly pointed out by Voigtlander (Zeit.
/. Phys. Chem. y 1889, 3, 316), who closely studied this
question. The influence of temperature on the rate
of diffusion is very marked. An increase in tem-
perature will greatly increase the rate at which the
salt will equalise itself over the whole solution system.
When the action of temperature on dyeing is
considered, it will be seen that this action is one of
special significance.
The following table indicates the relative rate of
diffusion through agar-agar of some typical sub-
stances at different temperatures.
Substance
at o
at 20
at 40
Formic acid .
Acetic acid
472
.318
.867
.640
1.49
1.04
KHO ....
I.OI
i-75
2.36
KC1 . .
.786
1.40
2.18
On the other hand, the so-called colloids cannot
pass through jellies or membranes except at very slow
rates. It is only recently that it has been recognised
that these bodies will pass at all. Dialysis, or the
separation of colloids from crystalloids in their solu-
tions is founded on this fact, and is a process in
common use in chemical analysis.
The explanation of this action is obscure. Our
knowledge of the subject is limited, and the possi-
SOLUTION AND THE PROPERTIES OF COLLOIDS 113
bility of colloids passing through membranes is one
which deserves further attention.
Just as it is possible to prepare membranes which
are permeable to water, but which will stop the
passage of some salts (crystalloids), so at least some
colloids are capable of slowly passing through certain
membranes.
These semi-permeable membranes, which will stop
the passage of crystalloids in some cases, are natur-
ally closer in their structure than the ordinary ones.
A porous pot holding in its structure a gelatinous
precipitate of ferrocyanide of copper will act in this
way. (Proc. Chem. Soc. y lix. 344.)
It is interesting as a matter of history to note that
this passage of liquids through films (parchment
paper, bladders, &c.,) which is called osmosis, was
first noticed by Abbe Nollet in 1748.
It may be here mentioned, and it is pointed out
in fuller detail elsewhere, that in considering the
cause of this action which leads to diffusion it is not
sufficient to assume that the size of the aggregates
in solution is the only controlling factor.
The author has attempted to explain the slow
dialysis of colloids by assuming that molecular migra-
tion takes place in pseudo solutions from one aggre-
gate to the other.
This idea of molecular migration in pseudo solu-
tions is founded by analogy, on the Poisson theory of
atomic migration. It offers a possible explanation
of the mechanism of the dialysis of colloids (Dreaper,
/. S.C.I., xxiv. 223, and J.S.D. and C. y May 1905).
8
H4 CHEMISTRY AND PHYSICS OF DYEING
This migration of the individual molecules from
one complex to another may explain the slow dyeing
action, or absorption of lakes like those of alizarine
by the one-bath method, where the so-called mole-
cular weight of the aggregates is a high one ; the
"levelling up'' action in dyeing; the passing of a
solution of gun-cotton through a membrane ; and the
slow "ripening" of solutions of cellulose, or its com-
pounds, in the manufacture of artificial silk.
By assuming this action, it is possible to explain
the slow passage of large aggregates through a
membrane, or "sieve," where the direct passage
is prohibited by size.
An alternative explanation given by Prof. Ramsay
(/.5.C.J., 1904, 296) is, that the cotton molecules
may become deformed in shape, and glide through
the interstices of the membrane like worms.
If a solution of a crystalloid be separated by a
porous membrane from pure water, certain so-called
osmotic phenomena are set up, and enormous pres-
sures may result from this action.
This osmotic pressure may be measured directly,
or, more easily calculated. In the case of mineral
acids and salts the actual pressure is in excess of the
calculated results. From certain theoretical conclu-
sions Arrhenius accounts for this by assuming the
dissociation of the acid, or salt. In this way the
number of individual units in solution is increased,
and with it the pressure, or osmotic effect.
There is no generally accepted view as to the
cause of osmotic pressure.
SOLUTION AND THE PROPERTIES OF COLLOIDS 115
The dissociation theory assumes that the dis-
solved substance exists in the solution in a state, so
far equivalent to a perfect gas, that it obeys laws,
which are similar to those governing the latter.
The association theory, on the other hand,
assumes some attractive force at, work which forms
aggregates consisting of solvent and solute mole-
cules. At any rate, the phenomena of osmosis are
directly connected with the state of the solution at
the time they are exhibited, varying with the con-
dition of the solute, and its solution state. Action
at the surfaces of the membrane also seems to play
an important part in these phenomena.
The absorption of water by colloids is clearly of
the first importance to the dyer. The preliminary
operations to dyeing, apart from the question of the
colour and gloss of the fibre, and its condition during
the mechanical stages of its manufacture, are chiefly
connected with the object of presenting the fibre in
a uniform condition to the dye-bath. All foreign
substances of a nature which will defeat this end,
such as wax, grease, &c., are as far as possible
removed by alkaline, or other treatment. The
thorough wetting out of the fibre before it is brought
into the presence of mordant, or dye, is also well
understood, and its need cannot be over-estimated.
From the theoretical point of view, all these
operations are conducted with the object of equally
permeating the fibre substance with the aqueous
solutions. The result of this is to obtain a fibre
condition, corresponding more, or less, to the so-called
n6 CHEMISTRY AND PHYSICS OF DYEING
hydrogel state and as far as possible an equal state
of hydration.
A study of the way in which silicic acid gives up
its water of hydration indicates the state in which it
is held. The elimination of water by this hydrogel
is a gradual and continuous one, decreasing as the
anhydrous state is reached (Bemmelen, Zeit. Anorg.
Chem. y 13, 233).
The influence of these hydrogels on the properties
of the tl solvent " is small.
The colloids exert little or no influence on osmotic
pressure, boiling-point, freezing-point, or electrical
conductivity of the solution, and in this way differ
entirely from crystalloids.
It has been shown that solutions of these colloids
may be made to gelatinise, or enter the hydrogel state,
by the addition of small quantities of certain sub-
stances. This action is different to that shown when
a crystalloid is made to partly leave the soluble state
in a supersaturated solution, by the addition of a
crystal, or other substance. It is only local in its
effect in the case of colloids.
The hydrogels have undoubtedly the power of
absorbing foreign substances in solution. For in-
stance, metastannic acid readily absorbs hydrochloric
acid, or sodium sulphate, and, probably, many other
substances (Bemmelen and Klobbie, Zeit. Anorg.
Chem., 23, in). The concentration of the hydro-
chloric acid was often found to be greater than in the
solution. The absorption factor
K = cone, in colloid / cone. in]H,O,
SOLUTION AND THE PROPERTIES OF COLLOIDS 117
is not a constant in this case, but is dependent on the
concentration at the point of equilibrium.
A further point is that the absorption of sub-
stances is proportional to the hydration of the colloid.
This is of the greatest interest from the dyer's point
of view. It is found that silicic acid absorbs com-
pounds in the ratio of its state of hydration (Bem-
melen, /. fur Chem., 23, 324). Similar interesting
results were also obtained with SnO 2 in different
states of hydration.
SnO 2 .2-3H 2 O absorbed more acid than SnO 2 .i.2 H 2 O.
When we consider the conditions of the fibres
which give the best dyeing results, so far as dye
absorption is concerned, it will at once be seen how
closely they approximate to those which give the
highest absorption results in the cases of inorganic
hydrogels given above.
The importance also of an equal state of hydration
from the dyeing point of view is clear when we
remember that it is very desirable to obtain an even
shade, or absorption of dye. This is a necessary
condition so far as piece or yarn dyeing is concerned,
in practically all cases, although not so necessary
in dyeing loose wool, or cotton.
So that the condition of the fibre at the time of
dyeing is of the first importance, and probably the
conditions of the dye solution are unconsciously
arranged or determined by the dyer as much with
the object of obtaining a correct fibre condition, as
modifying the physical (or chemical) state of the dye
n8 CHEMISTRY AND PHYSICS OF DYEING
solution. The dyer must recognise the possible and
variable action of the fibre as well as the dye-stuff,
when the conditions of dyeing are altered.
Hydrogels, particularly those of the dioxides of
silicon, tin, magnesium, &c., can form absorption
compounds with gases and liquids, and are able by
absorption to remove acids, bases, salts, &c., from
solutions in which they are placed.
This action goes on until a state of equilibrium is
established. The state of equilibrium alters under
changed conditions of temperature, strength of solu-
tion and amount of liquid per unit of hydrogel.
The principal phenomena of absorption have been
described as follows (Bemmelen, Landw. Versuchs.
Stat., 35, 69) :
(1) When an absorbent substance gains, or loses
some of the absorbed substance, in all probability
each particle becomes equally richer, or poorer, in the
absorbed substance. In this way they differ from
chemical compounds. When the latter suffer dis-
sociation a certain number of molecules are com-
pletely decomposed, and the rest remain intact.
(2) The power of absorption is not constant, but
varies as the action goes on. The attraction for the
first portion is strong. As more is absorbed the
tendency to absorb decreases rapidly. The action
takes place more slowly. In the same way the latter
portion is given up more readily to solutions.
(3) The absorptive power of colloids varies with
their method of production, and the subsequent
treatment they are exposed to.
SOLUTION AND THE PROPERTIES OF COLLOIDS 119
(4) Hydrogels may change into ordinary chemical
hydrates acquiring a definite composition, and even
a crystalline form. In doing so they lose the power
of forming absorption compounds.
It would seem, therefore, that at, say, a higher
temperature the residual chemical attraction is more
definitely confined to the hydrate complex.
This is indicated also in the fact that the forma-
tion of a colloid compound is accompanied by the
evolution of considerably less heat than is evolved
in the formation of the corresponding crystalline
form.
(5) Increase of temperature affects the absorptive
power. It sets free a certain amount of water from
the hydrogel, and also increases the solvent action of
the water, or the substance absorbed.
Consequently the rate of absorption decreases.
(6) Every hydrogel has its own specific rate of
absorption for each acid, base, or salt. One hydrogel
may absorb acids more powerfully than it does other
substances, another one will absorb bases more
powerfully, and another salts. In general, absorp-
tion is strongest when under the circumstances the
hydrogel, and the absorbed compound can combine
chemically. An example of this action is seen
in the case of stannic acid. This absorbs a good
deal of sulphuric acid, but much more potash.
(a) The substance dissolved may be proportionately
divided between the water of the hydrogel and the
water of the solution, as in the case where potassium
chloride is absorbed by the hydrogel of silica.
120 CHEMISTRY AND PHYSICS OF DYEING
(&) The hydrogel may absorb a larger proportion
of the dissolved substance. The hydrogel of meta-
stannic acid will absorb nearly all the potash from a
solution.
This absorption may even cause decomposition
of the dissolved substance. The hydrogel of silica
will remove potash from potassium carbonate, or soda
from disodium phosphate. On shaking up the same
hydrogel with calcium carbonate and potassium chlo-
ride, there is an absorption of lime and potash, and a
corresponding amount of calcium chloride and calcium
bicarbonate remains in solution. Some potassium
chloride is also absorbed.
(7) The condition of the hydrogel and its weight
being given, the temperature also being known
and remaining constant, and the hydrogel not being
soluble in the solution, the amount of a particular
substance absorbed by it varies with the state of
concentration, and with the amount of solution.
A state of equilibrium is established between the
absorptive action of the hydrogel on the one hand,
and the opposing action of the water on the other.
If chemical decomposition also takes place, the
attraction of chemical combination takes part in
producing the equilibrium.
The stronger the solution the more of the sub-
stance is absorbed, but in decreasing quantity. The
limit is reached when after the equilibrium is estab-
lished the liquid is in a saturated condition. No
satisfactory formula can be obtained to represent
the action generally, except in very dilute solutions,
SOLUTION AND THE PROPERTIES OF COLLOIDS 121
and where the absorptive power of the colloid is weak,
when the curve obtained is practically a straight line.
(8) One crystalloid absorbed by a hydrogel may
be replaced by another.
If a hydrogel which has absorbed A be placed in a
solution of a substance B, then the solvent will dis-
solve out some of A, and at the same time some of B
will be absorbed until equilibrium is established, but
no true substitution takes place.
If the absorption quantities are small, A and B
are absorbed without mutually influencing one other
to a noticeable extent. If the quantities of A be
large, there may be a loss by substitution.
The last part of A absorbed, which is not held
so strongly, may be replaced by B.
It has been noticed, however, that by repeatedly
treating the hydrogel with solutions of B, the
latter may entirely replace A. In the event of
chemical action taking place between A and B in
solution, the action maybe greatly complicated, and
even entirely altered.
The ultimate absorption of the substance by the
hydrogel depends entirely upon the final state of the
solution.
An important statement has been made by
J. Billitzer (Zeit. Phys. Chem., 1903, 45, 307), as a
result of some experiments on the " carrying down "
of calcium, chromium, sodium and potassium chlo-
rides when they precipitate colloids. The fact seems
to be established that they act in the ratio of their
chemical equivalents in their precipitating action.
122 CHEMISTRY AND PHYSICS OF DYEING
If potassium chloride is used as the precipitating
electrolyte, acid is set free when the colloid is electro-
negative ; on the other hand, when the colloid sub-
stance is electropositive alkali is liberated.
The colloids may be divided into two classes,
according to their action, when under the influence
of a high E.M.F., and may be classified into electro-
positive and electro-negative units, as the case
may be.
The electro-negatively charged particles move to
the anode, and the electro-positive ones to the cathode.
Colloids, or suspensions, which are charged in
opposite directions will precipitate each other if
present in certain proportions.
Aniline dyes act as colloids in this respect. The
acid dyes were found to migrate towards the anode
and the basic dyes towards the cathode (Neisser
and Friedemann, Chem. Centr, 1904, i, 1387).
The coagulating effect produced on solutions of
colloids by reagents is of a complicated nature. It
does not seem possible to give any definite reason for
their action. We must content ourselves with the
recorded facts which in themselves seem very con-
tradictory ; they at least indicate the very complex
nature of the phenomena before us.
The one thing which seems certain is that electro-
lytes, or soluble salts, have the power of degrading
hydrosols into hydrogels, and that in doing so the
precipitating reagent may be partly, or wholly,
precipitated at the same time. It must, however,
be remembered that other substances will also preci-
SOLUTION AND THE PROPERTIES OF COLLOIDS 123
pitate colloids. That this action may be of a
mechanical nature is seen in the fact that if barium
sulphate is shaken up with some hydrosols, it will
carry down with it a good deal of the colloid
substance.
In other cases, we may have a soluble salt
acting in this way, and being decomposed in the
process.
J. Duclaux (Compt. rend., 1904, 138, 571) affirms
that the precipitated colloid usually contains a
certain amount of one of the radicles of the salt used
to produce coagulation, the change being produced
by simple substitution of one of its radicles for an
equivalent amount of one of the constituents of the
colloidal substance. The solution after coagulation
will contain a small amount of the radicle displaced
from the colloid. Linder and Picton's recent work
seems to support this.
It seems that in the neighbourhood of the coagu-
lating point a slight change in equilibrium will pro-
duce a much larger visible effect on the colloid,
so that the latter is easily precipitated.
The precipitation of proteid substances by acids,
copper, or silver salts is in each case a reversible one,
the precipitate dissolving in excess of the reagent.
(V. Henri and A. Meyer, Compt. Rend., 1904, 138,
757.) This is a reaction which it will be advisable to
keep before us in the study of the action of mordants
and dyes. It may be possible to explain certain
reactions in this way, which at present are more or
less obscure.
124 CHEMISTRY AND PHYSICS OF DYEING
It would follow that the composition of the fibre
might be expected to have a great influence on the
results produced in different cases.
All inorganic colloids seem to be more or less
absorbed by cotton, wool, or silk fibres. This is
stated to be quite independent of the chemical
nature of the dissolved colloid. (W. Biltz, Ber. y
I94, 37, 1766-)
It is, perhaps, not safe to argue from the
inorganic to the organic colloids so far as their
general reactions are concerned, for the inorganic
colloids seem, at best, to be present in a very degraded
state in their solutions. As has before been pointed
out, they may be carried down in a mechanical way
by such rough suspensions as barium carbonate, and
are then firmly held against resolution. Organic
colloids such as dyes are not so readily carried down,
or held, in this way.
In passing it is interesting to note that the method
of precipitation of insoluble salts in colloids like
gelatine, is of an irregular nature, so far as distribu-
tion is concerned. Liesegang noticed, for instance,
that silver chromate precipitated in situ (in capillary
tubes) by the diffusion of silver nitrate solution
into gelatine in which potassium chromate has been
dissolved, gives rise to unequal precipitation. The
silver chromate occurs in laminae at right angles to
the direction of the tube.
The relative condition-state of hydrosols and
hydrogels so far as is known, is as follows. The two
states seem to be in a way, distinct, that is to say,
SOLUTION AND THE PROPERTIES OF COLLOIDS 125
there is generally a critical point in the passage from
one state to the other which corresponds, in a rough
way, with the difference between the solid and liquid
state in ordinary substances. This statement must
only be taken in a general sense. Further knowledge
may indicate that the dividing line is an imaginary
one, but for practical purposes we may consider the
two states as distinct. Taking the hydrogel state as
consisting of a framework, more or less perfectly
developed, as the case may be, permeated by a liquid,
it may be said to be a two-phase system the frame-
work or more insoluble portion corresponding with
the solid phase, and the other with the solution state.
In this gelatinised state the water may be partly held
by capillary action. The power with which colloids
will take up moisture is immense. The molecular
forces which come into play when colloids lose
water are correspondingly great. Gelatine on drying
will strip off the surface of a containing glass vessel.
The rate at which chemical action may take place
in colloid solutions is not altered to any great
extent.
The classification of the colloids is evidently
impossible at present. It has been proposed to
divide them roughly into two classes, having res-
pectively a molecular weight either above or below
20,000. In the former we find starch (25,000), silicic
acid (49,000), and in the latter would come tannin,
dextrin, ferric hydroxide (6000).
It would seem that it is the colloids of higher
molecular weight which give non-reversible solutions
126 CHEMISTRY AND PHYSICS OF DYEING
on freezing. (Linnebarger, /. Am. Chem. Soc. 20,
1898, 375.)
Such proposed methods of separation as that of
shaking up the solution with barium sulphate hardly
deserve attention.
Until we more thoroughly realise the state in
which colloids exist in pseudo solutions, it will be
impossible to derive any satisfactory method of
classification.
There is need for a standard of solution, and
a ready method of comparison with other states.
This may either take the form of a standard solu-
tion, or a calibrated porous partition for diffusion
experiments.
A colloid which seems dry to the touch (such as
gelatine or silk) contains a considerable amount of
water, which it may lose on further drying at a
temperature of 100 C., the state of the fibre continu-
ally changing with its composition. This action, at
ordinary temperature, may be a reversible one. If a
colloid be dried so that its vapour tension is nil,
it may regain its water partially, or entirely, on
exposure to the air. This will depend on the com-
plete reversibility of the process, and will vary with
different substances and conditions.
In a closed space partially saturated with mois-
ture, a colloid loses water until its vapour tension
is equal to that of the surrounding medium.
The rapidity of dehydration constantly diminishes
until it reaches a minimum as the vapour tension
approaches that of the enclosed air. For example,
SOLUTION AND THE PROPERTIES OF COLLOIDS 127
colloidal metastannic acid containing 2.2 mols. of
water lost .55 mols. the first day. The quantity
lost decreased gradually, until on the I3th day only
.01 mol. per day was lost, and the composition was
.79 mol. OH 2 . (Bemmelen, Rec. Trav. Chim., 7, 37.)
When this process of " hydration " becomes non-
reversible, which happens when most colloids lose
water, especially when drying at a high temperature
complicates the action/the non-reversible modifications
have a diminished absorptive power, but at the same
time they retain their water with more energy. This
is an indication that the secondary chemical action
involved may be constant in its amount, varying in
intensity with the ratio of colloid to water. In the
transformation of a colloid into a true hydrate a state
of equilibrium is reached with fewer molecules of
water, with the formation of correspondingly larger
aggregates. It may undergo modification at a
suitable temperature, so that it becomes insoluble
in the medium in which it was originally dissolved.
Colloidal silica will hold more water at 50, or
even at 100, in a medium saturated with aqueous
vapour, than at 15 in dry air. (Ibid. Rec. Trav.
Chim. y 7, 69.)
The precipitating action of salts on colloids seems
to be a general one.
The idea has been put forward that the precipita-
ting action of colloids is a dehydrating one. Tomasso,
(Compt. Rendus, 99, 37) does not agree with this, some
salts, it being held, acting in the opposite direction.
Sodium acetate, sodium sulphate, potassium bromide,,
128 CHEMISTRY AND PHYSICS OF DYEING
and potassium chlorate are said to act by retarding
the dehydration of cupric hydroxide into copper
oxide. On the other hand, potassium chloride and
sodium carbonate act in the reverse direction.
All proteids (except peptone) are precipitated by a
neutral solution of ammonium sulphate. All colloids
seem to act in this way, including soap, soluble carbo-
hydrates, glycogen, &c. (Nasso, Pfliiger's Archiv.
41, 5040
This writer will not allow, however, that the
cause of the precipitation is due to the struggle for
water which takes place between the colloid and the
salt. A series of experiments tend to show that this
is not sufficient to explain the results obtained.
The presence of a salt is not necessary to preci-
pitate the colloids. Plaff, Geiger, and Pay en have
shown that separation may take place by freezing
in some cases. A colloidal solution of antimony
trisulphide (Schultz's method) is entirely separated
by freezing. On the other hand, albumen is not
separated, or, if it is, the action is a reversible one.
(Lubavin, /. Russ. Chem. Soc.,. 21, 397.)
The reduction of the freezing-point of water by
colloids is very slight. This indicates very high
figures for the molecular weights.
Gallic and tannic acids are said by Paterno (Zeit.
Phys. Chem. 4, 457) to show a very high molecular
weight. When dissolved in acetic acid they are said
to give normal results. This is, however, denied by
Sabaneeff (/. Rus. Chem. Soc., 22, 102).
The state of egg albumen (15 per cent, sol.) is
SOLUTION AND THE PROPERTIES OF COLLOIDS 129
said by this investigator to correspond with a mole-
cular weight of 15,000.
On the other hand, Gladstone and Hibbert (Phil.
Mag., 26, 38) obtained results by Raoult's method,
which indicate a molecular weight of 2000.
Guthrie's original statement that colloids do not
influence the boiling-point (or freezing-point) of
water, or in other words, that the tension of aqueous
vapour of solutions of colloids equals that of water,
is not correct. Gelatine, for instance, is said to raise
the boiling-point.
The student is referred to the work done by
Morris (Trans. Chem. Soc. 1888, 610, and 1889, 466),
which indirectly is of interest to those engaged in
the study of the absorption of dyes.
Hydrolysis in solution certainly seems to take
place in many cases. For example, potassium
cyanide is partially decomposed into KHO and HCN
in aqueous solution (Shields, Phil. Mag., (5) 35, 365).
The action of water in producing this effect is called
hydrolysis.
Probably all salts are hydrolysed in aqueous
solution, but in many cases to an exceedingly
small extent.
Esters as well as salts are hydrolysed. Methyl
and ethyl acetates are decomposed into acetic acid
and the corresponding alcohol. The extent to which
hydrolysis takes place is regulated by mass action.
Veley (/.C.S., 1905, 26) considers that the de-
composition of ammonium salts on boiling is due to
hydrolysis, and not dissociation.
9
130 CHEMISTRY AND PHYSICS OF DYEING
The cases where hydrolysis is possible are said
to be :
(1) Salts from weak bases and strong acids.
(2) Salts from strong base and weak acid.
(3) Salts from weak base and weak acid.
It would therefore seem to be a function of an
unequal atomic bond, and this confirms the above
theory of association rather than dissociation, when
the actual reaction between the water molecules and
the solute is considered. For instance,
KCN + H 2 ^ HCN + KHO.
The laws for electrical conductivity in the above
cases are stated to be
, , C (acid) x C (base) v
~C~(salt)~
and in the case of (3)
C (acid) x C (base) K
C 2 (salt)
In (i) the amount of the action is stated to depend
on dilution. In (2) it is independent of dilution
beyond a certain limiting value. In (3) hydrolysis
is nil, or inappreciable.*
The influence of the dissociation of dyes in
solution has been discussed by Vignon (Bull. Soc.
Ind. de Mulh. 1893, 407 and J.S.D. and C. 1893, 44).
* For further information on this subject the following may be
consulted Walker: Zeit. Phys. Chem., 1889, 4, 319; Arrhenius
(ibid.) 1894, 13, 407, and Van't Hoff, Chemische Dynamik,
(1898) 121-126.
SOLUTION AND THE PROPERTIES OF COLLOIDS 131
From this point of view the three factors influ-
encing the action of dyeing would be :
(1) The absorbent fibre ;
(2) The dye-stuff ;
(3) The solvent ;
an equilibrium being established and determined
by chemical forces, and the conditions of dissocia-
tion, resulting in any case in the dye effect
observed.
This matter has been further studied in greater
detail by Knecht (J.S.D. and C. 1898, 59 ; 1903, 158 ;
r 94, 59);
Diamine sky blue, for instance, is said to dis-
sociate quite as readily as any basic dye, when tested
by the filter-paper method.
On the other hand, the sulphonated basic dyes like
acid green, or acid violet, show no dissociation by the
above test. These results are said to correspond very
closely with the dyeing effects of these dyes on wool.
The alcoholic solutions of these dyes do not show
dissociation by this test. They have also no dyeing
power on wool. It will be noticed, however, that
the possible difference in the action of alcohol and
water on the fibres themselves is disregarded.
The halo formed on paper by this method with
magenta can be prevented if hydrochloric acid is
present in the free state. Correspondingly, wool will
not dye in the same acid solution of the dye, and
this reagent may act by preventing the dissociation
effect in both cases.
Acid colours will show this separation of the
132 CHEMISTRY AND PHYSICS OF DYEING
colour acid (on acidifying the dye solution), but
as a general rule they will give no halo in neutral
solutions.
The colour acids are insoluble when compared
with their sodium salts. They are, therefore, prob-
ably in a state of high aggregation, and in this mole-
cular condition would be more under the influence
of surface action. This must not be overlooked.
It will be noticed that the influence of the solution
state on the rate of dyeing may be a very important
factor. Dyes may be attracted by the fibres from
some solutions, and not from others. They may
also be removed from the fibre in some cases by the
second solvent, in which they are more soluble.
That the presence of moisture is necessary in
order that the action may be complete seems to be
confirmed by the recorded fact that better results
are obtained by the use of very moist steam in fixing
direct cotton dyes on cotton after printing. (Wilhelm,
Proc. Soc. Ind. de Mulh. 1904.) The dyes would seem
to require a certain amount of steam (moisture)
to fix them under these conditions.
The exact cause of this action is unknown. The
increased hydration of the fibre may play some part
in the reaction.
Some experiments on the absorption of rhodamine
base from solution in benzene are also of interest
(Weber, Farb. Zeit. 1899, i). They indicate that a
highly hydrated fibre state is not necessary for the
" dyeing " to take place in this case. Cotton fibre
will absorb the base from this solution, but the
SOLUTION AND THE PROPERTIES OF COLLOIDS 133
resulting shade is not very fast against washing,
indicating that it is imperfectly fixed in the fibre
substance.
In the same way, precipitated cellulose, which is
in a more highly hydrated form, will dye more readily
than the original cotton with some dyes. They are
also faster against washing. It must be remembered
in connection with this subject that mercerised
cotton will give a darker shade with the same per-
centage of dye.
It may be argued that the increased absorp-
tion is due to the greater number of OH groups
present in the cellulose molecule, or aggregate. In
connection with this it may be noted that the
cellulose tetracetate, which is very resistant to any
ordinary hydrating action of water, as tested by its
physical properties, will not take up dyes under
these conditions.
It has been stated that alizarine lakes, which are
soluble in alcohol-ether, are readily dyed on cotton
from such a solution. If this is so, the matter is one
of interest, on which the writer hopes to give
further details later. It is difficult to see how
dyeing can be due to chemical action in this case.
It is possible that light may be thrown on the
subject of , the colloid state by the study of the
mutual solubility of liquids. J. P. Kuenen (Phil.
Mag. ,6, 1903, 651) expresses the opinion that
in these mixtures and at the point of satura-
tion, the molecular conditions set up, which may
probably be represented by a high molecular
134 CHEMISTRY AND PHYSICS OF DYEING
attraction, make it impossible for the solvent
to dissolve more than a limited amount of the
solute, or second substance, without entering upon
an unstable condition. If this is so with par-
tially miscible liquids, the same should apply to
pseudo-solutions. Beyond the point of saturation
the solute will be in a state of abnormal aggrega-
tion.
As has been pointed out by F. G. Donnan (Phil.
Mag. 6, vol. i. 647), we have to account for the fact
that a solid substance C, when brought in contact
with certain liquid media, breaks up, or disintegrates
into these media, but in such a manner that the dis-
integrating process does not proceed to the mole-
cular limit.
The liquid medium seems to be interspersed with
minute aggregates of C, which are still so much
larger than their molecular magnitudes, that they
are subjected to almost statistically uniform
bombardment. These complexes are such that
changes of temperature, or the addition of compara-
tively small quantities of other substances frequently
cause the sudden precipitation in mass of the sub-
stance C.
This view of the case may be regarded, if we may
use the term, as a very mechanical one. No provi-
sion is made for the possible arrangement of the
system into aggregates which are made up of mole-
cules of both solvent and solute such as we undoubt-
edly get in mixtures of alcohol and water, and in
many other cases.
SOLUTION AND THE PROPERTIES OF COLLOIDS 135
The first investigator to study the solution state
of the " direct " or cotton dyes was Picton (/.C. Soc.
1892, 148). He made use of certain tests to establish
the state of different solutions, and with them tested
an aqueous solution of Congo red.
Tyndall had noticed that light is polarised by its
passage through colloidal solutions. Congo red,
which dissolves easily in water, was found under
these conditions to give a well-marked polarised
beam.
Filtered under pressure for two hours through a
porous cell, the same solution passed through practi-
cally colourless. A slow diffusion experiment gave
a similar result.
The molecular aggregation in aqueous solution
of these dyes is also given by Krafft (Ber. 1899,
1608) as follows :
Benzopurpurin . 3000 . . 724 (normal calculation)
Diamine Blue . 3430 . . 999 ,,
The following figures are given for
Rosaniline hydrochloride (mol. wt. 337)
In alcohol . . . 330, 325, 343
In water . . . 520, 589, 617
Methyl Violet (mol. wt. 407)
In alcohol . . . 403.5, 421.1-
In water . . . 804.5, 838.7, 870.4
Methylene Blue (mol. wt. 319.8)
In alcohol . . . 321.4, 342.7
In water . . . 321.2, 492.4, 530.5
Tannic Acid (mol. wt. 322)
In water . . . 1587
Picton (ibid.} further pointed out that the degree
136 CHEMISTRY AND PHYSICS OF DYEING
of aggregation in the case of Congo red varied with
its state. An alkaline solution of this dye filtered
readily, but the dye would not pass through the
porous material in either the acid, or neutral state.
The " equalising " action of alkali when dyeing with
these colours may be explained on these lines.
It was also shown that Magdala red was not
present in such a state of aggregation in aqueous
solution, but would pass through the filter in neutral
or acid solutions.
With a solution of silicic acid the aggregates
were smaller than in the case of Congo Red, for they
neither polarised light, nor failed to pass through
the filter.
There are indications that the state of aggregation
may be greatly in excess of that indicated by Krafft
with the direct dyes.
It is interesting to note that there is certain
evidence to be gained from some experiments on the
effect of low temperature on dyes, that their solution
state is different to the solid one. It has been shown
that the effect of low temperature on the colour of
dyes in the solid state or when dyed on fibres is
nil. On the other hand, when in alcoholic solution
some of them alter altogether, while others do not.
This is a subject which is worthy of further study,
both from the point of dyeing and from that of
solution.
In the same way it is well known that the optical
properties of substances are modified by the nature
of the solvent. For instance, laevo-rotatory oil of
SOLUTION AND THE PROPERTIES OF COLLOIDS 137
turpentine (37.01 specific rotation) in 10 per cent,
solutions gave the following results (Walker) :
Solvent. Specific rotation.
