GIFT OF 
 MICHAEL REE^E 
 
TECHNOLOGICAL HANDBOOKS. 
 
 THE CHEMISTEY 
 
 OOAL-TAK COLOUES. 
 
 TRANSLATED FROM THE GERMAN OF 
 
 DR. E. BENEDIKT, 
 
 V * * 
 
 AND EDITED, WITH ADDITIONS, BY 
 
 E. KNECHT, PH.D., F.I.C., 
 
 IEAD MASTER OF THE CHEMISTRY AND DYEING DEPARTMENT OF THE TECHNICAL 
 
 COLLEGE, BRADFORD; EDITOR OF THE "JOURNAL OF THE SOCIETY 
 
 OF DYERS AND COLOURISTS." 
 
 SECOND EDITIQNrJ&YmEILAND ENLARGED. 
 
 .ONDON: GEORGE BETTSDSONS, YOEK STEEET, 
 COVENT GAEDEN. 
 
 1889. 
 

 BTJTLEK & TANNER, 
 
 THE SKLWOOD PRINTING WORKS, 
 
 FEOME, AND LONDON. 
 
 
PREFACE. 
 
 ALTHOUGH England may rightly be called the birthplace 
 of the coal-tar-colour industry, it is a remarkable fact 
 that the English literature on the subject is very scanty, 
 and that which does exist is now almost obsolete, owing 
 to the rapid strides which have been made during the 
 last ten years in the manufacture of coal-tar colours. 
 
 Numerous elaborate works are published from year to 
 year on this important subject both in France and in 
 Germany, but more especially in the latter country, by 
 means of which manufacturers and students are con- 
 tinuously kept informed of the latest methods and 
 theories. The want of a text-book of this kind contain- 
 ing a concise account of all the more important coal-tar 
 colours has long been felt by the author, and has prompted 
 him to undertake the present translation of Dr. Bene- 
 dikt's excellent little work, " Die Kiinstlichen Farbstoffe," 
 which has met with such success in all parts of the 
 Continent where German is spoken. The author may 
 therefore not be considered too sanguine in hoping that 
 the present volume will meet with some success in this 
 country, not only as a stepping-stone for those who wish 
 to make the subject a special study, but also among 
 students of chemistry in 'general. It will also be found 
 
 vii 
 
Vlll PREFACE. 
 
 useful to those engaged in the dyeing and printing of 
 textile fabrics. 
 
 The manufacture of coal-tar colours is an industry 
 which cannot possibly thrive by the old " rule of thumb " 
 way of doing business. It is a well-known fact that those 
 who succeed best in this industry now-a-days spare uo 
 means to bring the highest scientific training to bear on 
 the subject, while those who are " penny wise and pound 
 foolish" endeavour to save the expense of adequate 
 scientific advice, and thus ultimately find themselves 
 completely surpassed by more enlightened rivals. 
 
 E. K. 
 
 BRADFORD, 
 January, 188G. 
 
PREFACE TO THE SECOND EDITION. 
 
 THE larsre number of new coal-tar colours which has 
 
 O 
 
 come into the market since the publication of the first 
 edition- has necessitated a considerable increase in the 
 size of the present volume. The author has also con- 
 sidered it advisable to rearrange the matter so as to bring 
 the whole of the raw products under one heading, and to 
 make that chapter as complete as the conciseness and 
 scope of the work would allow. 
 
 During the same period the scientific development of 
 the subject has gone rapidly ahead, and the constitutional 
 formulae of many products of which we then knew little 
 more than the empirical formulte have been definitely 
 proved. 
 
 With the exception of these alterations, the general 
 arrangement of subjects does not differ materially from 
 that of the first edition. 
 
 At the suggestion of my friend, Mr. Christopher Rawson, 
 the symbolic rendering of the " azo " group, which is 
 generally represented as N = N , has been altered 
 throughout the work to N : N , because the two bonds 
 joining the nitrogen atoms might sometimes be mislead- 
 ing to beginners on account of the similarity they have 
 to the sign " equals." 
 
X PREFACE TO THE SECOND EDITION. 
 
 The author acknowledges his indebtedness to Drs. 
 Schulz and Julius, for permission to make use of their 
 excellent " Tabellarische Uebersicht der Kiinstlichen 
 Farbstoffe " in compiling the tables of the azo-dyes on 
 pp. 262-269. 
 
 E. K. 
 
 BRADFORD, 
 May, 1889. 
 
CONTENTS. 
 
 PAGE 
 
 INTRODUCTION 1 
 
 THE OPTICAL PROPERTIES OF COLOURING MATTERS ... 5 
 
 GENERAL CHEMICAL PROPERTIES OF THE COLOURING MATTERS . 27 
 
 METHODS OF DISSOLVING THE COLOURING MATTERS ... 35 
 
 DYEING WITH COAL-TAR COLOURS 39 
 
 THE TESTING OF COLOURING MATTERS 60 
 
 COAL-TAR AND THE RAW PRODUCTS USED IN THE MANUFACTURE 
 
 OF THE COAL-TAR COLOURS 69 
 
 THE COAL-TAR COLOURS 139 
 
 1. ANILINE DYES 140 
 
 (a) THE EOSANILINE GROUP 140 
 
 (b) INDULINES AND SAFRANINES 186 
 
 (c) OXAZINES 196 
 
 (d) ANILINE-BLACK AND NAPHTHAMEIN . . . .201 
 
 (e) COLOURING MATTERS CONTAINING SULPHUR (Tmo- 
 
 NINES) 208 
 
 II. PHENOL DYE-STUFFS 212 
 
 (a) NITRO-BODIES 213 
 
 (b) COLOURING MATTERS PRODUCED BY THE ACTION OF 
 
 NITROUS ACID ON PHENOLS 224 
 
 (c) EOSOLIC ACIDS . . . . . . . .227 
 
 (d) PHTHALEINS . 230 
 
 III. THE Azo DYES 247 
 
 (a) AMIDOAZO DYES .251 
 
 (b) AMIDOAZOSULPHONIC ACIDS 255 
 
 (c) OXYAZO DYES 259 
 
 DERIVATIVES OF QUINOLINE AND ACRIDINE . . . 283 
 
 IV. ARTIFICIAL INDIGO 286 
 
 V. THE ANTHRACENE COLOURING MATTERS . . . .291 
 
 INDEX 327 
 
 xi 
 
ERRATA. 
 
 Page 43,9th and 10th lines from top, read " basic constituent or constituents," 
 nstead of" basic constituent or constituent." 
 
 Page 42, 9th line from bottom, read " It contains besides carbon," instead of 
 " It contains, besides carbon." 
 
 Page 80, lines 4 and 7 from top, read " substitution derivatives," instead 
 of " substitutive derivatives." 
 
 Page 282, line 15 from bottom, read " Primuline," instead of " Primuine." 
 Page 304, line 7 from top, read " Liechti," instead of" Lie-chti." 
 
THE CHEMISTRY 
 
 OF THE 
 
 COAL-TAB COLOURS. 
 
 INTRODUCTION. 
 
 UNTIL the middle of this century the dyeing industry 
 was dependent upon those colouring matters which are 
 either found as such in the vegetable and animal kingdom, 
 or which are produced from some of the constituents of 
 the latter by very simple chemical processes. This whole 
 group of vegetable and animal colouring matters embraces 
 all the so-called natural colouring matters, while those 
 which the chemistry of modern times has evolved from 
 organic bodies possessing a comparatively simple com- 
 position, by operations which cause a total change of the 
 raw material, are generally designated as artificial colour- 
 ing matters. 
 
 In the manufacture of these artificial colouring matters 
 only very few of the many organic substances employed 
 are obtained from the vegetable kingdom (e.g., tannin, 
 which after its conversion into pyrogallol is used for 
 the preparation of ccerulein) . The greater part of the 
 materials which serve to furnish the artificial colouring 
 matters is obtained from coal-tar, a bye-product of the 
 manufacture of coal-gas. 
 
 It is owing to this fact that the history of the manu- 
 facture of artificial colouring matters, or "coal-tar colours," 
 
 i B 
 
X INTRODUCTION. 
 
 is to a great extent intimately connected with the history 
 of the manufacture of coal-gas, and there is no doubt that 
 the general introduction of coal-gas for illuminating pur- 
 poses within the first half of the present century has made 
 the manufacture of coal-tar colours possible. Neverthe- 
 less, from the 1st of April in 1814, when the parish of St. 
 Margaret in Westminster was first illuminated by coal- 
 gas, a period of no less than forty-two years elapsed be- 
 fore the manufacture of the first aniline dye, mauveme, 
 was taken in hand. 
 
 During this long period the constituents of coal-tar 
 were scientifically investigated, and thus a basis was 
 formed on which the subsequent development of the coal- 
 tar colour industry rested. 
 
 Great difficulties were encountered in the study of coal- 
 tar, for sixty years ago organic chemistry was only in its 
 childhood, and only with the gradual development of this 
 science to its present position has our knowledge of the 
 constituents of coal-tar become perfected. On the other 
 hand, the chemistry of to-day has been furthered to a 
 great extent by a thorough and incessant study of this 
 bye -pro duct. 
 
 But even at the present time our knowledge of the 
 chemistry of coal-tar is by no means complete. We know 
 that it consists of a mixture of a large number of com- 
 pounds, about 60 of which have been obtained in the pure 
 state ; but we nevertheless suppose that it contains other 
 compounds, which have hitherto not been isolated. 
 
 A short resume of the dates of discovery of the most 
 important constituents of coal-tar is given in the follow- 
 ing : 
 
 Naphthalene was first discovered in tar in 1820 by 
 Garden, anthracene in 1832 by Dumas, and phenol in 1834 
 by Mitscherlich. Benzene was discovered in 1825 by Fara- 
 day, but its presence in coal-tar was only recognised in 
 1845 by A. W. Hofmann. Toluene was discovered in 1837 
 
INTRODUCTION. O 
 
 by Pelletier and Walter, and in 1848 Mansfield showed that 
 it was contained in coal-tar. 
 
 Aniline was first discovered in 1826 by Unverdorben in 
 the products of the dry distillation of indigo, and in 1834 
 Runye proved it to be a constituent of coal-tar. The latter 
 contains it, however, in such small quantities that its 
 isolation on a large scale would not pay. The production 
 of aniline as a commercial product only became practicable 
 when Zinin showed in 1842 that it could be produced by 
 the reduction of nitrobenzene, a substance discovered in 
 1834 by Mitscherlich. Becl\amp greatly improved this 
 process in 1854 by the use of a mixture of iron and acetic 
 acid as reducing agents. Within the last few years the 
 method has been further improved by the employment of 
 hydrochloric acid instead of acetic acid. 
 
 Eunge first noticed in 1834 that aniline, when brought 
 in contact with chloride of lime, gave brilliant colours ; 
 but it was not until 1856 that Perkin prepared mauveine, 
 the first aniline dye, on a large scale. 
 
 In 1858 A. W. Hofmann published a work on the action 
 of carbon tetrachloride on aniline, by which reaction he 
 obtained aniline-red. It was in 1859 that Verguin first 
 manufactured aniline-red (magenta) in quantity. 
 
 During the following five years, violet, blue, and green 
 colouring matters were invented and manufactured. 
 
 Aniline-black was discovered in 1863 by Lightfoot. Graebe 
 and Liebermann effected in 1868 the synthesis of alizarin, 
 the most valuable colouring principle of madder, a dis- 
 covery which. had the greatest influence on the whole colour 
 industry. 
 
 The first Eosin dye was prepared in 1874 by Baeyer, 
 while in later years a large number of important dye- 
 stuff, such as the azo dyes, methylene-blue, malachite- green^ 
 etc., have been prepared. In the year 1880, Baeyer 
 was so far advanced in his experiments on the preparation 
 of artificial indigo, that the " Badische Anilin nnd Soda- 
 
4 INTRODUCTION. 
 
 fabrik" could venture to send into the market nitrophenyl- 
 propiolic acid, a product by means of which indigo can be 
 produced on the fibre. 
 
 The discovery of the benzidine dyes, of which Congo red 
 and Chrysamin were the first to appear in the market, 
 may be regarded as the most important discovery of 
 modern times as far as cotton dyeing is concerned. 
 
 In going through the large number of artificial colouring- 
 matters which have been brought into the market since 
 1858, it will be seen that those products which are dis- 
 tinguished by superior brilliancy and fastness have soon 
 taken the place of other colouring matters ; to such an 
 extent, indeed, that the manufacture of many dyes, which 
 at one time nourished, has either had to be relinquished 
 altogether, or has at least been considerably reduced. 
 And although it may seem to an outsider, while looking 
 through a collection of our modern silk and satin materials, 
 that the dazzling and pure shades obtained cannot be sur- 
 passed, those engaged in the manufacture of these dyes 
 are nevertheless well aware that even to-day they have 
 not yet arrived at their ultimate aim. Of all the artificial 
 dye-stuffs at present in use'there are perhaps only a few, 
 especially those which are distinguished by their superior 
 fastness, that will maintain a permanent position in 
 dyeing. 
 
 A popular prejudice still exists against the so-called 
 " Aniline Dyes " as being far behind the animal and vege- 
 table dye-stuffs with respect to fastness. But it is just 
 those loose artificial colouring matters which are so soon 
 replaced by other faster ones, and we now possess a con- 
 siderable number of coal-tar colours which are just as 
 fast, and often faster, than the natural ones. 
 
PAET I. 
 
 THE OPTICAL PROPERTIES OF COLOURING 
 MATTERS. 
 
 THE immense diversity of objects which surround us 
 appear to our eye in an infinite variety of colours and 
 shades. Bat the light which they reflect is, as will be 
 shown further on, very seldom perfectly uniform, and is 
 in most cases composed of a greater or lesser number of 
 rays of light differently coloured. The study of optics 
 affords us the means of finding out these different ele- 
 ments, i.e., of analysing the effect produced on our retina 
 by any given colour. 
 
 The colour chemist can make use of the results obtained 
 in this manner for the solution of many important ques- 
 tions, by the ordinary study of Avhich he could gain little 
 or no information. 
 
 The following will serve to illustrate a few questions 
 of this kind : 
 
 " What shades can be produced with a new colouring 
 matter ? " 
 
 " Can these shades be produced with other colouring 
 matters, already known ; or, cannot the shades obtained 
 with the new colouring matter be obtained just as well 
 with a mixture of two or more colouring matters, already 
 known ? " 
 
 " Do these shades possess the greatest purity and 
 brilliancy that can be expected of a colouring matter, or 
 may the colouring matter be surpassed by another of its 
 kind, perhaps one that has still to be discovered ? " 
 
 5 
 
6 COAL-TAR COLOURS. 
 
 Primary colours. However great the diversity of shades 
 which we perceive, the number of primary impressions 
 produced on the retina is very limited. These impressions 
 are those of white and black, and of red, yellow, green and 
 blue. The four last-named colours are termed primary 
 colours, for no human eye has yet been able to detect in 
 them two different colours, while all other colours contain 
 two or more primary colours. 
 
 By mixing white, black, and the primary colours in 
 different proportions, every impression is produced which 
 the eye is capable of receiving. The number of im- 
 pressions which can be produced by the mixture of these 
 colours is, however, diminished by the fact that the 
 primary colours will not produce an impression in every 
 combination of two. Thus the impression of red can be 
 mixed with blue or yellow, but not with green ; for 
 although we know a bluish-red and a yellowish- red, we 
 do not know a reddish-green. If red and green rays, or 
 blue and yellow rays, enter our eye simultaneously, we 
 have the impression of white. When two colours unite to 
 form white, they are called complementary colours. Green 
 would therefore be the complementary colour of red, blue 
 that of yellow. 
 
 Since, therefore, it is not possible for us to distinguish 
 in a colour red and green, or blue and yellow, the follow- 
 ing colours may be produced without the assistance of 
 white and black : 
 
 Red reddish-yellow yellow yellowish-green green 
 greenish-blue blue bluish-red. 
 
 These colours are called saturated as long as they do not 
 contain any ichite. The saturation is not diminished by 
 an addition of black, but the intensity of the colours is 
 diminished. The different gradations are called shades. 
 Thus it is possible to produce any number of shades 
 between blue and red, of which the first will contain a 
 large proportion of blue with very little red, while the 
 
DECOMPOSITION OF LIGHT BY THE PRISM. 7 
 
 last contain a large proportion of red and very little 
 blue. The shades produced in this manner are known 
 as bluish-violet, violet, reddish-violet, purple, and crimson. 
 
 All gradations or shades of grey lie between white and 
 black. All the primary colours and their shades or mix- 
 tures can be mixed with white or any shade of the grey 
 series, and thus an immense number of new colours would 
 be produced which would represent the shades obtained 
 with primary colours and shades. 
 
 Thus, by the construction of our eye and of our brain, 
 we cannot distinguish, even in the most complicated 
 colour, more than four elements ; viz., two primary colours, 
 white and black. 
 
 The marks or brands generally used in practice for 
 distinguishing the shades of a colour may be mentioned 
 here. For this purpose certain initials are placed after 
 the name of the colouring matter, viz. : R for red (roth, 
 rouge), for orange, G or J for yellow (gelb, jaune), 
 B for blue (blau, bleu), and V for violet. Thus we have a 
 Scarlet G and a Scarlet R, the redder shades being de- 
 noted by the terms Scarlet RR, Scarlet/RRRR or 4R, etc. 
 Ordinary aniline-blue possesses a red shade, and is known 
 as Aniline blue R, while the finest qualities are known 
 as Aniline-blue 6B, etc. 
 
 Decomposition of light by the prism. 
 
 White light contains a number of different coloured 
 rays, which are distinguished from each other by the 
 length of their waves and number of oscillations. By 
 means of the prism it is possible to isolate these ravs, 
 and to arrange them - systematically according to their 
 wave-lengths. 
 
 This can be demonstrated by the following simple ex- 
 periment : Direct or reflected sunlight is allowed to pass 
 
8 
 
 COAL-TAR COLOURS. 
 
 through a narrow slit A into a dark room. By means 
 of the lense L, the light passing through the slit is 
 made to converge so as to form a distinct image on the 
 screen 88. 
 
 If now the ray.i are intercepted by the prism P, the 
 white image at B will disappear, and a much broader 
 
 V 
 
 FIG. 1. 
 
 image R F, consisting of coloured bands, will be formed on 
 another part of the screen. White light contains, there- 
 fore, rays which are refracted from B to V (by the angle 
 a), and those which are refracted least, to R, along with 
 a number of intermediate ones. The rays which are re- 
 fracted most produce in the normal eye the impression 
 of violet, and then the other rays follow, passing through 
 
DECOMPOSITION OF LIGHT BY THE PRISM. 9 
 
 bluish-violet to blue, bluish-green to green, greenish- 
 yellow, yellow and orange to red. This coloured image 
 is called a spectrum. The spectrum of white light con- 
 tains all the pure colours, with the exception of those 
 lying between the red and the violet ; viz., crimson, purple, 
 etc. 
 
 Every point of the spectrum consists of homogeneous 
 light; i.e., light which cannot be further decomposed. 
 This can easily be proved by a slight modification of the 
 
 T 
 
 FIG. 2. 
 
 previous experiment. A narrow slit A' is made, parallel 
 to A in the screen 8 >S, which can be adjusted so as to 
 allow any portion of the spectrum to pass through. The 
 light passing through the slit A is caused to pass through 
 a second prism Q, and is cast on to a second screen T T. 
 It will then be seen that the orange rays, for instance, 
 cannot be resolved into red and yellow, as might have 
 been expected ; the new image remains orange. 
 
 The impression of orange can therefore be produced in 
 
10 
 
 COAL-TAR COLOURS. 
 
 our eye by homogeneous light of a certain refrangibility. 
 But when a mixture of red and yellow rays (that is, of 
 rays of greater and less refrangibility respectively than 
 the orange rays) enters our eye, we have again the im- 
 pression of orange. 
 
 The naked eye is not capable of discerning whether an 
 orange is homogeneous or mixed, and it is furthei'more, 
 as already stated above, not able to analyse colours or to 
 
 FIG. 3. 
 
 recognise the different coloured rays which produce a 
 certain impression of colour. It is invariably necessary 
 to make use of the prism or of some similar arrangement 
 in order to obtain an exact idea of the different compo- 
 nents of a colour. A convenient form of apparatus for 
 this purpose is the spectroscope, in which the spectrum 
 produced by the prism is not thrown on to a screen, but 
 is seen directly. 
 
 One of the best forms of spectroscope is the one given 
 
THE SPECTRA. 11 
 
 in Fig. 3. The light to be analysed enters the tube A 
 through a slit, the width of which can be regulated by 
 means of a screw. At the end of this tube there is a lens, 
 which is constructed so that the slit lies in the focus, and 
 the rays are thus caused to pass, parallel to each other, 
 into the prism P. The tube B is an astronomical teles- 
 cope, through which an image of the spectrum can be 
 seen. It can be turned around a vertical axis, and in this 
 way every part of the spectrum can be brought into the 
 middle of the plane of vision. The tube C also contains, 
 at the end adjoining the prism, a lens, in the focus of 
 which is placed a negative photographic image of a milli- 
 meter scale. This tube is placed so that its axis forms 
 with the front face of the prism an angle equal to the 
 one formed by the axis of the tube B, so that an eye look- 
 ing through B sees simultaneously the illuminated scale 
 and the spectrum, an arrangement which is of great ad- 
 vantage in the description and the comparison of the 
 spectra. 
 
 Another form of spectroscope is known as the spectro- 
 scope ivith direct vision. This form consists of a single 
 tube, containing, besides the slit and the lens, two or 
 more prisms composed of Crown glass and Flint glass 
 alternately. 
 
 The Spectra. 
 
 All solid or liquid bodies when heated to a white heat- 
 give a continuous spectrum; i.e., one which is not inter- 
 rupted by any dark lines or bands. 
 
 The rays which are emitted from the white-hot substance of the 
 sun have to pass, before reaching us, through the sun's atmosphere, 
 and in consequence of this the sun's spectrum is not a continuous 
 one, but is traversed by a large number of fine lines, known as 
 Frauenhofer's lines. Fig. 4 shows, according to Eood, the arrange- 
 ment of the colours in the sun's spectrum and the relative positions 
 of the most important of Frauenhofer's lines, 
 
12 
 
 COAL-TAR COLOURS. 
 
 Incandescent gases or vapours, on the other hand, give 
 discontinuous spectra, i.e., spectra in which the number of 
 rays of light is limited, and they appear in the spectroscope 
 only as lines of the breadth of the slit. These spectra are 
 called line-spectra, and every chemical element possesses in 
 the incandescent gaseous condition its own characteristic 
 lines by means of which it can be recognised. 
 
 The simplest way of observing these spectra is to place the non- 
 luminous flame of a Bunsen's burner in front of the slit of the 
 spectroscope, and to introduce into it on the end of a platinum wire 
 a volatile salt of the element to be examined. 
 
 Kb 
 
 Fio. 4. 
 
 These spectra are produced by luminous bodies. The 
 colouring matters, their solutions and the substances dyed 
 with them, are not luminous in themselves, but they 
 possess the property of converting white light which 
 strikes or traverses them into coloured light. The ex- 
 planation of this is, that they reflect or are traversed by 
 only a portion of the rays contained in white light, the 
 rest being hidden or destroyed by absorption. If, for 
 instance, a glass vessel containing a dilute solution of 
 magenta is placed between a luminous flame, which gives 
 a continuous spectrum, and the slit of a spectroscope, it 
 will be seen on analysing the transmitted light that an 
 essential change has taken place. Only the red rays of 
 the spectrum pass through unchanged ; the greenish- 
 yellow ones are extinguished, and blue and violet are 
 
ABSORPTION-SPECTRA. 
 
 13 
 
 considerably weakened. The result is, therefore, a discon- 
 tinuous absorption-spectrum, which consists of two parts, 
 one containing a large number of red rays and the other 
 the bluish-violet rays considerably diminished in intensity, 
 while the two portions are separated from each other by 
 a black interspace. 
 
 The light which strikes our eye from coloured surfaces 
 is not simply reflected light ; part of it has traversed the 
 uppermost layers of the coloured body, and being reflected 
 in the interior has then entered our eye, partially deprived 
 of its coloured rays. This coloured light is invariably 
 mixed with a certain proportion of white light, reflected 
 from the actual surface of the body before having entered 
 the uppermost layer. 
 
 If, therefore, dyed fabrics are to be examined by spec- 
 trum analysis, the same phenomena are in general observed 
 as the solutions of the corresponding colouring matters 
 show when in a state of solution. In both cases an 
 absorption-spectrum is obtained ; but the one gi ven by the 
 solution is the purer, because it does not contain the ad- 
 mixture of white light which is reflected from the surface 
 of the coloured objects. 
 
 FIG. 5. 
 
 Absorption-spectra of organic colouring matters. 
 
 The graphic representation of an absorption spectrum 
 may either be effected by shading the darkened parts 
 
14 
 
 COAL-TAR COLOURS. 
 
 according to the degree of absorption, and leaving those 
 parts Avhite which allow the rajs to pass unchanged ; or 
 by indicating the spectrum by a horizontal line and ex- 
 pressing the intensity of the absorption in each point by 
 means of co-ordinates. Fig. 5 shows, for the purpose of 
 illustration, the absorption-spectrum of blue cobalt-glass, 
 
 E 
 
 // 
 
 b a 
 
 1. Picric acid. 2. Eosin : , diltite, 1 1, concentrated. 
 3. Magenta. 4. M&thyl- violet. 
 
 represented according to each method. It will be seen 
 that cobalt-glass shows three bands of absorption, two of 
 which verge into each other. 
 
 The lines marked A, B, 0, a, d, etc., indicate certain 
 prominent Frauenhofer's lines which are present in the 
 
ABSORPTION-SPECTRA. 15 
 
 sun's spectrum, and which serve to determine relatively 
 the positions of the different bands of absorption. 
 
 The following absorption- spectra of solutions of four 
 well-known dye-stuffs picric acid, eosin, magenta and 
 methyl- violet (according to Yogel) will serve as ex- 
 amples : 
 
 Picric acid shows a total extinction of the blue side of 
 the spectrum as far as G F.* 
 
 Eosin in concentrated alcoholic solution absorbs chiefly 
 the green, while in dilute solution it shows a dark band 
 from D f E to 6. The absorption continues nearly as far 
 as F, where it terminates in an indistinct narrow band. 
 
 Magenta is characterized by a very distinct band of 
 absorption which, in dilute solutions, lies between D and 
 E. In concentrated solutions it allows only the red rays 
 to pass through. 
 
 By carefully considering the above examples, we arrive 
 at the following deductions: 
 
 The solutions of picric acid do not by any means possess 
 the appearance of yellow because they allow only the 
 yellow rays of the spectrum to pass through unabsorbed, 
 but because they absorb those parts of the spectrum 
 which are complenientary to yellow ; viz., the blue and the 
 violet. The red,^ green and bluish-green rays are not 
 absorbed any more than the yellow ones, but entering 
 our eye they produce the impression of white. Thus the 
 impression produced by picric acid is not a pure yellow, 
 but consists of a yellow mixed with a considerable propor- 
 tion of white. 
 
 In a similar manner, even concentrated solutions of the 
 fine red eosin dye do not allow red light only to pass 
 through ; they only absorb that portion which lies be- 
 tween the yellowish-green and the pure blue, and allow 
 part of the blue, the whole of the violet, red, orange and 
 
 * The expression G f F serves to indicate that the spectrum is 
 absorbed from the right end as far as of the space between G and F. 
 
16 
 
 COAL-TAR COLOURS. 
 
 yellow, to pass through unchanged. The red colour of the 
 eosin solution is therefore caused by a suppression of the 
 green in the white, and not, as may have been supposed, 
 by a special property of allowing only red rays to .pass 
 through. 
 
 The changes which the spectrum of a colouring matter 
 undergoes when dissolved in different neutral solvents are 
 
 C d 
 
 D 
 
 E b F 
 
 G II 
 
 FIG. 7. 
 
 1. Alizarin in alcoholic solution. 2. The same with ammonia. 
 3. Alizarin in aqueous ammonia. 4. Alizarin in alcohol and 
 caustic potash. 
 
 generally very small. The colour lakes, however, and the 
 solutions of the colouring matters in acids or alkalies give 
 spectra which differ greatly from those of the colouring 
 matters themselves. 
 
 Fig. 7 gives an example (according to Yogel) of the 
 
ABSORPTION SPECTRA. 17 
 
 changes which the spectrum of alizarin undergoes when* 
 converted into different salts. (2 and 4.) A comparison 
 of the spectra 2 and 3 shows the effect of different solvents 
 in the absorption. 
 
 Influence of concentration. If. the solution of a colour- 
 ing matter is diluted by degrees, it will be seen that the 
 lines and bands of absorption gradually become less 
 distinct, until at length in very great dilution they 
 become altogether invisible. If, on the other hand, the 
 quantity of colouring matter is increased, either by adding 
 more to the solution or by causing the light to pass 
 through a deeper layer of the liquid, a point is ultimately 
 arrived at when the liquid appears to be opaque and the 
 spectrum is completely absorbed. This shows that the 
 solutions of the colouring matters are neither perfectly 
 transparent nor perfectly opaque for any kind of light 
 rays. Dilute and concentrated solutions of one and the 
 same colouring matter do not give the same spectrum, 
 since the concentrated solutions always absorb a greater 
 proportion of the rays, while the unabsorbed rays are 
 considerably diminished in intensity. (See the spectrum 
 of eosin, p. 14.) It is therefore necessary, in giving an 
 exact description of the absorption-spectrum of a colouring 
 matter, to state the concentration of the solution, and at 
 the same time the depth of the layer through which the 
 light has passed. A change in the spectrum is often 
 accompanied by a change in the colour of the solution, 
 which does not simply appear more saturated in a deeper 
 layer, but has altogether changed colour. Chromic chloride 
 offers a very striking example of this ; in dilute solution 
 it appears green, while in concentrated solution it is red. 
 
 Solutions like that of chromic chloride, which possess 
 an essentially different colour in dilute and concentrated 
 solution, are called dichroistic. A solution of methyl - 
 violet, when acidulated with hydrochloric acid, shows this 
 property very distinctly. 
 
18 COAL-TAR COLOURS. 
 
 In dyeing a series of shades with one and the same 
 colouring matter, it is often seen that the light and the 
 dark shades do not appear to have been produced with the 
 same dye ; the dark shades of a series of blues may, for 
 instance, possess a distinct tint of red. This phenomenon 
 is caused by a slight dichroism of the colouring matter 
 used. 
 
 ABSORPTIOX-SPECTRA OF THE MOST PERFECT COLOURING 
 MATTERS. 
 
 In order to obtain a knowledge of the value of colouring 
 matters by means of their absorption-spectra, it is first of 
 all necessary to know the nature of the absorption-spectra 
 which the most perfect (purest) dyes give. Which rays, 
 for instance, must a colouring matter absorb in order to 
 impart to the material dyed with it the most brilliant 
 yellow corresponding to the line D of the sun's spectrum ? 
 In order to decide this question, we will first study the 
 impressions produced in our eye when two surfaces of 
 equal size, the one white, the other coloured, are illumi- 
 nated by lights of different colour. 
 
 If the white surface is illuminate^ by a sodium flame, 
 i.e., a light which contains only those rays of the spectrum 
 which correspond to the line D, it will have the appear- 
 ance of yellow, and will reflect only homogeneous yellow 
 light. If the second surface had been dyed with a colour- 
 ing matter, the absorption-spectrum of which contained 
 but one bright line at D (Fig. 8), and were illuminated by 
 white light (e.g., electric light), it would absorb all the 
 rays with the exception of those corresponding to the line 
 D, and would, like the first surface, reflect only homo- 
 geneous yellow light. 
 
 If now the illumination by the sodium light and the 
 electric light, respectively, were regulated so as to cause 
 the same quantity of yellow rays to fall on each surface, 
 
ABSORPTION SPECTRA. 
 
 19 
 
 they would, although in reality equal, in intensity, not 
 appear the same in our eye. This is due to the fact that 
 the sensibility of our eye for objects which emit or reflect 
 a limited number of rays decreases proportionately with 
 the intensity of the light which is reflected into our eye 
 from the surrounding objects. It is, for instance, well 
 known that a grey disc of paper appears much lighter on 
 a black ground than on a white one. 
 
 In the sodium light, all the objects surrounding the 
 white surface appear of a yellow colour, which varies in 
 intensity ; but the intensity never exceeds th at of the 
 
 white object, because the latter reflects the whole of the 
 yellow rays which strike it. 
 
 The yellow surface illuminated with the electric light 
 absorbs, as we have seen before, all the rays with the 
 exception of those corresponding to the line D of the 
 spectrum. The surrounding white objects reflect the 
 whole of the rays, while the coloured ones also reflect a 
 considerable proportion, and they will therefore all appear 
 in a much brighter light than the dyed object, which only 
 reflects a small quantity of light, and is therefore called 
 a dull or dead yellow. 
 
 We know from the preceding that brightly coloured 
 
20 COAL-TAR COLOURS. 
 
 objects reflect a number of different coloured rajs which, 
 correspond to large portions of the spectrum, so that the 
 reflected light contains a large proportion of the rays of 
 light which strike it. 
 
 Adhering to our previous example, the most intense 
 yellow will be produced in the following manner: If the 
 yellow space at D in the absorption-spectrum 1 (Fig. 8) is 
 gradually enlarged on each side until it reaches the lines 
 a a and b b in 2, besides pure yellow, a yellow containing 
 a small proportion of red along with a yellow with a 
 greenish tinge are allowed to pass through. The small 
 quantities of red and green combined produce the im- 
 pression of white in our eye, and we obtain therefore by 
 this enlargement of the spectrum a large addition of 
 yellow, but at the same time a small admixture of white. 
 If now each side of the spectrum is gradually increased 
 bit by bit, we shall find that the great increase of yellow 
 obtained by the first enlargement gradually diminishes 
 the more the ends of the spectrum deviate from the line 
 D, while at the same time the green and red increase ; i.e., 
 the colour is mixed with more and more white. 
 
 If the spectrum is extended as far as the reddish-orange 
 on the one side and a little further than the yellowish- 
 green on the other, we only obtain a very small addition 
 of yellow, whereas the white is considerably increased. 
 A further enlargement of the spectrum would be of no 
 use whatever, as the pure red and green would only com- 
 bine to form white, and would thus diminish the fulness 
 of the yellow. The most brilliant yellow corresponding 
 to the line D would therefore be produced by a colouring 
 matter which allows all the rays lying between reddish- 
 orange and greenish-yellow to pass through unchanged, 
 but absorbs all the other colours of the spectrum, as 
 indicated in 2, Fig. 8. 
 
 In a like manner it can be shown that the most intense 
 yreen nmstlallow all the rays lying between yellowish- 
 
ABSORPTION SPECTRA. 
 
 21 
 
 green and bluish-green to pass through, but must absorb 
 the yellow, blue, orange, red and violet. 
 
 The finest red would be given by a colouring matter 
 which allows red and orange, as far as pure yellow, and 
 the rays lying between bluish-violet and violet, to pass 
 through, and possesses, therefore, a spectrum consisting of 
 two parts. 
 
 The most perfect blue would allow the blue end 
 of the spectrum, beginning with bluish-green, to pass 
 through. 
 
 This deduction only holds good for the primary colours, 
 red, yellow, green, and blue, and must be somewhat 
 modified if ifc is to be applied to intermediate shades. 
 If, for instance, a colouring matter has to show an in- 
 
 FIG 9. 
 
 tense yellowish-green, corresponding to that part of the 
 spectrum which lies half-way between green and yellow, 
 in the first place all the rays lying between pure yellow 
 and green (from m n to q r) must pass through. The 
 colour of the solution will then appear saturated in 
 transmitted light, without any admixture of white. But 
 the intensity of the colour can be considerably increased 
 if the spectrum is enlarged on the one side as far as 
 orange, on the other as far as blue. The colour adjoining 
 the pure yellow is a yellow containing a very small 
 proportion of red, while the colour adjoining the pure 
 green is a green containing a very small proportion of 
 blue. The small quantities of red and blue contained 
 in the spaces m n o p and q r s t combine with the 
 
2'2 COAL-TAR COLOURS. 
 
 equally small quantities of green and yellow contained in 
 the spaces q r s t and m n o p to form a small quantity of 
 white ; but there still remains a considerable proportion 
 of green, which increases the intensity of the colour. If 
 the spectrum is gradually enlarged on both sides, the 
 yellowish-orange will first be neutralized by the greenish- 
 blue to white, while the red combines in a similar manner 
 with the green. The greenish-yellow is therefore not 
 intensified by a further increase of the spectrum. Hence 
 there is a limit to the perfection of a colouring matter. 
 It would be useless to try to obtain colouring matters 
 which impart shades to the dyed materials which corre- 
 spond exactly to those of the spectrum, for if an object 
 has to appear of a brilliant colour, it must always reflect 
 some rays which combine to form in our eye the impres- 
 sion of white. 
 
 Mixtures of colouring matters. 
 
 When a new dye- stuff comes into the hands of a dyer, 
 he generally tries by experimental dyeing whether it . is 
 available for the production of mixed shades; for the 
 most practised eye cannot foretell what shade will be 
 produced by mixing it with another colouring matter. 
 Thus two blues which cannot be distinguished from each 
 other in the pure state by the eye may yield when used 
 along with picric acid two shades which are as different 
 from each other as green from olive. 
 
 By an investigation of the green, for instance, which is 
 formed by indigo extract and picric acid, we obtain in 
 Fig. 10 an illustration of those parts of the spectrum 
 which are absorbed. 
 
 The solution of picric acid absorbs the violet and the 
 greater part of the blue rays, so that only those rays 
 which extend from the pure blue to the red end of the 
 spectrum can enter the solution of indigo extract, which 
 
ABSORPTION SPECTRA. 
 
 23 
 
 latter only allows the blue, bluish-green, and part of the 
 red to pass through unaltered, while the orange and the 
 yellow are almost completely absorbed, the green and 
 yellowish-green partially. By combining these two 
 spectra we obtain spectrum 3, which is characteristic for 
 the green produced by means of indigo extract and picric 
 acid. It consists of blue, bluish-green, green, and a 
 portion of the red. 
 
 FIG. 10. 
 
 Indigo extract and picric acid do not, therefore, as 
 may have been supposed, yield a green because one 
 allows only blue rays, the other only yellow rays, to pass 
 through, but because they both allow green light to pass 
 through. This is shown a little more clearly in the 
 following example : The spectrum 1 in Fig. 11 is that of 
 a pure blue colouring* matter which would not yield a 
 green with a pure yellow colouring matter possessing the 
 absorption-spectrum 2, since all the rays would be ab- 
 sorbed, and the result would be a black. 
 
24 
 
 COAL-TAR COLOURS. 
 
 If the spectra of these two colouring matters are en- 
 larged on each side, the single colours will not undergo 
 any appreciable change, only receiving an admixture of a 
 certain proportion of white. 
 
 Nevertheless, a very fair green is obtained by mixing 
 the two, which is shown in spectrum 3, Fig. 12. 
 
 A mixture of methyl- violet and Solid Green give a fine 
 though not intense blue, the explanation of which is simi- 
 lar to that of the formation of green by mixing blue and 
 yellow. 
 
 Violet yields with the yellow colouring matters dull 
 
 FIG. 11. 
 
 shades of green and yellowish-green, such as olives, moss- 
 green, etc. 
 
 Of the more brilliant colouring matters there are pro- 
 bably no two which would fulfil the conditions expressed 
 in Fig. 11, and would thus obstruct all the rays. This 
 result can, however, easily be arrived at by using three 
 colouring matters, which must be as different from each 
 other as possible. Thus the combination of a red, a yellow 
 and a blue colouring matter, when sufficiently concen- 
 trated, does not under ordinary circumstances allow any 
 light to pass through, and can therefore be used for the 
 production of blacks. This property is in fact made use 
 of in dyeing, and not only black, but also an unlimited 
 
FLUORESCENCE. 
 
 25 
 
 number of dark or dull shades of red, yellow and blue, 
 comprising the greys and browns, can be produced in this 
 manner. Light or dark greys are produced when small 
 quantities of colouring matter are employed, and the pro- 
 portions are chosen so that none of the three colours is 
 present in excess. The colour inclines to brown, if red 
 and yellow are in excess ; while if the quantities of red 
 and yellow are reduced, a bluish-grey is obtained. 
 
 FIG. 12. 
 
 
 
 Fluorescence. 
 
 The light which enters a coloured liquid is not in every 
 case simply divided into two parts, of which one is ab- 
 sorbed, while tlje other passes through. Some solutions 
 do not only appear coloured by transmitted light but also 
 in reflected light, in which case they appear to be rendered 
 turbid by an extremely finely divided luminous solid in a 
 state of suspension. Liquids which show this property 
 are called fluorescent. A splendid example of fluorescence 
 is shown, for instance, by an alcoholic, ammoniacal solu- 
 tion of Diazoresorufm. The liquid appears crimson by 
 transmitted light, but in reflected light bright brick-red. 
 
26 COAL-TAR COLOURS. 
 
 Fluorescein, some of the Eosins, Magdala-red, and Re- 
 sorcin-blue also show a marked fluorescence when in solu- 
 tion. 
 
 The fluorescent properties of a colouring matter are 
 shown to the best advantage on those fibres which possess 
 most lustre. Silk shows it best ; wool will also show it 
 under certain circumstances ; but cotton cannot be made 
 fluorescent, because the rough surface of the fibre dis- 
 perses, and thus thoroughly mixes the transmitted light 
 and the light of fluorescence. 
 
 The Spectroscope as a means of detecting colouring matters. 
 
 The absorption-spectra of the colouring matters can in 
 some cases be made use of for their detection, especially 
 when they contain characteristic lines of absorption, either 
 in neutral, acid or alkaline solution. Thus, alizarin can 
 be recognised by the bands shown in the spectroscope, by 
 allowing the light to pass through its alkaline alcoholic 
 solution. Reliable methods have indeed been devised 
 for detecting and distinguishing from each other certain 
 colouring matters in this way, but the field has not yet 
 been systematically worked. Colouring matters which 
 are closely allied to each other in chemical constitution, 
 and are therefore difficult to distinguish from each other 
 by their chemical reactions, generally give very similar 
 spectra; on the other hand, colouring matters which pos- 
 sess very different spectra may also be easily distinguished 
 from each other by chemical means. Analysis by means 
 of the absorption-spectrum, which has become of great 
 importance for many branches of science and practice, is 
 therefore only of minor importance to the colour chemist, 
 and it is only in a few cases that it renders him important 
 services. 
 
 The use of the spectroscope has also been suggested by 
 Schoop for the quantitative determination of the coal-tar 
 colours. (See Journ. Soc. Dyers and Col., 1886, p. 71.) 
 
GENERAL CHEMICAL PROPERTIES. 27 
 
 GENERAL CHEMICAL PROPEETIES OF THE 
 COLOURING MATTERS. 
 
 The term " colouring matter," in the strict sense of the 
 word, embraces all those coloured substances which in a 
 state of fine division are capable of imparting their own 
 colour to other objects. The term is, however, frequently 
 applied to other bodies, which of themselves possess little 
 or no colour, but can be transformed into colouring matters 
 proper by the action of bases or acids. The chemical 
 denomination has indeed become so usual that it has in 
 many cases almost completely replaced the former. Thus 
 alizarin is called a colouring matter, although it possesses 
 in the free state only a dull yellow colour, whereas the 
 beautiful red combination of alizarin with alumina is 
 generally known as a Colour-lake, and not as a colouring 
 matter proper. 
 
 Chemical constitution. This chapter will chiefly be de- 
 voted to the consideration of those chemical properties of 
 the colouring matters which are of importance in their 
 application, and especially in their fixation to the fibres ; 
 and since the terms " chemical constitution " and " consti- 
 tutional formula " will frequently be made use of in this 
 and the following chapters, it may bej well to give a 
 thorough explanation of their meaning. \ 
 
 According to the chemical theory at present generally 
 adopted, the smallest particles of the elements which can 
 enter into chemical combination are called atoms. These 
 atoms combine with each other according to definite laws, 
 in greater or smaller numbers, to form molecules, which 
 are simultaneously the smallest particles of matter capa- 
 ble of existing in the free state. Thus, each molecule of 
 magenta is composed of atoms of carbon, hydrogen, nitro- 
 gen and chlorine. 
 
 The abridged chemical notation by which the number 
 
28 COAL-TAR COLOURS. 
 
 of these atoms and the proportion in which they are con- 
 tained in the molecule are stated, is called an empirical 
 formula. Thus, the fact that the molecule of magenta 
 consists of twenty atoms of carbon (C), twenty atoms of 
 hydrogen (H), three atoms of nitrogen (N), and one atom 
 of chlorine (Cl), is expressed by the empirical formula, 
 CooHoo^Cl. 
 
 By a thorough investigation of the chemical properties 
 of these bodies, their modes of formation, products of de- 
 composition, and the compounds they are capable of form- 
 ing, modern chemistry has procured a deeper insight into 
 their interior structure. But although we have no de- 
 finite idea as to the actual relative position of the atoms 
 in the molecule, we are nevertheless enabled to lay down 
 a scheme in which the atoms given by empirical formulas 
 are arranged in such a manner as to show the whole 
 chemical nature of the compound. A scheme of this kind, 
 which simply serves to express our knowledge of the com- 
 pound to which it relates, is called a constitutional formula . 
 The determination of the constitutional formulas of bodies 
 like the organic colouring matters, the composition of 
 which is generally very complicated, is often a difficult 
 matter, and it is therefore not to be wondered at that 
 there are still many colouring matters the constitution of 
 which is unknown. 
 
 In the constitutional formulae certain groups of ele- 
 ments invariably indicate similar chemical properties. 
 Thus we know that bodies which contain one atom of 
 nitrogen and two of hydrogen combined, as N-H n , all have 
 the property of combining with acids. On the other 
 hand, each individual chemical property is not a function 
 of the arrangement of the total number of atoms, but only 
 of certain groups of atoms. 
 
 In order to obtain a general idea of the chemical nature 
 of the colouring matters, it will be found convenient to 
 divide these groups of atoms into two classes ; viz. (1), 
 
GENERAL CHEMICAL PROPERTIES. 
 
 I 
 
 those which cause the colour of the compound ; and (2) 
 those on which the acid or basic nature of the compound 
 depends. 
 
 1. The groups which cause the colour of a compound 
 are knows as chromopliorous or colour-bearing 1 groups. 
 They can often be discovered by carrying out certain 
 reactions with the compound, and observing in which 
 cases it loses its characteristic colour. It is then necessary 
 to find out which groups have undergone a chemical 
 change. If this has taken place with one group only, 
 then that group is the chromopliorous one ; while if several 
 groups have been affected, it is in most cases possible to 
 detect the chromophorous group by a comparison of the 
 results of several reactions. 
 
 Thus we know that the yellow colour of picric acid, 
 C 6 H 2 (N0 2 ) 3 OH, is due to the presence of the three nitro 
 (N0 2 ) groups ; because if this colouring matter is reduced 
 by means of tin and hydrochloric acid, it is decolourised, 
 and converted into triamidophenol, C 6 H 2 (NHo) 3 OH, in 
 which the nitro groups of the original compound have 
 been replaced by amido groups. 
 
 In a similar manner it has been ascertained that the 
 chromophorous group contained in all the azo-colours, 
 consists of two atoms of nitrogen, combined in the follow- 
 ing manner : N:N . But although it may have been 
 proved that a group of atoms has caused the colour of a 
 certain compound, it must not be concluded that this 
 group is chromophorous in every case, and that therefore 
 every compound that contains it must possess a similar 
 colour. Generally this is the case with bodies of similar 
 constitution, but although, for instance, most nitre-com- 
 pounds are coloured yellow or orange, there are others 
 which are colourless. The properties of the chromophorous 
 group are of special interest to the dyer when he wishes to 
 bring about a temporary or permanent decolourisation of 
 the colouring matter, such as is necessary in the prepara- 
 
30 COAL-TAB COLOURS. 
 
 tion of " vats " or in the production of " discharges " (in 
 calico-printing) . 
 
 Salt-forming groups. The groups of atoms which cause 
 the colouring matters to form salts can also easily be 
 recognised in the constitutional formulae, and by a know- 
 ledge of them we can see at a glance their relation to the 
 animal and vegetable fibres. For this purpose they may 
 be suitably classified, according to their property of 
 combining with acids or bases, or with neither, as basic 
 colouring matters, acid colouring matters, and indifferent or 
 neutral colouring matters. 
 
 The basic colouring matters are always used in dyeing 
 in the form of their salts i.e., of their compounds with 
 mineral or organic acids. Colouring matters possessing 
 a distinct basic character, which lose their colour in coming 
 in contact with acids, cannot be used in dyeing, as will be 
 shown further on. The only exceptions to this rule are 
 some very weak bases, which are absorbed by the fibre as 
 such and not in the form of their salts. Amidoazoben- 
 zene, C 6 H 5 N:N C fi H i 'NH 2 , a colouring matter which 
 was formerly sold and used under the name of "Aniline- 
 yellow," furnishes an example of this kind. Its salts are 
 decomposed by water ; if, therefore, silk is dyed with 
 an acidulated solution of its hydrochloride, and is then 
 washed with water, the free base only remains on the 
 fibre. If, however, the silk undergoes a subsequent treat- 
 ment with dilute acids (e.g., in brightening), the colouring 
 matter evinces a neutral reaction and remains unchanged. 
 The free colour- bases are for the most part colourless or 
 only slightly coloured. 
 
 All the known basic colouring matters contain nitrogen, 
 and it is to the presence of these nitrogen atoms that they 
 owe their basic properties. They are all derived from the 
 type ammonia : TT 
 
 Ts T -H 
 
GENERAL CHEMICAL PROPERTIES. 31 
 
 By replacing one, two or all three of the hydrogen atoms 
 in this compound by organic radicals, the amines or amido- 
 compounds are formed. These are of three kinds. The 
 primary amines contain two replaceable hydrogen atoms, 
 the secondary amines one, while in the tertiary amines 
 all the hydrogen atoms are replaced by organic radicals. 
 The following may serve as examples : 
 
 / CH 3 / CH, / CH 3 
 
 N-H ' N-CH 3 N-CH 3 
 
 \CH 3 
 
 Methylamine. Dimethylamine. Trimethylamine. 
 
 (Primary.) (Secondary.) (Tertiary.) 
 
 In place of methyl (CH 3 ) any other organic radical can 
 be substituted; e.g., ethyl (CoH 5 ), phenyl (C G H 5 ), benzyl 
 (C 7 H 7 ), etc. 
 
 In the amines, therefore, the nitrogen is always in 
 direct combination with carbon and hydrogen or with 
 three carbon atoms. The group NH which, is contained 
 in the secondary amines is known as the Imido group. 
 
 The colour-bases may either contain one or several 
 amido groups. Of two or more colour-bases possessing 
 similar constitution, the one containing the largest number 
 of amido groups will combine most easily with acids. 
 The number of equivalents of an acid with which the base 
 will combine is, however, limited according to the number 
 of hydrogen atoms it contains in direct combination with 
 the nitrogen atoms. Thus, rosaniline, C 20 H 19 N 3 , contains 
 six such, hydrogen atoms, and it yields, besides the 
 salts containing one equivalent of acid, such as ordinary 
 magenta, CooH^Ng'HCl, another series of salts, of which 
 C 20 H 19 N 3 '3HC1 would be a representative. 
 
 The basic properties of the primary amines, and also 
 of the colouring matters containing primary amines, are 
 much more marked than those of the secondary or tertiary 
 amines. They are also considerably diminished by the 
 
32 COAL-TAB COLOURS. 
 
 introduction of electro-negative elements or groups, such 
 as Chlorine, Bromine, Iodine or Nitro groups. Thus 
 aniline, NH 2 C G H 5 , which is a primary amine, is a strong 
 base; diphenylamine, jSTH(C 6 H 5 )o, which is a secondary 
 amine, forms salts which are easily decomposed ; while 
 hexanitrodiphenylamine, N(C c Ho[N0 2 ] s ) 2 H, is no base at 
 all, but, on the contrary, a strong acid. Its salts are known 
 in commerce as Aurantia. 
 
 The salts of those colour-bases which contain unsub- 
 stituted amido groups are generally soluble in water, but 
 if the hydrogen of these groups is partially or wholly 
 replaced by organic radicals, the solubility decreases 
 proportionately. Thus, magenta, which may be repre- 
 sented as pararosaniline hydrochloride, which has the 
 formula 
 
 C C H 4 NH-HC1. 
 
 and contains two amido and one imido group, is compara- 
 tively easily soluble in water, whilst aniline-blue or the 
 hydrochloride of triphenylrosaniline 
 
 C C fi H 4 NH.C 6 H, 
 (c 6 H 4 NC f) H 5 -HCl. 
 
 is insoluble in water. 
 
 Most of the colour-bases can be transformed into soluble 
 acid colouring matters by the action of sulphuric acid. 
 (vide Sulphonic Acids). 
 
