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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