Alcohol .... 38.49
Benzene . . . 39-45
Acetic acid . . . 40.22
It is clearly difficult exactly to define the nature
of a solution of a colloid, but information on this
point is being rapidly extended.
It has been stated by Henri and Mayer (Compt.
Rend. 57, 34) that, when solutions of aniline colours
are examined ultra-microscopically, they exhibit true
colloidal properties.
Some work by these same investigators on the
action of the /3-rays of radium on solution of colloids
is of interest. The solutions were exposed to the
action of these rays for five days. Magdala red,
methyl violet, and ferric hydroxide (positive) were
decomposed.
On the other hand, solutions of aniline blue
and some other negative solutions were unaltered.
The action is said to be due to the negative
charges of the /3-rays discharging the positively
charged colloids.
The stability of solutions of colloids may, in a
way, be estimated by their resistance to centrifugal
action. For instance, Franklin and Freudenberger
have shown that colloidal solutions of platinum black
and Prussian blue were completely separated at a
high speed from the solution. The cause of this
was attributed to supersaturation effects due
138 CHEMISTRY AND PHYSICS OF DYEING
to high acceleration of gravity (Elect. Rev. y vol. 47,
508). vSuch results indicate, within certain limits,
the relations which exist between the solvent and
solute in these special cases. The conception that the
precipitation is due to supersaturation effects is also
interesting, when it is remembered that the same
idea has been put forward to explain the action of
dyeing, the results in the latter case being attributed
to surface concentration effects.
Otto Weber (Chemistry of India Rubber, page 69)
contends that the term colloid should only be applied
to compounds, the solutions of which under all
conditions and in whatever solvents, behave as
colloids, and which in their solutions fully maintain
this character through all chemical changes.
As an absolute definition this may be satisfactory,
but from a practical point of view it is not so unless
we classify the substances as follows :
(1) Colloids (as Otto Weber's definition).
(2) Pseudo-colloids (substances which enter into
pseudo-solutions in some solvents and solutions in
others).
(3) Crystalloids (substances which behave with
water as perfect solutions).
It will be seen that on similar lines no substance
should be called a crystalloid unless it is perfectly
soluble in all solvents, and in these solutions
fully maintains this character through all chemical
changes.
Such definitions, with our present knowledge, are
perhaps out of place. The chief thing the dyer has
SOLUTION AND THE PROPERTIES OF COLLOIDS 139
to realise is the possibility of the solution state vary-
ing in the dye and mordant baths, the results
which may be expected to follow from these changes,
and their influence on the rate of absorption by the
fibres introduced into these baths in the ordinary
course of dyeing. Also that the state of solution
may be varied by corresponding variations in the
physical state of the dye liquor brought about by
altered temperature, concentration, or by the addition
of third substances (assistants, &c.) to the bath.
It is not advisable, perhaps, in a book devoted to the
subject of dyeing from a more or less practical point of
view, to dwell too closely on the theory of the constitu-
tion of colloids like cellulose, and their solution state.
This work is of great interest from a purely theoretical
point of view, and may ultimately influence the
practical side of the question. It is too far-reaching,
and perhaps at the present time too indefinite, to
be considered here. That such ideas should ever have
been put forward is, however, a sign that the future
theories which will be brought forward to explain
general reactions, may not be of a simple nature, but
will emphasise the extremely complex nature of the
reactions which make up some of our seemingly
simple, and everyday operations in the dyehouse.
CHAPTER VII
PHYSICAL ACTION AND SOLID SOLUTION
THE study of dyeing from the physical point of view
has served a purpose. The discussion of the subject
has been widened, and much experimental work
undertaken as a natural consequence.
In early days, as mentioned in chap, i., such
investigators as Hellot and Le Pileur d'Apligny,
with the support of Macquer, Berthollet, Bergman
and Chevreul, favoured a purely mechanical basis
for the actions involved.
Hellot in the year 1734 attributed to the pores
of the wool fibre the power of opening and closing,
and assumed that the dye particles lodged in these
interstices. The astringent substances, which took
part in the dyeing operations, were supposed to
form a coating over the colour particles so fixed.
A colour not protected in this way was assumed to
be fugitive.
The " invisible mechanics of dyeing " was due to
the opening of the pores in the fibre, the deposition
of the dye particles therein, and the subesquent action
of a material or cement, which held the particles in
their place. He likened the general action to the
PHYSICAL ACTION AND SOLID SOLUTION 141
very mechanical process of fixing a diamond in the
bezel of a ring. The hot water opened the pores,
the tiny atoms of dye entered, and the, tartar
and subsequent cooling completed the operation.
He also suggested that if only the correct astrin-
gent could be found for the fugitive colours, they,
too, would be fast. As it was they remained on the
surface of the fibre, or were imperfectly fixed in its
substance.
Le Pileur d' Apligny subsequently lent his support
to this theory, and extended it to other fibres, such
as silk, cotton, flax, &c., holding that the mechanical
state of the different fibres accounted for the varia-
tion in their dyeing properties. Wool, said he, was
composed of a number of individual hairs containing
a marrow, or fatty substance. These fibres, in fact,
were pipes perforated through their whole length, and
laterally, with an infinitude of orifices. By these the
foreign substances were admitted to the central
cavity, after the removal of this marrow. In this
way he claimed that wool was the most porous of all
fibres, and is, therefore, the most easily dyed, and at
the same time absorbs a relatively large proportion
of dye substance.
Silk he considered to be only dried animal jelly,
which in its natural drying only produces pores and
inequalities on its surface. These only admit colours
in a dilute form, and with great difficulty. iThus,
said he, silk is the most difficult fibre to dye, and
cotton stands half way between wool and silk. In
trying to follow his arguments it is necessary to
142 CHEMISTRY AND PHYSICS OF DYEING
remember the conditions under which he worked,
and the dyes at his command.
In this way it was assumed that dyeing was
purely a mechanical process. Wool might be dyed a
scarlet colour, cotton remain colourless, and silk only
take a dirty hue. He contended that the cochineal
tin lake particles were too large to enter the cotton,
or silk fibres, but that they would readily enter the
wool pores. Silk admitted the impurities because
they were simple (soluble ?).
He further pointed out that this varying action
might come into play even in the same fibre.
For instance, the condition of the fibre as regards
weaving and spinning might influence the result. In
this way he explained the incomplete dyeing in the
interior of wool dyed with this scarlet lake, as com-
pared with goods alumed before dyeing. This ultra-
mechanical theory passed from the hands of these
two early experimenters in a highly developed state,
and little seems to have been done in adding to, or
elaborating it until one hundred years later.
At this point, and under the altered conditions of
dyeing, the additional knowledge of the fibres, and
general science, Walter Crum published some further
work on this subject (J.C.S. 16. i. 404). This in-
vestigator seems to have been profoundly impressed
by the work of De Saussure, on the absorption of
different substances and gases by charcoal, and he
came to the conclusion that several of the opera-
tions in dyeing were due to the capillary action
described by this chemist, thus introducing a new
PHYSICAL ACTION AND SOLID SOLUTION 143
refinement into the theory at the end of this long
interval of time. He also based his application of
this theory to the dyeing of fibres, on the physio-
logical work of Thompson and Bauer. Their work
introduced the microscope in the study of fibres, and
thus established a fresh method of examination. As
the result of their investigation they set forth the
idea that the vegetable fibres were glass-like tubes.
After the ripening of the fibre, the central orifice,
owing to the flattening of the fibre, presented the
aspect of two separate tubes.
This next step in the mechanical theory was the
result of four experimenters' work, and to the re-
search student in dyeing this affords a simple yet
satisfactory example of the possible influence of
one worker's results on those of others.
Crum held that mordants are decomposed in the
interior of these tubes, having entered by the lateral
openings ; the oxide being set free in these narrow
passages is effectually held in position. When,
therefore, the washed cotton passed into the madder
bath, the mordant and dye combined chemically to
form the dye lake. This investigator explained the
fixings of the oxide to the fibre in the following way.
A natural decomposition of the mordant solution
took place " just as it would be decomposed in similar
circumstances without the intervention of the
cotton." He speaks also of sacs in the fibre sub-
stance lined by metallic oxides. The arguments he
based these theoretical conclusions on may be summed
up as follows :
144 CHEMISTRY AND PHYSICS OF DYEING
(i) If it is assumed that the mordant enters into
chemical combination with the fibre, it must lead to
its disintegration. He removed the mordant from
the fibre by chemical means, and found that this
was not the case.
(2) Under the microscope the colour is distributed
on the internal sides of the tubes.
(3) The dyeing of indigo blue supports the idea
that there is no chemical combination in the proper
sense of the word between the fibre and the dye, when
the nature of the reaction is considered.
Whatever may be the ultimate place assigned to
these theoretical considerations, this investigator
introduced a new method, of examination, viz.,
comparison of the physical properties of the fibres
by the aid of the microscope before and after dyeing.
Again we have a long interval before these
ideas were directly attacked, and disproved in
some details. De Mosenthal has recently shown
(/.S.C.I. 23, 292) Crum's idea that the cotton
fibre is dyed by capillary action to be incorrect.
Single cotton fibres exhibit no capillary action.
Several fibres must be in contact for the liquid
to rise. Crum's idea that the cuticle is non-porous
is also incorrect. It is very porous. These ex-
periments are calculated to modify our ideas on
the action of dyes on the cotton fibre, and to throw
us back to the ideas advocated in the eighteenth
century as to the physical nature of the cotton
fibre.
We now consider in detail the many arguments
PHYSICAL ACTION AND SOLID SOLUTION 145
and experiments brought forward in favour of a
simple mechanical theory.
It was pointed out many years ago that neutral
niters, such as sand in layers, will remove colouring-
matters and salts from solutions. Here we have
large surfaces of such an inert substance as fused
silica retaining, in some way, or other, notable quanti-
ties of salts, coloured or otherwise. This filtering
action must undoubtedly be intimately connected
with surface action.
We pass on to the careful work of Mills and
Hamilton (f.S.C.I. 1889, 263), dealing with the
action of mixed colours on wool and their relative
absorption by the fibre.
The colours chosen were Victoria Blue 4 R and
berberine hydrochloride. The conditions of experi-
menting were exact. The temperature chosen might
.have been higher than 40 C. The authors indicate
that different results might have been obtained at
95. The result arrived at is expressed in the
following rule: " The proportion of blue to yellow
deposited in the fibre is the same as that in which
they existed in the vat before dyeing."
That is to say, the shade of the mixture in the
dye-bath remained the same as that which existed
in the vat before dyeing. The shade of the dye-
bath was tested by the detached colorimeter (Phil.
Mag. 1879, 437).
With varying quantities of the colours it was
found that the total quantity of colouring-matter
deposited on the fibre is least when the weights of
zo
146 CHEMISTRY AND PHYSICS OF DYEING
the blue and yellow are equal, and that it becomes
greater as the disparity between the weights in-
creases. The simple mathematical treatment of
finding an equation for each of the dyes separately
was adopted. The equation was of the following
order :
8x
y = a +
i - T*
y being the reciprocal (= 5) of the total constant
quantity (.2) of dye-stuff taken as a reagent, and /3
and a constants of attraction and other conditions.
The constant a represents an attraction not directly
due to the dyeing process as such, x is the weight of
the colour taken, y the weight of the colour de-
posited on the fibre.
The conclusions arrived at from these equations
are that in the case of dyeing wool with mixed solu-
tions of these dye-stuffs, there is deposited at first a
certain small amount of dye-stuff (x) irrespective of
the amount of each dye-stuff taken, and then the
dye-stuff taken up is proportional to its own mass,
and inversely proportional to the mass of the other
colours.
The mechanical theory also receives the support
of L. Hwass (Farb. Zeit. 1890-1, 224) ; von Prager
(ibid. 356), and Spon (J. S.C.I. 1893, 559).
The assumption is made that the dye-stuff is the
same in the fibre as in the free state, for it may be
diazotised and combined with phenols and amines to
form azo dye-stuffs. The writer of this book pointed
out that this is not so in all cases, or at any rate,
PHYSICAL ACTION AND SOLID SOLUTION 147
the " developing " of some colours on silk is exceed-
ingly slow; therefore, when Mohlau (Zeit. Ang.
Chem. 1893, 225) shows that sand will " dye " with
naphthol azo colours which are insoluble in water,
the case for a mechanical theory is on this point
made out. The dye is said by this investigator to
enter the pores of the silica. The dyeing method
is as follows :
(1) Dyeing with /3-naphthol dissolved in NaHO.
(2) Diazobenzene chloride added to this solution
after sand has been worked in it.
Asbestos, in the same way as sand, will dye in
solutions of some colours (Spon, Dingl. Polyt. f.
1893, 287).
It has been noticed by Pokorng (Bull. Soc. Ind.
Mulh. 1893, 282), that wool and silk are able to
attract from aqueous suspension certain insoluble
amines. All that is necessary is that they shall be
present in a state of fine division. Naphthylamine
dissolved in a small quantity of alcohol and poured
into water will impregnate wool if left overnight.
This matter will be further discussed elsewhere.
The fact that many colours " rub off " is held
to be in favour of the mechanical theory, it being
assumed that this is an indication that the colours
are not in chemical combination with the fibre.
The influence of temperature on dyeing action
is a very important factor, and may indicate the
nature of the reactions which take place in the
dye-bath. Chemical action, generally speaking, was
calculated by Hood (Phil. Mag. May. 1878), from
148 CHEMISTRY AND PHYSICS OF DYEING
data obtained from Harcourt and Esson, to be pro-
portional to the square of the temperature.
The results obtained by Mills and Rennie (f.S.C.I.
3, 215,) by experimenting with wool, and dyeing
with rosaniline acetate, will be remembered (see
page 99).
The results then obtained may be tabulated as
follows :
Temperature of dyeing. Result.
i.i6C. . . No colour deposited
3i.nC. . . Maximum colour deposited
8i.i5C. .. Very little deposited
ioo.oC. '.. Fair amount deposited
Hood's law is not obeyed here. The reversal
of action above the comparatively low temperature
of 31 C. may be due to the increasing solubility of
the dye in aqueous solution.
The reverse action above 80 C. may be due to
the fact that basic dyes undergo some change above
this temperature.
It is stated that somewhere about the boiling
temperature rosaniline salts are dissociated. In
weak solutions the colour is entirely destroyed if
adequate time be allowed for this action (/.C.5. 35,
38). In practical dyeing with these colours very
slight excess of colour should be used, and the
temperature kept about 4O-5o.
The action of direct dyes on cotton, which has
been a difficulty in the way of a chemical theory,
has been studied in more or less detail by Gnehm
and Kauffler (Zeit. Ang, Chew, 1902, 15, 345).
PHYSICAL ACTION AND SOLID SOLUTION 149
The barium salt of benzopurpurin dyes without
decomposition, and a similar result is obtained
with the sodium salt. The free acid seems to dye
equally well when a time allowance is made for the
decreased solubility of the same in water. Similar
results were obtained in the case of benzoazurin,
which contains no amido groups, and, therefore,
cannot form a salt with cellulose.
A hank of cotton dyed with benzopurpurin
(sodium salt) will on prolonged boiling with a
similar but undyed skein, give up its dye until an
equilibrium of colour is obtained on both skeins.
The action of acids on Congo Red dyed on cotton
is said to indicate that the dye is present in
the free state, and not combined with the fibre.
Weber stated that the cellular cotton absorbed
the hot solution of the dye, and that on cooling the
skein the dye was precipitated. This is, of course,
the idea of some of the early investigators. If this
method of argument is correct, the action of acid
proves equally well that the dye is free in the case
of silk dyeing, for the same effect is noticed there
with this dye. It is interesting to note that the
natural moisture in the cotton fibre is said to be
essential to colour-production. If this is removed
(by alcohol) the colours are dirty and dull. It
will be remembered that drying does not seem to
produce this effect. The idea that the benzidine
or direct colours dye because their rate of diffu-
sion is less, is supported by the same authority.
Croceine 3 B will not dye cotton, but its barium
150 CHEMISTRY AND PHYSICS OF DYEING
salt will do so. Fairly dark shades are produced
even after washing. The rate of diffusion is said
to be greatly retarded in this case.
In 1894 (J.S.C.1. 13. 95) I assumed a mechanico-
chemical theory of dyeing to be the correct one, a
theory which depended primarily on a diffusion pro-
cess obeying a modified form of the general laws of
osmosis as then stated, supplemented by a chemical
reaction or series of chemical reactions between
the fibre and the dye, Fick's law being held to
govern the introduction of the colour to the fibre.
Zacharias (Farb. Zeit. 1901, 1149) also brings this to
notice, and seems to favour it.
As I then pointed out, Fick's law had been verified
for gelatine and agar-agar solutions. In the case
of animal membranes a retarding action was noticed
and the results obtained here were roughly one
half those obtained by the purely osmotic pressure.
The flow of the dissolved substance was hindered,
but not stopped, by the organised nature of the
membrane.
The possible influence of dissociation on the action
of dyes in solution must be considered. Briefly, the
condition of electrolysis in solution has been stated
as follows.
Neutral salts, as a general rule, are strongly dis-
sociated in aqueous "solutions. In dilute solutions
it is held that they are entirely dissociated.
The salts of the alkalies are very readily dis-
sociated. The acids vary in their degree of dis-
sociation. Their acid properties seem to be due to
PHYSICAL ACTION AND SOLID SOLUTION 151
the hydrogen ions. The strongest acids are those
which are most completely dissociated.
Water itself is dissociated to a small extent, so
that it can act as an extremely weak acid or base,
as the case may be. Thus, Walker has shown that
when hydrochloric acid is added to a solution con-
taining urea, the acid divided itself between the
water and the base.
Dissociation of dyes may possibly take place
in dye solutions of the ordinary strength.
Magenta is dissociated in water and alcohol.
The experiments of Fischer and Schmidner with
strips of blotting-paper are well known. They
show the dissociation of double salts, the salts rising
according to their relative rates of diffusion. It
has been shown (v. Georgievics) that with magenta,
twenty times the amount of chlorine necessary for
the magenta base diffused in this way. The exa-
mination of the electrical conductivity of magenta
solutions leads to the same conclusions (Miolati,
Ber. 26, 1788), viz., that dissociation takes place in
aqueous solutions.
It has been pointed out by Silbermann (Chem.
Zeit. 19, 1683), that in any specific series of dye-
stuffs, increase in molecular weight is accompanied
by decreased solubility, and it is stated that the
rate of absorption of the dye is correspondingly
decreased. Assuming that high molecular weight
means high molecular volume, the dyes will take
longer to diffuse between the intermolecular spaces
of the fibre and longer to leave it also.
152 CHEMISTRY AND PHYSICS OF DYEING
This does not seem to be the case with the
primuline colours (Dreaper, J.S.C.I. 1894, 95). It
may be, however, that the fact that the heavier
dyes take longer to diffuse, indicates that in practice
they are fixed in greater proportions on the external
area of the fibres. This might confuse and obscure
the real nature of the reaction, so far as pure absorp-
tion results are concerned.
Hallitt (J.S.D. and C. 15, 30) has made a num-
ber of interesting experiments with the object of
explaining the action of sodium sulphate in the
dyeing of wool. The ideas in vogue when he wrote his
paper were expressed in the "Manual of Dyeing"
as follows :
(1) That the raising of the temperature in dyeing
by the addition of the sulphate increased the dyeing
effect.
(2) The sulphate keeps the dye in a fine state of
suspension.
(3) Bisulphate is formed with the H 2 SO 4 , and
as a consequence the dye is not so rapidly trans-
ferred to the fibre.
The fact that 100 per cent, on the weight of
wool of sulphate of soda will only raise the boiling-
point .75C. shows that the effect on temperature of
the bath may be neglected in practice. It may be
mentioned in passing that we have no knowledge of
the effect of increased temperature on dyeing above
100 C. Hallitt does not consider that the sulphate
acts by keeping the dye in a fine state of suspension.
He points out that acid colours are more easily
PHYSICAL ACTION AND SOLID SOLUTION 153
stripped off wool by sodium sulphate than by either
water or sulphuric acid.
Yarn boiled for ten minutes in the following
solutions after being dyed with Carmoisine B. lost
the following amounts of dye.
Solution. Colour extracted.
Water 15 % of total present.
5 per cent. H 2 SO 4 . . .18
50 Na,SO 4 . . 4.40
50 NaCl. . . 2.40
The percentage of substances added is on the
weight of yarn, and the proportion of yarn to liquor
is 1/50.
In some cases the stripping of the colour goes on
beyond the point of saturation of the dye in the
solution. This remarkable result is seen when dark
shades of indigo extract on wool are treated in this
way. The dye may be partly thrown out of solu-
tion as a precipitate.
It is noticed, too, that an amount of sodium
sulphate in excess of that required to form the
bisulphate still acts, and will influence the dyeing.
Uneven skeins, where the dye is in patches, will
equalise, if boiled with a solution of sodium sul-
phate. This equalising action is seen when Palatine
Red A is dyed with
(a) 6.8 per cent. HC1.
(b) 6.8 per cent. HC1. + 20 per cent. Na 2 SO 4 (cryst.)
The first solution gives a very uneven result,
and the second an even one on wool fibre. .
In considering these experiments with wool where
154 CHEMISTRY AND PHYSICS OF DYEING
the dyeing occupies some time at the boil, it is as
well to remember that the wool has an absorbing
action on the acid. Knecht found that if 5 per cent.
of acid was present in the bath at the beginning of
an experiment, only 1.5 per cent, remained in solu-
tion at the end of the dyeing (J.S.D. and C. 1888,
105). These experiments are said to indicate that the
action of dyeing is equivalent to chemical action
in dilute solutions.
From this point of view, the point of equilibrium
between the amount of dye in the solution and on
the fibre is a movable one. The addition of acid
increases the amounts fixed on the fibre, while the
addition of sodium sulphate has the opposite effect.
The effect produced by either of these additions
varies with different colours.
When hydrochloric acid and sodium sulphate
are in solution together, we can express the reaction
between them as follows :
2HC1 + Na 2 S0 4 ^ H 2 SO 4 + 2NaCl.
ByGuldberg andWaage's law of chemical action
we know that the velocity of change at any moment
varies directly as the product of the number of
equivalents of the factors of change present in unit
volume of the medium of change.
The result arrived at is, that the even dyeing of
any acid is proportional to its acidic intensity.
An exception has to be made in the case of
sulphuric acid, which gives abnormal results. The
intensity values of acids are as follows :
PHYSICAL ACTION AND SOLID SOLUTION 155
Nitric acid
Hydrochloric acid
Sulphuric acid
Oxalic acid .
Citric acid
Acetic acid
i.oo
i.oo
49
.24
05
03
Taking values from this table, and with quanti-
ties of acids representing equal intensities, we obtain
the following results, one per cent, of Palatine Red
being used in each case.
Acid in dye bath.
6.84 per cent, hydrochloric acid
15.62 ,, oxalic acid
6.12 sulphuric acid
477.6 ,, acetic acid
Colour left in bath.
.13 per cent.
.15
.90
Here we have a fairly close agreement, if we
except the case of sulphuric acid.
A possible reason for this action is that the wool
removes an abnormal amount of sulphuric acid
from the solution. The following results seem to show
this is the case.
Per cent, of acid
Proportion of free acid Proportion of colour
present.
left in solution. left in solution.
11.4 HC1.
36.4
.08
5.0 HS0 4
26.6
.90
6.1 oxalic acid
35-5
30
23.8 acetic acid
60.0
5-25
A much smaller proportion of sulphuric acid is
left in the solution. This action, therefore, may be
156 CHEMISTRY AND PHYSICS OF DYEING
due to greatly . decreased mass action. The chief
action of acids has been said to be on the wool fibre
itself. Knecht has shown that wool treated with
acid and washed to neutrality, dyes well in a
neutral solution of colour acid.
This matter is not, however, clear. If the sul-
phuric acid is taken up in abnormal quantities, it
would follow that the fibre is more acted on in this
case, and, therefore, other things being equal, the
dyeing should be more complete.
It is clear, at any rate, that the direct action
of the acid is modified in some way by the
presence of sodium sulphate or sodium chloride.
Sodium sulphate is one of the products of the direct
change which takes place between colour acid and
salt, and by largely increasing its mass in the solu-
tion by direct addition, the point of equilibrium is
pushed back, and more free acid remains in solution.
Therefore, by the addition of sulphate the dye
is stripped from the fibre. The facts seem to be in
accordance with the laws of equilibrium.
_The colour acids of Scarlet 2R and Orange G will
dye wool very feebly. In fact, they are said hardly
to stain the fibre at all, and in the former case not
so deeply as its sodium salt.
An addition of 3 per cent, sulphuric acid will
drive on a large proportion of these dyes, and 3 per
qent. hydrochloric acid will exhaust the bath.
With Cardinal red the colour acid gives a better
result. In this case about half the dye goes on to
the fibre without the addition of any acid.
PHYSICAL ACTION AND SOLID SOLUTION 157
This research, which is clearly of interest to the
wool dyer, is also of equal interest in other ways.
It is an example of the work that might be done in
our dyeing colleges if some definite scheme for
technical research was adopted. - ;
The effect of varying temperatures of the dye-
bath may be mentioned here.
We have seen the extreme importance of tem-
perature in mordanting, and how this varies with
the fibre. Silk and cotton give the greatest effect
in the cold (except when tannic acid is used as
mordant).
The dehydrating effect of a high temperature
in dyeing on some mordants may even prevent the
formation of a lake, as has been pointed out in
dyeing cotton with alizarine; and every dyer ex-
perienced in dyeing alizarine on alumed silk will
have noticed the same effect.
The action of tannic acid on animal fibres and
substances generally is an important one. There
are dye-houses in the south of France, and else-
where, entirely devoted to dyeing silk black with
tannin extracts on mordants. Before the intro-
duction of the direct dyes tannic acid was very
largely used in mordanting cotton for basic colours.
Its action in the case of tanning leather is well
known. The tannin is said to combine with the
material, reducing its permeability by water and
modifying it in other ways.
A similar action is noticed with silk. Gallic acid
is not absorbed jto the same extent as tannic acid,
158 CHEMISTRY AND PHYSICS OF DYEING
although a process proposed some time ago for the
separation of these two acids by absorption by
silk is of little value.
Gallic acid will not precipitate so soluble a pro-
teid as gelatin, but in the presence of tannic acid
both acids are carried down.
Tannic acid is absorbed by cotton, but gallic
acid is not under ordinary circumstances. It is not
known whether it is absorbed in the presence of
tannic acid.
Tannic acid is absorbed by cellulose in its various
forms as follows (Knecht, J.S.D. and C. 1892, 40) :
Form of cellulose. Tannic acid taken. Tannic acid absorbed.
Bleached cotton . . .25 grms. . . .0513 grms.
Unbleached cotton . do. . . .0563
Mercerised cotton . do. .. .1033
Pptd. cellulose . . do. .. .1525
Further work on this subject has been done by
Gardner and Carter (f.S.D. and C. 1898, 143), and
the relative action of tannic and gallic acids on
cotton confirmed. The theory that absorption is
mainly due to physical action is not considered
by these investigators to be supported by the fact
that the regenerated or precipitated cellulose has an
increased affinity for tannic acid. On the other
hand, the acid is easily removed by cold, or boiling
water.
The action may be of a secondary nature, and
the water replace the tannic acid by mass action.
A series of experiments with different aromatic
phenols was made with the following results, the
PHYSICAL ACTION AND SOLID SOLUTION 159
conditions of the experiments being as follows :
Strength of solution I grm. per litre; 10 grms. of
cotton were soaked in this for three hours. The
percentage of substance absorbed is given in each
case.
Reagent. l x .
OH
Gallotannic acid
Catechutannic acid
Gallic acid
Pyrogallol
Phloroglucinol
Protocatechuic acid
COOH
OH
OH
OH
OH
Pyrocatechol
Resorcinol
Percentage
absorbed.
4-5
24-26
\/
OIL
45-50
166 CHEMISTRY AND PHYSICS OF DYEING
OH
CO.OH
Salicylic acid
Guaiacol
t CH(OH).COOH 7-8
Mandelic acid
OH
0(CH 3 )
The difference between the absorption of tannic
and gallic acids is very marked.
The difference between the 1.2.3 trihydroxy-
benzene and the 1.3.5 compound is also noticeable.
The different results obtained with the 1.2 and
1.3 dihydroxybenzenes is still more marked and, if
it were not that the suggestion is negatived by the
figures for pyrogallol, would indicate that the meta
position has some influence on the absorption factor.
A general survey of these effects of the OH and
COOH groups on the rate of absorption makes it
difficult to imagine that the action is a chemical
one. There is no question here of a phenol combin-
ing in some way with a diazonium compound.
Kcechlin found that cotton saturated with tannic
acid in a 50 grm. per litre solution was still able
to absorb tannic acid from a 20 grm. solution. It
retained the whole of its tannic acid in a 5 grm.
solution, and only began to lose it when the strength
was reduced to 2 grms. This action is discussed
PHYSICAL ACTION AND SOLID SOLUTION 161
elsewhere. The action seems to be reversible in
this case.
The effect of the addition of fatty acids to the
tannic acid solution is as follows :
Solution. Absorbed.
Tannic acid alone (as above) . . 32 per cent.
+ formic acid . . 48-50 ,,
+ acetic acid . . 48-50 ,,
+ propionic acid . . 48-50 ,,
The acids were present in quantities equivalent
to 4.5 grm. acetic acid per litre. From a chemical
point of view the increased absorption of one acid
in the presence of another is an abnormal one.
With stronger acids this ratio does not hold, as
the following figures will show.
Solution. Absorbed.
Tannic acid alone . . . . 32 per cent.
+ acetic acid . . 48-50
+ citric acid . . 19-21 ,,
+ tartaric acid . . 20-22 ,,
+ sulphuric acid . . 18-20
+ hydrochloric acid . 30-32 ,,
+ sodium acetate . 16-18
The effect of varying the percentage of acetic
acid on a solution of tannic acid (i grm. to litre) is
as follows :
Acetic acid per litre. Tannic acid absorbed.
grms. .... 30-32 per cent.
1 * ... 35-36
2 .. V . 40-42
5 . - 49-51
10 H . ; . 32-34
20 ; . . 31-32
II
i6a CHEMISTRY AND PHYSICS OF DYEING
This rather negatives the idea that the action
of the acetic acid is on the fibre rather than on the
acid in solution.
An action of a similar order is noticed in the
case of gallic acid (i grm. per litre).
Acetic acid per litre. Gallic acid absorbed.
.o grms. . . o per cent.
5 .2
2-5 .'.- .. 8.5
5 ' . . -7-5
25 . . ; . 5-5
These results should be extended to the animal
fibres, and to precipitated cellulose (artificial silk).
They are of great interest from a theoretical as well
as from a practical point of view. The influence of
the addition of acetic acid to the solutions is clearly
shown in the 'following curves, the figures being
taken from the above results.
o
o o
' No. i
No. 2
5 10 15 20 25 grms.
Acetic Acid" per litre
ABSORPTION OF TANNIC AND GALLIC ACIDS IN PRESENCE OF
ACETIC ACID
PHYSICAL ACTION AND SOLID SOLUTION 163
These curves show clearly the influence of the
addition of acetic acid on the absorption of tannic
and gallic acids by cotton. The concentration of
the aromatic acid was in each case i grm. per litre,
and the acetic acid was added up to a strength of
25 grms. per litre.
The reversal in the action is clearly seen in both
cases, and occurs at a comparatively early stage.
Perhaps the influence is the more pronounced
in the case of gallic acid, for in this case the amount
of acid absorbed in the absence of acetic acid is said
to be nil.
The absorption of gallic acid by a tannic acid
collin (soluble gelatine) coagulum gives figures
which do not correspond with the above results.
The curves on p. 164 (Dreaper and Wilson,
Proc. Chem. Soc. 1906, 22, 70) indicate generally
the influence of the presence of salts and acids on
the amount of gallic acid absorbed. Curve No. i
shows the increase in the gallic acid absorbed as the
amount of tannic acid increases when the collin is
added to the mixed acids. When the gallic acid is
added after precipitation the result is practically the
same. Nos. 2 and 3 indicate the increased absorption
in the presence of sodium and ammonium chlorides,
Nos. 4 and 5 the decreased absorption in the pre-
sence of hydrochloric and acetic acids respectively.