 The acid colouring matters contain, like all acids, 
 hydrogen atoms which can easily be replaced by metals ; 
 in other words, they possess the property of combining 
 with bases to form salts with the simultaneous evolution 
 
GENERAL CHEMICAL PROPERTIES. 33 
 
 of water. Thus, picric acid, C G H 2 (N0 2 ) 3 OH, contains a 
 hydrogen atom which can be replaced by metals : 
 
 C 6 H 2 (N0 2 ) 3 OH + KOH - H 2 + C 6 H 3 (N0 2 ) 3 OK. 
 
 Picric acid. Caustic potash. Water. Picrate of potash. 
 
 As will be seen from the above example, not all the 
 hydrogen atoms contained in an organic compound are 
 replaceable by metals, but only those which are contained 
 in certain groups, and it is to these that the compound owes 
 its acid character. They present themselves in the form 
 of the hydroxyl (OH!) group or of the sulplionic acid group 
 (S0 3 H) ; sometimes, also, as in aurantia, in the form of 
 the imido group (NH), or as in the yellow obtained from 
 salicylic acid and benzidine, in the form of the carboxyl 
 group (COOH). All those colouring matters which 
 owe their acid properties to the presence of hydroxyl 
 groups are only weak acids. Thus the salts of fluorescein, 
 Co H 10 3 (OH) 2 , are decomposed by acetic acid. Their acid 
 properties are, however, considerably intensified by the 
 introduction of chlorine, bromine, iodine, or nitro groups. 
 It is well known that picric acid, C fi H 2 (N0 2 ) 3 OH, is a 
 much stronger acid than phenol, C 6 H 5 OH. Again, tetra- 
 brom-fluorescein, or eosin, C 20 H 6 Br 4 3 (OH) 2 , is a much 
 stronger acid than fluorescein. The colouring matters of 
 this group are either insoluble or only sparingly soluble 
 in water. Alizarin dissolves in 3,000 pts. of boiling 
 water, picric acid in 86 pts. of water at 15 C. The sub- 
 stitution products containing Chlorine, Bromine, Iodine, 
 etc., are still less soluble. Thus, whereas fluorescein can 
 be dissolved in a large quantity of boiling water, eosin 
 (free) is completely insoluble. 
 
 On the other hand, most of these colouring matters 
 are easily soluble in dilute alkaline solutions, or in other 
 words, their alkali salts are soluble in water. The solu- 
 bility of these salts in water lies in a direct ratio to the 
 number of hydroxyl groups ; but if the hydrogen of these 
 
 D 
 
34 COAL-TAR COLOURS. 
 
 groups is replaced by organic radicals, such as methyl, 
 ethyl, benzyl, etc., the compounds are again rendered less 
 soluble or even insoluble in water. Thus, the ethyl ether 
 of eosin, C 20 H 6 Br 4 3 (OH)(OC 2 H 5 ), yields a potassium salt 
 which is insoluble in water. 
 
 Many of the colouring matters of this class yield in- 
 soluble compounds with the metallic hydrates, such as 
 those of chromium, iron, aluminium, etc., which are known 
 as colour lakes, or simply as lakes. 
 
 SULPHONIC ACIDS. The sulphonic acids can either be 
 derivatives of the basic or of the phenol colouring matters. 
 They all contain one or more sulpho groups, and are 
 characterised by their strongly acid properties. They 
 can either be obtained by the action of sulphuric acid on 
 the colouring matters themselves ; e.g. : 
 
 C 88 H 81 N 8 + H 3 S0 4 = C S8 H 30 N 3 ;S0 3 H + H 2 0, 
 
 Spirit blue. Alkali blue. 
 
 or by the direct transformation of the sulphonic acids into 
 colouring matters : 
 
 Diazobenzene chloride. Beta naphthol sulphonic acid. 
 
 C 6 H 5 - N : N - C 10 H 5 + HC1. 
 
 Tropaeolin. 
 
 The sulpho group is not chromophorous ; it has so little 
 influence on the colour of the compound that the original 
 and the sulpho derivative are generally of exactly the 
 same colour. The sulphonic acids of the colouring 
 matters are of great importance in practice, as they are 
 generally soluble in water and can be dyed in acid baths. 
 Colouring matters which are volatile in steaming can be 
 
METHODS OF DISSOLVING. 35 
 
 rendered non- volatile by transforming them into their 
 su] phonic acids. The salts of the dyes containing sulpho 
 gronps are much more soluble in water than those of the 
 dyes containing only hydroxyl groups. They either 
 possess a dull, indefinite colour (Alkali-blue, etc.), or they 
 show their characteristic colour (Azo-dyes). 
 
 Some colouring matters belonging to this class also 
 yield lakes with metallic hydrates. 
 
 Neutral colouring matters. Very few artificial colour- 
 ing matters possess neither acid nor basic properties. As 
 an example, we may mention the artificial indigo, obtained 
 from propiolic acid. 
 
 METHODS OF DISSOLVING THE COLOURING MATTEHS. 
 
 The colouring matters are generally added to the dye- 
 bath in a state of solution, sometimes also in the form of 
 a paste (e.j/., alizarin paste), which latter does not contain 
 the colouring matter in solution, but in a very fine state 
 of division. As solvents, only those liquids which are 
 miscible with water can be used for dyeing purposes ; 
 petroleum, benzene, etc., are therefore excluded. The 
 most usual solvents are water, alcohol (methylated 
 spirits), and acetic acid. 
 
 The water which is used for dissolving should be as 
 pure as possible, especially with respect to lime salts, 
 since the latter tend to precipitate part of the colouring 
 matter. This evil can, however, be remedied by neutra- 
 lizing the water with a few drops of acetic acid. 
 
 The solutions are usually prepared hot, and are then 
 either filtered or decanted in order to retain insoluble 
 impurities, or particles of the dye which may not have 
 been dissolved. If this operation is omitted, the goods 
 are liable to become spotted or stained. 
 
 Many colouring matters dissolve 
 
3(5 COAL-TAR COLOURS. 
 
 but are so sparingly soluble in cold water that they 
 separate out again on cooling. It is advisable, in making 
 large quantities of such solutions for use, to add methy- 
 lated spirits or acetic acid. 
 
 The term " soluble in spirit " implies at the same time 
 that the colouring matter in question is insoluble in water. 
 There are, however, many colouring matters which dissolve 
 easily in both these solvents. The use of the colouring 
 matters soluble in spirit is very limited, owing to the fact 
 that their application is not only more expensive, but also 
 more difficult than that of the colouring matters soluble in 
 water. 
 
 The aqueous solutions of the coal-tar colours are often used as 
 coloured inks, for the preparation of which 1 pt. of colouring matter 
 is dissolved in about 50 pts. of water, with the addition of a little 
 gum. "Aniline inks," which are made in pretty concentrated 
 solution, show after drying on paper the characteristic metallic 
 lustre of the colouring matter itself. Thus, marks produced with 
 strong violet ink show a green reflex. Copying inks are produced 
 by adding, besides gum, glycerin to the solution of the colouring 
 matter. Important manuscripts or documents should not be written 
 with these inks, as the colours gradually fade, especially when ex- 
 posed to light. 
 
 The methylated spirits used for dissolving should be as 
 concentrated as possible, and at the same time free from 
 impurities, especially such as aldehyde and acetone, which 
 act very injuriously on certain dyes. It is well known 
 that magenta, for instance, when treated with aldehyde 
 is transformed into a fine blue colouring matter. The 
 small quantity of aldehyde which might be contained in 
 the methylated spirits would, however, suffice to convert 
 the fine red shade of magenta into a violet. Other 
 colouring matters, such as violet soluble in spirit, are 
 similarly affected. This reaction can, on the other 
 hand, be employed as a qualitative test for impurities in 
 methylated spirits. In order to carry out the test, small 
 
METHODS OF DISSOLVING. 37 
 
 quantities of magenta are dissolved in pure methylated 
 spirits and in the methylated spirits to be tested. The two 
 liquids are then brought to the same intensity of colour 
 by diluting one of them, and the shades are compared. 
 If the spirits in question are of exactly the same colour 
 as the pure spirits, this is a sig'n that it contains no 
 acetone or aldehyde ; but if it is coloured violet, it is 
 impure. 
 
 Open vessels should not be used for dissolving colouring 
 matter in methylated spirits, on account of the loss which 
 would be incurred by evaporation. The most useful form 
 of vessel for this purpose is a small copper boiler, having 
 a capacity of several litres, and provided with a lid which 
 can be screwed down like that of a Papin's digester. The 
 lid should be provided with a safety-valve. The boiler 
 containing the colouring matter and the methylated spirits 
 is placed in boiling water, when, taking into account that 
 pure alcohol boils at 78'4 C., water at 100, a con- 
 siderable pressure will be formed in the interior. (For 
 absolute alcohol the presure would represent somewhat 
 more than two atmospheres.) Solution is effected much 
 more rapidly in this way than under the ordinary atmo- 
 spheric pressure. After some time, the boiler is taken out, 
 allowed to cool, and the clear liquid is decanted from any 
 insoluble residue. Alcoholic solutions, prepared in this or 
 other ways, should not allow the colouring matter to pre- 
 cipitate on being diluted with a small quantity of water, 
 otherwise it would not be evenly divided throughout the 
 dye-bath. Some colouring matters, e.g., blue soluble in 
 spirit, are of necessity precipitated, but in such a fine 
 state of division that they are evenly assimilated by the 
 fibre. 
 
 Colouring matters which require large quantities of 
 methylated spirits for their solution are objectionable in 
 many respects, and are therefore not much used in practice. 
 For besides materially increasing the cost of dyeing, a 
 
38 COAL-TAR COLOURS. 
 
 large quantity of spirits is apt to coagulate * the " boiled- 
 off liquor," and thus render it useless in dyeing. 
 
 If a colouring matter is only sparingly soluble in water 
 and in strong methylated spirits, it is advisable to try 
 whether it will not dissolve in a mixture of the two liquids. 
 There are, in fact, colouring matters which dissolve much 
 more easily in a 50 per cent, solution of methylated spirits 
 than in either water or spirits alone. 
 
 The alcoholic solutions of the coal-tar colours are used to some 
 extent in the preparation of brightly coloured varnishes. These are 
 prepared by dissolving different resins (shellac, copal, dammar, 
 sandarac, etc.) in strong spirits of wine, and adding to the concen- 
 trated solution sufficient colouring matter to produce the required 
 shade. 
 
 Acetic acid, CH 3 'COOH, acts in many cases as an effective 
 solvent for the artificial colouring matters. 
 
 Glycerin, C 3 H-(OH) 3 , dissolves many of the coal-tar 
 colours in large quantities, and is often used in the mixing 
 of printer's colours. What makes it so valuable an agent 
 in this respect is its property of simultaneously dissolving 
 many other constituents of the printer's colours, especially 
 albumen, gum, arsenic, etc. Glycerin is also sometimes 
 used, on account of its viscosity, in the preparation of 
 colour-pastes. 
 
 Solutions of gum and glue can also be used as solvents 
 for many aniline dyes. The solutions may be prepared 
 in the following manner : 
 
 The solution of the colouring matter in alcohol or 
 methylated spirits is added to a concentrated solution of 
 gum-arabic, and the whole is well stirred. The colouring 
 matter passes from the alcoholic solution into the gum, 
 from which latter it is not precipitated by a subsequent 
 dilution with water. 
 
 Another method is to dissolve glue in acetic acid at 10 to 
 
 * The sericine is precipitated. See p. 41. 
 
CHEMISTRY OF THE FIBRES. 39 
 
 12 Tw. and add to this solution the finely- pulverized dye. 
 The mass is then well stirred and heated in a closed vessel, 
 until a sample taken out and treated with water dissolves 
 without any residue. The solution obtained in this 
 manner can be allowed to solidify, in which state it can 
 be kept for future use. 
 
 Very few of the coal-tar colours are soluble in petroleum, 
 benzene, and ether, but many organic liquids of higher 
 boiling-points, such as nitrobenzene, aniline oil, fusel oil, 
 and carbolic acid, act as eminent solvents. 
 
 In the neutral oils and fats, most of the aniline dyes 
 are insoluble (methyl- violet is an exception) . The basic 
 colouring matters will, however, dissolve readily in fatty 
 acids, or in oils containing fatty acids. 
 
 Fatty compounds of the aniline dyes can be prepared by adding 
 the free bases to olei'c or stearic acid. These compounds are used 
 for colouring oils, fats, oil-varnishes, etc. Another method of 
 preparing fatty compounds of the basic colouring matters is to 
 precipitate the solution of the dye with a solution of soap. Thus, 
 magenta and soap would yield by double decomposition sodium 
 chloride and a fatty compound of rosaniline. 
 
 Turkey-red oil is the ammonia or soda- soap of castor oil, and acts, 
 therefore, as a solvent for aniline dyes. 
 
 For the preparation of coloured cosmetics or candles, special care 
 should be taken in selecting colouring matters which are absolutely 
 free from poisonous constituents. 
 
 DYEING WITH COAL-TAR COLOURS. 
 Chemistry of the fibres. 
 
 Although the question as to whether the colouring 
 matters enter into a chemical or a mechanical combination 
 with the fibres still remains undecided, it is nevertheless 
 certain that the relation of the colouring matters to the 
 fibres does not only depend upon the physical structure of 
 the latter, but also to a great extent on their chemical 
 
40 COAL-TAR COLOCES. 
 
 composition It is therefore necessary to say something 
 here on the chemistry of the fibres. 
 
 Of the numerous fibres used in the textile industries, 
 three viz., silk, wool, and cotton form the chief bulk, 
 and it will suffice to give a description of these as repre- 
 sentatives of the textile fibres in general. 
 
 SILK. Silk does not consist of one homogeneous sub- 
 stance. It is possible, by means of the microscope alone, 
 to discern two, sometimes three different layers, which 
 differ from each other chiefly in their chemical properties. 
 In the natural state the silk fibre proper is enveloped in 
 a coating (silk-gum), which in the case of yellow silk 
 contains the colouring matter. 
 
 The chemical compound of which silk consists is known 
 as fibroine, and somewhat resembles in its properties 
 keratine, the substance of horn, wool, hair, etc. The 
 relative quantities of silk-gum and actual fibre contained 
 in the raw silk vary considerably, according to origin, 
 quality, etc. ; but in practice 18-27 per cent, of silk-gum 
 and 73-82 per cent, of fibroine are generally calculated 
 upon. 
 
 Neutral solvents have no action on fibroine. Prolonged 
 heating with water, even under pressure, will not render 
 it soluble. By caustic alkalies it is easily dissolved, and is 
 attached by the same even in dilute solutions. Ammonia, 
 however, as well as the carbonates and sulphites of the 
 alkalies, and neutral soaps, have very little action. Con- 
 centrated mineral acids, such as sulphuric acid, nitric 
 acid and hydrochloric acid, dissolve the silk fibre, while 'it 
 is deeply attacked by chlorine, bromine, and iodine. Sul- 
 phurous acid has little action, and can therefore be used 
 for bleaching silk. 
 
 The external covering of raw silk, which is also known 
 as " silk-gum " or " silk-glue," can be removed by boiling 
 the silk for several hours in water under pressure. The 
 solution obtained in this manner solidifies on cooling to a 
 
CHEMISTRY OF THE FIBRES. 41 
 
 gelatinous mass, which when evaporated to dryness yields 
 a product closely allied to glue. The solutions of silk- 
 o-lue are precipitated by alcohol ; tannin substances also 
 produce insoluble precipitates in them. 
 
 Both fibroine and sericine (silk-glue) consist of carbon, 
 nitrogen, hydrogen, and oxygen. They do not contain any 
 sulphur. Raw silk leaves on ignition from 1 to 1*5 per 
 cent, of ash, consisting chiefly of carbonate of lime. The 
 percentage of ash is often considerably increased by the use 
 of hard water in softening the cocoons, and is in many cases 
 the cause of unfavourable results in dyeing, since insoluble 
 lime lakes are formed, which render the shade of the 
 material " cloudy." The injurious effect of lime in the 
 fibre is most prominent when the oxalates of the colour- 
 ing matters are used in dyeing, owing to the fact that in- 
 soluble oxalate of lime is formed in the fibre, and thus 
 prevents the dye being absorbed evenly. Most of the 
 lime can, however, be got rid of by treating the silk, 
 previous to dyeing, with very dilute lukewarm hydrochloric 
 acid. 
 
 Silk is very seldom dyed as raw silk ; in the majority of 
 cases it is first "discharged," or deprived to a greater or 
 less extent of its external covering, the silk-glue. By 
 this means it becomes more glossy, and a better feel is 
 imparted to it, while at the same time it loses in weight. 
 
 The stripping or discharging of silk is effected by boiling 
 the raw silk in strong soap solutions. On the large scale 
 this is generally carried out in two operations. In the 
 first soap-bath, the temperature of which is not quite 
 100 C., the hanks of silk are worked until the silk-glue 
 swells up and falls from the fibre. 
 
 In the next operation it is sewn up in linen bags and 
 boiled in a fresh soap- bath, until it has acquired its proper 
 feel and handle. 
 
 This second bath can be used again for ungumming a 
 fresh portion of silk, and is used lastl in the form of 
 
42 COAL-TAK, COLOURS. 
 
 loiled-off liquor as an addition to the dye-bath (in silk 
 dyeing) . 
 
 The loss in weight in these two operations varies from 
 18 to 27 per cent. It is sometimes desirable to transform 
 raw silk into a glossy and " scroop " product without in- 
 volving such a considerable loss in weight. This is done 
 by treating the silk with water containing tartar and some 
 sulphuric acid, heated nearly to the boiJ. By this method 
 the silk is only partially discharged, and the loss in weight 
 is only from 4 to 8 per cent. The product is known as 
 souple, and lies, with respect to its properties, between raw 
 and discharged silk. 
 
 It follows from this that raw silk, souple and discharged 
 silk, must be acted upon differently by chemical agents, 
 and must therefore not all be treated in a like manner. 
 Thus, boiled-off silk, which consists of almost pure fibroine, 
 can be dyed in very hot acidulated or slightly alkaline 
 baths ; while raw silk and souple will not stand this treat- 
 ment, on account of the silk-glue they contain. 
 
 WOOL. Wool is never dyed in the raw state i.e., as it 
 comes from the sheep's back but is always previously 
 washed and scoured. By these operations the " suint " or 
 " yolk " (a substance consisting of cholesterin, the alkali 
 salts of certain organic acids, earthy impurities, etc.) is 
 removed, thus leaving behind almost pure wool. Wool 
 consists of a substance chemically known as keratine, 
 an albuminoid body, which is also the chief constituent of 
 hair, horn, feathers, etc. It contains/ besides carbon, 
 nitrogen, hydrogen, and oxygen, a certain percentage of 
 sulphur, which causes it to differ considerably from silk 
 in its properties. 
 
 Wool is completely dissolved by hot solutions of caustic 
 alkalies. It is not much affected by dilute acids, but 
 concentrated mineral acids attack the fibre ; in strong 
 sulphuric acid it dissolves readily at 100, while strong 
 nitric acid dissolves it with a yellow colour, producing 
 
CHEMISTRY OF THE FIBRES. 43 
 
 xanthoproteic acid. When boiled with dilute acids, wool 
 absorbs a considerable percentage of acid, which can only 
 be removed by neutralising with an alkali or by long- 
 continued boiling with water. Thus wool which had been 
 boiled in water containing 10 per cent, of sulphuric acid 
 (of the weight of the wool) had to be boiled nine times in 
 succession for an hour each time, in fresh distilled water, 
 before all the acid could be removed. A small propor- 
 tion of the acid appears to be neutralized by some basic 
 constituent or constituen^of the fibre. It is interesting 
 to note that wool treated in this manner (one might even 
 say mordanted) can be dyed a full shade in neutral solu- 
 tions of the acid coal-tar colours. It should be borne in 
 mind that the sulphurous acid which is used almost ex- 
 clusively in the bleaching of wool also adheres to the 
 fibre very tenaciously after the operation is over. After 
 stoving, the material should first be rinsed in a weak 
 solution of soda and then thoroughly washed with water 
 containing hydrogen peroxide. If this latter operation 
 is omitted, and the material is subsequently dyed with 
 an aniline dye, the sulphurous acid retained by the fibre 
 may gradually reduce and decolourise the colouring mat- 
 ter. This is sometimes seen very distinctly in certain 
 fabrics in the places where dyed and bleached yarns cross 
 each other. 
 
 COTTON. Clean and well-bleached cotton consists, like 
 most other perfectly bleached vegetable fibres, of almost 
 pure cellulose. Cellulose consists of carbon, hydrogen, and 
 oxygen in the proportions expressed by the formula, 
 (C 6 H 10 5 )n. The only portion of the cotton fibre which 
 does not consist of cellulose is the extremely thin mem- 
 brane or cuticle which envelopes it, and to which it 
 owes its tenacity in a great measure. The chemical com- 
 position of this cuticle is not known. If it is destroyed, 
 the fibre falls to a powder. Cotton is dissolved by con- 
 centrated sulphuric acid ; nitric acid converts it into gun- 
 
44 COAL-TAR COLOURS. 
 
 cotton ; while hydrochloric acid disintegrates the fibre. 
 Caustic alkalies and dilute solutions of bleaching powder 
 have very little action on the cotton fibre. 
 
 For the dyer, the most important chemical properties of 
 the fibres are those which bear directly on the colouring 
 matters themselves, or on the additions made to the dye- 
 bath. In dyeing, it is not only necessary to see that the 
 colours produced on the different materials are as full and 
 as fast as possible, but also that the fibre should not lose 
 in strength, and in the case of wool or silk, that it should 
 not part with any of its lustre or pliability. After dyeing, 
 wool should still feel soft, and not harsh or "hask"; while 
 silk should retain its peculiar feel, and when compressed or 
 twisted strongly, should emit a peculiar crackling sound. 
 
 From these short notes on the chemistry of the fibres, it 
 will be seen that strongly acid or alkaline baths cannot be 
 used indiscriminately for any kind of fibre without some- 
 times incurring considerable injury, and it is therefore 
 advisable to observe the following rules in dyeing. 
 
 Action of acids and alkalies on the fibres. Wool and silk 
 will stand the action of dilute acids without injury, and as 
 long as strong solutions of the mineral acids are not made 
 use of, it is not to be feared that the fibres will undergo 
 any change when dyed in acid baths. Indeed, silk only 
 acquires its peculiar crackling or " scroop " feel after a 
 treatment with an acid ; after being dyed and washed, it 
 is therefore almost invariably passed through a weak acid 
 bath, an operation known as developing (brightening). 
 Acetic, tartaric, or citric acids are generally used for this 
 purpose ; but it is preferable to use one of the latter two, 
 as the acetic acid absorbed by the fibre gradually eva- 
 porates, and the silk then loses its peculiar feel. 
 
 Hot solutions of mineral acids, even when very dilute, 
 have an injurious effect on cotton and other vegetable 
 fibres ; they weaken or " tender " the material. If it is 
 
SUBSTANTIVE DYEING. 45 
 
 necessary to dye cotton in an acid bath, the material 
 should be thoroughly washed subsequently, for if a 
 mineral acid, even if very dilute, is allowed to dry on the 
 fibre, the latter will be gradually destroyed. 
 
 The animal fibres are very easily attacked by caustic and 
 even by carbonated alkalies. An 8 per cent, solution of 
 caustic soda will dissolve them completely. Even dilute 
 soda solutions, which are sometimes used for discharging 
 certain kinds of silk, have a destructive action on the 
 iibre if allowed to lie in contact with it for a length of 
 time. The use of baths which contain either caustic or 
 carbonated alkalies should therefore be avoided as much 
 as possible in the dyeing of wool or silk. 
 
 On the other hand, the alkalies have not an injurious 
 effect on cotton. Even concentrated solutions of the 
 caustic alkalies do not tender the fibre, but only cause it 
 to contract and become more dense (mercerised cotton). 
 
 THE RELATIONS OF THE FIBRES TO COLOURING MATTERS. 
 
 Taking exception to artificial indigo, aniline-black, and 
 one or two other colouring matters, the coal-tar colours 
 can be divided into two classes with respect to their re- 
 lation to the fibres : 
 
 1. The colouring matter is absorbed directly from its 
 solution by the fibre. In this case the fibre is said to be 
 snbstantively dyed, and the colouring matter is called a 
 substantive colouring matter. 
 
 2. The fibre does not combine directly with the colour- 
 ing matter, and must first be charged with metallic salts 
 or hydrates {mordanted), or prepared in some other way 
 before it will receive the colour. These are known as 
 adjective colouring matters. 
 
 SUBSTANTIVE DYEING. The animal fibres possess great 
 affinity for most of the coal-tar colours, and in many cases 
 they absorb them so completely that the liquid is rendered 
 colourless. Many colouring matters are taken up by wool 
 
46 COAL-TAR COLOURS. 
 
 and silk from an acid bath much more readily than from 
 a neutral bath. The bath is rendered acid (soured) by the 
 addition of acetic acid, tartaric acid or sulphuric acid. 
 When sulphuric acid is used, Glauber's salts (sodium sul- 
 phate) are usually added simultaneously, and the two 
 combine to form sodium bisulphate, which has less action 
 on the fibre than free sulphuric acid. Some dyers prefer 
 to add the sodium bisulphate as such, instead of forming 
 it in the dyebath. In this case, care should be taken to 
 see that the commercial product is free from nitric acid, 
 which has a very injurious action on many colouring mat- 
 ters. In wool-dyeing, sodium sulphate or magnesium 
 sulphate are frequently added to the dye-bath, in order to 
 reduce the solubility of the colouring matter, and thus to 
 obtain more even and faster colours. 
 
 Silk absorbs many colouring matters so rapidly that 
 the colour produced is uneven or " cloudy." In order 
 to prevent this, silk is usually dyed in a weak soap-bath. 
 Neutral or alkaline soap-baths are made up with Marseilles 
 or good olive-oil soap ; while for acid soap-baths, boiled-off 
 liquor is used, along with acetic or sulphuric acid. 
 
 Cotton evinces very little affinity for most of the coal-tar 
 colours. Thus picric acid, naphthol yellow, the azo- 
 scarlets, and most other so-called acid dyes, cannot be fixed 
 permanently in cotton ; the basic dyes can be fixed by 
 the aid of mordants (tannin), while chrysamine, Congo 
 red, and other dyes of this class, will dye cotton directly in 
 an alkaline bath. Gun-cotton, collodion, and vegetable 
 parchment, on the other hand, possess considerable affinity 
 for the coal-tar colours. The same is the case with jute, 
 which consists essentially of bastose, a substance closely 
 allied to, but not identical with, cellulose. Chinagrass 
 also evinces a certain affinity for the basic coal-tar colours. 
 
 It is at present almost generally admitted that the 
 combinations of the substantive colouring matters with 
 the fibres are of a chemical nature. In certain cases, 
 
SUBSTANTIVE DYEING. 47 
 
 however, it is difficult to conceive that a chemical com- 
 bination takes place, and in these it seems more rational 
 to ascribe the dyeing to a mechanical adhesion or attraction 
 than to a chemical reaction. Thus, alkali-blue, which is 
 the sodium salt of the mono-sulphonic acid of aniline- 
 blue, is absorbed from its neutral, colourless solution by 
 wool or silk ; but the actual colour, the free sulphonic acid, 
 is only produced by a subsequent development in an acid 
 bath. In this case, taking the chemical theory as the 
 correct one, a chemical combination must have taken place 
 between the fibre and the colourless sodium salt, a reaction 
 which it is not easy to conceive from a chemical point of 
 view. Another striking example is furnished by the 
 indiqo vat. If cotton is immersed for some time in an 
 
 u 
 
 indigo vat, it will withdraw from the vat a much larger 
 proportion of indigo-white than would correspond to the 
 amount of liquid absorbed. A precipitation has therefore 
 taken place in or on the fibre, but at the same time it 
 cannot be supposed that a chemical combination has taken 
 place between the indigo-white and a totally neutral and 
 indifferent substance like cotton. 
 
 The substantive colours when dyed on the fibre possess, 
 as a rule, the same colour as their solution in transmitted 
 light. The adjective colours are, on the other hand, apt 
 to vary considerably in shade, according to the mordant or 
 other substances used in preparing the material. In silk 
 or wool- dyeing, these variations in shades are sometimes 
 brought about by first mordanting the material with a 
 substantive colouring matter, and then dyeing with an 
 adjective one. 
 
 Another .method of fixing the substantive colouring 
 matters is often resorted to in the printing of silk fabrics. 
 The pieces are first charged with stannic oxide or alumina, 
 by passing them through dilute solutions of stannate of 
 soda or basic aluminium sulphate, after which they are 
 dyed and steamed. The colours obtained in this way are 
 
48 COAL-TAK COLOURS. 
 
 much brighter than those obtained on materiLl which has 
 not been previously prepared. If, however, the silk is 
 charged with a lai^ge amount of tin, the light shades are 
 apt to be spoiled. This is the case with silk which ha; 
 been weighted by being immersed repeatedly in a con- 
 centrated solution of stannic chloride and then washed in 
 running water.* 
 
 ADJECTIVE DYEING. There are, with the exception of ttf 
 so-called benzidine colours, only a few of the coal-tah 
 colours which possess a direct affinity for cotton, and tr? 
 shades obtained with them are not permanent. Before 
 dyeing, cotton must therefore be mordanted ; i.e., it mu^ 
 be charged with some substance or substances which caus 
 it to take up the colour. The mordants w T hich are use . 
 for the aniline dyes can be divided into two classes. 
 
 One of these yields insoluble compounds with the 
 colouring matters which are precipitated on the fibi ? in 
 definite quantities corresponding to chemical equations ; 
 as an instance of this class, we may mention the metallic 
 hydrates which are used as mordants. 
 
 The other class of mordants does not yield de 
 chemical compounds with the colouring matters 
 simply absorbs the dye substantively. Thus, alb 
 belongs to this class, as well as a large number of 
 substances which are chemically quite indifferent \ 
 colouring matters, and only assimilate them on accou? 
 their physical structure, just as animal charcoal act n 
 coloured solutions. Many finely-divided precipitates, ich 
 as calcium phosphate, carbonate of lime, silicic acid, starch, 
 etc., produced on the fibre, possess this property. 
 
 Metallic hydrates. The principal mordants belonging 
 to this category are salts of chromium, iron and alumina, 
 tin and lead. They are used chiefly for the fixation of the 
 acid colouring matters, such as eosin, coarulein, alizarin, 
 
 * Silk is sometimes weighted as much as 25 per cent, in {his 
 manner. 
 
ADJECTIVE DYEING, 49 
 
 etc., with \v.iioh they yield insoluble salts or lakes. These 
 mordants are generally used in dyeing in the shape of 
 
 .soluble salts, such as lead acetate, stannic chloride, ferrous 
 
 ^acetate, aluminium acetate, etc. 
 
 The usual process of mordanting cotton yarn with 
 mordants like lead or alumina may be explained in the 
 following manner : If soda is added to a solution of lead 
 Acetate or aluminium sulphate in small quantities at a 
 
 . inie, it will be noticed that these additions can be con- 
 inued for some time without the appearance of a pre- 
 ipitate, soluble basic salts of lead, or alumina, being 
 
 r formed. 
 
 )s If cotton yarn is now immersed in a solution prepared 
 
 jj',n this manner, these basic salts are decomposed even in 
 the cold, but much more rapidly on the application of 
 
 Jieat, into more basic, insoluble ones, which are fixed by 
 
 ,thq fibre, while at the same time acid salts are formed which 
 remain in solution. The fibre possesses, therefore, an 
 
 < affinity for the mordant, which is most likely due to a 
 dialytic action of the former. 
 
 >;i$be complete fixation of the mordants is effected by 
 Tfi sing the material after mordanting through dilute 
 
 iFK ,;ifLons of soap, soda, or chalk, or by washing in calca- 
 
 t9i ! \t8 8 water. 9 
 
 \ 'Jilt o? e affinity of the woollen fibre for mordants is much 
 
 k>^^ er than that of cotton. For if wool is heated in a 
 
 \ 'lotion of alum, the assimilation of basic salts of alumina 
 begins at once. An addition of tartar to the solution of 
 the mordant is beneficial, since it not only renders the 
 deposition of alumina on the fibre more copious, but more 
 even. In the case of bichromate of potash or bichromate of 
 soda, which are used largely in mordanting wool for the 
 alizarin colours, the action appears to be essentially of a 
 strictly chemical nature, the chromic acid combining with 
 some constituent of the fibre to form an insoluble or 
 sparingly soluble chromate, while neutral chromate re- 
 
 E 
 
50 COAL-TAR COLOURS. 
 
 mains in solution (See Journ. Soc. Dyers and Col., 1887, 
 p. 118). 
 
 The chromium precipitated in this manner on the fibre 
 is consequently still in the form of chromic acid, orchromate, 
 and is in this form not suitable for the fixation of certain 
 colouring matters, like gallein, alizarin-blue, etc. For the 
 purpose of obviating this, and in order to obtain the chro- 
 mium on the fibre in the green state i.e., as chromic 
 hydrate tartar is used along with the bichromate in mor- 
 danting; the tartar is oxidized at the expense of the 
 chromic acid on the fibre, which is reduced to chromic hy- 
 drate. In place of tartar, tartaric acid or oxalic acid may 
 be used. " Green mordanted " AVOO! may also be obtained 
 by using chromium fluoride (about 6 per cent.) in place of 
 bichromate. 
 
 As a rule, mixed mordants yield more stable colours 
 than single ones, and experience has shown that it is most 
 advantageous to use a sesqui-oxide (ferric oxide, chromic 
 oxide, alumina) along with a monoxide (lime, magnesia, 
 stannous hydrate, zinc hydrate). The double colour-lakes 
 subsequently produced in dyeing are characterized by 
 their fastness to acids and alkalies ; an admixture of mag- 
 nesia makes the alumina-lakes fast to alkalies. 
 
 The application of these mordants in printing will be 
 referred to again under alizarin. 
 
 Sulphur. The insoluble modification of sulphur has no 
 affinity whatever to the colouring matters, but the amor- 
 phous modification has a very peculiar action. If wool 
 is impregnated with a solution of sodium hyposulphite 
 (sodium thiosulphate) and is then passed through a dilute 
 mineral acid, such as sulphuric acid, amorphous sulphur is 
 precipitated on the fibre, according to the following equa- 
 tion . 
 
 Na 2 S 2 3 + HoSO^ = NagSO^ + H 2 + S0 2 + S. 
 The fibre is thus rendered capable of absorbing certain 
 
ADJECTIVE DYEING. 51 
 
 colouring matters much better than before this treatment. 
 This is especially the case with methyl-green, with which 
 it is difficult to obtain bright and even colours on unmor- 
 danted wool ; malachite green is also improved. 
 
 Metallic sulphides. The sulphides of zinc and tin pre- 
 cipitated on the cotton fibre by double decomposition 
 render the latter capable of being dyed with magenta, 
 methyl-violet, and Bismarck-brown. Very full shades can 
 be obtained in this manner, which are at the same time 
 pretty fast to washing. Aniline-blue and safranine do 
 not give satisfactory results by this process. 
 
 Silica. Finely-divided or gelatinous silica readily ab- 
 sorbs the aniline dyes. Although it has not yet been 
 positively proved, it is nevertheless probable that the 
 combinations obtained in this manner are not of a chemical 
 nature, but purely mechanical, and are due to the structure 
 of the finely- divided silica. This property of silica is 
 sometimes made use of in dyeing with alkali-blue. Soluble 
 glass is added to the dye-bath when, in the subsequent 
 development with acid, hydrated silica is separated out on 
 the fibre, thus rendering the colour both faster and fuller. 
 Double cyanides. The insoluble salts of hydroferro- 
 cyanic and hydroferri cyanic acids possess an eminent affin- 
 ity for the basic aniline dyes. Thus, cotton first passed 
 through a solution of ferrocyanide or ferricyanide of 
 potash, and then through zinc sulphate, can be dyed with 
 magenta, methyl- violet, methylene-blue, etc. 
 
 Oil mordants. Several methods of dyeing cotton are 
 based on the relations of the colour-bases to the fatty 
 acids and soaps described on p. 39, all of which effect in 
 one way or another the formation of the insoluble fatty 
 acid compounds on the fibre. Acid colouring matters, 
 like the eosines and the azo dyes, can also be fixed 011 the 
 vegetable fibres previously prepared with fatty acids, the 
 latter being dyed substantively. 
 
 One of the most usual oil mordants is the so-called 
 
2 COAL-TAR COLOURS. 
 
 Turkey-red Oil, which is prepared by adding castor oil 
 or olive oil very gradually to concentrated sulphuric acid 
 (D. 0. V.), care being taken to avoid any rise in tempera- 
 ture. The liquid is then neutralized with soda-ash, and 
 ammonia is added until a sample dissolves completely in 
 water. The whole is then allowed to stand for about 
 twelve hours, in order to allow the sodium sulphate to 
 crystallize out when the clear oil is decanted. 
 
 The oil mordants are seldom used alone, but generally 
 along with inorganic mordants, which cause them to 
 combine more intimately with the fibre, while at the same 
 time the colour becomes much faster. As an example of 
 the use of oil mordants in dyeing, the following process, 
 used in the manufacture of half silk fabrics, may be 
 described here. 
 
 Cheap fabrics consisting of silk and cotton are dyed in 
 the piece, because the silk used in their manufacture is of 
 so poor a quality that it will not stand the weaving opera- 
 tions if discharged in the yarn. It is therefore necessary 
 to prepare the cotton before weaving in such a manner as 
 to render it capable of absorbing the dye in exactly the 
 same proportion as the silk does. For this purpose the 
 cotton yarn is first impregnated with Turkey- red oil and 
 then" aged " i.e., exposed for some time to the action of 
 air and light by which latter process the fatty acids are 
 liberated and undergo a peculiar partial oxidation, which 
 renders them insoluble in weak soda solutions. The yarn 
 is then passed through a bath of neutralized alum. After 
 having been prepared in this manner, it is made up into 
 fabrics with the raw silk, which is discharged in the piece, 
 and the fabric is finally dyed with magenta, eosin, aniline- 
 blue, scarlet, etc. Another way of making up this kind 
 of goods is first to weave the material, then discharge, 
 mordant, oil, and steam, in order to fix the oil, pass 
 through weak soda solution (to remove the surplus of 
 oil), and dye. 
 
ADJECTIVE DYEING. 53 
 
 The colours produced with the basic coal-tar colours on 
 cotton mordanted with Turkey-red oil are very brilliant, 
 but are not at all fast to light. 
 
 Oil mordants are also used for colouring matters which 
 can be fixed with" inorganic mordants alone, e.g., for 
 coerulein and alizarin ; the shades obtained are much 
 faster and more brilliant than those obtained without 
 the use of oil mordants. 
 
 In yarn-dyeing, it is not always necessary to make use 
 of Turkey-red oil when an oil mordant is required. A 
 very good substitute can be prepared by gradually mixing 
 1 kilo, of olive oil with 50 c.c. of concentrated sulphuric 
 acid. The milky liquid thus obtained is added to the 
 lukewarm bath, in which the yarns are worked until they 
 are sufficiently impregnated. They are then wrung and 
 transferred to the dye-bath, which contains, besides the 
 dye, a small quantity of alum and soda. 
 
 Soap has also been proposed as a mordant for the aniline 
 dyes. The cotton is first passed through a soap solution, 
 dried and dyed without being previously washed. By 
 the double decomposition of the soap and the colouring 
 matter, insoluble compounds of the fatty acids and colour- 
 bases are formed on the fibre. The colours obtained by 
 this method are not stable. 
 
 Soap is also sometimes employed for the precipitation 
 of the compounds of the higher fatty acids (olive, palmitic, 
 and stearic acids), with alumina or lead on the vegetable 
 fibres, in mordanting for such colours as spirit-blue 
 and the eosins. The method usually adopted is to work 
 the material first in a strong soap bath, wring it out 
 well, and then pass it, without washing, into a bath of 
 alum or lead acetate. 
 
 Sometimes fatty acids are introduced into the colouring 
 matters after the latter have been fixed on the fibres by 
 inorganic mordants, in order to produce brighter and 
 faster colours. This is effected by passing the goods, after 
 
54 COAL-TAR COLOURS. 
 
 dyeing, through a boiling soap solution, or by oiling them 
 with. Turkey-red oil, or by other similar methods. 
 
 The important part which the oil mordants play in 
 alizarin-dyeing will be referred to later on under that 
 heading. 
 
 Tannin mordants (astringents). Taimic acid will com- 
 bine with the basic aniline dyes to form either soluble 
 compounds or insoluble lakes, according to the proportions 
 of tannic acid and colouring matter used. 
 
 According to the experiments of Juste Koechlin, in- 
 soluble lakes are obtained when the following proportions 
 are made use of : 
 
 4 pts. Magenta 5 pts. tannic acid 2 pts. soda crystals. 
 
 4 Malachite-green 5 ., ,, 1 ,, ,, ,, 
 
 4 ,, Parma-violet 5 ,, ,, ,, 1 ,, ,, ,, 
 
 4 Methyl-greeu 10 ,, ,, ,, 4 ,, ,, ,, 
 
 If cotton is steeped for some time in a solution of tannic 
 acid, it will absorb a certain proportion of the latter, and 
 is thus rendered capable of fixing the basic aniline dyes. 
 The affinity of cotton for tannin is not, however, a very 
 strong one, since by long-continued washing the latter can 
 all be removed again from the fibre. Cotton is seldom 
 mordanted with tannin alone, since the colours obtained 
 in this way are not stable. They are soluble in excess 
 of tannic acid. The tannin is usually fixed on the fibre 
 in an insoluble form, by passing it after the tannin bath 
 through a solution of some metallic salt or other substance 
 capable of yielding an insoluble compound with tannin 
 (e.g., gelatine). 
 
 Tartar emetic* or stannic chloride (tin spirits) are most 
 
 * Within the last few years a number of substitutes for tartar 
 emetic have appeared in the market, for nearly all of which it is 
 claimed by the inventors that they are cheaper and give equally good or 
 better results than tartar emetic. Without discussing their relative 
 merits, the following may be mentioned here : The double oxalate of 
 antimony and potash, the double fluoride of antimony and soda, 
 lactate of antimony, and an alkaline solution of antimony in glycerin. 
 
ADJECTIVE DYEING. 55 
 
 generally used for this purpose, bat in many cases it is 
 more advantageous to use other metallic salts, such as 
 ferrous acetate, ferric sulphate, zinc acetate, neutralized 
 alum, lead acetate, etc. In working on the large scale, it 
 is first necessary to find out experimentally the most 
 suitable proportions between the tannic acid and the 
 metallic mordant. Thus it has been found that 5 pts. of 
 tannic acid require for their complete precipitation 1 pt. of 
 tartar emetic and 1 pt. of soda crystals. 
 
 The choice of the inorganic mordant to be used along 
 with the tannin depends on the nature of the colouring 
 matter, and on the shade required, since one and the 
 same colouring matter can give very different shades with 
 different mordants. In dyeing cotton prepared in this 
 manner, a treble compound or lake is obtained, consisting 
 of tannin, metallic oxide, and colouring matter. 
 
 The compounds of tannic acid with the aniline dyes are 
 soluble in methylated spirits and in acetic acid. If the 
 solutions obtained in this way are thickened with starch, 
 gum, etc., and then printed on mordanted fabrics, inso- 
 luble compounds of colouring matter, tannin, and mordant 
 are obtained on the fibre in the subsequent operation of 
 steaming. This process is used largely in calico-printing. 
 By subsequently passing the material through a bath of 
 tartar emetic the colours are rendered faster. 
 
 Weighting of silk with tannin. The coal-tar colours 
 seldom lose any of their brilliancy in being combined with 
 tannin substances, providing the latter are not coloured in 
 themselves. It is thus possible to weight silks dyed in 
 bright colours, in all but very light shades, from 12 to 15 
 per cent., by steeping them for some time in cold solutions 
 of pure tannin. The silk combines directly with the 
 tannin, and though materially increased in weight, it does 
 not part with any of its valuable properties by this 
 treatment. 
 
 Albuminous and gelatinous substances. The coal-tar colours 
 
56 COAL-TAR COLOURS. 
 
 behave similarly with substances like albumen and gela- 
 tine as they do with silk and wool, which are indeed 
 chemically closely allied to the former. Vegetable fibres 
 which have been " animalised " i.e., coated with a thin 
 layer of some albuminous substance can therefore be 
 dyed like wool or silk. 
 
 This property of the coal-tar colours is very seldom made 
 use of in dyeing, but it is used on a large scale in calico- 
 printing. For this purpose a concentrated solution of egg 
 albumen, or, for dark shades, blood albumen, is mixed with 
 the colouring matter, printed, and steamed. In this way 
 the albumen is coagulated, and remains behind on the 
 fibre as an adhesive coloured coating. In place of albumen, 
 an ammoniacal solution of casein, or alkaline, or slightly- 
 acid solutions of gluten can be used, but the results 
 obtained are not so good. 
 
 Solutions of glue containing the aniline dyes, along with 
 a small percentage of bichromate of potash, can also be 
 used for printer's colours. The printed fabric is exposed 
 to the action of the light, which renders the glue insoluble. 
 
 Colouring matters as mordants. In some cases the 
 colouring matters themselves which have been fixed on 
 the fibre can act as mordants. Thus, aniline-violet, which 
 of itself has very little affinity for the cotton fibre, can be 
 dyed very well on fast violet (ferric alizarate). 
 
 The fact that colours obtained with two substantive 
 colouring matters are often much faster than either 
 colouring matter by itself is most likely also due to a 
 similar cause. 
 
 Most of the benzidine colours act, when dyed on cotton, 
 as excellent mordants for the basic coal-tar colours. Thus 
 cotton dyed with chrysamine readily absorbs magenta, 
 safranine, malachite green, etc., from their cold or tepid 
 dilute aqueous solutions producing compound shades of 
 great brilliancy. For the production of bright shades 
 in this manner, it is essential in the case of chrysamine, 
 
FAST AND LOOSE COLOUES. 57 
 
 at least, that the temperature of the bath containing the 
 basic dye should not exceed 60 or 70. 
 
 Fast and loose colours. 
 
 The fastness of colours produced on the fibre not only 
 depends on the stability of the colouring" matter itself 
 against external influences, but also on the stability of the 
 combination between fibre and colouring matter. Thus a 
 very fast colouring matter, such as Guignet's green, may 
 be combined with the fibre in so loose a manner (by means 
 of albumen) that it falls off in a powder in washing or 
 wearing, without undergoing any material change itself. 
 
 A material is usually called fast-dyed if it will with- 
 stand every action to which it is likely to be exposed in 
 the course of the use for which it was intended. Cotton 
 fabrics, for example, ought to stand the process of wash- 
 ing much better than silk, since the latter is generally 
 cleansed in quite a different way ; while the Turkish fez, 
 which is exposed all day to the action of the sun's rays on 
 the head of the dockyard workman, must naturally be 
 much faster to light than the costly silk dress, which is 
 carefully stowed away in a dark wardrobe and but seldom 
 sees the daylight. 
 
 General regulations as to the experiments which should 
 be carried out in order to test the fastness of a colour can 
 therefore not be of much use, and in every case the judg- 
 ment should be guided by circumstances. 
 
 A material is called fast to ivashing if it will stand boil- 
 ing with a neutral or slightly alkaline soap, without 
 changing or losing any appreciable quantity of its colour. 
 Some colours will stand boiling with dilute solutions of 
 caustic alkalies, and are then called fast to alkalies ; they 
 are very valuable on cotton or linen goods. 
 
 In the cloth manufacture it is of great importance that 
 the colours should be fast to milling. , The term " milling " 
 
58 COAL-TAR COLOURS. 
 
 embraces all those operations which are calculated to 
 effect the felting of the woollen fibres in the fabric by 
 means of pressure or friction, along with fuller's earth and 
 solutions of soap, soda, stale urine, etc. The better quali- 
 ties of cloth are dyed in the yarn, or sometimes in the 
 loose wool. From this it is evident that the colours must 
 necessarily withstand the subsequent treatment with alka- 
 line liquids. 
 
 Some colours can be rendered faster in milling by the 
 addition of certain substances to the dye-bath. Thus, an 
 addition of magnesium sulphate has the effect of neutra- 
 lizing the effect of the liquid used in milling by the separa- 
 tion of indifferent magnesium hydrate. 
 
 Every fabric should be sufficiently fast to acids to with- 
 stand the action of perspiration, and should therefore not 
 be changed by the organic acids contained in the latter 
 Most of the dyes used for silk must of necessity possess 
 this property, in order to stand the brightening process 
 to which silk yarns or fabrics are almost invariably sub- 
 jected after dyeing. Sulphurous acid has a peculiar bleach- 
 ing action on many colouring matters. It is therefore a 
 frequent occurrence that dyed goods which are stored in 
 places where gas is burnt, fade in colour. 
 
 Heat, also, has an injurious action on many colouring 
 matters, and this is especially seen in steaming silk or 
 woollen fabrics after printing. The operation of steam- 
 ing is carried out in the following manner: The fabrics, 
 after having been printed, are exposed in air-tight boxes 
 or cylinders to the action of low-pressure steam, the tem- 
 perature of which is not much above 100 C. Colours 
 which will bear this treatment are called fast to steaming. 
 Some colours begin to sublimate at this temperature, and 
 are partially deposited on the white parts of the fabric, 
 while others undergo a chemical decomposition. Thus, 
 methyl-green, when steamed for some time, is transformed 
 into methyl-violet. The blue obtained from propiolic acid 
 
ACTION OF LIGHT AND AIR. 59 
 
 is also affected in steaming. Some colouring matters are 
 so volatile that fabrics dyed with them, colour the paper 
 in which they are wrapped. 
 
 Nearly all organic colouring matters are bleached by 
 the continued action of light and air. Light alone is able 
 to cause chemical changes, but at the same time it favours 
 the formation of small quantities of ozone and peroxide of 
 hydrogen, especially when water gradually evaporates 
 from the surface of the fibre. But even if we do not take 
 into consideration that fabrics become wet with rain, etc., 
 this gradual evaporation and absorption is an almost con- 
 tinuous process, since the degree of moisture of the fibre is 
 dependent upon the temperature and moisture of the sur- 
 rounding atmosphere. Ozone and peroxide of hydrogen 
 belong to the most powerful bleaching agents known, and 
 exercise, therefore, a destructive action on the colouring 
 matter. 
 
 The chemical effects which the different-coloured rays 
 are able to produce vary greatly, the red, yellow and 
 green rays having little or no effect, while the blue, violet 
 and ultra-violet rays possess the most powerful chemical 
 action. For this reason, materials which are worn in gas- 
 light or candle-light do not fade as rapidly as those which 
 are exposed to daylight ; for the light emitted by these 
 artificial illuminating agents contains a much smaller 
 proportion of blue and violet rays than daylight. 
 
 It can easily be ascertained whether a colour is fast to 
 light by exposing one-half of the material to the action of 
 direct sunlight, while the other is covered up. Colours 
 which are not fast to light will sometimes show a marked 
 change between the two halves within an hour or two, but 
 certainly within twenty-four hours of direct sunlight. In 
 carrying out the above experiment, it is advisable to 
 expose simultaneously some other colour, which is con- 
 sidered sufficiently fast to light, since nearly all colouring 
 matters lose some of their brilliancy by the action of light. 
 
60 COAL-TAR COLOURS. 
 
 In place of direct sunlight, which is not always at hand, 
 a powerful electric arc light may be nsed; or, failing this, 
 diffused daylight may be collected and made to fall upon 
 the material by means of a large lens. One and the same 
 colouring, matter may vary in fastness according to the 
 material on which it is fixed, Thus, vat-indigo, when dyed 
 on wool, fades much more rapidly than on silk or cotton ; 
 a fact which is most likely due to a reduction of the 
 colouring matter in the interior of the fibre. 
 
 THE TESTING OF COLOURING MATTERS. 
 
 The complete analysis of a colouring matter is, generally 
 speaking, one of the most difficult subjects which can be 
 placed before a chemist. For it is not only necessary to 
 determine the actual percentage of pure colouring matter, 
 but also that of the impurities which are generally formed 
 in the manufacture, and often so closely resemble the 
 pure colouring matter in their chemical properties that 
 their separation and estimation is rendered extremely 
 difficult. The results of a complete analysis of a colouring 
 matter do not, however, always give an exact criterion of 
 the quality, since the presence of very small quantities of 
 certain impurities may alter the shades considerably in 
 dyeing ; while, on the other hand, the presence of other 
 impurities may not have any injurious effect on the 
 shade. 
 
 -7 
 
 Comparative dye-trials. 
 
 In order to obtain a rapid and reliable estimate of the 
 value of a colouring matter, the best method is to dye 
 with it on the small scale, using for the purpose the same 
 material for which the colouring matter is intended on 
 the large scale. 
 
 In carrying out these comparative dye-trials, hanks of 
 yarn of pieces of cloth are generally used, which are all 
 
TESTING. 
 
 61 
 
 wound or cut to a certain weight, which varies for wool 
 and cotton from 5 to 20 grm., and for silk 2 to 5 grm. 
 
 The dye-trials are either carried out in beakers (glass 
 or porcelain) or in small vessels of tin or tinned copper, 
 having about the shape indicated in Fig. 13. They are 
 much higher than broad, and the rim is provided with 
 two indentures calculated to hold the glass rod on which 
 the yarn is suspended. Never less than two dye-trials 
 
 FIG. 13. 
 
 should be carried out at once, viz., one with the new 
 colouring matter, the other with a colouring matter of 
 known value, which is taken as the standard. It is, how- 
 ever, frequently necessary to compare a larger number of 
 samples with the standard. 
 
 It is absolutely necessary that all trials should be 
 carried out under exactly the same conditions as to tem- 
 perature, time of immersion, etc. In order to effect this, 
 it is necessary in the first place to have the dye vessels 
 all of the same material, as -uniform as possible in thick- 
 ness, the quantity of liquid the same in all cases ; and in 
 order, lastly, to ensure that the temperature is the same 
 in each vessel, they should all be placed in a water- bath, 
 or if a higher temperature is necessary, in a glycerin or 
 oil-bath. 
 
 The following example will serve to illustrate the 
 method of testing a new colouring matter in the manner 
 described above. Two vessels (glass or tinned copper) 
 are chosen of equal size, and into each is placed the same 
 
62 COAL-TAE COLOURS. 
 
 amount (200 to 600 c.c.) of lukewarm water, as well as 
 equal amounts of those additions which are necessary in 
 using the dye on the large scale, such as sulphuric acid, 
 soap, boiled-off liquor, etc. The weighed hank of yarn or 
 " swatch " of cloth to be used in the experiment is then 
 thoroughly wetted, and immersed in the liquid. 
 
 Solutions of known strength of the two colouring 
 matters to be compared are then made by dissolving 
 accurately weighed quantities (from O'l to 1 grm.) in 100 
 c.c. of water or methylated spirits. 
 
 The hanks or swatches are then taken out, and equal 
 volumes of each colour solution are added to the respec- 
 tive dye vessels, and after stirring the contents well, the 
 material is again introduced and dyed with a gradual rise 
 of temperature. When the baths are exhausted, further 
 quantities of the colour solutions are added gradually, 
 until both patterns have acquired the proper degree of 
 saturation and appear equal in shade. In working in this 
 manner, it is often found that unequal quantities of the 
 colouring matters are necessary to produce the same 
 shade ; and if the quantities added have been accurately 
 measured as described above, this method will not only 
 serve as a comparative test for the purity of shade, but 
 Avill also give an idea as to the quantitative value of the 
 colouring matter. If, for instance, 9 c.c. of the solution 
 of the colouring matter taken as type had given the same 
 depth of shade as 13 c.c. of the solution of the new colour- 
 ing matter, we should infer that 100 pts. of the type were 
 as strong as 144 pts. of the sample. 
 
 Although it is possible to compare the shades of the 
 two samples while they are being dyed, it is nevertheless 
 advisable to make the final comparison only after they 
 have been washed and dried. With some practice, it can 
 easily be seen whether two colours are identical, or whether 
 one of them appears a little less pure or duller. Even 
 very slight differences in the tone of the colour, which an 
 
TESTING. bo 
 
 outsider can scarcely distinguish, are readily perceived 
 by a practical man. Artificial light is a very important 
 item in comparing shades, especially for the green, blue, 
 and violet, since by this means certain peculiarities are 
 brought out very distinctly. Thus, a blue with a slight 
 cast of red appears almost violet in artificial light (gas or 
 lamp light), while a blue with a slight shade of green 
 appears distinctly bluish-green. 
 
 It should still be mentioned that, if possible (see below) 
 the dye-bath should be completely exhausted, i.e., the 
 whole of the colouring matter should be taken up by the 
 fibre, and the bath should appear colourless or nearly so. 
 Otherwise erroneous results may be obtained, since the 
 impurities which have the power of dyeing are generally 
 fixed last by the fibre. The presence of impurities of this 
 kind can easily be detected by preparing a solution of the 
 colouring matter and then dyeing two hanks in it, one after 
 the other, so that the second completely exhausts the bath. 
 The second hank may then be compared with the first, or 
 with another dyed to the same depth of shade in a fresh 
 solution. 
 
 Many colouring matters, such as picric acid, etc., cannot 
 be completely withdrawn from their solutions in dyeing. 
 In these cases, equal weights of the colouring matters in 
 question are used for the dye-trials, and the colours pro- 
 duced are compared directly with respect to saturation 
 and purity. 
 
 In testing adjective colouring matters, mordanted yarn 
 or cloth must be used, and, after dyeing, the material must 
 be made to pass through all those operations (soaping, clear- 
 ing, etc.) which it has to undergo on the large scale. 
 Since the treatment of the different adjective colouring 
 matters varies considerably, no general instructions can 
 be given here. 
 
 Lastly, in giving preference to one of several samples of 
 a colouring matter, the price should be taken into account, 
 
b'4 COAL-TAR COLOURS. . 
 
 besides the results of the dye-trials, since it may in many 
 cases be more advantageous to make use of a weaker dye, 
 in case the price is considerably lower. Besides, in dyeing 
 dark or mixed shades, cheaper qualities of a colouring 
 matter can often be used, which may not yield pure shades 
 by themselves. 
 
 Color imetry. 
 
 The estimation of the amount of pure colouring matter 
 contained in a sample by means of a colorimeter does not 
 give as reliable results as a comparative dye-trial, and has 
 therefore but little technical importance. For this reason 
 the principle of the colorimeter will only be inferred to in 
 a few words. Two glass tubes, closed at one end, and being 
 of exactly the same diameter, are placed close to each other 
 on a stand. Each tube is divided into a certain number 
 of equal parts, say, from to 200. Equal weights of 
 the colouring matters to be compared are dissolved in 
 water (alcohol, etc.), and the solutions are poured into the 
 tubes np to the mark 100, when as a rule one will appear 
 somewhat darker than the other. The darker liquid is 
 then diluted with water in small quantities at a time, 
 until both liquids, when looked at horizontally, appear to 
 have the same strength. If, in order to effect this, 35 c.c. 
 had been added to the normal solution (the solution of the 
 type), we should conclude that the dyeing power of the 
 type compared with that of the sample is as 135 : 100. 
 
 An ingenious instrument for the measurement of colour, 
 either in solution or on dyed fabrics, is the tintometer, de- 
 vised by Lovibond, for a full description of which, see 
 Journ. Soc. Dyers and Col, 1887, p. 186. 
 
 Quantitative determination of the coal-tar colours. 
 
 Until recently no ready and accurate methods were 
 known by means of which the coal-tar colours could be 
 quantitatively determined. In a communication to the 
 

 TESTING. 65 
 
 Society of Dyers and Colourists (Journ. Soc. Dyers and 
 Col., 188$, p. 82), however, Rawson describes a process 
 for the valuation of naphthol yellow, by means of which 
 the percentage of pure colouring matter can be accurately 
 and rapidly determined in a very simple manner. The 
 process, which is also applicable to picric acid, tartrazine, 
 and most of the azo dyes, depends upon the complete 
 precipitation of these dyes by a solution of night-blue * 
 in acetic acid. The following is the modus operandi in 
 the case of naphthol yellow or picric acid : 
 
 A standard solution of night-blue is prepared by dis- 
 solving 10 grms. of the dye in 50 c.c. glacial acetic acid 
 and diluting to 1 litre. Solutions of the samples of 
 naphthol yellow or picric acid are then prepared so as to 
 contain 1 grm. of the dye per litre. 10 c.c. of the night- 
 blue solution are now carefully measured into a small 
 flask, and then about 30 c.c. of the yellow run in from a 
 burette. After shaking and allowing to stand for about a 
 minute, the contents of the flask are poured through a 
 filter into a colourless Nessler glass. If the nitrate is blue 
 or colourless, more of the yellow solution is added until the 
 filtrate shows a very faint yellow tint. The value of the 
 samples under examination will be in inverse proportion 
 to the number of cubic centimetres required to precipitate 
 10 c.c. of the night-blue solution. Thus if of two samples, 
 28 c.c. are required in the one case, and 35 c.c. in the 
 other, their relative value will be as 35 : 28, or as 100 : 80. 
 
 In applying the method for the valuation of azo-dyes, it 
 is necessary to use it with discretion, since colouring 
 matters to be compared with each other must possess the 
 same chemical constitution. It would not be admissible to 
 compare, for example, a crocein scarlet with a xylidine 
 scarlet in this manner ; but a number of samples of either 
 of these scarlets, containing various proportions of either 
 
 * Tetramethyltolyltriamidodiplienylnaphthylcarbinol hydrochloride. 
 
 F 
 
66 COAL-TAR COLOURS. 
 
 mineral or organic impurities, can be valued by the night- 
 blue process with great precision. 
 
 The reverse process is applicable for the estimation of 
 night-blue and of crystal violet. 
 
 Impurities in colouring matters, 
 
 The impurities found in the artificial colouring matters 
 may either be accidental, and result from the mode of 
 manufacture, or they may have been added for special 
 purposes. In the latter cases, however, this is seldom 
 done for the purpose of adulteration. Thus, pastes are 
 often mixed with glycerin, in order to prevent the solid 
 constituents settling into a hard cake. On the other hand, 
 many very powerful dyes would necessitate great care in 
 weighing when used in small quantities, and are there- 
 fore delivered, according to the wish of the consumer, in 
 a state of dilution, which is effected by mixing them with 
 a certain precentage of dextrin, sugar, salt, or some other 
 harmless substance. 
 
 The substances used for the adulteration of colouring 
 matters are usually chosen so as to fit the nature of 
 the respective dyes, and are not easily detected in the 
 ordinary application of the same. In many cases a mi- 
 croscopical investigation renders good services. For the 
 detection and quantitative estimation of the admixtures, 
 it is, however, necessary to resort to special methods de- 
 pending on the properties of the adulterated dye-ware, 
 and it is therefore difficult to give any general instruc- 
 tions here. 
 
 In all cases, the water and the ash of the sample should be 
 estimated. The estimation of the water is best effected by 
 beating a weighed quantity of the sample in a drying oven 
 to about 160 C. Some colouring matters contain water 
 of crystallization, which is also given off at this tempera- 
 ture, and should be subtracted from the total, to obtain the 
 
ESTIMATION OF IMPURITIES, ETC. 67 
 
 actual percentage of moisture. In estimating the dry sub- 
 stance of pastes, it is not sufficient to take a weighed 
 sample, dry and weigh it, since any other substances con- 
 tained in the water, such as inorganic salts, glycerin, 
 etc., would also be contained in the residue. Since pastes 
 are often difficult to filter after having been diluted 
 with water, the best method is to evaporate to dryness in 
 a small mortar, after which the residue is finely pul- 
 verized, and treated with water. The residue, which has 
 now assumed a pulverulent condition, is collected on a 
 tared filter, washed out well with water, dried at 100 
 and weighed. 
 
 By the estimation of the ash, the presence of inorganic 
 adulterants can easily be detected. It should, however, 
 be borne in mind that certain salts may have become 
 mixed with the dye in the ordinary process of manufac- 
 ture, and that many colouring matters are combined with 
 inorganic bases, or are brought into commerce in the shape 
 of double salts, and must therefore of necessity contain a 
 certain precentage of ash, which can easily be calculated 
 from the formula. 
 
 Organic impurities can frequently be detected by dissolv- 
 ing a sample in water, and withdrawing the colouring 
 matter from the solution by means of wool or silk. The 
 impurities which have remained in solution will be con- 
 tained in the residue on evaporation, and can then be 
 subjected to a closer investigation. An admixture of 
 cane sugar can easily be detected in the following manner, 
 should the colouring matter be soluble in absolute 
 alcohol : The sample is extracted with absolute alcohol 
 containing a little ether, until the residue of sugar is 
 rendered almost colourless, when it is collected on a tared 
 filter and weighed. In case the colouring matter is 
 soluble in water and can be precipitated by acetate of 
 lead, another method may be used. A weighed quantity 
 of the sample is dissolved in water and treated with ex- 
 
68 COAL-TAR COLOURS. 
 
 cess of acetate of lead, when the liquid is filtered, and the 
 sugar is estimated in the nitrate by means of the polari- 
 scope. For the estimation of cane sugar in magenta, a 
 colouring matter which is not precipitated by acetate of 
 lead, this method has been modified in the following 
 manner: A weighed sample is dissolved in water, the 
 rosaniline is precipitated by picric acid, the picric acid by 
 acetate of lead, and the liquid thus freed from colouring 
 matter is analysed in the polariscope. 
 
 Dextrin, too, is often used for adulterating or diluting 
 the coal-tar colours, and in some cases gum-arabic is used 
 for this purpose. The detection of these substances de- 
 pends upon their insolubility in alcohol. If the colour- 
 ing matters are soluble in water, the following is the best 
 method to adopt : 
 
 From 1 to 2 grams of the substance are dissolved in as 
 little water as possible, and the solution is filtered into a 
 beaker, which has been previously weighed, along with a 
 glass rod. On adding a sufficient quantity of alcohol, the 
 whole of the dextrin is precipitated in flakes, which on 
 stirring form a coherent mass, which adheres partly to the 
 glass rod and partly to the sides of the vessel. The liquid 
 is poured off, while the beaker and glass rod are washed 
 with absolute alcohol, dried at 110, and weighed. 
 
 The quantitative estimation of dextrin in colouring 
 matters which are soluble in alcohol is effected by ex- 
 hausting repeatedly with strong alcohol, after which the 
 residue is dissolved in water and reprecipitated with alco- 
 hol in the manner described above. 
 
PART IL 
 
 COAL-TAR AND THE RAW PRODUCTS USED IX 
 
 THE MANUFACTURE OF THE COAL-TAR 
 
 COLOURS. 
 
 IF animal or vegetable substances are heated in vessels 
 without access of air, a complete decomposition takes 
 place. A large number of volatile products is formed, 
 which are partially condensed in the receivers in a liquid 
 or semi- solid state ; another portion passes over in the 
 form of gases, while the residue which remains in the re- 
 tort consists chiefly of carbon. The condensed product 
 usually consists of two distinct layers : an aqueous one, 
 containing several substances in solution ; and another 
 one, which is generally of a dark colour, and is known as 
 tar. 
 
 The products of the dry distillation of coal, which is 
 carried out on the large scale for the manufacture of 
 coal-gas, may be conveniently divided into four classes : 
 Coal-gas, ammoniacal liquor, coal-tar, and coke. Coal-tar 
 is the only one of these which is of importance in the 
 manufacture of the artificial colouring matters. It consists 
 of a large number of different substances, which, according 
 to their chemical reactions, can be divided into three 
 groups. 
 
 The first of these comprises the hydrocarbons, which', as 
 their name implies , consist of carbon and hydrogen. They 
 are in different substances, possessing neither acid nor basic 
 
 69 
 
70 COAL-TAR COLOURS. 
 
 properties, and are therefore insoluble in dilute acids and 
 alkalies. They constitute the principal part 1 , and at the 
 same time the most valuable part, of coal-tar. Benzene, 
 toluene, xylene, naphthalene, and anthracene are the most 
 important of these hydrocarbons. 
 
 The number of substances contained in the second group 
 is limited, but they exceed those of the third group in 
 quantity. They consist of the phenols, bodies which are 
 composed of carbon, hydrogen, and oxygen. The phenols 
 are weak acids, and therefore dissolve in caustic alkalies, 
 whereas in dilute acids they are insoluble. The most im- 
 portant phenols contained in coal-tar are carbolic acid and 
 cressol. 
 
 The third group, lastly, comprises a large number of 
 bases, but none of these are contained in sufficiently large 
 quantity to admit of their technical preparation from this 
 source. The bases are composed of carbon, hydrogen, and 
 nitrogen. They are soluble in acids, but insoluble in 
 alkalies. As characteristic members of this group may 
 be mentioned aniline, toluidine, etc. 
 
 Almost all those products which are contained in coal- 
 tar in large quantities have been successfully utilised in 
 the manufacture of colouring matters. The most impor- 
 tant of these are benzene, toluene, xylene, naphthalene, 
 anthracene, and phenol. 
 
 The separation and preparation of these products in the 
 pure state forms a special branch of industry, the distilla- 
 tion of coal-tar. The portions of coal-tar which cannot be 
 made use of in the preparation of colouring matters are 
 generally used for other purposes. Thus one portion of 
 the hydrocarbons is used as a solvent, under the name of 
 " solvent naphtha " ; crude carbolic acid is used for im- 
 pregnating sleepers and for disinfecting purposes, while 
 other portions of coal-tar are used as lubricants, and so 
 on. 
 
 According to G. Schultz (Chemic des Steinkohlentheers), 
 
} DISTILLATION OF COAL-TAR. 71 
 
 the amount of coal-tar distilled annually in Europe is 
 about 590,000 tons. This amount is subdivided as 
 follows : ^ 
 
 England about 400,000 tons. 
 
 Germany ,, 65,000 
 
 France 60,000 
 
 Belgium 50,000 
 
 Holland 15,000 
 
 The distillation of Coal-tar. 
 
 The separation of the different constituents of coal-tar 
 is effected by means of fractional distillation, a process 
 Avhich depends upon the fact that, on heating a mixture of 
 different liquids, the one which has the lowest boiling- 
 point will pass over first into the distillate, the others 
 following in order according to their boiling-points. As 
 a simple example, we will take a mixture of absolute 
 alcohol, which boils at 78 C., and water, which boils at 
 100 C. If this mixture is distilled, it will begin to boil 
 at 78, and at first almost pure alcohol will pass over. 
 The separation by this ready means is, however, not an 
 exact one, since very soon a part of the liquid of higher 
 boiling-point is drawn over. If we were to divide the 
 distillate obtained in our example into three equal parts, 
 we should find that the first contained a strong alcohol, 
 the second a very aqueous alcohol, while the third fraction 
 would consist almost of pure water. 
 
 The boiling-points of the different constituents of coal- 
 tar vary very considerably ; benzene, for instance, boils at 
 80, while anthracene boils at 370. It is therefore pos- 
 sible in separating the fractions of the first distillation 
 to obtain certain constituents in the first fraction only, 
 while others are contained in the second or third. 
 
 The process of distillation is carried out in large iron 
 retorts. The first distillate is divided into three portions, 
 the first of which contains all the products which pass over 
 
72 COAL-TAR COLOURS. 
 
 up to 180, and which are technically known as light oil. 
 The second fraction consists of the heavy oil, so called be- 
 cause it sinks in water. The first portions of the heavy oil 
 which pass over remain liquid on cooling, but after a time 
 the distillate assumes the consistency of butter, owing to 
 the separation of solid naphthalene. The distillate then 
 becomes liquid again, and it is not until solid constituents 
 have begun to separate out again that the third fraction, 
 the so-called green grease or anthracene oil, is collected. 
 The residue which remains in the retort is known asjpi/c//, 
 and is used in the preparation of asphalt, or of a fuel 
 known as " briquettes." 
 
 The light oil which passes over between 80 and 180 is 
 treated successively with soda ley, water, sulphuric acid, 
 and again with water, in order to free it from small 
 quantities of phenols and basic constituents, after which 
 it is distilled again. 
 
 The manufacture of pure benzene, toluene, and xylene 
 from the light oil purified in the manner described, is 
 carried out by fractional distillation. The stills used for 
 this purpose are provided with dephlegmators, by which 
 means it is possible to obtain almost pure products in one, 
 or at most in two operations. 
 
 The principle of these distilling apparatus is, not to 
 allow the vapour which is given off by the boiling liquid 
 to pass immediately into the condenser; but it is first 
 caused to pass through a series of pipes and vessels, 
 which are so arranged as to allow any liquid condensing 
 on their walls to flow back into the still. The temperature 
 of these vessels is regulated so as to allow only a portion 
 of the vapour, i.e., that of the liquid of lowest boiling- 
 point, to pass through, while those possessing higher 
 boiling-points will be condensed and will flow back. If, 
 for instance, the liquid in the still consisted of a mixture 
 of benzene (B.P. 80) and toluene (B.P. 111), and the 
 vapour of the two were caused to pass through a series of 
 
DISTILLATION OF COAL-TAR. 73 
 
 pipes heated to 80, it is evident that the toluene will be 
 condensed, while the benzene will pass through and can 
 subsequently be liquefied in an ordinary condenser. It 
 should not be imagined that by this process a quantitative 
 separation can always be effected in one operation, although 
 one form of condenser which is used on the large scale, 
 and is known as " Savalle's column apparatus," will pro- 
 duce an almost pure benzene by the first distillation. 
 
 When the greater part of the benzene has been obtained, 
 the temperature of the condensing vessels is raised, when 
 a small quantity of liquid, consisting of a mixture of ben- 
 zene and toluene, passes over and is collected separately. 
 Afterwards pure toluene passes over for a length of time. 
 Then comes xylene, which can also be isolated in a like 
 manner ; but this is not always done. The liquid remain- 
 ing in the stills after distilling off the benzene and toluene 
 is generally made use of for other purposes (solvent naph- 
 tha, etc.). 
 
 The heavy oil yields carbolic acid and naphthalene. The 
 naphthalene is separated out in the solid state when the 
 oil cools. It is pressed, treated alternately with caustic 
 soda ley and sulphuric acid, after which it is purified by 
 distillation or sublimation. 
 
 The separation of the crude carbolic acid, which consists 
 chiefly of a mixture of phenol and cressol, is based upon 
 the property of all phenols to dissolve in caustic alkalies. 
 The heavy oil is agitated with caustic soda ley, and the 
 aqueous layer having been drawn off, is exposed to the 
 air for some time. This exposure causes certain im- 
 purities to separate out in the form of a brown resinous 
 substance. The liquid is then filtered and the phenols 
 are set free by the addition of an acid, when they are 
 obtained in the form of an oil. Many methods are in 
 vogue for the separation of pure phenol and cressol from 
 this product, but the most rapid is a fractional distillation 
 in a dephlegmation apparatus. 
 
/4 COAL-TAR COLOURS. 
 
 Commercial anthracene is obtained in the following 
 manner from the so-called " green grease " : The oil is 
 removed as much as possible by filtration, and the residue 
 is pressed between warm plates, after which it is treated 
 in a fine state of division with solvent naphtha. It is then 
 pressed again, and finally sublimated with a current of 
 steam. In this form the product is adapted for the manu- 
 facture of alizarin, although it still contains from 50 to 55 
 per cent, of impurities, which are very difficult to remove 
 on the large scale. 
 
 The following is a list of the most important consti- 
 tuents of coal-tar : 
 
 CONSTITUENTS OF COAL-TAR. 
 
 A. Neutral substances. 
 Those printed in italics are commercially the most important. 
 
 Name. 
 
 Formula. Melting point. 
 
 Boiling point. 
 
 Fatty hydrocarbons . 
 
 59 55 
 
 CnHill + 2 
 CnHsa 
 
 
 
 Benzene . . . 
 
 Toluene . . . 
 
 Orthoxylene . . 
 
 Metaxylene . . 
 
 Paraxylene . . 
 
 Mesitylene . . 
 
 Pseudocumene . 
 Naphthalene 
 
 Diphenyl . . . 
 
 Fluorene . . . 
 
 Phenanthrene . 
 
 Anthracene . . 
 
 Thiopheue . . 
 
 Carbazol . . . 
 
 CH 
 
 C 1: <H 
 
 C 14 H 10 
 C 4 bf,S 
 C P H 9 N 
 
 -f3 
 liquid 
 
 15 
 
 liquid 
 
 99 
 
 80 
 
 71 
 113 
 100 
 213 
 liquid 
 236 
 
 81 
 111 
 141 
 141 
 137 
 103 
 166 
 217 
 254 
 295 
 340 
 360 
 
 84 
 S55 U 
 
COAL-TAR RAW PRODUCTS. 
 
 B. Acid substances. 
 
 Name 
 
 
 
 
 
 Formula. 
 
 Melting point. 
 
 Boiling point. 
 
 Phenol . 
 
 
 
 
 
 CrHcO 
 
 42 
 
 182 
 
 Orthocressul 
 Metacressol 
 Paracressol 
 a Naphthol 
 Naphthol 
 
 
 
 
 
 C 7 H 8 
 C 7 H 8 
 C-H 8 
 C 10 H 8 
 C 10 H 8 
 
 31 
 liquid 
 86 
 94 
 123 
 
 188 
 201 
 199 
 
 280 
 286 
 
 C. Basic substances. 
 
 Name. 
 
 Formula. 
 
 Melting point. 
 
 Boiling point. 
 
 Pyridine 
 
 0-H N 
 
 liquid. 
 
 115 
 
 Lutidine . 
 
 C-H N 
 
 
 154 
 
 Aniline 
 Quinoline .... 
 
 v ^7 J " l< J 
 C 6 H 7 N 
 C 9 H 7 N 
 
 ;; 
 
 j > 
 
 182 
 239 
 
 COAL-TAR RAW PRODUCTS. 
 
 Constitution of the aromatic compounds. 
 
 According to the chemical theory at present generally 
 adopted, the smallest particles of the elements which can 
 enter into chemical combination are called atoms. These 
 atoms combine with each other according to definite laws, 
 in greater or smaller numbers, to form molecules, which are 
 simultaneously the smallest particles of matter capable of 
 existing in the free state. Thus each molecule of magenta 
 is composed of atoms of carbon, hydrogen, nitrogen, and 
 chlorine. '. 
 
 The abridged chemical method of specifying the num- 
 ber of these atoms and the proportion in which they are 
 contained in the molecule constitutes what is known as an 
 empirical formula. Thus the fact that the molecule 
 of magenta consists of twenty atoms of carbon (C), 
 
76 COAL-TAR COLOURS* 
 
 twenty atoms of hydrogen (H), three atoms of nitrogen 
 (N), and one atom of chlorine (Cl), is expressed by the 
 empirical formula, Co H 20 ]SgCl. 
 
 By a thorough investigation of the chemical properties 
 of these bodies, their modes of formation, products of de- 
 composition, and the compounds they are capable of form- 
 ing, modern chemistry has produced a deeper insight into 
 their interior structure. But although we have no definite 
 idea as to the actual relative position of the atoms in the 
 molecule, we are nevertheless enabled to lay down a 
 scheme in which the atoms given by empirical formulae are 
 arranged in such a manner as to show the whole chemical 
 nature of the compound. A scheme of this kind, which 
 simply serves to express our knowledge of the compound 
 to which it relates, is called a constitutional formula. The 
 determination of the constitutional formulae of bodies like 
 the organic colouring matters, the composition of which is 
 generally very complicated, is often a difficult matter, and 
 it is therefore not to be wondered at that there are still 
 many colouring matters the constitution of which is un- 
 known. 
 
 It is usual in chemical literature to deal with the 
 elements and their compounds under two distinct head- 
 ings; viz., Inorganic Chemistry and Organic Chemistry. The 
 chief reason for this classification is that the organic 
 compounds, or compounds of carbon with hydrogen, oxygen, 
 nitrogen, etc., by far outnumber those of all the inorganic 
 elements put together. The carbon compounds are again 
 subdivided into (a) The fatty series, (b) The aromatic 
 or benzene series, (c) Pyridine and quinoline derivatives. 
 (d) Bodies of unknown constitution. The coal-tar colours 
 belong essentially to the second of these great classes; i.e., 
 they are derivatives of benzene and its homologues, of 
 which benzene itself may be taken as the simplest repre- 
 sentative. It contains six atoms of carbon, which are 
 bound together (according to Kekule's hypothesis, first 
 
COAL-TAR RAW PRODUCTS. 77 
 
 expressed in 1865) by alternate double and single bonds 
 in the form of a ring 
 
 C 
 
 c x c 
 
 II ! 
 
 C C 
 
 \ // 
 
 c 
 
 I 
 
 Carbon being a tetrad or tetravalent element, it is 
 obvious that each of these carbon atoms must still have 
 one free bond. In benzene itself these bonds are satu- 
 rated with hydrogen, and we have the empirical formula, 
 C 6 H fi , or the constitutional formula 
 
 H 
 C 
 
 HC X CH 
 
 II I 
 
 HC CH 
 
 \ // 
 
 C 
 
 H 
 
 By substituting for one of the hydrogen atoms in ben- 
 zene other elements, or groups, such as Cl, NOo (nitro)- 
 NH 3 (amido),OH (hydroxyl), etc., we obtain the so-called 
 mono-substitution derivatives. The mono- derivatives 
 are of one kind only; i.e., there is only one nitrobenzene, 
 C G H 5 NO , one chlorbenzene, C fi H 5 N"Oo, one amido-benzene, 
 C () H 5 NH^ etc. 
 
 When two of the hydrogen atoms in benzene are 
 substituted by other elements or groups, the so-called 
 disubstitution derivatives are obtained. Thus by treat- 
 ment with chlorine we get dichlorbenzene, C fi H 4 Clq, with 
 
78 COAL-TAR COLOURS. 
 
 nitric acid, dinitrobenzene, C 6 H 4 (N0 2 ) 2 , and so on. But 
 it is found in treating benzene with nitric acid, for 
 instance, that not one, but three bodies are formed, each 
 of which possesses different properties to the other two, 
 while at the same time analysis shows them all to have 
 the empirical formula, C 6 H 4 No0 4 . It is here that Kekule's 
 benzene theory comes to our aid, and explains clearly why 
 these three dinitrobenzenes should show different pro- 
 perties. As we have already seen, benzene contains a 
 ring of six atoms of carbon. These carbon atoms are 
 usually numbered for convenience thus: 
 
 A 
 
 C G 
 
 -c, s c- 
 
 \ .// 
 c 
 
 If now, in our example of dinitrobenzene, one X0 2 
 group attaches itself at 1, the other at 2, we shall get a 
 dinitrobenzene of the formula 
 
 NO, 
 
 C " 
 / ^ 
 
 HC cm 
 
 II ! 
 
 HC CH 
 
 \ // 
 
 C 
 
 H 
 
 The substitution has taken place in two adjoining 
 carbon atoms, and all such derivatives are known as ortho- 
 Qompounds. The same compound would be formed if we 
 
COAL-TAR RAW PRODUCTS. 79 
 
 substituted, instead of at 1 and 2, at 2 and 3, or 3 and 4, 
 etc. 
 
 If the nitro groups are substituted at 1 and 3 (or 2 and 
 4, or 3 and 5, etc.), we obtain what is known as a meta- 
 compound 
 
 NOo 
 
 C " 
 / ^ 
 HC CH 
 
 II ! 
 
 HC CNOo 
 
 \ // 
 
 C 
 
 H 
 
 If, lastly, the substituting groups or elements lie oppo- 
 site to each other in the benzene ring, the so-called para- 
 compounds are produced. These may have the position 
 1 4, 2 5, or 3 -6, and paradinitrobenzene would be repre- 
 sented thus : 
 
 NOo 
 
 C " 
 / -^ 
 HC CH 
 
 II I 
 
 HC CH 
 
 \ // 
 
 C 
 
 N0 3 
 
 Now what has been said of dinitrobenzene applies 
 equally to all disubstitution derivatives of benzene. We 
 invariably find three disubstitution derivatives, possessing 
 the same empirical formula, but different constitutional 
 formulae. Such bodies are said to be isomeric, or are 
 known as isomers. 
 
 When three elements, or groups of elements, are intro- 
 duced into the benzene ring, the following cases of 
 
80 COAL-TAR COLOURS. 
 
 isomerism are observed in case the substituting groups 
 are of the same kind (A) : 
 
 A A A 
 
 /\ A X\ A /\ 
 
 A. 
 
 V 
 
 A 
 
 A 
 
 There are therefore three isomeric trisubstitutise. deriva- 
 tives. 
 
 Under similar conditions there are three tetra, one 
 penta, and one hexa substituti$e?derivative. When, how- 
 ever, in the tri, tetra, penta, and hexa derivatives the 
 substituting elements or groups are of different kinds, the 
 number of isomers is considerably increased. 
 
 The Hydrocarbons. 
 
 These bodies may be looked upon as the first raw 
 materials for the manufacture of the coal-tar colours. 
 They are obtained exclusively from coal-tar. 
 
 Benzene, C G H 6 . 
 
 Chemically pure benzene is a colourless mobile liquid, 
 possessing a specific gravity of 0*885 at 15 C. It boils at 
 80 C., and solidifies at to a colourless mass, consisting of 
 rhombic crystals, which melt at 4-4. It is almost in- 
 soluble in water, dilute acids, and alkalies, but it is easily 
 soluble in or mixable with alcohol, ether, chloroform, etc. 
 Benzene is an excellent solvent for fats, resin, etc., and 
 the impure product is frequently used on this account for 
 removing grease stains, etc. Benzene is easily acted upon 
 by concentrated sulphuric acid, niti'ic acid, and chlorine, 
 
THE HYDROCARBONS. 81 
 
 with formation of the corresponding substitution deriva- 
 tives. 
 
 The purest form of commercial benzene is known as 
 benzole for blue. Although it possesses exactly the same 
 boiling point as pure benzene, it is not a chemically pure 
 product, and contains, besides benzene, thiophene, and fatty 
 hydrocarbons, which latter remain behind in the manu- 
 facture of nitrobenzene as " neutral oils." Besides benzole 
 for blue, there are three other commercial products which 
 are known respectively as 30 per cent., 50 per cent., and 
 90 per cent, benzole. The percentage indicates here the 
 parts per hundred which pass over in the process of dis- 
 tillation under 100 C. 
 
 The valuation of commercial benzoles is effected by 
 fractional distillation, and by determining the amount of 
 nitrobenzene which they yield. 
 
 Toluene, C H 5 CH 3 . 
 
 Toluene may be regarded as the moiiomethyl derivative 
 of benzene. It forms a colourless liquid, which boils at 
 111 C., and remains liquid at '20. At 15 it has a 
 specific gravity of 0'872. With respect to solubility, etc., 
 it possesses great similarity with benzene. By oxidizing 
 agents it is converted into benzoic acid, C 6 H 5 COOH. 
 
 Toluene is contained in most commercial benzoles, in 
 some of which it actually forms the chief constituent. 
 Its presence in benzene for magenta is a matter of necessity. 
 The pure product obtained by fractional distillation is 
 used in the manufacture of malachite green and artificial 
 indigo. 
 
 Xylenes, C 6 H 4 (CH 3 ) 2 . 
 
 If two atoms of hydrogen in the benzene ring are re- 
 placed by methyl, three isomeric xylenes are formed which 
 each possess the formula C 6 H 4 (CH 3 ) 2 , but are dis- 
 
 G 
 
COAL-TAB COLOURS. 
 
 tinguished from each other by their constitutional formulae 
 in the following manner :- 
 
 c.cm 
 
 C.ClIj 
 
 C.CH? 
 
 C.C1I 3 
 
 CII 
 
 Orthoxylene. 
 
 CII 
 
 Metaxylene. 
 
 That portion of coal-tar which passes over at about 
 140 consists of a mixture of the three xylenes, in which 
 metaxylene invariably predominates. The isolation of the 
 three isomers from commercial ;< xylole" cannot be effected 
 by fractional distillation, since their boiling points lie so 
 close together. 
 
 The preparation of metaxylene may be effected by 
 boiling coal-tar xylole with dilute nitric acid for a length 
 of time. The ortho and para xylenes thus become oxi- 
 dized to the corresponding xylilic acids, while metaxylene 
 is not acted upon. By a subsequent treatment with 
 caustic soda the acids are removed and pure metaxylene 
 is obtained. 
 
 Pure paraxylene can be obtained, according to Levinstein, 
 by distilling commercial xylol with steam. The first 
 portions of the distillate are cooled, and the crystals which 
 separate are pressed and redistilled. 
 
 The separation of all the three isomers from xylole 
 may be effected by Jacobsen's method. Xylol is shaken 
 with strong sulphuric acid. Meta and orthoxylene are 
 thereby converted into sulphonic acids, while paraxylene 
 is not affected. The sulphonic acids are then converted 
 into the corresponding sodium salts, which are separated 
 from each other by crystallisation. The hydrocarbons 
 
THE HYDROCARBONS. 
 
 are then regenerated by distilling the sodium salts of the 
 sulphonic acids with ammonium chloride. 
 
 Ortlioxylene is a colourless liquid, which boils at 
 141-142. 
 
 Metaxylene, which forms about 70 per cent, of com- 
 mercial xylole, is also a colourless liquid, has a specific 
 gravity of 0'S668 at 19, and boils at 139. 
 
 Paraxylene forms colourless crystals, which melt at 15, 
 and boil at 138. 
 
 Commercial xylole was formerly used as a solvent, under 
 the name of " solvent naphtha," but since the discovery 
 of the azo dyes it is used in large quantities for the pro- 
 duction of xylidine and cumidine. 
 
 Hydrocarbons, C 6 H 3 (CH 3 ) 3 . 
 
 Of these, mesitylene and pseudocumene are found in 
 those portions of coal-tar which pass over between 140 
 and 180. Mesitylene is symmetrical (1, 3, o), trimethyl- 
 benzene, boiling point 163; pseudocumene is asymmetrical 
 (1, 3, 4), trimethylbenzene, boiling point 166. 
 
 Stilbene, C U H 12 , or C C H 5 CH:CHC 6 H 5 . 
 
 This hydrocarbon has not hitherto been isolated from 
 coal-tar. It is obtained by distilling sulphbenzaldehyde 
 with finely divided copper. It forms colourless crystals, 
 which melt at 125, and boil at 307. Diamidostilbene 
 is used in the manufacture of one or two azo dyes which 
 closely resemble the benzidine dyes. 
 
 DipTienyl, C 13 H 10 , or C 6 H 5 -C 6 H 5 . 
 
 Diphenyl may be regarded as phenylbenzene ; i.e., as 
 benzene, in which one hydrogen atom has been replaced 
 by phenyl (C 6 H 5 ). Although contained in coal-tar, it 
 is not isolated, the quantity present being too small. It 
 is best obtained bypassing the vapours of benzene through 
 
84 COAL-TAR COLOURS. 
 
 red-hot tubes, and subjecting the product obtained to 
 fractional distillation. Diphenyl forms colourless crystals, 
 which melt at 71. It boils at 254. 
 
 Naphthalene, C 10 H 8 . 
 
 Naphthalene contains two benzene rings, and its con- 
 stitution is shown by the formula 
 
 HC 
 
 It will be seen, in looking at this formula, that in the 
 formation of mono- substitution products two isomers are 
 obtained, according as the hydrogen atoms marked ft or 
 those marked a are replaced in the following scheme : 
 
 Thus, by replacing one hydrogen atom by OH two 
 isomeric naphthols are obtained, which are known as 
 alpha-naphthol and beta-naphthol respectively, but both 
 possess the rational formula C 10 H 7 OH. For describing 
 the monosubstitution derivatives, this designation would 
 be sufficient, but in derivatives containing more than one 
 substituting group it is necessary, in order to specify the 
 
THE HYDROCARBONS. 85 
 
 constitution, to introduce the letters o^a., and ft/So, as in- 
 dicated in the diagram. When both substituting groups 
 are contained in the same benzene nucleus, this is indicated 
 in writing by joining the two letters with a single hyphen. 
 Thus we should have for a dichlornaphthalene, in which 
 the two chlorine atoms are in the same nucleus, and stand 
 to each other in the orthoposition, the formula C 10 H 6 C1. 3 
 ( a i~&) ^ in the metaposition, C 10 H 6 C1 3 (c^ /3 3 ); and if 
 in the paraposition, C 10 H C C1 2 (a l a 3 ). 
 
 When the substituting groups or elements are contained 
 in different nuclei, this is represented by joining the letters 
 with a double hyphen. Thus for a dichlornaphthalene, in 
 which the two Cl atoms are not in the same nucleus, we 
 should have the following possible cases of isomerism : 
 C 10 H 6 C1 2 (a l = a 2 ), or (fl^ft), or (a^ft), or (a l = a 2 ), or 
 (ft = ai ), or (ft = ft),or (ft = /3 2 ), or (ft = a 3 ), in all eight 
 possible isomers. 
 
 The possible number of substitution derivatives in the 
 naphthalene series, when the substituting elements or 
 groups are of the same kind, will be, 
 
 2 Monoderivatives. 
 10 Biderivatives. 
 14 Tri 
 22 Tetra 
 14 Penta 
 10 Hexa 
 
 2 Hepta 
 
 1 Octo 
 
 When the substituting elements or groups are of differ- 
 ent kinds the number of possible isomers becomes much 
 larger. 
 
 Naphthalene was first discovered in coal-tar by Garden 
 in 1820, but it was not until the introduction of the azo 
 dyes that it became of much importance, The commer- 
 
86 
 
 COAL-TAR COLOURS. 
 
 cial product is obtained by the purification (crystallising, 
 pressing, distilling, etc.) of that portion of coal-tar which 
 passes over between 180 and 250. 
 
 Pure naphthalene crystallises in leaflets or monoclinic 
 tablets. It melts at 80, and boils at 217. The greater 
 part of the naphthalene produced is used in the manufac- 
 ture of the oxy-azo dyes. 
 
 Anthracene, C 12 H H . 
 
 The manufacture of this hydrocarbon has already been 
 referred to in the distillation of coal-tar. It forms in the 
 pure state colourless crystals, which show a beautiful blue 
 fluorescence. Anthracene melts at 213, and boils at a 
 little above 360 C. Its constitutional formula is repre- 
 sented graphically in the following manner : 
 
 ^/ 
 
 CH 
 
 Anthracene is used almost exclusively for the manufac- 
 ture of alizarin, anthrapurpurin, and flavopurpurin. The 
 valuation of the commercial product is best effected by 
 treating a known quantity with chromic acid in acetic 
 acid solution. The crude anthraquinon. thus formed is 
 then treated with concentrated sulphuric acid at 100 C. 
 for a few minutes, after which it is washed first with 
 water, then with alkali, and then with water again. The 
 pure anthraquinon is then dried at 100 C, and weighed, 
 
HALOGEN DERIVATIVES. 87 
 
 Halogen derivatives. 
 
 By treating benzene and its homologues with chlorine, 
 bromine, or iodine, substitution derivatives are obtained ; 
 
 e.g. 
 
 C c H c + Clo C 6 H.C1 + HC1. 
 
 Monochlorbenzene. 
 
 As a rule, chlorine acts most energetically (especially in 
 presence of a trace of iodine), bromine less so, while iodine 
 acts only very slowly. In the case of methylbenzene 
 (toluene) and its homologues, the temperature plays a very 
 important part in the formation of halogen substitution 
 derivatives. If, for instance, chlorine is allowed to act 
 on toluene in the cold, the hydrogen atoms of the benzene 
 ring only are replaced, and we obtain C 6 H t ClCHo, 
 C C H 3 C1 2 CH 3 , etc. If, on the other hand, chlorine is 
 passed into boiling toluene, it is found that the hydrogen 
 atoms of the methyl (CH 3 ) group only are replaced, and 
 we get C ? H 5 CHoCl, C 6 H-CH C1 2 , etc., bodies which differ 
 entirely in their behaviour from those obtained in the 
 cold. 
 
 The number of halogen derivatives in the aromatic series 
 is great, but the following only are of commercial impor- 
 tance : 
 
 BenzylcMoride, C fi H 5 CH 2 Cl. This compound is ob- 
 tained by passing chlorine into boiling toluene, until the 
 latter has absorbed the theoretical quantity. It forms a 
 colourless liquid, which has a specific gravity of I'll, and 
 which boils at 179. It possesses a sharp, penetrating 
 smell, and is converted by boiling with water (or better 
 still, with a solution of KoC0 3 ) into benzyl-alcohol, 
 C 6 H 5 CH 2 OH. 
 
 Benzalchloride, C 6 H 5 CHC1 2 , is obtained like benzyl- 
 chloride by the direct action of chlorine on boiling toluene. 
 It forms a colourless, oily liquid, which has a specific 
 gravity of 1:295, and which boils at 207, 
 
88 COAL-TAR COLOURS.. 
 
 Benzotrichloritle, C 6 H-CC1 3 , is formed, like the two pre- 
 ceding compounds, by the direct action of chlorine on 
 boiling toluene. The crude product is purified by wash- 
 ing with water and dilute alkaline carbonates, after which 
 it is dried with potash and distilled in a vacuum. It 
 forms a colourless, highly refractive liquid, which has a 
 specific gravity of T3S (at 14), and boils at 213. 
 
 These products are used, either directly or indirectly, in 
 the manufacture of malachite green. 
 
 Naphthalene ietrachloride, C 10 H 8 C1 4 , is a chlorine addi- 
 tion product of naphthalene, formed by the direct action 
 of gaseous chlorine on molten naphthalene. It forms 
 colourless rhomboledric crystals* which melt at 182. 
 When treated with nitric acid, it is converted into phth- 
 alic and oxalic acids. 
 
 Nitro derivatives. 
 The nitro derivatives contain the group -N0 3 or -N ~ Q. 
 
 They possess great importance, not only as intermediate 
 products, but also in the form of colouring matters. They 
 are formed by the action of concentrated nitric acid upon 
 the hydrocarbons and their derivatives. Dilute nitric 
 acid has only an oxidising action, and does not form nitro 
 compounds. If energetic nitration is required, fuming 
 nitric acid (nitric acid containing lower oxides of nitrogen 
 in solution) is frequently employed, either alone or in con- 
 junction with concentrated sulphuric acid. The object of 
 the latter is simply to absorb the water formed in the re- 
 action, which would otherwise dilute the nitric acid and 
 render it less efficient. 
 
 C C H 6 + HN0 8 - C 6 H 5 N0 2 + H 2 0. 
 
 In the manufacture of " nitrobenzole " on the large 
 scale, sulphuric acid is almost invariably used for this 
 reason. Great care has to be taken to have the liquids 
 
XITRO DERIVATIVES. 
 
 thoroughly mixed, and to avoid (in most cases) any con- 
 siderable rise in temperature. In the manufacture of 
 mononitro derivatives it is usual to allow the theoretical 
 quantity of nitric acid (mixed with sulphuric acid) to flow 
 into the hydrocarbon, so as always to have the latter in 
 slight excess, and thus to avoid the formation of dinitro 
 compounds. In the case of di- and tri- nitro compounds, 
 the reverse is the case ; i.e., the hydrocarbon is allowed to 
 flow into the mixture of the two acids. 
 
 The nitro compounds form either yellow or colourless 
 oils or crystals, sparingly soluble in water. Treated with 
 alkaline reducing agents, they yield azo compounds, 
 whereas by acid reducing agents they are converted into 
 the corresponding amines. 
 
 Nitrobenzene, C 6 H 5 N0 3 . The manufacture of nitro- 
 benzene (nitrobenzole) on the large scale is usually 
 effected in large cast-iron cylinders of 200-400 litres 
 capacity, which can be cooled from the outside by means 
 of fine jets of water. 100 parts of purified benzene are 
 (according to Gr. Schultz) introduced into the cylinder, 
 and a mixture of 115 parts nitric and 160 parts sulphuric 
 acids (both concentrated) is allowed to flow in gradually. 
 At the beginning of the reaction it is necessary to cool, 
 but towards the end (the reaction lasts from 8 to 10 hours) 
 the temperature is allowed to rise gradually to 80-90. 
 The contents of the cylinder are now run into a reservoir 
 and allowed to settle. Two layers are formed, the lower 
 one consisting of the refuse acid (spec. gr. 1*63), the top 
 one of nitrobenzene and unchanged benzene.* The acid 
 is drawn off, and the nitrobenzene, after having been 
 washed with water, is freed from the unchanged benzene 
 by treatment with a current of steam. The benzene 
 
 * Besides unchanged benzene, this layer contains a certain propor- 
 tion of hydrocarbons, possessing the same boiling point as benzene, 
 which are not acted upon by nitric acid, and which appear to belong 
 to the paraffin series. 
 
90 COAL-TAR COLOURS. 
 
 which distills off along with a small quantity of nitro- 
 benzene is used over again. The yield of nitrobenzene 
 from pure benzene is about 150 per cent, (theoretical, 157 
 per cent.). 
 
 Nitrobenzene forms a yellowish, oily liquid, with a 
 peculiar smell, similar to that of bitter almonds ; it was, 
 in fact, at one time sold as a perfume, under the name of 
 Essence de Mirbane, but it is not used as such at present 
 on account of its poisonous properties. It boils at 
 206-207, and solidifies on cooling to needle-shaped crys- 
 tals, which melt at +3. Its specific gravity at 15 is 
 1'208. In water nitrobenzene is insoluble, but it dis- 
 solves easily in other ordinary solvents, such as alcohol, 
 ether, etc., while at the same time it is itself an excellent 
 solvent for many substances. 
 
 Commercial nitrobenzene is known either as nitrobenzole 
 for blue or nitrobenzole for red. Heavy nitrobenzole contains 
 very little nitrobenzene, and consists chiefly of nitro- 
 toluenes and nitroxylenes. The first of these is used 
 chiefly in the manufacture of aniline for blue and black 
 and for induline, besides for the preparation of quinoline 
 and benzidine. Nitrobenzole for red is used in the manu- 
 facture of magenta. 
 
 Dinitrobenzenes, C 6 H 4 (NOo) 2 - According to theory, 
 three isomeric dinitrobenzenes exist. They are all formed 
 by the direct action of an excess of strong nitric acid on. 
 benzene or nitrobenzene. The meta compound forms the 
 chief product of the reaction, while the ortho and para 
 compounds are formed in comparatively small quantity 
 only. 
 
 Metadinitrobenzene, CgH^j^-Q 2 ><, is obtained on the 
 
 large scale by allowing 100 pts. of benzene to flow into 
 100 pts. cone, nitric acid and 156 pts. cone, sulphuric 
 acid. The nitrobenzene thus formed is then warmed for 
 some time with a mixture of 100 pts. cone, nitric acid 
 
N1TRO DERIVATIVES. 91 
 
 156 pts. cone, sulphuric acid. The product is poured into 
 water (when it solidifies) and washed. 
 
 Pure metadinitrobenzene forms well-defined, almost 
 colourless, needle-shaped crystals, which melt at 89*8, 
 and dissolve in 17 pts. of alcohol at the ordinary tempera- 
 ture, while in boiling alcohol the compound dissolves very 
 readily. It boils at 297. Dinitrobenzene is used chiefly 
 in the manufacture of phenylene diamine (for Bismarck 
 brown) . 
 
 f PIT 
 Nitrotoluenes, C 6 H 4 |^-Q 3 . By the action of concentrated 
 
 nitric acid on toluene the three isomeric nitrotoluenes 
 (ortho, meta, and para) are formed. The ortho and para 
 compounds are the chief products of the reaction, while of 
 the meta compound a small quantity only is formed. The 
 relative quantities of ortho and para nitrotoluerie formed 
 by the direct action of nitric acid depend to a great 
 extent upon the concentration of the latter. The manu- 
 facture on the large scale is effected by allowing 10 pts. 
 toluene to flow gradually into a mixture of 10 pts. cone, 
 nitric acid and 15 pts. cone, sulphuric acid, contained in a 
 vessel provided with a stirrer. The product of the re- 
 action is washed and subjected to fractional distillation. 
 In this manner the commercial ortho and para nitro- 
 toluenes are obtained. 
 
 {PTT (~\ ^ 
 3 ) (, is liquid, and 
 JNOo (2) 
 
 223. 
 
 M etanitrotoluene, C G H 4 < 3 ^ ^ melts at 16, and boils 
 at 230-231. 
 
 c CH f i) 
 
 Paramtrotoluene.LfiH., 1 ^3>,(,forms colourless prisms 
 4 (.NOoW 
 
 which melt at 54 and boil at 236. 
 
 Dinitrotoluenes, CgH 3 (CH 3 ) (N0n) 3 . According to theory, 
 
92 -COAL-TAR COLOURS, 
 
 four isomeric dinitrotoluenes exist, but of these the fol- 
 lowing only is of commercial importance : 
 
 (1) 
 Alpha-dinitrotoluene, C 6 H 3 < N(X (2). This compound is 
 
 formed by the action of nitric acid (in excess) on toluene. 
 It forms long yellowish, needle-shaped crystals, which melt 
 at 71. 
 
 Nitroxylenes, C 6 H 3 (CH 3 ) 3 (NOo). 
 
 According to theory, six isomeric nitroxylenes are 
 possible. The most important (commercially) of these is 
 the 
 
 (CH 3 (1) 
 Alplia-nitrometaxylene, C 6 H 3 <CH 3 (3). It forms the 
 
 ( NO, (4) 
 
 chief product of the action of nitric acid or metaxylene ; 
 it boils at 238. 
 
 Dinitrometaxylene 
 
 (CH S (1) 
 
 /~1 TT ) C-H..5 (o) 
 
 CcH ^N0 2 (4)' 
 
 is obtained by the action of excess of nitric acid on 
 metaxylene. 
 
 Nitronaplitlialenes, C 10 H 2 (NOo) . 
 
 According to theory, two isomeric mononitronaphtha- 
 lenes are possible ; viz., the alpha and the beta compound. 
 The first of these is of commercial importance. It is 
 obtained by the direct action of nitric acid on naphthalene, 
 and forms fine yellow shining crystals, which melt at 61. 
 The boiling point is 304. 
 