Gelatin in the hydrogel state absorbs gallic
acid, although no coagulation takes place when
these two substances in solution are mixed together.
Salts increase this absorption and alcohol reduces it.
164 CHEMISTRY AND PHYSICS OF DYEING
Albumin absorbs gallic acid when precipitated by
tannic acid or heat. Alcohol prevents this action
and also the absorption of tannic acid. In very con-
centrated solutions gallic acid precipitates albumin.
No. i
No. 2
No. 3
No. 5
No. 4
Addition of Reagents
ABSORPTION OF GALLIC ACID BY COLLOIDS
Similar results were obtained when silk or hide
powder took the place of albumin, and there seems
to be a great similarity in the reactions with these
different organic colloids the curves, so far as they
go, indicating that the taking up of tannic and
gallic acids by organic colloids is chiefly a matter of
absorption.
The writer has pointed out that as osmosis
probably plays an important part in the process of
PHYSICAL ACTION AND SOLID SOLUTION 165
dyeing, it might be possible to institute experiments
comparing the relative osmotic pressure of dyes
through inert membranes on the one hand and
fibres on the other.
Whatever the ultimate process of dyeing may be,
it seems necessary to assume that the dye enters
the fibre substance by direct diffusion.
As I then pointed out, the general laws of diffu-
sion would probably govern this method of intro-
duction, although it must be remembered that these
will only apply to substances in a more or less perfect
state of solution. The laws are as follows :
(1) The pressure (osmotic) is proportional to
the concentration of the solution, or proportional
to the volume in which a definite mass of the sub-
stance is contained. This law only holds good for
inert substances.
(2) The pressure increases for constant volu e
proportionately to the absolute temperature.
(3) Quantities of substances (dissolved) which
are in the ratio of the molecular weights of the
substances exert equal pressure at equal tempera-
tures.
It should not be impossible to find whether the
dyeing action is in conformity with these laws, or
is complicated by further reactions as indicated
elsewhere.
The present state of our knowledge does not
supply figures which are available for this investi-
gation. As mentioned elsewhere, it is known that
animal fibres materially modify^this process. The
166 CHEMISTRY AND PHYSICS OF DYEING
results obtained are, roughly, half those obtained
by the true osmotic pressure, when exhibited in the
case of solutions of agar-agar or gelatine.
It would seem from the above recorded experi-
ments with tannic and gallic acids, that the absorp-
tion of the latter acid was as perfect when the
coagulum of tannic acid and collin was first formed
as when the gallic acid was actually present at the
time of formation. The rate of diffusion in the
former case is therefore very rapid and complete.
Fick's law " that the quantity of salt which
diffuses through a given area is proportional to the
difference between the concentration of the two
areas infinitely near to each other," was found not
to be true for animal membranes. An osmotic
pressure exists, but it does not reach its true value
(Zeit. /. Phys. Chem., 3, 316).
It is clear that the fibre substance must be per-
meable in order that dyeing may take place ; this is
indicated by the fact that nitrocellulose in the fibre
state will dye readily, but when ,in the state of a
film (prepared by dissolving in acetone) it will not
do so, or at any rate the action is a very slow one.
The dyeing of wool may be prevented by treat-
ment with sulphuric acid, hypochlorite of soda, and
stannous chloride (Fr. Pat., 318741). So that here
we have a mineral acid, an oxidising agent, and an
acid reducing reagent acting in the same direction, so
far as colour absorption is concerned.
The action of solvents for dyes on dyed fabrics
also gives interesting results.
PHYSICAL ACTION AND SOLID SOLUTION 167
This action is noticed in other parts of this
book. Most colouring-matters, acid, basic, or direct,
and even the mordant and developed colours are
all said to be soluble in either go per cent, acetic
acid, or absolute alcohol, if not in the cold, at any
rate when heated.
It is an interesting fact that some of the acid
colours on wool will not yield to alcohol, but will
readily leave the fibre if a small quantity of water
is added (Pokorng, Bull. Soc. Ind. de Muhl. 1902, 245).
This may be due to the fact that absolute alcohol
cannot penetrate the wool substance. When a small
quantity of water is present the fibre substance
becomes sufficiently hydrated for the spirit to enter.
Patent Blue and New Crocein are examples which
will illustrate this action.
The successive action of 90 per cent, acetic acid
and spirit will remove almost any colour.
In the case of cotton it would seem that the
structure of the fibre will allow of the action of
other liquids than water.
It is recorded, for instance, that alizarine lakes
dissolved in alcohol-ether will dye cotton. It is
not known, however, if silk and wool will dye in
this solution.
Amyl alcohol will apparently act in the same
way. Rosaniline dyed on silk from an aqueous
solution is partly soluble in this solvent, and an
equilibrium is said to be established between the
dye in solution, and the dye on the fibre (Sisley,
Bull. Soc. Chem. 1900).
168 CHEMISTRY AND PHYSICS OF DYEING
Solid Solution. The phenomenon of solid solu-
tion was first noticed by van't Hoff in 1890 (Zeit.
f. Phys. Chem. 5, 322). This idea of the solution
of one solid in another was brought forward to explain
certain facts recorded in connection with alloys, and
salts of similar molecular constitution, or structure.
The suggestion that solid solution might be a
universal phenomenon was not put forward, but
that sodium sulphate and potassium sulphate, or
silver and lead respectively, were capable of dis-
solving one another under certain conditions.
Witt, in 1890 and 1891, advanced the hypothesis
that dyeing might be a case of solid solution.
If this were so, the range of solid solution must
be widened to include the solution of various in-
organic and organic substances in the fibres. The
idea presented here is that the dye-stuffs are not
only held by the fibre substance, but actually enter
into solution in it.
The dye in the fibre was considered to be in the
same state as the oxides which are soluble in precious
stones (Farb. Zeit. 2, 1-6). Witt considered that
the fact that fibres are red, and not bronze green,
when dyed with magenta, and blue, and not bronze
green when dyed with aniline blue, supported this
idea. Rhodamines, also, will only fluoresce in solu-
tions, and they do so on fibres. That magenta is
taken up by silk would be explained by its being
more soluble in it than in water. If a solution
(alcohol) in which the dye is more soluble be taken,
the fibre will not dye to the same extent.
PHYSICAL ACTION AND SOLID SOLUTION 169
The effect of trying to dye cotton with magenta
may be likened to the action of benzene on a solution
of resorcinol in water. The relative solubility of the
latter is so much in favour of the water that the
benzene cannot absorb it. On the other hand, ether
is able to do so, and removes the resorcinol. In
this way the action of the ether is compared to
that of silk. The benzene may, in the same way,
be compared to the cotton fibre.
Again, amyl alcohol may be compared with a
phase where the dye is imperfectly removed from
the dye-bath, for it only partly removes the resor-
cinol from aqueous solution.
The w r eak point in this argument is the in-
discriminate way in which ordinary solution and
solid solution are assumed to be similar in
nature so far as their actions are concerned, and
the universal nature of the interchange. This is
not in accordance with the recognised theory of
solid solution, nor have any facts been brought
forward which would allow of such an arbitrary
extension of this theory to cover the reactions which
take place in dyeing.
It is considered also that the different shades
given by the same dye to different fibres may be
explained by solution. Isonitrolic acid, which is
colourless, dissolves in benzene with a blue colour.
Why should not the changes in dyeing be due to a
similar condition ? The action of dyeing in the
case of adjective colours is said to be similar to the
action of benzene to which benzoyl chloride has been
170 CHEMISTRY AND PHYSICS OF DYEING
added. The resorcinol in this case is taken up by
the water.
It may be gathered from this statement that
Witt even suggests that the adjective colours are
soluble in the mordants. If this is so, we must
assume that no definite chemical combination takes
place between the mordant and dye, and that the
definite lakes isolated by Liechti do not exist.
The weak points in the above argument have
been pointed out by v. Georgievics (/.5.C.7., xiv.
149).
Magenta finely powdered and mixed with chalk
gives a red, and not a bronze colour. If the crystals
are rubbed between glass plates, the same result is
noticed. The colour of the crystals is, therefore,
shown not to be the natural colour, but an abnormal
one, due to the dispersion of the light on the surface
of the crystals or thick layers. If wool be dyed
with a very concentrated solution of magenta it
bronzes.
Fluorescence is held to be possible in the solid
state. Fluorspar and barium platinocyanide are
notable examples of this. Silk dyed with rhoda-
mine is fluorescent, wool is not. Is the first an
example of solid solution, and the second not ?
Fluorescence in fibres, it is contended, is due to a
surface action.
If the dyeing of wool is due to selective solution
it should be correspondingly reversible. This is not
the case with many dyes. Also, if wool takes up
more colour at 100 C, the dye should be more
PHYSICAL ACTION AND SOLID SOLUTION 171
soluble at that temperature, and consequently might
be expected to give up its dye again to water at a
lower temperature.
The fact that the structure of the fibre also
plays some part in the reaction is also against this
theory.
On a later occasion (Monatsh. filr Chem. 25,
705) v. Georgievics gives the results of experiments
with indigo carmine, varying the ratio of fibre to
solution, concentration, and amount of sulphuric
acid present, singly, and in pairs.
The following law was found to express the
results obtained :
,/cw
~~cs~
CW = dye-stuff in 100 cc. after the process of dyeing.
CS = dye-stuff in 100 grms. silk after the process of dyeing.
This would agree with the requirements of van't
Hoff and Nernst's modification of Henry's law of
solution, and it would follow that the dye-stuff
exists in silk in a simpler molecular condition than
in water. With concentrated solutions the value
increases. This would point to the presence
of more complex molecules in solution. In spite of
these results the non-reversibility of the process is
against a theory of solid solution. The writer of
this book has given figures showing the extra fast-
ness of dyes dyed ingrain over the same colours
dyed direct, in terms of their resistance to the
action of boiling soap solution. This result seems
172 CHEMISTRY AND PHYSICS OF DYEING
to be a general one, and extends over the dyeing of
silk, wool and cotton.
These results are very difficult to explain by the
solid solution theory. No explanation can be given
which will explain this difference in " solubility.''
It has been claimed that the abnormal action
of jute fibre (lignocellulose) on ferric ferricyanide
solution supports the solid solution theory (Cross
and Bevan, J. S.C.I. 12, 104). If such a solution
be prepared by mixing equal parts of N/2O ferric
chloride and potassium ferricyanide solutions, and
the fibre be soaked in this colourless solution, it is
dyed a dark blue shade, and gains 20-50 per cent,
in weight. Under the microscope the fibre appears
an intense transparent blue, exhibiting, it is claimed,
all the characteristics of solid solution.
This is possibly not a correct assumption ; the
ferric ferricyanide may be present in the colloid
state. Jute fibre will not absorb the oxide from ferric
chloride solution alone (only 0^4 per cent.). The
small amount fixed is partially reduced. The
absorption of oxide from a ferric chloride solution
by a fibre would be an extraordinary one. The
authors are perhaps straining a point in arguing
from the ferric chloride solution to the ferric ferri-
cyanide one.
They claim that the action in the case of the ferric
ferricyanide is a specific one, and contend that the
necessary reduction to the ferrous state takes place
in the fibre, and not in the solution. It is argued
that the fibre precipitates the ferricyanide, and that
PHYSICAL ACTION AND SOLID SOLUTION 173
this is followed by a rearrangement of its constitu-
ents and production of the blue compound.
A solution of gelatine was found to precipitate
this ferric salt in an almost quantitative way. This
may confirm the writer's opinion that the ferric
ferricyanide is present in the colloid form, and not
in a state of solution as supposed by Cross and
Bevan.
As the jute fibre contains an aldehyde group,
and a lignone, or quinone containing a CO group
and OH groups with phenolic functions (Chem.
Soc.-J. 55, 199), it is contended that this will account
for:
(i) The deoxidation of Fe'" ; (2) union of ferric
and ferrous oxides; (3) combination with HCN.
The authors do not consider that dyeing can be
of such a simple nature as Vignon assumes, viz.,
the interaction of groups of opposite nature (acid
and basic).
So far as the colour is concerned, they assume
that in the complicated cyanide we have to do with
a C 6 ring and a quinoid constitution. This falls in
with Armstrong's theory of colour (Proc. Chem.
Soc. 1888, 27 ; 1892, 101).
Returning to this subject when criticising two
papers attacking the solid solution theory (Weber,
J.S.C.1. 13, 120 ; andDreaper 13,96), Cross and Bevan
(/.S.C.I. 13, 354) deny that the reduction and fixing
is caused by contact action with the aldehyde groups
of the fibre, and they distinguish between the
process, which may be chemical, and the product,
174 CHEMISTRY AND PHYSICS OF DYEING
which is a solid solution. The authors consider
that in the dyed fibre the state of the dye is one
of dissociation or molecular simplification, similar
to that known to prevail in gases. At any rate, in
dilute solutions they regard the action of dye and
fibre as a case of ordinary solid solution. Magenta
can be dissociated in solution by prolonged heating,
but with a complete loss of colour. They also
consider that the extreme sensitiveness of diazotised
primuline produced in the fibre is a result of
solution.
In a fully developed ingrain dye they consider
that we have a chemical bond of union between the
dye and fibre. The fact, however, that this diazo-
tised primuline " is capable of further synthesis to
produce ingrain colours is one of the essential fea-
tures of solution as opposed to chemical action."
Why this is so they do not, however, explain. It is
even known (Dreaper, J.S.C.I. 13, 96), that in
some cases this action of developing cannot take
place. There seems to be as much evidence for, as
against this proposition.
While arguing that dyeing is a matter of solution
they hold that the molecular configuration of the
reagents plays a part. One of the principal arguments
against the solid solution theory is that solid solution
is practically impossible when the varied nature of
these reagents is taken into account.
Their contention, too, that the action is aided
by the presence of salt-forming groups (chiefly OH),
modified by the groups with which they are in
PHYSICAL ACTION AND SOLID SOLUTION 175
proximate or immediate contact, at once brings us
back to the chemical theory, and with this the need
of a solid solution theory vanishes.
We here have a singular division of the action
of dyeing ; and solid solution relegated to the product
to the exclusion of the process of dyeing, which may
be either physical, or chemical.
The claim made by Weber that once grant a
chemical action, and the solid solution theory is no
longer required to explain the action of dyeing,
seems a reasonable one. The claim that the sub-
stance in solid solution is different from the one in
solution is an arbitrary one.
Weber contended that the differentation between
the process of dyeing, and the final state of the dye
" contains all the elements of a scientific abortion/'
Furthermore, that the writer's investigations,
coupled with his own (above), lead to "an un-
conditional rejection of the solid solution theory
as proposed by O. N. Witt."
It is of interest to note that S. E. Sheppard
(Photo. Journal, 1903, 271) holds that the colour
sensibility of silver haloids, when treated with certain
dyes, is due to the formation of loose compounds of
the dye and the haloid. The extra sensitiveness of
these silver salts to the action of certain rays of
light might be, in a way, comparable to the results
obtained with primuline diazotised in situ.
The results obtained by Walker and Appleyard
(J.C.S. 1896, 1334) with picric acid, and its dis-
tribution between water and silk, do not confirm
176 CHEMISTRY AND PHYSICS OF DYEING
v. Georgievics' experiments with indigo carmine, or
at any rate, do not agree with them.
In this case they found that
Here we have a case where the simple rule is not
followed, which it would be if the molecular state
were the same in both solvents. The solid solution
theory requires that the ratio of dye in solution to
that in the fibre will be a constant irrespective of
concentration.
If, however, the molecular weight is n times as
great in the one solvent as in the other, then the
nih root of the concentration in the first solvent will
have a constant ratio to the concentration in the
other solvent.
In the latter case
c~T
_ TT
cw
will apply.
Walker and Appleyard found that with picric
acid and silk an equilibrium was established between
the fibre and solution (dyeing at 100 C.).
Also, if the dyed silk was treated with successive
baths of water the action was reversible, but the
time taken to reach a state of equilibrium was much
longer (seven hours). It did not matter if the dye
was on the fibre or in the solution, a constant ratio
was ultimately obtained.
The result does not necessarily uphold the solid
solution theory. It is equally in agreement with
PHYSICAL ACTION AND SOLID SOLUTION 177
any theory which requires a state of equilibrium,
be it physical, or chemical.
The law of the distribution of picric acid at
60 C. was found to be
yw = 35-5
This result does not give support to the solid
solution theory, for it indicates that the molecule
of picric acid in solution is 2.7 times as great as
the molecule " dissolved " in the silk.
The freezing-point and electrical conductivity
determinations indicate that picric acid is present
in water in a simple molecular state. Therefore, so
far as our knowledge goes, it is impossible to recon-
cile these figures with any theory of solid solution.
By a mathematical transformation of the above
formula we obtain
log S = log 35.5 + log W.
which when differentiated becomes
^S_ _i_ dW
S ~ 2.7 ' W.
This indicates that if the concentration in the
water is increased by any volume, the concentration
in the silk will increase by of its own value.
Formulae of this nature apply in many cases to
absorption phenomena. Schmidt and Kiister have
shown this to be the case (Annalen, 283, 360).
By substituting alcohol for water in these
experiments, in which picric acid is more soluble,
less was taken up by the fibre. The ratio of the two
12
178 CHEMISTRY AND PHYSICS OF DYEING
concentrations to produce the same shade remains
fairly constant, and is nearly the ratio of the relative
solubility of picric acid in water and alcohol at 60 C.
When benzene was used as a solvent, abnormal
results were obtained. The silk would not take up
any dye, in spite of the fact that rosanilme at once
colours silk from this solution. Some peculiarity
in the system is indicated here, or some joint property
of the picric acid and benzene is possibly the cause
of the different action. The difference between the
dyeing action of picric acid in water, and benzene
might be due to the fact that in the former it is
said to be in a state of almost complete dissocia-
tion, and in the latter it is scarcely dissociated at all.
In this case it would be the H ions which influ-
ence dyeing, as sodium picrate will not dye at all.
It is stated also that picric acid dissociates in
alcohol.
Benzoic acid is readily absorbed by silk. A
solution of this acid was dissociated to the extent
of 6 per cent. The salts of this acid are also
highly dissociated, and any addition of the latter
to solutions of benzoic acid reduces its dissocia-
tion from 6 per cent, to zero. It would be
expected that a smaller percentage of acid would
be absorbed under these conditions. The absorp-
tion is actually reduced from 17 per cent, to 1.5
per cent. The reaction does not hold however for
alkaline benzoates.
Further experiments with other weak acids did
not corroborate these results. No relation could be
PHYSICAL ACTION AND SOLID SOLUTION 179
traced between the relative rate of dissociation as
measured by the presence of H ions in solution, and
the relative rate of absorption by silk. If, however,
the acids be divided into the two classes of aromatic
and fatty acids, a much closer agreement exists
between the constants.
The average absorption of the aromatic acids
was 23 per cent., that of the fatty acids 5 per cent.
In most cases the proportion of acid absorbed
to acid in solution bears an almost constant ratio,
yet in some cases the absorption increases rapidly
as the acid becomes more dilute. With citric acid
the action is abnormal. The amount taken up by
the silk is almost independent of the concentration,
and is constant in amount.
o These results seem to indicate that a solid
solution theory is unsatisfactory. Solid solution
was originally defined by van't Hoff (Zeit. Phys.
Chem. 1890, 5, 322), as being a " solid homogeneous
complex of several substances, the proportions of
which may vary without affecting the homogeneity
of the system. "
Schneider (Zeit. Phys. Chem. 1895, 10, 425)
suggested that when barium sulphate carried down
ferric sulphate from its solution, the action was of
this nature, although he noticed that the ferric salt
carried down was proportional to the amount of
the insoluble barium compound present, up to the
limits of occlusion. Beyond this point the presence
of excess of iron salt in the solution had no effect.
More recent investigators do not seem to agree
i8o CHEMISTRY AND PHYSICS OF DYEING
with this suggestion. Jannasch and Richards (/.
pr. Chem. 1889, 39, 321) consider the action to in
some way involve chemical action, rather than solid
solution. Ostwald and others seem to agree with
this view of the case. This subject received further
consideration from Hulett and Duschak (Zeit. Anorg.
Chem. 1904, 40, 196), who have further noticed
that when barium chloride is absorbed in this way
by barium sulphate, it is not necessary that the
soluble salt be present at the time of precipitation.
When finely divided crystals of the sulphate are
suspended in the solution the same action takes
place. They further consider that this phenomenon
may be due to the formation of complex salts, such
as (BaCl 2 )SO 4 or (H.SO 4 )JBa.
Quite recently Korte (/. Chem. Soc. 1905, 1508),
as a result of further investigation of this subject,
does not agree that solid solution is the cause of
this action.
It is also known that barium sulphate will absorb
metals from colloidal solutions of the same (Vanino
and Hartl, Ber. 1904, 37, 3620). These absorption
results with such a comparatively inert substance
as barium sulphate will give the dyer an insight
into the possibility of some such action taking
part in the phenomena of dyeing, and lake formation.
These results suggest rather that " absorption "
is possible under such conditions as are indicated,
and that this is by no means confined to such
conditions as approximate to those which obtain in
the dye-house.
CHAPTER VIII
EVIDENCE OF CHEMICAL ACTION IN DYEING
THE suggestion that the dyeing action is primarily
a chemical one, has received support in the past
from many investigators who have brought forward
evidence in favour of this hypothesis.
If it is possible to prove that the many and
varied operations in dyeing and mordanting are
governed by the laws which control ordinary chemical
reactions, it is evident that our knowledge of the sub-
ject is at once put on a satisfactory and simple basis.
It is, therefore, of interest to follow closely the
arguments, and facts, which have been recorded in
favour of this view.
Unfortunately, the conditions under which much
of the work on the subject has been effected are
not entirely satisfactory. As a result, some of the
data available are unreliable, and it is impossible
to allot to some of the work its true value as
evidence in favour of such action.
As early as the year 1737 Dufay drew attention to
the possibility of the dyeing action being a chemical
one. This view was also supported by Bergmann
in 1776.
182 CHEMISTRY AND PHYSICS OF DYEING
In these early days the relative affinities of
different fibres for the same dye-stuff were considered
to be evidence in favour of chemical action. Berg-
mann, for instance, specially pointed out that
sulphate of indigo is attracted by wool in greater
proportion than by silk. He attributed this to
the greater attraction of the substance of the former
fibre for the dye.
Wool was said to exert such an attraction for
the dye that the dye-bath was completely ex-
hausted. On the other hand, silk could only
reduce the amount present in the dye-bath.
From this it is evident that these early investiga-
tors realised this factor in dyeing, viz., the attrac-
tion of the fibre for the dye ; and in this way they
differed from those who at this same period
ascribed the action to purely mechanical pheno-
mena. If it can be established that dyeing is
primarily due to this cause, the subject is at once
narrowed within definite limits.
Macquer in 1778, in his " Dictionnaire de Chimie,"
confirmed the idea that wool and all animal fibres are
the materials which lend themselves most readily
to the dyeing action. He stated that linen and all
the vegetable fibres are the most difficult to dye,
taking the least number of dyes, and holding them
loosely. He placed silk in an intermediate posi-
tion, not classifying it as a purely animal fibre. He
did not deny that this variable facility of taking
and retaining different substances is greatly due
to the number, size, and arrangement of the pores,
EVIDENCE OF CHEMICAL ACTION IN DYEING 183
and their relative size as compared with the dye
particles, but he did not allow that this is the only
cause of the differences experienced in dyeing dif-
ferent fibres, and of the results obtained.
In support of this statement the following ex-
perimental evidence was advanced. If one-pound lots
of wool and silk be mordanted with alum in excess,
and dyed separately in a dye-bath containing
cochineal, with one ounce of dye in each case, the
wool will take a much darker colour. To obtain
the same shade on the silk 2\ ounces of colour are
necessary. In both cases the dye-bath is exhausted.
This effectually disposed of the idea put forward by
d'Apligny that the pores are smaller in the case of
silk, and can only take the finest particles of dye.
Dyeing, therefore, is not simply a question of
encased particles. There is a real " adherence on
contact," and even a chemical combination varying
with the properties of the dyes and fibres entering
into the reaction. He was of opinion that the
effect of a surplus number of pores might even
diminish the colour-effect by concealing the coloured
particles. Dyeing was largely a question of surface
action.
Berthollet in his " Elements of Dyeing " collected
all the facts bearing on the subject, arid favoured
the chemical theory as a result of his investigations.
Chevreul also came to the conclusion that the
action of dyeing was of the same order as chemical
action, which takes place slowly, when two or more
bodies are in contact.
184 CHEMISTRY AND PHYSICS OF DYEING
Persoz, in criticising Crum's mechanical theory,
held that the view that acetate of alumina is de-
composed naturally by the cotton fibre, just in
the same way as it would be if the fibre were
absent, is untenable. He refused to believe that
the same amount of alumina would be given up by
the acetate in contact with mica plates. This
difference would be still more marked at an elevated
temperature. He therefore considered that the
cotton fibre exerted a powerful influence on the
decomposition of the aluminium salt. (See p. 143.)
He actually gave particulars showing, in the
case of alum solution, that actual decomposition
of the solution took place when cotton or silk was
in contact with it. He recorded that the solution
became more acid, owing to its being deprived of
a notable amount of its base.
These experiments are probably the first of a
series dealing with the decomposition of salts in
solution by fibres. They may be regarded as the
first direct indication that the action might be a
chemical one. Macquer's results might have been
due to mechanical, or even optical causes, but this
experiment stands on a different basis, and the
proof of chemical action was thought to be a con-
vincing one.
These results do not agree with Crum's con-
tention that the rate of change in a solution of
acetate of alumina is the same whether a fibre be
present or not. Persoz also asked how the colour
mixed with so viscous a solution as gum or starch
EVIDENCE OF CHEMICAL ACTION IN DYEING 185
can occupy these sacs expelling the air and taking
its place in the printing of fabrics.
He stated also that a fibre impregnated with
manganese dioxide should not dye, yet it is in a
very favourable state to take up indigo. The fact
that some substances, such as baryta, calcium
sulphate, &c., are never fixed by the fibre, while
others are, is, he claimed, in favour of the chemical
theory.
Muspratt (" Chemistry as applied to Arts," p.
766) thought that compounds deposited on wool
or cotton became fixed through different causes.
" Wool is strongly contracted by acids, and it is
only under their influence that we can fix colours
upon it. Cotton is contracted by alkali, a colour
adheres to it only in so far as it presents an alkaline
reaction." The idea was also" advanced that the
different colours assumed by wool, silk, and cotton
with the same dye, were due to configuration of the
fibres.
Kuhlmann (Compt. Rend., April 1856) dyed
samples of cotton and linen which had been nitrated,
and noted the results obtained. The pyroxylin was
well washed with water, and ultimately with soda.
After mordanting and " ageing," samples of these
materials were dyed. All the nitrated fibres gave
excessively pale shades, as compared with the
natural fibres. There seemed to be evidence that
although the treated fibres rejected the mordants, yet
they had increased attraction for the madder itself.
Similar results were obtained with Prussian blue.
186 CHEMISTRY AND PHYSICS OF DYEING
To obviate the possibility of these results being
due to physical alteration in the fibre, he used
Bechamp's process to denitrate the fibre, and noted
that the cotton immediately recovered its property
of receiving mordants and colours. The effect of
varying the degree of nitration was to give varying
results. He extended those experiments to wool,
silk, hair, &c.
It was also noticed that picric acid gave a very
strong tint on nitrated cotton.
Kuhlmann concluded that the chemical com-
position of the bodies to be dyed had the greatest
influence upon the dyeing; also that dyeing is due
to chemical combination, and that the effects due
to capillarity, and the peculiar structure of the
material, were of secondary importance.
It may be pointed out that the early authorities
who favoured a chemical theory, based their theo-
retical conclusions on the hypothesis that the dyeing
action was similar to, say, the reaction between
caustic soda and hydrochloric acid. In other words,
that it was a definite, and simple one.
It is assumed to-day by those who favour chemi-
cal action, that the animal fibres possess acid and
basic properties. They therefore combine with
and fix the dye-stuff, at least those which possess
either acidic or basic properties themselves. We
may therefore get actual salt formation.
The fact that the animal fibres contain amido-
acids is therefore the basis of this theory. The fibre
substance therefore contains both amido and
EVIDENCE OF CHEMICAL ACTION IN DYEING 187
hydroxyl groups, which play their part in the respec-
tive cases where basic and acid dyes are used.
These two species of dyes might even be dyed
on a fibre already mordanted and dyed with alizarine
the lake of which would be held mechanically. The
mordant in this case would also be attracted chemi-
cally, and then by double decomposition, or otherwise
the lake would be formed.
The statement has been made that " there is no
colouring-matter which does not possess either acid
or basic properties" ("Manual of Dyeing," page 8).
The first time that the idea was put forward
that wool plays the part of an acid in the dyeing
of basic dyes (magenta) was in 1884 (J.S.D. and
C. i, 209), when Hummel likened the action of
the fibre to the fixing action for dyes of oleic, or
tannic acid on cotton, &c. Although Hummel did
not state in terms the decomposition which must
take place when a basic hydrochloride combined
with the wool substance in this way, yet it is
clear that the hydrochloride must split up in order
to enable the base to combine with the acid.
In the case of wool it was afterwards pointed out
by Knecht (J.S.D. and C. 1888, page 72), that when
this fibre is dyed with basic dyes (hydrochloride),
that the whole of their acid is left in the solution.
If the amido theory is correct, it is difficult to
explain why the acid does not combine with the
fibre. The writer doubts if the same result would
be found^ with silk when the affinity of that fibre
for acids is considered.
188
CHEMISTRY AND PHYSICS OF DYEING
Hummel also claims that this action is visible
to the eye. When a colourless rosaniline salt is used,
the fibre is coloured magenta.
It is claimed ("Manual of Dyeing/' p. 8) that
this conclusively proves the chemical theory, and
that a coloured salt is formed with one of the con-
stituents of the fibre.
If the action is a chemical one, it will follow
that a point will be reached when the fibre sub-
stance will all be used up, and a point of maximum
absorption attained. The following experiments
are put forward by Knecht and Appleyard (f.S.D.
and C. 1889, p. 74), to prove that this is the case.
Silk was dyed with a large excess of picric acid and
naphthol yellow respectively, with the following
results.
Picric acid.
Naph.Yel.S
Tartrazine.
Amount fixed .
Do. in solution
13.2%
37 o%
20.8%
29.2%
22.65%
27-35%
Fifty per cent, of dye was taken in each case on
the weight of the fibre dyed. The ratio taken up
of Naphthol Yellow to picric acid 20.8/13.2 is in the
ratio of their molecular weights.
Tartrazine does not seem to follow this law,
however. As picric acid contains one OH group,
Naphthol Yellow one OH and one SO 3 Na, and
tartrazine 2CO.OH and 2SO 3 Na groups, it is
difficult to decide in what way they might, or
might not, combine with the fibre substance.
EVIDENCE OF CHEMICAL ACTION IN DYEING 189
Von Prager and Ulrichs (Farb. Zeit. 1891, 373)
hold that these results are unreliable, and v.
Georgievics denies that the Naphthol Yellow and
picric acid are taken up in molecular proportions.
Recently (J.S.D. and C. 1904, p. 242), Knecht
has brought forward results which he contends add
support the chemical theory.
By an improved method of analysis and work-
ing with pure dyes, the following absorption results
were obtained :
Dye used.
Amt. used.
Taken up.
Calculated.
Orange G.
50%
16.24%
Crystal Scarlet
50%
18.23%
18.02%
Scarlet 2 G. .
50%
16.37%
Xylidine Scarlet
50%
17.12%
J 7-30%
Orange G.
25%
15.68%
Crystal Scarlet
25%
1742%
*74%
Scarlet 2 G. .
25%
15.53%
Xylidine Scarlet
25%
16.22%
16.40%
Orange G., Atomic wt. 452, Crystal Scarlet 502,
Scarlet 2G. 452, Xylidine Scarlet 479.