AMIDO DERIVATIVES. 93 
 
 Amido derivatives. 
 
 The aromatic amido derivatives, or amines, form the 
 most important class of coal-tar raw products used in the 
 manufacture of colouring matters. They may all be re- 
 garded as derivatives of ammonia 
 
 /H 
 
 N-H, 
 \H 
 
 and are formed by replacing one, two, or all three of the 
 hydrogen atoms in this compound by organic radicals. 
 The amines are of three kinds. The primary amines con- 
 tain two replaceable hydrogen atoms, the secondary amines 
 one, while in the tertiary amines all the hvdrogen atoms 
 are replaced by organic radicals. The following may 
 serve as examples : 
 
 /CH, 
 
 /CH 3 
 
 /CH 3 
 
 N-H ' 
 
 N-CH 3 
 
 N-CH 3 
 
 \H 
 
 \H 
 
 \CH 3 
 
 Methylamine. 
 
 Dimetliylamine. 
 
 Trimethylamine. 
 
 (Primary.) 
 
 (Secondary.) 
 
 (Tertiary.) 
 
 In place of methyl (CH 3 ) any other organic radical can 
 be substituted ; e.g., ethyl (CoH 3 ), phenyl (C 6 H 5 ), benzyl 
 (C 7 H 7 ), etc. 
 
 In the amines, therefore, the nitrogen is always in 
 direct combination with carbon and hydrogen, or with 
 three carbon atoms. The group NH which is contained 
 in the secondary amines is known as the Imido group. 
 
 The amido compounds are (with the exception of 
 triphenylamine) of a basic character and combine with 
 acids to form salts. The primary diamines contain two 
 'NHo groups, the triamines, three. 
 
 The aromatic amines are usually prepared by the re- 
 duction of the nitro compounds, in one or two instances 
 
94 COAL-TAR COLOURS. 
 
 also by redaction of the nitroso compounds by nascent 
 hydrogen 
 
 C 6 H 5 NOo + 3H 3 - 2H.O + C 6 H 5 NH 2 
 Nitrobenzene. Aniline. 
 
 This may be effected 
 
 (1) With tin and hydrochloric acid. 
 
 (2) ,, iron and acetic acid. 
 
 (3) ,, hydrochloric acid. 
 
 (4) ,, sulphuretted hydrogen in ammoniacal alcoholic 
 
 solution. 
 
 Of these methods, 3 and 4 only are used on the 
 large scale, the first for the complete reduction, the last 
 for the partial reduction, of the nitro compounds. 
 
 Amido compounds are also formed by the action of 
 ammonia on the phenols at high temperatures 
 
 C 10 H 2 OH + NH 3 = C 10 ] H 
 
 Naphthol. Naphthylarnine. 
 
 Primary amines. 
 
 Aniline, or phenylamine, C 6 H 5 NH 2 , commercially known 
 as "aniline oil," was first discovered by Unverdorben in 
 1826, who obtained it, among other substances, by the dry 
 distillation of indigo. Aniline is a constituent of coal-tar, 
 but occurs there in such small quantities that its isolation 
 could not be made to pay. 
 
 The manufacture of aniline on the large scale is effected 
 by reducing nitrobenzene with iron and hydrochloric acid. 
 The operation is carried out in large cast-iron cylinders 
 provided with stirrers. The materials are used in about 
 the following proportions : 40 pts. water, 25 pts. iron 
 borings, and 8-10 pts. hydrochloric acid, are placed in the 
 apparatus, and 100 pts. nitrobenzene are allowed to now 
 
AMIDO DERIVATIVES. 95 
 
 in, the stirrer being in motion. The contents of the 
 \-essel are then heated by means of steam, in order to 
 start the reaction. The rest of the iron (85-100 pts.) is 
 then added gradually during eight hours. When all the 
 nitrobenzene has become converted into aniline, slaked 
 lime is added to the contents of the apparatus, in order to 
 liberate all the aniline, which is ultimately blown off by 
 a powerful current of steam. 
 
 Aniline forms a colourless oily liquid with a peculiar, 
 not disagreeable, smell. It boils at 182, and has a specific 
 gravity at 15 of T0265. Aniline dissolves at the ordinary 
 temperature in 31 times its weight of water, and mixes 
 in all proportions with alcohol, ether, and other ordinary 
 solvents. When exposed to air and light, it soon tarns 
 brown. Aniline possesses a burning taste, and acts when 
 taken internally as a powerful poison. By the action of 
 oxidising agents, aniline is transformed into various 
 colouring matters, many of which possess great com- 
 mercial importance and will be referred to again. 
 
 Commercial " aniline oil " comes into commerce in four 
 different qualities, which are known as 
 
 1. Aniline oil for blue and black. 
 
 2. ,, for red (magenta). 
 
 3. ,, ,, safranine. 
 
 4. Liquid toluidine. 
 
 The first of these is almost chemically pure aniline. It 
 is used principally for aniline black and for the pre- 
 paration of dimethylaniline, diphenylamine, quinoline, 
 phenylhydrazine, sulphanilic acid, and induline. Aniline 
 for black is usually tested by fractional distillation ; 90 
 per cent, should pass over up to 182 C. 
 
 Aniline combines with the acids to form well char- 
 acterised salts which contain one equivalent of acid. Of 
 these, the hydrbchloride only possesses commercial im- 
 
96 COAL-TAR COLOURS. 
 
 portance. ^Aniline JiydrocJdoride, C 6 H 5 NH 3 'HC1,* com- 
 mercially known as " aniline salt," is obtained by mixing 
 pure aniline (100 pts.) with strong hydrochloric acid 
 (130-135 pts.) in stone-ware vessels. The salt is allowed 
 to crystallise out, and is freed from the mother liquors by 
 centrifugal force. Aniline hydrochloride forms colourless 
 crystals, which are easily soluble in water and alcohol and 
 which sublimate at 192. With platinum chloride it forms 
 a double salt (C 6 H 5 NH 2 HC1) 2 PtCl 4 , which is sometimes 
 used in the quantitative determination of aniline. 
 
 Aniline salt is used in the dyeing and printing of aniline 
 black. 
 
 Acetanilide, C f) H 5 .NH.C;,H 3 0. If aniline is mixed with 
 glacial acetic acid, acetate of aniline is formed, but if 
 the mixture is boiled for some hours, a further change 
 takes place and acetanilide is formed, while at the same 
 time water is evolved 
 
 C 6 H 5 NH 3 .C 2 H 4 3 = H 3 + C 6 H 6 NH.C S H 8 
 
 Aniline acetate. Acetanilide. 
 
 Acetanilide forms colourless crystals, which melt at 
 115. It boils without decomposition at 295. It is used 
 in the manufacture of flavaniline. 
 
 Diamidobenzenes, C 6 H J: (NH:,) 2 . 
 
 The three isomeric diamidobenzenes which are possible 
 according to theory are formed by the complete re- 
 duction of the corresponding dinitrobenzenes. 
 
 * In the free ainine bases the nitrogen is triatomic, but in, their 
 salts it usually becomes pentatomic (as is ammonia salts). The 
 formula of aniline hydrochloride might therefore be represented 
 graphically thus 
 
 /H 
 
 N-H 
 
 \H 
 
 \C1 
 
AlllDO DERIVATIVES. 97 
 
 The most important of these is the metapliemjlene- 
 diamine, which is formed by the complete reduction of 
 ordinary (meta) dinitrobenzene with iron and hydro- 
 chloric acid. It forms colourless crystals, which melt at 
 63 and dissolve easily in water. It boils at 287. Meta 
 phenylenediamine is used in the manufacture of chryso- 
 idine and Bismarck brown. 
 
 ParapJienylenediamine is obtained by the reduction of 
 paranitraniline (from paranitroacetanilide). It forms 
 crystals, which melt at 147 and dissolve easily in water. 
 When melted with sulphur it forms a thio compound 
 which yields on oxidation Lauth's violet. 
 
 {flTT 
 VTTT 8 ' 
 JNJ1 2 
 
 The three isomeric toluidines may be obtained by the 
 reduction of the corresponding pure nitrotoluenes. Com- 
 mercial toluidine consists essentially of ortho and para- 
 toluidines ; metatoluidine occurs only in very small 
 quantities and has little or no commercial interest. The 
 separation of ortho and paratoluidine may be effected in 
 several ways. 
 
 According to one method, the mixture of the bases is 
 partially saturated with oxalic or sulphuric acid, and 
 that which is left uncombined is driven over with steam. 
 The principle of the method is that the paratoluidine 
 combines with the acid first, and the orthotoluidine con- 
 sequently distills over in the subsequent distillation. 
 
 According to another method, which has for its object 
 the 'separation of orthotoluidine from paratoluidine and 
 aniline, the mixture of the bases is neutralised with 
 hydrochloric acid and mixed with a solution of phosphate 
 of soda in excess. The contents of the vessel solidify, 
 forming a crystalline paste, which dissolves on heating, 
 the orthotoluidine floating to the surface as an oily layer, 
 which is removed. On cooling the aqueous solution, the 
 
 H 
 
98 COAL-TAR COLOURS. 
 
 aniline and paratoluidine separate out completely as 
 phosphates, while a small quantity of phosphate of 
 orthotoluidine remains in the mother liquor. The bases 
 are now liberated by means of caustic soda, whereby the 
 
 phosphate of soda is regenerated. 
 ( PTT f\\ 
 Orthotoluidine, C c Hj. j -\r-tT 3 /ov forms a colourless liqnid, 
 
 which boils at 19 7-1 9 7' 5. Its specific gravity at 15 is 
 0'9978. It becomes brown when exposed to light and 
 air, and dissolves in water in about the same proportion 
 as aniline does. Orthotoluidine is a constituent of all 
 commercial aniline oils except that which is used for 
 black. In the pure state it is used in the manufacture of 
 some azo dyes. 
 
 ( C 1 TT C\ ^ 
 Metatoluidine, C 6 H 4 j -^^ L<, is a colourless oil, which 
 
 boils at 197. 
 
 ( PTT fl ^ 
 
 Paratoluidine , C 6 H 4 < -^^ Jr^<j, forms colourless leaf- 
 shaped crystals, which melt at 45 ; it boils at 198. It 
 is only sparingly soluble in water, but dissolves easily in 
 alcohol and ether. It is used in the manufacture of 
 magenta. 
 
 Commercial products containing toluidine. 
 
 Aniline oil for red. The aniline oil used in the manu- 
 facture of magenta consists of a mixture of the two 
 toluidines (ortho and para) and aniline in about the 
 proportion of one molecule of each. Its specific gravity 
 may vary in oils destined to be used in the arsenic acid 
 process from T001 to I'OIO. 
 
 Aniline oil for safranine. This product is the distillate 
 (echappe) obtained in the manufacture of magenta. It 
 consists essentially of aniline and orthotoluidine, and 
 only contains a comparatively small quantity of para- 
 toluidine. 
 
AMIDO DERIVATIVES. 99 
 
 Liquid toluidine consists of a mixture of ortho and 
 paratoluidine. It boils at 197-199. 
 
 Tolylenediamines, C 6 H 3 (CH 3 ) (NH 3 ) 3 . 
 
 Of the six isomeric tolylenediamines possible accord- 
 ing to theory, only five are known, and of these the most 
 important is 
 
 (CH 3 (1) 
 Alphatolylenediamine, C 6 H 3 < NH (2). This com- 
 
 (NH; (4) 
 
 pound is formed by the reduction of ordinary (1,2,4) 
 dinitro toluene. It forms colourless crystals, which melt 
 at 99, and dissolve easily in water. It is used, like 
 metaphenylenediamine, in the manufacture of chrysoidine 
 and Bismarck brown. 
 
 Amidoxylenes, or xylidines, C 6 H 3 (CH 3 ) 2 (NH 2 ). 
 
 According to theory, six isomeric xylidines are possible, 
 of which two are derived from orthoxylene, two from 
 metaxylene, and one from paraxylene. 
 
 Commercial xylidine contains one amidoparaxylene, two 
 amidoorthoxylenes, and two amidometaxylenes. It forms 
 an oily liquid, which boils between 211 and 219. Xyli- 
 dine is used almost exclusively in the manufacture of the 
 azo dyes. 
 
 Cumidines, C G Ho (CH 3 ) 3 
 
 According to theory, six isomeric amidotrimethyl- 
 benzenes are obtainable, of which only two have been 
 properly investigated. 
 
 Commercial cumidine 
 
 CH 3 C 1 ) 
 CH 3 (3), 
 
 3 (4) 
 
 , (6) 
 
100 COAL-TAR COLOURS. 
 
 is obtained by heating xylidine hydrochloride with 
 methyl alcohol in closed vessels to about 300. 
 
 p TT _ 
 Dipara-amidodiplienyl (JBenzidine), \ 
 
 CH. 
 
 This base, which was first obtained by Zinin in 1845, 
 did not possess practical interest until the discovery of 
 chrysamine and Congo red. 
 
 It is obtained by the reduction of azobenzene with 
 stannous chloride in alcoholic solution, or by treating a 
 solution of hydrazobenzene in warm hydrochloric acid 
 with sulphurous acid. In the pure state it forms colour- 
 less shining crystals, which melt at 122, and are almost 
 insoluble in water. The sulphate is very sparingly 
 soluble in water. 
 
 f 1 IT fPTT ^ 1VTT 
 Diamidoditolyl (tolidine), < 3V 3 ' *, is obtained 
 
 C (i H 3 (CH 3 )NH 2 
 
 from orthohydrazotoluene, and forms colourless crystals, 
 which melt at 128. It is used, like the preceding com- 
 pound, in the manufacture of azo dyes. 
 
 Amidonaphthalenes, or Naphthylamines, C 10 H 7 NH 2 . 
 
 The two isomeric amidonaphthalenes possible according 
 to theory are both known, and are of commercial im- 
 portance. 
 
 Alplianaplitliylaiiiine, C 10 H 7 NH 2 , is obtained by the re- 
 duction of alphanitronaphthalene with iron and hydro- 
 chloric acid. It forms colourless crystals, which possess 
 a disagreeable smell, and which melt at 50 ; the boiling 
 point is 300. With acids it combines to form well 
 characterised salts, the aqueous solutions of which yield 
 with mild oxidising agents a blue precipitate of naph- 
 thamein. Alphanaphthylamine is used in the manu- 
 facture of azo dyes, naphthol yellow, and Magdala red. 
 
 Betanaphtliylamine, C 10 H 2 NH 2 . This amine is ob- 
 
AMIDO DERIVATIVES. 101 
 
 tained on the large scale by heating the corresponding 
 phenol or hydro xy compound with ammonia to a high 
 temperature in closed vessels. The phenol used in this 
 c ise is betanaphthol, and the reaction is expressed by the 
 equation : 
 
 C 10 H 7 OH + NH 3 - H 2 + C 10 H 3 NH 3 . 
 
 Betanaphthol. Betanaphthylamine. 
 
 On the large scale, the following directions may be 
 adhered to: 10 pts. betanaphthol are intimately mixed 
 with 4 pts. caustic soda, and 4 pts. sal ammoniac, 
 and heated for 60-70 hours in closed vessels to 150- 
 160. 
 
 Betanaphthylamine forms colourless crystals, which 
 melt at 112, and are devoid of smell. It is used chiefly 
 in the manufacture of certain red azo dyes. 
 
 Secondary amines. 
 
 As has already been pointed out, the secondary amines 
 may be regarded as derivatives of ammonia, NH 3 , in 
 which two hydrogen atoms have been replaced by organic 
 radicals. They are formed in many ways, but the two 
 chief reactions by means of which they are obtained on 
 the large scale are the following : 
 
 1. By heating equal molecules of a primary amine and 
 its hydrochloride 
 
 o + C 6 H 5 NH 2 -HC1 = NH 4 C1 + NH (C 6 H 5 ) 2 . 
 Aniline. Aniline hydrochloride. Diphenylamine. 
 
 2. By heating primary aromatic amines with the 
 chlorides of the alcohol radicals (methylchloride, ethyl- 
 chloride, etc.) 
 
 CH 3 C1 - HC1 + jra.CgHjCHg 
 
 Aniline. Methylaniline. 
 
102 COAL-TAR COLOURS. 
 
 On the large scale a modification of this reaction is 
 employed, and in place of using the chloride of the alcohol 
 radical the hydrochloride of the amine is heated with 
 the alcohol in presence of zinc chloride 
 
 3 OH = NH.C C H 5 .CH 3 + HC1 + H 2 0. 
 Aniline hydrochloride. Methylaniline. 
 
 The zinc chloride employed simply plays the part of 
 a dehydrating agent. 
 
 /C 6 H B 
 
 Monomethylaniline, C 6 H 5 NH.CH 3 . or N CH 3 , is obtained 
 
 \H 
 
 on the large scale by heating together equal molecules 
 of aniline hydrochloride and methyl alcohol to 200. It 
 forms a colourless liquid, which boils at 192, and has a 
 specific gravity at 15 of 0'976. 
 
 Monoetliylaniline, C 6 H 5 NH.CoH 5 , is obtained in an 
 analogous manner to that used for the preceding com- 
 pound. It boils at 204, and has a specific gravity at 
 18 of 0-954. 
 
 Diphenylamine, NH(C 6 H 5 ) 2 . On the large scale this 
 compound is obtained by heating equal molecules of ani- 
 line and aniline hydrochloride to 220-230 in closed vessels. 
 It forms colourless crystals, which melt at 54, and which 
 possess an agreeable smell, somewhat similar to that of 
 violets. Diphenylamine is a weak base, the salts being 
 decomposed by water. It is used in the manufacture of 
 diphenylamine blue, diphenylamine orange, and auraniia. 
 
 Tertiary amines. 
 
 If all three hydrogen atoms in ammonia are replaced 
 by organic radicals, tertiary amines are formed. This 
 may be effected in the aromatic series by heating the 
 
AMIDO DERIVATIVES. 103 
 
 primary amines with the chlorides of methyl, ethyl, 
 propyl, etc. 
 
 C 6 H 5 NH 2 + 2 CH 3 C1 = C 6 H 5 (CH 3 ),N + 2HC1. 
 Aniline. Dimetbylaniline. 
 
 According to another method, the hydrochlorides of 
 the amines are heated with the fatty alcohols and zinc 
 chloride 
 
 C 6 H 5 NH 2 .HC1 + 2C i H 5 OH = C H 5 (C 2 H 5 ) 3 N + HC1 + 2H 3 0, 
 Aniline hydrochloride. Diethylaniline. 
 
 The most important of the tertiary amines are : 
 
 Dimethylaniline, C G H 5 N(CH 3 ) 2 . For the preparation on 
 the large scale, aniline and caustic soda are mixed in a 
 closed vessel provided with a stirrer and pressure gauge. 
 The contents of the vessel are heated to 100, and the 
 calculated quantity of methyl chloride is allowed to flow 
 in, care being taken not to allow the pressure to exceed 
 six atmospheres. 
 
 According to another method also employed 011 the 
 large scale, 100 pts. aniline hydrochloride are treated 
 with 50-80 pts. methyl alcohol, in closed enamelled vessels, 
 to 180-200. The dimethylaniline obtained according to 
 this method contains more bye-products than that ob- 
 tained by the preceding method. 
 
 Dimethylaniline is a colourless liquid, which solidifies 
 at 0*5 and boils at 192. Its specific gravity at 15 is 
 0'96. It may be readily recognised by its property of 
 forming methyl-violet, when heated with mild oxidising 
 agents, such as copper chloride. Dimethylaniline is a 
 very important commercial article, since it forms the 
 chief raw material for the manufacture of a large number 
 of coal-tar colours, including methyl-violet, crystal-violet, 
 malachite green, auramine, Victoria blue, etc. 
 
104 COAL-TAR COLOURS. 
 
 NitrosodimethylaniUne^^ j ^ CH ^ 2 ffi, is formed by 
 
 the action of nitrous acid on dimethylaniline. For its 
 preparation 10 pts. dimethylaniline are dissolved in 
 30 pts. hydrochloric acid and 200 pts. water. To the 
 cooled solution a cold solution of 5*7 pts. sodium nitrite 
 in 200 pts. water is added. 
 
 The free base forms green leaf-shaped crystals, which 
 melt at 92, and dissolve in water with a yellow colour. 
 The salts are yellow. By reducing agents, nitrosodi- 
 methylaniline is converted into para-amidodimethylaniline, 
 which on oxidation in presence of sulphuretted hydrogen 
 yields methylene blue. When acted upon by phenols it 
 yields a series of basic colours, which range from blue to 
 violet, and are known, according to the discoverer, as 
 Meldolas colours. Another colouring matter, known as 
 gallocyanin, is obtained by heating together in solution 
 nitrosodimethylaniline and tannic acid. 
 
 Diethylaniline, C 6 H 5 ]S r (CoH 5 ).,, is formed by the action 
 of ethylchloride on aniline, or by heating aniline hydro- 
 chloride with ethyl alcohol under pressure. 
 
 It forms a colourless liquid, which boils at 213'5 and 
 has a sp. gravity of 0'936 at 18. Its use is analogous 
 to that of dimethylaniline. 
 
 Methyldiphenylamine, (C 6 H 5 ) 2 N.CH 3 , is formed by heat- 
 ing diphenylamine hydrochloride with methyl alcohol 
 under pressure to 250-300. It forms a colourless oil, 
 which boils at 282, and which yields, when treated with 
 oxidising agents, colours ranging from blue to violet. 
 Heated with oxalic acid it forms methyldiphenylamine 
 blue. 
 
 Pyridine bases. 
 
 These basic substances are found in coal-tar and in large 
 quantities in the tar obtained by the distillation of animal 
 substances (animal oil). Their simplest representative 
 
PYEIDINE AND QUINOLINE. 105 
 
 is pyridine itself, a body which possesses the empirical 
 formula C 5 H 5 N. According to Kdrner (and this view has 
 since been generally adopted), pyridine may be regarded 
 as a benzene, in which one CH group has been replaced 
 by an N atom, and the constitutional formula would there- 
 fore be : 
 
 C 
 
 / ^ 
 C C 
 
 II I 
 
 C C 
 
 \ // 
 
 N 
 
 Pyridine forms a colourless oil, which boils at 116, and 
 possesses a penetrating smell. Its homologue, methyl- 
 pyridine, or picoline, C-H^N.CHg, forms, according to 
 theory, three isomers, two of which only are known. 
 
 These substances possess very little interest in the coal- 
 tar colour industry. 
 
 Quinoline, C 9 H 7 N. 
 
 . Quinoline bears the same relationship to naphthalene 
 as pyridine to benzene. Its constitutional formula is 
 represented thus : 
 
 H H 
 
 C C 
 
 / ^ / ^ 
 
 HO C CH 
 
 II I I 
 
 HC C CH 
 
 \ // \ // 
 
 C N 
 
 H 
 
 It is contained in coal-tar, and may be isolated from 
 that portion of the heavy oil which is soluble in sulphuric 
 
106 COAL-TAR COLOURS. 
 
 acid. Quinoline is obtained, according to Skraup's 
 synthesis, by the action of aniline and sulphuric acid on 
 glycerin in presence of nitrobenzine 
 
 C H S NH 3 + C 3 H 5 (OH) 3 + = C 9 H 7 N + 4H 2 0. 
 
 Aniline. Glycerin. Quiuoline. 
 
 It forms a colourless oily liquid, which boils at 238 
 and has a sp. gravity of T094 at 20. With the acids 
 it forms usually well characterised salts. 
 
 Quinoline is used in the manufacture of quinoline Hue 
 (cy&nw) t quinoline red and. quinoline 2/eZZow(quinophthalon). 
 
 Quinaldine, or methylquinoline, C 9 H C N".CH ;5 , occurs 
 along with quinoline in coal-tar. The methyl group is in 
 the ortho position to the N atom. It can also be obtained 
 synthetically. 
 
 Acridine, C 13 H 9 N, bears the same relationship to anth- 
 racene as quinoline to naphthalene. It is almost invari- 
 ably a constituent of crude anthracene. 
 
 Diazo compounds. 
 
 These peculiar substances are only known in the 
 aromatic series. They all contain the group -N:N- which 
 is combined on the one side with a carbon atom of the 
 benzene (naphthalene, etc.) ring, on the other with an 
 acid radical or with a basic radical. 
 
 The diazo compounds are formed by the action of 
 nitrous acid on the salts of the amido compounds in the 
 cold. Formerly this was effected by passing nitrous 
 fumes (from nitric acid and arsenious oxide) into the 
 solution of the sulphate or chloride of the amine, but 
 at present the calculated quantity of nitrite of soda and 
 sulphuric acid are added. The formation of the nitrous 
 acid is shown by the equation : 
 
 2NaN0 3 + H 2 S0 4 - 2H1S T 3 + Na 2 S0 4 . 
 
DIAZO COMPOUNDS. 107 
 
 This latter method is much more convenient than the 
 old one, since, in the first place, no special apparatus is 
 required ; and secondly, the amount of nitrous acid required 
 can be accurately gauged. On the large scale ice is 
 usually added during the operation, or the liquid is 
 cooled by other artificial means. The following equation 
 expresses the formation of one of the simplest diazo com- 
 pounds : 
 
 2 .HC1 + HN0 3 = C G H 5 .N: N- Cl + 2H 2 0.. 
 Aniline hydrochloride. Diazobenzene chloride. 
 
 The free diazo compounds are very unstable, and their 
 salts, especially the nitrates, are in the dry state extremely 
 explosive. They are never prepared on the large scale 
 in the dry state, this being unnecessary. They are 
 formed in solution, and are converted as a rule without 
 delay into the corresponding oxyazo or amidoazo dyes. 
 
 When boiled in acid solution they are converted into 
 the corresponding phenols with evolution of nitrogen 
 
 C 6 H 5 N : KC1 + HoO - HC1 + N 2 + C 6 H 5 OH. 
 Azobenzene chloride. Phenol. 
 
 When treated in solution with the salts of the amido 
 compounds, the diazo compounds yield amidoazo com- 
 pounds 
 
 C 6 H 5 N:NC1 + C G H 5 NH 2 HC1 
 
 Azobenzene chloride. Aniline hydrochloride. 
 
 = C fl H 5 N : KC 6 H 4 lSrHo-HCl + HC1. 
 Amidoazobenzene hydrochloride. 
 
 With the phenols in alkaline solution oxyazo com- 
 pounds are formed 
 
 C 6 H 5 N:]SrCl + C fl H B OK = KC1 + C C H 5 N:NC 6 H 4 OH. 
 
 The two latter reactions are of great importance in the 
 manufacture of the azo dyes. 
 
108 COAL-TAR COLOURS. 
 
 Hydrazines. 
 
 The hydrazines are derived from the hypothetical 
 radical NH 2 NH 2 . The only compound of this class 
 which appears to possess commercial importance is 
 
 Phenylhydrazine, NH 2 - NH - C 6 H 5 . It is obtained by 
 reducing diazobenzene chloride in solution either with 
 sodium sulphite and zinc dust, or with an acid solution of 
 stannous chloride. Phenylhydrazine forms in the freshly 
 prepared state a colourless oil possessing an aromatic 
 odour. It melts at 23 and boils at 233-234. The 
 hydrochloride NHo-NH-C c H 5 . HC1 crystallises in fine 
 colourless leaflets. 
 
 The Azo compounds. 
 
 The azo compounds contain the group - N" : N" which is 
 combined on both sides with carbon atoms of the benzene 
 ring; e.g., azobenzene, C C H 5 -N: jS"-C G H-. The simple azo 
 compounds are obtained by the reduction of the primary 
 amines in alkaline alcoholic solution 
 
 2C c H 5 NOo + 4H 2 - C 6 H S N:N.C 6 H 3 + 4H 2 0. 
 
 By treating the diazo compounds in solution with salts 
 of the amido compounds, or of the phenols, the amidoazo 
 compounds and oxyazo compounds are obtained. This 
 method, which has already been alluded to in speaking of 
 the diazo compounds, is of great technical importance, 
 since it forms the basis of the manufacture of the azo 
 dyes. 
 
 The azo compounds are characterised by their great 
 stability as compared with the diazo compounds. They 
 are not changed by boiling in either acid or alkaline 
 solution, and are not explosive. Some of them can even 
 be distilled without undergoing decomposition. By mild 
 
SULPHONIC ACIDS. 109 
 
 reducing agents they are converted into the hydrazo com- 
 pounds 
 
 C 6 H 5 tf :NC 6 H 5 + H 2 + C 6 H 5 NH - NHC 6 H 5 . 
 Azobenzene. Hydrazobenzene. 
 
 Strong reducing agents convert the -N:N- group into 
 two amido groups. In this manner amidoazo compounds 
 yield a monamine and a diamine 
 
 C G H 5 N :N.C 6 H 4 NH S + 2H 2 - C r H 5 lS T H 2 + C 6 H 4 (NH 2 ) 2 . 
 Amidoazobenzene. Aniline. Phenylenediamine. 
 
 Oxyazo compounds yield under similar circumstances 
 an amine and an amido phenol 
 
 C 6 H 5 .N:NC 6 H 4 OH + 2H 2 - C 6 H 5 NH 2 + C 6 H 4 NH 2 OH. 
 Oxyazobenzene. Aniline. Amidophenol. 
 
 This latter reaction is sometimes employed in finding 
 the composition of azodyes. 
 
 The Sulphonic acids. 
 
 The aromatic sulphonic acids contain the group S0 3 H 
 in combination with one of the carbon atoms of the ben- 
 zene ring. They are obtained almost exclusively by 
 treating the aromatic hydrocarbons or their derivatives 
 with strong sulphuric acid. Sometimes fuming sulphuric 
 acid is used for the purpose. According to temperature 
 and duration of the operation, either mono or disulphonic 
 acids are formed 
 
 C 6 H 6 + H 2 S0 4 = C 6 H 5 .S0 3 H + H 2 0. 
 Benzene. Benzene monosulphonic acid. 
 
 C 6 H 6 + 2H 2 S0 4 C 6 H 4 (S0 3 H) 2 + 2H 3 0. 
 
 Benzenedisulphonic acid. 
 
 The trisulphonic acids are as a rule difficult to obtain, 
 and are not of much commercial value. 
 
HO COAL-TAR COLOURS. 
 
 The conversion of the aromatic compounds into sul- 
 phonic acids is technically known as the sulplionation. and 
 the resulting substances are sometimes known as sul- 
 phonated products. Amines and phenols are as a rule 
 more readily acted upon by sulphuric acid that the hydro- 
 carbons. Amidosulphonic acids can sometimes be 
 obtained even by heating the sulphate to about 180. In 
 the majority of cases the free sulphonic acids are not 
 prepared, but in their place the sodium salts. The 
 following is the general method followed for their isola- 
 tion : 
 
 After the action of the strong or fuming sulphuric 
 acid has proceeded sufficiently far,* the product is poured 
 into water, and the free sulphuric acid removed by satu- 
 rating the liquid with barium carbonate, lead carbonate, 
 chalk or milk of lime. On the large scale chalk or 
 milk of lime are preferred for cheapness sake. The greater 
 part of the free sulphuric acid is thus precipitated as 
 gypsum, while the sulphonic acid combines with the lime 
 to form a soluble lime salt. The liquid is now filtered 
 hot, and the lime salt converted in the nitrate into the 
 soda salt by the addition of the necessary amount of 
 sodium carbonate. The following example (preparation 
 of benzene monosulphonate of soda) will serve to illus- 
 trate the reactions which take place : 
 
 HoS0 4 (in excess) 
 
 2<5 6 H 5 S0 3 H + Ca(OH) 2 = Ca(C 6 H 5 S0 3 ) 2 + 2H 2 0. 
 
 Benzene monosulphonate of calcium. 
 Ca(C 6 H 5 S0 3 ) 2 + Na 2 C0 3 = CaC0 3 + 2C 6 H 5 S0 3 tfa. 
 
 The liquid is now simply decanted or filtered from the 
 precipitated calcium carbonate and evaporated to dryness. 
 
 * If sulphurous acid is evolved during the process of sulplionation, 
 this is a sign that an oxidation and probably a more or less complete 
 destruction of the molecule is taking place. 
 
SULPHONIC ACIDS. Ill 
 
 The pure sulphonic acids are as a rule deliquescent 
 substances, difficult to crystallise, and not characterised 
 by definite melting or boiling points. In order to char- 
 acterise them, they are either converted into the corre- 
 sponding chlorides or amides. The chlorides are best 
 obtained by treating the free sulphonic acids with phos- 
 phorus pentachloride 
 
 C 6 H 5 S0 5 H + PC1 5 - C 6 H 5 S0 2 C1 + POC1 3 + HC1. 
 
 The amides are obtained by the action of ammonia on 
 the corresponding chlorides 
 
 CTT C1 f\ /""1 1 t "VT TT TT /~] 1 . /""I TT O f~\ "\T TT 
 G M 5 bU 2 L<l + JN M 3 = MUi + U 6 i 5 bU 2 lN -Ho- 
 
 Benzene monosulphonic acid, C 6 H 5 S0 3 H, forms colour- 
 less crystals, easily soluble in water and alcohol. By the 
 action of caustic soda at a high temperature it is con- 
 verted into phenol. With concentrated nitric acid it 
 yields the isomeric nitrophenols. Treated in aqueous 
 solution with nitrous acid it yields nitrosophenol. 
 
 Benzene disulphonic acids, C 6 H 4 (S0 3 H)o. All the three 
 isomers are known. By the direct action of sulphuric 
 acid (fuming) on benzene or benzene monosulphonic 
 acid a mixture of the meta and paradisulphonic acids is 
 obtained. This mixture is prepared on the large scale 
 for the manufacture of resorcin either by passing the 
 vapour of benzene into concentrated sulphuric acid heated 
 to 240, or by dissolving 1 pt. benzene in 4 pts. fuming 
 sulphuric acid, and heating the solution of the mono- 
 sulphonic acid obtained in this manner for two hours to 
 275. When treated with caustic soda both these pro- 
 ducts are converted into metadioxybenzene (resorcin). 
 
 Toluene also yields sulphonic acids, which are, however, 
 not of great importance. 
 
 Naphthalene monosulphonic acids, C 10 H 7 (S0 3 H). By 
 heating naphthalene with an equal weight of concentrated 
 
112 COAL-TAR COLOURS. 
 
 sulphuric acid both alpha and betanaphthalene mono- 
 sulphonic acids are formed. By regulating the tempera- 
 ture it is possible to produce the one or the other of these 
 isomers in excess. Thus if the sulphonation is carried 
 out at 100 the product contains about 80 per cent, of 
 the alpha sulphonic acid and 20 per cent, of the beta 
 acid, whereas at a temperature of 160-170 about 75 per 
 cent, of the beta acid and 25 per cent, of the alpha acid 
 are obtained. The separation of the two products on the 
 large scale is based upon the different solubility of their 
 lime or lead salts, those of the beta acid being sparingly 
 soluble in water, while those of the alpha acid are easily 
 soluble. When melted with caustic soda the alpha acid 
 yields alphanaphthol, the beta acid betanaphthol. 
 
 Alphanaphthalene sulphonic acid, C 10 H 7 (S0 3 H) (a), 
 forms a crystalline deliquescent mass, which melts at 
 85-90. Heated to 180 with dilute sulphuric acid it 
 is resolved into naphthalene and sulphuric acid. When 
 treated with concentrated sulphuric acid it is converted 
 into the isomeric beta acid. 
 
 Betanaphthalene sulphonic acid, C 10 H 7 (S0 3 H) (/?), 
 forms leaf-shaped crystals, which do not deliquesce. 
 
 Nitrosulphonic acids, The three isomeric benzene nitro- 
 sulphonic acids are formed simultaneously when nitro- 
 benzene is treated with fuming sulphuric acid, or when 
 benzene monosulphonic is treated with concentrated nitric 
 acid. The chief product of the reaction is in either case 
 metanitrobenzene sulphonic acid. 
 
 By the sulphonation of the nitronaphthalenes, or the 
 nitration of the naphthalene sulphonic acids, several 
 isomeric nitronaphthalene sulphonic acids have been 
 obtained. 
 
 Amidosulphonic acids. The amidosulphonic acids are 
 formed : 
 
 1. By the direct action of strong sulphuric acid on the 
 amines. 
 
AM1DOSULPHONIC ACIDS. 113 
 
 2. In some cases by simply heating the sulphates of 
 the amines to 180-230. 
 
 3. By the reduction of the nitrosulphonic acids in acid 
 solution. 
 
 Amidobenzene sulphonic acids, CgH^ < ~ _ ^ All the 
 
 (. oUgll. 
 
 three isomers are known. The meta and para com- 
 pounds are of technical importance. 
 
 Meta-amidobenzene sulplionic acid, C fi H 4 5 ~ * > ( is 
 
 ( b(J 3 i (6) 
 
 obtained by the reduction of the corresponding nitro- 
 benzene sul phonic acid with iron and dilute sulphuric acid. 
 In the anhydrous state it forms long, fine, needle-shaped 
 crystals, while from aqueous solution it crystallises with 
 1J mol. H 2 in clinorhombic crystals. 
 
 Para-amidolenzene sulplionic acid, C C H, * Qr > VT fA {, 
 
 C O<JgH (4s) 
 
 commonly known as sulplianilic acid, is obtained by heat, 
 ing aniline (1 pt.) with strong sulphuric acid (3 pts.) to 
 180-190. In the pure state it forms colourless crystals, 
 which contain one molecule of water of crystallisation, 
 which latter is given off on exposure to the air, the pro- 
 duct falling to a white powder. It is sparingly soluble 
 in water, and combines with both acids and bases to 
 form salts. 
 
 ids, C 6 H 3 j 
 
 CH 3 
 
 Amidotoluene sulplionic acids, C 6 H 3 <J NHo. The ortho- 
 
 S0 3 H 
 
 OzII) (1.2.5), 
 
 is obtained by the direct action of sulphuric acid on ortho- 
 toluidine, or by heating orthotoluidine sulphate to 200. 
 By the action of fuming sulphuric acid on paratoluidine 
 two isomeric sulphonic acids are formed. 
 
 Xylidine sulphonic acids, CgHo(CH 3 ) 2 NH 2 S0 3 H. Nu- 
 merous isomers are possible, but the only one which 
 
 I 
 
114 COAL-TAR COLOURS. 
 
 appears to possess technical importance is the product 
 obtained by treating the ordinary xylidine of commerce 
 (alpha-amidometaxylene) with concentrated sulphuric 
 acid. 
 
 Benzidine sulplionic acids. By heating benzidine with 
 fuming sulphuric acid, mono, di, tri, and tetra-sulphonic 
 acids are formed. If the temperature is kept below 120, 
 the chief product of the reaction is benzidine-sulphon, 
 
 2 g wh . ch ig conTerted at 150 _ 1CO o into sul . 
 C C H 3 NH 2 ) 
 
 phonic acids of benzidine sulphon, at higher temperatures 
 into benzidine sulphonic acids. 
 
 Amidonaphtlialene sulplionic acids. 
 
 The sulphonic acids of the two amidonaphthalenes can 
 be obtained either by the direct sulphonation of the bases, 
 or by heating the corresponding naphthol sulphonic acids 
 with ammonia under pressure. Sulphonic acids of alpha- 
 naphthylamine can also be obtained by the reduction of 
 the alphanitronaphthalerie sulphonic acids. The number 
 of possible isomers is very great. 
 
 Sulphonic acids of alpTianaplithylamine. By heating 
 alphanaphthylamine with from 3 to 5 times its weight 
 of strong sulphuric acid, or by heating alphanaphthyl- 
 amine sulphate to 200, a monosul phonic acid 
 
 C 10 H 6 (NH 2 )(SO s H)a r o 2 , 
 
 is obtained, which is known as Naphthionic acid (Piria's 
 acid). It is not easily soluble in water, and crystallises 
 with 1 mol. H 2 O in small shining needles. 
 
 In addition to Piria's acid, the following alphanaphthyl- 
 monosul plionic acids are also known* : 
 
 Nolting and Eeverdin, Lull de la Soc, wd. de Mullwuse^ 1887, 
 
AMIDOSULPHONIC ACIDS. 115 
 
 C 10 H 6 (NH 2 )(S0 8 H)a 1 -/? 1 by treating alphanaphthyl- 
 amine hydrochloride with fuming sulphuric acid in the cold 
 (Witt). 
 
 C 10 H G (NH 2 )(S0 3 H)a 1 =^ 1 . By reduction of the beta- 
 nitronaphthalene sulphonic acid (Cleve). 
 
 C 1() H G (NH 2 )(S0 3 H)a 1 = a 2 . By the reduction of the 
 alpha-nitronaphthalene sulphonic acid (Cleve). This is 
 the acid L of Schoellkopf & Co. 
 
 Two further isomers have been obtained by Cleve, by 
 the reduction of a nitronaphthalene sulphonic acid. Their 
 constitution is not known. 
 
 By treating alphanaphthylaraine or naphthionic acid 
 with fuming sulphuric acid, several isomeric alpha- 
 naphthylamine disulplionic acids are obtained, the con- 
 stitution of which is not known. 
 
 The sulphonic acids of betanaphthylamine are of more 
 importance in the manufacture of azo dyes than those of 
 alphanaphthylamine. The following are known : 
 
 C 10 H 6 (N"H 2 )(S0 3 H) ft- ttl . (Alpha acid.) By treating 
 betanaphthylamine with strong sulphuric acid (Bad. Anil, 
 und Soda Fab.) (Dahl & Co.), or by the action of ammonia 
 on the corresponding naphthol sulphonic acid. 
 
 C 10 H G (NH ) (S0 3 H) ft = ai . Acid y III. of Dahl & Co. 
 
 C 10 H 6 (NHo)(S0 3 H) ft -ft. (Delta acid.) From be- 
 tanaphthylamine and concentrated sulphuric acid at 170- 
 180 (Bayer & Duisberg), or by the action of ammonia on 
 Cassella's naphthol sulphonic acid. 
 
 C 10 H C (NH 2 ) (S0 3 H)ft -ft. Bronner's acid (beta acid) 
 from Schaeffer's betanaphtholsulphonic acid and ammonia. 
 
 Quinoline monosulphonic acid, C 9 H c N(SOoH). 
 
 By the action of fuming sulphuric acid on quinoline, 
 the ortho and meta sulphonic acids are formed. The para 
 compound is obtained by heating sulphanilic acid (100 
 pts.) with glycerin (120 pts.), concentrated sulphuric acid 
 
116 COAL-TAR COLOURS. 
 
 (150 pts.), and nitrobenzene (50-60 pts.). By heating the 
 two first monosulphonic acids with fuming sulphuric acid 
 to 200-240, two isomeric disulphonic acids, C 9 H 5 N(S0 3 H) 2J 
 are formed. 
 
 The phenols. 
 
 The phenols, sometimes known as oxy compounds, are 
 formed by the substitution of one or more of the hydrogen 
 atoms of the benzene ring by the hydroxyl (OH) group. 
 
 These are formed : 
 
 1. By the decomposition of organic substances at high 
 temperatures, and are consequently contained in coal-tar. 
 
 2. By boiling the diazo compounds with dilute acids 
 
 C 6 H 5 N : KN0 3 + H 2 - C 6 H 5 OH + N 2 + HN0 3 . 
 Diazobenzene nitrate. Phenol. 
 
 Although this method is generally applicable, it is not 
 used on the large scale, on account of the expense it 
 incurs. 
 
 3. By melting the salts of the sulphonic acids or the 
 halogen substitution derivatives with caustic soda or 
 caustic potash 
 
 Benzene sulphonate of soda. Phenol. 
 
 C 14 H 6 3 Br + 2KOH = C 14 H 6 2 (OH) 2 + 2KBr 
 Dibromanthraquinon. Alizarin. 
 
 The other modes of formation are of theoretical interest 
 only. 
 
 The phenols are characterised by the following pro- 
 perties : 
 
 The hydroxyl hydrogen is easily replaceable by metals 
 or basic radicals 
 
 C r ,H 5 OH + NaOH = C c H 6 ONa + H 2 0. 
 Phenol. Sodium phenate, 
 
PHENOLS. 117 
 
 This acid property, which is common to all the phenols, 
 is increased by the introduction of halogen atoms or 
 nitro groups 'into the benzene ring. Thus, whereas 
 phenate of soda (C 6 H 5 ONa) can be decomposed by car- 
 bonic acid, the corresponding compound of trinitro-phenol 
 (picrate of soda) is unacted upon. 
 
 The ethers of the phenols are most readily obtained by 
 acting on the solution of the phenol in caustic alkali with 
 the alkyl halogen derivatives 
 
 C 6 H 5 OH + KOH + C 2 H 5 Br = KBr + H 2 + C 6 H 5 OC 2 H 5 . 
 
 Phenol. Ethyl bromide. Ethyl phenol. 
 
 When distilled with zinc powder the phenols are con- 
 verted into the corresponding hydrocarbons 
 
 C 6 H 5 OH + Zn = ZnO + C 6 H G . 
 Phenol. Benzene. 
 
 The compounds of the phenols with soda or potash 
 when acted upon at high temperatures with carbonic 
 anhydride yield oxycarboxylic acids 
 
 C fi H 3 OH + C0 3 = C 6 H 4 (OH)COOH. 
 
 Phenol. Salicylic acid. 
 
 When brought into contact with diazo compounds in 
 alkaline solution they form oxyazo compounds. This re- 
 action is of great importance, as in this manner the 
 majority of the azo dyes are obtained. 
 
 Nitrous acid readily acts upon the phenols, converting 
 them into nitrosophenols. 
 
 When heated with ammonia they are more or less 
 readily converted into the corresponding amines : 
 
 C 10 H 7 OH + NH 3 - C 10 H 7 NH 2 + H 2 O. 
 Naphthol. Naphthylamine. 
 
118 COAL-TAR COLOURS. 
 
 This reaction takes place much more readily in presence 
 of dehydrating agents, such as zinc chloride or calcium 
 chloride. 
 
 Phenol. Carbolic acid or phenic acid, C G H 5 OH, was 
 first discovered in 1834, by Runge, in coal-tar. It is 
 obtained exclusively from coal-tar by the method de- 
 scribed on p. 73. 
 
 In the pure state phenol forms long, colourless, pris- 
 matic crystals, which possess a powerful and charac- 
 teristic smell. It melts at 42 and boils at 182. At the 
 ordinary temperature phenol dissolves in about fifteen 
 times its weight of water ; at 80-84 it will mix with 
 water in all proportions. In alcohol and ether it is 
 soluble in all proportions. When exposed to light and 
 air it is soon coloured red. The aqueous solution gives 
 with ammonia and chloride of lime a blue colouration, 
 with ferric chloride a violet colouration, and with bromine 
 water a yellowish precipitate of tribromphenol 
 
 C 6 ELBr 3 OH. 
 
 With concentrated nitric acid phenol yields, first mono- 
 nitrophenols, then dinitrophenols, and ultimately tri- 
 nitrophenol, or picric acid. With nitrous acid phenol 
 yields nitrosophenol C 6 H 4 (OH)NO. In concentrated 
 sulphuric acid it dissolves with the formation of ortho- 
 phenol sulphonic acid. 
 
 When heated with oxalic acid and concentrated sul- 
 phuric acid the rosolic acids are formed. 
 
 Phenol is used chiefly in the manufacture of picric 
 acid, salicylic acid, rosolic acid, and as a disinfectant. 
 
 Phenate of soda, C 6 H 5 ONa, is obtained by dissolving 
 phenol in caustic soda, and is used in the manufacture of 
 salicylic acid. 
 
 Phenol methyl ether, or Anisol, C 6 H 5 -OCH 3 , obtained by 
 treating potassium phenate with methyl iodide or acid 
 
PHENOLS. 119 
 
 sulphate of methyl, forms a colourless liquid, which boils 
 at 152, and possesses an aromatic smell. 
 
 Dioxy benzenes. 
 
 All the three dioxybenzenes theoretically possible are 
 known. 
 
 
 , is formed by the dry dis- 
 
 Pyrccatecliin, C 6 H 4 - 
 
 tillation of catechu ; also by melting orthophenol sulphonic 
 acid with caustic potash. It forms colourless crystals, 
 dissolves easily in water, melts at 104 and boils at 245. 
 The aqueous solution gives an intense green colouration 
 with ferric chloride. 
 
 C OTT 
 The methyl ether, C 6 H 4 < xj ? i g contained in the tar 
 
 N. 
 
 obtained by the dry distillation of beechwood. 
 
 Resorcin, C G H 4 < QJT o, is obtained on the large scale 
 
 by heating benzene disulphonate of soda with caustic soda. 
 liesorcinate of soda is thus formed : 
 
 C 6 H 4 (S0 3 ]S T a) 2 + 2 NaOH - 2 ]STa 2 S0 3 + C 6 H 4 (ONa)o. 
 Benzene disulphonate of soda. Besorcinate of soda. 
 
 The mass is then extracted with water, acidulated with 
 sulphuric acid, in order to liberate the resorcin, and the 
 aqueous solution evaporated down in shallow vessels. 
 The crystals of sodium sulphate which separate out are 
 removed from time to time by centrifugal action, and 
 ultimately, when nearly all has crystallised out, a mother 
 liquor remains, which contains nearly all the resorcin in 
 aqueous solution. This is evaporated to dry ness and 
 distilled under reduced pressure. 
 
 Resorcin forms colourless crystals, which are easily 
 soluble in water. The aqueous solution is neutral, pos- 
 sesses a sweet taste (poisonous), and soon turns red when 
 
120 COAL-TAR COLOURS. 
 
 exposed to the air. With ferric chloride it gives a dark 
 violet ; with chloride of lime, a violet colouration. 
 
 When melted with phthalic anhydride resorcin yields 
 fluoresce'in, which dissolves in alkalies with an intense 
 green fluorescence. This reaction is so delicate that it 
 can be used as a test for resorcin, but it is not possible to 
 distinguish it in this manner from its homologue cresor- 
 cin. When heated with citric acid in presence of con- 
 centrated sulphuric acid resorcin yields resocyanin, which 
 dissolves in alkalies with a beautiful sky-blue fluorescence. 
 
 Hydroquinon, 
 
 OH 
 
 A, is obtained by oxidising ani- 
 
 line to quinon, reducing the solution with sulphurous acid 
 and extracting with ether. It forms colourless crystals, 
 which melt at 169 and which dissolve in seventeen parts 
 of water. 
 
 Trioxybenzenes. 
 
 Three trioxybenzenes are possible according to theory, 
 and all of these are known. 
 
 OH 
 
 Pyrogallic acid, or pyrogallol, C 6 H 3 OH 
 
 OH 
 
 1 
 
 2, was first 
 
 3 
 
 obtained in 1786 by Scheele, by the dry distillation of 
 gallic acid, but was considered by that chemist to be pure 
 gallic acid. 
 
 It is prepared on the large scale by heating gallic acid 
 with two to three times its weight of water, in closed 
 vessels, to 200-210, for about half an hour. The forma- 
 tion is represented by the equation : 
 
 C 6 H 2 (COOH) (OH) 3 = C0 2 + C 6 H 3 (OH) 3 . 
 Gallic acid. Pyrogallic acid. 
 
 Pyrogallic acid forms white shining crystals, which melt, 
 at 131. It boils at 210 with partial decomposition. In 
 
PHENOLS. 121 
 
 th e dry state it remains unchanged on exposure to the 
 air, but in alkaline solution it rapidly absorbs oxygen 
 and assumes a dark or black colour. The aqueous solu- 
 tion is coloured red by ferric chloride. With ferrous sul- 
 phate containing small quantities of ferric salt it yields a 
 deep indigo-blue colouration. 
 
 Pyrogallic acid is used in the manufacture of gallein, in 
 photography, as a dye for the hair and for analytical 
 purposes. 
 
 OH 
 
 PUoroglucin, C 6 H 3 OH 
 OH 
 
 1 
 
 3, is best obtained by melting 
 
 5 
 
 resorcin with caustic soda. It crystallises with two mol. 
 H 2 in large colourless crystals. 
 
 Oxyhydroquinon, C 6 H 3 (OH) 3 (1, 2, 4), is formed by 
 melting hydroquinon with caustic soda. 
 
 Oxyloluenes, or cressols, C 6 H 4 (CH 3 ) (OH). 
 
 All the three isomers are contained in coal-tar, in 
 which the ortho and para compounds exist in much larger 
 quantities than the meta compound. They may be con- 
 veniently prepared in the pure state by transforming the 
 corresponding amido compounds (toluidines) into diazo 
 compounds and boiling these with dilute sulphuric acid. 
 
 Orthocressol melts at 32 and boils at 188. 
 
 Metacressol is liquid at the ordinary temperature and 
 boils at 201. 
 
 Paracressol melts at 36 and boils at 199. 
 The cressols show great similarity in their properties 
 with phenol. 
 
122 COAL-TAR COLOURS. 
 
 Dioxytoluenes, C fi H 2 CH 3 (OH) 2 . 
 
 Orcin, C 6 H 3 J OH 
 (OH 
 
 1 
 
 3, may be obtained most readily by 
 5 
 
 extracting certain lichens (the Roccella tinctoria answers 
 the purpose best) Avith milk of lime. The extract is 
 boiled for some time and then treated Avith carbonic acid 
 for the removal of the lime. The solution is then fil- 
 tered and the filtrate evaporated to dryness on a Avater- 
 bath. The residue is then crystallised first from alcohol, 
 and then from benzene. 
 
 There are, besides, numerous methods for the synthet- 
 ical preparation of orcin. Thus it can be obtained by 
 melting toluenemetadisulphonic acid or metadibromtol- 
 uene with caustic alkali. 
 
 Orcin crystallises with 1 mol. H 2 0, in large colourless 
 crystals, Avnich melt at 58. In the anhydrous state it 
 melts at 106'5-108 and boils at 290. By the simul- 
 taneous action of air and ammonia orcin is conA'erted into 
 orcein, a colouring matter Avhich forms the chief con- 
 stituent of orchil and cudbear. Orcin dissolves easily in 
 water. 
 
 1 
 
 * OH 
 
 (OH 
 
 2, is obtained by converting ortho- 
 4 
 
 amido paracressol into the diazo compound, and boiling 
 this with dilute sulphuric acid. It forms colourless crys- 
 tals, which dissolve easily in water and melt at 104-105. 
 Cresorcin shows a remarkable similarity to resorcin in its 
 reactions. 
 
 Xylenols, C 6 H 3 (CH :5 ) n (OH). Six isomers are known. 
 
 Iso-butylphenol, C 6 H 4 (CH 3 'CH(CH 3 ) 2 )(OH), is obtained 
 by heating phenol with isobutyl alcohol and zinc chloride. 
 It melts at 98. 
 
PHENOLS. 123 
 
 The higher oxy compounds in the benzene series are 
 not of much technical importance. 
 
 The naphthols. 
 
 Both alpha and beta naphthol are contained in coal-tar, 
 but in such small quantities that their isolation would not 
 pay. They are both prepared on the large scale, the 
 alpha compound being used chiefly in the manufacture 
 of nitro-compounds, while the beta compound is used in 
 the manufacture of azo dyes. They are prepared by 
 melting the corresponding naphthalene sulphonic acids 
 (q.v.) with caustic soda. 
 
 Alphanaphthol, C 10 H 7 OH(a), forms lustrous monoclinic 
 needles, which are sparingly soluble in water and which 
 melt at 94. It boils at 278-280. A chip of pitch 
 pine dipped into the aqueous solution of alphanaphthol 
 and then into hydrochloric acid, soon turns green when 
 exposed to sunlight, and ultimately brown. Ferric 
 chloride yields in the aqueous solution a violet colouration, 
 and on warming a violet precipitate of alphadinaphthol, 
 
 Chlorate of potash and hydrochloric acid convert alpha- 
 naphthol into dichlornaphthoquinon. 
 
 In the alkalies alpha-naphtol dissolves easily with form- 
 ation of crystallisable naphtholates. 
 
 Alphanaphthol is rarely used in the manufacture of 
 azo dyes. It is used chiefly in the manufacture of naph- 
 thol-yellow and as a disinfectant. 
 
 Betanaphthol, C 10 H 7 OH (/?), is obtained by heating a 
 mixture of betanaphthalene sulphonic acid (1 pt.) with 
 caustic soda (2 pts.), and just sufficient water to dissolve 
 the caustic soda gradually to 300. When the reaction is 
 over, the mass is dissolved in water, acidulated with 
 hydrochloric acid, and the liberated betanaphthol purified 
 by distillation. 
 
124 COAL-TAR COLOURS, 
 
 Betanaphthol forms in the pure state small lustrous 
 crystals, which melt at 123, and are only sparingly 
 soluble in boiling water. It boils at 285-286, with partial 
 decomposition, can be sublimated, and distils over with 
 steam. When treated with concentrated sulphuric acid 
 (l|-2 parts) in the cold, betanaphthol yields betanaphthyl 
 sulphate, C 10 II 7 O.S0 3 H, analogous to acid ethyl sulphate. 
 When heated, this compound undergoes a molecular 
 change and is transformed into betanaphthol sulphonic 
 acid. Heated with ammonia in closed vessels, beta- 
 naphthol is easily transformed into betanaphthylamine. 
 
 The aqueous solution yields with chloride of lime solu- 
 tion a yellow colouration, with ferric chloride a slight 
 green colouration. Nitrous acid yields with betanaphthol 
 only one nitrosonaphthol, while with alphanaphthol two 
 isomeric nitroso compounds are formed. 
 
 NaplitTiolsulplionic adds. 
 
 By treating the naphthols with strong sulphuric acid 
 the first products of the reaction are naphthyl sulphates, 
 which on further heating pass over into naphtholmono- 
 sulphonic acids, of which numerous isomers exist. By 
 the further action of sulphuric acid the naphthols are 
 transformed into disulphonic and trisulphonic acids, of 
 which a still greater number of isomers exists. In the 
 preparation of these sulphonic acids on the large scale 
 great care must be taken in regulating the temperature 
 and time of sulphonating, as well as in the relative pro- 
 portions of naphthol and sulphuric acid. Frequently 
 several isomers are formed in the process of sulphonation, 
 which may as a rule be separated by the different solu- 
 bility of their salts. The sulphonic acids of the naph- 
 thols, more especially those of betanaphthol, are of the 
 greatest importance in the manufacture of the oxy-azo 
 dyes, and their preparation and use for this purpose form 
 the subject of numerous patents. 
 
NAPHTHOLSULPHONIC ACIDS. 125 
 
 Sulphonic acids of alphanapJithol. 
 
 I. Alplianaplifholmonosulplionic acids, C 10 H 6 OH.S0 3 H. 
 The following are known : 
 
 C 10 H G OH.S0 3 H c^-/?! is probably formed along with its 
 isomer, aj-cto, by the action of sulphuric acid on alphanaph- 
 thol. It is obtained by the action of fuming sulphuric 
 acid on a solution of alphanaphthol in glacial acetic acid. 
 The ammoniacal solution shows a pure blue fluorescence. 
 
 C 10 H G OH.S0 3 H aj-c^ (Schaeffer's acid) is obtained by 
 acting on alphanaphthol (1 pt.) with sulphuric acid 
 (2 pts.) for two hours at 100. The ammoniacal solution 
 shows a violet fluorescence. 
 
 The acid having the constitution a x = a 2 forms an anhy- 
 dride, C 10 H G j Q ^> at once. It is obtained by diazotising 
 
 Schoellkopf's naphthylatnine sulphonic acid and boiling 
 the diazo compound in acid solution. 
 
 C 10 H r) OH.S0 3 H a l = ft l . From betanaphthalene sul- 
 phonic acid and nitric acid (Cleve). 
 
 C 10 H 6 OH.S0 3 H a 1 = a 3 from the corresponding naph- 
 thylamine sulphonic acid, treated with nitrous acid and 
 boiled (Cleve). Also by the reduction of the nitro 
 compounds formed by alphanitronaphthalene and nitric 
 acid or of the sulphonic acid formed from alphanaphtha- 
 lene sulphonic acid and nitric acid. 
 
 C 10 H C OH.SO S H (Acid of Nevile and Winther). This 
 acid, the constitution of which has not hitherto been de- 
 termined, is obtained by diazotising naphthionic acid and 
 boiling the diazo compound thus formed with dilute sul- 
 phuric acid. It is prepared in large quantities for subse- 
 quent use in the manufacture of azo-blue, brilliant scarlet, 
 azo-orseillin, and azorubin S. 
 
 Alphanaphtholdisulphonic acids, C 10 H 5 OH(S0 3 H) 2 . Only 
 one of the numerous possible isomers appears to be 
 known. This is obtained by dissolving 1 pt. alphanaph- 
 
126 COAL-TAR COLOURS. 
 
 thol in 3 pts. concentrated sulphuric acid, and heating 
 the mixture for ten hours to 100-110. 
 
 By dissolving alphanaphthol in fuming sulphuric acid, 
 and treating the disulphonic acid thus formed with one 
 mol. sodium nitrite in aqueous acid solution a nitroso- 
 alphanaphthol disulphonic acid, C 6 H 4 NO.OH (SO 3 H) 2 , 
 is formed, which dyes wool and silk a bright yellow in an 
 acid bath (Seltzer). 
 
 Alphanaphtholtrisulphomc acid, C 10 H 4 (OH)(S0 3 H)(S0 3 
 H)(SO;}H), i-/?i-ao = a 2 , is obtained by the further sal- 
 phonation of Seltzer's acid. 
 
 SulpJionic acids of betanapJithol. 
 
 By the action of concentrated sulphuric acid on beta- 
 naphthol at the ordinary temperature, naphthyl sulphate, 
 C 10 H 7 O.SO :V H, is at first formed. On heating this gives 
 rise to a mixture of betanaphtholmonosulphonic acids. 
 The chief products of the reaction (at 100) consist of 
 two monosulphonic acids, which are known respectively 
 as Schaeffer's and as Bayer's betanaphtholmonosulphonic 
 acids. The relative quantities of the two acids formed 
 depend upon the conditions observed during the process of 
 sulphonation. Thus at 50-60 both acids are formed 
 in about equal quantities, whereas at 100 Schaeffer's acid 
 is formed in larger quantity. 
 
 By the further action of strong sulphuric acid on beta- 
 naphthol, disulphonic acids are obtained. If one part beta- 
 naphthol is heated with three parts strong sulphuric 
 acid to 110, there are formed (along with other sub- 
 stances) two betanaphtholdisulphonic acids, which are 
 known respectively as betanaphtholdisulphonic acid R 
 and betanaphtholdisulphonic acid G. The acid R yields 
 with diazo compounds redder azo dyes than acid Gr. 
 
 By the action of fuming sulphuric acid on betanaphthol 
 trisulphonic acids are formed, 
 
XAFHTHOLSULPHON1C ACIDS. 127 
 
 Mono sulphonic acids of betanaplithol. 
 
 C 10 H 6 .OH.S0 3 H, ft-ap This acid, which is generally 
 known as Bayer's acid, is the chief product of the con- 
 tinned action of strong sulphuric acid on betanaphthol at 
 the ordinary temperature. It has also been obtained by 
 diazotising the corresponding naphthylaminesulphonic acid 
 and boiling the resulting diazo compound in acid solution. 
 
 The free acid has not been obtained in the crystallised 
 state. With diazo compounds it yields azo dyes, but in 
 the case of diazoxylene it combines only in concentrated 
 and not in dilute solution. With the bases it forms neu- 
 tral and basic salts ; thus with soda it forms a neutral 
 sulphonate, C 10 H c .OH.S0 3 ]S"a, and a basic sulphate, 
 C 10 H 6 .ONa.S0 3 Na. 
 
 C 10 H C OH.S0 3 H, J3 l =fiv. This acid, which is known as 
 Schaeffer's acid, is formed along with the preceding by 
 the action of strong sulphuric acid on betanaphthol at 
 50-100. For its preparation 1 pt. betanaphthol is dis- 
 solved in 2 pts. concentrated sulphuric acid, and the 
 temperature maintained for some time at about 60. The 
 mass is then poured into water, neutralised with lime, 
 filtered from the calcium sulphate formed, and the lime 
 salts of the two isomeric sulphoiiic acids converted into 
 the neutral sodium salts by the addition of sodium car- 
 bonate. The separation of the sodium salts may be 
 effected either by treatment with boiling alcohol, in which 
 the salt formed by Bayer's acid dissolves easily, while the 
 salt of Schaeffer's acid remains behind, or by diluting the 
 solution of the sulphonic acids in sulphuric acid with 
 twice its weight of water, and then neutralising with 
 sodium carbonate. In this manner four-fifths of Schaeffer's 
 acid are separated out as a white crystalline precipitate. 
 Another method of separation is based upon the fact that 
 when a dilute ammoniacal solution of the two sulphonic 
 acids is treated with diazoxylene, Schaeffer's acid at 
 
128 COAL-TAR COLOURS. 
 
 once combines to form colouring matter, while Bayer's 
 acid remains unaltered. 
 
 Schaeffer's acid may also be obtained by diazotising the 
 corresponding naphthylamine sulphonic acid, and decom- 
 posing the resulting diazo compound by boiling. 
 
 Schaeffer's acid crystallises in leaflets, which melt at 
 125, are easily soluble in water and alcohol, and do not 
 deliquesce. 
 
 C 10 H 6 OH.S0 3 H, ft = 04. The acid obtained by Dahl 
 & Co. by the action of nitrous acid and boiling on y 
 naphthylamine sulphonic acid probably possesses this 
 constitution (Nolting & Beverdin). 
 
 C 10 H C .OH.S0 3 H, ft -ft. From the alphanaphthalene 
 disulphonic acid of Ebert & Merz, and caustic soda at 
 200-250. The same compound is produced by the action 
 of nitrous acid and boiling on the deltanaphthylamine 
 sulphonic acid (Bayer & Duisberg). 
 
 Disulplwnic acids of betanaplithol. 
 
 When betanaphthol is treated for several hours with 
 2-3 times its weight of concentrated sulphuric acid at 
 100-110, the chief product of the reaction is found to 
 consist of a mixture of two disulphonic acids, which are 
 characterized respectively as betanaphtholdisulphonic 
 acid R and betanaphtholdisulphonic acid G. This denomi- 
 nation has been chosen in order to express the fact that the 
 former yields with diazo compounds red shades, while the 
 latter yields yellow shades (German, gelb) of scarlet, etc. 
 The two acids are also known as betanaphthol-A-disul- 
 phonic acid and betanaphthol-B-disulphonic acid respec- 
 tively. The latter of these is also sometimes referred to in 
 patent literature as the y disulphonic acid of betanaphthol. 
 
 The separation of these two acids on the large scale 
 forms the subject of numerous patents. According to 
 Griess, they may be separated by the different solubility 
 
AROMATIC ALDEHYDES. 129 
 
 of their barium salts, that of the G acid being much more 
 easily soluble in water than that of the R acid. 
 
 According to another method patented by Meister 
 Lucius & Broiling, the separation may be effected by 
 treating the mixture of the sodium salts (prepared in the 
 usual way) with alcohol, in which that of the G acid 
 dissolves, while that of the B acid remains undissolved. 
 
 Another method of separation patented by Beyer & 
 Kegel is based upon the different behaviour of the sodium 
 salts towards a saturated salt solution. By adding a 
 saturated salt solution to the solution containing the two 
 sodium salts, that of the E/ acid is separated or salted 
 out, while that of the G acid remains in solution. 
 
 BetanapJifholdisulphonic acid, R,C 10 H 5 OH(S0 3 H) 2 , forms 
 white silky crystals, which deliquesce rapidly in the air. 
 
 Betanaphtholdisulphonic acid, G, C 10 H 5 OH(S0 3 H) 2 , 
 strongly resembles the former, but is more deliquescent. 
 
 Both acids are used extensively in the manufacture of 
 azo dyes. 
 
 Betanaphtholtrisulphonic acid, C 10 H 4 OH(S0 3 H) 3 , is ob- 
 tained by treating betanaphthol at 140-150 with 4-5 
 times its weight of a 20% solution of sulphuric anhy- 
 dride in sulphuric acid. 
 
 Aromatic aldehydes. 
 
 The aromatic aldehydes contain, like those belonging 
 to the fatty series, the group C ~TT. 
 They 'are formed : 
 
 1. By the oxidation of the aromatic alcohols 
 
 C 6 H 5 CH 2 OH + = H 2 + C 6 H 5 COH. 
 
 Benzylalcohol. Benzaldehyde. 
 
 2. By the reduction of the aromatic acids - 
 
 C 6 H 5 COOH + H 2 = H 2 0+ C 6 H 5 COH, 
 Benzole acid. Benzaldehyde. 
 
 K 
 
130 COAL-TAR COLOURS. 
 
 3. By the action of boiling alkaline solutions on certain 
 halogen disubstitution derivatives, in which the halogen is 
 contained in the side chain 
 
 C 6 H 5 CHC1 ? + 2NaOH - 2NaCl + H 2 + C 6 H 5 COH. 
 Benzal chloride. Benzaldehyde. 
 
 The aldehydes show the following characteristic reac- 
 tions : 
 
 By oxidising agents they are converted into the cor- 
 responding aromatic acids, while reducing agents produce 
 the corresponding alcohols. 
 
 With alcaline bisulphites they yield double compounds. 
 By ammonia and the amine bases they are acted upon 
 with the formation of more or less complicated compounds. 
 
 Benzaldehyde, C 6 H 5 COH. This compound is by far 
 the most important of the aromatic aldehydes from a 
 commercial point of view. It was formerly obtained from 
 bitter almonds, and is hence often known as oil of bitter 
 almonds. 
 
 Benzaldehyde may be obtained on the large scale accord- 
 ing to several methods. Thus it is formed, as stated above, 
 by the action of boiling caustic soda on benzal chloride. 
 It can also be obtained by boiling a mixture of benzal 
 chloride and benzyl chloride (C 6 H 5 CH 2 C1) (obtained by 
 passing chlorine into boiling toluene, until the specific 
 gravity has reached 1*175) with water containing finely 
 divided peroxide of manganese in suspension. According 
 to another method, it is obtained by boiling benzyl chloride 
 (1 part) with lead nitrate (1J parts) and water (10 parts) 
 in a vessel provided with a reflux condenser, and passing 
 at the same time a current of carbonic acid through the 
 liquid. 
 
 Benzaldehyde forms a colourless liquid, which refracts 
 light powerfully and which boils at 179-180. It has a 
 specific gravity of 1'053 and is sparingly soluble in water. 
 It possesses an agreeable smell, resembling that of bitter 
 
AROMATIC ALDEHYDES. 131 
 
 almonds. When exposed to the air it is rapidly oxidised 
 and transformed into benzoic acid. 
 
 The commercial product usually contains benzoic acid, 
 chlorinated benzaldehydes, and sometimes nitrobenzene, 
 which latter substance must be regarded as an adultera- 
 tion. The following are the usual tests applied : When 
 distilled, 90 volumes should pass over between 176 and 
 180. 10 c.c. of the benzaldehyde should dissolve com- 
 pletely in 100 c.c. of a solution of sodium bisulphite 
 (23 Tw.) at 40-50. In order to test rapidly for nitro- 
 benzene, two parts of the benzaldehyde are mixed with 
 1 pt. caustic potash ; if nitrobenzene be present, the 
 mixture will become green. 
 
 Benzaldehyde is used chiefly for the manufacture of the 
 aniline greens ; smaller quantities are used in making 
 benzoic acid and cinnammic acid. 
 
 By the direct action of chlorine on benzaldehyde in 
 presence of zinc chloride the meta and para substitution 
 
 ( POTT 
 products C 6 H 4 j are formed. 
 
 Nitric acid produces ortho and meta nitrobenzal- 
 
 ( POTT 
 
 dehydes C 6 H 4 j -^-Q . The para compound is best ob- 
 tained by oxidising the corresponding para nitrobenzyl 
 chloride with lead nitrate. By reducing agents these 
 three nitro compounds are converted into the correspond- 
 ing amido compounds. 
 
 Cinnammic aldehyde, C 6 H 5 'CH : CH'COH. This alde- 
 hyde is contained in oil of cinnamon and in oil of cassia. 
 It may be prepared artificially by allowing benzaldehyde 
 (10 pts.), ordinary aldehyde (15 pts.), water (900 pts.), 
 and a ten per cent, solution of caustic soda (10 pts.), to 
 stand with frequent agitation for 8-10 days at 30. The 
 liquid is then extracted with ether, and the residue left 
 after distilling off the ether is subjected to dry distillation 
 in a partial vacuum. 
 
132 COAL-TAR COLOURS. 
 
 Cinnammic aldehyde forms a colourless oil, which is 
 insoluble in and heavier than water. By the action of 
 nitric acid it is converted into ortho-nitro cinnammic 
 aldehyde (m.p. 127) and para-nitro cinnammic aldehyde 
 (m.p. 141-142). 
 
 Ketons. 
 
 i 
 
 The ketons contain the group C 0, combined on 
 
 I 
 
 either side with carbon atoms. They are formed : 
 
 1. By the oxidation of the secondary alcohols 
 
 (C 6 H 5 ) 2 CHOH + = H 2 + (C 6 H 5 ) 2 CO. 
 
 Diphenylcarbinol. Benzophenon. 
 
 2. By the oxidation of certain- hydrocarbons 
 
 C 6 H 4 CH C 6 H 4 CO 
 
 C 6 H 4 CH C 6 H 4 CO 
 
 Phenanthrene. Phenanthrenequinon. 
 
 3. By distilling the lime salts of the aromatic acids, and 
 besides, by several other methods, which are chiefly of 
 scientific interest. 
 
 P TT ) 
 
 Benzophenon, Q 6 -rr 5 f CO, is best obtained by the dry 
 
 distillation of benzoate of lime. It is insoluble in water, 
 but easily soluble in alcohol and ether, and forms crystals, 
 which melt at 27 or 49, and boil at 300. Benzophenon 
 itself is not of much importance, but its amido derivatives, 
 especially the tetramethyldiainidobQnzophenon, form the 
 raw materials for the manufacture of certain important 
 colouring matters. 
 
 /C 6 H 4 N(CH 3 ) 2 
 Tetrametliyldiamidoltenzophenon, CO . This 
 
KETONS. 133 
 
 base is obtained on the large scale by the action of carbon 
 oxychloride on dimethylaniline 
 
 2C 6 H 3 N-(CH3) 2 + COC1 2 = 2HC1 + CO[C 6 H 4 N(CH 8 ) a ] 3 . 
 
 For its manufacture carbon oxychloride is passed into 
 dimethylaniline until the increase in weight corresponds 
 to the above equation. The crystalline paste thus ob- 
 tained is heated for some time in closed vessels on a water- 
 bath. When the reaction is over, the mass is dissolved in 
 water, the unchanged dimethylaniline driven off by steam, 
 and the residue is purified by dissolving in hydrochloric 
 acid and precipitating with caustic soda. 
 
 Tetramethyldiamidobenzophenon forms colourless leaf- 
 lets, which melt at 170 and are easily soluble in ether and 
 hot alcohol. When heated with salts of ammonia or of 
 the primary amines, in presence of zinc chloride, it yields 
 yellow and orange colouring matters ( Auramines) . 
 
 Tetra-ethyldiamidobenzophenon resembles in its pro- 
 perties the preceding compound and is obtained in a 
 similar manner from diethylaniline. 
 
 O 
 
 /<j\ 
 
 . Anthraquinon, C 6 H 4 C 6 H 4 . This body was first ob- 
 
 \C/ 
 
 
 
 tained by Laurent in 1840 by the oxidation of anthracene 
 with nitric acid. The oxidation is at present effected by 
 means of bichromate of potash and sulphuric acid. For 
 its manufacture on the large scale the crude anthracene, 
 containing 60-80% of pure substance, is first subdivided as 
 finely as possible by sublimation and grinding. 100 kilos, 
 anthracene are then added to a boiling solution of 100-150 
 kilos, bichromate of potash in 1,500 litres of water con- 
 tained in a large lead-lined vessel. To the hot solution 
 are then added, during 9-10 hours, 140-210 kilos, sul- 
 
134 
 
 COAL-TAR COLOURS. 
 
 phuric acid at 168 Tw. previously diluted. The tem- 
 perature generated by the reaction is sufficient to keep 
 the liquid boiling during the operation. After all the 
 acid has been added, the boiling is continued for a short 
 period, when the whole is allowed to cool and the crude 
 anthraquinon is separated by nitration or centrifugal 
 force. The mother liquors which contain all the chromium, 
 in the form of chrome alum, are not wasted, but are 
 treated separately for the regeneration of bichromate. 
 At this stage of the manufacture the anthraquinon 
 appears as a reddish-yellow powder. For its further 
 purification, it is heated in cast-iron vessels provided with 
 stirrers with 2-3 pts. strong sulphuric acid to 80 and 
 the temperature then gradually raised to 110 until all 
 the anthraquinon is dissolved, and a sample of the liquid 
 poured into water gives a pure white precipitate. On 
 allowing the sulphuric acid solution to cool, part of the 
 anthraquinon separates out in a crystalline form; the 
 rest is precipitated by diluting the solution in leaden 
 vessels with twenty times its volume of water. The pre- 
 cipitate, which contains about 90 per cent, anthraquinon, is 
 collected in filter presses and presents now the appearance 
 of a light-grey or yellowish-green crystalline powder. It 
 may be still further purified by boiling with soda. The 
 average yield from 100 pts. of 60 per cent, anthracene is 
 from 50-55 pts. anthraquinon. 
 
 Anthraquinon, the constitution of which is represented 
 by the formula : 
 
AROMATIC ACIDS, 135 
 
 forms golden-yellow needles or prisms which melt at 277. 
 It is insoluble in water, and only sparingly soluble in 
 alcohol and ether. It can be distilled without undergoing 
 decomposition, and begins to sublimate in needles below 
 its melting point. It dissolves in strong warm sulphuric 
 acid, and the solution can be heated to 130 without any 
 chemical action taking place, but at higher temperatures 
 it is transformed into the mono- and di-sulphonic acids. 
 
 AntJiraquinonmonosulphonic acid, C^H^SC^EQOj, is ob- 
 tained by the action of fuming sulphuric acid (containing 
 about 50 per cent, anhydride) on anthracene at 160. 
 
 The free acid forms fine yellow leaflets, and is easily 
 soluble in water. When melted with caustic soda it 
 yields alizarin. 
 
 Anthraquinondisulphonic acids, C 14 .H 6 (S0 3 H) 3 0. 2 . Two 
 disulphonic acids are known which are designated re- 
 spectively as the alpha and beta compounds. By dissolv- 
 ing anthracene in fuming sulphuric acid of the same 
 strength as that used in the preparation of the monosul- 
 phonic acid, and keeping the temperature for a considerably 
 longer period at 160-170, the chief product of the 
 reaction will be the betasulphonic acid which crystallises 
 with one molecule of water of crystallisation in fine 
 golden yellow leaflets. 
 
 By raising the temperature for a short time to 180-185, 
 the alphadisulphonic acid is obtained as chief product. 
 It also contains one molecule of water, and forms a golden 
 yellow crystalline mass. 
 
 The alphasulphonic acid yields, when melted with 
 caustic soda, flavopurpurin ; while the beta sulphonic acid 
 treated in a similar manner gives rise to anthrapurpurin. 
 
 Aromatic Acids. 
 
 The aromatic acids contain, like other organic acids 
 (carboxylic acids), the carboxyl group CO'OH. They 
 may be mono, di, or tri-basic, etc., according to the 
 
136 COAL-TAR COLOURS. 
 
 number of such carboxyl groups contained in the mole- 
 cule. 
 
 They are formed by the oxidation of the aromatic 
 alcohols and aldehydes and of the aromatic hydrocarbons 
 which contain one or more methyl, ethyl, etc., groups 
 attached to the carbon atoms of the benzene ring. The 
 following are the only bodies of this class which have any 
 great importance in the coal-tar colour industry. 
 
 Benzoic acid, C 6 H 5 'COOH. This compound was dis- 
 covered as far back as 1608, by Blaise de Vigenere, who 
 obtained it by heating gum benzoe. Benzoic acid occurs, 
 besides, naturally in several other resins and balsams, and 
 as a constituent of many plants. 
 
 Small quantities of benzoic acid are still prepared from 
 gum benzoe, but only for pharmaceutical purposes. Ac- 
 cording to v. Rad, artificial benzoic acid is best obtained 
 by heating benzotrichloride with water under pressure. 
 The conversion takes place according to the following 
 equation : 
 
 C 6 H 5 CC1 3 + 2H 3 = C 6 H 5 -COOH + 3H01. 
 Benzotrichloride. Benzoic acid. 
 
 Pure benzoic acid forms long white needle-shaped 
 crystals which melt at 120 and boil at 250. It sub- 
 limates easily below the boiling point, emitting a vapour 
 which rapidly irritates the mucous membranes and causes 
 coughing. It is sparingly soluble in water, but dissolves 
 readily in alcohol and ether. With chlorine, bromine, 
 nitric acid, and sulphuric acid it yields substitution 
 derivatives of which those containing the substituting 
 element or group in the meta-position to the carboxyl 
 group are the chief products of the reaction. 
 
 Benzoic acid is employed in the manufacture of aniline 
 blue and for pharmaceutical purposes. 
 
 Salicylic acid or orthoxybenzoic acid, C 6 H 4 \ QTT Vo\ 
 occurs naturally in the blossom of the Spiraea ulmaria, and 
 
AROMATIC ACIDS. 137 
 
 as methyl ether in the oil obtained from Gautheria pro- 
 cumbeus (winter-green oil). 
 
 Salicylic acid is obtained artificially by heating phenate 
 of soda in a current of dry carbonic acid gradually from 
 100 to 200 during 6-8 hours. The grey mass of sali- 
 cylate of soda thus obtained is dissolved in water, and 
 treated first with a small quantity of sulphuric acid, in 
 order to precipitate resinous and coloured impurities. 
 Excess of acid is then added in order to precipitate 
 all the salicylic acid, which is further purified by crys- 
 tallisation. According to another method, salicylic 
 acid may be obtained by heating diphenyl carbonate 
 (obtained by the action of carbonoxychloride on phenol) 
 to 200 in an indifferent atmosphere. 
 
 /OC 6 H 5 /OH 
 
 CO +NaOH-C 6 H 4 +C 6 H 5 OH. 
 
 \OC 6 H 5 \COONa 
 
 Salicylic acid crystallises in long needle-shaped crystals, 
 which sublimate easily when heated gently, but when 
 heated rapidly decompose into phenol and carbonic acid. 
 It is only sparingly soluble in cold water, but dissolves 
 readily in boiling water, alcohol, and ether. The aqueous 
 solution gives with ferric chloride a violet colouration. 
 Like carbolic acid, free salicylic acid possesses the pro- 
 perties of a strong antiseptic. The solution in soda 
 possesses an intensely sweet taste, but no longer possesses 
 antiseptic properties. It is used in the manufacture of 
 chrysamine and other azo dyes, for surgical and medicinal 
 purposes, for the manufacture of artificial winter-green 
 oil, and in large quantities as an antiseptic in checking 
 fermentation, putrefaction, etc. 
 
 Gallic acid, C 6 H 2 (OH) 3 'COOH, and gallotannic acid, 
 C 14 H 10 9 , also belong to the aromatic acids. They are 
 not obtained from coal-tar, but are used as raw products 
 in the manufacture of one or two artificial colouring 
 
138 COAL-TAR COLOURS. 
 
 matters. Gallic acid occurs in many natural tannins, and 
 may also be obtained by allowing tannic acid to ferment 
 or by boiling it with dilute sulphuric acid. It dissolves in 
 100 pts. cold water, easily in alcohol and ether, and crys- 
 tallises from water with one molecule of water of crystal- 
 lisation. It melts at 222, and is resolved at higher 
 temperatures into pyrogallic acid and carbonic acid, 
 Gallic acid is not precipitated from its solutions by 
 gelatine. 
 
 Tannin or tannic acid forms a yellowish amorphous 
 powder, which is easily soluble in water ; but insoluble in 
 ether. It is precipitated from its aqueous solution by 
 gelatine, and yields with salts of iron intense blue-black 
 precipitates (ink). 
 
 Phthalic acid, C 6 H 4 1 COOHY2V This Sul3stance is 
 formed by the oxidation of many aromatic substances. 
 For its preparation, naphthalenetetrachloride, dinitro- 
 naphthol, or similar substances are oxidised by chromic 
 or nitric acid. 
 
 Phthalic acid is sparingly soluble in cold, easily in hot 
 water, and crystallises in short prisms or leaflets which 
 melt at 213 ; at 130, however, they are already converted 
 into phthalic anhydride. 
 
 Phthalic anhydride, C 6 H 4 j QO/^' ^^ S com P oun( ^ 
 which is commercially known as phthalic acid, is obtained 
 from the preceding compound by sublimation, in long white 
 flexible needles. It melts at 128 and boils at 284'5. 
 When boiled for a length of time with water it is recon- 
 verted into phthalic acid. When heated with the phenols 
 (sometimes in presence of dehydrating agents) it yields 
 an important and interesting class of bodies known as 
 the phthaleins, some of which are colouring matters in 
 themselves, whereas others (e.g., fluoresce'in) form the raw 
 products for the manufacture of certain colours. 
 
 
PART III. 
 
 THE COAL-TAR COLOURS. 
 
 THE coal-tar colours are usually divided into a number 
 of groups, each of which deals with those products which 
 are obtained from the same constituents of tar. Thus we 
 have : 
 
 1. Colouring matters from benzene and toluene. 
 
 2. Phenol colouring matters. 
 
 3. Naphthalene colouring matters. 
 
 4. Anthracene colouring matters. 
 
 The materials used in the preparation of many colouring 
 matters are, however, sometimes derived from two, some- 
 times from three constituents of coal-tar. Thus, the eosins 
 are obtained from phthalic acid and resorcin. The former 
 is again obtained from naphthalene, while the latter is 
 obtained from benzene. Eosin can therefore either be 
 classed among those colouring matters which are obtained 
 from benzene, or among the naphthalene colouring matters. 
 Resorcin itself is a phenol, so that eosin might also be 
 regarded as a phenol dye. 
 
 In order to overcome these difficulties, and especially in 
 order to describe all those colouring matters which possess 
 similar properties (although they may have originated 
 from different sources) under one heading, the following 
 classification of the most important colouring matters will 
 be adhered to in this work : 
 
 139 
 
140 COAL-TAR COLOURS. 
 
 I. Aniline dyes. 
 
 (a) Rosaniline group. 
 
 (6) Indulines and Safranines. 
 
 (c) Oxazines. 
 
 (d) Aniline -black. 
 
 (e) Colouring matters containing sulphur (tliionines) . 
 
 II. Phenol dyes. 
 
 (a) Nitro bodies. 
 
 (&) Colouring matters which are formed by the 
 action of nitrous acid on the phenoles. 
 
 (c) Rosolic acid. 
 
 (d) Phthaleins and Indophenols. 
 
 III. Azo dyes. 
 
 (a) Amidoazo dyes. 
 
 (6) Amidoazo sulphonic acids. 
 
 (c) Oxyazo dyes. 
 
 IV. Artificial indigo. 
 
 V. Anthracene dyes. 
 
 I. ANILINE DYES. 
 
 The denomination " aniline dyes " is not applicable to 
 all the colouring matters described in this section. The 
 term " amine dyes " would perhaps be more suitable, as it 
 would include dye-stuffs from naphthylamine, as well as 
 from aniline and toluidine; "aniline dyes" of known 
 constitution may indeed be regarded as complicated 
 amines. In the following, all dyes are described as 
 " aniline dyes " which contain nitrogenous bases, or their 
 derivatives, for example, their sulphonic acids, with 
 the only exception of those which can with certainty be 
 called " azo dyes." 
 
 (a) THE ROSANILINE GROUP. 
 
 The most important colouring matters of this group 
 may be regarded as derivatives of two hydrocarbons : 
 
THE ROSANILTNE GROUP. 
 
 141 
 
 triphenylm ethane, C 19 H 16 , and tolyldiphenyl methane, 
 C 30 H 18 . Their constitution is expressed by the following 
 f ormulee : 
 
 OH 
 
 ,H 6 
 
 Triphenylmethane. 
 
 C 
 
 C 6 H 4 CH 2 
 
 H 
 
 Tolyldiphenylmethaue. 
 
 C 6 H 4 NH 2 
 
 v-lr. TT 
 
 The carbon atom which joins the three benzene rings to 
 each other is distinguished as " methane carbon." 
 
 If one hydrogen atom in two or three phenyl groups is 
 replaced by NH 2 , and further, the hydrogen of the NH 2 
 group is replaced by methyl, benzyl, phenyl, etc., we 
 obtain a series of nitrogenous compounds ; e.g. : 
 
 C 
 
 Triamidotriphenylmethane. 
 (Para-leucaniline.) 
 
 C 6 H 4 NH-C 6 H 5 
 C 6 H 4 NH-C 6 H 5 
 C 6 H 4 NH'C 6 H 5 
 IH 
 
 Diamidotriphenylmethane. 
 
 C 
 
 C 6 H 4 N(CH 3 ) 2 
 C 6 H 4 N(CH 3 ) 2 
 
 IH 
 
 Tetramethyldiamidotriphenylmethane. Tripnenylleucaniline. 
 (Leuco-base of malachite-green.) 
 
 C 6 H 4 N(CH 3 ) 2 
 C 6 H 4 N(CH 3 ) 2 
 C 6 H 4 N(CH 3 )H 
 H 
 P en tamethy lleucaniline, 
 
142 
 
 COAL-TAR COLOURS. 
 
 These compounds, called "leuco-bases," are colourless, 
 and yield colourless salts with acids. By oxidation they 
 are transformed, more or less readily, into the colour-bases, 
 which differ from the "leuco-bases" by containing one 
 atom of oxygen. 
 
 C . 
 
 C 6 H 4 NH 
 
 ' 
 
 H 
 
 Para-leucaniline. 
 
 6 H 4 NH 3 
 
 C 6 H 4 NH 2 
 OH 
 
 Para-rosaniline. 
 
 The colour-bases are generally colourless, or nearly so. 
 They unite with acids, with elimination of water to form 
 coloured salts, the real dye-stuffs. The manner in which 
 this splitting off of water takes place has not been satis- 
 factorily explained for all colouring matters. In the 
 case of para-rosaniline it takes place according to the 
 equation : 
 
 c 
 
 C 6 H 4 NH 3 
 C 6 H 4 NH 3 
 C 6 H 4 NH 2 +HC1 
 OH 
 
 'C 6 H 4 NH 3 
 
 C 6 H 4 NKHC1 
 
 Beside these mono- acid, coloured salts, the bases yield 
 a series of compounds containing two or more equivalents 
 of acid, which are generally yellow or brown. Thus, 
 hydrochloride of rosaniline, or magenta, C 20 H 19 N" 3 HC1, 
 will unite with two further molecules of hydrochloric 
 acid to form the triacid salt, C 20 H 19 N 3 .3HC1. 
 
 This explains the behaviour of the colouring matters of 
 this group in aqueous solution, or on the fibre, towards 
 concentrated acids. Decolonisation takes place, but on 
 adding water, the acid salt is decdmposed, and the original 
 colour is restored. 
 
THE EOSANILINE GROUP. 143 
 
 There exists also, in dilute solutions, a certain attrac- 
 tion between the normal salts (with one molecule of 
 hydrochloric acid) and the free acid, and the consequence 
 is that, in dyeing, the colouring matters of this group are 
 either not absorbed at all, or only very imperfectly so, 
 from a bath acidified with a mineral acid. For this reason 
 these dyes must be dyed in a neutral or only very slightly 
 acid bath. 
 
 The colouring matters of this group unite with the 
 fibres as salts, and not as free bases. This is conclusively 
 proved, in the first place, by the fact that when wool, for 
 instance, is heated in a colourless solution of magenta- 
 base, the fibre is soon dyed an intense red, which can only 
 result from the combination of the magenta-base with 
 some acid constituent of the fibre to form a coloured 
 insoluble salt or lake. Furthermore, it has been shown 
 than when wool or silk is dyed in neutral solutions of 
 the basic dyes (hydrochlorides), such as magenta, crystal 
 violet, chrysoidine, etc., all the hydrochloric acid remains 
 in the solution, and the only conclusion which can be 
 drawn is that a double decomposition has taken place 
 between a constituent or constituents of the fibre and the 
 hydrochloride of the colour-base. (See Journ. Soc. Dyers 
 Sf Col, 1888, p. 72.) They give with some acids precipi- 
 tates insoluble in water (colour-lakes). The tannic acid 
 lakes are soluble in alcohol. They also possess to some 
 extent the property of uniting chemically with basic 
 oxides, such as stannic oxide and alumina. 
 
 Thus, magenta may be fixed on cotton, if it is printed 
 with acetate or arseniate of alumina and then steamed, 
 but the colour is not fast. The weak affinity which 
 fibres prepared with mineral mordants possess for some 
 aniline dyes may, however, be ascribed in most cases to 
 physical influences. 
 
144 COAL-TAR COLOURS. 
 
 Malachite-green. 
 
 (Solid Green, Victoria Green, New Green, Benzal Green, Benzoyl 
 Green, Fast Green.) 
 
 The colouring matter prepared by heating benzotri- 
 chloride and dimethylaniline, is known as malachite-green. 
 Technically, the following method is more advantageous. 
 
 Benzaldehyde is heated with dimethylaniline and zinc 
 chloride in alcoholic solution. The leuco-base of the 
 green is thus formed : 
 
 n TT - 
 
 6 -i n FT 
 = 
 J _H 
 
 Benzaldehyde. Dimethylaniline. Tetramethyldiamido- 
 
 triphenylmethane. 
 
 The leuco-base is precipitated with water, freed from 
 unchanged dimethylaniline, dissolved in hydrochloric acid, 
 and oxidised with lead peroxide. The free colour-base 
 has the formula 
 
 C 6 H 4 N(CH 3 ) 3 
 
 V-/ /"I TT ~Vr//~1TT "\ 
 
 vygJILjI.1 \\jtt-vjv 
 
 OH 
 
 The manner in which it unites with acids, with 
 elimination of water, is not yet explained. Probably the 
 hydrochloride has the formula : 
 
 1 C 6 H 4 K(CH 3 ) 2 C1 
 
MALACHITE GREEN. 145 
 
 The hydrochloride is not well defined, and more difficult 
 to separate than the oxalate and zinc double salt, both of 
 which are commercial articles. 
 
 Properties. The oxalate has the composition 
 
 It forms tablets possessing a green metallic lustre, which 
 dissolve easily in water, alcohol, and amyl alcohol. 
 
 The zinc double salt, 3 (C 23 H 24 ]Sr 2 HCl) + 2ZnCl2 + 2H 3 0, 
 also crystallises well, with a yellow-green cantharides 
 lustre. An inferior quality consists of the ferric chloride 
 compound with the hydrochloride of the base. 
 
 The picrate is insoluble in water, and comes into 
 commerce under the name of Malachite green soluble in 
 
 By adding caustic potash solution to a solution of one 
 of the above salts, the free base separates out. It crystal- 
 lises from petroleum spirit in colourless needles, which 
 melt at 126 to 130. 
 
 The solutions of the colouring matter are bluish-green ; 
 concentrated acids turn them orange-yellow, but the 
 original colour is restored on dilution. Stannous chloride 
 produces a green precipitate, chloride of lime decolourises 
 the solution. 
 
 Application. Silk is dyed in a pure soap bath, and 
 brightened with acetic acid. Wool is dyed in a very 
 weak acid bath. If too much acid is present, the colour- 
 ing matter is not taken up completely. For dyeing 
 and printing cotton, tannin is used, along with alumina 
 mordants, or tartar emetic. 
 
 This green will not stand either soaping or milling, 
 nor is it fast to light. 
 
 It may be detected on the fibre by the reaction with 
 soap, or the orange colour with hydrochloric acid, which 
 is restored by water. Acetic acid removes the colouring 
 matter with a bluish-green tint, ammonia and alkalies 
 
 L 
 
146 COAL-TAR COLOURS. 
 
 completely decolourise. By heating, tlie colour does not 
 change to violet. (Distinction from methyl-green.) 
 
 Other greens belonging to this class are Ethyl-green, 
 Solid Green J (New Victoria Green, Brilliant Green). 
 They are obtained when diethylaniline, C 6 H 5 N(C 3 H 3 ) 2 , is 
 used instead of dimethylaniline, C 6 H 5 lSr(CH 3 ) 2 . These 
 colouring matters also occur in commerce as oxalates or 
 sulphates. The oxalate, C 27 H 32 N 2 + C 2 H 3 4 + H 2 0, loses 
 its golden lustre by the action of the light. The zinc 
 double salt has a red metallic lustre. 
 
 These colouring matters have a yellower tone than 
 those obtained from dimethylaniline. 
 
 Helvetia- green, Acid Green. 
 
 These colouring matters are the sulphonic acids of the 
 various sorts of benzaldehyde-greens. They are prepared 
 by two methods : either the green base is treated with 
 concentrated sulphuric acid, or the leuco-base is treated 
 with sulphuric acid, and the resulting leuco- sulphonic 
 acids are oxidised. 
 
 The monosulphonic acid of solid green, C 23 H 33 No'S0 3 H, 
 crystallises in green needles, with a reddish-brown reflex. 
 It is easily soluble in hot water, with a green colour, but 
 only sparingly soluble in cold water. The sodium salt 
 is sparingly soluble in water. It forms white, silvery 
 needles, which gradually become green in the air. The 
 calcium, and most other salts, are sparingly soluble in 
 water. 
 
 The sulphonic acid of solid green J is darker coloured, 
 and possesses very little reflex. 
 
 Acid green dyes a brighter colour than solid green. It 
 may be dyed from baths containing more acid, but is far 
 less productive. Caustic soda solution gives no precipitate 
 in dilute solutions (difference from solid green) ; strong 
 soda ley gives a white precipitate. When dyed on the 
 
ACID GEEEN. 147 
 
 fibre, it gives nearly the same reactions as benzaldehyde- 
 green. The behaviour towards concentrated hydrochloric 
 acid serves to distinguish between the two. Helvetia- 
 green is turned greenish-yellow, and the liquid is coloured 
 yellow, while benzaldehyde-green turns a bright orange 
 and gives up very little colour. Water reproduces the 
 
 colour in both cases. 
 
 
 
 Light green $, Light green SF (yellow shade), Acid Green 
 SOF, Acid Green. 
 
 This colouring matter, which is the sodium salt of the 
 diethyldibenzyldiamidotriphenylcarbinol trisulphonic acid, 
 is obtained by acting upon benzaldehyde with benzyl - 
 ethyl aniline, C 6 H 3 N(C 2 H 5 )(C 7 H 7 ), sulphonating the re- 
 sulting diethyldibenzyldiamidotriphenylmethane and oxi- 
 dising the sulphonic acid thus obtained. Its constitution 
 is represented by the formula : 
 
 C 6 H 4 -S0 3 Na 
 
 C 6 H 4 N(C 2 H 5 )(CH 2 -C 6 H 4 'S0 3 Na) 
 C 6 H 4 tf (C 2 H 5 ) (CH 2 -C 6 H 4 -S0 3 Na) 
 OH 
 
 The commercial product forms a light-green amorphous 
 powder which dissolves in water with a green colour. The 
 aqueous solution gives with hydrochloric acid a yellow- 
 brown colouration, and a slight dirty violet precipitate 
 with caustic soda. 
 
 Light green S dyes wool and silk a bright green in an 
 acid bath, and is used largely, especially in wool-dyeing, in 
 conjunction with other acid dyes for the production of com- 
 pound shades. Thus, it may be used along with acid violet 
 for the production of various shades of peacock blue. 
 
 Guinea green J3 is the sodium salt of the ^'sulphonic 
 acid of diethyldibenzyldiamidotriphenylcarbinol, and 
 forms a dark-green powder which resembles Light-green S 
 in its properties and application. 
 
148 COAL-TAR COLOURS. 
 
 Viridine, Alkali-green. 
 
 If in the preparation of malachite-green, the dimethyl- 
 aniline is replaced by diphenylamine, NH(C 6 H 5 ) 2 , viridine 
 is obtained. It probably possesses the constitution 
 
 C ^ C 6 H 4 -N-C 6 H 5 -H 
 C 6 H 4 -N-C 6 H 5 -HC1. 
 
 It forms microscopic, bronze-colonred crystals, which are 
 insoluble in water, but are soluble in alcohol with green 
 colour. 
 
 By treating it with sulphuric acid, a sulphonic acid, 
 insoluble in water, is formed. The soluble salts of the 
 latter form the alkali-green of commerce. 
 
 A green colouring matter, probably identical with 
 viridine, is formed by the oxidation of benzyl diphenyl- 
 amine, N(C 6 H 5 ) 2 C 7 H 7 , with chloranil. It also yields an 
 alkali-green with sulphuric acid. 
 
 Alkali-green only finds a very limited application, as it 
 cannot be dyed in an acid bath. It is dyed in the same 
 manner as alkali-blue, and may be used along with it for 
 producing greenish-blue shades. 
 
 Aniline-red, Magenta. 
 
 Commercial analine-red is not a uniform substance, 
 but a mixture of the salts of two bases para-rosaniline, 
 C 19 H 19 N 3 0, and rosaniline, C 20 H 21 N 3 0. 
 
 Since Hofmann's important investigations on aniline 
 dyes, numerous attempts have been made to discover the 
 constitution of the above bases. This question was first 
 solved by MM. Emil and Otto Fischer. 
 
 One of the two bases, para-rosaniline, like benzaldehyde- 
 green, is a derivative of triphenylmethane. The other, 
 
MAGENTA. 
 
 149 
 
 rosaniline, is derived from tolyldiphenymethan. They 
 possess the formulae 
 
 (C^-NH, 
 
 )C 6 H 4 -NH 2 
 ^C^-ira, 
 VOH 
 
 Para-rosaniline. 
 
 -NH 2 
 
 C 6 H 4 'NH 3 
 
 OH 
 
 Eosaniline. 
 
 They unite with acids with elimination of water. Thus, 
 with hydrochloric acid, they form 
 
 -NIL 
 
 C <J C 6 H 4 -NH 2 and 
 
 C 6 H 4 -NH'HC1 
 
 C 
 
 C 6 H 4 -NH 3 
 C 6 H 4 -NH-HC1. 
 
 In order to give a clearer idea of the formulae, a descrip- 
 tion of the synthesis of rosaniline will be given here. 
 
 (1.) If triphenylmethane is treated with nitric acid, 
 trinitrotriphenylmethane is obtained. 
 
 C, 
 
 CH 4 -N0 
 
 C^ 6 ^ 5 yields 
 
 ,H 
 
 Triphenylmethane 
 
 .H 
 
 Trinitrotriphenylmethane. 
 This, when treated with chromic acid, yields 
 
 OH 
 
 Trinitrotriphenylcarbinol 
 
150 COAL-TAR COLOURS. 
 
 which, when partially reduced by zinc powder and acetic 
 acid, is converted to para-rosaniline ; i.e., triamidotri- 
 phenylcarbinol. 
 
 The para-rosaniline immediately unites with acetic acid, 
 to form acetate of para-rosaniline. 
 
 ( C 6 H 4 -NH 2 
 C 4 C 6 H 4 'NH 2 
 
 Rosaniline may be prepared from tolyldiphenyl methane 
 in a similar manner. 
 
 (2.) A method, analogous to the preparation of benzalde- 
 hyde-green, has been patented, but is without practical 
 value. 
 
 By heating the hydrochlorides of aniline, and para- 
 amidobenzaldehyde with zinc chloride, para-leucaniline is 
 obtained according to the equation : 
 
 - 
 
 6Ba - C H . 
 
 -H (.H 
 
 Ainidobenzaldehyde. Aniline. Para-leucaniline. 
 
 The para-leucaniline may be oxidised with chloranil, 
 C 6 C1 4 2 , or manganese dioxide, to para-rosaniline. 
 
 (3.) Para-nitrobenzaldehyde acts oh aniline sulphate 
 according to the equation : 
 
MAGENTA. 151 
 
 
 
 -H VH 
 
 Nitrobenzaldehyde. Aniline. Nitrodiamidotriphenylmethane. 
 
 The purified product is heated with ferrous chloride, 
 whereby the nitro group is reduced to an amido group, 
 and the ferric chloride formed converts the methane 
 hydrogen into hydroxyl, so that in one operation para- 
 rosaniline is produced. 
 
 Rosaniline may be prepared by this method, if 1 mole- 
 
 cule of nitro-benzaldehyde acts on 1 molecule of ortho- 
 
 _ PTT 
 toluidine, C 6 H 4 _ -M-rr 3 , and 1 molecule of aniline. 
 
 (4.) Further, by the action of benz aldehyde on aniline 
 or a mixture of aniline and toluidine : 
 
 I + 2CH-NH = C + H0 
 
 52 = 2 
 
 n = I ^G 
 
 -H In 
 
 Benzaldehyde. Aniline. Diamidotriphenylmethane. 
 
 The diamidotriphenylmethane is treated with nitric 
 acid, and the resulting iiitrodiamidotriphenylmethane 
 
 c |cX'NHs 
 
 ( 
 
 H 
 
 is converted into para-rosaniline by method 3. 
 
 The formation of rosaniline from para-nitro, and from 
 para- amido benzaldehyde, proves that at least one of the 
 amido groups must be in the para position as regards the 
 methane carbon. The study of the decomposition pro- 
 ducts of rosaniline has further shown the relative positions 
 
152 
 
 COAL-TAR COLOURS. 
 
 of the amido and methyl groups, so that the constitu- 
 tion may be expressed as follows : 
 
 NIIsC 
 
 NHiz.C 
 
 C.NHz. 
 
 N.H2 
 
 Para-rosaniline. 
 
MAGENTA. 
 
 153 
 
 Commercial rosaniline is obtained by oxidation of aniline 
 oil. From the constitution of rosaniline, it follows that 
 para-toluidine 
 
 OCH 
 
 must be contained in it, as it is the only toluidine which 
 can yield the methane carbon in the para position, with 
 regard to the amido groups. 
 