Picric acid is now said to act in an abnormal
way, and not in the way originally stated. In
dyeing wool with increasing amounts of dye-stuff,
a limit of absorption is reached in each case.
For instance, with Crystal Scarlet the following
results were obtained :
Percentage of colour used :
50 25 22.5 20 17.5 15 12.5
Percentage of colour taken up by fibre :
18.2 17.3 17.0 16.6 15.3 14.2 11.9
10 7.5 5.0 2.5
9.6 7.2 4.7 2.2
I 9 o CHEMISTRY AND PHYSICS OF DYEING
This author holds that these experiments favour
a chemical theory, from the fact that the dyes are
taken up in molecular proportions.
The effect of excess of acid in dyeing is said to
be due to the production of degraded products in
the fibre, which resemble lanuginic acid in their
chemical action.
The fact that the water can be varied, within
limits, without altering the percentage of dye taken
up is held to disprove the solid solution theory. If
this is so, and with such a definite chemical action
as is claimed, the fact that up to the point of satura-
tion the dye is not all removed from the liquid
would seem equally to point against a chemical
action on the old hard and fast lines.
The law of mass action might possibly influence
the result however.
Alizarine S. (powder), oxalic acid and alum can
be boiled together indefinitely without combination
or at any rate, any visible change. If lanuginic
acid, said to be present in wool, is added, a bright
scarlet precipitate is formed. This is said to give
additional evidence in favour of the chemical view.
As before pointed out the above ratio breaks
down entirely in the case of the sulphonic acids of
phenols and amines. Dehydrothiotoluidinesulphonic
acid is readily absorbed by silk, yet Prof. Green
could not find any of the above which had an
affinity for the animal or vegetable fibres. It is
very difficult to explain why these sulphonic acids
are not attracted by the animal fibres. The amido
EVIDENCE OF CHEMICAL ACTION IN DYEING 191
acid theory requires that they shall be readily
absorbed. If the animal fibres have in their sub-
stance a compound which readily combines with
acid compounds, the only explanation of the above
is that soluble compounds are formed.
In the case of wool very little dyeing action
takes place in a simple solution of these dyes in
water. No figures are available for silk. If, how-
ever, an acid be added to the solution the colour
acid is set free, and rapidly dyes the fibre, in the
case of silk at ordinary temperatures.
A preliminary treatment of wool with sulphuric
acid, followed by very thorough washing, will cause
this fibre to dye rapidly, when introduced into a
neutral solution of an acid dye in the form of its
sodium salt.
It is claimed that this can be satisfactorily
explained by assuming that the wool fibre has affinity
for the acid, and retains sufficient to set free the
colour acid. It would seem, however, that this
explanation is not altogether satisfactory.
An addition of sulphuric acid over and above
that necessary to decompose the dye acid salt has
an altogether abnormal effect on the rate of dyeing.
If the dyeing action is a strictly chemical one, the
excess of sulphuric acid might be expected to have
the opposite effect. The nature of this reaction
is well illustrated by the following experiment.
Boiling in distilled water will partly remove
the dye (colour acid) from a silk skein. If then
a few drops of a strong acid are added to the
192 CHEMISTRY AND PHYSICS OF DYEING
solution nearly all the colour will return on to the
fibre.
It is difficult to understand this action from
the chemical point of veiw. In what form is
the re-dissolved colour in the solution ? If present
as free acid, why should the addition of acid influence
the result ? If, on the other hand, the colour acid
fibre compound is not decomposed, but dissolves
out in the hot water, can the conditions exist under
which this fibre compound is decomposed on the
addition of acid, the colour acid set free, and the
latter combine to form the same compound in the
fibre again in the presence of the acid which has
decomposed it in the solution ? The opposite
effect might be expected, viz., that the sulphuric
acid would partly replace the colour acid. This
matter seems to deserve special attention.
It is contended that the substances in the
animal fibres which produce these dye lakes or
compounds can be isolated.
Prof. Liechti states that albumin will decompose
a basic dye in much the same way as an animal
fibre. In this case also, the acid remains in the
solution. It will be remembered, however, as
mentioned elsewhere, that this decomposing action
is not confined to organic compounds of animal
origin, but may take place with such inert substances
as porcelain. It is claimed for the above reaction
that " here there can be no doubt that chemical
combination takes place, as the coagulated albumin
is dyed magenta. "
EVIDENCE OF CHEMICAL ACTION IN DYEING 193
The proof here is not more satisfactory than it
is in the case of magenta-dyed wool. In order to
uphold such a statement it is necessary to ignore
the general reactions obtained with substances of
the above nature.
Knecht states that if wool, or silk, be dyed with
night blue, and the dye subsequently extracted
with alcohol, the compound actually formed between
the dye and the fibre is extracted. If this solution
be treated with barium hydroxide, the night blue is
precipitated, and the fibre substance can be recog-
nised in the solution.
This has been denied (Zeii. fur Farb. und Text.
Ch. 1903, 215), it being maintained that no such
action will take place if the wool is purified with
alcohol before dyeing. The organic matter extracted
is not of the nature stated, but consists of substances
extracted by alcohol alone.
This criticism has been answered (f.S.D. and C.
1904, 72), by Knecht repeating his experiments after
a preliminary treatment with alcohol. Under these
conditions he states that he obtained a yellow
residue, smelling of burning wool after ignition, and
precipitated by an aqueous solution of night blue,
or magenta. It would have been more satisfactory
if a blank experiment had been . made side by side
with the night blue one, in addition to the pre-
liminary purification.
At first sight the case for the chemical theory
seems to receive support from the action of nitrous
acid on the fibre, and subsequent development with
13
194 CHEMISTRY AND PHYSICS OF DYEING
phenols, &c. There does not seem to be any doubt
as to the action in this case. The silk shows by its
altered colour that the nitrous acid has acted on it
and the subsequent development with phenols, or
amines, is rapid and startling in its nature. It
is certainly the case that some constituent of
the fibre actually enters into the reaction, which
produces these "dyes." An attempt made by the
writer to isolate these compounds was not very
successful. They seemed to be present in very
small quantities.
No other experiments seem to afford such a clear
indication that chemical action may take place in
the process of dyeing. It might be fairly argued
that the dyeing action is of a strictly chemical
nature, if the matter rested here.
Unfortunately, these experiments and their influ-
ence on the action of dyeing have been discounted
by some experiments of Bentz and Farrell (J. S.C.I.
16, 405). After confirming the above reactions, and
that silk contains amido groups, the fibre was
treated with nitrous acid for thirteen hours. After
washing the fibre was boiled with alcohol, or an
acid solution of cuprous chloride. This removed the
amido groups. The fibre would not then rediazotise.
The NH 2 (or NH) groups had been removed. From
the chemical point of view it is, therefore, clear that
the fibre should not dye under these conditions.
But the " deamidated" fibre takes acid colours
equally as well as the original fibre. Therefore,
the inference is drawn that the amido groups play
EVIDENCE OF CHEMICAL ACTION IN DYEING 195
little or no part in the dyeing of silk (or wool)
with acid colours.
These experiments need to be extended ; they
should cover the subsequent resistance against soap,
water, and alcohol. This should show if the amido
groups play any secondary part by holding the dye
when it is once on the fibre.
The writer (J.S.C.I. 13, 96) gave the results of
a number of experiments on dyes dyed direct
and ingrain respectively. Figures are given, show-
ing by curves and tables the differences obtained by
dyeing primuline colours " direct " and " ingrain "
on silk.
Their fastness against soap and alkali solutions
at a high temperature, was taken as a compara-
tive measure of the way the dyes are held by the
fibre. A standard solution of neutral soap, or
sodium carbonate was used in all cases.
The general results obtained were as follows :
The difference in fastness of the dyes when dyed
" ingrain " and direct was very noticeable. This is
clearly shown in the series of curves accompanying
the paper.
The dyes when dyed direct were not so fast as
the original primuline against soap solution.
The developed amine dyes are, with one excep-
tion, very much faster in their resistance to soap
than the corresponding alcoholic or phenolic dyes.
It may be argued from this, either that the fibroin
shows a stronger acid than basic reaction, as mea-
sured in this way, or that the solvent action of
196 CHEMISTRY AND PHYSICS OF DYEING
the soap is greater in the case of the alcoholic dyes
than in the other. Either of these explanations is
possible.
It will be noticed that in the one case given of
an azo triple dye, that the resistance against soap
is increased in the ratio of 1.7 to i. This may, again,
be due to increased molecular volume, or to a
state of greater insolubility. It would have been
interesting to have used a phenol in the case of
the second development, and also to have dyed the
azo dye direct, and noted the effect of one or two
developments on the fastness against soap. The
only possible comparison given is that of Atlas Red
R developed with /3-naphthol. This dye is prepared
by diazotising primuline, and combining with
w-tolylenediamine .
This dye was not so fast as might be reasonably
expected. It was argued from these figures that
the relative fastness of these two classes of developed
dyes was not so much due to internal molecular
structure as to the phenolic, or basic nature of the
dye.
Some " developers " will not act on the diazo-
tised primuline on silk. /3-naphtholsulphonic acid
(R salt) is an example. This can hardly be due
to a simple matter of diffusion of the developers,
for substances (dissolved) which are present in the
ratio of their molecular weights, exert equal
pressure at the same temperatures.
If this is so, it should be easily confirmed by
nothing the relative amount of the " developers"
EVIDENCE OF CHEMICAL ACTION IN DYEING 197
absorbed by equivalent solutions. An alternate
suggestion is that the diazotised primuline has
an affinity for this silk fibre which the R salt cannot
overcome. The presence of a sulphonic acid group
in the developer may influence the reaction, and
also the solution state of the developer.
The fact remains, at any rate, that the R salt
is unable to combine with the diazotised primuline
in a silk fibre, but able to do so in a cotton one.
The relative rate of development with R salt
on cotton and mercerised cotton where the fibre
is in a higher state of hydration might throw
further light on this subject.
The relative amounts of dye taken up under
standard conditions from soap solution do not seem
however, to indicate that the fibre has much chemi-
cal influence on the amount of dye absorbed by
the dye, as the following table taken from my paper
(ibid.) will show.
D Per cent, of dye taken
up by fibre.
Primuline and C,,H 5 .OH . 0.18
C 6 H 5 NH 2 . . 0.19
C 6 H 4 (NH 2 ) 2 | o.n
/3C ]0 H 7 .OH ^f 0.12
C 6 H 4 .COOH.OH o.n
The table on p. 198 shows the result obtained
in the experiments by boiling for different times in
standard soap solution, and covers most of the
developers used in practice.
The samples of silk were dyed with the equiva-
lent quantities of the dyes, or equivalent propor-
198 CHEMISTRY AND PHYSICS OF DYEING
d . d d . d d d d . d . d . d . . d
riOaSOaSortOnJortOrtortortoaSOOrtO
^Q ^Q ^Q ^3 ^Q ^Q ^Q ^Q *'& ^Q Q ^Q
Remarks.
Ml I I I I I '8 till ill
rt ; ,3;
Ml 1 1 1 1 1 o : : : 8 | | | | | |
_d
O ' T ^" lx ^-^ ^-^ *^ oo O c^ '-o O O tx, O 1J ~* " ^-^ O tx Q\ O tx *O
s
oooooooooooocoooooooooo
1
2^^SS^R8''^J15 > ^S'R S-K.
3
ddoddddddddddddddddd do
1
iOt^O\OO O O > J ^N tXOOVO O Tfuiro>J^rOJ-iO' Lr 'O\O N
&
ooooooooooooooooooooooo
1
i
sa^^o^^o'^^^o^a^SS^S^^vS^^^
M
ooooooooooooooooooooooo
d
i
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
d
i
' dddddddddddddddddddddd
i
i
= ^?
i
1
^"^ * ffi /~\ ^ " K
5"5 = l ^ S $ S : & 5 J '5
.
JH ^
o
. . J*
^ S
EVIDENCE OF CHEMICAL ACTION IN DYEING 199
tions of primuline. The conditions of dyeing were
kept constant in all cases. After drying the
sample lots of silk were boiled out for the periods
indicated, and the resulting shades were carefully
compared with standard samples ; or else the dye
in the soap solution was estimated by colorimetric
methods. In this way, the loss of colour on boil-
ing off was estimated with a sufficient degree of
accuracy.
The ratio of colour removed in the case of these
Dye.
Developer.
"In-
grain" x.
"Direct"
y-
X
y
Remarks.
Primuline
C 6 H 5 .OH
0.20
0.74
i
-
C 6 H 4 (OH) 2 (i. 3 )
0.17
0.75
i
"
C 6 H 4 .OH.COOH(i.2)
0. 12
0.75
i
6^2"
"
C 10 H 7 .OH/3 .
0.15
0.63
i
4.2
'
NH 4 .OH
0.08
0.50
i
^
"
C 6 H 5 .NH 2 .
O. IO
0.70
i
Azo dye.
"
C 6 H 5 .NH 2
0.05
0.61
\
I2.O
Azo triple dye.
C 6 H 5 .NH 2 .
0.07
0.32
I
4T6
Na 2 CO 3
"
C 6 H 4 .(NH 2 ) 2 (i. 3 ) .
0.052
0.80
i
15.4
"
C 10 H 7 .NH 2 /3 .
0.27
0.79
i
"
C 10 H 7 .OH/3 .
0-27
0.76
I
200 CHEMISTRY AND PHYSICS OF DYEING
dyes is seen in the table on p. 199. The influence
of the solvent (soap, or sodium carbonate) seems to
alter the rate of "boiling out" materially.
It is very difficult to reconcile these results with
any purely chemical, or solid solution, theory. The
stumbling-block is the altered fastness of dyes dyed
ingrain and direct, and the indication that the dyes
may be fixed in two ways. The difference between
the fastness of the phenolic and amine dyes respec-
tively may be explained in other ways.
The affinity of these dyes from primuline for
cotton seems to vary greatly, and here again the
metaphenylenedi amine colour has a fair affinity
for this fibre, and the beta-naphthol one very little.
These results are obtained when dyeing this fibre
direct. It is therefore quite clear that a difference
in dyeing properties is apparent when amines are
used in place of phenols in the production of these
dyes.
Another point of importance was indicated. It
was shown that the colours produced in the two
cases, direct and ingrain, were not identical in shade,
as shown in the table on p. 201.
This might indicate some difference either in the
action or state of the dye. This has since been
suggested by Brand (Proc. Soc. Ind. de Mulh., Feb.
and April 1901) as being due to a secondary action
between the diazo compounds and the wool. In
my paper I indicated that the fact that some
developers w r ould not act on the diazotised primu-
line might be taken as a possible proof that there
EVIDENCE OF CHEMICAL ACTION IN DYEING 201
was some action between the diazo compound and
the fibre. The same explanation has more recently
been put forward by Hepburn (J.S.D. and C. 1901,
279).
Taking the case of para-nitraniline, the fastness
of the dye against washing is said by Brand to be
due to the paranitrodiazobenzene being partially
reduced at the expense of the fibre substance to
Dye.
Developer.
Colour obtained.
Method of
dyeing.
Primuline
C C H,OH . .
Yellow.
Ingrain.
5 J
Do., slightly darker.
Direct.
C (i H 3 .NH 2 . .
Yellow (brown shade).
Ingrain.
? j
Do., slightly darker.
Direct.
C 6 H 4 (OH) 2 i. 3 .
Orange.
Ingrain.
Do., redder shade.
Direct.
C t; H 4 (NH) 2 i. 3 !
Red-brown.
Ingrain.
5 1
Do., redder shade.
Direct.
C,H 4 .OH.COOH
Yellow.
Ingram.
5?
Do., slightly duller.
Direct.
para-nitraniline. The excess of diazo compound
would react, forming dinitrodiazoamidobenzene.
This substance is very insoluble.
It is just possible that a similar reaction may
take place in the case of diazotised primuline, and
that it is this compound which is so sensitive to
light, but it is not so easy to explain the subsequent
action of the developers.
It is held by Rossi (Rev. Gen. Chem. 1901, 670)
that silk will also act on diazo compounds as a
reducing agent, diazoamido or azoamido compounds
202 CHEMISTRY AND PHYSICS OF DYEING
being formed, the difference being determined by
the stability of the diazoamido compounds. This
reaction once ended, the resulting compounds are
held mechanically by the fibre.
The reduced action of some developers may,
Resistance of Phenolic dyes to the action of soap. (Dreaper.)
10 20 30 40 50 6omins.
Time of boiling out. -
FASTNESS OF INGRAIN COLOURS.
A : C 6 H 5 .OH (ingrain). B ; do. (direct). C : C 10 H r .OH/3 (ingrain).
D : do (direct). E : Primuline (direct).
however, be due either to the diazo compounds
being held by the fibres by some secondary chemi-
cal action, or else to the molecular aggregates of
these developers being too large to enter the fibre
substance in the form in which they are present
in the solution.
EVIDENCE OF CHEMICAL ACTION IN DYEING 203
If some such reducing action takes place as is
indicated when these dyes are developed in silk, what
is the corresponding action in the case of cotton ?
The curves drawn from the above tables (see
Resistance of Amine dyes to the action of soap. (Dreaper.)
10 20 30 40 50 6omins.
Time of boiling out.
FASTNESS OF INGRAIN COLOURS.
A :C 6 H 5 .NH 2 (ingrain). B : do. (direct). C : C 10 H 7 .NH 2 /3 (ingrain).
D; do. (direct). E: Primuline (direct).
p. 202) will also illustrate the relative resistance of
the phenolic dyes towards the action of the standard
soap solution. They show the general results which
may be expected in practice, and the relative fast-
ness of the dyes.
The extra fastness of the ingrain dye in the
case of, say, cotton fibre and the phenolic dyes
204 CHEMISTRY AND PHYSICS OF DYEING
after a treatment with soda is certainly difficult to
understand, from a purely physical point of view.
Mineral colours, however, which are " developed "
or formed on the fibre are certainly more resistant
to the action of such solutions, and it is not likely
that anything more than a modification in the
physical state of the precipitate, and its position
in the fibre, are the cause of this extra fastness over
that of the same mineral colours applied direct.
In the same way, the similar curves obtained
from the corresponding amines are recorded (see
p. 203). It will be noticed that in this case the
amine with the higher molecular weight is the less
resistant to the action of the soap liquor.
In this respect it differs from the corresponding
phenol. No general law can be given, as it is
known that the resorcinol dye is not so fast as
either the phenol or naphthol compounds.
Pauly and Binz (Zeit. /. Farb. Text. Chem. 1904,
373) consider that the dyeing property of silk and
wool is due to the tyrosine present in albuminoid
combination, and that it reacts by virtue of its
phenolic character. Pure tyrosine gives similar re-
sults, but some albuminoids like salmine and scorn-
brine, do not react in this way. Silk reacts (dyes)
better than wool, because it has more tyrosine in
its composition in the ratio of 10 per cent, to
3-3i P er cent -
It is not clear, however, that silk does dye better
than wool. It is generally acknowledged that the
reverse is the case. Silk may dye more readily, it
EVIDENCE OF CHEMICAL ACTION IN DYEING 205
is true, but these authors do not attempt to show
that a standard dye will be taken up in the ratio
of 10 to 3. 5 at the saturation-point by the two fibres,
which should follow if this theory is correct.
The presence of tyrosine in the silk fibre is
indicated as follows. This fibre gives on oxidation an
indophenol or oxazine reaction in a similar way to
that obtained with a mixture of a />-diamine and
a phenol.
If silk be soaked in a .05 per cent, solution of
dimethyl />-phenylenediamine in the presence of
acetic acid and sodium acetate, and bromine water
added, the silk fibre takes a slate grey colour. In
the absence of silk (or wool) no such colour is pro-
duced. This reaction takes place with tyrosine
itself.
1.4 amidonaphthol will react in the same way.
Erdmann's patented process for dyeing feathers,
&c., is based on this reaction.
Some evidence brought forward by Knecht
(J.S.D. and C. 1902, p. 103) complicates, and in
a way tends to disprove the amido-acid theory.
The substances he isolated from wool and silk
dyed with night blue would only combine with
basic dyes, and not with acid ones. He also separ-
rated a compound from silk which was stated to
combine only with acid dyes.
The results obtained up to the present time by
different investigators may be summed up as follows.
Colours may be obtained by treating silk and
wool with nitrous acid, and phenols or amines,
206 CHEMISTRY AND PHYSICS OF DYEING
Therefore, silk or wool may be dyed in this way.
Deamidated fibres can be dyed as well as the original
ones, so that the dyeing property of silk or wool is
not necessarily due to NH or NH. 2 groups.
The relative action of the diamine colours on
animal and vegetable fibres is difficult to under-
stand, when considered from the chemical point
of view. For instance, cotton may be dyed black,
and wool be left white on dyeing in the cold with
Diamine Black, BWH.
In a paper on the " Chemistry of Wool/* M.
Matthews (/. Franklin, Inst. CLIX., No. 5, 397)
favours the amido-acid theory for the following
reasons :
(1) NH 3 is among the products of destrutcive
distillation of wool.
(2) Wool is easily hydrolised by dilute alkaline
solutions.
(3) It readily combines with acids, and even
with boiling dilute sulphuric acid.
(4) The nitrous acid reaction.
(5) The well-defined basic properties of the fibre.
The following so-called " coefficients of acidity "
are given:
Wool ... 57
Silk . . . 143
Albumin . . 20.9
Gelatin . . . 28.4
All these facts may be readily allowed, but the
evidence of the chemical nature of dyeing must
ultimately rest on a more direct foundation, in view
of the conflicting nature of the evidence, when it is
EVIDENCE OF CHEMICAL ACTION IN DYEING 207
considered from a general point of view, and is
taken in conjunction with other recorded facts.
Even if the substantive colours owe their attri-
butes to the grouping>N - R - N<as held by Vignon,
this theory is not applicable to many colours like
primuline, the mono-azo dyes, &c., as pointed out
by Green and Levy (J.S.D. and C. 13, 1898).
As far back as 1886 Mohlau attributed the sub-
stantive qualities to the alleged fact that benzidine
could be extracted from its solutions by bleached
cotton.
The above authors show that no affinity exists
between benzidine and the cotton fibre, or even
mercerised cotton. Dianisidine hydrochloride gave
the same negative results.
It is considered by Willstatter (Ber. 1904, 3758)
that if the dyeing of wool is due to salt formation,
the fibre as an optically active substance should
be capable of transforming, or " splitting," a racemic
dye-stuff into its optically active constituents.
No racemic dye-stuff being available, the hydro-
chlorides of atropine and homatropine were used
in the experiments.
An examination of the alkaloids left in the bath
still showed that they were in no way changed, and
remained optically inactive.
The inference is that no salt formation takes
place.
CHAPTER IX.
EVIDENCE OF CHEMICAL ACTION IN DYEING
(continued)
THE suggestion that dyeing is primarily due to
chemical action rather than physical action has re-
ceived the support of R. Hirsch (Chem.Zeit. 13, 432).
He assumed that " Knecht has established be-
yond doubt /that dyeing of animal fibres is a chemical
process. "
Such being the case there is no reason why dyes
alone should be regarded as capable of absorption
unless these compounds have something in common
from a chemical point of view, which distinguishes
them from other compounds. Nietzki has endea-
voured to show that this is the case (Chem. d. org.
Farbst., 2nd ed.).
The difficulty in including the nitro bodies in such
a scheme is evident. Nietzki meets this objection
with the statement that nitrophenols have most
probably a similar constitution to the nitrosophenols,
which are now generally regarded as quinone oximes.
Hirsch does not, however, agree with this view.
Experiments were made to ascertain if wool has any
affinity for organic substances in general.
EVIDENCE OF CHEMICAL ACTION IN DYEING 209
If wool is " dyed " with /3-naphtholsulphonic
acid R, the greater part of the sulphonic acid is
absorbed, and resists the action of boiling water;
when the wool is put into a solution containing diazo-
benzene, or diazoxylene, the corresponding colour is
developed with ease.
The nature of the alkali added to the bath
greatly influenced the rapidity of the development.
With sodium carbonate the action was very slow.
Similar results were obtained by producing Naphthol
Green (Cassella)on the fibre. Naphthionic acid was
fixed on wool in either acid or alkaline solutions.
On the other hand, sulphanilic acid combined
with great difficulty with wool.
G. H. Hirst's statement that a benzidine sulphate
solution boiled with silk, or cotton, contains all its
sulphuric acid at the end of the experiment, is no
proof that the benzidine is taken up by the fibre.
These experiments seem to indicate that wool
will absorb organic substances of the nature of
naphtholsulphonic acids, and that an acid state of
the solution is more favourable for absorption than
an alkaline one.
The fact that naphthionic acid is fixed by the
wool in both acid and alkaline solutions is probably
against <a chemical theory. Sulphanilic acid (p.-
amidobenzenesulphonic acid) is absorbed with great
difficulty, and only in concentrated solutions.
Three years later, Binz and Schroeter (Ber. 1902,
p. 4225) supported the chemical theory, but they did
not admit that in all cases the fixation of substantive
14
210 CHEMISTRY AND PHYSICS OF DYEING
dyes is due to salt formation between dye-stuff and
fibre.
The fact that certain acid dyes will dye wool and
silk in the presence of either acid, or alkali (caustic
alkali), and that there are basic dyes which will dye
in strongly acid solutions, is against any simple theory
of salt formation. It is clear that some other action
is involved.
Azobenzene-w.w'-disulphonic acid and p.-a.zo-
benzenemonosulphonic acid will both dye wool in
an acid bath. The " colours" will stand washing
with water, but are instantly discharged by dilute
sodium hydrate solution. These examples therefore
conform to a salt producing theory. If, however,
we dye with />.-hydroxyazobenzene we get an intense
yellow in acid, neutral, or alkaline solutions. Salt
formation is therefore unlikely in this case.
Again, />.-amidoazobenzene and p. -dimethyl
amidoazobenzene dye wool an intense yellow in a
solution containing a small proportion of acid. The
same shade is obtained, however, if the proportion
of acid is increased to 6, 12, 20, or even 120 molecules
of acid to each molecule of dye.
Further experiments showed that the hydro-
chlorides of w.w'-diamidoazobenzene and tetra-
methyl-w.w'-diamidoazobenzene gave different re-
sults. After an addition of 6 to 10 molecules of
hydrochloric acid to each molecule of base the wool
remained quite white.
The following conclusions were drawn from the
experiments. The groups NH 2 and N(CH 3 ) 2 in
EVIDENCE OF CHEMICAL ACTION IN DYEING 211
the meta-position to the azo groups, and the pre-
sence of the sulphonic acid groups impart to the
chromogen dyeing properties which result in the
formation of loose salts with the animal fibres.
A different state of affairs is assumed in the case
where the OH, NH 2 , or N(CH 3 ) 2 groups are in the
para-position. In the latter case the dyeing pro-
perties cannot be overcome by the addition of alkali
to solutions of the phenDlic dye-stuff, or of acid to
the basic substances.
Most of the substantive dyes for wool and silk
contain the amido- and hydroxyl-groups in the ortho-
and para-positions relatively to the chromophor,
and can be regarded as giving quinone derivatives
as isodynamic forms. When, however, these groups
are present in the meta-position, quinone formation
does not occur, and the dyeing is only a question of
salt formation, and that of a loose nature.
In the other cases where true dyeing is said to
take place, the action is probably due to a condensa-
tion in the nucleus between the dye-stuff and the fibre.
In answer to a severe criticism by v. Georgievics,
which is noticed elsewhere, in which the conditions
of the experiments are attacked, Binz and Schroeter
they bring further evidence in support of their case
(Ber. 1903, 3008).
Azobenzenecarboxylic acid is a dye-stuff in the
same sense as the corresponding sulphonic acid,
but it will dye only in neutral solution.
Again, />-.benzeneazo-trimethylammonium hy-
droxide dyes wool, but the colour is destroyed by the
212 CHEMISTRY AND PHYSICS OF DYEING
addition of hydrochloric acid in equivalent quantity
to the dye-stuff fixed.
The fact that chrysoidine and Bismarck brown
give darker shades in the presence of hydrochloric
acid is noted in confirmation of the idea that p.-
amidoazobenzene yields with the fibre a condensation
product, and not a salt. It is therefore contended
that azobenzenesulphonic acid and carboxylic acids,
m-amidoazobenzenes and quaternary ammonium
bases of the azo compounds dye with simple salt
formation.
On the other hand, ortho- and para-amido-
azobenzenes and most of the ortho- and p.-
hydroxyazo compounds cannot give normal salts.
Here a condensation of the fibre substance with
the quinoid nucleus of the dye-stuff is said to take
place.
These experiments will require extending before
such definite statements can be accepted. For
instance, they do not agree with Prof. Green's results
obtained with the sulphonic acids.
These authors still further defend themselves
against a second criticism by v. Georgievics (Ber.
1904, 727). They deny that the neutral sodium
salt of azobenzene-/>. -sulphonic acid is capable of
dyeing wool in neutral solution. They claim that
the wool used must have contained free sulphuric
acid.
They also consider that the fact that alcohol
will remove the dyes from the fibre is not proof that
there is no combination between the dye and fibre.
EVIDENCE OF CHEMICAL ACTION IN DYEING 213
The solvent action may be due to decomposition
of the fibre dye compounds first formed.
They do not seem to meet the statement that
benzene will act in the same way. They also deny
that picric acid is extracted by alcohol from wool
after dyeing.
Many of the contradictory results obtained by
different observers may be due to the different con-
ditions of dyeing, fibre state, &c.
Hirsch's experiments might well be compared
with the above in their general effect.
Examining the tinctorial values of the three
isomeric hydroxyazobenzenes (Zeit. /. Farb. und
Text. Ind. 1904, p. 177), Prager criticises the results
obtained by Binz and Schroeter. He will not allow
that dyeing may be a condensation in the nucleus
between the quinoid dye-stuff, and the substance
of the fibre.
The ortho- and para-hydroxyazobenzenes are
capable of assuming the quinone type, but the
meta-compound cannot apparently assume an
isodynamic form. The meta-compound should
therefore not act as a dye.
In practice it is found that the meta-compound
will dye wool, as well as the para-compound. These
results are held not to favour the condensation
theory.
Collecting some of the facts recorded in this
chapter and elsewhere, the conflicting nature of the
evidence in favour of a simple chemical theory will
be at once realised.
214 CHEMISTRY AND PHYSICS OF DYEING
1884. Miiller Jacobs. Amido-azobenzene will
not dye cotton, di- and triamidobenzenes will do so.
1889. Ewer and Pick. Naphthylenediamines.
Position of amido groups determines dyeing power
on cotton ( QI a 3 positive dyes).
1889. Hirsch. /3-Naphtholsulphonic acid R.
dyes wool. Naphthionic acid fixed by wool (acid
or alkaline). Sulphanilic acid has very slight
affinity for wool.
1894. Green. Colourless sulphonic acids have
no affinity for animal or vegetable fibres. Dehydro-
thiotoluidinesulphonic acid an exception in the case
of animal fibres.
Colour derived from metaphenylenediamine and
primuline will dye cotton, that from /3-naphthol
will not.
1902. Binz and Schroeter. Azobenzene m.m'-
disulphonic acid and />.-azobenzenesulphonic acid
dye wool from an acid bath ; />.-oxy-azobenzene dyes
wool in acid, neutral, or alkali bath, />.-amidoazo-
benzene and />.-dimethylamidoazobenzene dye in
acid bath of any strength.
Hydrochlorides of w.w'-diamidoazobenzene and
tetramethyl-w.w'-diamidoazobenzene, dye wool in
neutral solution, but not acid.
1903. Binz and Schroeter. Azobenzenecarb-
oxylic acid and ^.-benzeneazotrimethylammonium
hydroxide will dye in neutral baths, but not in acid.
1904. Prager. o.- w.-and />.-bydroxyazobenzenes
dye wool in acid solutions.
1904. Binz and Schroeter. The sodium salt of
EVIDENCE OF CHEMICAL ACTION IN DYEING 215
azobenzene ^.-sulphonic acid is not capable of dyeing
wool.
It will be at once seen that the reactions which
take place in dyeing are, from a chemical point of
view, of such a nature that it is difficult to appreciate
their true value.