 The most beautiful reds are obtained when para-toluidine 
 and aniline, or para-toluidine, aniline, and ortho -toluidine 
 are oxidised according to the following equations : 
 
 + 2C 6 H 5 NH 2 + 30 - C 19 H 17 N ? + 3H 2 0. 
 Para-toluidiue. Aniline. Para-rosaniline. 
 
 + 30 
 
 Ortho-toluidine. 
 
 + C 6 H 5 NH 2 
 
 Para-toluidine. Aniline. 
 
 Bosaniline. 
 
 Meta-toluidine only occurs in small quantities in com- 
 mercial toluidine. It yields no red with para-toluidine. 
 
 The aniline oil containing aniline and toluidine in the 
 proper proportions for aniline-red is known as " red oil," 
 or aniline oil for red. 
 
 Manufacture of Magenta. 
 
 (1) Arsenic acid method. 100 pts. of aniline oil are heated 
 with 125 pts. of 75 per cent, arsenic acid for eight hours, in 
 a boiler fitted with distilling tube. The temperature must 
 
 - 
 
154 COAL-TAR COLOURS. 
 
 be somewhat above the boiling-point of aniline (182) 
 Water, and a part of the aniline, distil over. The residue 
 is then boiled with water, and filtered from the insoluble 
 part. The solution contains arseniate and arsenite of 
 rosaniline, a yellow bye-product (chrysaniline), besides 
 excess of arsenic acid and resinous substances. 
 
 The residue consists of mauvaniline, violaniline, and 
 some chrysaniline. 
 
 To the solution containing arsenic a large excess of 
 common salt is added. A double decomposition takes 
 place, rosaniline hydrochloride (magenta) and arseniate 
 of soda being formed. The excess of salt dissolves, and 
 the colouring matter, being sparingly soluble in salt solu- 
 tion, separates out. This method of separating colouring 
 matters by salt is much used, and is technically known as 
 " salting out." 
 
 The separated magenta is then crystallised from water, 
 or dissolved again, salted out, and crystallised. The 
 mother-liquors yield an impure magenta (cerise, gera- 
 nium, etc.). 
 
 (2) Nitrobenzene process. Instead of using arsenic acid 
 as an oxidising agent, nitrobenzene and ferrous chloride 
 are employed. The latter is oxidised by the nitrobenzene, 
 and then oxidises the aniline, so that it acts as a trans- 
 mitter of oxygen. 100 pts. of aniline oil are mixed with 
 two-thirds of the quantity of hydrochloric acid necessary 
 to saturate them, then with 50 pts. of nitrobenzene, and 
 heated, with gradual addition of 3 to 5 pts. of iron filings. 
 The magenta is prepared from the crude melt, as in the 
 arsenic-acid process. The bye-products contain much 
 induline, but no chrysaniline. 
 
 (3) Mercury Process* By oxidation of aniline with 
 mercuric nitrate, a very pure nitrate of rosaniline is 
 obtained, which may be converted into the hydrochloride 
 (rubine) by double decomposition with common salt. 
 * This process is at present obsolete. 
 
MAGENTA. 155 
 
 Properties of the Rosaniline Salts. 
 
 Commercial rosaniline contains besides para-rosaniline ; 
 but as the properties of the two are almost identical, we 
 shall not distinguish between them here. The salts with 
 one molecule of acid have a metallic-green appearance 
 in reflected light; in transmitted light, in thin layers, 
 they are red. The solutions are crimson, and are not 
 fluorescent. 
 
 Hydrochloride of rosaniline, Magenta, C 20 H 19 N 3 HC1, forms 
 rhombic crystals, rather sparingly soluble in pure water, 
 but more readily in acidified water and in alcohol. Amyl 
 alcohol also takes it up. It absorbs moisture, on standing 
 in the air. With concentrated hydrochloric acid it gives 
 brown needles of the triacid salt, C 20 H 19 N 3 '3HC1, which 
 dissolve with a brown colour. By pouring into excess of 
 water, the original mono-acid salt is produced. 
 
 Caustic alkalies, ammonia, baryta, and lime decompose 
 magenta solutions, and separate free rosaniline in a crystal- 
 line state. Pure, freshly prepared rosaniline is colourless. 
 
 Reducing agents, as zinc and acetic acid, stannous 
 chloride, sulphurous acid, decolourise magenta, forming 
 salts of leucaniline. Leucaniline is not reconverted into 
 rosaniline by atmospheric oxygen ; the reduced solutions 
 of rosaniline remain colourless. (Distinction from Mag- 
 dala-red and safranine.) 
 
 Aldehyde and alcoholic shellac solution convert ma- 
 genta into blue colouring matters. 
 
 Strong oxidising agents (chlorine, chloride of lime, 
 permanganate of potash) decolourise magenta solutions. 
 Limited oxidation produces a new colouring matter. 
 
 A yellowish-red colouring matter, aniline-scarlet, is 
 obtained by the action of hydrogen peroxide or nitrate of 
 lead on magenta. Chromic acid gives a brown colouring 
 matter. 
 
 Thus rosaniline shows some resemblance to aniline in 
 
156 COAL-TAR COLOURS. 
 
 its reactions with, oxidising agents. The reason of this 
 is, that the amido groups of aniline and toluidine are 
 contained in it in an unaltered state. 
 
 Nitrate of rosaniline, C 20 H. 19 N S ''H.'NO^ is sometimes pre- 
 pared on a small scale by the mercury process, and occurs 
 in commerce as a very pure colouring matter known as 
 azaleine. 
 
 Acetate of rosaniline, C 20 H 19 N 3 *C 2 H 4 02,is the most soluble 
 rosaniline salt. It forms large green crystals, which 
 after some time become brownish-red. 
 
 Chromate of rosaniline is a brick-red powder, nearly 
 insoluble in water. 
 
 Dilute magenta solutions give a red precipitate with 
 tannic acid. 
 
 Commercial magenta. Pure magenta should consist only 
 of the salts of rosaniline and para-rosaniline. Commercial 
 magenta generally contains water, mineral impurities, 
 resinous substances, and if prepared by the arsenic-acid 
 process, more or less arsenic (up to 6'5 per cent.). 
 
 The purest qualities are the blue shades. The yellow 
 ones contain a yellow colouring matter, phosphine. 
 Magenta prepared by the nitrobenzene process contains 
 no phosphine. 
 
 Aniline-red is sold under many different names, as 
 magenta, azaleine, roseine, fuchsine, new red, rubine, 
 etc. 
 
 Magenta-violet, fuchsine V, is a mixture of magenta and 
 mauvaniline hydrochloride. 
 
 Cerise is a colouring matter containing magenta, which 
 is used in dyeing browns. The mother-liquors after salt- 
 ing out still contain small quantities of magenta, phos- 
 phine, and a brown colouring matter. They are pre- 
 cipitated with milk of lime ; the precipitate is dissolved in 
 acidulated water, and salted out. It forms an amorphous 
 brown mass, with a vitreous fracture. 
 
 Cardinal, amaranth, are names applied to mixtures of 
 
PETECTION OF MAGENTA. 157 
 
 colouring matters of which the chief constituent is 
 magenta. 
 
 Pure para-rosaniline hydrochloride, obtained by heating 
 together nitrobenzene and para-nitrotoluene with aniline, 
 para-toluidine, iron, and hydrochloric acid, is also a com- 
 mercial product. The crystals are somewhat more com- 
 pact than those of ordinary crystallised magenta. 
 
 Testing of magenta. Good magentas are always well 
 crystallised, and dissolve in pure water, without leaving 
 any residue. The testing of magenta by comparative dye- 
 trials, as well as the testing for adulteration and impurities, 
 has already been referred to in the general part. 
 
 A solution of pure magenta is entirely decolourised by 
 sulphurous acid, while impure samples remain yellow or 
 brown. 
 
 For the qualitative estimation of arsenic in magenta 
 made by the arsenic-acid process, Marsh's test is used. 
 
 In order to estimate arsenic quantitatively the ma- 
 genta is fused with soda and nitre, dissolved in water, 
 filtered, the arsenic precipitated with magnesia mixture, 
 and the precipitate weighed as magnesium ammonium 
 arseniate. 
 
 Application of magenta. Silk and wool are dyed in 
 neutral baths, silk may also be dyed in a bath containing 
 boiled-oif liquor. In brightening silk, the shades become 
 slightly bluer. 
 
 In the preparation of magenta for printing, it must be 
 remembered that by warming with many organic bodies, 
 a violet is produced. Such substances are impure spirit, 
 shellac, some gums, tannin, and fats. 
 
 Fibres dyed with magenta give up part of their colour 
 to boiling water, while soap removes it completely. 
 
 In calico-printing, magenta is used for the production 
 of a brown colour (magenta-puce). Suitably thickened 
 magenta is printed, and passed through a hot bath con- 
 taining bichromate of potash and sulphuric acid, a process 
 
158 COAL-TAR COLOURS. 
 
 which resembles the production of aniline-black on cotton 
 yarn. Magenta-puce is also obtained, if, in the receipts 
 for printing aniline-black, the aniline salt is replaced by 
 magenta, that is, a mixture of magenta, chlorate of soda, 
 and copper sulphide are printed and steamed. This pro- 
 cess is, however, not used on a large scale. 
 
 Detection on the fibre. The decolonisation with acids 
 (formation of triacid salts), with alkalies (separation of 
 free rosaniline), and with sodium sulphide (reduction to 
 leucaniline), are characteristic. When dyed along with 
 vegetable colouring matters, the detection is easy. An 
 alcoholic extract is made, which is described below. 
 
 Detection of magenta in food, etc. Chemically pure 
 magenta, and that which is prepared without arsenic 
 acid, is not poisonous. The use of magenta for colouring 
 articles of food, toys, and confectionery, is nevertheless 
 forbidden in some countries. 
 
 In late years, magenta has been largely used for 
 colouring wines, and many methods have been proposed 
 for distinguishing between magenta and the natural 
 colouring matter of wine, and also for the recognition of 
 other artificial and natural colouring matters used for 
 colouring wines. 
 
 Romei bases his process for the detection of magenta in 
 coloured liquids, upon its solubility in amyl alcohol. 50 
 c.c. of the wine are warmed with 10 c.c. of lead acetate solu- 
 tion, sp. gr. 1'32, in order to remove the natural colouring 
 matters. To the filtered solution, 1 drop of acetic acid 
 and 10 c.c. of amyl alcohol are added, when the whole is 
 well agitated. If the wine is pure, the amyl alcohol will 
 remain colourless. If magenta is present, it is coloured 
 red ; rosolic acid yields a yellow, and orchil a red-violet. 
 The layer of amyl alcohol is removed, and shaken with 
 dilute ammonia. If a red- violet colour is formed, rosolic 
 acid is present ; a blue-violet colouration indicates orchil, 
 and a decolourisation indicates magenta. 
 
ACID MAGENTA. 159 
 
 I> runner's method is to stir the warmed wine with stearic 
 acid. On cooling, the stearic acid is violet in presence 
 of magenta. Falieres method is also easy to carry out. 
 The wine is treated with caustic baryta or ammonia, when 
 the rosaniline is liberated. The liquid is then shaken 
 with ether, and a piece of silk or wool placed in the ethereal 
 solution. When the ether has evaporated, the red colour 
 on the fibre is developed with acetic acid, and the fibre is 
 tested for magenta in the usual manner. 
 
 From some red wines, magenta separates along with the 
 natural red colouring matter (oenolin) on the sides of the 
 vessel. Cotton collects this precipitate, treats it with 
 water, adds ammonia, and shakes with ether, etc. 
 
 Preserved fruits and confectionery 5 give red-coloured 
 solutions with water, and the aqueous solution is tested 
 according to the method adopted for the red wines. 
 
 For the detection of magenta in orchil and cudbear, for 
 the adulteration of which it has been used extensively, 
 Rawsons method (see Journ. Soc. Dyers and Col., 1888, 
 p. 68) is the most exact. 
 
 From 1 to 2 grms. of cudbear (or an equivalent amount 
 of orchil liquor) are boiled with 50 c.c. of alcohol, and 
 afterwards diluted with 100 c.c. of water ; 15 to 20 c.c. of 
 a strong solution of basic acetate of lead-(sp. gr. 1*25) are 
 then added, followed after stirring by a similar quantity 
 of strong ammonia. The mixture is filtered, and if the 
 amount of magenta present is to be estimated, the precipi- 
 tate is washed with a solution containing 1 part of 
 ammonia, 5 parts of alcohol, and 10 parts of water ; other- 
 wise the washing may be neglected. With pure cudbear 
 the filtrate is quite colourless ; if magenta be present it 
 is either colourless or pink, according to the amount of 
 ammonia present in the solution. The liquid is then 
 acidulated with acetic acid, when the presence or absence 
 of magenta is at once made apparent ; in the case of pure 
 cudbear or orchil the solution remains colourless, whereas, 
 
160 COAL TAR COLOURS. 
 
 if a salt of rosaniline be present, the well-known colour of 
 magenta is immediately developed. If further proof be 
 wanting, a small piece of worsted yarn may be dyed in 
 the solution and afterwards tested in the usual way with 
 such reagents as hydrochloric acid, caustic soda, and a 
 mixture of hydrochloric acid and stannous chloride. 
 
 By means of this method it is possible to detect with 
 certainty 1 part of magenta in 100,000 parts of cudbear. 
 
 Acid Magenta, Magenta S t Rubine S. 
 
 A mixture of the trisulphonic acids of rosaniline and 
 para-rosaniline is obtained by heating dried rosaniline 
 with fuming sulphuric acid to 100 170. The product 
 is poured into water, and neutralised with milk of lime. 
 After filtering from the gypsum, the lime salts are de- 
 composed with soda. The carbonate of lime is removed 
 by filtration, and the soda salts are evaporated to dryness. 
 The normal soda salt is hygroscopic, and is converted by 
 hydrochloric acid into the acid salt. 
 
 The constitution of the para-rosaniline trisulphonic acid 
 is 
 
 G \ 
 
 C 6 H NH 
 
 Acid magenta forms a green metallic-looking powder, 
 easily soluble in water, with a red colour. The solution is 
 decolourised by alkalies, but no precipitate is formed. 
 Dilute acids (also carbonic acid) reproduce the colour. 
 The colour of the solution is only slightly altered by 
 acids. Acid magenta is about half as strong, in dyeing, as 
 ordinary magenta ; but it can be dyed from strong acid 
 baths, and may therefore be combined with other acid 
 
ANILINE-BLUE. 161 
 
 dyes and mordants. Thus it gives good results with 
 indigo extract, Helvetia-green, and acid yellow. 
 
 On the fibre, acid magenta may be distinguished from 
 magenta by its behaviour towards a mixture of equal 
 parts of water and hydrochloric acid. Magenta is de- 
 colourised, acid magenta is unaltered, but the solution 
 takes up some of the colour, and becomes cherry-red. 
 
 Magenta S has been used for colouring wines. It can- 
 not be detected in the same manner as magenta, as it is 
 insoluble in ether, and does not unite with stearic acid. 
 
 Aniline-blue. 
 
 (1.) Spirit soluble Slue. Gentian-blue 6J5, Spirit-blue 0, 
 Opal-blue, Bleu de nuit, Bleu lumiere. 
 
 If the hydrogen atoms of the amido groups of magenta 
 are replaced by organic radicals, the colour becomes violet 
 or blue. The shade is bluer, the more hydrogen atoms 
 are replaced in this manner. The ethyl derivatives are 
 the reddest, then come the salts of the methyl and benzyl 
 rosaniline, and the purest blue is the hydrochloride of 
 triphenylrosaniline. 
 
 Blue from rosaniline. In order to prepare commercial 
 spirit-blue, rosaniline (prepared from the purest blue 
 shade of magenta by precipitation with ammonia or lime) 
 is heated with a large excess of aniline (ten times the 
 quantity) and some benzoic acid. The operation takes 
 place in a distilling vessel. The temperature is the 
 boiling-point of aniline, the excess of which distils over, 
 along with ammonia water. 
 
 When a small test taken out shows that the action is 
 finished, the whole is cooled to 60, and saturated with 
 hydrochloric acid. The blue separates, and the aniline 
 hydrochloride dissolves. The precipitate is well washed 
 with dilute hydrochloric acid, and then with water, dried 
 and powdered, and sold as spirit-blue. 
 
 M 
 
162 COAL-TAR COLOURS. 
 
 The formation of the blue base is shown in the following 
 equation : 
 
 O so Hi fl N s + 3C 6 H 5 -NH 2 = C 20 H 1? (C 6 H 5 ) 3 N 3 + 3NH 3 . 
 Rosaniline. Aniline. Triphenylrosaniline. 
 
 The part which benzoic acid plays in the manufacture 
 is not known; bat it is necessary, in order to obtain good 
 results, to add a monobasic acid, such as stearic or benzoic 
 acid. 
 
 Spirit-blue is further purified by dissolving in aniline, 
 and precipitating with hydrochloric acid, or by other 
 methods. This finer product is known as basic-blue or 
 opal-blue. 
 
 The less pure products have a reddish shade, which is 
 especially noticeable in artificial light. The best qualities 
 give colours which appear pure blue by gas- or lamp-light, 
 and are sometimes sold as light-blue (bleu lumiere). 
 They are also distinguished as spirit-blue 5B or 6B, the 
 direct blue as B, while the intermediate products are 
 known as 2B, 3B, 4B, according to their purity. 
 
 A blue with a decided red tone is obtained when 
 magenta is used instead of rosaniline, and acetate of soda 
 instead of benzoic acid, in the manufacture. Spirit-blue 
 R, or Parma-blue, is an intermediate product between the 
 spirit-blues and the spirit-violets. 
 
 Spirit-soluble Diphenylamine-blue. 
 
 Aniline-blue may also be prepared from diphenylamine. 
 Diphenylamine, C 12 H n N, is a crystalline body, possessing 
 an agreeable smell. It dissolves easily in alcohol and 
 ether, sparingly in water. It is a weak base. 
 
 In order to prepare it, equal molecules of aniline and 
 .aniline hydrochloride are heated to 250. 
 
 C 6 H 5 NH 2 + C 6 
 
 Aniline. Aniline hydrochloride. Diphenylamine-hydrochloride. 
 
METHYL- AND ETHYL-BLUE. 163 
 
 Diphenylamine forms a blue colouring matter when 
 heated with oxalic acid to 120-130. 
 
 3(C 6 H 5 ) 2 ira + C 2 H 2 4 = CO + 3H 2 + C 19 H 14 (O a H 6 ) s N 8 . 
 
 Diphenylamine. Oxalic acid. Diphenylamine-blue. 
 
 The excess of oxalic acid is removed by washing with 
 water, unaltered diphenylamine by boiling with benzene, 
 when the residue is transformed into the hydrochloride 
 and purified in the usual manner. 
 
 Diphenylamine-blue is of a finer quality, but at the 
 same time more expensive than rosaniline-blue. 
 
 The chemical constitution of these two dye-stuffs is not 
 identical. The rosaniline-blue is a derivative of com- 
 mercial rosaniline, which consists chiefly of rosaniline, 
 C 20 H 19 N 3 . On the other hand, diphenylamine-blue is the 
 hydrochloride of triphenylated para-rosaniline, and has 
 the formula : 
 
 H 
 
 H 
 
 (C 6 H 4 -N-C 6 H 6 -HC1. 
 
 Methyl- and ethyl-Hue. The above constitutional formula 
 of diphenylamine-blue shows that it still contains two 
 replaceable hydrogen atoms in the amido groups. 
 
 It has hitherto not been possible to introduce more than 
 three phenyl groups, but the hydrogen atoms are easily 
 replaceable by ethyl and methyl, and the colouring 
 matters produced possess a still purer tone than diphenyl- 
 amine-blue. In order to produce methyl- or ethyl-blue, 
 methyldiphenylamine or ethyldiphenylamine 
 
 C 6 H 5 N C 6 H 5 
 
 <-CH 3 , 
 
164 COAL-TAE COLOURS. 
 
 is heated with oxalic acid. These bases are produced by 
 the action of methyl or ethyl alcohol on diphenylamine 
 hydrochloride : 
 
 (C 6 H 5 ) 2 NH-HC1 + CH 3 OH - (C 6 H 5 ) 3 N-CH S -HC1 + H 2 0. 
 
 Or the colouring matters may be prepared by the action of 
 methyl or ethyl chloride on diphenylamine-blue. 
 
 The purest aniline-blue is obtained by melting methyl- 
 diphenylamine on a water-bath, with chloranil (C 6 Cl 4 Oo), 
 and then heating to 130. The cooled mass is powdered, 
 washed with hydrochloric acid, dissolved in alcohol and 
 precipitated with water. 
 
 The chloranil used in this process is obtained by the 
 action of hydrochloric acid and chlorate of potash on 
 phenol. In the pure state it forms golden leaflets, in- 
 soluble in water. It sublimes at 150. It is a tetrachlor 
 derivative of quinon, C 6 H 4 H 2 . Its oxidising property 
 depends on the fact that it readily takes up hydrogen, 
 like quinon itself, and is converted into tetrachlorohydro- 
 quinon : 
 
 Chloranil. Tetrachlorohydroquinon. 
 
 Commercial chloranil contains besides trichloroquinon, 
 which is, however, as powerful an oxidising agent as 
 chloranil. 
 
 Properties of aniline-blue. The hydrochloride of tri- 
 phenylrosaniline is a brownish powder, which becomes 
 pure blue at 100. It is insoluble in water, but dissolves 
 in boiling alcohol with a beautiful blue colour. 
 
 The acetate is more easily soluble in alcohol, and some- 
 times occurs in commerce in a state of solution. 
 
 Hydrochloric acid, nitric acid, and stannous chloride give 
 blue precipitates in an alcoholic solution of aniline-blue. 
 Caustic sodaand ammonia give violet-blue precipitates, and 
 
SOLUBLE-BLUE. 165 
 
 at the boil, colourless solutions. If water is added to these 
 solutions, free triphenylrosaniline, C 2 oH 17 (C 6 H 5 ) 3 N 3 'OH, 
 is thrown down as a white precipitate, which rapidly 
 becomes blue in the air. 
 
 Application. The greatest part of the spirit-blue made 
 is used in the manufacture of soluble-blue and alkali-blue. 
 
 The finest qualities, as spirit-blue 5B and 6B, diphenyl- 
 amine-blue, methyl- and ethyl-blue, are used in silk-dyeing 
 for producing light and very pure shades, which cannot 
 be obtained with soluble blue. The colouring matter is 
 dissolved in 40 to 50 parts of methylated spirits, filtered, 
 and dyed in a bath containing boiled-off liquor. 
 
 In wool-dyeing, spirit-blue has been used for producing 
 bright blues which have to stand milling ; but it has been 
 superseded for this purpose by Victoria-blue and night- 
 blue, which yield faster colours. It is dyed in a bath con- 
 taining alum or sulphuric acid. Brighter shades can 
 be obtained by the addition of a little stannic chloride. 
 On cotton it is best fixed by means of an alumina mor- 
 dant. The material is first worked in a strong soap 
 solution, well wrung and passed into a bath of alum, when 
 oleate or stearate of alumina will be fixed on the fibre. 
 The dye-bath is made up as for wool. 
 
 (2.) Soluble-blues. 
 
 Spirit-blue, on being heated with sulphuric acid, is 
 easily transformed into sulphonic acids, some of which are 
 soluble in water in the free state, others as their alkali 
 salts. 
 
 Diphenylamine-blue, soluble in water, may be obtained 
 direct by heating diphenylamine sulphonic acid 
 
 ( C G H 4 -S0 3 H 
 
 N C 6 H 5 
 
 (H 
 
 with oxalic acid. 
 
166 COAL-TAR COLOURS. 
 
 The first blue soluble in water was prepared by Nichol- 
 son in 1862, and was called, after him, "Nicholson's Blue." 
 
 The more sulpho groups are introduced into triphenyl- 
 rosaniline, the more easily soluble the products become ; 
 but their fastness decreases in the same proportion, both 
 as regards the action of light and air, soap and alkalies. 
 The higher sulphonic acids, such as rosaniline tetrasul- 
 phonic acid, C 38 H 27 N 3 (S0 3 H) 4: , are therefore never pre- 
 pared. 
 
 The sulphonic acids are distinguished as follows : 
 
 The monosulphonic acid is insoluble in pure or acidified 
 water ; its alkali salts dissolve with a light-brown colour, 
 the solution becomes red-brown, when heated with an 
 excess of alkali. 
 
 The disulphonic acid is soluble in water, but insoluble 
 in water containing sulphuric acid. The solution in 
 excess of alkali is yellow. 
 
 The trisulphonic acid dissolves both in pure water and 
 in water containing sulphuric acid. Its alkaline solution 
 is colourless with excess of alkali. 
 
 Alkali-blue. Nicholson's blue. 
 
 Alkali-blue is the soda-salt of the monosulphonic acid, 
 and is represented by the formula 
 
 NH-CH 
 ( M 
 
 
 It is obtained by treating spirit-blue with sulphuric acid 
 at 30 to 35 C., and pouring the resulting brown-yellow 
 solution into water. The precipitate is collected, washed, 
 and dissolved in the required (calculated) quantity of 
 soda. The dye-stuff is then salted out, or evaporated to 
 dryness, with addition of a little carbonate of ammonia. . 
 
ALKALI-BLtJE. 167 
 
 Alkali-blue D is obtained by the action of strong sul- 
 phuric acid on diphenylamine blue, and is probably the 
 sodium salt of the corresponding monosulphonic acid, 
 C 37 H 28 N 3 S0 3 Na, while Bavarian-Hue DSF is the sodium 
 salt of the disulphonic acid with some of the trisulphonic 
 acid. 
 
 Properties. Alkali-blue comes into commerce as a 
 brownish powder, or in lumps. It should dissolve with- 
 out residue in about 5 parts of water. 
 
 By acidifying with acetic acid, the liquid is coloured 
 blue ; and on boiling, the free sulphonic acid separates as 
 a blue precipitate. 
 
 By acidifying with hydrochloric acid, the free acid is 
 completely precipitated; and the solution is rendered 
 colourless when pure alkali-blue is present; but if the 
 di- and tri-sulphonic acids are present, the solution 
 remains coloured. If the test sample gives off carbonic 
 acid on acidifying, it most likely contains soda. 
 
 Concentrated soda solution colours the solution red- 
 violet; on boiling, red-brown. Excess of ammonia de- 
 colourises the solution. Stannous chloride produces a blue 
 precipitate. 
 
 Application. -Alkali-blue is generally dyed in a feebly 
 alkaline solution. It is not used in cotton- dyeing, as it 
 will not combine with acid mordants ; but it is used very 
 extensively for bright-blue shades on silk and wool. 
 
 The dye-bath should be made perfectly free from lime- 
 salts, as the lime- salt of the sulphonic acid is insoluble in 
 water. Calcareous water can be made suitable by boiling 
 with a small quantity of tin-salt. The dyeing is effected 
 nearly at a boil, borax, soluble glass, soda or stannate of 
 soda being added to the dye-bath, to render the dye more 
 even and faster. 
 
 Alkali-blue is taken up by the fibre in an almost 
 colourless condition. In order to develop the colour, the 
 material is passed after dyeing through a weak, hot acid 
 
168 COAL-TAR COLOURS. 
 
 bath (" developing "). The dyes are made faster to mill- 
 ing by employing alumina or tin-salts as mordants. Alkali 
 blue is little used for producing mixed colours, as it re- 
 quires this peculiar treatment in dyeing, which is essen- 
 tially different to the application of most other colouring 
 matters. Mixed shades can, however, be produced by add- 
 ing various acid colours to the developing bath. 
 
 Soluble-blue, Water-blue, Cotton-blue. 
 
 Spirit-blue is heated with 3 to 4 parts of sulphuric acid 
 to 60 for a length of time, and finally the temperature is 
 raised to 100-110. After cooling, the product is mixed 
 with three or four times the quantity of water, to pre- 
 cipitatf the colouring matter. It is then filtered off, 
 dissolved in a large quantity of boiling water, and the 
 excess of sulphuric acid removed by cautious addition of 
 milk of lime. The calcium sulphate is filtered off, and 
 the filtrate mixed with soda or carbonate of ammonia, 
 and evaporated to dryness. 
 
 Soluble-blue contains principally salts of triphenyl- 
 rosaniline- and triphenylpararosaniline- trisulphonic acid, 
 C 38 H 28 N 3 (S0 3 H) 3 and C 37 H 26 N 3 (S0 3 H) 3 . The ammonia- 
 salt forms a mass with a coppery lustre, or a granular 
 powder; the soda-salt generally occurs as dark-blue 
 irregular lumps. 
 
 China-blue is a name given to a very porous water-blue, 
 which is obtained by adding to a very concentrated and 
 slightly acidulated solution of water-blue, carbonate of 
 ammonia. Methyl-blue, Methyl-blue SI. for cotton, Brilliant 
 cotton-blue greenish, methyl water-blue is the sodium salt of 
 pure triphenylpararosaniline trisulphonic acid, C 37 H 26 N 3 
 (SO 3 Na) 3 . The reactions of water-blue are similar to those 
 of alkali-blue. The colouring matter is not precipitated 
 by acids. Caustic soda decolourises the solution. 
 
PHENYL-VIOLET. 169 
 
 Application. Soluble-blue is principally used in cotton 
 dyeing. It is either fixed by means of tannin, along with 
 alum, tartar emetic, or tin-salts. For some purposes it 
 suffices to treat the cotton in a cold solution of the dye to 
 which alum has been added. 
 
 This dye-stuff further serves for producing compound 
 colours on wool and silk ; it possesses the advantage over 
 alkali-blue that it may be dyed from acid-baths, and may 
 thus be combined with many other colouring matters. 
 As a self-colour on wool and silk it is never used, as it is 
 not so fast and not so productive as alkali-blue. 
 
 Detection of aniline-blue on the fibre. Concentrated sul- 
 phuric acid decolourises. Water-blue gives a blue solu- 
 tion. Hydrochloric acid nearly decolourises spirit-blue 
 and alkali-blue. 
 
 Spirit-blue first becomes light-blue and is then gradually 
 decolourised by ammonia, while alkali- and water- blue 
 disappear immediately. 
 
 Caustic soda turns spirit-blue to a grey- violet ; alkali- 
 blue to a yellow-brown ; and water-blue to a red-brown. 
 
 Stannous chloride and hydrochloric acid decolourise 
 spirit-blue and alkali- blue gradually, and remove water- 
 blue with a pure blue colour. 
 
 Alcohol strips spirit- and alkali-blue even in the cold, 
 while water-blue is not taken up even at a boil. 
 
 Phenyl-violet. Spirit-violet. 
 
 If the manufacture of aniline-blue is altered, so that 
 less aniline is used, and the mixture heated for a shorter 
 period, a mixture of mono- and a diphenylrosaniline is 
 obtained, which contains very little triphenylrosaniliiie, 
 and which, when combined with hydrochloric acid, finds 
 a limited application as "spirit-violet." 
 
 It does not give as bright colours as methyl-violet, but 
 they stand milling better, and therefore find some appli- 
 cation in wool-dyeing. 
 
170 COAL-TAB COLOURS. 
 
 Detection on the fibre. Alcohol removes the colour, 
 ammonia decolourises, caustic soda turns brown. Its 
 behaviour towards stannous chloride serves to distinguish 
 it from other violets. It is removed with a blue colour, 
 and is only decolourised very slowly. 
 
 Hofmann's Violet. Dahlia, Primula. Red-violet, 5 R 
 extra, Violet 5 R. 
 
 The Hofmann's violets consist of various ethyl and 
 methyl derivatives of rosaniline. 
 
 For their preparation, an alcoholic solution of rosaniline 
 is treated with methyl or ethyl iodide and caustic soda. 
 
 The quantity of iodide used depends upon the shade 
 required ; for red shades it is least, and for pure violet 
 greatest. At most three methyl or ethyl groups may be 
 introduced in this manner, according to the equation 
 
 C 20 H 21 N 3 + 3CH 3 I + 3NaHo = 
 Bosaniline. 
 
 C 20 H 18 (CH 3 ) 3 ON 3 + SSTal + 3H 2 O. 
 
 Trimethylrosaniline. 
 
 The ethyl derivatives are redder than those of methyl. 
 
 The salt used in dyeing is the hydrochloride. It yields, 
 when carefully prepared, a very pure, reddish violet. 
 
 The application of this dye is very limited, as it has 
 been almost completely replaced by methyl-violet. 
 
 Methyl-violet. Paris-violet. 
 
 Preparation. This violet is produced by direct oxida- 
 tion of the purest dimethylaniline, C 6 H 5 N(CH 3 ) 2 , (free 
 from methyl toluidine), with copper chloride. 
 
 The copper chloride is prepared by double decomposi- 
 tion of nitrate or sulphate of copper with common salt. 
 The solution is mixed with a large quantity of common 
 
METHYL-VIOLET. 171 
 
 salt, and dimethylaniline and acetic acid are poured in. 
 The mass is moulded into cakes, and dried at 40 to 50, 
 when it assumes a green metallic appearance. It is then 
 extracted with a quantity of boiling water, insufficient to 
 dissolve all the salt. The violet is insoluble in the salt 
 solution, and therefore remains behind. 
 
 The residue is dissolved in water and the copper pre- 
 cipitated by sulphuretted hydrogen. The copper sulphide 
 is removed by nitration, when the colouring matter is 
 salted out, and is purified by re-dissolving in water and 
 salting out again ; the product is then either crystallised 
 or converted into the zinc double salt. 
 
 In place of the large quantity of salt used to modify the 
 action of the copper chloride on dimethylaniline, sand 
 may be conveniently substituted. To remove the copper, 
 gaseous sulphuretted hydrogen, or sodium sulphide, is 
 used. 
 
 A colouring matter known as chlor -anil-violet : , which is 
 probably identical with methyl-violet, is obtained by 
 the oxidation of dimethylaniline with chloranil. (See 
 p. 164.) 
 
 The base contained in methyl-violet is pentamethyl- 
 pararosaniline 
 
 C 6 H 4 -N-(CH 3 ) 2 
 C \ C 6 H 4 -N-(CH 3 ) 2 
 
 Its formation is expressed by Caro and Graebe in the 
 equation 
 
 3C 6 H 5 tf (CH 3 ) 2 + 30 = 3H 2 + C 19 H 12 (CH 3 ) 5 N 3 . 
 Dimethylaniline. Pentamethylpararosaniline. 
 
 It is distinguished from Hofmann's violet in its chemical 
 constitution, being a pentamethylated pararosaiiiline, 
 while Hofmann's violet is only trimethylated rosaniline. 
 
172 COAL-TAK COLOUES. 
 
 Properties. Methyl- violet (mark B) comes into com- 
 merce as a hydrochloride, C 19 H 12 (CH 3 ) 5 N 3 'IIC1, or as a 
 zinc doable salt. The latter forms small crystals, while 
 the first either consists of a powder, or of irregular lumps. 
 Methyl-violet has a green metallic reflex ; it is easily 
 soluble in water and alcohol. 
 
 Dilute solutions are turned pure blue by very little 
 hydrochloric acid; more acid makes them dichroic. Thin 
 layers are then green, while thicker ones are much less 
 transparent, and of a red colour. An excess of acid turns 
 the solution yellow, owing to the formation of acid salts. 
 Ammonia produces a lilac- coloured precipitate, and caustic 
 soda a brown-violet one, the solution becoming colourless 
 on boiling. 
 
 Chromic acid gives a dirty violet precipitate, chloride 
 of lime decolourises, and stannous chloride gives a blue- 
 violet precipitate, becoming lighter on boiling. 
 
 For dyeing, 1 part of colour is dissolved in 50 to 100 
 parts of water, and the solution filtered. Silk is dyed in 
 a bath of acidulated " boiled-off liquor." The shades 
 may be brightened by tartaric acid or very little sulphuric 
 acid. Cotton is dyed by the tannin and tartar-emetic 
 process. 
 
 Methyl-violet is also used in calico-printing. It is fixed 
 by albumen, glycerin and arsenic or some form of tannin. 
 It is also used for topping goods dyed with iron mordants 
 and alizarin, in order to brighten and beautify the fast 
 violet produced. Its aqueous solution thickened with 
 glycerin is also used for marking with india-rubber 
 stamps, 
 
 Detection on the fibre. Methyl- violet is gradually re- 
 moved from the textile fibres by boiling with water. 
 Hydrochloric acid removes part of the colour ; the fibre 
 is coloured greenish yellow, but the original colour is 
 restored on washing with water. Ammonia decolourises, 
 caustic soda turns it red-violet and gradually decolourises 
 
BENZYL-ROSANILINE-VIOLET. 173 
 
 it. A mixture of stannous chloride and hydrochloric acid 
 gives a greenish yellow to yellow colour. 
 
 Eegina-purple. 
 
 This colouring matter consists of the acetate of ortho- 
 tolylpararosaniline, and is obtained by acting upon the 
 product which distils over in the manufacture of magenta 
 by the arsenic acid process with magenta base and acetic 
 acid at 120. It forms a green powder which dyes a red 
 shade of violet. 
 
 Benzyl-rosaniline-violet. 
 (Methyl-violet 6B.) 
 
 On heating methyl- violet with benzyl chloride, 
 C 6 H 5 CH 2 C1, alcohol, and soda or lime, in a vessel pro- 
 vided with an upright condenser, part of the methyl 
 groups are replaced by benzyl, C 7 H 7 , and a series of bases 
 is formed, of which the first members are 
 
 C 19 H 13 (CH 3 ) 4 (C 7 H 7 )N 3 OH 
 
 and 
 C 19 H 13 (CH 3 ) 3 (C 7 H 7 ) 2 N 3 OH. 
 
 The excess of alcohol and benzyl chloride is distilled off, 
 and the colouring matter is purified in the usual manner, 
 by salting out, etc. 
 
 It comes into commerce as the hydrochloride or the zinc 
 double salt. The highest benzylated product is marked 
 6B, and between it and methyl-violet are 2B, 3B, 4B, 5B, 
 produced by mixing the brand B and 6B. 
 
 Benzyl-violet is very similar in its reactions to methyl- 
 violet. It gives somewhat bluer colours. 
 
 Detection on the fibre. Treated with caustic potash ley, 
 methyl-violet becomes red-violet ; benzyl- violet, light-blue. 
 Both are decolourised on standing. 
 
174 COAL-TAB COLOURS. 
 
 Crystal-violet. Violet 6J3. 
 
 This colouring matter is the hydrochloride of hexa- 
 methylpararosaniline 
 
 ( C 6 H 4 N(CH 3 ) 2 
 C C 6 H 4 N(CH 3 ) 2 
 I C 6 H 4 N(CH 3 )oCl. 
 
 It may be obtained by the action of perchlormethyl 
 formiate or dimethylaniline in presence of aluminium 
 chloride. It is also formed, according to another method, 
 by the action of carbon oxychloride COC1 2 on dimethyl- 
 aniline : 
 
 3C 6 H 5 N(CH 3 ) 2 + 2COC1 2 = 
 Dimethylaniline. 
 
 CC1[C 6 H 4 N(CH 3 ) 2 ] 3 + 3HC1 + C0 2 . 
 
 Crystal- violet. 
 
 It occurs in the form of well-defined crystals which 
 possess a peculiar greenish brown metallic reflex. They 
 dissolve in water and alcohol with a deep violet-blue 
 colour, and crystallise easily from the former, but not 
 from the latter solution. The leuco-base has the formula 
 C 25 H 21 ISr 3 and melts at 173. 
 
 The colouring matter yields in dyeing a very blue 
 shade of violet ; otherwise it resembles ordinary methyl- 
 violet, not only in its application, but also in its reactions 
 
 Ethyl-violet. 
 
 This colouring matter is formed by the action of di- 
 ethylaniline on tetraethyldiamidobenzophenon chloride. It 
 is the hydrochloride of hexaethylpararosaniline, C 19 H 10 N 3 
 (C S H,),C1. 
 
METHYL-GREEN 175 
 
 The commercial product forms a green crystalline 
 powder easily soluble in water with a violet colour. It 
 resembles methyl- violet in its properties and application. 
 
 Acid-violet, 6B. 
 
 This colouring matter consists essentially of the sodium 
 salt of pentamethylbenzylpararosanilinemonosulphonic 
 acid 
 
 C 6 H 4 N(CH 3 ) 3 
 CH 3 
 CH 2 -C 6 H 4 -S0 3 Na 
 
 and is obtained by the oxidation of the corresponding 
 leuco-compound. 
 
 The commercial product forms a dark-violet powder, 
 soluble in water with a violet, in alcohol with a blue 
 colour. It dyes wool and silk violet in an acid bath, and 
 is largely used along with other acid colours for the pro- 
 duction of mixed shades. 
 
 Bed-violet 4 B.8. is the sodium salt of dimethylrosani- 
 linetrisulphonic acid, and is formed by the action of 
 fuming sulphuric acid on dimethylrosaniline. It forms a 
 reddish- violet powder which dyes wool and silk in an acid 
 bath. The -shades obtained are somewhat bluer than 
 those obtained with acid magenta. 
 
 Methyl- green. 
 
 Preparation. Green colouring matters are formed when 
 methyl- and ethyl-rosanilines are heated with excess of 
 methyl chloride, or iodide, or ethyl chloride and iodide. 
 
 A similar dye was formerly prepared by the action of 
 methyl iodide on Hofmann's violet or rosaniline, and was 
 known as iodine-green, bright-green, or vert lumiere. It is 
 now replaced by methyl-green, which is prepared from 
 methyl chloride and methyl-violet. Methyl-violet is 
 
176 COAL-TAR COLOURS. 
 
 dissolved in alcohol, and the free base precipitated in a 
 fine state of division, by caustic soda or baryta. The base 
 is mixed with methyl-chloride, and heated some hours to 
 60-70 in horizontal, closed cylinders. The mass is 
 poured into water, the unaltered violet base* filtered off, 
 and the filtrate neutralised with hydrochloric acid. By 
 the addition of a very small quantity of salt solution a 
 further quantity of methyl-violet is precipitated. The green 
 dye is then precipitated with salt or zinc chloride, and the 
 precipitate purified by boiling with alcohol. Methyl- 
 green is formed by the addition of methyl-chloride to 
 methyl- violet, as is expressed by the equation 
 
 C 19 H 13 (CH 3 ) 5 N 3 -HC1 + CH 3 C1 = 
 Methyl-violet. Methyl- chloride. 
 
 C 19 H 13 (CH 3 ) 5 N 3 CH 3 C1HC1. 
 Methyl-green. 
 
 Accordingly, it possesses the constitution 
 
 C 6 H 4 -N"(CH 3 ) 2 -CH 3 C1 
 C ^ C,H 4 -N-(CH 3 ) 2 
 C 6 H 4 -N-CH 3 HC1. 
 
 L' 
 
 Properties. Methyl-green comes into commerce as the 
 zinc double salt, in small crystals. The salt 
 
 C 19 H ia (CH 3 ) 5 -N 8 -CH 8 Cl-HCl + ZnCl 2 + H 2 0, 
 
 forms green needles ; a salt containing more zinc forms 
 large coppery prisms. Another variety occurs in the form 
 of a light-green powder. 
 
 All the varieties dissolve in water and alcohol, with a 
 green colour, but they are insoluble in amyl alcohol. 
 (Distinction from benzaldehyde-green.) 
 
 Hydrochloric acid colours the solution greenish yellow, 
 
 * The green base is soluble in water. 
 
METHYL-GREEN. 177 
 
 a triacid salt being formed. On diluting with water, the 
 original colour is produced. Stannous chloride gradually 
 decolourises, and chloride of lime destroys the colour. 
 
 The behaviour of methyl-green towards alkalies requires 
 a short explanation. The constitutional formula shows it 
 to be the chlormethylate of a tertiary base, containing a 
 pentatomic nitrogen atom, N v , which is combined with 
 phenylene, C 6 H 4 , three methyl groups, CH 3 , and one 
 chlorine. The simplest example of this class of bodies is 
 tetramethylammonium chloride 
 
 CH 3 
 CH 3 
 CH 3 
 CH 3 
 01, 
 
 which is not decomposed by alkalies, but which gives up 
 its chlorine to moist silver oxide. A strong base, soluble 
 in water, is thus formed : 
 
 ( N 
 
 =2 N * +2AgCl. 
 
 Tetramethylammonium Tetramethylammonium 
 
 chloride. hydrate. 
 
 By decomposing methyl-green solution with dilute al- 
 kalies, a reddish solution is produced, which on dilution 
 becomes colourless. Concentrated alkalies produce a 
 resinous precipitate, containing chlorine, which is soluble 
 in pure water. This compound is the base corresponding 
 to rosaniline : 
 
 C 6 H 4 N-(CH 3 ) 3 C1 
 
 VOH. 
 
 When its aqueous solution is treated with silver oxide, 
 
 N 
 
178 COAL-TAR COLOURS. 
 
 the chlorine is removed, and the easily soluble ammonium 
 base is produced : 
 
 By heating methyl-green to 100, methyl chloride is 
 gradually given off, the decomposition being very rapid 
 at 130. Methyl-violet remains behind : 
 
 C 19 H 12 (CH 8 ) 5 N 3 -CH 8 C1-HC1 = C 19 H 12 (CH 3 ) 5 -N 3 'HC1 + 
 
 Green. Violet. 
 
 CH 3 C1. 
 
 Methylchloride. 
 
 Picric acid, C 6 H 2 (N0 2 ) 3 OH, produces in solutions of 
 methyl-green a dark-green, crystalline precipitate, which 
 contains no chlorine. 
 
 The picrate of methyl-green is nearly insoluble in water, 
 but soluble in alcohol. It is sometimes sold as " spirit- 
 soluble green." Methyl-green is easily distinguished 
 from other dye-stuffs by the above reactions. 
 
 In order to test the value of methyl-green, a dye-trial 
 and an estimation of the ash are made. The sample 
 should be entirely soluble in water, with a blue-green 
 colour. If a green residue remains, it may consist of the 
 picrate, which, however, dissolves completely in alcohol or 
 dilute soda solution. 
 
 If the picrate contains excess of picric acid, this is easily 
 detected by a dye-trial. A skein of silk or wool is placed 
 in the solution, and removed. A second skein placed in 
 the same solution is dyed yellow, if excess of picric acid 
 is present. 
 
 If the aqueous solution of methyl-green gives a pre- 
 cipitate with alkalies, the presence of methyl- violet is in- 
 
METHYL-GREEN. 179 
 
 dicated; this is owing to defective purification. The pre- 
 cipitate is filtered off, and the colour of its solution in 
 hydrochloric acid is noticed. 
 
 An adulteration with soluble blue is recognised by 
 adding a saturated solution of picric acid. The green is 
 completely precipitated, and the liquid acquires a greenish 
 tinge in presence of aniline-blue. In extreme cases it 
 may be bluish-green, indicating the presence of large 
 quantities of aniline-blue. 
 
 Methyl-green should be entirely soluble in boiling al- 
 cohol. Frequently a residue remains of a greenish-white 
 powder, which is also, like methyl-green, turned violet on 
 being heated to 130. It is the chloride of nona-methyl 
 para-leukaniline : 
 
 It is often formed, as a bye-product, in considerable 
 quantities. In purifying methyl -green with alcohol, on 
 a large scale, it is left behind ; and when dried and 
 powdered, often serves for adulterating methyl-green. It 
 is easily soluble in water, and is therefore not detected in 
 the ordinary use of the dye-stuff. 
 
 Application. In dyeing with methyl-green, the dye-bath 
 should never reach the boil, as some violet is likely to be 
 produced, and this would influence the desired colour. 
 This decomposition takes place still more readily in 
 presence of mineral acids. For the same reason, goods 
 printed with methyl-green should not be steamed for a 
 long time. 
 
 Silk is dyed in a lukewarm bath containing boiled-off 
 liquor. In brightening, tartaric or acetic acid is used. 
 If a yellower tone is required, picric acid is added to the 
 brightening bath. 
 
180 COAL-TAR COLOURS. 
 
 An aqueous, warm solution of methyl-green does not 
 dye wool well, only bluish-grey shades being produced. 
 Better results are obtained when the dyeing is done in an 
 alkaline bath, and the colour is subsequently developed 
 with acid. Another method is to fix with tannin. 
 
 But the best results are obtained when the wool is mor- 
 danted with sulphur, according to Lauth's process. For 
 this purpose, the wool is first mordanted with hyposulphite 
 (thiosulphate) of soda and hydrochloric acid, alum or 
 sulphuric acid. It is then w^ell washed and dyed with 
 methyl-green. Acetate of zinc is frequently added to the 
 dye-bath, and this is especially necessary when picric acid 
 has been added for the production of a yellower shade. 
 The zinc salt is gradually decomposed by the sulphur con- 
 tained in the wool, zinc sulphide being formed ; and this 
 is as good a mordant for methyl-green as free sulphur. A 
 little of the methyl-green is taken up by the fibre, the 
 acetic acid produced by the action of the sulphur on the 
 zinc acetate fixes a quantity of picric acid, and then a 
 little acetate of soda is added, and the methyl-green is all 
 fixed. For wool-dyeing, methyl-green has been almost 
 entirely replaced by acid-green and benzaldehy de-green, 
 as these dyes require no mordant, are not altered by heat, 
 and they serve better for compound colours. Cotton is 
 mordanted by the tannin process. 
 
 Detection on the fibre. The reaction on heating is very 
 characteristic for methyl-green. A bit of the material is 
 heated a little above 100, when it becomes violet if dyed 
 with methyl-green. 
 
 The following reactions also serve for its detection : 
 Excess of hydrochloric acid colours the fibre yellow ; on 
 washing with water, the original colour is reproduced. 
 Stannous chloride, ammonia, and soda-ley decolourise. 
 Acetic acid or alcohol remove the colour, yielding blue- 
 green solutions. 
 
AUKAMINES. 181 
 
 Colouring matters derived from tetrametliyldiamidobenzo- 
 plienon. 
 
 These colouring matters are obtained by the action of 
 tetramethyldiamidobe.nzophenon, 
 
 /C 6 H 4 N(OH 3 ) 3 
 CO 
 \C 6 H 4 N(CH S ) 2 , 
 
 on the hydrochlorides of certain amines in presence of 
 condensing agents. They are all basic colouring matters, 
 and are used chiefly in the dyeing of cotton. 
 
 Aur amines. Ordinary auramine is obtained in the 
 following manner : 25 kilos, tetramethyldiamidoben- 
 zophenon are well mixed with 25 kilos, ammonium 
 chloride and 25 kilos, zinc chloride, and the mixture is 
 heated for 4-5 hours to 150-160 C., care being taken to 
 agitate it well from time to time. The reaction is over as 
 soon as a sample taken out dissolves in water. The melt 
 is then allowed to cool, when it is broken up and extracted 
 first with cold water, acidulated with hydrochloric acid 
 in order to remove most of the unchanged ammonium 
 chloride and the zinc chloride. It is then extracted with 
 boiling water, and the colouring matter is precipitated 
 from the filtered solution by the addition of common salt. 
 The crystalline precipitate obtained in this way can be 
 further purified by crystallising from water. 
 
 Auramine is the hydrochloride of imidotetramethyldi- 
 amidodiphenylmethane, a colourless base which forms 
 with acids intensely yellow and for the most part well 
 crystallised salts. It possesses the formula 
 
 /C 6 H 4 N(CH 3 ) 
 C = NH +H 0. 
 
 \C 6 H 4 N(CH 3 ) 3 -HC1 
 
182 COAL-TAR COLOURS. 
 
 The hydrochloride, sulphate, and acetate are easily soluble 
 in water, while the double compound with zinc chloride, 
 as wejl as the sulphocyanide, are only very sparingly 
 soluble in cold water. Mineral acids, when added to the 
 solution, produce at first no change, but if allowed to act 
 for a length of time, or if boiled with them, the solution 
 is decolourised, the colouring matter being reconverted 
 into the ketonbase and ammonia. Alkaline reducing 
 agents, such as sodium amalgam, gradually decolourise 
 the alcoholic solution. On adding water, a colourless 
 crystalline reduction product is thrown down, which, 
 when treated with acetic acid and heated, gives a deep 
 blue colouration. If auramine is heated, with aniline up 
 to the boiling point of the latter, the mixture evolves am- 
 monia and becomes orange, phenylauramine being formed. 
 The auramine of commerce is a yellow powder which 
 dissolves easily in water with a yellow colour. It is 
 fixed on cotton with tannin and tartar emetic, and yields 
 an extremely pure and brilliant yellow, which is suffi- 
 ciently fast to soap and light for ordinary purposes. It 
 can also be dyed on cotton mordanted with Turkey-red 
 oil. The temperature in dyeing should not exceed 70 C., 
 since at higher temperatures the colouring matter is dis- 
 sociated with re-formation of ketonbase and ammonium 
 chloride. 
 
 Detection on the fibre. The fibre is decolourised by 
 strong sulphuric or hydrochloric acid, as well as by 
 caustic potash solution. 
 
 If, in the preparation of auramine according to the 
 above method, the ammonium chloride is replaced by the 
 hydrochlorides of aniline, toluidine, naphthylamine, or 
 other aromatic amines, substituted auramines are formed, 
 which vary in shade from yellow to light-brown. Thus 
 metaxylyl auramine yields in dyeing golden-yellow shades, 
 phenyl- and paratolyl-auramines yield orange shades, 
 
VICTORIA-BLUE, 183 
 
 while the metaphenylenediamine derivative yields an 
 orange -brown. 
 
 Victoria blue B. If tetramethyldiamidobenzophenon is 
 treated with phenyl-a-naphthylamine and phosphorus 
 oxychloride, a blue melt is obtained. The melt is first 
 extracted with cold water and is then dried, in which 
 state it comes into the market as Victoria blue B. 
 
 Victoria blue B possesses the constitutional formula 
 
 (C,,H 4 N(CH 3 ) 2 
 C ] C c H 4 lSr(CH 3 ) 2 
 (C 10 H 6 N(C 6 H 5 ). HOI, 
 
 according to which it is represented as the hydrochlo- 
 ride of tetramethyl-phenyl-triamido-diphenyl-naphthyl- 
 carbinol hydro-chloride. 
 
 It forms a dark-blue powder with coppery reflex, which 
 dissolves in water with a deep-blue colour. On boiling, 
 the solution is rendered turbid and the free colour base is 
 gradually thrown down as a reddish resinous precipitate. 
 In presence of acetic acid this decomposition does not 
 take place. Dilute sulphuric acid added to the aqueous 
 solution turns it first green and then orange, but on 
 neutralising the original blue colour is restored. This 
 change is no doubt due to the formation of salts contain- 
 ing more than one equivalent of acid. 
 
 Victoria blue B may be dyed on wool or silk in a bath 
 acidulated with acetic acid. The colours obtained are 
 very fast to soap, but not to light. Cotton is first mor- 
 danted with Turkey-red oil and aluminium acetate. 
 
 Detection on the fibre. Sulphuric acid changes the colour 
 of the fibre to a reddish-brown, which is, however, re- 
 stored to the original on washing with water. 
 
 Victoria blue 4 R, is obtained by the action of methyl- 
 
184 COAL-TAR COLOURS. 
 
 phenyl-a-naphthylamine on tetramethyldiamidobenzophe- 
 non and probably possesses the formula 
 
 r C 6 H 4 N(CH 3 ) 2 
 C ] C 6 H 4 N(CH 3 ) 2 
 
 (C 10 H G N(C 10 H 7 )(CH 3 )C1. 
 
 It dyes a much, redder shade than Victoria blue B, 
 but otherwise resembles it closely in application and pro- 
 perties. 
 
 Night blue. This colouring matter is obtained by the 
 action of paratolyl-a-naphthylamine on tetramethyl- 
 diamidobenzophenon and is represented by the formula 
 
 C C 6 H 4 N(CH 3 ) 2 
 
 I (C 10 H 6 N(C 6 H 4 -CH 3 ). HC1. 
 
 Night blue forms a violet powder with a bronze reflex. 
 It is soluble in water with a blue colour and is com- 
 pletely precipitated from its aqueous or slightly acid 
 solution by picric acid, naphthol yellow and many other 
 acid colouring matters. 
 
 In its application and properties night blue resembles 
 Victoria blue B. It dyes an extremely pure shade of blue, 
 which is fast to soap on wool or silk. 
 
 Maroon ( Chestnut- brown) . 
 
 The resinous magenta residue is boiled with dilute 
 hydrochloric acid, as in the manufacture of phosphine. 
 After filtering, without further separation, all the bases 
 are precipitated with milk of lime. After washing, the 
 colour is sold as " maroon paste," or is neutralized with 
 hydrochloric acid, and thus rendered soluble in water. 
 
ALDEHYDE-GREEN. 185 
 
 The various sorts of maroon give various reactions, 
 according to the proportion of the bases contained in 
 them. The solutions of the hydrochloric acid compound 
 in water may vary in colour from red to brown-violet. 
 Hydrochloric acid colours it yellow to brown ; ammonia 
 produces a dark, amorphous, flocculent precipitate, the 
 solution being nearly colourless. 
 
 The blue-violet colouring matter contained in maroon, 
 which is the hydrochloride of mauvaniline, may be pre- 
 pared by dissolving in water or dilute hydrochloric acid, 
 and isolating by fractional precipitation with salt. 
 
 The mauvaniline salt is precipitated first, and the 
 rosaniline and chrysaniline remain in solution. The 
 precipitate is purified by crystallising from boiling 
 water. 
 
 The salts of mauvaniline crystallise well, and possess a 
 beautiful bronze reflex. They dissolve sparingly in water, 
 with a light blue-violet colour. They are easily soluble 
 in hot water, especially after the addition of a little acid. 
 Alkalies and ammonia precipitate the free base, which 
 possesses the formula C 19 H 17 N 3 'H 3 0. Pure mauvaniline 
 gives beautiful and fast violet shades, but it cannot 
 be used along with other dye-stuffs. 
 
 Maroon gives a fine chestnut-brown. Silk is dyed in 
 a bath containing boiled- off liquor, wool in pure water. 
 Cotton is first mordanted with sumach or other tannin 
 matter. 
 
 Aldehyde-green. 
 
 This colouring matter is prepared by mixing a solu- 
 tion of rosaniline in sulphuric acid with aldehyde, and 
 warming, till a sample dissolves in water with a beautiful 
 green colour. It is then poured into a boiling solution of 
 hyposulphite of soda, boiled for some time, and filtered. 
 Silk and wool may be dyed directly in the filtrate, 
 
186 COAL-TAR COLOURS. 
 
 Aldehyde-green is now entirely replaced by other ani- 
 line greens. 
 
 5 INDULINES AND SAFRANINES. 
 
 This division of basic dyes includes two small groups 
 of dye-stuffs, which neither resemble each other in their 
 relation to the fibres, nor in their chemical constitution. 
 The only reason why they are described together is that 
 the representatives of the safranines, as well as those of 
 the indulines, may be obtained by the combination of the 
 same mother substances. 
 
 If an amine, such as aniline, is allowed to act upon 
 an amidoazo compound, as amidoazobenzene (aniline- 
 yellow), so that a compound is formed with evolution of 
 ammonia, an induline is formed : 
 
 C 6 H 5 NH 2 + C 6 H 5 N : N-C 6 H 4 NH 3 =NH3 + C 18 H 15 N 3 . 
 Aniline. Amidoazobenzene. Induline. 
 
 If, however, in the place of ammonia, hydrogen is 
 liberated, in other words, if the mixture of amine and 
 amidoazo body is oxidised, saf ranine is formed : 
 
 3 + = 
 
 O. Toluidine. Amidoazotoluene. 
 
 Saf ranine. 
 
 INDULINES. 
 
 Induline, Nigrosine, Indigen, Coupler's Blue. 
 
 Violaniline. In the blue, bluish-grey, grey-violet, or 
 black-coloured indulines and nigrosines of commerce. 
 
INDULINES AND SAFRANINES. 187 
 
 there are a number of colouring matters which are seldom 
 prepared in the pure state. They are, however, all closely 
 related to one well-studied base violaniline. 
 
 Viol aniline is formed, as has been stated on one or 
 two previous occasions, as a bye-product in the manu- 
 facture of magenta, by the arsenic-acid or nitrobenzene 
 process. 
 
 In order to prepare it, magenta residues are boiled with 
 hydrochloric acid, when the violaniline hydrochloride 
 remains insoluble, along with resinous matter. In order 
 to remove the latter, it is dissolved in hot aniline and 
 filtered. On cooling, pure violaniline hydrochloride is 
 precipitated. Violaniline is formed by the oxidation of 
 aniline free from tolnidine : 
 
 3C 6 H 5 -NH 2 + 30 - Cj 8 H 15 N 3 + 3H 2 0. 
 Aniline. Violaniline. 
 
 It may also be obtained by a direct process viz., by 
 heating aniline and nitrobenzene with iron, a process 
 greatly resembling the one used for magenta. The 
 only differences are, that different temperature and pro- 
 portions, and aniline free from, toluidine, are used. If 
 hydrochloride of aniline is heated, in alcoholic solution, 
 with amidoazobenzene to 160, a blue is obtained, accord- 
 ing to the above equation, which is apparently identical 
 with violaniline, and is known as azodiphenyl Hue. 
 Properties of violaniline. The hydrochloride 
 
 C 18 H 15 N 3 HC1, 
 
 is an amorphous, bluish-black powder, insoluble in water, 
 soluble in alcohol. By adding caustic alkalies to the al- 
 coholic solution, the free base is precipitated in flakes. 
 
 The alcoholic solutions of the spirit soluble nigrosines 
 and indulines are used in the preparation of black spirit 
 varnishes. They are also employed to some extent in 
 
188 COAL-TAR COLOURS. 
 
 calico-printing, and are fixed either by means of acetin or 
 ethjltartaric acid. 
 
 Indulines and nigrosines soluble in water, Fast blue R, 
 Fast-blue B, Blackley-blue, Guernsey-blue, Indigo substitute. 
 Yiolaniline contains, like rosaniline, hydrogen atoms 
 which are replaceable by organic radicals. Spirit- 
 soluble induline is obtained by phenylising violaniline. 
 The solubility in alcohol of the product obtained stands in 
 a direct ratio to the number of phenyl groups introduced. 
 The highest substituted product is triphenylviolaniline, 
 C 18 H 12 (C 6 H 5 ) 3 N' 3 . These colouring matters may be 
 rendered soluble in water by treating them with sulphuric 
 apid. The soluble indulines of commerce are generally 
 mono- and disulphonic acids. 
 
 The manufacturer has it in his power, by varying the 
 proportions, etc., in the nitrobenzene process, to prepare 
 dye-stuffs of various shades and solubility. 
 
 The addition of certain metallic salts (zinc or copper 
 chloride, etc.) has an influence on the shades of the pro- 
 duct. The composition of the aniline oil alters the 
 product, toluidine producing browner shades. The tem- 
 perature to which the melt is heated in the process of 
 manufacture is 230 C. By observing certain precautions 
 the product may be obtained directly soluble in water ; 
 others are sulphonated afterwards. 
 
 Properties. As shown above, the indulines and nigro- 
 sines vary considerably in their composition, and conse- 
 quently their reactions are not in all cases identical. The 
 following rules, however, hold good for both : 
 
 Hydrochloric acid produces in the blue-violet or blue 
 solution a similarly coloured precipitate ; alkalies and 
 ammonia redden the colour, but no precipitate is formed ; 
 tin- salts give a blue precipitate ; zinc powder and ammonia 
 decolourise the solution, especially on warming, but the 
 original colour is rapidly restored on exposure to the 
 air, / 
 
SAFRANINES. 189 
 
 Application. Silk is dyed in a bath containing boiled- 
 off liquor, and is afterwards brightened with acetic 
 acid. 
 
 Wool may be dyed in the same way as with alkali-bine 
 viz., first in an alkaline bath, and then developed with 
 acid. A better method is to treat the wool first with 
 chloride of lime solution, pass it into hydrochloric acid, 
 and then dye in a bath containing sulphuric acid. Indu- 
 lines and nigrosines yield very fast colours. 
 
 Detection on the fibre. The colours resist the action 
 of acids. Hydrochloric acid turns it, indeed, somewhat 
 bluer, but nitric acid is almost entirely without action. 
 Ammonia and caustic soda take up the colour, forming a 
 red-violet solution, which is decolourised by zinc powder ; 
 the colour is restored on filtering and exposure to air 
 Stannous chloride and hydrochloric acid strip the colour, 
 forming a green solution. Some nigrosines are decolour- 
 ised by chloride of lime, others are coloured reddish 
 grey. 
 
 SAFRANINES. 
 
 According to the most recent investigations of Witt, 
 Nietzki, and others, the safranines must be regarded as 
 derivatives of the hypothetical base azonium, and the 
 general formula for the chlorides would be represented 
 thus : 
 
 I \C1 
 X 
 
 in which R^ and R 2 each represent a bivalent and X a 
 monovalent radical. 
 
 Phenosafranine or Safranine B extra is the simplest 
 representative of this class of dyes, and is obtained by 
 
190 COAL-TAR COLOURS. 
 
 the oxidation of a mixture of one molecule paraphenylene- 
 diamineand two molecules aniline. It is para-amidophenyl- 
 para-amidophenazonium chloride and its constitution is 
 represented thus : 
 
 CH ' ~ N ~ 
 
 \ N / 6 * or 
 
 \n g ra p u i ca iiy NH 2 L > N- 
 
 /\ 
 
 u 
 
 The commercial product forms green glittering crystals 
 which dissolve in water with a red colour, and resemble 
 ordinary safranine in properties and application. 
 
 Safranine, Safranine T, Pink. 
 
 Safranine derives its name from the French safranon 
 (safflower). Preparation. It was formerly obtained by 
 the oxidation of a mixture of amidoazotoluene and tolui- 
 dine. 
 
 Amidoazotoluene is obtained by passing nitrous acid 
 into aniline oil rich in ortho-toluidine (" aniline for safra- 
 nine"). 
 
 Toluidine. 
 
 Amidoazotoluene. 
 
 The product is mixed with the aniline oil, and carefully 
 
SAFRANINES. 191 
 
 oxidised with arsenic acid, then washed, and the oxidation 
 completed by boiling with potassium bichromate. The 
 boiling solution is mixed with milk of lime, which pre- 
 cipitates arsenic compounds, a violet bye-product, and 
 chromic hydrate, while the safranine remains in solution. 
 The whole is filtered, the filtrate neutralised with hy- 
 drochloric acid, and the dye-stuff salted out. The last 
 impurities are removed by dissolving in water and salting 
 out again. 
 
 According to a more recent and improved process, 
 safranine is manufactured by the oxidation of a mixture 
 of monamines and diamines. As in the old process, the 
 aniline oil is converted into amidoazo compounds (amido- 
 azobenzene and amidoazo-orthotoluene). The product is 
 treated with zinc and hydrochloric acid, and there are 
 formed, on the one hand, aniline and ortho-toluidine, and 
 on the other, paraphenylenediamine, C 6 H 4 (NH 2 ) 2 , and 
 toluylene diamine, C 6 H 3 * CH 3 (N"H 2 ) 2 . For amidoazo- 
 toluene the reaction takes place according to the equa- 
 tion 
 
 Amidoazotoluene. Toluidine. 
 
 Toluylene diamine. 
 
 The product of the reaction is diluted with water, one 
 molecule of hydrochloride of toluidine added, and the 
 whole oxidised with potassium bichromate. The base is 
 purified as in the old process. 
 
 Properties. Safranine comes into commerce as a brown- 
 red powder. 
 
 The pure salt forms fine, reddish crystals, with a green 
 reflex, soluble in water and alcohol with a red colour. 
 The alcoholic solution shows a beautiful yellowish fluor- 
 
192 COAL-TAR COLOURS. 
 
 escence. It is insoluble in ether. Ammonia and alkalies 
 produce no considerable change in colour, and no pre- 
 cipitate, the base being easily soluble in water. 
 
 To prepare the pure base, a solution of the hydro- 
 chloride is digested with silver oxide, the silver chloride 
 filtered off, and the filtrate carefully evaporated to dry- 
 ness. The residue acts very much like the hydrochloride. 
 With picric acid, safranine forms a compound insoluble in 
 water. 
 
 Concentrated sulphuric acid turns an aqueous solution 
 of safranine blue, excess of strong acid turns it violet, and 
 then green. Zinc powder and acetic acid reduce it even 
 in the cold, leucosaf ranine being formed ; but the solution 
 becomes red again on exposure to the air. 
 
 Ordinary safranine consists of a mixture of tolusa- 
 franines and phenosafranines, C 21 H 21 N 4 C1, C 20 H 19 N 4 C1, 
 and C 19 H 17 N 4 C1, of which the following may serve as a 
 typical representative 
 
 | C 6 H 3 'CH 3 
 / 
 \C1 
 
 Application. Safranine belongs to the small group of 
 dye-stuffs which are taken up by animal fibres in alkaline 
 solutions. Silk is dyed in a bath containing boiled-off 
 liquor, wool in pure water. 
 
 In alkaline or neutral solutions, safranine possesses 
 some affinity for vegetable fibres, but the colours pro- 
 duced are not fast. Cotton is therefore mordanted first. 
 The best results are obtained by the use of tannin and 
 tartar emetic. 
 
 Detection on the fibre. Alcohol takes up the colour, 
 forming a red solution which possesses a yellow fluor- 
 escence. Dilute hydrochloric acid is without action, while 
 
NAPHTHALENE-RED. 193 
 
 concentrated acid colours it blue-violet. Ammonia and 
 caustic soda remove the colour, but without much altera- 
 tion. Stannous chloride and hydrochloric acid decolourise 
 on warming. 
 
 Naphthalene-red, Magdala-red, rosa-naphthylamine. 
 
 Preparation. This beautiful dye-stuff is obtained from 
 naphthylamine, C 10 H 7 NH 2 , in the same manner as azodi- 
 phenyl-blue is derived from aniline. It is prepared as 
 follows : 
 
 Alpha- naphthylamine is first converted into amidoazo- 
 naphthalene, C 10 H 7 N : N'C 10 H 6 'NH 2 ; for which purpose 
 naphthylamine hydrochloride is dissolved in water, and 
 mixed with a solution of caustic soda and sodium nitrite. 
 The formation takes place according to the equation 
 
 2 C 10 H 7 -NH 2 -HC1 + NaHO + NaN0 2 - 
 Alpha-naphthylamine 
 hydrochloride. 
 
 C 10 H 7 N : N -C 10 H 6 -KH 2 + 2NaCl + 3H 2 0. 
 Amidoazonaphthalene. 
 
 The amidoazo compound separates out. In the pure state 
 it forms beautiful red needles with a green reflex. The 
 product is finely powdered, and mixed with the requisite 
 quantity of alpha-naphthylamine, and so much acetic acid, 
 that on heating to 150 complete solution is effected. 
 The mass contains a violet colouring matter and excess 
 of alpha-naphthylamine, and it has therefore to undergo 
 a purification. The melt is boiled with a great excess of 
 hydrochloric acid and filtered. The filtrate is neutralised 
 with soda, and salt is added. Naphthalene-red being 
 sparingly soluble in water, is precipitated, whilst the violet 
 colour and naphthylamine remain in solution. The pre- 
 cipitate is purified by crystallisation from alcohol. 
 
 Properties. Magdala-red is the chloride of diamidonaph- 
 
194 COAL-TAR COLOURS. 
 
 thylnaphthazonium, and has the composition C 30 H 21 N 4 C1. 
 It is a dark-brown crystalline powder, which, may be 
 obtained in large crystals, with a greenish reflex, by 
 crystallization. It is only sparingly soluble in boiling 
 water, but dissolves in alcohol with a cherry-red colour, 
 the solution showing a cinnabar-red fluorescence. 
 
 This property is the best reaction for recognising naph- 
 thalene-red, as it is only resembled by some resorcin deri- 
 vatives, such as diazoresorufin. The latter differ, however, 
 from naphthalene-red in their behaviour towards caustic 
 alkalies. 
 
 Ammonia and caustic soda produce no precipitate ; with 
 soda the colour becomes violet, and the fluorescence dis- 
 appears. 
 
 Dilute acids are almost without action. 
 Concentrated sulphuric acid dissolves it with bluish- 
 black colour. 
 
 Zinc powder and acetic acid decolourise ; the colour 
 returns on exposure to the air. 
 
 Application. Naphthalene-red is used in silk-dyeing, 
 especially for light shades. It gives a beautiful pink 
 colour, with strong fluorescence, which is especially 
 beautiful on velvet. Artificial light affects neither the 
 colour nor the fluorescence. Darker shades are not bril- 
 liant, and may be produced better and cheaper than with 
 other colouring matters, such as eosin, safranine, etc. 
 
 Silk may be dyed in a bath containing pure soap, or 
 boiled-off liquor. One part of dye serves to produce a light 
 rose colour on 1,000 parts of silk. The shades may be 
 brightened with acids (tartaric, sulphuric). 
 
 The colouring matter is not suitable for wool, and 
 indeed, its high price would prevent it ever being used in 
 wood-dyeing. 
 
 Detection on the fibre. It is faster than magenta, eosin, 
 and safranine, and is neither affected by dilute acids nor 
 alkalies. Its fluorescence is very characteristic. Alcohol 
 
NEUTRAL-BLUE. 195 
 
 does not dissolve it from the fibre, a characteristic dif- 
 ference from eosin, which is readily removed. 
 
 The following colouring matters also belong, according 
 to their chemical constitution, to the group of the safra- 
 nines : 
 
 Girofle. This colouring matter is obtained by the 
 action of nitrosodimethylaniline hydrochloride on a mix- 
 ture of metaxylidine and paraxylidine hydrochlorides. It 
 is xylyldimethylamidophenylxylylazonium chloride, and 
 has the empirical formula C 24 H 27 N" 4 C1. The commercial 
 product forms a brown paste or a greyish-green powder, 
 which dissolves in water with a magenta colour. It dyes 
 a red-violet, and is used in calico printing for toning 
 colours printed with alizarin violet. 
 
 Basle-Hue is tolyldimethylamidophenotolylimidonaphth- 
 azonium chloride, C 32 H 29 N 4 C1, or 
 
 /N\ 
 
 (CH 3 ) 2 NC 6 H 3 | C 10 H 5 NH-C 6 H 4 -CH 3 
 \N/ 
 | \C1 
 
 ^6^4, *CH 3 , 
 
 and is obtained by the action of nitrosodimethylaniline 
 hydrochloride on ditolylnaphthylenediamine. It forms a 
 brown crystalline powder, which dissolves in water with 
 a blue- violet colour and dyes cotton mordanted with 
 tannin and tartar emetic blue. 
 
 Neutral-Hue is phenyldimethylpara-amidophenonaphth- 
 azonium chloride, C 24 H 20 N 3 C1, or 
 
 (CH 3 ) 2 NC 6 H 3 | C 10 H 6 
 \N/ 
 
 | \C1 
 
 w 6-*-M>" 
 
 f Neutral-blue is formed by the action of nitrosodi- 
 methylaniline hydrochloride on phenylnaphthylamine. It 
 
196 COAL-TAK, COLOURS. 
 
 forms a brown amorphous powder, which dissolves easily 
 in water with a violet colour. 
 
 Mauvein, Rosolan, Chrome-violet. 
 
 Violet colouring matters are obtained when aniline 
 containing toluidine is oxidised with chloride of lime, 
 permanganate of potash, lead peroxide, etc. 
 
 Amongst these is mauvem, Co 7 Ho 5 N 4 Cl, the first aniline 
 dye introduced into commerce, which was discovered by 
 Perldn in 1856. He obtained it by the oxidation of aniline 
 oil containing toluidine with chromic acid. It is not much 
 used in dyeing at present. 
 
 The two following colouring matters belong to the 
 eurhodines, which are closely allied to the safranines in 
 their chemical constitution. 
 
 Neutral-violet is the hydrochloride of dimethyldiamido- 
 phenazine 
 
 (CH 3 ) 2 NC 6 H 3 | C 6 H 3 -NH S -HC1. 
 
 The commercial product forms a greenish-black pow- 
 der, the dust of which, when inhaled violently, irritates the 
 mucous membranes, causing sneezing, etc. It dissolves 
 in water with a violet-red colour, and yields on cotton 
 mordanted with tannin and tartar emetic a red- violet. 
 
 Neutral-red is the hydrochloride of dimethyldiamido- 
 toluphenazine, C 15 H 17 N 4 C1, and is formed by the action of 
 nitrosodimethylaniline hydrochloride on metatolylene- 
 diamine. It dyes cotton mordanted with tannin and 
 tartar emetic bluish-red. 
 
 THE OXAZINES. 
 New-blue, Naphthylene-blue R, Fast-blue 2 B or R for 
 
NILE-BLUE. 197 
 
 cotton, Cotton-blue R, Meldolas-blue, is obtained by the 
 action of nitrosodimethylaniline hydrochloride on (3 naph- 
 thol. It is the chloride of dimethylphenylammonium-/?- 
 naphthoxazine, C 18 H 15 N" 2 OC1, or 
 
 I 
 
 The commercial product forms a dark -violet powder 
 with bronze reflex, the dust of which violently attacks the 
 mucous membranes. It dissolves in water with a blue- 
 violet colour, and yields on cotton mordanted with tannin 
 and tartar emetic, or, better still, with tannin, and iron, a 
 deep indigo-blue shade. 
 
 Muscarin is the chloride of dimethylphenylpara- ammo- 
 nium-/?- oxynaphthoxazine, C 18 H 15 N 2 O 2 C1, and is obtained 
 by the action of nitrosodimethylaniline hydrochloride on 
 a dioxy naphthalene. Its constitution is represented by 
 the formula 
 
 j~~ "I 
 
 C1N(CH 3 ) 2 C 6 H 3 ()C 10 H 5 OH. 
 
 Muscarin forms a brown -violet powder, sparingly 
 soluble in cold but easily soluble in hot water, with a 
 blue-violet colour. The aqueous solution is decolourised 
 by zinc powder, but the colour is restored on exposure to 
 the air. It dyes cotton mordanted with tannin and tartar 
 emetic blue. 
 
 Nile-Hue is the sulphate of dimethylphenylpara-ammo- 
 nium a amido - naphthoxazine, (C 18 H 16 N 3 O) 2 S0 4 . The 
 constitution of the corresponding hydrochloride is repre- 
 sented by the formula 
 
198 COAL-TAR COLOURS. 
 
 Nile-blue is formed by the action of nitrosodimethyl- 
 meta-amidophenol on a naphthylaruine. 
 
 The commercial product forms a dull -green crystalline 
 powder, which dissolves easily in hot water Avith a blue 
 colour. By the addition of hydrochloric acid to the 
 aqueous solution, the hydrochloride is precipitated in 
 minute needle-shaped crystals, which appear violet in 
 transmitted light and green in reflected light. Caustic 
 soda produces a red precipitate, which is taken up by 
 ether, producing a brown-orange solution with a charac- 
 teristic dark-green fluorescence. 
 
 Nile-blue dyes wool and silk in a neutral bath a red 
 shade of blue. Cotton is previously mordanted with 
 tannin and tartar emetic. 
 
 Gallocyanine, Solid-violet, also belongs to this class, and 
 is the chloride of dimethylphenylammoniumdioxyphen- 
 oxazine carboxylic acid, C 15 H 13 N 2 5 C1, or 
 
 COOH 
 
 OH 
 
 Gallocyanine is formed by the action of nitrosodi- 
 methylaniline hydrochloride on gallic acid or tannic acid. 
 It comes into commerce as a greenish paste, which is 
 insoluble in water, but dissolves in alcohol with a blue- 
 violet colour. In can be dyed directly on wool in presence 
 of sulphuric acid, but much better results are obtained if 
 the wool is previously mordanted with bichromate of 
 potash. Gallocyanine is also used along with a chrome 
 mordant in calico-printing. It produces blue shades of 
 violet. 
 
 Prune is the methyl ether of gallocyanine. 
 
 INDOPHENOLS. 
 
 These colouring matters are produced by the simul- 
 
INDOPHENOLS. 199 
 
 taneous oxidation of a phenol and a paradiamine. This 
 process resembles the manufacture of safranine, the only 
 difference being that a phenol is oxidized with a para- 
 diamine instead of a monamine with a paradiamine. 
 
 The following substances are used in the manufacture 
 of indopheriols : 
 
 Phenol Paraphenylenediamine 
 
 Besorcin Dimethylparaphenylene- 
 
 Alpha- and beta-iiaphthol diamine. 
 
 Preparation. Commercial indophenol is prepared as 
 follows : One molecule of nitrosodimethylaniline 
 
 C 6 H 4 -NO-N(CH 3 ) 2 , 
 
 is reduced in aqueous solution to dimethylparapheny- 
 lene diamine, C 6 H 4 'NHo'N(CH 3 ) 2 , filtered, and mixed 
 with a solution of two molecules of alpha-naphthol 
 dissolved in soda. Bichromate of potash is then added, 
 and acetic acid is gradually run in until the liquid 
 shows an acid reaction, when the colouring matter is 
 precipitated. 
 
 Properties.- Indophenol comes into commerce as a blue 
 paste or powder (indophenol N). The dried paste has 
 a coppery lustre, and very much resembles Guatemala 
 indigo in appearance. It sublimates in needles. 
 
 Indophenol is an oxidation product of dimethylpara- 
 amidophenyl-a-oxy-a-naphthylamine. It possesses the 
 empirical formula, C 18 H 16 N 3 0, and the constitution 
 
 C 6 H 4 lSr(CH 3 ) 2 
 C 10 H G 
 
 It dissolves in concentrated sulphuric acid, with a dingy 
 yellow colour. It is insoluble in water, but soluble in 
 alcohol, with a blue colour. Alkalies are without action 
 on the solutions : acids colour them yellow. 
 
200 COAL-TAR COLOURS. 
 
 Indophenol is reduced by glucose and caustic soda, 
 forming a vat which resembles the indigo vat. This 
 solution contains leucoindophenol, which is also a com- 
 mercial article (indophenol-white, or indophenol prepara- 
 tion), and forms a white paste soluble in pure and in 
 acidified water. 
 
 The reduced product has the composition 
 
 (C 6 H 4 N(CH 3 ) 2 
 N J C 10 H 6 OH 
 (-H, 
 
 and contains, therefore, two hydrogen atoms more than 
 indophenol. 
 
 Application. Indophenol gives very beautiful indigo- ^ 
 blue shades on cotton and wool. It is perfect!^" fast to 
 light and weak chloride of lime solutions, but even weak 
 acids decolourise it. 
 
 For printing on cotton, a mixture of indophenol and 
 stannous hydrate (from stannous chloride and soda) is 
 warmed with acetic acid until decolourised. It is then 
 thickened with tragacanth, printed and steamed. The 
 development of the leucoindophenol in the air is very 
 slow, and it is therefore more advantageous to develop 
 the colour in a bath of bichromate. 
 
 For dyeing wood and cotton, indophenol- white is dyed 
 in neutral or slightly acid solution, and the colour subse- 
 quently developed with bichromate or chloride of lime. 
 
 When used along with indigo in the hyposulphite vat 
 (with the addition of a little stannite of soda) it becomes 
 fixed like indigo, and produces brighter and cheaper shades 
 of blue than those obtained with indigo alone. 
 
 Detection on the fibre. The reaction with dilute acids 
 is most characteristic. A 10-per-cent. solution of hydro- 
 chloric acid turns it grey-brown or dark-grey, while 
 other colouring matters are scarcely altered. 
 
ANILINE-BLACK. 201 
 
 (d) ANILINE-BLACK AND NAPHTHAMEIN. 
 
 The colouring matters of this division are formed by 
 the oxidation of amines of the aromatic series. They are 
 characterised by their insolubility, and little tendency to 
 crystallise. The dye-stuffs themselves are, on account of 
 their insolubility, little suited for dyeing and printing. 
 When fixed on the fibre, however, by means of oxidation, 
 shades are obtained which are characterised by their 
 extreme fastness. 
 
 Only two colouring matters of this division are tech- 
 nically applied viz., aniline-black and the " direct naph- 
 thylamine- violet ." 
 
 Aniline-black. 
 
 Preparation. For the preparation of aniline-black in 
 substance, aniline hydrochloride is very carefully oxidised. 
 If the oxidation is carried too far, quinone, C 6 H 4 2 , is 
 produced ; but if the oxidation is too feeble, green or 
 violet colours are formed. 
 
 The following may be used as oxidising agents : 
 Chromic acid (potassium bichromate), permanganate of 
 potash, and such metallic salts as easily give off oxygen. 
 These metallic salts are generally employed along with 
 potassium chlorate. 
 
 The most suitable combination is copper sulphate and 
 potassium chlorate. The action of this mixture may be 
 explained by the equation 
 
 2 KC10 3 + CuS0 4 - K 3 S0 4 + Cu(C10 3 ) 2 . 
 
 The copper chlorate formed is very easily decomposed ; its 
 solutions give off gases at 60, which consist essentially 
 of chlorous anhydride. 
 
 A very useful material is a salt of vanadium, vanadiate 
 of ammonia. In the formation of aniline-black, vanadium 
 
202 COAL-TAR COLOURS. 
 
 chloride is formed, which is immediately converted to 
 vanadic acid by the potassium chlorate. One part of 
 vanadium will do the work of 4,000 parts of copper, and 
 will form from 10,000 to 200,000 parts of aniline -black. 
 
 Iron, chromium, and osmium salts may be used in place 
 of copper sulphate, but do not possess any special advan- 
 tages. Sulphate of cerium, however, is preferred by some 
 to any other oxidising agent. 
 
 The finest aniline-black is obtained from pure aniline ; 
 ortho-toluidine gives a bluish -black, para-toluidine a 
 brown-black. Aniline oil for black should boil at 182. 
 Aniline-black is also formed by the action of a galvanic 
 current on a concentrated solution of an aniline salt. In 
 this case, the oxidation is effected by the electrolytic oxy- 
 gen evolved at the positive pole. 
 
 The following method serves for preparing aniline-black 
 in substance : Dissolve 40 parts of aniline hydrochloride, 
 20 parts of chlorate of potash, 40 parts of copper sulphate, 
 and 16 parts of sal ammoniac, in 500 parts of water, and 
 warm to 60. 
 
 The crude aniline-black may be purified for analysis by 
 boiling the precipitate obtained successively with hydro- 
 chloric acid, alcohol, ether, benzene, etc. The residue 
 consists of the hydrochloride, from which the base is pre- 
 pared by decomposition with dilute alkalies. 
 
 Properties. Aniline-black has a formula consisting of 
 some multiple of C 6 H 5 1S", probably C 30 H 2B !N" 5 . 
 
 The salts of aniline-black are unstable, as by drving or 
 washing the acid is given off. To the hydrochloride the 
 formula C^ ( fL 2 -'N-' < '2 HC1 is usually given.* 
 
 In the dry state, aniline-black and its salts form black 
 amorphous powders, which are insoluble in acids and 
 alkalies. Crude aniline-black contains many other colour- 
 
 * According to Liechti and Suida, aniline-black possesses the 
 formula C 18 H 16 C1N 3 , in which the chlorine is not present as hydro- 
 chloric acid. It is thus represented as a chlorine- substitution product. 
 
ANILINE-BLACK. 203 
 
 ing matters, which may be removed by different solvents. 
 Thus boiling chloroform removes a blue-violet colouring 
 matter, derived from ortho-toluidine, which possesses the 
 empirical formula C 7 H7^T. 
 
 Acetic acid; alcohol and benzene remove brown and red 
 impurities. 
 
 Concentrated sulphuric acid dissolves aniline-black, with 
 formation of a sulphonic acid. The new colouring matter 
 is insoluble in acidulated water, and therefore separates 
 out when the solution is poured into water. By continued 
 washing with water, it dissolves with a green colour. 
 This sulphonic acid serves for the preparation of an aniline- 
 black vat, as its weak alkaline solutions are reduced by 
 zinc-powder, grape-sugar, ettr s^^^ 
 
 Fibres placed in this solution, and exposed to air, rapidly 
 turn blue ; acids turn the colour green. By subsequent 
 treatment with bichromate of potash, a fast grey is pro- 
 duced. Hitherto, this process has not found any technical 
 application. 
 
 Strong oxidising agents, such as chromic acid, convert 
 aniline-black into quinon. Energetic reducing agents 
 completely destroy aniline-black, forming chiefly para- 
 phenylenediamine, C 6 H 4 (NH 2 ) 2 , and diamidodipheiiyl- 
 amine : 
 
 N-C 6 H 4 -NH 2 
 \H. 
 
 Application. Aniline-black comes into commerce as a 
 paste, and finds a limited application as a steam black. 
 The colour is thickened with albumen and fixed by 
 steaming. 
 
 Aniline-black fixed direct on the fibre is of great im- 
 portance in calico-printing, where it has to a great extent 
 replaced the blacks formerly produced with logwood and 
 
204 COAL-TAR COLOUKS. 
 
 In Lightfoot's original patent, granted in 1863, a thick- 
 ened mixture of aniline, hydrochloric acid, copper chloride, 
 and chlorate of potash is printed on the cotton. This 
 method resembles the one given above for the preparation 
 of aniline-black in substance, and produces, a very good 
 black. 
 
 The above mixture has, unfortunately, an injurious 
 action on the steel " doctors " of the cylinder printing 
 machine, because of the action of the copper salts on the 
 iron, which is eaten away, while an equivalent quantity of 
 copper is deposited. 
 
 Lauth overcame this drawback by using copper sulphide 
 in place of the copper chloride. Lauth's method is used, 
 with one or two variations, for ordinary aniline-black at 
 the present time. 
 
 The colour consists of 
 
 10 litres starch paste. 
 350 grams chlorate of potash. 
 300 copper sulphate. 
 300 sal ammoniac. 
 800 ,, aniline hydrochloride. 
 
 After printing, the fabrics are hung up in the aniline- 
 black chamber, till a dark-green colour is developed. The 
 temperature of this room is generally 30 to 40, the 
 degree of moisture being exactly regulated. The develop- 
 ment generally lasts two days. The fabric is then passed 
 through an alkaline bath of silicate of soda, chalk, or, if 
 possible, ammonia. If the pieces are treated with am- 
 monia, before the black is completely developed a blue 
 shade is produced. Acids reproduce the green. This 
 intermediate product is called emeraldine, and the blue 
 produced by alkalies, azurine. Even the completely de- 
 veloped aniline-black appears to contain some emeraldine, 
 as it becomes green when treated with acids. Aniline- 
 black sometimes turn green if the pieces are allowed to 
 
ANILINE-BLACK. 205 
 
 lie in the air for some time. This alteration is most 
 probably caused by sulphurous acid from the gas, where 
 gas-lights are used. The black is reproduced, on washing, 
 in its original beauty. 
 
 A black which does not turn green is obtained by a 
 subsequent oxidation of the pieces which have been, passed 
 through ammonia. The best materials for this purpose 
 are an acidified solution of bichromate of potash or a 
 ferric salt. By this process iron or chromium lakes of 
 aniline-black seem to be produced on the fibre, as the 
 latter is found to absorb considerable quantities of the 
 oxide unless great care is taken. Another method of 
 obtaining aniline-blacks which do not turn green is based 
 upon the fact that xylidine when used in place of aniline 
 yields a black which after some time assumes a red cast. 
 Pure aniline, as is well known, yields a black which turns 
 green. If now the two bases are used together in the 
 proper proportion, the green and the red which are sub- 
 sequently formed neutralise each other, and the fabric 
 consequently retains its original colour. 
 
 During the development of aniline-black, oxides of 
 chlorine are formed, and these tend to injure the fibre. 
 For very delicate fabrics, the hydrochloride of aniline 
 may be replaced by a mixture of the tartrate with sal 
 ammoniac. 
 
 In this process chlorate of soda is used instead of chlorate 
 of potash, since the sparingly soluble potassium bitar- 
 trate would crystallise out, and either prevent or consider- 
 ably retard the formation of black on the fibre. 
 
 The pieces printed by the above processes cannot be 
 steamed, as the mixture would act violently on the fibre at 
 such a temperature. Pieces have even been known to fire 
 on steaming. Ordinary aniline-black cannot, therefore, 
 be combined with steam colours. In producing mixed 
 colours, the following process is adopted. 
 
 If it is desired to produce aniline-black and alizarin- 
 
206 COAL-TAR COLOURS. 
 
 red on a white ground, first print for the red with thick- 
 ened acetate of alumina, then print the aniline-black, and 
 develop in the usual manner. Pass through a chalk- 
 bath, which effects the development of the black and the 
 fixation of the alumina mordant. Then dye with alizarin 
 and wash, clear, etc., in the usual way. (See Alizarin.) 
 This process gives very beautiful results, but is rather 
 difficult to manage. 
 
 A good steam black is obtained when aniline hydro- 
 chloride is completely replaced by aniline ferrocyanide. 
 The chlorous acid developed in the nascent state acts 
 on the hydroferrocyanic acid, producing hydroferricyanic 
 acid. 
 
 On an aniline-black ground it is impossible to produce 
 discharges, owing to the great stability of the colour. On 
 this account, reserves have to be used. Reserves are 
 generally alkaline, and act by the neutralisation of the 
 acid colour, as aluminate or citrate of soda, etc. 
 
 Sulphocyanides form very suitable reserves ; they absorb 
 the chlorine, forming persulphocyanogen. The steam 
 alizarin-red produced with aluminium sulphocyanide 
 may be printed over with aniline-black, without being 
 spoiled. 
 
 Aniline-black is as yet not suitable for wool- and silk- 
 dyeing, since the feel, lustre and tenacity of the fibres are 
 thereby injured. 
 
 Aniline-black is easily produced on cotton yarn. The 
 dye-bath is prepared with potassium bichromate, aniline 
 hydrochloride, and excess of hydrochloric acid, and the 
 slightly soaped yarn is placed in the cold solution. After 
 some time the bath is slowly heated to 60 C. The dyed 
 goods are then washed in water, soda, and soft soap, to 
 remove free acid, etc. 
 
 In this process it is very important to observe the 
 proper proportions, and the concentration of the bath, 
 rihe right proportions are not adhered to, the aniline- 
 
NAPHTHAME1N. 207 
 
 black may be precipitated before the yarn is introduced, 
 and a loss is thus caused. By using dilute solutions the 
 black produced has a greyish cast. 
 
 The following proportions give good results : 
 
 For 100 kg. yarn- 
 Dissolve 2 kg. aniline in 
 
 32 lit. hydrochloric acid, and 
 42 lit. water, 
 
 pour into the dye-bath, containing a solution of 8 kg., 
 potassium bichromate. 
 
 Detection on the fibre. The colour is either unaltered by 
 acids, or turned slightly greenish ; alkalies restore the 
 original colour. 
 
 Alkalies are without action. 
 
 If passed several times through strong solutions of 
 permanganate of potash and oxalic acid, alternately, the 
 colour is destroyed. Chloride of lime turns the colour 
 brown-red. Weak oxidising agents are without influence. 
 
 NaphtJiamem. 
 (Naphthalene-violet.) 
 
 Alpha-naphthylamine, C 10 H 7 N"H 2 , yields by suitable 
 oxidation naphthamein, a violet colour, which is in many 
 respects very similar to aniline-black. 
 
 It separates as an amorphous, purple precipitate, when 
 an aqueous solution of hydrochloride of naphthylamine is 
 treated with ferric chloride. 
 
 Naphthamein is insoluble in water, dilute mineral acids, 
 and alkalies, and is sparingly soluble in alcohol ; but easily 
 in acetic acid or ether. The acetic-acid solution may be ' 
 used for dyeing and printing, but the colours produced 
 with it are very dull. 
 
 Naphthamein dissolves in concentrated sulphuric acid 
 with a blue colour. 
 
208 COAL-TAE COLOURS. 
 
 No formula has yet been assigned to this dye-stuff. A 
 colouring matter similar, or identical, is obtained by 
 printing with the aniline-black mixture, in which aniline 
 is replaced by naphthylamine. The development and 
 fixing is the same. The copper sulphide may be re- 
 placed by ferric chloride. After oxidation it is ad- 
 vantageous to pass the material through a solution of 
 ferric chloride. 
 
 The shades produced vary from a grey- violet to a grey- 
 brown. It is not nearly as fast to light, etc., as aniline- 
 black. 
 
 Detection on the fibre. Concentrated hydrochloric acid 
 changes to a light grey ; ammonia and caustic soda have 
 little action. 
 
 (d) THIONINE COLOURING MATTERS. 
 
 Red, violet, and blue colouring matters containing 
 sulphur are obtained when the hydrochlorides of some 
 aromatic diamines are dissolved in sulphuretted hydrogen 
 water and oxidised with ferric chloride. 
 
 The diamines used must have their amido groups in 
 the para position to each other, ortho- and meta-diamido 
 compounds yielding no colouring matters. 
 
 Of this class of colouring matters, only one viz., 
 methylene-blue has become of technical importance, as 
 it possesses a very beautiful colour, and the diamine, 
 dimethylparaphenylenediamine, used in its preparation 
 is more easily manufactured than the other diamines. 
 
 Hethylene-blue. 
 
 Preparation. The crude material for the manufacture 
 of methylene-blue is dimethylaniline, C 6 H 5 N(CH 3 ) 2 . This 
 is dissolved in hydrochloric acid, and a solution of the 
 
METHYLENE-BLUE. 209 
 
 exact equivalent of sodium nitrite added ; para-nitroso- 
 dimethylaniline is produced, according to the equation 
 
 C 6 H 5 -N(CH 3 ) 2 HC1 + NaN0 2 = 
 Dimethylaniline hydrochloride. 
 
 ]TO-C 6 H 4 -N(CH 3 ) 2 + NaCl + H 2 0. 
 Nitroso dimethylaniline . 
 
 The liquid is then diluted with water and hydrochloric acid 
 and placed in a vessel fitted with stirrer and flue, and is 
 treated with sulphuretted hydrogen. The nitrosodimethyl- 
 aniline is thereby reduced to dimethylparaphenylene- 
 diamine. When the reaction is over, the solution, which 
 was yellow at first, is found to be completely decolourised. 
 
 The reaction is not a quantitative one, as by the action 
 of the sulphuretted hydrogen a by-product is formed, 
 which is converted to methylene-blue by mere exposure 
 to air. 
 
 After decolourisation, small quantities of ferric chloride 
 solution are added, till a slight excess of the latter is 
 present. Then the solution is saturated with salt, and the 
 dye separated by zinc chloride. A red colouring matter, 
 not precipitated by zinc chloride, remains in solution. 
 This colouring matter may be obtained as chief product, 
 if the sulphuretted hydrogen is allowed to act for a longer 
 period and more ferric chloride is used. 
 
 An interesting method of producing methylene-blue is 
 described in a patent of Messrs. Ewer & Pick. It is based 
 upon the following facts : 
 
 If two plates of platinum, which constitute the two poles 
 of an electric generator, are immersed in a solution of sul- 
 phuretted hydrogen, and paradimethylphenylenediamine 
 
 r* TT C NHn 
 
 in dilute sulphuric acid, an active development of hydrogen 
 takes place at the negative pole ; while the fluid which 
 
 P 
 
210 COAL-TAR COLOURS. 
 
 surrounds the positive pole becomes blue. The reaction 
 ceases, however, in a short time, the positive pole becom- 
 ing coated with a grey deposit. But if the plate is kept 
 clean by means of a small brash, the whole of the sul- 
 phuretted hydrogen disappears, and the liquid begins to 
 assume a blue colour. It is then found to contain chiefly 
 reduced methyl ene-blue (methylene-white), along with a 
 small quantity of methylene-blue in solution. 
 
 Properties. Commercial methylene-blue is the chloride, 
 or the zinc chloride, double salt of tetramethylthionin, 
 C 16 H 18 N 8 S-C1, or 2(C 16 H 18 T 3 SC1) + ZnCl 2 + H 2 0. 
 
 The constitutional formula of the hydrochloride is re- 
 presented thus : 
 
 /N(CH 3 ) 2 
 
 __ _ I \ 
 Cl 
 
 It forms a dark-blue or reddish-brown powder, easily 
 soluble in alcohol or water. The chloride, CjgHjgNn-S'Cl, 1 
 may be prepared from the zinc compound by evaporating 
 the aqueous solution to dryness, dissolving the residue 
 in water, and adding concentrated hydrochloric acid. 
 It forms dark-blue leaflets, easily soluble in alcohol and 
 in water. 
 
 Ammonia does not precipitate methylene-blue solutions ; 
 potash and soda produce blue precipitates. 
 
 The free base forms green needles with a metallic lustre, 
 and may be crystallised from hot water. 
 
 Hydrochloric acid and nitric acid turn the solutions 
 of methylene-blue greenish. Methylene-blue is easily 
 decolourised by reducing agents, such as stannous chloride, 
 zinc and acetic acid, etc. With tannin it forms a com- 
 pound soluble in water, which is taken up by metallic 
 mordants. 
 
METHYLENE-BLUE, 211 
 
 Application. Methylene-blue has no special value for 
 wool- and silk-dyeing, as for these materials other dye- 
 stuffs are used which possess greater fastness and bril- 
 liancy. 
 
 On the other hand, it is of considerable importance in 
 cotton-yarn dyeing, and still more so in calico-printing. 
 The blue produced is of a greenish shade, and possesses 
 great fastness. In artificial light the shades appear 
 greenish. 
 
 Tannin and various mineral mordants are used in fixing ; 
 the mordant depends on the shade required. 
 
 For pure blue, the following method may be used : 
 Mordant the oiled goods with alum, and fix the alumina 
 in a chalk bath containing some sodium arseniate. Then 
 heat in a weak tannin-bath, and dye the mordanted goods 
 in a dye-bath containing methylene-blue, phosphate of 
 soda and soda, beginning cold and raising the temperature 
 gradually to the boil. 
 
 For dark-blue (indigo) : The goods are mordanted after 
 oiling in acetonitrate of iron. They are then placed in an 
 ageing chamber, and the mordant is finally fixed in a 
 chalk bath. On treating with tannin, a dark ground is 
 produced, on which methylene-blue dyes a beautiful blue 
 resembling indigo. 
 
 The tartar-emetic process is also applicable for methy- 
 lene-blue. The methylene-blue and tannin, thickened with 
 gum tragacanth, is printed and steamed, and subsequently 
 fixed in a bath of tartar-emetic. 
 
 Detection on the fibre. Methylene-blue is faster on cotton 
 than aniline-blue. It resists the action of neutral soaps 
 and dilute chloride of lime solutions, and is very fast 
 light. 
 
 Ammonia is without action, but caustic alkalies and 
 alkaline soaps remove the blue colour. 
 
 Hydrochloric acid takes up the blue, forming a green 
 solution. 
 
212 COAL-TAR COLOURS. 
 
 The following reactions are very characteristic : Moist- 
 ened with hydrochloric acid, the sample first turns green, 
 and is gradually decolourised. Stannous chloride and other 
 reducing agents reduce methylene-blue much quicker than 
 other blue colouring matters. It is especially sensitive 
 towards chromic acid. A three per cent, solution of potas- 
 sium bichromate renders it violet, and finally discharges it. 
 If fixed with tannin, a dark catechu-brown is produced. 
 
 Uthylene-blue is, according to Schulz and Julias (Tabell. 
 Uebers. d. kiinstl. org. Farbstoffe), an impure methylene- 
 blue, obtained by transforming nitrosodimethylaniline in 
 strong sulphuric acid solution into the leucobase of 
 methylene-blue by means of zinc sulphide and oxidising 
 the product obtained. 
 
 Lauth's violet, or Thionin, is the hydrochloride of thio- 
 nin 
 
 /NH 
 
 \NH 2 'HC1, 
 
 and is obtained by the oxidation of paraphenylene diamine 
 in presence of sulphuretted hydrogen with ferric chloride. 
 It forms a dark-green powder with metallic reflex, which 
 dissolves in water with a violet colour. 
 
 II. PHENOL DYE-STUFFS. 
 
 The phenol dyes are of an acid nature, which is due to 
 the hydroxyl group or groups contained in them. 
 
 They are taken up by animal fibres, either in the free 
 fitate, or in form of their soluble salts. Many give in- 
 soluble lakes with metallic oxides, and may therefore be 
 dyed on animal fibres mordanted with alumina, iron, lead, 
 etc. Other colouring matters of this group are applied 
 with oil and tannin mordants. 
 
PICRIC ACID. 213 
 
 The phenol dye-stuffs may be classified as follows : 
 (a) Nitro- derivatives. 
 
 (6) Colouring matters produced by the action of nitrous 
 acid on phenols. 
 
 (c) Rosolic acids. 
 
 (d) Phthaleins. 
 
 In addition to the colouring matters described under 
 section (a), a nitro-derivative of diphenylamine, Au- 
 rantia, will be considered. 
 
 This substance contains no hydroxyl group, and really 
 belongs to the aniline dyes ; but it also stands in close re- 
 lation to the nitrophenols. 
 
 (a) NITRO-BODIES. 
 
 These dyes are as a rule of a yellow colour. They 
 are stronger acids than the phenols from which they are 
 derived. 
 
 They possess the following characteristics in common : 
 Strong acid reducing agents, such as stannous chloride 
 and hydrochloric acid, convert them into the colourless 
 amido derivatives. They dissolve in concentrated sul- 
 phuric acid, yielding either yellow or colourless solutions. 
 Their solutions, or fibres dyed with them, are but slightly 
 altered by hydrochloric acid, while ammonia and caustic 
 soda tend to darken, or redden the colour. When dyed in 
 acid baths, the colour may subsequently be partly re- 
 moved from the fibre by boiling water. These reactions 
 serve to distinguish these yellow colouring matters from 
 others. Thus, phosphine is turned lighter by ammonia, 
 while the yellow azo dyes are reddened by acids. 
 
 Picric Acid. 
 