It is not easy to explain the action of some dye
solvents on dyed mixtures of cotton and silk. It
is well known that some dyes may be dissolved out
of the silk fibre and not taken out of the cotton by
a solution of ammonium acetate. In this way
" shot " effects may be produced.
It is generally agreed that cotton is comparatively
inert as an absorbent of dyes, yet under these con-
ditions we have an enormously increased attraction
as compared with silk. With these dyes we may
even obtain black cotton and white silk.
A further study of the relative " absorption "
of the dyes in the respective fibres under varying
conditions may clear up this point, and will be
considered.
In the year 1884 Bcettinger discovered a dye
which he named Congo Red. He found that it
possessed the then extraordinary property of dyeing
cotton direct from aqueous solution as well as it
dyed silk.
The whole subject of the action of these direct
dyes on cotton (and other fibres) is little understood.
In a general way, there seems to be some connec-
tion between the constitution of the dye molecule
and its action. It seems to be important that the
216 CHEMISTRY AND PHYSICS OF DYEING
amido-groups occupy the para-position, and that
the ortho-positions be occupied by a hydrogen
radical. The meta-position seems to have little
influence in the dyeing or tinctorial properties.
The double chromophorous group ~ N ^ N I^ in
the tetrazo dyes seems to influence the dyeing in
some way, but the presence of this group alone does
not suffice to make the dye a " direct " one.
The primuline dyes do not contain this group,
nor are they azo dyes at all.
They possess the chromophorous group <^> c -
Some dyes contain both this and an azo group ; a
dye of this nature is Cotton Yellow R.
It may be said here that the view of chemical
action occurring in the dyeing of these colours is
unsatisfactory so far as the dyeing of cotton is con-
cerned. In fact, the advent of these dyes has
been as unexpected, and revolutionary, from the
theoretical as from the practical point of view.
The fact remains that there are many dyes which
dye cotton direct under conditions which seem to
exclude any chemical action.
In certain cases, the affinity of the cotton for
the dye is so great that the bath is almost exhausted.
This is so in the case of Diamine Fast Red F. In
other cases a great proportion of the dye is left in
the solution. The facts known about the dyeing
of these dyes are incomplete. The dye in most
cases is readily removed by water. This is, of course,
noticed with other dyes on silk. The amount of
EVIDENCE OF CHEMICAL ACTION IN DYEING 217
dye taken up seems to vary with the concentration
but no careful work has been done on this subject.
The results could not fail to be interesting. The
addition of neutral salts and their great effect on
the rate of dyeing in solutions containing these
substances is very instructive. Their action from
a chemical point of view is difficult to gauge. The
fact that these dyes are less soluble in the salt solu-
tions possibly accounts for their action, and this
fact seems to point to a physical rather than a
chemical process. The fact also that these dyes will,
when on the fibre, combine with or form lakes with
the basic dyes seems to show that the dyes are not
in combination with the fibre (Knecht, J.C.D. and
C. 1886, 2).
The attraction of these dyes for wool and silk
is also a strong one, as is seen when the test of
resistance is applied to the action of the ordinary
solvents (water, &c.).
The factor which operates in the case of cotton
therefore seems to have a similar value in the dyeing
of silk or wool.
A point which must be noticed is, that these
dyes seem on the animal fibres to have a greater
resistance to the action of light than the same
colours on cotton.
It seems strange, also, that these dyes are taken
up more readily in alkaline solutions by cotton, and
more readily in acid solutions by silk.
Diamine Milling Black is even said to dye
well in a solution containing 7 ozs. of soap and
2i8 CHEMISTRY AND PHYSICS OF DYEING
ij ozs. of soda to a gallon (Text. Manuf. 1901, p.
3I9).
In the practical dyeing of cotton three supple-
mentary processes are used to increase the fastness
of these dyes, viz., diazotising ; treatment with
metallic salts; or the "coupling" process. From
their action it will be necessary to briefly describe
them here.
Diazotising produces shades which are very
resistant to the action of soap solutions at the boil,
and sometimes to light.
After dyeing, the fibre is put through a solution
of nitrous acid, subsequently washed, and " devel-
oped " in solutions of amines, or phenols.
In practice /3-naphthol, m.-phenylenediamine
or resorcinol are chiefly used as developers.
In the case of primuline, chloride of lime gives
a very fast yellow if it follows the diazotising process.
The increased fastness produced by the treat-
ment with metallic salts is also noticeable.
The shades are faster against the action of soap
and light.
Treatment with copper sulphate, although it
does not act so universally as was at first claimed,
gives very satisfactory results in many cases.
Diamine Sky Blue F.F. is greatly increased in
fastness. Diamine Brill. Blue G. is claimed to give
as fast colours as vat indigo blue in this way.
At one time it was thought that treatment with
copper sulphate would increase the fastness of all
dyes.
EVIDENCE OF CHEMICAL ACTION IN DYEING 219
Bichromate of potash gives greater fastness
against soaping with Diamine Jet Black and Diamine
Brown M.
Fluoride of chrome is also used with Diamine
Bronze, Fast Red F., &c., to produce the same effect.
Where the action is not that of a mordant it is obscure.
The process known as coupling has been already
referred to. Here basic dyes are added to the bath
and fixed by direct combination, or lake formation.
The difficulty attending the production of a
satisfactory theory to explain the varied results
obtained in the dyeing of cotton has been increased
by the addition of still another class of dyes, viz.,
the sulphur dyes ; it would, perhaps, be more
correct to say by the extension of this class, for
Cachou de Laval may be considered a member of
this group.
These colours are produced by soaking the cotton
fibre in a hot alkaline bath in the presence of sul-
phide of sodium.
The colours are developed and fixed by subse-
quent exposure to the air (oxidation).
The extra fastness of dyes produced in the fibre
is generally noticeable.
In this case the dye is soluble in the alkaline
bath by reduction, and subsequently by oxidation
insoluble dyes are produced in the fibre itself. In
some cases a more energetic oxidation is necessary.
Immedial Blue C. may be developed by hydrogen-
peroxide or by the combined action of steam and
alkali.
220 CHEMISTRY AND PHYSICS OF DYEING
Until we know more about the constitution of
these dyes it is only possible to speculate as to the
exact nature of their development.
In the dyeing of indigo, also, some similar action
plays at least a secondary part. Indigo is present
in the dye vat in a soluble and reduced form.
Subsequent oxidation of the indigo white after
absorption in the fibre produces the insoluble indigo
in situ. The dye so formed is remarkably fast
against the action of light, or soap solution. It
may, however, " rub " badly if the operation of
developing is improperly conducted.
So far as we know we can reproduce the condi-
tions of formation of these " oxidation " dyes as
they exist in the presence of a fibre. There is no
reason to think that the formation of the insoluble
dye-substances in the fibre material takes a different
course to that taken in solution, in the above cases.
The action of tannic acid on organic colloids is
an instructive one. The tanning of leather is of
such a nature, that the theoretical work connected
with tanning should be closely followed by those
interested in the general operations of dyeing.
The nature of the attraction which silk exhibits
for tannic acid is indicated as follows. It is more
readily removed from the fibre by a dilute solution
of hydrochloric acid than by a solution of sodium
carbonate.
The reaction between oxy cellulose and basic dyes
has been studied by Vignon (Compt. Rend. 125, 448).
It is found that this substance has a greater
EVIDENCE OF CHEMICAL ACTION IN DYEING 221
attraction for these dyes than the unaltered cellu-
lose. This will be seen in the following table, which
gives the results obtained with one gramme of fibre.
Fibre, Safranine, Methylene blue,
Cellulose . . .000 g. absorbed .002 g. absorbed
Oxycellulose . .007 g. ,, .006 g. ,,
The same investigator (Compt. Rend. 1887, 125,
357) has made an attempt to determine the mole-
cular groups which confer on certain dyes the property
of dyeing cotton direct. Compounds having similar
constitutions to these dyes were taken. The basic
substances were employed in the form of their hydro-
chlorides, and their action in the presence of cotton
carefully noted.
The following table shows the relative absorp-
tion of a number of organic substances.
Substances absorbed by cotton, Neutral bath, Alkaline bath,
Ammonia .... .2--4 . . .2
Hydroxylamine . . . .o-.3 . . .2
Hydrazine . . . . 1.2 .. 1.7
Phenylhydrazine . . . 3.6 . . 2.9
Aniline ..... .1 .1
Dimethylaniline ... .o .o
Diphenylamine .... .4 .4
o.-Phenylenediamine . . .4 .6
m -Phenylenediamine . . 6.4 . . 2.4
/>.-Phenylenediamine . . 6.7 3.2
Benzidine . . . . 6.0 .. 5.6
Tetramethylbenzidine . . 7.0 6.3
Benzidinesulphonic acid . . 7.4 . . 4.8
Diamidostilbenedisulphonic acid . 3.5 .. 3.6
Dianisidine .... 6.Q . . 5.7
Diamidonaphthalene . . . i.o 1.7
The following conclusions are drawn by Vignon
222 CHEMISTRY AND PHYSICS OF DYEING
from the results recorded in this table. Fixation
is held to be due to chemical action depending on
molecular grouping. The dyeing is not due to the
benzene nucleus containing free nitrogen atoms, or
two nitrogen atoms joined together to form azo-
groups, since diphenyl, ammonia, hydroxylamine, and
azobenzene are not absorbed. The diamines, with the
exception of o.-phenylenediamine and the hydrazines
are absorbed to a considerable extent, and the
absorption appears to be independent of the degree
of saturation of the azotised molecular groups.
It is argued from these results that the dyeing
property seems to be due to the grouping
>N R N< or >N N<
that is to say to the hydrazine N atoms united
directly, or indirectly by means of aromatic residues.
It is further argued that in the case of the direct
colouring-matters the nitrogen atoms unite with the
cellulose molecule and then become pentatonic.
>N-N<
A A
The fact that benzidine and tetramethylene-
benzidine are absorbed by cotton, whereas the methyl
iodide compound of the latter in which the nitrogen
atoms are already pentatonic is not taken up, also
lends support to this theory.
The thermo-chemical investigations of Vignon
are instructive (Bull. Soc. Chim. 1890, 3, 405 and
Compt. Rend, no, p. 909), and are held by that
investigator to support a chemical theory. Dealing
EVIDENCE OF CHEMICAL ACTION IN DYEING 223
first with silk in the " raw " and " boiled off " state,
the following results ware obtained :
Raw Silk,
Boiled-off Silk,
Reagents N/i sols.
Calc. for
Cal.formolJ Calc. for
Calc. for
100 grms.
wt. in grms.
100 grms.
mol. wt.
Water .
.10
3-5
-15
5-2
Pot. Hydrate .
i-35
47.0
1.30
45-25
Sod. Hydrate .
i-55
53-95
1.30
45-25
Ammonia
65
22.65
50
I 7-4
H 2 S0 4 .
95
33-iQ
.90
31-35
HC1
95
33-10
.90
31-35
HNO 2 .
.90
31-35
85
29.60
KC1
.20
6-95
.10
3-50
6.65
6.00
The above figures represent the heat-units
evolved, the average temperature of the experiments
being 12 C. The formula for gum silk was taken
as C 141 H 232 N 48 O 56 , and that of the boiled off silk as
the same.
The alkalies removed some of the silk gum. The
total number of heat-units evolved was 6.0 in the
case of ungummed silk, and 6.65 in the case of the
raw silk.
The results obtained in the case of wool were
different.
Reagent N/i sol.
KHO
NaHO .
HC1
H,S0 4 .
Heat-units per
i oo grms.
1.16
95
99
Heat-uuits for
24.50
24.30
20.05
20.90
224 CHEMISTRY AND PHYSICS OF DYEING
These experiments were made on unbleached
woollen thread.
Turning to cotton it was noticed that the rise in
temperature took seven or eight minutes to reach
its maximum. The following results were obtained :
Reagents. Cotton thread unbleached. Cotton wool bleached.
per 100 grms.
C 6 H 10 5 .
per 100 grms.
C 6 H 10 5 .
KHO .
.80
1-3
- . . 1.4 . .
2.27
NaHO .
. .65
1.05
1-35 , -
2. 2O
HC1
.40
65
.40 ..
.65
H 2 S0 4 .
. .38
.60
.. .36 ..
.58
The effect of bleaching on the thermo-chemical
reactions in the case of cotton is important. Vignon
considers that the difference is due to the presence
of oxycellulose in the latter.
These results would in themselves indicate that a
chemical reaction may take place under the recorded
conditions. It has, however, been shown (Goppels-
roeder, Centr. /. Text. Ind., No. 38) that both
indigo and Turkey Red are attracted with greater
avidity by oxycellulose and chlorocellulose, but
there does not seem to be much evidence that chemi-
cal action can take place in the dyeing of these
colours.
Furthermore (Chem. Zeit. 23, 1891), Vignon ex-
perimented with the object of increasing the activity
of cellulose fibre by chemical means. Treatment
with ammonia at 100 200 C resulted in the fibre
taking up nitrogen. The result in the calorimeter
with this product indicated that the fibre was more
EVIDENCE OF CHEMICAL ACTION IN DYEING 225
basic. This treated fibre will attract large quantities
of acid dyes giving dark shades.
The influence of this treatment seems to be very
great, and the attraction for dyes is increased.
Experiments with stannic and metastannic acids
also give important results when they are " dyed "
with phenosafranine.
Stannic acid absorbed 63 per cent, of the dye in
a standard solution.
Metastannic acid absorbed o per cent, of the dye
in a standard solution. The more strongly acid
oxide fixes the most colour.
Vignon sums up the results of his experiments
(Chem. Zeit. 10, 1891), and considers that the following
facts are in favour of a chemical theory.
(1) Thermo chemical reactions of fibres.
(2) Increased affinity shown by ammonia treated
cotton.
(3) Action of the oxides of tin.
The chief arguments in favour of chemical
action are summed up by v. Georgievics as follows :
(1) Magenta, methyl violet and chrysoidine are
decomposed by silk and wool, hydrochloric acid
remaining in solution.
(2) Rosaniline base is colourless. The salts
are coloured. Wool is coloured when dyed from
an ammoniacal solution of the base (Jaquemin).
(3) The red solution of amidoazobenzenesulphonic
acid dyes a yellow shade. This is the colour of its
salts.
(4) Picric acid and Naphthol Yellow are taken
15
226 CHEMISTRY AND PHYSICS OF DYEING
up in quantities proportional to their molecular
weights.
(5) The thermo- chemical reactions of the fibres.
It is pointed out, however, that the decomposition
of the basic dyes is brought about also in the presence
of porous inorganic materials, as the following figures
will show. The presence of an animal fibre is not
necessary.
Colouring-matter.
Amount
taken.
Cl in same,
Colour left
in sol,
Cl left in
sol.
Magenta
.2045
.0166
.08
.0158
Methyl violet
.2007
.0152
.09
.0152
Chrysoidine
.2015
.0309
.122
.0265
It will be seen that the proportion of colour
base taken up by the porous material is 53 per cent,
against only 8 per cent, of the chlorine.
Glass beads will act in the same way, decompos-
ing the hydrochloride of the base.* Wool takes up
more hydrochloric acid at 45 than at 100 C, so
does porcelain.
It is said that a rosaniline base can exist in two
forms, and that the base is dark violet if precipitated
in neutral solutions. The base, therefore, may exist
in two forms : (i) As carbinol (colourless) ; (2) As
ammonium base (coloured).
A colourless aqueous solution of the base does
not, therefore, exist as Knecht states, and Jacque-
* It has recently been stated that Jena glass will not act in
this way, owing probably to its great insolubility.
EVIDENCE OF CHEMICAL ACTION IN DYEING 227
min's experiments may be explained as follows.
The wool and silk absorb the base from the solution,
and since the alkali is not taken up by the fibre the
wool is coloured red.
There seems to be some doubt as to the existence
of the coloured ammonium base. H. Weil considers
that the colour is due to unchanged magenta in the
precipitate.
V. Baeyer (Ber. 1904; 2849) also doubts the
existence of v. Georgievics' coloured ammonium base.
Hantzsch (Ber. 1900, 752), on the other hand,
holds that the rosaniline bases are capable of
existing.
(i) True colour base :
H;N.C 6 H 4
(2) Pseudo ammonium base :
(3) Imide or anhydride base :
H,N.C fl H c /^-=-\.
H 2 N.C (; H 4 > -\ = /
Further work on the absorption of dyes by in-
organic substances has been undertaken by Gmelin
and Rotheli (Zeit. f. angew. Chem. 1898, 482).
Glass beads were dyed for eleven weeks under
identical circumstances with (i) Magenta ; (2) Ma-
genta and ammonia ; (3) Rosaniline base. They
were all dyed to the same shade.
Each lot was then washed with alcohol. The
two last lots soon lost their colour. The first kept
its colour for some time, and was even then not
decolourised.
228 CHEMISTRY AND PHYSICS OF DYEING
It is argued from these results that magenta
may dye in two ways, the one chemical, and the
other mechanical.
These results are held to confirm the existence
of two states of one magenta base, and that the
carbino] base is fairly stable, and requires strong
acids to convert it into the ammonium base. The
conversion of the one into the other in the presence
of silk is explained by assuming that the silk acts as
an acid.
Some experiments on the alkylation of magenta
compounds also seemed to point to chemical action.
A skein of silk dyed with magenta was allowed
to stand in the cold in contact with methyl iodide
in methyl alcohol. Side by side, and in the same
mixture, were rosaniline base, rosaniline hydro-
chloride (magenta), rosaniline stearate, and the
amido-stearate of the same base.
The only change noticed was the alkylation of
the rosaniline base. This changed to a deep blue.
The inference is that the magenta is present in the
silk in a state corresponding to the hydrochloride,
stearate, &c. In other words, it is combined with the
silk. Unfortunately, it was not proved at the same
time that the insoluble basic salts act in the same
way as the base itself, and not as the normal hydro-
chloride. Until it is settled that the magenta is not
present in this state on the silk, these results are
inconclusive. At a temperature of 35-4o C
alkylation took place in all cases. They all turned
dark blue.
EVIDENCE OF CHEMICAL ACTION IN DYEING 229
The colour of amidoazobenzenesulphonic acid on
the fibre is held by v. Georgievics to be yellow because
the amount of dye present is not sufficient to dye it
red.
Attempts have been made by Prudhomme (Rev.
Gen. des Mat. Col. 1900, 4, 189) to replace the fibre
by a liquid for experimental purposes, with the
object of studying the results obtained under these
conditions. Taking a solution not miscible with
water, he dissolved salicylic acid or a weak base
(acetanilide) in the same. A substance like phenylgly-
cocoll may be added containing both basic and acid
groups. " Dyeing " with basic colours, different shades
to those of the solution were obtained in the " artifi-
cial fibre." They corresponded with those obtained
on silk with the same dyes. Similar results were
obtained with the sulphonated acid colours, using
acetanilide as the " artificial fibre." That silk and
wool behave like amyl alcohol containing the above
substances is the conclusion drawn from these ex-
periments.
The presence of salt-forming groups in the alky-
lated diazo direct dyes is said to be proved (Mayer
and Schafer, Ber. 27, 3355), and this is put forward
as a possible explanation of the absorption of these
dyes by cotton.
The impurities present in the cotton fibre may
influence its dyeing properties in some cases.
Schunck suggested (/.S.C./., 815), that this should
be tested by dyeing samples of the cotton after each
of the following operations ; treatment with carbon
230 CHEMISTRY AND PHYSICS OF DYEING
disulphide, alcohol, boiling water, hydrochloric acid,
and then alkali.
The evidence in favour of the presence of carboxyl
groups in the silk molecule is fairly satisfactory.
Carboxyl compounds are formed when silk is decom-
posed by barium hydroxide (Schutzenberger and
Bourgeois), and by dilute sulphuric acid (Cramer),
or alcoholic potash (Richardson).
The result of dyeing wool with both acid and basic
dyes at the same time, seems to offer some support to
the chemical theory. Weber shows that this may be
done if a skein of wool be dyed with Scarlet R. After
being carefully washed, it will take up magenta. The
percentage of this second dye will also be the same
as that taken up by a white skein. Furthermore,
the lakes produced by the combination of acid, and
basic dyes are soluble in alcohol, but this solvent
will not remove these dyes from the fibres.
It has not yet been shown that a second acid dye
will not enter a saturated fibre already dyed with a
colour of this class, or that a basic dye will not ad-
here to a basic dyed fibre. This would necessarily
follow if the second colour did not displace the
original one. Further work is necessary before these
points can be cleared up.
Weber's statement that the benzidine dyes are
attracted both in the free state and as salts, is con-
firmed by Gmelin and Rotheli (Zeit. /. angew. Chem.
1898, 482). The barium salts of benzopurpurin
4B and benzoazurin %G were prepared in as pure
a state as possible. They both dyed cotton, and
EVIDENCE OF CHEMICAL ACTION IN DYEING 231
subsequent analysis proved that the dye was present
on the fibre as the barium salt, and that no decom-
position had taken place during the process of dyeing.
Owing to their reduced coefficients of diffusion
they dyed very slowly. Correspondingly they did
not bleed when once on the fibre.
A microscopical examination of fibres in sections
gives the following results : Wool dyed with Crystal
Violet or Malachite Green shows equal distribution
of dye throughout the fibre.
Cotton dyed with the direct dyes shows in cross
section that the dyes are more concentrated in the
centre of the fibre.
Under the same conditions silk seems to be dyed
equally throughout. A similar result was noticed
by the writer with the primuline dyes in the case
of silk.
Returning to the basic dyes, these authors pre-
pared the salts of palmitic and stearic acids, and
dyed silk with them. The fibre was then dissolved
in hydrochloric acid, but no fatty acids could be
traced in the solution.
They also record the fact that the benzidine
salts of Naphthol Yellow S were decomposed on
dyeing, the benzidine remaining in the solution.
This is, perhaps, the place to notice some ex-
periments of Schunck and Marchlewski (J.S.D.
and C. 1894, 95). The tinctorial effect of plant
extracts is greatly increased by boiling with acids,
and the conclusion arrived at is that the effect pro-
duced is due to the decomposition of the glucoside
232 CHEMISTRY AND PHYSICS OF DYEING
and rhamnosides of the colour-substances present
in the extracts. It is, therefore, necessary to
assume hydrolysis to explain the actions noticed in
practice when glucosides are used in dyeing.
It has been assumed that chrome mordants split
up the glucosides in dyeing, and fix their colour
constituents only (Hummel and Liechti).
The authors find that in practice this assumption
is correct. In dyeing cotton with datiscin, rutin
and quercitrin the sugar is left in the solution.
In the case of ruberythric acid the decomposition
did not take place.
It will be seen from the facts recorded in the
last two chapters, that the evidence brought forward
to prove that the action of dyeing is a chemical one,
is both voluminous, and diverse, in its nature, and
that many of the facts which at first sight seem to
support this hypothesis appear less definite on
further examination.
One of the most striking examples of this is seen
in the fact that such an inert substance as porcelain
will split up the basic hydrochlorides, in much the
same way as silk will do under similar conditions.
The base may be held by combination in the
second case ; but it is clear that the action may take
place in the absence of any organic matter whatso-
ever, be it an amido-acid, or of any other constitution.
It is therefore a matter of difficulty to give
to the recorded facts their true significance.
The fact that most of the work done on this
subject is of a qualitative nature, whilst in many
EVIDENCE OF CHEMICAL ACTION IN DYEING 233
cases the reagents, and fibres, are in an unknown
condition of purity, greatly increases the difficulty
of the problem.
It is not possible therefore to do more than
record the results obtained in many cases, and
leave the future to sift out the grain, and carefully
weigh it as evidence against the facts which seem
to favour a wider theory of dyeing.
It would seem that generally speaking, certain
facts indicate that dyeing may be due to chemical
action ; but it is an exceedingly difficult thing to
prove from these that the action is really of this
order.
Until the time comes when we are able to
explain the actions which take place when colloids
react in the presence of solvents, and definitely
assign to these phenomena their true value, it will
be difficult to establish a strictly chemical basis for
the reactions which take place in dyeing ; or even
to prove that such action is a determining factor
in the processes of dyeing, mordanting, and the
formation of certain lakes.
CHAPTER X
PART PLAYED BY COLLOIDS IN DYEING AND
LAKE FORMATION
IT will have been gathered from the reactions shown
by colloids in general, and from the fact that both
dyes and fibres belong to this class, that the part
played by these bodies in dyeing may be an import-
ant one.
It has even been suggested that the fixation of
the dye-stuff on vegetable fibres is analogous to
the act of diffusion through colloids. This idea
was first put forward by Muller Jacobs (Text. Colour-
ist, Oct. and Nov. 1884).
Some time before this Schumacher (Physik der
Pftanze\ experimenting with such typical colloids
as starch, cellulose fibre, membranes, &c., noticed
that there was not only an absorption of liquids,
but also of the solids in solution. He noticed that :
(1) The relative absorption of solids is greater,
the more dilute the solution.
(2) The absorption decreases as the temperature
increases.
(3) Total exhaustion does not take place even
in very dilute solutions.
COLLOIDS IN DYEING AND LAKE FORMATION 235
These results are applied to the absorption
phenomena of vegetable fibres, and an attempt
made to explain the action of dyeing with these
fibres, which, unlike the animal ones, do not so
directly absorb ordinary acid and basic dyes, and
therefore cannot be so readily brought into line
with any so-called chemical theory.
This explanation of the action of dyeing there-
fore originated in an attempt to explain more
particularly the specific action of vegetable fibres
towards dye-stuffs.
To accept this theory we must allow that the
action of dyeing is due to the separation of the
sparingly soluble colloid dye from the diffusible
crystalloid, or solvent, by the dialytic action of the
membrane itself ; which then becomes obstructed,
(1) by the formation of insoluble precipitates ;
(2) by the gradual obstruction of the colloids
in the interstices of the fibres.
In order to dissolve these sparingly soluble or
non-permeable bodies, we must first dissolve them
in crystalloids or easily permeable solvents.
Dr. Jacobs describes an interesting series of
experiments with the artificial membranes obtained,
when a concentrated and neutral solution of alu-
minium sulphate is introduced into a not too dilute
solution of Turkey Red oil. Membranes are in this
way formed round the drops ; and the diffusion of
substances through them can be easily observed.
For instance, when alizarine is mixed with the
outer solution the colour diffuses into and colours
236 CHEMISTRY AND PHYSICS OF DYEING
the cell walls, but there is a total absence of colour
in the interior solution. These experiments were
carried further, and alizarine and a neutral solution
of alumina gave a red lake in the cell wall, but
here again the interior remained colourless.
This investigator proposed the following classifi-
cation of dyes in the place of Bancroft's scheme,
which divide them into substantive and adjective
colours :
(1) Such substances as easily pass through
colloids or fibres.
(2) Such substances as pass with difficulty
(colloids).
(3) Substances which will not pass at all.
These classes are not considered to be distinct
but to merge into one another and overlap.
The object of dyeing is, therefore, to fix certain
substances within the fibre in such a way that the
fibre cannot be easily deprived of them by the action
of solvents. The means by which this action may
take place are considered to be
(1) By producing precipitates in the fibre.
(2) By complete separation of a sparingly soluble
colloid from the diffusible crystalloid or solvent, by
the dialytic action of the membrane itself.
The mordanting and dyeing actions are therefore
considered by this investigator to be based on the
action of two, or more, differently permeable bodies.
It is claimed also that this action may even give rise
to actual decomposition of certain chemical com-
pounds.
COLLOIDS IN DYEING AND LAKE FORMATION 237
The action of mordants in the fibre is a double
one. It may either form precipitates with the dyed
material, or else reduce the permeability of the
fibre substance.
The reason why vegetable fibres do not dye easily
is also explained by assuming that they are more
easily permeable than the other fibres. This is
perhaps not the generally recognised view of the
case.
Similarly, mercerising or oxidation of the fibre
does not act by reducing this action, but by
increasing it in some cases.
The presence of albumin, casein, &c., on the
fibre increases the colloidal nature of the fibre, and
therefore the laws of dialysis will produce more
powerful effects.
In this way Miiller Jacobs attempts to explain
the action of dyeing.
The effect of tannic acid in its mordanting
action is to narrow the interstices of the fibre, and
then combine with the dye to form a precipitate.
The proof of this action is said to be demonstrated
by the fact that in dyeing alizarine on an aluminium
mordant the latter must be present in great excess.
Fifteen times the alumina necessary to form the
normal salt (C 14 H 6 O 2 .A1 2 O 5 ) must be present to
give the best result.
The action of acids, tartar, &c., is said to prevent
the superficial fixing of colours.
An attempt to extend this theory to the animal
fibres is based on the fact that oiled cotton will dye
238 CHEMISTRY AND PHYSICS OF DYEING
red with rosaniline hydrochloride. It is considered
that this is evidence that the dyeing of animal fibres
is not a chemical action.
In this and in other ways this theory is supported.
For instance, many organic colloids are hardly
diffusible into animal fibres owing to their insoluble
nature. The sulpho-acids of these substances being
more soluble in water give better results. They
can more readily penetrate the fibres. Alizarine
carmine and sulph-indigotine are given as examples.
They are both more soluble than alizarine and
indigo, and therefore dye the fibres in a more
satisfactory way.
On the other hand, these sulpho-acids may be
too diffusible for vegetable fibres.
Assuming also that the dyes become more like
precipitates, as their nature becomes more compli-
cated, and as the amount of carbon they contain
increases, it might be expected that the complex
members of a group of colouring-matters would
require to be present as sulpho-acids for dyeing
purposes. This seems to be the case with the rosani-
lines.
The ami do-benzenes are also quoted as an example.
(1) Amido-azobenzenes (Aniline Yellow) is spar-
ingly fixed on cotton even as the sulpho-acid.
(2) Diamido - azobenzene (Chrysoidine) dyes
cotton well.
(3) Triamido - azobenzene (Phenylene Brown)
dyes well.
This action with the sulphonic acids is not a
COLLOIDS IN DYEING AND LAKE FORMATION 239
general one. For instance, the indulines are in-
soluble, and sulpho-acids form more or less readily,
but these will not dye cotton. It is considered
that they are, in this case, too diffusible.
The general conclusions arrived at were as
follows. The permeability of a substance increases
with rise in temperature, and fibres with narrow
interstices require a higher temperature in dyeing.
Wool would come into this class. It is also con-
sidered that when mordanted cotton is dyed at a
low temperature, the relatively large interstices
become smaller by deposition of the dye-stuff, and
then a gradual rise in temperature is required to
complete the dyeing operation.
If, on the other hand, the cotton is immersed
initially in the boiling dye-bath, the colour will pass
through these large interstices, and the material
remain undyed. The mordant in this case is
dehydrated, and the colour cannot be fixed.
From this point of view the case of the colour-
less sulphonic acids and their absorption is of in-
terest. Is dehydrothiotoluidine sulphonic acid the
only one in a highly colloidal state ? This might
be capable of direct proof. This theory has been
roughly outlined. Further particulars will be found
in the original papers.
There is direct evidence from the work of
Picton and also from that of Krafft (Ber. 1899,
32, 1608), that high molecular dye-stuffs, such
as the direct azo dyes, are colloids.
A series of experiments with Magenta, Methyl
240 CHEMISTRY AND PHYSICS OF DYEING
Violet and Methylene Blue gave values by the
ebullioscope in alcoholic solutions very near to the
true molecular weights. In water, however, the
colloidal state is taken up.
This result may be due to dissociation, and the
less soluble nature of the base ; or perhaps to asso-
ciation.
It is interesting to note also that tannic acid
is said to be a very perfect colloid (Strutz and
Hofmann), and to consider, as we have done else-
where, the action of this acid.
In the case of wool and silk, Krafft considered
that the fibre itself takes part in the interaction in
dyeing ; but that in the case of cotton the action
is of a more indeterminate nature.
We may learn much concerning the properties
of colloids in the hydrogel state, and their action,
from a study of the phenomena which occur in the
formation of coloured lakes, for pigments and print-
ing purposes. This subject has been more or less
exhaustively studied from the practical point of
view by O. Weber. The results in detail may be
studied in the original papers.
It is well known that basic dyes (hydrochlorides)
will fix themselves on indifferent substances, such
as starch, cellulose, alumina, china clay, &c. In
this way pigments may be formed.
The dyes are, however, very loosely held, yield-
ing readily to water. They are also very fugitive
to light (Weber, J.S.C.I. 10, 896).
It is also noticed that these dyes do not give
COLLOIDS IN DYEING AND LAKE FORMATION 241
identical shades on these different media. This
effect is also noticed in the case of dyeing on
fibres, with this class of dyes. The shades
obtained on cotton, wool, and silk, will often
materially differ from one another, so that this
action seems to be a general one. The student
will at once realise the general nature of these
dyeing operations.
It is interesting to note that tannic acid, which
has been of great value in the dyeing of cotton
with basic dyes, is not much used in the pro-
duction of lakes. When, however, the manufac-
turers will trouble to prepare their basic lakes in
this manner, they are well repaid. The fastest
possible lakes are produced from these dyes in this
way.
The fact that those lakes produced in indifferent
substances, are so extremely fugitive under the
action of light deserves attention. A comparison
between their fastness on textile fibres, and on the
indifferent substances, should be of interest.
It is noticed also that the attraction which
these inert substances have for basic dyes is modified
by the nature of the acids which enter into their
constitution.
Roughly speaking, the amount of dye fixed is
inversely proportional to the respective strengths of
the acids, with which the bases are in combination.
As a proof of this Weber gives the following results,
which show the relative amounts of colour taken
up by 100 parts of alumina. Under the standard
16
242 CHEMISTRY AND PHYSICS OF DYEING
condition of the tests 2 grams of alumina were sus-
pended in 500 cc. of water.
Colour used. Absorbed by 100 pts. A1 2 O 3 .
Bismark Brown G. 8.3
Acetate of Magenta 7.13
Methyl Violet B. 4.87
Brilliant Green 3.85
Magenta 3.53
Indazine M. 1.96
Methylene Blue B. 1.62
Thioflavine T. 1.43
Solid Green, Cryst. 1.21
Safranine G.G.S. .83
There seems to be a good deal of evidence to
prove that these dyes when present on inert sub-
stances are in the form of basic salts, varying in
constitution between the normal salts, and the bases
themselves.
That they are not present as simple colour bases
is proved by the fact that the bases themselves are
for the most part colourless. This fact is to be
remembered in connection with the dyeing of these
colours on fibres. These basic salts, unlike the
normal ones, are very insoluble in water. For
example, a " dissociation " lake may be produced
on china clay by precipitating Benzaldehyde Green
in the presence of Glauber's salt, or acetate of soda. ;
With this reduction in the "acidity" of these
precipitated basic compounds, a corresponding loss
in intensity of colour is noticed. The lakes pro-
duced in this way are partly decolourised, and an
addition of tannic acid will develop the colour in
some cases to the extent of fifty per cent.
COLLOIDS IN DYEING AND LAKE FORMATION 243
If one of these basic lakes be washed with boil-
ing water, only traces of colouring-matter go into
solution, and the lakes ultimately become colour-
less. In the same way, tannic acid, by reducing
the basicity of the colour salt, will bring the colour
back to a great extent. This reaction is important
and the action of solvents on basic dyes present
in the fibre area cannot be correctly estimated by
the altered colour-effect produced in this way.
It is known to every silk dyer, that washing with
water will decrease the intensity of the shade in many
cases, and a subsequent treatment with weak acid
will bring the colour back. This subject should
receive further attention. Light should be thrown
on the state in which these dyes are present in
the silk fibre. In the formation of lakes with
tannic acid the action seems to be of an indefinite
nature (O. N. Witt). The amount of tannic acid
required to produce a true lake of a thoroughly
saturated nature, as compared with the amount
required to precipitate the basic dye perfectly from
an aqueous solution, is indicated in the following
table.
Colouring-matter. T ' ^ actually T. A. required for
absorbed. mere precipitation.
Magenta . . . 622 .. 173
Methyl Violet . . 510 . . 138
, v Solid Green . . 1324 .. 456
Methylene Blue . . 620 . . 198
Chrysoidine . . 322 . . 194
Weber was unable to indicate the course taken
by the interaction between the dye and tannic
244 CHEMISTRY AND PHYSICS OF DYEING
acid. It does not follow in the lines of chemical
attraction, as indicated by the constitution of these
dyes. The action seems rather to be on the lines
of colloid precipitation, and may be regulated by
the state of the precipitate. For instance, 100
parts of the magenta tannic acid compound will
absorb 160 extra parts of tannic acid if present in
excess, while 100 parts of the chrysoidine tannic
acid compound will only absorb 60 extra parts of
tannic acid under the same conditions.
The fact that the tannates of antimony, zinc,
tin, lead, or iron will give better and faster lakes
than tannic acid alone (Witt) is an interesting point.
Many organic acids form lakes (or insoluble
compounds) with the basic dyes, and nearly all the
aromatic acids act in this way. A similar result
is also obtained with phosphoric acid, arsenious
acid, or silicic acid when present as their alkaline
salts.
The action of albumin on some dyes is of
interest. For instance, Diamine Scarlet B
C 6 H 4 .N = N C H 4 .O.C 2 H 5 .
QTT
C 6 H 4 .N = N-C 10 H 4 ; SQ3Na
SO 3 Na
gives a very clear solution, and is not precipitated
by dilute acids. If this be added to a solution
of albumin a decided precipitate is obtained. It is,
however, very difficult to filter, being of a slimy
nature. To precipitate all the dye a large excess
of albumin is necessary. If, however, the solution
COLLOIDS IN DYEING AND LAKE FORMATION 245
be heated to 80 C the albumin coagulates, and
carries down with it the whole of the dye, in the
form of brilliant scarlet flakes.
If this precipitate is boiled with water it will
give up some of its colour to the solution. The lake
is also slowly decomposed by soap solution at 50 C.
The lake on drying gives a heavy solid, which shows
little sign of swelling, or solution, in water, and soap
solution at 80 C scarcely affects it.
Acetic acid may take the place of heat in pre-
cipitating the lake, but this acid will not precipitate
either the dye, or the albumin by itself.
This action is not confined to direct dyes. Sul-
phonated basic dyes, azo dyes, and sulphonated
nitro bodies act in the same way.
It would seem that for two substances of the
above nature to " precipitate " one another, one
of them must be in a state near to the point where
actual precipitation, or coagulation, takes place.
Gelatin, for instance, is incapable of this precipi-
tating action, but albumin in a sensitive condition,
at either 80 C or in the presence of cold acetic
acid, will precipitate the dye.
The influence of the dye itself also helps, or
retards, this action. Diamine Scarlet will precipi-
tate albumin in the cold. Eosine, on the other
hand, will only act in this way at a high temperature.
It is said that the shades obtained correspond
exactly with those obtained on wool, or silk.
If the basic dye had combined with the albumin
in the cold, a precipitate would probably have been
246 CHEMISTRY AND PHYSICS OF DYEING
formed, and this indicates, so far as it goes, that the
action between the albumin and the basic dye is not
of a chemical nature.
For some reason the fastness against light of
these precipitated lakes varies with the nature of
the precipitant. Albumin lakes are said to be four
times as fast as the corresponding barium lakes,
using the same dyes. The extremely fugitive
nature of the basic dyes on a china clay basis has
been already noticed.
This may be due to two causes :
(1) Difference in size of the dye aggregates.
(2) Difference in the way the dyes are held.
Arguing from the extraordinary sensitiveness
of diazotised primuline, when produced in a colloid
substance, the size of the aggregates may affect the
action. The matter is one which demands attention,
and a further study of this matter may lead to
interesting results.
Surface-Concentration and Devolution Effects.
A modified theory on the above lines was recently
brought forward (Dreaper, J. S.C.I. 1905, 233),
to explain the general action of dyeing. It is
founded on the work of Linder and Picton (J.C.S.
1892, 61, 148 and 1895, 63) and others, and attempts
to explain the dyeing action on lines which are
usually regarded as physical, although it is not
denied that chemical action may supplement the
actions, which lead to the general absorption of the
dye by the fibre.
The work on pseudo-solution undertaken by
COLLOIDS IN DYEING AND LAKE FORMATION 247
Linder and Picton has hardly received the notice
it deserves by those interested in the subject of
dyeing.
The dividing line between perfect solution, and
suspension has broken down. The difference be-
tween the two states, is only one of aggregation ;
although it is not to be inferred from this, that any
substance may, by successive stages, pass from the
former to the latter state. This action is neither
a reversible one in many cases, nor is it necessarily
a complete one. In solutions of colloids the relation-
ship between the solution, and the colloid (solute),
is never complete, as in the case of a crystalloid.
Solution stops short at some intermediate stage,
and consequently, as has been explained elsewhere,
the usual phenomenon of a lowered freezing-point
of the solution is not in evidence to the same degree
as in a perfect solution of a crystalloid. So far as
appearance goes there is little difference between a
colloid, and a crystalloid in dilute solutions ; but an
examination of the physical properties of the former
in solution indicates that the differences in the solu-
tion state must be appreciable.
An interesting case of a colloid in a state of
pseudo-solution is that of arsenious sulphide, which
can be prepared in a state of such fine suspension,
that the solution will pass easily through a porous
pot without separation of the solid.
This is in itself a fact of general interest, but
when we study the action of metallic salts on these
pseudo-solutions the results at once become of
248 CHEMISTRY AND PHYSICS OF DYEING
interest to the dyer. In their action on these solu-
tions, the different salts divide themselves into
sharply denned groups, corresponding with their
valency. As a general result the effect of the addition
of these salts, is to degrade the state of the pseudo-
solution. The aggregates become larger in size, and
may even be precipitated. The salts of tervalent
metals possess the highest coagulating power. Biva-
lent metals only act with one tenth of the effect
and univalent metals with less than one five-
hundredth part of the intensity in the first case.
This difference in the power of precipitation, even
extends to the same metal when the valency varies
(e.g., with iron). One molecule of aluminium chloride
possesses the same coagulating power as 16.4 mole-
cules of cadmium chloride, or 750 molecules of sul-
phuric acid.
When the coagulating action of salts on a solu-
tion of arsenious sulphide is studied in detail,
unexpected results are obtained. As an example,
when barium chloride is used as a coagulating
medium, the barium is carried down, and the
chlorine left in solution. Similar results are
obtained with calcium chloride. The precipitated
metal is retained, even after thorough washing
with water, but another salt in solution will
replace it.
This action is one of mass, and is not due to selec-
tive affinity, as it is reversible, and depends entirely
on the proportion of the second salt in solution. For
example, both calcium and cobalt salts will coagu-
COLLOIDS IN DYEING AND LAKE FORMATION 249
late in this way, yet either will replace the other
if present in sufficient quantity in the solution.
It will at once be seen that the influence of these
experiments, on a strictly definite chemical theory
of dyeing, is a disturbing one. A theory of mass
action and the resulting affinity which is able to
disturb such a system as that represented by
barium chloride in solution might clearly take the
place of a chemical theory of dyeing, and explain
the experiments of Vignon and Knecht on the one
hand, and of v. Georgievics on the other.
It will be seen, that we may equally expect a
similar action with, say, rosaniline hydrochloride.
In fact, with such an example before us, we can
hardly set any limit to this action.
Extending their experiments to other substances
Linder and Picton found that dye-stuffs such as
Hofmann's Violet, Methyl Violet, and Magenta, gave
interesting results.
The solutions of these dyes are so far perfect
that the aggregates present are not sufficiently large
to scatter light, as some of the arsenious sulphide
solutions do, yet they were non-filterable. These
results are altogether abnormal, from the point of
view of the standards set up by these investigators
for arsenious sulphide solutions, and we are clearly
here face to face with an extension of the action
in the case of these basic dyes.
Further experiments, however, showed that the
porous material itself will absorb the dye if broken
pieces of it were left in the dye solution. The
250 CHEMISTRY AND PHYSICS OF DYEING
authors did not carry these experiments to their
logical conclusion, by identifying the action as
similar in its nature to that of barium chloride,
or they would have looked for a decomposition of
the basic hydrochloride in the porous material.
The cause of the decomposition of basic dye-stuffs
in this porous material is uncertain. It is either
due to a colloid state set up on the surface of
the porous material, or else is due to " surface
action."
Our knowledge of the actions which are associated
with surfaces is incomplete, at the present time.
It is possible to explain them in the following
way. The material of which a porous pot is com-
posed, by virtue of its liberal surface, and, as we
know, slight solubility, will present to the solution
a large surface in a colloidal state, and this by its
action may decompose the basic hydrochloride, and
precipitate the base.
It is just possible that capillary action may
play a considerable part in the action. It must,
however, not be lost sight of, that this action is
directly connected with surface action. In fact, it
is caused by it. The secret of capillary action being
the greatly increased attraction at small distances
(Hawkesbee).
The dissociation of the basic dye in solution, if
it takes place, and its influence on such an action
as the above, should make experiments on this subject
important. Dyeing fibres and porcelain material,
with dyes dissolved in mixtures of alcohol and water
COLLOIDS IN DYEING AND LAKE FORMATION 251
in varying proportions, should be undertaken, and
their relative actions noticed.
The influence of the addition of sodium chloride,
or other salts, on pseudo-solutions of arsenious sul-
phide is, by analogy, of great importance.
The solution becomes non-filterable, and there-
fore degraded in the scale of solubility. The action
of such substances on dye-solutions is well known.
The importance of this action is considered by the
writer, to be not so much that caused by a decreased
solubility of the dye in the solution, as the solid
solution theory requires, but that the increase in
the size of the aggregates and their degradation in
the scale of solution, is the important condition;
and that this is the cause of the modified result
obtained in the presence of a suitable fibre.
Furthermore, the effect produced by filtration
shows that the degradation of the arsenious sulphide
solution is specific. The effect is as if all the
aggregates present are increased in size.
From this and other considerations, the writer
has put forward the hypothesis that in any system
of a hydrosol, and to a modified extent in the case
of a hydrogel, the size of the aggregates is determined
by the two factors, the mutual attraction of the
molecules and the solvent action of the solution.
This latter factor may be the attraction of the solute
molecules for those of the solution. When an equili-
brium is actually set up between these two opposite
forces, the aggregates will be of a definite size, and
remain so until the system is modified by some
252 CHEMISTRY AND PHYSICS OF DYEING
secondary action, and the colloid either degraded
in the scale of solubility, or the reverse.
It will be seen that the action of salts on a
solution of a direct dye is capable of explanation.
It has already been pointed out that the direct
dyes do not give true solutions in water. That
is to say, they give pseudo-solutions. The action
of salts should give the same results in both cases,
and there is no evidence at present that such is
not the case.
The influence of different solvents on the mole-
cular weights, or size of the aggregates, is undoubted.
For instance, the following table shows the number
of double molecules of nitrogen peroxide in different
solvents (Walker).
Solvent. Double mols. at 20. Double mols. at 90 C.
Per cent. Per cent.
Acetic acid . . 97.7 ... 95.4
Ethylene chloride .95.8 ... 91.3
Chloroform . . 92.3 ... 85.5
Carbon bisulphide . 87.3 ... 77.5
Silicon tetrachloride . 84.3 ... 77.4
It will therefore be seen that for some reason,
probably owing to the relative attractions between
the solvent molecules, and those of the solute, the
state of aggregation varies greatly with different
solvents. In the case quoted the state of aggrega-
tion is never very great, at least, as compared with
that known to exist in the case of the so-called
colloids, but it will sufficiently well indicate the
action which takes place.
The influence of increased temperature may also
COLLOIDS IN DYEING AND LAKE FORMATION 253
be indicated in terms of the molecular state of the
solution.
The increase in molecular weight in more concen-
trated solutions, is indicated also in the case of a
solution of alcohol in benzene, and for this purpose
the following table is quoted.
Concentration. Mol. weight
Per cent. (Alcohol = 46).
494 -. 5
2.29 . . .-. . . .82
3.48 .100
8.8 . . . . . . . 159
14.6 . . . . * . . 209
This would also seem to indicate that association
increases with molecular strength of solution.
Effect of concentrated solutions. The increased
effect produced in concentrated solutions of dyes is
also 'explained by assuming that the size of aggre-
gates is constant in any solution of this nature. From
this point of view, the aggregates are larger rather
than more numerous in the more concentrated
solution.
So that we have alternate means of producing
larger aggregates.
(1) By degrading the solution by means of the
addition of salts.
(2) By increasing the concentration of the dye
solution.
Both of these methods answer in practice, but
as will be pointed out later on, the former is
likely to be the more efficient, owing to the addi-
tional effect produced by " surface concentration/'
254 CHEMISTRY AND PHYSICS OF DYEING
and, in practice, the saving in dye material is an
important factor.
We know that molecular aggregation extends
to the state we call solution, and this is a further
proof that there is no dividing line between a colloid
and a perfect solution.
It is therefore suggested that the aggregates
are, within certain limits, constant in number rather
than in size, as the strength of the solution alters.
With increased concentration, there comes a time
when the aggregates are so large that their relations
to the solvent assume a new phase. The point at
which they occupy a space larger than the physical
conditions of the liquid will allow may be a critical
one. In crystalloids, which do not pass through the
colloid state, but are controlled in their desolution
by molecular forces which directly determine their
ultimate solid state, this point is a sharp one, and
gives rise to a separation of the salt, probably in
the crystalline form.
With colloids, or substances which take a hy-
drated form, the course adopted is a different one,
and between the pseudo-solution state, and that
of the absolutely dry substance, there is no sharply
defined dividing line ; but merely a slow passage
from one state to the other as determined by the
relative proportion of water molecules present,
although the actual point at which the hydrosol
is coagulated, may be a critical one.
With decreased amount of solvent certain
other phenomena come into more active play, and
COLLOIDS IN DYEING AND LAKE FORMATION 255
an automatic separation of the colloid material may
actually take place from these secondary causes.
Closely connected with the subject of the con-
stant size of the aggregates in a hydrosol is the
mechanism by which this can be determined ; here
we must assume molecular migration (Dreaper,
J.S.D. and C. 1905).
This is not an impossible condition. Actual
atomic migration has already been assumed by
Poisson, and this being so, it is held by the writer
that the forces which are called molecular are similar
in their nature to those which are called atomic.
Such a migration is a necessary adjunct to any
theory of association between a liquid, and a solute.
There is also a certain amount of evidence that
these changes do occur in a solution, and that
they can be actually observed, as the case of
very viscous solutions, like those of nitrocellulose
in organic solvents. The observed fact of the
" ripening " of such solutions is held to be due to
an action of this kind. Several months elapse in
some cases before the ultimate state of equilibrium
between the solvent and solute is reached.
If we assume this action, it is also possible to
explain the slow dialysis of colloids through mem-
branes, which is theoretically possible, and has
been observed in the case of nitrocellulose by de
Mosenthal (J.S.C.I. 1904, 292). If we assume
the migration of individual molecules from one
aggregate to another, it is possible for these
aggregates to pass gradually through a membrane,
256 CHEMISTRY AND PHYSICS OF DYEING
by some such secondary action, although they
themselves are incapable of passing directly from
one side to the other.
In the action of dyeing there is a constant play
of altered conditions due to temperature, alteration
in concentration, &c., and consequently, a constant
variation in size of the aggregates, which in itself
will entail this roving state of the individual mole-
cules.
It has also been established by Linder and Picton
(ibid.) that a 4 per cent, solution of arsenious sul-
phide is non- filterable under ordinary conditions.
This would indicate that the aggregates are larger
in size, and support the above conceptions.
Support is seemingly given to these views by
the observed action of the following complicated
and obscure cases in general dyeing.
If a logwood iron lake be dissolved in a dilute
solution of oxalic acid, it will, as is well known, dye
silk and other fibres a deep black colour. In its
original state the lake is insoluble. The particles
or aggregates have in its preparation been so de-
graded in the scale of solution, that they are no
longer within the limits of dyeing requirements.
By the gradual addition of oxalic acid to a suspen-
sion of this lake in water, the size of the aggregates
is in some way gradually reduced, passing by stages
of colour from black through brown to an almost
golden colour, as the proportion of oxalic acid is
increased.
Assuming that the lake in its more soluble state
COLLOIDS IN DYEING AND LAKE FORMATION 257
passes through a corresponding state of pseudo-
solution, we arrive at the following conclusions.
The aggregates in this state come into close enough
relation with the fibre substance for de-solution
to take place from whatever cause, be it surface
attraction, or concentration, or mass attraction at
short distance. At any rate, the solution state,
whatever it be, is disturbed by the presence of the
fibre, and the solution state is degraded with the
precipitation of the lake in the substance of the
fibre. Alizarine lakes in the " one bath " method
of dyeing also seem to act in the same way.
From the above theoretical considerations, it
would also be expected that, if the molecular pro-
portion of oxalic acid be increased, a point will
ultimately arrive when from one cause or the other
a decreased de-solution effect will be produced.
This actually occurs in practice.
It would follow also that at this stage a further
addition of lake, or a reduction in the amount of free
acid, would increase the size of the dye aggregates,
and cause a reversal of the action. This is also
actually observed.
The colour-effect in the solution is also completely
reversible, and runs parallel with the dyeing results.
Under certain conditions silk and wool fibres
are capable of attracting from aqueous suspension
certain insoluble amines (Pokorng, Bull. Soc. Ind.
Mulh. 1893, 282), if they are in a state of fine
division.
Naphthylamine, if dissolved in a small quantity
17
258 CHEMISTRY AND PHYSICS OF DYEING
of alcohol, and poured into water, will impregnate
wool in twelve hours in the cold.
The fixing is said to be entirely mechanical, and
the amine is easily removed by water.
These results have been confirmed by P. Werner
(ibid.), and further experiments show that the result
is directly influenced by the proportion of alcohol
to water. As the alcohol increases from 5 to 30
per cent, the absorption increases. Beyond this
a reverse action sets in on similar lines to that of
the logwood-iron-lake solution, and with essentially
different substances he obtained the same effect.
As the alcohol increases so does the solubility. Up
to a certain point this leads to increased dyeing
effect. Beyond this, the action of the alcohol on the
hydrated fibre state, and the decreased size of the
aggregates, tell against absorption.
The action of a more efficient solvent (alcohol)
on dyes in fibres is to reduce the size of the aggre-
gates. Under these circumstances the dye, or part
of it, may leave the fibre. This is noticed in many
cases, and it tends to indicate that such dyeing
actions in mixed solvents is more due to the solution
state than to the fibre state, but a great deal more
work will have to be done on this subject before
it will be possible to apportion to each action its
qualifying effect.
The action played by water is still obscure.
It may be that it is indicated by the statement
made by Pokorng, that while pure alcohol will not
extract some dyes from the fibre, yet 95 per cent.
COLLOIDS IN DYEING AND LAKE FORMATION 259
alcohol will do so. (See page 167.) This may indi-
cate that the pure alcohol cannot enter the fibre,
and that a semi-hydrated state is necessary before
the colour can be extracted. Otherwise some more
complicated and unknown action is involved.
Experimental evidence as to the relative solu-
bility of the dyes in mixtures of alcohol and water,
both in the presence, and absence, of a fibre substance
are wanting. Also there is no evidence available
to show whether the fibre absorbs more water than
alcohol from mixtures of the same. Both these
points will be made the subject of investigation.
It is possible that the dye aggregates are
associated with solvent molecules, in fact, are doubly
complex in this way. The same applies to the
fibre. If we have molecular migration, the aggre-
gates may even join up loosely with the fibre aggre-
gates, and in this way the fibre and dye be held
together by some such secondary attraction.
The third case given as evidence in favour of
these theoretical conclusions is taken from some
work done by Binz and Bing (Zeit. /. angew. Chem.
25, 1902), on the relative action of salts on the dyeing
of wool with indigo, in cases where the alkalinity
of the bath varies.
The addition of neutral salts, such as Glauber's
salt, sodium chloride, &c., does not intensify the
shade so long as the alkali is only present in sufficient
quantity to dissolve the indigo white. In the pre-
sence of excess of alkali, the addition of neutral
salts has an intensifying action, and as a result,
260 CHEMISTRY AND PHYSICS OF DYEING
darker shades are produced on the fibre. The
presence of i - 8 per cent. Nad, for instance, doubles
the amount of indigo absorbed by the fibre.
In the presence of a large excess of alkali, this
increased dyeing effect on the addition of salts is
not nearly so pronounced.
It is not difficult to see that here, also, we may
find an explanation of the effect of these substances
in the presence of excess of alkali ; when the state
of solution is of a more perfect nature, it
might be expected that the action of salts would
be correspondingly reduced, and this would natur-
ally effect the dyeing result. It must always be
remembered that the fibre state may also be pro-
foundly modified by the presence of these substances
in solution.
So that, as is pointed out, by a careful adjust-
ment of the excess of alkali to that of the salt, a
satisfactory state of the fibre, or one of maximum
absorption, may be obtained, and the best dyeing
effect be produced.
This is the condition which would naturally be
aimed at by the practical dyer, from the point of
view of economy.
It is of great importance to note that the alkali
is evidently not fixed on the fibre in any way, and
it is only necessary to take account of the fixation
of the indigo white. V. Georgievics (Der Indigo,
1892, 55) has shown that it is only the latter which
is fixed, the alkali remaining in the solution. The
results obtained by Koechlin as a result of a study
COLLOIDS IN DYEING AND LAKE FORMATION 261
of the absorptive power of cotton for tannic acid
are of interest from this point of view. It is known
that tannic acid gives pseudo-solutions.
Experimenting with different strengths of solution
abnormal results were obtained.
The point of maximum absorption seemed to
coincide with a concentration of .2 per cent.
Beyond this reversal seemed to set in, for a cotton
saturated in a .5 per cent, solution still absorbed
tannic acid in a .2 per cent, solution. The
state of aggregation, or else the mutual attraction
of the tannic acid for the cotton fibre, is altered
subsequently in a .02 per cent, solution, for in this
the cotton just begins to lose tannic acid.
If figures could be obtained showing the relative
action of cotton and mercerised cotton with regard
to this reversal, the results would be of interest. In
some such way as this it might be possible to indicate
whether the action was due to the fact that the
latter is in a more highly colloidal state, or whether
the additional hydroxyl groups play a part in the
action. A further study of this subject is contem-
plated.
It has already been noticed that the addition of
acetic acid to the tannic acid solution greatly in-
creases the proportion of the latter acid absorbed
by the fibre. Apart from the value of this observa-
tion from the practical point of view, its possible
influence on our knowledge of dyeing is obvious.
The action is as difficult to explain in this case
as in the case of silk or wool dyeing with sulphonic
262 CHEMISTRY AND PHYSICS OF DYEING
acids, or carboxyl dyes in the presence of stronger
acids.
Surface concentration also, as the writer has
pointed out, must play an important part in any
theory of dyeing.
If the action of dyeing were purely chemical in
its nature, this concentrating effect would have an
important bearing on the rate of dyeing, but from
the point of view of pseudo-solution it occupies a
still more important position.
Assuming that dyeing is an action which is
independent of any actual attraction between the
fibre substance and the dye, it is very difficult to
see how the fibre can attract the dye, or hold it.
It is this difficulty which made Cross and Bevan
(J.S.C.I. 13. 354) accuse O. Weber of assuming
a one-sided penetrability for the dye substance.
That is to say, that the dye would diffuse into the
fibre, but would not diffuse out again. If, however,
one realises the possibility of this concentrating
action at surfaces, the matter at once assumes a
different aspect.
J. J. Thomson (App. of Dynamics to Phys. and
Chem., p. 251) pointed out that the most stable
arrangement of any solution will be accompanied
by minimal surface energy. The result of this
action is distinctly seen in practice. There is a
tendency with most salts to concentrate at surfaces,
and for a similar reason, and to a correspondingly
greater extent, in capillary tubes.
For instance, in the case of graphite or meer-
COLLOIDS IN DYEING A ND LAKE FORMATION 263
schaum, this concentration in the case of potassium
sulphate is nearly 25 per cent.
It will be seen that the influence of this
action in dyeing may be a profound one, for with
the additional concentration of the pseudo-solution
of the dye we shall have a rearrangement of the
aggregates. The size of these will correspondingly
increase within the capillary spaces of the fibre
substance owing to this action.
The rate of diffusion will correspondingly de-
crease, and we shall arrive at a state where the
osmotic action is greatly in excess of the exos-
motic one. This can produce but one effect, viz., a
concentration of the dye substance in the fibre area,
and a state of " one-sided penetrability" is arrived
at. When it is also recognised that the salts will
also concentrate about and in the fibre area, it is
easy to realise the possible result of this general
action.
The effect of the concentration of the assistant
and its influence on the state of aggregation
may, it is held, be seen in the dyeing of silk
with ordinary acid colours. If the dyed silk be
introduced into water, some of the dye is readily
removed. With the decrease in the concentra-
tion of the acid the aggregates may decrease in
size, and be partly removed, or tend to re-
enter the dye solution. This action is, therefore,
a reversible one.
As a result, therefore, of this concentration
effect, it is obvious that the dye may be degraded
264 CHEMISTRY AND PHYSICS OF DYEING
in the scale of solubility ; that it may actually
become insoluble.
In the case of dyeing with logwood lake by the
a one bath" method, the fact that the colour of the
silk fibre is not black, but dark brown, until the
skein is finally washed in water, indicates that
the dye state is one of degradation, rather than
complete dissociation from the solution state during
the time of dyeing.
In this case it is probable that the concentration
of oxalic acid in the fibre area is small as compared
with that of the dye-stuff. If this were found not
to be the case it might indicate that some secondary
attraction between the dye and fibre substances
comes into play, and to that extent accounts for
the displacement of the equilibrium of the dye
solution within the fibre area.
The intensity of this surface concentration varies
with different acids and salts. An elaborate series
of experiments was conducted by Gore on this
subject (Birmingham Nat. Hist, and Phil. Soc. IX. i,
1893). The effect is directly dependent on the
area of the surface. For instance, if a dilute solu-
tion of acetic acid be filtered through fine white
sand, nothing but pure water will percolate through,
the whole of the acetic acid being kept back by
this action.
The following results chosen at random from
a very full list in the original paper will illustrate
the relative action of substances. Ten per cent,
solutions were used in each case.
COLLOIDS IN DYEING AND LAKE FORMATION 265
HC1 lost 2.88 per cent. Tartaric acid lost 1.42 per cent.
HI ,, i.o Citric acid nil ,,
HN0 3 ,, 2.5 CaCl, 3.1
HC10 45 , 4.4 NaCl 2.77
We have therefore, a physical reason for the
concentration of substances in solution at surfaces,
and the influence of this action cannot be neglected.
It will be seen that this is still more evident
when it is noticed that this tendency to concentrate
is stronger in the case of substances, in a state of
pseudo-solution, than with salts which are more
soluble.
In the case of substances of high molecular
weight these surface concentrations may be so in-
tensified by mechanical movement that the sub-
stances may heap up and form visible films of solid,
or very viscous matter (Ramsden, Proc. Roy. Soc.
72, 156).
The size of the aggregates undoubtedly affects
the general result. For instance, Gore found that
the following substances gave positive, or negative
surface attraction results, as indicated. It will be
seen that substances in suspension give abnormal
results.
Picric acid in solution ... No result
in suspension . ; Result
Salicylic acid in solution No result
in suspension . . . Result
Methyl orange . . . .
Orange G. ....
It may be that the molecules of soluble substances
like, say, sodium chloride "salt out" dyes by means
266 CHEMISTRY AND PHYSICS OF DYEING
of the greater attraction between the solution and
solute molecules in the case of more perfect solutions.
In the case where these colloid substances are separ-
ated by the above mechanical means, they are not
always resoluble in the solution. They are some-
times even insoluble. The action of aggregation
is non-reversible under these conditions.
These separated films vary greatly in their
physical properties. They may be membranes,
membrane-fibrous, or fibrous as the case may be;
or they may even consist of particles lying side by
side.
The special surface viscosity which accompanies
these separations, and which is indicated by a
resistance to " shear," develops at very different
rates.
These concentrations also occur at the inter-
surfaces of two solutions, and give rise to distinct
surface tension phenomena at the junction of
aqueous colloid solutions of different concentrations
(Quincke, Drudcs Ann. 10, 478).
In this action, coupled with the above laws of
aggregation, and possibly, molecular migration, we
have an explanation which will satisfy the dyeing
conditions in a great many cases such as the " one
bath " method, indigo and Cf sulphide " dyeing,
the dyeing of direct colours on cotton, &c., without
bringing in any complication due to chemical action.
Dr. W. H. Perkin, senr., has pointed out (J.S.C.I.
1905, p. 235), that the surface character of silk,
wool and cotton respectively can be shown to pro-
COLLOIDS IN DYEING AND LAKE FORMATION 267
duce different results under the following conditions.
A skein of cotton was worked for some time in an
emulsion of olive oil and carbonate of potash, such
as was used by Turkey-red dyers. On wringing it
out afterwards, nothing but pure water left the
skein; the cotton was practically free from oil.
On repeating this experiment with a silk skein
the water was still nearly pure, but the silk retained
a large amount of oil.
By substituting a wool skein for silk, and after
rinsing the skein in water, the oil ran from the wool
in quantity on wringing.
These experiments are of interest. The oil
particles, or aggregates are of course much larger
than in any case of pseudo-solution met with in
dyeing, but the results produced show the very
different nature of the absorption of such substances
by these three typical fibres, and also indicate that
the absorption which may, in this case, be taken
to be of a physical nature, is very pronounced.
Dr. Perkin states also that the behaviour of these
different fibres in relation to the oil corresponds
closely to their dyeing power. This would not,
however, seem to be a universal rule, especially
with the direct colours, yet the phenomena recorded
are certainly suggestive in their nature.
Some experiments of Chabrie (Comptes Rend.
115, 57) roughly indicate the limit at which it might
be expected that concentration might take place
in the fibre area. Experimenting with capillary
tubes of a diameter of .07 mm., interesting results
268 CHEMISTRY AND PHYSICS OF DYEING
were obtained; on passing a solution of albumin
slowly through such a tube a separation takes
place, and only pure water passes through. The
albumin is concentrated in the tube to such an
extent that ultimately all flow is stopped. This
would, in a case of dyeing, indicate the ultimate
absorption point, or the dyeing limit, and the size
of the inter-spaces in different fibres, and of the
same fibre in different states of hydration, would of
course greatly modify the action. The influence of
this action is, therefore, evident, and will have a
definite bearing on the best condition of the fibre
substance for dyeing purposes, the object being to
bring the greatest possible number of fibre molecules
in contact with the dye aggregates without ultimate
damage to the fibre itself by disintegration. A
good example of this action is seen in the in-
creased action of dyes on powdered wool under
standard conditions.
In the cotton fibre, when the cellulose which has
once been dried is not easily rehydrated, the aid of
hydrating substances is necessary to obtain the best
effect. Mercerising increases the power of the fibre
in this direction. The mass action of a fibre will
depend on its original construction modified by its
capability of entering the hydrogel condition in the
presence of water.
Extended treatment with water itself will, to
a certain extent, take the place of the action of
reagents in inducing this state. Continued boiling
in water will induce this state in the cotton
COLLOIDS IN DYEING AND LAKE FORMATION 269
so that its attraction for certain dyes is materially
increased (Hiibner and Pope).
The bleeding of direct dyes on cotton indicates
that the dye is loosely held, in fact, very much in
the way it might be expected if the dye were precipi-
tated, or held by de-solution, and subject to re-
solution, either by molecular migration, or otherwise.
The experiments on the influence of temperature
on the ultimate dye state of the fibre made by Brown
indicate some such action as the above.
When the solubility of a dye increases with
temperature, we may assume that, in the case
of the direct dyes, which give pseudo -solutions
(Schultz), the aggregates are correspondingly smaller
at higher temperatures. Keeping this in mind, let
us examine the results obtained with Kalle's Direct
Yellow G. The amount of dye absorbed by silk,
wool, or cotton increases up to 80 C. Beyond this
point the curves for silk and cotton turn one way,
and that for wool the other.
In the case of a fibre which gives increased
absorption beyond this point, we must either have
a more or less sudden change in the fibre state, or
else the decrease in the size of the dye aggregates
will allow of their more rapid diffusion into the fibre
area.
In the case where a decreased absorption is
recorded, the increase in dye absorption may be
due to the aggregates becoming too small to be
degraded in the fibre substance under the altered
conditions. Such a case, where the absorption of a
270 CHEMISTRY AND PHYSICS OF DYEING
colour by silk and wool becomes greater in the one
case, and decreases in the other, does not support
a theory of dyeing which assumes a common cause
of attraction (tyrosine) in these two fibres. The
action may be complicated by changes in the fibre
state, and it is necessary to consider the possibility
of dissociation effects.
The writer has for some time sought an explana-
tion of the abnormal fastness of Night Blue on silk
fibres against the action of boiling soap solution,
in light shades. In darker colours the fastness is
not anything like so pronounced. Up to a certain
shade the dye will withstand a treatment extending
over half an hour. It would seem that here we
have a case of dyeing, where the dye is held in two
ways. The first portion is either in a very degraded
state of solution, or else it is held by direct attraction
or affinity.
This may be one of the cases in which dyeing
is in one stage a process of chemical action.
Taking everything into account, the writer suggests
that the natural order of the phenomena which
take place in dyeing is something of the following
nature, depending on the factors ;
(1) A solution state of the dye, within certain
limits of aggregation, determined by the laws of
size.
(2) A fibre state corresponding to this state of
aggregation, and of a permeable nature.
(3) Effective localisation of the dye within the
fibre area, due to surface concentration phenomena.
COLLOIDS IN DYEING AND LAKE FORMATION 271
(4) Localisation of any salts, acids, &c., within
the fibre area.
(5) The indirect entrance of the dye aggregate
by molecular migration, with subsequent reforma-
tion of an even more complex nature within the
fibre area, under conditions mentioned under (4).
(6) De-solution, due to secondary attraction
between the fibre substance and the dye, or by
reduced surface energy phenomena, or concentration
effects.
(7) In some cases, primary or chemical action
may play some part at this stage. This may, even in
some cases, take the place of de-solution phenomena.
(8) In the case of basic dyes, dissociation effects
may lead to the isolation of very basic salts in a
state of high aggregation within the fibre area.
We have seen that barium chloride and other
salts undergo decomposition in the presence of
colloids, like arsenious sulphide. It is, therefore,
not to be wondered at if actual decomposition
of the basic hydrochlorides takes place within
the fibre area. It is known that these dyes suffer
decomposition of a partial nature, at any rate, by
capillary action. It is also well known that the
basic dyes become very insoluble when, by losing
part of their hydrochloric acid, they become basic
salts.
It is not difficult to indicate a state of affairs
which would offer a satisfactory explanation of the
fixing of these dyes in animal fibres, or degraded
hydrogels, or even in the pores of such a com-
272 CHEMISTRY AND PHYSICS OF DYEING
paratively inert substance as porcelain, or china
clay.
It is difficult to imagine that the action of
dyeing is a strictly chemical one. For instance,
it is noticed that in mordanting cotton with tannic
acid the best results are obtained by immersing the
cotton in the boiling solution and allowing it to cool.
The mordanting takes place at the lower temperature.
The solution of tannic acid will be of a more perfect
nature at higher temperatures, and therefore the
aggregates will be correspondingly smaller. They
will increase in size as the solution cools, and there-
fore become more readily fixed, especially if they
re-form within the fibre area. This action is recorded
by Brown (J.S.D. and C. 1901, p. 94), and is an
interesting one, which is comparable in many ways
to the reduced dyeing effect noticed in certain cases,
at temperatures above 80 C.
The solvent action of alcohol, or benzene, on dyes
which are already fixed on the fibre is an indication,
perhaps, that these dyes are chiefly held by de-
s olution rather than by any process of primary, or
chemical attraction.
In the presence of a solvent of higher power the
aggregates are correspondingly smaller. A new
system is set up, and the dye, or part of it, leaves
the fibre. There is no question here of solid solution,
but simply that of solution following de-solution.
The direct fixation of the dye may be due there-
fore to three causes :
(i) De-solution, including dissociation effects.
COLLOIDS IN DYEING AND LAKE FORMATION 273
(2) Pseudo or secondary action.
(3) Primary or chemical action.
These three phenomena may overlap each other,
there being no strict, or hard and fast division
between them. It is held that there is evidence to
indicate, that all substances during precipitation
pass through the pseudo solution state.
An equilibrium between the relative attraction of
the solution and solute molecules, on the one hand,
and the molecular attraction of the solute molecules
for each other will be established in any system.
In the case of very insoluble compounds the
solution attraction is unable to break down the
aggregates of the solute beyond a certain point.
In some cases, and by certain means, an abnormal
state of aggregation may be induced in the case of
these very insoluble substances, and we then arrive
at a condition which, as in the case of some metals,
is regarded as the colloid state. Analogy would
suggest that this state is equivalent to the state of
supersaturation in the case of a crystalloid, or a gas.
At this point in the case of a dye which
is in a state of pseudo-solution, the only change
which will take place will be due to molecular migra-
tion owing to local influences; or to the tendency
to set up an ultimate state of equilibrium over
the whole system.
Such is the de-solution theory advanced to explain
the action of dyeing. The chief objection to it
is, perhaps, that this action will be of too irregular
a nature to explain the definite results obtained
18
274 CHEMISTRY AND PHYSICS OF DYEING
in some cases, which indicate that the ratio of
absorption of certain dyes is in direct relation to
the combining weights of the dyes absorbed.
It has, however, been recently shown (see p. 121)
that the salts of calcium, strontium, barium and
potassium are precipitated by colloids in the ratio
of their chemical equivalents (J. Billitzer, Zeit.
Phys. Chem. 1903, 45, 307).
The phenomena which present themselves in the
presence of pseudo-solutions are sufficiently well
marked to demand attention.
The conditions of surface concentration have
been observed, and studied from a mathematical
point of view ; the experimental results recorded
are beyond dispute.
The fact that de-solution may take place in the
presence of a liberal surface has also been observed
in the case of pseudo-solutions.
The action of precipitating agents on colloids
is a definite one, as shown by the replacement of
one metal by another, under the laws of mass action,
as recorded by Linder and Picton, and the addi-
tional statement made by Billitzer, that the different
metals are originally precipitated in the ratio of
their chemical equivalents, when they are carried
down by the degraded colloids. These precipitating
actions are clearly definite, although they may
not be strictly chemical in their nature.
This phenomenon of de-solution is, it is held, seen
in the remarkable result obtained by Hallett on
dissolving the colour off dyed yarn.
COLLOIDS IN DYEING AND LAKE FORMATION 275
When dark shades of indigo were stripped in
this way, the dye extracted by the solvent was also
thrown out in the insoluble form as a precipitate.
So that we have here a system where the one-bath
method of dyeing may be seen reversed. Start-
ing with the dye already fixed on the fibre, the
conditions of dyeing may, from this point of view,
be so far realised, that a condition of equilibrium
may be established in which the indigo may be
present on the fibre, in solution, and in the insoluble
state as an actual precipitate.
The suggestion I have made, that an arsenious
sulphide solution may be regarded as equivalent
to an " artificial fibre substance," and that if we
can have such an action with barium chloride, a
similar action with a basic hydrochloride, or even a
sulphuric acid salt is quite possible, has recently
received confirmation (see p. 278). W. Biltz (Chem.
Centr. 19052, 524) has shown that if the ordinary
dyeing process be represented by the formula
Cn fibre
C dye liquor '
where C fibre is the concentration of dye-stuff in
the dyed fibre, C dye liquor is that in the dye-bath,
and the index n is greater than i (it is frequently
found to be a whole number), then working with
inorganic colloids and a suitable dye-stuff, there
is no essential difference between the dyeing
properties of coloured inorganic colloidal substances
and organic dye-stuffs.
The comparative experiments were conducted
276 CHEMISTRY AND PHYSICS OF DYEING
with benzopurpurin on the one hand, and molyb-
denum blue, and vanadium pentoxide on the
other.
In both cases the composition of the coloured
fibre after dyeing, at a given temperature, depends
on the conditions of the dyeing process, the con-
centration of the dye-stuff, and the nature of the
salts added to the dye-bath.
Furthermore, with the substitution of the hy-
drogel of alumina for the organic fibre the same
relations hold.
In the same way some experiments made by
W. Biltz and P. Behre (ibid.) with dialysed solutions of
Immedial sulphur dye-stuffs, which were free from
alkaline sulphides, showed that these dyes were
"coagulated" (or salted out) by electrolytes, and that
the coagulating power of these substances increased
with the valency of the cathion. This same effect,
it will be remembered, is noticed in the coagulating
experiments with arsenious sulphide solutions.
Again, in the case of these dyes similar absorp-
tion results were obtained when the hydrogels of
alumina, zirconium dioxide, ferric oxide, and stannic
oxide were substituted for textile fibres.
In this way the experimental results have shown
that in the cases under consideration there seems
to be a direct relation between the dyeing of the
fibre, and that of inorganic hydrogels.
It is interesting to note that in the original work
on the subject of the absorption of inorganic colloids
by fibres (Biltz, Chem. Centr. 1904, i, 1039), the
COLLOIDS IN DYEING AND LAKE FORMATION 277
absorption is also increased by the addition of salt
to the solution.
The general conclusions arrived at were that,
by comparison, the solutions of the organic dye-
stuffs were subject to more complete exhaustion
than those of the inorganic colloids, and that the
shades produced are faster against washing, and
rubbing. The addition of electrolytes to the solu-
tion led to more complete absorption in both
cases. Increasing the temperature of the dye-bath
also has the same general effect.
Weighted silk had an increased affinity for
inorganic and organic colloids. The absorption
was retarded by the presence of ' protective col-
loids " in both cases.
A direct comparison between the dyeing action
of molybdenum blue, vanadium pentoxide, ruthenium
oxychloride, and silver, with benzopurpurin also
indicated that they were of the same order when
dyed on silk and cotton. The concentration, con-
dition, and additions to the dye liquor affected the
results (Ber. 1905, 2963).
The hydrogel alumina absorbed methylene blue,
colloidal silver, and benzopurpurin ; the fibre being
replaced by this inorganic hydrogel without the
absorption effect being altered.
In the case of the sulphur dyes colloidal solu-
tions were prepared by dialysing solutions for
ten to fourteen days. Cotton, aluminium hydrate,
ferric hydrate, and oxide of tin, absorbed the dyes
from these solutions (Ber. 1905, 2973).
278 CHEMISTRY AND PHYSICS OF DYEING
Certain absorption results may take place with
inorganic colloids, which have been long recognised
in the preparation of lakes. The absorption seems
to be of the same order as that which occurs in the
dyeing of silk, or cotton with certain colours.
If the inorganic colloids are in the hydrosol
state they may be absorbed by fibres or inorganic
colloids. They may even be carried down by
barium sulphate.
If the inorganic colloids are in the hydrogel
state, they may absorb dyes in the same way as
fibres.
Quite recently Linder and Picton, returning
to this subject (Trans. Chem. Soc. 1905, 1930), show
that ferric hydroxide is coagulated by a solution
of Soluble Blue, C 38 H 28 N 3 (SO 3 Na) 3 , or Nicholson's
blue (C 37 H 28 N 3 .SO 3 Na) in the same way as it is
by ammonium sulphate.
At a certain critical point a red coagulum
separates which contains all the iron and the sul-
phonic acid, an equivalent amount of sodium
chloride remaining in solution.
After extraction with alcohol a red precipitate
remains, which, is decomposed by dilute sulphuric
acid, or salt solution. The hydrox3r-ctye-sulphonate
is decomposed. The solution takes a deep blue
colour.
With Methyl Violet, C 19 H 12 (CH 3 ) 5 N 3 .HC1, no
coagulation takes place. Chlorides only coagulate
ferric hydroxide in highly concentrated solutions. .
With arsenious sulphide the order is reversed.
COLLOIDS IN DYEING AND LAKE FORMATION 279
With Methyl Violet a hydrosulphide derivative
is precipitated and hydrochloric acid remains in
solution. Aniline Blue has no such power, but
sodium salts only coagulate arsenious sulphide in
highly concentrated solutions. Hofmann's Violet
or Magenta acts in the same way.
These dye salts continue to take up the dye
with avidity to an extent equal to four or five times
the amount required to coagulate the hydroxide.
No decomposition takes place here ; the dye
is absorbed as a whole, not as a sulphonic acid.
Similar results we :e obtained with Methyl Violet
and arsenious sulphide. These absorption results
are^confined to the class of dye originally taken up.
The action here is therefore of a different nature
from that by which basic dyes are held by a direct
dye already present in a fibre.
It will be remembered that similar absorption
results were obtained with tannic acid lakes.
The evidence here is, therefore, that the original
action by which the two hydrosols are coagulated
is of a chemical nature. This practically exhausts
itself before the colour absorption stage commences ;
and this is of a physical rather than of a chemical
character , in the case of the mutual attraction be-
tween the dye and the coagulum. These results led
Linder and Picton to support the writer's de-
solution theory rather than Witt's hypothesis of
solid solution. They further consider that the
action itself is of an electrical character depending
on the properties of the reacting units, by reason
280 CHEMISTRY AND PHYSICS OF DYEING
of which two oppositely charged hydrosols in strong
aqueous solution seem to be mutual coagulants.
The fibre substance is of course already present
in the insoluble state, and when in a hydrated
condition may possibly be taken as equivalent to
the coagula of the above experiments.
It must not be taken for granted in the present
state of our knowledge that the dyes are always
precipitated in the fibre by direct attraction. To
do this it would be necessary to ignore the phenomena
of surface concentration, which is particularly
marked in the case of pseudo-solutions. This may,
of course, be an electrical phenomenon. It will be
realised that the influence of these general actions
in the case of colloids cannot fail to be of value to
the dyer in the art of dyeing and printing. These
reactions also explain much that is obscure in the
formation of lakes within the fibres, as in the case
of alizarine colours ; or in their direct production for
industrial purposes.
They may equally modify our ideas on tanning,
and the manufacture of leather.
CHAPTER XI
THE ACTION OF LIGHT ON DYEING OPERATIONS,
AND DYED FABRICS
THERE seems to be evidence that the presence of
light may materially alter the dyeing results
obtained in some cases. The action of light in
causing the fading of dyes present on the fibres is
also a very important one to the dyer.
The action of light on organic compounds in
general is but little understood. Our knowledge of
this subject is incomplete, but it is already clear
that the further study of it will bring forward
many interesting facts for the consideration of the
dyer. The list of substances which may be altered
by the direct action of light under certain conditions
is an extensive one. This has long been known
to those specially interested in this subject from
a light recording, or photographic point of view.
The action of light has been divided into two
classes, viz., Photo-chemical and Photo-physical.
The division is perhaps an arbitrary one, but
in the first case it is assumed that a direct action
takes place which involves re-arrangement in the
molecule itself. In the second case, the action is
282 CHEMISTRY AND PHYSICS OF DYEING
said to be equivalent to, say, the polymerisation
of formaldehyde.
Marckwald, in attempting to explain the action
which takes place in cases where the alteration
is followed by a reverse action in the dark,
considers that the actions which take place in this
case are not to be explained by either of these
causes. To the above classes he therefore adds a
third, and suggests that this special reversible action
shall be termed photo-tropical. Examples of this
are seen when] light acts as quinoquinoline, or
t etrachlor-/3-ket onaphthalene .
In comparing "_; the action of light on organic
compounds we can either estimate the change which
takes place in colour, or in the absence of this,
by some direct chemical change which is brought
about by the action itself. The latter method is
of course of a more direct and satisfactory nature
than the former, in most cases, although variations
in colour are valuable indications that some change
is in progress.
As an introduction to the study of this subject
the following researches on the general action of
light on organic substances are of interest. They
indicate the possible nature of these reactions in the
case of dyes.
For example, Ciamician and Silber have con-
clusively shown that this action may give rise to
chemical change. Benzophenone dissolved in alco-
hol is reduced to benzpinacone and aldehyde.
Under the same influence the aromatic orthonitro-
ACTION OF LIGHT ON DYEING OPERATIONS 283
benzaldehyde is transformed into nitrosobenzoic
acid. The action is indicated as follows :
CHO f XOOH
4 ^
Here we have an action which leads to the
internal re-arrangement of the molecule rather
than to decomposition.
Sachs and Kempf (Ber. 1902, 2707) have also
shown that a similar change takes place with the
aniline compound of orthonitrobenzaldehyde. As
a result of the action nitrobenzanilide is produced
as follows :
CH:NC, ; H 5 CO.NH.QH 5
The conclusion arrived at is that all aromatic
compounds containing nitro groups in the ortho
position are sensitive to light.
From a general point of view this is of interest,
the action of the light being sufficient to induce
intra-molecular change or migration when the side
groups are in close proximity (the ortho position).
The mordanting power of ortho-hydroxy compounds
probably depends in the same way on the proximity
_ Q TT
and combined action of the _ Q H groups, as has
been noticed elsewhere.
When the action of light is accompanied by
colour change, as it is in many cases, the actions
of this class are classified under the term chromo-
tropy. This phenomenon is very clearly shown
284 CHEMISTRY AND PHYSICS OF DYEING
by the various substitution - products of buta-
dienedicarboxylic acid; for instance of
H,C = C - CO.
>0
H 2 C = C - CO/
These compounds are all coloured. They are red,
brown, violet, or yellow, as the case may be.
These compounds undergo more or less rapid
change under the influence of light. The ultimate
effect of this change varies in its nature ; it is some-
times permanent and sometimes temporary.
The triphenyl derivative, when exposed to the
direct action of sunlight for a few minutes, changes
its colour to blood -red. Its original colour is,
however, slowly recovered in the dark.
If, however, the first exposure is greatly pro-
longed, and extends for several days, or even months,
the change is of too profound a nature for any subse-
quent reversal of the action, with regeneration of
the original form, to take place.
In this case the final products of the action
seem to be two white aldehydes, with different
melting-points, but with the same composition, and
molecular weight as the original substance.
The yellow diphenyl derivative yields three
distinct and colourless aldehydes with different
melting-points.
It is not to be supposed, however, that the
products of the action of light are always colourless.
The dark red piperonyl derivative yields two new
aldehydes, which possess great tinctorial properties.
ACTION OF LIGHT ON DYEING OPERATIONS 285
These results indicate that our present view of
chromophores must be widened (Stobbe, Chem.
Zeit. 1904, 919).
The conversion of anthracene into dianthracene
under the influence of light is a reversible one. The
exact conditions of this change have been 'examined
by Weigert (Chem. Zeit. 1904, 923), and Luther and
Weigert (Zeit. Phys. Chem. 1905, 53,385), who have
found that under definite conditions, and with dilute
solutions true equilibria are established. The source
of light in the case of these experiments was the elec-
tric arc. As a result of this investigation it was found
that the amount of dianthracene formed depended on :
(1) The character of the light.
(2) The change is proportional to the light
intensity, and the surface exposed, or to the radius
of the cylindrical vessels used.
(3) The action is independent of the thickness
of the layer through which the light passes.
(4) The action is ! inversely proportional to the
volume of the solution, and independent of the
amount of anthracene in solution.
Both the temperature and the nature of the
solvent have an influence on the result, and are
important factors in determining the equilibrium.
As is well known, the leuco bases of many organic
substances are readily oxidisable. Others are rela-
tively stable. The action of light seems to influence
these results. If these substances are embedded
in collodion their sensitiveness is greatly increased.
This is said to be due to the combined nitric
286 CHEMISTRY AND PHYSICS OF DYEING
acid affording an additional supply of oxygen under
the influence of light. The fact has been noticed
also that an addition of quinoline to the collodion
greatly increases the sensitiveness to light. We
have here, therefore, a second, or foreign, substance
influencing the reaction (Konig. Chem. Zeit. 1904,
922).
In these actions it has been noticed that the
greatest effect is produced by complementary light.
This result seems to be a general one, as noticed
later on.
A very decided colour-change which is brought
about only in the presence of a third substance,
which happens in this case to be a textile fibre,
is seen in the following instance. When cotton
yarn is padded with a 5 per cent, solution of meta-
tungstate of soda, and exposed to light, a rapid
change takes place with the production of a blue
colour. This is evidently due to the reduction of
the salt. The action is seemingly a reversible one,
for if the yarn is subsequently stored in a dark
place, the blue shade is discharged.
If the blue fabric, or yarn be immersed in water,
the coloured compound is removed from the fibre.
In this state, and away from the influence of the
fibre substance it gradually resumes its colourless
form, even under the influence of strong light.
It would seem, therefore, that the presence of the
fibre substance is the modifying factor in this
reaction.
Turning to the action of dyes themselves under
ACTION OF LIGHT ON DYEING OPERATIONS 287
the disturbing action of light, the following facts
have been noticed. The constitution of the dye
has a great influence on the " fastness " of the dye
against light. An elaborate series of direct trials
have been made by Brownalie (J.S.D. and C. 1902,
296) and as a result the following tabulated con-
clusions have been arrived at.
(1) The diphenyl base plays little, or no part in
the action.
(2) Colours derived from phenol, or its homo-
logues, and their sulphonic, or carboxylic acids are
fast to light.
(3) Colours derived from hydroxybenzenes and
homologues containing more than one hydroxyl
group are fugitive.
(4) Colours derived from the amines of the
benzene series, and their sulphonic acids, or car-
boxylic acids are fugitive.
(5) Colours derived from alpha and beta naph-
thols, and their sulphonic acids are not fast to light.
(6) Colours from alpha and beta naphthylamines,
and their sulphonic acids are fugitive.
(7) Those from amido naphthols, and their sul-
phonic acids vary. The 2.6.8 monosulphonic acid,,
and the 2.3.6.8 disulphonic acids are fast. The
1.8.3.6, and 1.8.2.4 acids are fugitive colours.
(8) The colours from the dihydroxynaphthalenes,.
and their sulphonic acids agree closely with the
corresponding amidonaphthols.
(9) Replacing amido by hydroxyl groups results
in increased fastness.
288 CHEMISTRY AND PHYSICS OF DYEING
(10) The salt-forming groups SO 3 H and CO. OH
cause no difference in fastness. The auxochromic
NH 2 and OH groups play important parts in the
action.
In the case of mixed colours the same rules are
followed. If the two separate constituents are fast,
so is the dye. This is very well seen in the case of
the direct colour Diamine Fast Red F, the com-
position of which is
-p . ,. ^Salicylic acid
^Amidonaphtholsulphonic acid.
If, on the other hand, both are loose, the dye itself
will be an unsatisfactory one in this respect. Delta-
purpurine 56 is given as an example.
Benzidine^ 3 naphthylaminesulphonic acid 2.6
^3 naphthylaminesulphonic acid 2.7
In mixed dyes, that is to say, where one of the
constituents is fast and the other loose, the dye
generally stands midway between the two in the
scale of fastness, but there are many exceptions to
this rule.
Three theories have been put forward to explain
the cause of this action. They are of an indirect
nature, and may be briefly summarised as follows :
(i) The oxygen theory. The dyes under the
influence of light interact with oxygen, and form
colourless compounds.
Berthollet in 1792 came to the conclusion that
oxygen combined with the colours, and made them
pale.
ACTION OF LIGHT ON DYEING OPERATIONS 289
The colour at the end of the exposure is, from
this point of view, proportional to the resistance
to this action.
(2) The ozone theory. The colours are decom-
posed or altered by the production of ozone (or
hydrogen peroxide) in the fibre, chiefly by evaporation
of moisture.
(3) Reduction theory. The dye is reduced by
cotton fibre, or directly by the action of light.
Experiments conducted in the presence of oxi-
dising agents have given conflicting results. The
presence of sodium hydrosulphite solution also gives
varying results.
Whatever be the cause of the results obtained
in the presence of oxidising, or reducing reagents, it
is important to note that dyed fabrics always show
an increased fastness against the action of light in
vacuo. This effect is very marked.
Similar experiments with sensitive organic com-
pounds are wanting. They should be of equal
interest.
A typical example of this action may be seen
when cotton dyed with Diamine Sky Blue B is placed
in long glass tubes, which are subsequently exhausted
by water suction to a pressure of 10 mm. (9 mm. of
which are due to water vapour), and exposed for
fourteen days to bright light. The shade remained
absolutely unchanged. A comparison trial, which
was exposed to the light side by side with the other
one, but under ordinary conditions, had entirely
lost its colour. The cotton was quite white-
2QO CHEMISTRY AND PHYSICS OF DYEING
The same blue cotton sealed in a tube in an
atmosphere, of oxygen gas lost its colour even more
rapidly than the above comparison sample. On
the other hand, the colour remained unaltered in
an atmosphere of either hydrogen, carbon dioxide,
sulphur dioxide, or coal gas. When exposed in
nitrous oxide gas the effect produced was very
similar to that noticed in the case of oxygen.
It is evident, therefore, that dyed samples in the
absence of oxygen will not fade.
Berthollet in 1792 noticed that the fading action
of colours seemed to be intensified in the presence
of an alkali. In the same way an acid condition
seems to retard the fading action.
The fact that the fading is intimately connected
with the presence of oxygen may, therefore, be taken
as established. It remains to trace the actual
action which takes place. It has been noticed that
the evaporation of water at ordinary temperatures
leads to the formation of ozone in very small
quantities.
The fading of the colours may, therefore, be
due to the direct interaction between the ozone, or
hydrogen peroxide so formed, from the oxygen
in the air ; colourless compounds of unknown
composition being produced. The action seems also
to be proportional to the moisture present at the
time of the experiment.
Under the influence of the light vibrations the
oxygen molecule may be more readily split up, and
an action of the following order induced :
ACTION OF LIGHT ON DYEING OPERATIONS 291
2 ^ O + O
and this may take place more readily when the
oxygen is associated with water molecules.
Whatever the action, the result is clearly seen
in the alteration in colour.
The most favourable atmosphere for this lading
action is a hot, moist, and alkaline one.
It has also been noticed that the presence
of such seemingly inert substances as alcohol
and pyridine vapour will greatly influence the
rate of fading. It is greatly accelerated in their
presence.
Although our knowledge is incomplete, we may
at least assume that the action is a very com-
plicated one, and beyond recording certain facts,
we are confined to most indefinite speculations.
The influence of the fibre is also a factor to be
considered. All fibres do not act in the same way.
The fastness of the same dye varies on different
fibres. Methylene b]ue on cotton is faster than on
wool. Indigo on the other hand gives more
fugitive shades on wool than on cotton.
Colours dyed on cotton, oxycellulose, trinitro-
cellulose and jute are said to be all equally fast.
This might be put forward as an argument that
there is no chemical action in dyeing these fibres,
the dye being present in all cases in the same state.
On silk eighty-four per cent, of the colours experi-
mented with showed no difference ; sixteen per cent,
were said to be slightly faster.
292 CHEMISTRY AND PHYSICS OF DYEING
There are therefore three factors, at least, which
may, under these same conditions, influence the rate
of fading, viz., the physical condition of the dye in
the fibre, that is to say, its state of division ; the
possibility of some chemical action between the
fibre and dye, and the transparency of the fibre
substance in its relation to the passage of the light
rays.
The statement that cotton colours are fast in
solution, but not on the fibre, is not correct.
The general conclusion arrived at, therefore, in
the present state of our knowledge, is that the
action is an oxidising, and not a reducing one. In
the absence of oxygen there is no change in colour,
due to the direct action of light. The action is also
proportional to the moisture present on the fibre.
It is clear also that the constitution of a colour
determines its stability.
An advance in our knowledge of this subject
was made by Depierre and Clouet (J.S.D.
and C. 1885, 245), when these authors discovered
that the action of light depended upon its
nature. It might be expected that the so-called
chemical rays would have a greater efficiency in
this action in the same way that they have a
greater influence in the decomposition of photo-
chemical salts. As a matter of fact, this is not the
case. It must, however, be remembered that we
have here a disturbing action in the case of dyes,
due to colour-filtering effect. This natural screen
may therefore in its action veil, or modify, the
ACTION OF LIGHT ON DYEING OPERATIONS 293
original effects of the light. The most active rays
may only have a chance of acting superficially in
some cases, at any rate, and, therefore, have their
normal action incidentally modified. Less active
rays which are passed on through the superficial
screen may actually have a greater cumulative
effect.
Dufton (J.S.D. and C. 1894, p. 92) has shown
that in any case the waves which are most readily
absorbed are the most active ones. That is to say,
the colours complementary to those reflected pro-
duce the greatest effect. This seems to be a
general law. The absorption of rays may, as in
the cases given at the beginning of this chapter,
produce a state of strain in the dye molecule leading
to a different state of equilibrium, or formation of
fresh compounds, and apart from this the formation
of active " oxygen " compounds would seem to
bring about the change in the dye which leads to the
change in colour. Assuming the quinonoid theory
of colour, it would be necessary to allow that the
structure of the dye molecule is profoundly
modified.
The whole subject is of extreme importance to
the dyer, and should receive more attention.
For instance, it has been generally allowed that
the basic colours produced on an antimony tannin
lake are fast as compared with those on tannic
acid itself. This action is an obscure one, and
hardly agrees with the contention that dyes in the
presence of acids are faster against light.
294 CHEMISTRY AND PHYSICS OF DYEING
It has been stated elsewhere that the action of
light is an important factor in the dyeing of Turkey
Red on cotton.
Another case of the influence of light in the
process of dyeing is that noticed by Pokorng
(Bull. Soc. Ind. Mulh. 1893, 282). Wool and silk
" dyed " with naphthylamine become darker in
shade on exposure to light. The shades produced
by subsequent treatment with nitrous acid are also
much darker than those from the original skein.
The action of light on diazotised primuline or silk
has even been made the basis of a photographic
process by Messrs. Green, Cross and Bevan and
Farrell respectively.
There is clearly plenty of scope for further re-
search on this interesting and almost untouched
branch of the subject.
The action of light on the natural colouring-
matters present in the vegetable fibres is well known.
It is taken advantage of in the bleaching of linen,
and was at one time universally used for this purpose.
In the case of cotton the action is greatly in-
creased if the fibre is previously treated with a
soda dye-bath. Such a sample will be well bleached
before the other one is appreciably lightened in
colour, under the same conditions.
The fact has been recorded that some dyes in
solution will dye the glass containing vessel to a far
greater extent on the side which faces the light.
This is possibly due to the more solvent action of
the water on the glass in the presence of light, or
ACTION OF LIGHT ON DYEING OPERATIONS 295
even to its decomposition, rather than any action
in the dye itself. The action seems to be a very
slow one.
To the student this subject is an absorbing one.
It may be attacked either from the point of view
of the fibres, or from that of the reactions which take
place when light acts on organic compounds. In
either case important results must follow a careful
study of the subject.
Two changes which take place under the influ-
ence of light rays, and which are both connected
with indigo, are of interest.
The first is that noticed by Kopp (Bull, Soc.
Ind. de Mulh). Kalle's indigo salt is very sen-
sitive to light when present as the bisulphate
compound. A dyeing process has even been
founded on this fact. The nature of the reaction is
unknown.
The second is that benzylidineorthonitroaceto-
phenone is converted into indigo by the action of
light by intermolecular oxidation. No action takes
place in the dark, very little in the red rays, more
in the green, and the influence reaches a maximum
in the violet (Engler and Dorant, Ber. 28, 2497).
The inference is that the action is closely connected
with the presence of the chemical rays.
The student might also refer to some work done
by W. Straub (Archiv fur Exp. Path, und Pharm.
5 1 * 383), on the action of light on eosin under
special circumstances.
The complete decolorisation of this dye required
296 CHEMISTRY AND PHYSICS OF DYEING
65 molecules of oxygen. The action is ascribed to
the production of eosin peroxide in the case in
question.
It will be remembered that the fastness of lakes
depends on the nature of the " absorbing" material.
Quite recently W. E. Evans (Eng. Pat. 19795, 1905)
has shown that light influences the drying of
materials. It is said that the action may either
hasten, or retard this operation according to its
nature.
CHAPTER XII
METHODS OF RESEARCH
IT is considered advisable for the benefit of students
and others, who contemplate starting original work
on this subject to outline briefly the methods used
by previous workers, so far as they have been
published.
The methods used are simple in their nature,
and in many cases are similar to those used in the
practice of dyeing.
Direct weighing method. The fibre is carefully
weighed on a chemical balance, before and after,
the experiment.
The process is not, as a rule, a satisfactory one.
For instance, it has been used to record the actual
gain in weight of fibres which have been mordanted
under different conditions. The net gain in weight
is registered, and this, perhaps, in ordinary dyeing,
mordanting, or weighting, experiments may be
satisfactory, yet the actual nature of the addition
in many cases, can be only guessed at, or is even
unknown.
This must be determined by actual chemical
analysis. This, in many cases, is a very difficult
298 CHEMISTRY AND PHYSICS OF DYEING
operation, and entails the elaboration of special
methods.
It is probable that in the future such a rough
and ready method of estimation will receive little
support except, of course, in cases where the re-
action between fibre and substance absorbed can
be readily ascertained, and is beyond question.
For instance, it might be a satisfactory method of
showing the different results obtained by the treat-
ment of silk with pure tannic acid. On the other
hand, it would be a very unsatisfactory way of
indicating the action of silk on stannic chloride
solution, or wool on bichromate solution. Any
further experiments on the action of mordants, can
have very little value, if they are simply of this
nature. The composition of the salt fixed must
be clearly determined, and any alteration in the
composition of the mordant solution itself,
noted.
The condition of the fibre, in these experiments
may have a disturbing effect on direct weighing.
The percentage of moisture must be estimated, and
allowed for.
This method is not satisfactory in the case of
dyeing with aniline colours, unless they are present
in large quantities. Even here, it is advisable to
check the amount of dye left in the solution, by
processes mentioned further on in this chapter.
Much of the present uncertainty of the reactions
in dyeing, is clearly due to the primitive nature of
many of the recorded experiments. Such a state of
METHODS OF RESEARCH 299
affairs would not be tolerated in any other branch
of chemical or physical work.
The conditions of the fibre state must not be
allowed to vary without record. Perhaps the most
difficult problem in connection with such work is
the standardising of a fibre state, which shall be
constant and easily reproduced at will. Such treat-
ment as is generally adopted in practice, which may
entail the use of solutions of acid or alkaline
reaction, is of a doubtful nature.
The action of such reagents is disturbing and
specific and, with our present knowledge, it is im-
possible to estimate their influence on the fibres,
with any certainty, or indicate their effect on the
absorption values.
Ultimate analysis. This is only satisfactory in
rare instances, for the reasons which hold in the
above case.
It may be used to estimate the percentage of
nitrogen in silk. The percentage present in the
fibre is 17.6. The greatest care must, however, be
taken to exclude the possibility of any other nitro-
genous substances being present, and so interfering
with the result.
Persoz (Monit. Sclent. 1887, 597) suggests that
silk be reduced to a powder after treatment with
30 per cent, hydrochloric acid. The nitrogen factor
is then increased to 18 per cent. The advantage
of this procedure is doubtful.
Estimation of ash. This may be useful to indi-
cate the presence of mineral matter in the case of
300 CHEMISTRY AND PHYSICS OF DYEING
the absorption of inorganic mordants. The com-
position of the ash should, however, be determined
and the possible action of incineration on its com-
position allowed for.
Direct analysis. Wherever possible this method
should be adopted. For instance, if this method
had been used throughout in Heermann's ex-
perimental work on the action of mordants the
results obtained would have been of greater
value.
The work necessary to devise special methods
of analysis to meet the requirements of the work
is often of a tedious nature. It may even be im-
possible to devise such direct methods of determining
the actions involved, but whenever possible they
should be used. The methods in use for ordinary
analysis are, of course, available.
Acidimetric methods are useful to estimate
acids, alkalies, and the absorption of these sub-
stances by fibres, if special precautions are
taken.
In some cases acid colours may be directly
estimated by a standard solution of Night Blue.
In the same way tannic acid is said to give good
results when used to estimate basic colours.
Knecht has recently recommended the use of
titanium salts for the volumetric method of esti-
mating dye-stuffs insolution(/.S.C. and D. 24. 154).
This should be useful in many cases.
The estimation of alizarine and mordant colours
is a difficult operation. Their " mordant value "
METHODS OF RESEARCH 301
may be obtained by the method suggested by the
writer (J.S.C.I., 12, 997).
Solvent action of reagents. This has been used
to indicate the way in which colours are held by
fibres.
This method was adopted by the writer to
determine the relative " fastness " of ingrain and
direct dyed colours. Other cases will also have
been noticed where this method is made use of,
particularly where alcohol has been used to extract
dye from the fibre. Benzene, and amyl alcohol,
have also been used for this purpose with
success.
Direct colour estimation. The numerous tincto-
meters in vogue may be used for this purpose. With
the Lovibond instrument a direct colour-record may
be kept of any dye solution. It may even be used
for the estimation of dyes on fabrics.
Mills and Hamilton used the tinctometer to
estimate the relative absorption of dyes by
fibres.
This method is a very accurate one when the
amount of colour present in a solution is small.
Estimation by dyed sample. A shade is matched
by direct dyeing on the same fibre under standard
conditions. This method is useful in cases where
the dye-bath is exhausted.
Relative dyeing properties of fibres. This may
sometimes indicate changes like those which take
place during the mercerising action, or in the nitra-
tion of cotton fibre.
302 CHEMISTRY AND PHYSICS OF DYEING
Thermo chemical reactions are recorded by special
means, and involve the use of a calorimeter.
Dissociation and association effects in solution.
-The student is referred to the standard books
on physical chemistry for information on this
subject.
Temperature. The control of the temperature
during experiments in dyeing is often of great
importance. This may be effected by the use of
a thermostat.
Spectroscopic examination. Formanek recom-
mends this process of analysis for the detection
of colouring-matters, particularly of the variations
in colour noticed after treatment with certain
reagents, such as ammonia, nitric acid, &c.
Polarised light. Chardonnet has used this
method to distinguish the different states of ni-
tration in nitrocellulose.
Hiibner and Pope indicate that they are using
this to indicate change in the fibre state during
the process of mercerising.
To a great extent the investigator must be guided
by the problems before him, and the general and
recognised methods of analysis should be utilised
wherever possible to the exclusion of such tests as
the mere weighing of the fibres before and after
treatment, or comparative dye trials.
The student should make certain that when-
ever possible his work shall be of a quantitative
nature, and that the conditions of the experiments
are accurately recorded.
METHODS OF RESEARCH 303
Special attention should be given to reactions
which take new directions or are modified in the
presence of fibres.
Such particulars as deal with the physical con-
stants of solutions must be sought for in the recog-
nised text-books on the subject.
INDEX OF AUTHORS
ABEGG, 64
Armstrong, 37, 103
Appleyard, 25, 175, 188
Arrhenius, 114
BANCROFT, 33
Baeyer, 227
Bauer, 143
Behre, 276
Benedikt, 59
Bemmelen, 116, 118, 127
Bentz, 194
Bergmann, 140, 180
Berthollet, 5, 140, 183, 288
Bevan, see Cross
Billitzer, 121, 274
Biltz, 43, 124, 275, 276
Binder, 59
Bing, 259
Binz, 204, 209, 213, 214, 259
Bolby, 6 1
Bourry, 30
Boettiger, 215
Brand, 200
Bretonniere, 47
Bronnert, 21
Brown, 100, 269, 272
Brownalie, 287
Buntrock, 40
CAREA LEA, 63
Carter, 158
Chabrie, 267
Champion, 25
Chaptal, 5
Chardonnet, 302
Chevreul, 5, 61, 140, 183
Ciamician, 282
Clouet, 292
Collingwood, 98
Coninck, 60
Cox, 64
Cramer, 28, 80, 230
Croissant, 47
Crompton, 103
Cross, 15, 21, 79, 172, 173, 262.
294
Crum, 142
D'APLIGNY, LE PILEUR, 5, 55,
140, 183
De Girardin, 5
De Saussure, 142
De Mosenthal, 144, 255
De Vitalis, 5
Depierre, 292
Donnon, 134
Dorant, 295
Dreaper, 18, 39, 104, 113, 152,
163, 165, 173, 174, 195, 202,
246, 255
Duclaux, 123
Dufay, 181
Dufton, 293
Duschak, 180
ENGLER, 295
Erdmann, 80
Esson, 148
Evans, 296
Ewer, 214
FABER, 13
Far r ell, 194, 294
20
306
INDEX OF AUTHORS
Fischer, 29, 151
Fischli, 60
Flick, 30
Fornianek, 302
Franklin, 137
Freudenberger, 137
Friedemann, 122
GARDNER, P., 19
Gardner, W. M., 97, 158
Geiger, 128
Geigy, 35
Georgievics, v., 34, 40, 46, 62,
151, 170, 176, 189, 211, 215,
229, 249, 260
Gelmo, 77, 91
Gillet, 93
Gladstone, 129
Gmelin, 227, 230
Gonfreville, 61
Goppelsroeder, 224
Gore, 264
Graham, 109
Green, 13, 37, 47, 49, 190, 207,
214, 294
Guthrie, 129
HALLITT, 152
Hamilton, 145, 301
Hanofsky, 21
Hantzsch, 227
Harcourt, 148
Hartl, 1 80
Harvey, 62
Hawkesbee, 250
Heermann, 67, 300
Hellot, 4, 140
Henri, 123, 137
Hepburn, 201
Hibbert, 129
Hirsch, 93, 95, 208, 213, 214
Hirst, 209
Hoff, Vant, 168, 179
Hollman, 83
Hood, 147
Hiibner, 82, 269, 302
Hulett, 1 80
Hummel, 62, 187, 232
Hwass, 146
JACOBS, MULLER, 214, 234
Jannasch, 180
Jaquemin, 225
Jones, 49
Jones, H. C., 103
KAUFER, 148
Kempf, 283
Kilmer, 81
Klobbie, 116
Knecht, 25, 26,63, I 3 I T 54> i$6,
158, 187, 188, 193, 205, 217,
249, 300
Krechlin, 260
Kohlrausch, 106
Konig, 286
Kopp, 295
Korte, 1 80
Kostanecki, v., 39, 40
Kraflt, 135, 239
Kuenen, 133
Kuhlmann, 185
Kurz, 201
Kuster, 177
LEFEVRE, 19
Levy, 207
Liechti, 54, 56. 62, 170, 192,
232
Liebermarm, 39
Liesegang, 124
Linder, 43, 123, 246, 256, 274
_2 7 8
Linnebarger, 126
Lowry, 104
Lubavin, 128
MACQUER, 140, 182
Masson, 22
Marchlewski, 231
Marckwald, 51, 282
Martini, 22
Matthews, 206
Mayer, 123, 137, 229,
INDEX OF AUTHORS
307
Mendeleef, 103
Mercei. 17
Meyenberg, 47
Mills, 84, 145, 148, 301
Minajeff, 82
Moehlau, 40
Mohlau, 65, 147, 207
Morris, 129
Musprat, 185
NASSO, 128
Neisser, 122
Noetling, 40, 59
Nollet, 113
Nietzki, 64, '.08
ORICELLI, 2
Ostwald, 1 80
PALEWSKY, 51
Paterno, 128
Pauly, 204
Payen, 128
Perkin. 33, 266
Persoz, 5, 58, 184, 299
Picton, 123, 135, 239, 246, 274
Pick, 214
Pickering, 103
Plaff, 128
Pliny, 2
Pollak, 47
Pokorng, 147, 167, 257, 258, 294
Pope, 82, 269, 302
Pouillet, 22
Prager, von, 33, 146, 189, 213
Prud'homme, 42, 94, 229
QUINCKE, 266
RAMSAY, 1 14
Ramsden, 265
Rennie, 148
Richard, 24
Richards, 180
Richardson, 27, 230
Rossi, 201
Rotheli, 227, 230
Rouard, 61
SACHS, 283
Sabaneeff, 128
Schafer, 229
Schaposchnikoff, 82
Scheurer, 17, 82
Schmidt, 177
Schmidner, 151
Schneider, 179
Schroeter, 209, 213, 214
Schultz, 269
Schumacher, 234
Schunck, 229, 231
Schiitzenberger, 61, 230
Sheppard, 175
Shields, 129
Silber, 282
Silbermann, 151
Sisley, 51, 167
Skita, 29
Steimmig, 40, 65
Stern, 17
Stobbe, ^85
Storck, 6u
Straub, 295
Suida, 20, 21, 54, 56, 77, 91
Spon, 146, 147
TAKAMINE, 84
Tauss, 80
Thenard, 61
Thompson, 143
Thomson, 262
Tollens, 13
Tomasso, 127
Tompkins, 18
Trantmann, 42
Tyndall, 135
ULRICKS, 189
Ulzer, 59
VANINO, 180
Veley, 129
Vergnaud, 5
Verguin, 33
308
Vidal, 47
Vignon, 95, 130, 207, 220, 224,
249
Voigtlander, 112
WALKER, 137, 175, 252
Washburn, 77
Weber, 132, 138, 149, 173, 175,
230, 240, 262
Weigert, 285
INDEX OF AUTHORS
Weil, 227
Werner, 258
Wilhelm, 132
Willstatter, 207
Wilson, 163
Witt, 34, 66, 1 68, 173, 243, 279
YEOMAN, 49
ZACHARIAS, 150
INDEX
ABSORPTION, 42, 44, 86, 1 17, 1 18,
124, 1 60, 171, 177, 179, 1 80,
197, 207, 234, 276, 279
causing decomposition, 24
compounds, 44, 279
strength of, solution on, 44,
171, 179, 234
maximum, 188, 261
of organic substances, 221
Absorptive power of silk, 85
cotton, 87
wool, 85
Acids., action of, 84, 162, 167
in dyeing, 89, 149, 154
basic colours
acid colours, 93, 154,
191
Acid salts, 18
Adjective colours, 33
Aggregates, size of, 251, 254
Alanine, 28, 29
phenyl, 3, 29
Albumen, action of, 128, 192,
244
Albumenoids, reactions of, 83
Alcohol, action of, 213, 227, 272
Alkalies, action of, 95, 261
absorption by fibres, 87
Aluminium chloride, 21
salts, 54, 59
Alizarates, 49, 61
solution in alcohol-ether, 60
Alizarines, 38, 43, 45, 56
quinoid form of, lakes, 45
Alkylated diazo dyes, 229
Alum, 61, 183
Amido acids, 25
Amido acids, theory of, 25, 186,
206
Amidoazobenzenes, 210, 238
Amidoglyceric acid, 28
Amido groups, 35, 36, 39
Amine dyes, 195, 211
Amines, absorption of, 147, 257
Ammonium sulphate, action of,
128
acetate, 215
Amorphous substances, 109
Amyl alcohol, 169
Aniline, black, 48
yellow, 238
Antimony mordants, 67
Animalising fibres, 224
Arganine, 29
Aromatic acids, absorption of,
179
oxy derivatives, 30
phenols, 159
Arsenious sulphide, 247, 251, 256
Artificial fibre substance, 228, 275
membranes, 235
Asbestos, dyeing of, 147
Assistants, action of, 64
Association theory, 103
Atomic migration, 255
Atropine hydrochloride, 207
Auxochromes, 35
Azobenzenecarboxylic acid, 211
Azo dyes, 35, 212
Azo triple dyes, 196
BARIUM chloride, action of, 180,
271
salts, dyeing with, 149, 230
3io
INDEX
Basic colours, 34, 48, 91, 242
action of light on, 240, 241,
246
decomposition of, 93, 187,
226, 241, 250
dyeing with, 91, 93, 99
lakes of, 48, 244
Benzidine salts, 207, 209
Benzoic acid, 178
Berberine hydrochloric! e, 145
Bleaching, 82
cotton, 82
silk, 75
wool, 78
" Boil off " liquor, 75
standard, 76
Borax, action of, 74
Bronzing effect, 168, 170
CACHOU de Laval, 47
Calcium salts, influence of, 45, 56,
58, 65, 81
Calico-printing, 5
Capillary action, 142, 144, 250
Carboxyl groups, 38
Casein, 237
Cellulose, 12, 79
action of reagents on, 12,
15, 18, 20, 224
acyl derivatives, 20
alkyl derivatives, 20
catalysing action of, 2 1
constitution of, 13
regenerated, 13
thiocarbonate, 13
Centrifugal action, influence of.
137
Chemical action, 147, 154, 180,
192, 208, 222, 225
Chemical theory of dyeing, 7,
1 80, 1 86
Chromate of chromium, 64
Chromium mordants, 43, 63, 65
Chromogens, 34
Chromophores, 34, 42
Chrysoidine, 238
Classification of dyes, 33, 236
Coagulation, an electrical effect,
280
Cochineal, 2
Colloid theory of dyeing, 234
Colloids, 9, 102, 107, 239
absorptive power of, 115,
276
action of barium sulphate
on, 126, 176, 180
action of electrolytes on, 127
carrying down power of,
120
classification of, 122, 125,
138
dehydration of, 126
diffusion of, 112, 135
electrically charged, 122
hydration of, 127
inorganic, absorption of, 124,
i 86, 276
molecular weight of, 125
power of coagulating, 122,
127
precipitation of insoluble
salts, 124
reactions of, 116, 120, 128,
248, 274
separation by centrifugal
force, 137
freezing, 128
water in, 126
Colloidal silica, 127
Colour acids, 90, 132, 156, 191
Colour of dyed fabrics, 200
sensibility, 175
Complementary light, 286
Condensation theory of dyeing,
212
Congo Red, 46, 215
Constitution of dyes, 34
influence on fastness, 287
Copper mordants, 45, 65
Cotton, 12, 142
acid salts, 18
acids on, 16, 84
alkalis, 18, 79
reagents on, 8 1 , 1 84
INDEX
Cotton dyes, 46, 135
mercerised, 18
mordants on, 54
nitrated, 16, 20
preliminary treatment of,
230
solutions of, 12, 17
Coupling dyes, 218
Crystalloids, 109
DEAMIDATED fibres, 194
Degraded solutions, 265
Dehydration of colloids, 127, 157
Dehydrotheotoluidine sulphonic
acid, 190
De-solution, 104, 246, 251, 272
by capillary action, 268
cause of, 207
Developed dyes, 202
Developers, action of, 196
Diamine colours, 39, 131 ,206, 2 1 8
Diamino acids, 29
Dianisidine hydrochloride, 207
Diazobenzene, 209
Diazo reaction with silk, 29
wool, 200
Diazotised fibres, 29, 193
primuline, 190
Diazoxylene, 209
Diffusion, 112
through membranes, 112,
236
of colloids, 112, 135
of dyes, 135, 136
Dinitrodiazoamidobenzene, 201
Dye in free state, 149, 230
Dyes, 32, 34
acid, 34
action of /3 rays on, 137
basic, 34
classification of, 33, 236
constitution of, 34, 36
dissociation of, 130, 150
identification of, 49
influence of constitution on
shade, 37
solubility of, r 5o, 122, 151
Dyes, solution state of, 1 36
vegetable dyes, 32
Dyeing, 57, 94, 131, 140, 165,
214, 270
cause of, 211
cotton, 82, 99, 169, 200
and silk, 215
conditions of, 72, 197, 204,
260
deamidated fibre, 206
inert substances, 226, 232,
240
inorganic colloids, 277, 278
in alcohol, 167, 178
in alcohol-ether, 60, 133
in benzene, 132, 178
in different solvents, 132,
167
in molecular proportions,
189
in neutral solutions, 91
ingrain colours, 173, 195, 200
jute, 12
part played by water, 258
with acid colours, 93, 192
with mixed colours, 145
with nitro colours, 208
wool, 91, 145
Dyewoods, 2
EBULLIOSCOPE, 240
Electrical dissociation, 51
Endosmosis, 263
Exosmosis, 263
Exothermic reaction, 22
FARADAY'S LAW, 106
Fastness of colours, 241, 287
Fibres, n
action on mordants, 56, 58
dye compounds, 193
microscopical examination
of, 231
physical properties of, 1 1 ,
141, 142, 171
reactions of, 76, 169, 186
state of, 72, in, 1 17
312
INDEX
Fibroin, 27, -195
Pick's law, 1 66
Flax, 79
Fluorescence, 170
Formaldehyde, action of, 98
Fuchsine, 33
GALLIC acid, action of, 128, 158
absorption by colloids, 158,
163
cotton, 162
silk, 158
hide powder, 164
Gelatine, action of, 163, 173
Glucosides, 231
Gly eerie acid, 28
Glycocol, 29
Greiss' reaction, 36
Guldberg's law, 154
HEMP, 79
Homatropine hydrochloride, 207
Hood's law, 99, 148
Hydrate theory of solution, 103
Hydrated irons, 104
Hydration, non-reversible, 268
Hydrazine grouping, 222
Hydrocellulose, 13, 79, 82
Hydrogels, in, 116
Hydrogel state, in, 116, 125
Hydrolysis, 21, 129
Hydrosol state, in, 116, 125
Hydrosols, in, 279
Hydrosulphites, 50
Hydroxyanthraquinones, 40
Hydroxyazobenzenes, 213
Hystazarine, 40
INDIGO, 32, 295
dyeing, 144, 185, 220, 259,
275
salt, 295
Ingrain colours, 173, 197
resistance to soap, 198, 202
on cotton, 204, 218
on silk, 195, 217
Ionic theory, 104
Ionic hydrates, 104
Ions, 1 06
Isonitrolic acid, 169
Iron mordants, 43, 60, 65, 68
JUTE, 79, 172
dyeing of, 172
KERATINE, 24, 98
Kermes, 2
LACTIC acid, 28
Lakes, 56, 61, 240
albumen, 83, 192, 244
alizarine, 38, 43, 56
double, 56
fatty acids in, 60
fugitive, 241
nature of. 58, 43, 190, 241,
243
steaming, 60
Lanuginic acid, 25
reactions of, 25
Laws of aggregation, 266
chemical action, 148, 154
diffusion, 165
distribution, 154
dyeing, 146, 154, 171, 176
levelling up, 114
Leucine /3, 29
Leuco compounds, 37, 48, 50
Lichens, dye from, 2
Liebermann and v . Kostanecki's
law, 39
Light, action of, 30, 60, 135, 281,
282, 291
in vacuo, 289
on anthracene, 285
on dehydration, 296
on dyes, 291, 295
onnatural colouring-matters,
294
on organic compounds, 282,
294
theory of, 288
Liquids degraded to solid state,
23
INDEX
313
Liquids, mutual solubility of , 133
Liquocellulose, 81
Logwood, 32
lakes, 256
MADDER, 32
Magenta, 170, 188, 193, 239, 249
alkylation of, 228
base, 227
Magnesium chloride, 21
Mass action, 190, 248
laws of, 190
Mauveine, 33, 100
Mechanical theory of dyeing, 7,
142
Mechanico-chemical theory, 150
Membranes, 112
diffusion through, 1 1 2
inert, 112
semi-permeable, 113
Mercerised cotton, 19, 133, 237
heat developed during, 20
linen, 20
Metallic salts, 218
Metastannic acid, 225
Metatungstate of soda, 286
Methyl violet, 249
Millon's reagent, 25
Mineral colours, 4
Moisture, influence of, 132,
149
Molecular conductivity, 106
migration, 113, 255
state, 51, 252
Mordants, 4, 53, 61
aluminium, 53, 61, 65
basic, 53
chromium, 43, 63, 68
copper, 45, 65
fatty acids, 56
iron, 43, 60, 65, 68
nickel, 66
on cotton, 53
silk, 53
wool, 53
tin, 43, 57, 68
titanium, 66
Mordant dyes, 38, 40
Mordanting action, 143, 157, 184,
236
i
NAPTHIONIC acid, 209
Naphthol sulphonic acid R., 209
Neutral salts, action of, 96, 259
Nickel mordants, 66
Night blue, 193, 270
lakes, 193, 205
Nitro-amidophenolsulphonic
acid, 41
Nitro-cellulose, 16, 20, 185
Nitrophenolsulphoazo - j3 - naph-
thol, 41
Nitrosalycilic acid, 46
Nitroso dyes, 41, 45
Nitrosophenols, 40
Nitrous acid, action of, 194
OIL mordants, 57
One-bath dyeing, 114
Optical properties of solutions,
137
Orchil, 32
Orthohydioxyazobenzol - p.- sul-
phonic acid, 41
Ortho-oximes, 40
Orthoquinonedioximes, 40
Osmosis, 114, 164
Osmotic pressure, 114
Oxycellulose, 19, 220
Oxygen theory, 289
Ozone, action of, 289
PARANITRANILINE red, 201
Paranitrodiazobenzene, 201
Pentatomic nitrogen, 222
Persulphates, 50
Phenolic dyes, 40, 195
Photochemical rays, 28 1
Phototropical rays, 282
Photophysical rays, 281
Physical action, 8, 140
Picric acid, 40, 51, 52, 176, 186,
189
Primary attraction, 104
21
INDEX
Primuline colours, 152, 200
Pseudo solution, 104, 108, 134,
246
of dyes, 239
Purple of Tyre, i
Pyrogallol, 160
QUINIZARINE, 40
Quinone theory, 37
RAMIE, 79
Research, methods of, 297
Reversible actions, 99, 161, 171,
248
Rhamnosides, 232
Ricinoleic acid, 59
aluminium, salt of, 59
Rosaniline hydrochloride, 48
acetate, 99
SALTS, action of, in dyeing, 96
Salt formation theory, 228
Sand, action of, on solutions, 145
action in dyeing, 147
Schiff's reaction, 19
Secondary attraction, 104, 273
Serene, 28
Sericine, 28
Silica, effect of wetting, 22
Silicic acid, 1 16
Silk, 27, 141, 182, 204
acids on, 30, 84, 179
alkalies on, 30, 76
analysis of, 27
bleaching, 75
boiling off, 73
composition of, 27, 230
decomposition of, 28
fibroin, 27
gum, 27, 73
mordants on, 68
theories of, 70
primuline dyes on, 201
solution of, 31
Single bath dyeing, 62, 114, 256
Soap, action on silk, 75
in Turkey Red dyeing, 58
Sodium carbonate, 74
sulphate, 98, 152
Solid solution, 8, 43, 168, 174,
190
Solids, action on wetting, 22
Soluble oil, 59
Solutions, 51, 103, 104, f26, 249
chemical action in, 125
concentrated, 253
non-reversible, 125
of colloids, 1 08, 246, 256,
277
Solubility, 105
of dyes, 132, 166
Solvent action, 166
Stannic acid, 225
Stannic chloride, 68
Steaming, 60
Stereochemical examination, 207
Strength of fibres, 17
dye solutions, 102
Suint, 78
Sulphanilic acid, 209
Sulphonic acids, 35, 95, 190, 238
Sulphur dyes, 46, 219, 276
Sulphuric acid on wool, 88
Sumacing, 57
Surface action, 183
Surface character of fibres, 266
Surface concentration, 246, 253,
262, 264
Surface energy, 262
Surface tension, 266
Surface viscosity, 265
TANNIC acid, 66, 128, 240, 272
absorption of, 66, 158, 160,
164, 220, 237
lakes, 66, 237
nature of, 66, 237
Tanning, 157
Temperature of dyeing, 100, 102,
147, 152, 269
mordanting, 69, 157
on wetting solids, 22
influence of, 69, 100, 234
Tervalent oxygen, 105
INDEX
315
Tetranitrochrysazarine, 40
Tetrazo dyes, 36
Thermochemical reactions, 223
Thiazine derivatives, 47
Tin mordants, 59
Trihydroxybenzenes, 160
Trinitroresorcinol, 40
Turkey Red, 55
Tyrosine, 28, 29, 204, 205
ULTRA-MICROSCOPICAL measure-
ment, 157
VARIATION in shade on dyeing,
241
Victoria Blue 4R., 145
Viscose, 13
WEIGHTED silk, 277
Woad, 3
Wool, 24, 141
acids on, 24, 62, 77, 84, 87,
154, 156
alcoholic potash on, 77
alkalies on, 26, 77
bleaching, 94
composition of, 26
dyeing, 91, 153, 166, 170,
182, 204, 230
fatty acids in, 78
hydrolysis of, 77
ingrain colours on, 217
mordants on, 26, 61
nitrous acid on, 24, 30
physical structure of, 24
preliminary treatment of,
94, 191
sodium sulphate, on, 98
sulphonic acids on, 95, 154
sulphur in, 24
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