 Preparation. Picric acid or trinitrophenol may be ob- 
 tained by warming pure carbolic acid with nitric acid : 
 
 C 6 H 5 OH + 3HN0 3 = C 6 H 2 (Np 2 ) 3 OH + 3H 2 0. 
 Phenol. Picric acid. 
 
214 COAL-TAR COLOURS. 
 
 The process is much better, and less by-products are 
 formed, if the phenol is first converted into its sulphonic 
 acid. For this purpose, carbolic acid is heated with 
 sulphuric acid to 100 till a sample dissolves completely 
 in water. The liquid is then slightly diluted, run into 
 strong nitric acid, and warmed. The reactions are ex- 
 pressed by the following equations : 
 
 . C C H 5 OH + H 2 S0 4 = C 6 H 4H + 3H 3 0. 
 
 Phenol. Phenolsulpkonic acid. 
 
 Phenolsulphonic acid. Picric acid. 
 
 The acid liquor contains picric acid, nitric acid, sul- 
 phuric acid, and resinous impurities. It is diluted with 
 water, and soda added till the resins are separated, after 
 which it is filtered and excess of soda solution added. 
 The precipitated sodium picrate is dissolved in water 
 and decomposed with sulphuric acid. The 'picric acid is 
 salted out. t 
 
 Picric acid has the constitution : 
 
 N0 2 (6) 
 
 Properties. Picric acid forms light-yellow leaflets, m.p. 
 122'5. It may be sublimated by cautious heating ; rapid 
 heating causes it to explode. It possesses an extremely 
 bitter taste (hence its name, from Trt/c/oos = bitter) . One 
 part of picric acid dissolves in 86 parts of water at 15 ancl 
 in 26 parts at 76; it is easily soluble in alcohol, ether and 
 benzene. The solutions are yellower than the free acid ; 
 the addition of a little sulphuric acid causes the colour to 
 become much lighter. 
 
PICRIC ACID. 215 
 
 Picric acid is a strong, monobasic acid ; its salts are of 
 a yellow or orange colour. They explode with great 
 violence on heating. The potassium salt, C 6 H 2 '(N0 2 )3OK, 
 is distinguished by its comparative insolubility, 1 part 
 requiring 288 parts of water at 15 to dissolve it. The 
 ammonium and sodium salts are more easily soluble. The 
 salts with the alkaline earths are soluble in water. One 
 part of the lead-salt dissolves in 119 parts of water at 15. 
 
 By warming with tin and hydrochloric acid, picric 
 acid is completely reduced ; the colourless solution con- 
 tains the hydrochloric acid compound of triamidophenol, 
 C 6 H 2 (NH 2 ) 3 OH. 
 
 If alkaline reducing agents are used, the reduction is 
 not carried so far. Thus, if sulphuretted hydrogen is 
 passed into a solution of picric acid in alcoholic ammonia, 
 only one nitro group is reduced, and dinitroamidophenol, 
 or picramic acid is produced : 
 
 OIL 
 
 The latter dyes wool and silk brown. 
 
 If concentrated solutions of picric acid and potas- 
 sium cyanide are mixed, a dark-red solution is formed, 
 and on standing reddish-brown crystals are deposited. 
 They consist of the potassium salt of isopurpuric acid, 
 C 8 H 4 ,KN 5 6 , and are produced according to the equation 
 
 C 6 H 2 -(N0 2 ) 3 OH + 3CNK + 2H 2 = 
 
 Picric acid. . 
 
 C 8 H 4 KN 6 6 + K 2 C0 3 + NH 3 . 
 
 Potassium isopurpurate. 
 
 Free isopurpuric acid is very unstable, and is only 
 known in the form of salts. Its potassium or ammonium 
 
216 COAL-TAR COLOURS. 
 
 salt was formerly used as a dye, under the name of 
 " Grenat soluble." It dyes a brown upon wool or silk. 
 The baths must not be strongly acid ; the addition of a 
 little acetic or tartaric acid is best. 
 
 Testing of picric acid. Commercial picric acid is gene- 
 rally crystallised. It should dissolve in water, acidified 
 with sulphuric acid, without any residue. It should be 
 entirely soluble in 10 parts of alcohol. If alcohol leaves 
 a residue, the latter will most probably consist of inorganic 
 salts (Glauber's salts, nitre, etc.), which maybe recognised 
 in the usual manner. 
 
 Oxalic acid is sometimes added. To detect it, the 
 sample is dissolved in ammonia, and calcium chloride is 
 added. A white precipitate indicates oxalic acid. 
 
 Sugar is detected by saturating the aqueous solution 
 with sodium carbonate, evaporating to dryness, and ex- 
 tracting with diluted alcohol ; sugar is dissolved while 
 picrate of soda remains. Pure picric acid should be easily 
 soluble in benzene. 
 
 The quantitative estimation of picric acid may be 
 effected by the method described on p. 65. 
 
 Application of picric acid. Picric acid is a substantive 
 colour on silk and wool. Its dyeing power is-rery great, 
 one part being sufficient to dye a thousand parts of silk a 
 distinct yellow. 
 
 Animal fibres are dyed in acid baths. Sulphuric acid 
 is the most advantageous for this purpose, as it causes the 
 colour to deposit more evenly. 
 
 Picric acid yellow is darkened by the action of light 
 and air. It may be removed from the fibre by repeated 
 washing. 
 
 In order to fix it upon wool, alum or bichromate of 
 potash are sometimes used. The picrates of alumina and 
 chromium are soluble in a large quantity of water ; thus 
 no lakes are formed on the fibre, and the only advantage 
 of this method is that picric acid possesses a somewhat 
 
/ / II 
 
 PICRIC ACID. 217 
 
 greater affinity to alumina and chromium salts than to the 
 free fibre. 
 
 A method of producing weighted yellow silks is based 
 upon the fact that picric acid forms a sparingly soluble 
 lead-salt. For this purpose the silk is first mordanted 
 y with lead acetate, and then dyed in picric acid. Silk con- 
 taining picrate of lead is, however, very liable to take 
 fire, the flame being very difficult to extinguish. The 
 sulphuretted hydrogen in the air is also liable to blacken 
 it, owing to the formation of lead sulphide. 
 ~On cotton, picric acid may be fixed with albumen ; but 
 the colours are so dull as to have no practical value. 
 
 Picric acid gives a somewhat greenish yellow, and 
 thus is seldom used for pure yellow. 
 
 On the other hand, it is very suitable for dyeing mixed 
 colours. It may be combined with methyl-green for 
 yellow-green, indigo-carmine or aniline-blue for green, 
 with violet for olive, and with magenta for scarlet. 
 
 A very good green is obtained on wool with indigo- 
 carmine and picric acid. 
 
 The picrates of the rosaniline bases are sparingly soluble 
 or insoluble. 
 
 Besides, in dyeing, picric acid is used extensively in the 
 manufacture of explosives. 
 
 Detection on the fibre. Picric acid yellow is reddened 
 by a mixture of stannous chloride and alkali (formation 
 of picramic acid), and also by potassium cyanide (forma- 
 tion of isopurpuric acid). 
 
 In order to detect it in fabrics dyed with mixed colours, 
 the best method is to extract with dilute alcohol, evaporate 
 to dryness, and test the residue with ammonium sulphide 
 or potassium cyanide. 
 
 All fabrics dyed with picric acid possess a bitter taste. 
 
 In some cases picric acid is added to beer, to give it 
 the required bitter taste. In order to detect an adul- 
 teration of this kind, 10 c.c. of the beer are shaken with 
 
218 COAL-TAR COLOURS. 
 
 5 c.c. of amyl alcohol, the extract evaporated, and tested 
 with potassium cyanide or ammonium sulphide. 
 
 Phenicienne. Phenyl-brovm. 
 
 If phenol is nitrated by another process, instead of picric 
 acid, a brown colour, phenyl-brown, is obtained. 
 
 In order to prepare it, 10 to 12 parts of a mixture of 
 two volumes of sulphuric acid and one volume of nitric 
 acid, sp. gr. 1'35, are gradually added to 1 part of cooled 
 phenol. A considerable amount of nitrous fumes is 
 evolved. The product is then poured into water, collected 
 on a filter, and the precipitate washed. 
 
 Phenyl-brown consists of two substances. The brown 
 portion is amorphous, insoluble in water, but soluble in 
 alkalies and spirits of wine. Its . chemical composition 
 is unknown. The second constituent is a dinitrophenol, 
 C 6 H 3 (OH)'(N0 2 )2; it dyes yellow, is crystallisable, and 
 dissolves in hot water, alkalies and alcohol. 
 
 Phenyl-brown is a yellowish-brown powder, which melts 
 on gentle heating, and on stronger heating deflagrates, 
 owing to the dinitrophenol it contains. It is only par- 
 tially insoluble in water, but dissolves completely in 
 alcohol. 
 
 The yellowish-brown solution is turned yellow by 
 hydrochloric acid, and after some time a precipitate is 
 produced. 
 
 Caustic soda and ammonia turn the liquid bluish violet. 
 Metallic salts produce precipitates. 
 
 Phenyl-brown is often used in dyeing leather. 
 
 On wool it produces Havanna-brown shades, which are 
 very fast to light. The colours are spoiled by steam- 
 ing. 
 
 By chroming, i.e., passing through a bath of bichromate 
 acidified with sulphuric acid, the colour is turned to a 
 ruby-red. 
 
Victoria-yellow 
 
 is the potassium salt of dinitroparacresol, and is produced 
 by the action of nitric acidonparatoluidine, C 6 H 4 'CH 3 'NH 2 , 
 or on paracresol, C 6 H 4 'CH 3 > OH. 
 
 It forms red crystals, which dissolve in water with a 
 yellow colour. Hydrochloric acid decolourises the solution, 
 and precipitates the free acid in the form of light-yellow 
 needles. Caustic alkalies and ammonia produce no altera- 
 tion. By warming with potassium cyanide, a red colour 
 is produced, similar in composition to isopurpuric acid. 
 
 Victoria-yellow produces yellow shades on wool and 
 silk, which are somewhat redder than those obtained with 
 picric acid. The colours are, however, so unstable that 
 they are seldom used in dyeing. 
 
 Detection. Warm water removes the colour from the 
 fibre. The dilute yellow solution is decolourised by 
 hydrochloric acid ; if concentrated, a precipitate is formed. 
 
 Hydrochloric acid decolourises the fibre ; water repro- 
 duces the original colour. 
 
 Naphthol-yellow. 
 (Martius-yellow. Manchester-yellow.) 
 
 Naphthol-yellow is the soda, potash, or lime-salt of 
 dinitronaphthol : 
 
 Oo (1) 
 
 OH. (4) 
 
 Preparation. Alpha-naphthol is treated at 100 with a 
 mixture of nitric acid and sulphuric acid, and the nitro- 
 
220 COAL-TAR COLOURS. 
 
 compound formed is precipitated by pouring the product 
 into water. 
 
 Or, the alpha-naphthol is converted into the moiiosul- 
 phonic acid with sulphuric acid, and then nitrated. 
 
 The sulpho group is thus removed, and substituted by 
 N0 2 , as in the preparation of picric acid. 
 
 Martius-yellow is also formed by the action of nitric 
 acid on a naphthylamine. 
 
 Properties. Dinitronapthol forms yellow needles, which 
 are insoluble in water. It melts at 138. It is a strong 
 acid, forming yellow or orange salts. 
 
 The sodium salt, C 10 H 5 (N0 2 ) 2 ONa + H 2 0, forms needles 
 which are easily soluble in water. The lime-salt possesses 
 the formula (C 10 H 5 (NO 2 ) 2 0) 2 Ca + 6H 3 O. 
 
 The solutions of naphthol-yellow are decolourised by 
 hydrochloric acid, a precipitate of the free acid being 
 produced. Ammonia is without action ; caustic potash 
 or soda produce precipitates of an orange-red colour. 
 Potassium cyanide gives the isopurpuric-acid reaction ; 
 ammonium sulphide colours the solution red. 
 
 Naphthol-yellow is sometimes adulterated with picric 
 acid, to detect which a sample is dissolved in water, and 
 the dinitronaphthol precipitated by hydrochloric acid. In 
 presence of picric acid the filtrate has a yellow colour. 
 The picric acid may be crystallised on evaporation. 
 
 Application. Naphtbol-yellow gives a very beautiful 
 golden-yellow on silk and wool, and is sometimes used 
 for mixed colours. A great drawback to its application is 
 its sensibility to heat. A very slight increase of tem- 
 perature causes it to volatilise ; this even takes place in a 
 summer heat. 
 
 Silk and wool are dyed in a bath containing acetic acid. 
 
 Naphthol-yellow, like picric acid and Victoria-yellow, 
 is not applicable to cotton. 
 
 Detection on the fibre. Water takes up the colouring 
 matter. The yellow solution is decolourised by dilute 
 
NAPHTHOL- YELLOW. 221 
 
 sulphuric acid (picric acid is only turned lighter). Boil- 
 ing potassium cyanide gives it a red colour. Hydro- 
 chloric acid completely decolourises. If a sample of the 
 material is wrapped in a piece of white paper and heated 
 to 120 in an air-bath, part of the yellow colour is trans- 
 ferred to the paper. 
 
 NapJitJiol-yellow S. 
 
 Preparation. Naphthol-yellow S is a sulphonic acid of 
 Martius-yellow. The free acid has the formula 
 
 S0 3 H 
 
 -VT-Q 2 Dinitroalphanaphtholsulphonic acid. 
 HO 2 
 
 By nitration of alpha-naphthol monosulphonic acid 
 C 10 H 6 (S0 3 H)OH, 
 
 the sulpho group is eliminated, and Martius-yellow 
 is formed. If alpha-naphthol trisulphonic acid, 
 C 10 H 4 (S0 3 H) S OH, is nitrated, two sulpho groups are 
 eliminated, and naphthol-yellow S is formed. 
 
 Alpha-narphthol is warmed with twice its weight of 
 sulphuric acid (containing 25 per cent, anhydride) to 
 40-50, and the monosulphonic acid is then converted 
 into the trisulphonic acid by the addition of sulphuric 
 acid containing 70 per cent, of anhydride. The mass is 
 diluted with a little water, and treated with concentrated 
 nitric acid. On cooling, dinitronaphthol sulphonic acid 
 crystallises out. It is purified by recrystallisation, and is 
 converted into the ammonium or sodium salt. From the 
 mother-liquor the sulphuric acid is removed by lime, and 
 the rest of the colouring matter is precipitated by potash. 
 
 Properties. The free acid forms long yellow needles 
 easily soluble in hot water. It is a strong acid, sometimes 
 replacing even sulphuric acid in its compounds. If, for 
 
222 COAL-TAR COLOURS. 
 
 instance, its aqueous solution is mixed with potassium 
 sulphate, the sparingly soluble potassium salt is precipi- 
 tated, while free sulphuric acid remains in solution. 
 The potassium salt 
 
 r(No 2 ) 2 
 
 C 10 H 4 J SO S K 
 
 (OK, 
 
 is sparingly soluble in cold water, more readily in hot 
 water. If treated with strong sulphuric acid, the free acid 
 is not precipitated, but an acid salt is formed, which pos- 
 sesses the formula 
 
 ( 
 C 10 H 4 ]S0 8 K 
 
 (OH. 
 
 Application. Naphthol-yellow S is faster to washing 
 than picric acid and Martins-yellow. It does not vola- 
 tilise on steaming. Silk and wool are dyed in a bath 
 acidified with sulphuric acid. The addition of stannic 
 chloride brightens the colour on wool. 
 
 Detection on the fibre. Boiling water does not remove 
 the colour; a sample does not stain at 110 to 120. Other- 
 wise the reactions are the same as those of naphthol- 
 yellow. 
 
 Brilliant yellow is the sodium salt of a dinitro a 
 naphtholmonosulphuric acid C 10 H 4 OH(ET0 2 ) 2 SO 3 Na ob- 
 tained by the action of nitric acid on the alpha- 
 naphtholtrisul phonic acid of the Schollkopf Aniline Co. 
 It resembles naphthol-yellow S. 
 
 Heliochrysin (Sun-gold). 
 
 This beautiful yellow colouring matter is the sodium 
 salt of tetranitronaphthol : 
 
 (NO s ) 4 
 
 QNa. 
 
AURANTIA. 223 
 
 It is obtained by energetic nitration of monobromnaph- 
 thalene, C 10 H 7 Br, and warming the tetranitrobromnaph- 
 thalene with soda solution : 
 
 + NaBr + C0 2 . 
 Tetranitrobromnaphthalene Helioclirysin. 
 
 This colouring matter is not fast enough to light to be 
 of much technical importance. 
 
 Citronine is a mixture of tetranitrodiphenylamine and 
 dinitrodiphenylamine obtained by the action of nitric acid 
 on diphenylamine. It produces a golden yellow on wool 
 and silk in an acid bath. 
 
 Aurantia. 
 
 Diphenylamine, N(C 6 H 3 ) 2 H, or better, methyldiphenyl- 
 amine, N(C 6 H 5 ) 2 'CH 3 , yields, on warming with nitric 
 acid, a yellow substance, insoluble in water hexanitro- 
 diphenylamine : 
 
 (C 6 H 2 (N0 2 ) S 
 N C 6 H 2 (N0 2 ) 3 
 (H. 
 
 This nitro product is a strong acid, the hydrogen atom 
 bound to the nitrogen being easily replaced by metals. 
 
 The ammonium salt, N(C 6 H 2 (N0 3 ) 8 ) 2 i NH 4 , comes into 
 commerce as aurantia. 
 
 Aurantia is a crystalline, reddish-yellow powder, which 
 deflagrates slightly on heating. It is easily soluble in 
 water and alcohol. The aqueous orange-yellow solution is 
 darkened and reddened by alkalies. Acids precipitate the 
 free acid as a sulphur-yellow, flocculent precipitate, the 
 solution being rendered nearly colourless. 
 
 An acid solution of stannous chloride gives the same 
 reaction ; but on boiling, the yellow precipitate becomes 
 
7 
 
 224 COAL-TAR COLOURS. 
 
 dark brown. Copper salts also turn the solution 
 browner. 
 
 Application. Silk and wool are dyed in baths containing 
 a little sulphuric acid. The above remarks on the action 
 of metallic salts render it necessary that aurantia must be 
 dyed in vessels of wood or glass, 
 
 The application of aurantia has one very great draw- 
 back. It is not entirely harmless. Professor Gnehm, the 
 discoverer, states, that even dilute solutions of aurantia 
 produce very painful blisters on the skin. The medical 
 faculty of Cologne have, on the other hand, sanctioned 
 its manufacture, as being harmless. 
 
 Detection on the fibre. Hydrochloric acid turns it lighter 
 yellow ; ammonia and alkalies produce little alteration. 
 The most characteristic reaction is shown on warming with 
 stannous chloride, which turns it dark-brown. 
 
 (fr) COLOURING MATTERS PRODUCED BY THE ACTION OF 
 NITROUS ACID ON PHENOLS. 
 
 Some phenols, such as carbolic acid, thymol, resorcin, 
 orcin, and napbthol, a.re converted into dye-stuffs when 
 treated with nitrous acid, in ethereal or sulphuric acid 
 solution. 
 
 For this purpose the phenol is dissolved in strong sul- 
 phuric acid, and a solution of nitrous acid in strong 
 sulphuric acid is added. The nitrous solution is prepared 
 by gradual addition of 5 per cent, of sodium nitrite to 
 concentrated sulphuric acid. 
 
 The mixture is warmed on the water-bath till the 
 reaction is finished, and the product is precipitated by 
 pouring into water. 
 
 Phenol, C 6 H 5 *OH, treated as above, gives a brown 
 flocculent precipitate, which dissolves in sulphuric acid 
 and alkalies, with a beautiful blue colour. It is known 
 as " Liebermann's Phenol Dye-stuff." From orcin colour- 
 
FLUORESCENT RESORCIN-BLUE. 225 
 
 ing matters are obtained which are closely related to the 
 orchil colours, especially orcein. 
 
 Of all these colouring matters, the one derived from 
 resorcin alone has technical importance. 
 
 Fluorescent Resor tin-blue. 
 
 Resorcin gives, when treated as above, a red substance, 
 diazoresorufin, C 18 H 10 N" 2 5 . 
 
 Diazoresorufin is also produced by warming moiiom- 
 trosoresorcin with resorcin and sulphuric acid : 
 
 2C 6 H 3 -NO (OH) 2 + C 6 H 4 (OH) 2 = C 18 H 10 N S B + 3H 8 0. 
 Nitrosoresorcin. Eesorcin. Diazoresorufin. 
 
 This confirms the above formula. 
 
 Diazoresorufin is nearly insoluble in water and alcohol. 
 It is a very weak acid, and forms salts with alkalies which 
 dissolve in water with a cherry-red colour, the solution 
 showing a beautiful cinnabar-red fluorescence. 
 
 Diazoresorufin itself is not suitable for dyeing, for the 
 beautiful colours of the alkaline salts are only shown in 
 neutral or alkaline solutions, while in acid baths wool and 
 silk only assume a dirty-brown colour. 
 
 By the action of bromine on diazoresorufin, a hexabrom- 
 diazoresorufin is obtained, C 18 H 4 Br 6 N 2 5 (?), which resists 
 the action of acids. Its ammonium- salt is the commercial 
 resorcin-blue, or "bleu fluorescent." 
 
 It forms a 10 per-cent. paste, in which the green metallic 
 needles of the colouring matter may be distinguished. It 
 is sparingly soluble in water or absolute alcohol ; the best 
 solvent is a mixture of equal parts of alcohol and water. 
 The solutions are blue by transmitted light, red by 
 reflected light. Strong acids, like hydrochloric or sul- 
 phuric acid, precipitate brown hexabrom-resorufin. 
 
 Silk is dyed with resorcin-blue in a neutral soap- 
 bath. The paste is added to the bath, and dissolves 
 easily. 
 
 Q 
 
226 COAL-TAR COLOURS. 
 
 Brightening is effected by tartaric or sulphuric acid. 
 
 The colour produced upon silk and wool is blue with a 
 slight admixture of red and grey, and has a character- 
 istic red fluorescence, especially in artificial light. It is 
 perfectly fast to light, washing, and acid. 
 
 By combination with a yellow colouring matter, a beau- 
 tiful fluorescent olive is produced. 
 
 On the fibre, resorcin-blue is easily distinguished by 
 its fluorescence, and the action of dilute sulphuric acid. 
 Ammonia and alkalies take up the colour, forming a blue 
 solution with red fluorescence. 
 
 Resor tin- green. Dark-green. 
 This colouring matter is dinitrosoresorcin, 
 
 NOH 
 
 and is obtained by the action of nitrous acid on resorcin. 
 The commercial product forms a dirty-green paste, which 
 is sparingly soluble in water. 
 
 Application. Cotton is mordanted with tannin and 
 nitrate of iron ; wool with copperas and tartar. Various 
 shades of dark-green may thus be obtained which are 
 characterised by their fastness. 
 
 Gambine. 
 
 Gambine is nitroso ft naphthol. The commercial pro- 
 duct forms a dirty-yellow or brown-yellow paste. 
 
 Application. On wool mordanted with iron, gambine 
 produces full shades of olive-green. With bichromate of 
 potash as mordant, dull shades of yellow are obtained. 
 
EOSOLIC ACIDS. 227 
 
 Naphthol- green. 
 
 This colouring matter is the ferrous-sodium salt of 
 nitroso /3 naphtholmonosulphonic acid, and has the com- 
 position, Fe(C 10 H 5 > ONO'S0 3 Na) 2 . It is prepared by first 
 treating ft naphtholsulphonic acid S with nitrous acid 
 and combining the product found with soda and ferrous 
 oxide. 
 
 Naphthol-green forms a dark-green powder which dis- 
 solves in water with a green colour. 
 
 Application. Naphthol-green may be dyed on wool in 
 presence of copperas and sulphuric acid. It produces full 
 shades of olive-green which are quite fast to light. 
 
 (c) EOSOLIC ACIDS. 
 
 The rosolic acids are derivatives of triphenylmethane, 
 and stand in close relation to the rosanilines. They are 
 rosanilines, in which the amido groups are substituted by 
 hydroxyl. A product corresponding to pararosariiline 
 would thus be constituted as follows: 
 
 (C 6 H 4 -NH 3 (C 6 H 4 -OH 
 
 C \ C 6 H 4 -NH C J C 6 H 4 -OH 
 
 IC 6 H 4 -NH; (C 6 H 4 -OH 
 
 OH. OH 
 Pararosaniline. 
 
 The intermediate product expressed by the last formula 
 is, however, not known ; it splits off water, forming para- 
 rosolic acid or aurin 
 
 (C 6 H 4 OH 
 CJC 6 H 4 OH 
 [C 6 H 4 
 
 just like pararosaniline splits off water in uniting with 
 acids. 
 
228 COAL-TAE COLOURS. 
 
 Pararosaniline may be converted into aurin in the fol- 
 lowing manner. 
 
 The hydrochloride of pararosaniline treated in dilute 
 solution with sodium nitrite, yields diazopararosaniline 
 chloride : 
 
 C C 6 H 4 -NH 2 + 3NaNO, + 5HC1 + H<>0 = 
 .C 6 H 4 -NH-HC1 
 
 Pararosaniline hydrochloride. 
 
 C 6 H 4 ]S T :NC1 
 C 6 H 4 N : NCI 
 
 OH 
 
 Diazopararosaniline chloride. 
 
 The liquid is then boiled, with the addition of sulphuric 
 acid, when aurin is formed : 
 
 , r 
 
 C 
 
 C NO 
 
 Diazopararosaniline chloride. Aurin. 
 
 On the other hand, aurin heated to 200 with aqueous am- 
 monia is reconverted into pararosaniline : 
 
 = C 19 H 17 N ? 
 Aurin. Pararosaniline. 
 
 From rosaniline, rosolic acid may be prepared in a 
 similar manner. 
 
 These two colouring matters are now only of secondary 
 importance, but were formerly manufactured on a very 
 large scale. 
 
CORALLIN. 229 
 
 Corallin. 
 
 Yellow corallin. To prepare this colouring matter, 8 
 parts of pure phenol are mixed in the cold with 3'2 parts 
 of concentrated sulphuric acid, and after some hoars 
 4 ! 8 parts of oxalic acid are added, and the whole heated 
 to 110 for twenty-four hours. The mass is then poured 
 into water, and extracted several times with boiling 
 water. 
 
 This product is yellow corallin. It contains about 20 
 per cent, of aurin, formed by the action of the nascent 
 formic acid from the oxalic acid, upon phenol. 
 
 H 2 C0 3 + 3C 6 H 5 OH = C 19 H K 3 + H 3 0. 
 Phenol. Aurin. 
 
 The other constituents are crystalline derivatives of 
 rosolic acid, and resinous bodies, which are mostly colour- 
 less. 
 
 'Yellow corallin is a brown mass possessing a green 
 metallic lustre. It is almost insoluble in water, but 
 easily soluble in alcohol. The yellow, alcoholic solution is 
 turned red by alkalies, and yellow again by acids. This 
 reaction is so delicate as to render corallin useful as an 
 yidicator in volumetric analysis. 
 
 Pure aurin, C 19 H 14 3 , forms ruby-red crystals, with a 
 blue fluorescence. It forms unstable salts with bases. 
 
 Red corallin. If 2 parts of yellow corallin are heated 
 with 1 part of ammonia liquor in a closed vessel to 120- 
 140, a red colouring matter is formed, which is precipi- 
 tated by pouring the product into water and acidifying. 
 
 It has been stated before, that at 200 pararosaniline 
 is formed. Red corallin is an intermediate product, in 
 which only one hydroxyl group of the aurin is replaced 
 by NH 2 : 
 
 C^H! A + NH 3 = C J9 H 13 2 NH 3 + H 2 0. 
 Aurin. Bed corallin. 
 
230 COAL-TAR COLOURS. 
 
 Red corallin comes into commerce as peonin. " Spirit- 
 soluble" if in the free state, and "water-soluble" as the 
 ammonium salt. 
 
 In the first case it forms lumps with a metallic lustre, 
 in the latter a brown-red porous mass. It dissolves in 
 concentrated sulphuric acid with a yellow colour. 
 
 The red solution of the ammonium salt is unaltered by 
 alkalies, and is precipitated yellow by acids. Metallic 
 salts, as basic acetate of lead, acetate of alumina, tin 
 chloride, etc., produce orange-red or yellow precipitates. 
 
 Application. Neither the red nor the yellow corallin 
 is used in dyeing, as the yellow or red orange shades 
 produced are very unstable. It can be washed with water, 
 but will not stand the action of either acids, alkalies, or 
 light. 
 
 Somewhat better results are obtained in printing. 
 
 For printing on wool, the colour is thickened with gum 
 water or glycerin, and a little magnesia or zinc oxide 
 added, to overcome the action of acids. The colours can 
 be steamed. 
 
 For printing on silk, the colour is prepared by dissolv- 
 ing the tin lake in oxalic acid. 
 
 For calico-printing, the same process can be used as for 
 wool, only albumen is substituted for the gum-water. 
 
 Detection on the fibre. The reaction with dilute acids 
 (yellow) is characteristic. Alkalies and ammonia produce 
 red solutions, which do not fluoresce. Chloride of lime 
 decolourises immediately. 
 
 Rosophenolin is obtained by the action of alcoholic 
 ammonia or aurin in presence of phenol or benzoic acid. 
 
 (d) PHTHALEINS. 
 
 Crude materials. The crude materials for the prepara- 
 tion of the phthaleins are the phenols and phthalic acid 
 or its anhydride. 
 
 Reactions of phthalic acid and phenols. If a phenol is 
 
PHTHALEINS. 231 
 
 heated with phthalic anhydride, a combination takes 
 place, with elimination of water. At a moderate tem- 
 perature, two molecules of the phenol unite with one 
 molecule of phthalic anhydride, forming a "phthalein." 
 At higher temperatures with one molecule of each, a de- 
 rivative of anthracene is formed. From phenol, C 6 H 5 OH, 
 phthalic anhydride and sulphuric acid are produced, 
 according to the temperature. 
 
 (1) C 6 
 
 Phthalic anhydride. Phenol. 
 
 /C 6 H 4 -OH 
 
 Phenol phthalein. 
 
 Phthalic anhydride. Phenol. Oxyanthraquinon. 
 
 The formula of phenol phthalein is better expressed as 
 
 (C 6 H 4 -OH 
 
 C-|C 6 H 4 -OH 
 
 
 
 The phthaleins are, therefore, along with rosaniline 
 and rosolic acids, derivatives of triphenylmethane, 
 C(C 6 H 5 ) 3 H. 
 
 The relation between these groups of colouring matters 
 is shown by the constitutional formula : 
 
 (C 6 H 4 -]ra 3 (C 6 H 4 -OH (C 6 H 4 -OH 
 
 I IcX'ffH? I IcX'O. (C 6 6 H 4 'CO. 
 
 Pararosaniline. Aurin. Phenol phthalein. 
 
232 
 
 COAL-TAR COLOURS. 
 
 A confirmation of this formula is obtained as follows : 
 Diphenyl phthalid 
 
 /C 6 H 4 
 C-C G H 5 
 | \C 6 H 4 CO 
 
 o, 
 
 gives successively 
 
 /C 6 H 4 N0 2 
 C-C 6 H 4 NO a 
 \C 6 H 4 CO 
 
 o 
 
 /CeH^NH, 
 C-C 6 H 4 -NHo 
 \C 6 H 4 -CCT 
 
 o 
 
 /C 6 H 4 OH 
 C-C 6 H 4 OH 
 \C 6 H 4 CO 
 
 n 
 
 Dinitrodiphenyl 
 phthalid. 
 
 Diamidodiphenyl Phenol phthalein. 
 phthalid. 
 
 if it is warmed with nitric acid, the product reduced 
 with zinc and hydrochloric acid, and the dilute aqueous 
 solution heated with nitrite of soda and sulphuric acid. 
 
 The phthaleins, like the rosanilines and rosolic acids, 
 give leuco compounds on reduction, which are known as 
 phthalins. 
 
 Phenol phthalin has the formula 
 
 C 6 H 4 OH 
 C 6 H 4 OH 
 C 6 H 4 COOH 
 H. 
 
 The phthaleins of resorcin and pyrogallol are the only 
 ones of commercial importance. 
 
 Fluorescein. 
 
 Fluorescein, C 20 H 12 5 . All the colouring matters known 
 as eosins are derived from fluorescein, an anhydride of 
 resercin phthalein. Te prepare it, the molecular propor- 
 
FLUORESCEIN. 233 
 
 tions of plithalic anhydride and resorcin are heated to 
 1 95 200 till no more steam is evolved, and the mass has 
 become solid. The melt is cooled, and pulverised, and 
 serves as crude fluorescein for the preparation of the eosins. 
 Fluorescein is formed according to the equation : 
 
 p TT /OH 
 
 /^eH-s \ 
 
 p TT /OH / )0 
 yprix ^G-ti-iv nTT / r 1 TT ' 
 r TT /^Ux^ / / ^6 1 3v OTI 4- 2TT O 
 
 > /^VTT r\ * ^ V/JC1 T ^yJLlovy , 
 
 , 
 
 
 
 Phthalic anhydride. Eesorcin. Fluorescein. 
 
 Pure fluorescein forms a yellowish-red crystalline 
 powder, which is sparingly soluble in cold water, with 
 a yellow colour. It is a weak acid, being displaced in its 
 salts by acetic acid. 
 
 Its alkaline solution possesses a bright-green fluores- 
 cence, which is so intense that 1 part dissolved in alkali, 
 and diluted with 2,000,000 parts of water, still shows a 
 fluorescence. Whole rivers may be coloured for a time 
 with a single kilogram. This property has been made 
 use of for determining the course of rivers which sink for 
 a time into the ground. Thus it has been proved by this 
 means that there is an underground connection between 
 the Danube and the Ach, a small river which flows into 
 the Lake of Constance. 
 
 By warming with soda and zinc powder, it is reduced to 
 fluorescin 
 
 an, -OH 
 
 C6 H 3 -OH 
 
 C 6 H 4 -COOH 
 
 H, 
 
234 COAL-TAR COLOURS. 
 
 the alkaline solution of which is gradually oxidised in the 
 air to fluorescein. 
 
 Fluorescein dyes silk and wool yellow, but is seldom 
 used in dyeing, as the colours are not fast. Its sodium 
 salt com.es into commerce under the name of Uranin, and 
 finds a limited application in woollen printing. It 
 forms insoluble lakes with lead, silver, etc., which being 
 non-poisonous, may be used for colouring toys, india- 
 rubber goods, etc. 
 
 From fluorescein, two series of commercial dye-stuffs are 
 derived. The first comprises the unsubstituted ethers of 
 fluorescein, and the other the nitro and halogen deriva- 
 tives and their ethers, which are generally called eosins. 
 
 Chrysolin. 
 
 Benzyl fluorescein, C 20 H 10 3 (OC 7 H 7 )OH, is produced by 
 heating phthalic acid, benzyl resorcin (C 6 H^OC 7 H 7 'OH) 
 and sulphuric acid. Its sodium salt is the chrysolin of 
 commerce. 
 
 Chrysolin is a reddish-brown powder ; the larger pieces 
 possess a greenish reflex. It dissolves in water and 
 alcohol with a green fluorescence. From the solutions, 
 acids precipitate free benzyl fluorescein. 
 
 With stannous chloride and with lead-salts, it gives 
 beautifully coloured lakes. 
 
 On silk and wool it yields a fast yellow, very similar to 
 that produced with turmeric. It is used in cotton-dyeing 
 for topping quercitron-yellow, the quercitron itself acting 
 as a mordant for benzyl fluorescein. 
 
 Eosins. 
 
 Tetrdbromfluorescein, Eosin yellowish, Eosin A, Eosin GGf, 
 Soluble Eosin, Eosin B, Eosin A extra, C 20 H 8 Br 4 5 . If a 
 dilute solution of fluorescein in soda is mixed with the 
 calculated quantity of bromine dissolved in soda, and dilute 
 
EOSINS. 235 
 
 hydrochloric acid is then added, free fluorescein is first 
 precipitated, but this . unites immediately with the liber- 
 ated bromine. The precipitate is filtered, pressed, neu- 
 tralised with soda or potash, and the solution evaporated 
 to dryness. 
 
 The product comes into commerce as eosin yellow 
 shade, soluble eosin, or eosin J. The pure re- crystallised 
 potash salt has the composition C 20 H 6 Br 4 5 K 3 + 6H 2 0. It 
 forms a red powder, or red crystals with yellowish-green 
 reflex. One part dissolves completely in 2 to 3 parts of 
 water ; it is not easily soluble in absolute alcohol. 
 
 Its dilute aqueous solutions are rose-coloured, with 
 an intense green fluorescence ; alcohol renders the fluor- 
 escence still more intense. Free tetrabromfluorescein is 
 nearly insoluble in water, while its reddish-yellow alco- 
 holic solution shows no'fluorescence. It is a pretty strong 
 acid, its salts not being decomposed by acetic acid. 
 
 It combines with metallic oxides, producing sparingly 
 soluble or insoluble lakes. They are prepared by mixing 
 aqueous solutions of metallic salts and eosins, when they 
 separate as amorphous, bright-coloured precipitates. 
 Silver and lead salts give red, aluminium, zinc, tin, cobalt, 
 iron, manganese and bismuth salts give reddish-yellow 
 lakes. 
 
 Eosin orange and Eosin 5G are mixtures of dibrom- 
 fluorescein and tetrabromfluorescein. 
 
 Tefraiodfluorescein, C 20 H 8 I 4 5 , is prepared in a similar 
 manner to tetrabromfluorescein. Its alkaline salts are 
 sold as eosin blue shade (soluble in water), erythrosin, 
 py rosin R, soluble primrose, Dianthin B, Rose B soluble in 
 water, Eosin J. Its aqueous solutions are not fluorescent, 
 otherwise it resembles eosin J. 
 
 Aureosin J" is a chlorinated fluorescein. 
 
 Bromnitrofluoresceins are produced by the action of 
 dilute nitric acid on tetrabromfluorescein. Their salts 
 are known in commerce as eosin BN or saf rosin. 
 
236 COAL-TAR COLOURS. 
 
 A mixture of bromnitrofluoresceiii with di- and tetra- 
 nitrofluorescein is known as lu-tecienne. Rubeosin is a 
 nitrochlorofluorescein obtained by the action of nitric 
 acid on aureosin. 
 
 The alcohol-soluble eosins are substitution products of 
 the methyl and ethyl ethers of fluorescei'n. 
 
 The methyl and ethyl ethers of tetrabromfluorescein 
 are produced by heating" tetrabromfluorescein with Avood 
 spirit, or ethyl alcohol, and sulphuric acid. They may 
 also be produced by heating eosin with methyl or ethyl 
 bromide. Their potassium salts 
 
 and 
 
 are commercial products under the names, eosin soluble in 
 spirit, ethyl eosin, methyl eosin, spirit primrose^ rose JB 
 soluble in spirit, primrose, eosin B B. 
 
 They are sparingly soluble in water, but dissolve easily 
 in alcohol of 50 per cent., while they are insoluble in 
 absolute alcohol. The dilute solutions possess a beautiful 
 fluorescence. 
 
 These eosins contain the substituted halogen atoms in 
 the resorcin rest. Eosins may also be prepared contain- 
 ing the halogen atoms in the phthalic-acid rest, thus 
 dichlorphthalic acid acts on resorcin, producing dichlor- 
 ttuorescein : 
 
 G 
 
 C 6 H 3 -OH 
 C 6 H 2 C1 2 -CO 
 
 
 
EOSINS. 237 
 
 Rose Bengale is the sodium salt of tretraioddichlor- 
 fluorescein : 
 
 C 6 HI 2 -OH 
 
 CM 
 
 C 6 H 2 C1 2 -CO 
 
 C 6 HI 2 -OH 
 
 Phloxiu TA, Phloxin, Eryturosin B, is the potassium salt 
 of tetrabromtetrachlorfluorescem, Co H 2 Cl 4 Br 4 5 Na 2 , and 
 cyanosine B, is the sodium salt of the ethyl ether of 
 phloxin, a o H 2 C! 4 Br 4 5 C 2 H 5 Na. 
 
 Phloxin P, Phloxin is the potassium salt of tetrabrom- 
 dichlorfluorescein, C 20 H 4 01 2 Br 4 5 K 2 . Cyanosin is the 
 potassium salt of the methylether of tetrabromdichlor- 
 fluorescein. 
 
 Reactions of the eosins. The fluorescence of the eosins 
 is most intense in alcoholic solutions. It is the brightest 
 in the " alcohol-soluble eosins," then comes eosin G. 
 Safrosine fluoresces very little, somewhat more in 
 presence of ammonia, while eosin B does not fluoresce at 
 all in aqueous solution and very little in alcoholic solu- 
 tion. 
 
 The eosins dissolve in cold concentrated sulphuric 
 acid with a yellow colour, which generally becomes 
 darker on heating. Eosin G and BN are turned dark- 
 red, and, on adding water, a new colouring matter 
 separates in dark flakes. On heating eosin B with sul- 
 phuric acid, iodine separates out. 
 
 Hydrochloric acid separates from eosin solutions the 
 free fluoresceins. Eosin G gives a yellow, eosin B an 
 orange-red, safrosin a yellow-brown, and spirit-soluble 
 eosin a beautiful red, precipitate. 
 
 Metallic salts give coloured precipitates. 
 
238 COAL-TAR COLOURS. 
 
 Chloride of lime decolourises the solutions on heating. 
 
 With the exception of eosin B, all eosins may be recog- 
 nised by their fluorescence, especially in presence of 
 ammonia. The reactions with sulphuric and hydrochlo- 
 ric acids are also characteristic. 
 
 The recognition of eosin B, and the separation of the 
 colouring matters, is best carried out by the reactions 
 with zinc powder and ammonia. The iodine is thus 
 removed from eosin B, and the fluorescem produced is 
 reduced to colourless fluorescin, which on oxidation in 
 the air yields fluorescein. 
 
 Eosin Gr does not lose any bromine, but is reduced to 
 colourless tetrabromfluorescin, which yields the original 
 tetrabromfluorescein. 
 
 Eosin BN" is reduced to colourless fluorescin, and the 
 nitro groups are simultaneously reduced ; on oxidation a 
 non-fluorescent cherry-red solution is produced. 
 
 The " spirit-soluble " methyl and ethyl eosins react in 
 the same way as eosin G. 
 
 The oxidation of the reduced solutions in the air takes 
 place immediately only with saf rosin; the other colouring 
 matters require to stand a longer time. Characteristic 
 colourations are obtained by proceeding as follows : 
 
 A small quantity of the very dilute aqueous solution 
 of the colouring matter is mixed with a few drops of 
 ammonia and zinc powder till completely decolourised; 
 it is then filtered, and the filtrate boiled till the excess of 
 ammonia is removed, and a precipitate of zinc hydrate is 
 produced. Then hydrochloric acid is added till the pre- 
 cipitate re-dissolves, when the liquid is treated with 
 excess of ammonia. 
 
 The following table of reactions will be understood 
 without further explanation : 
 
EOSINS. 
 
 239 
 
 
 Original dilute 
 solution. 
 
 Filtrate 
 immediately after 
 boiling with 
 Zn. and NH 3 . 
 
 After oxidation 
 by boiling, etc. 
 
 Eosin G. 
 
 Cherry-red, 
 yellow-green 
 fluorescence. 
 
 Nearly colourless. 
 
 Cherry-red 
 yellowish-green 
 fluorescence. 
 
 Eosin B. 
 
 Cherry-red, 
 without fluores- 
 cence. 
 
 Nearly colourless. 
 
 Yellow, with 
 strong green 
 fluorescence. 
 
 Eosin BN. 
 
 Cherry-red, 
 yellowish-green 
 fluorescence. 
 
 Cherry-red, 
 non-fluorescent. 
 
 Cherry-red, 
 non-fluorescent. 
 
 Spirit- soluble 
 Eosin. 
 
 Cherry-red, 
 strong green 
 fluorescence. 
 
 Nearly colourless. 
 
 Cherry-red, 
 yellow-green 
 fluorescence. 
 
 The eosins also give characteristic colour reactions, 
 when a small quantity is boiled with strong potash lye 
 (containing 20 to 40 per cent, of solid KOH). 
 
 Eosin G gives in the cold an orange-red solution, which 
 on boiling becomes purple-red, violet, and pure blue, with 
 a strong green fluorescence. The colour and fluorescence 
 are unaltered on dilution, if the boiling has been con- 
 tinued long enough. 
 
 Eosin B, on boiling with potash, first turns purple-red 
 and then blue-violet, with a weak, green fluorescence. 
 On dilution the solution becomes purple-red. 
 
 Eosin BN becomes lighter and yellower with potash, 
 and on boiling turns olive-green, without fluorescence. 
 
 Spirit-soluble eosins are insoluble in the concentrated 
 lye; on boiling the same reactions as with eosin G gradu- 
 ally take place. 
 
 Application. Eosins yield bright shades on silk, wool, 
 and cotton, comprising all the shades from a reddish- 
 
240 COAL-TAR COLOURS. 
 
 orange to a cherry-red and purple. The bluest shades are 
 produced by rose Bengale ; then come safrosin, phloxin, 
 and eosin B, and the methyl and ethyl eosins. The 
 yellowest is eosin G. 
 
 Safrosin is very bright on wool, but is surpassed on 
 silk by the other bluish eosins. The spirit-soluble eosins 
 are brighter than those soluble in water, but they are not 
 often used, as they are more expensive. It is necessary 
 to dissolve them for use in methylated spirits, and the 
 colours produced have a strong fluorescence, which is 
 seldom desirable. 
 
 Silk is dyed in boiled-off liquor, and brightened with 
 acetic or tartaric acid. 
 
 Wool is dyed with alum or acetic acid. A good result 
 is obtained by the sulphur mordant, as applied in dyeing 
 methyl-green. 
 
 Cotton is mordanted with alumina or stannate of soda 
 for yellow shades, with lead-salts for blue shades. In 
 mordanting with alumina, the cotton is first passed 
 through a hot, strong solution of soap, and, after squeezing 
 through a solution of aluminium acetate at about 12 Tw. 
 Oleate, palmitate or stearate of alumina is thus precipi- 
 tated on the fibre, which now takes up the dye very readily. 
 
 Eosins are often used mixed with other colouring 
 matters, such as red, yellow, and violet, and mixtures of 
 this kind are sometimes sold as commercial products. 
 Nopaline, or Imperial-red, contains Martius-yellow, while 
 eoccine contains aurantia. 
 
 Safrosin, when mixed with yellow colouring matters, 
 is sold as cochineal substitute, and yields a scarlet very 
 similar in appearance to cochineal- scarlet. 
 
 Detection on the fibre. Warm water removes a trace of the 
 colouring matter, especially if a little ammonia is added, 
 from goods 'dyed with eosins soluble in water. Spirit- 
 soluble eosins are not affected by water, but alcohol removes 
 them, and leaves the eosins soluble in water on the fibre. 
 
RHODAMINE. 241 
 
 Concentrated potash solution gives the reactions de- 
 scribed above. Hydrochloric acid or acidulated stannous 
 chloride decolourise or turn the fabric yellow. Sulphuric 
 acid turns them yellow, chloride of lime decolourises on 
 warming. 
 
 The colours produced on cotton are not so fast as on 
 wool or silk. They are not fast to light. 
 
 Rhodamine. 
 
 By heating phthalic anhydride with diethylamido- 
 phenol, C 6 H 4 1 ^2 H 5)2 a phthalein is formed which 
 
 possesses simultaneously basic and acid properties and 
 the hydrochloride of which forms the commercial rhoda- 
 mine. Its constitution is represented by the formula 
 
 /C 6 H 3 N(C 2 H 5 ) 2 
 
 C 6 H 3 N(C 2 H 5 ) ;HCl 
 C 6 H 4 CO-0 
 
 Commercial rhodamine forms a reddish-coloured pow- 
 der easily soluble in water with a magenta colour. The 
 dilute aqueous solution shows a strong fluorescence. The 
 free base is precipitated from the aqueous solution by 
 caustic soda, in red flakes, soluble in ether. With stan- 
 iious chloride rhodamine gives a brilliant scarlet pre- 
 cipitate, which in a fine state of division shows a 
 remarkable fluorescence ; the reflected light is scarlet, 
 while the transmitted light is of a bright-blue colour. 
 
 Application. Bhodamine produces on wool and silk an 
 exceedingly bright pink with yellow fluorescence, which 
 is especially valuable on account of its comparative fast- 
 ness to light. Cotton is previously mordanted with 
 tannin and tartar emetic. 
 
 R 
 
1'lithalic anhydride. Pyrogallic acid. 
 
 242 COAL-TAE COLOURS. 
 
 Gallein. 
 
 Gallein, C 20 H 10 7 , is obtained by heating phthalic anhy- 
 dride and pyrogallic acid to 190-200 till a solid mass 
 is formed. The melt is boiled with water, dissolved in 
 sodium carbonate, filtered, and the colouring matter pre- 
 cipitated with an acid. 
 
 A combination of phthalic anhydride and pyrogallic 
 acid takes place with elimination of water, but at the 
 same time an oxidation takes place : 
 
 C 6 H 2 OH-0 
 
 (ol+O C S ' 
 
 ! COH C 6 H,OH-0 
 
 C 6 H~-CO'0 
 
 Gallein. "" 
 
 Gallein forms either a brown-red powder or green 
 i-ietallic-looking crystals, which are almost insoluble in 
 \v r ater, but soluble in alcohol. It is a weak acid, form- 
 ing a blue solution with alkalies. Its alkaline solution 
 assumes a dirty colour on standing. It dissolves in 
 ammonia with, a violet colour, which solution gives 
 violet precipitates with metallic salts. 
 
 Gallein yields on wool, mordanted with bichromate and 
 tartar, dark shades of violet which are characterised by 
 their beautiful." bloom." On mordanted cotton, it produces 
 fast violet shades. Lead mordants give a fine grey- violet. 
 
 In calico-printing, it has been superseded by the fast 
 alizarin-violet. It may be fixed, like coerulein, with 
 chromium acetate. 
 
 Gallein is most important as a raw material for the 
 preparation of coerulein. 
 
 Coerulein. 
 
 Gallein is heated to 200 with twenty times its weight 
 of strong sulphuric acid, when the red colour gradually 
 
COERULEIN. 243 
 
 changes to a brownish-green. The mixture is cooled and 
 poured into water, and the black precipitate washed and 
 dried. 
 
 The formation of coerule'in is expressed by the 
 equation 
 
 ? H 2 = C 20 H 8 6 . 
 Gallei'n. Coerulein. 
 
 Its constitution has not been determined with certainty, 
 but, according to Buchka, it is a derivative of phenyl 
 anthracene 
 
 C 6 H 5 
 
 C 6 H/ I 
 ^ 
 H 
 
 and thus belongs to the anthracene colours. 
 
 Properties. Dry coerulem forms an amorphous, almost 
 black mass. It is nearly insoluble in water, alcohol and 
 ether. The best solvent is acetic acid. Commercial 
 coerulein forms a thick, dark-coloured paste. It dissolves 
 in alkalies with a beautiful green colour. This solution 
 gives with mordants very stable lakes. On warming 
 with ammonia and zinc powder, a brown-red solution is 
 formed, containing coeruliii, the phthalin of coerulein. 
 The solution is oxidised in the air, the original green 
 colour being restored. It may be used for dyeing as a 
 coerulein vat, and acts in the same way as the indigo vat. 
 
 Bisulphite compound. On stirring the commercial 
 coerulein paste with a concentrated solution of sodium 
 bisulphite, N"aHS0 3 , a colourless compound of coerulein 
 and bisulphite is formed, which can be removed from the 
 unaltered coerulein by extracting with cold alcohol. The 
 best proportions are one molecule of coerulem to two 
 molecules of bisulphite. 
 
244 COAL-TAE COLOUKS. 
 
 Sulphurous acid or ammonium bisulphite acts in a 
 similar manner. 
 
 The coerulein sulphite does not contain a reduced 
 colouring matter, but is a double compound, analogous 
 to those formed with aldehydes and ketones. It is 
 colourless, and soluble in water and alcohol. On boiling, 
 the greenish-yellow solution turns green, and becomes 
 alkaline, sulphurous acid being ' evolved. Acids and 
 alkalies decompose coerulein sulphite in the cold, with 
 evolution of sulphurous acid. 
 
 Coerulein sulphite comes into commerce as coeruleiu S. 
 It is easier to dye with than the paste. It forms a black 
 powder, which dissolves in water with a dull-green colour, 
 the solution giving all the reactions of the solid com- 
 pound. The pure compound may be obtained by crystal- 
 lising coerulein from alcohol. 
 
 Application. Coerulein is used in large quantities for 
 dyeing or printing cotton fabrics. With chromium mor- 
 dants it gives a very fast, but dull olive-green, which, 
 however, in point of fastness equals the alizarin colours. 
 Other green dyes, such as chrome-green (Guignet's green) 
 and aniline-green, are brighter, but not nearly so fast. 
 
 For printing with coerulein S, the latter is mixed with 
 chromium acetate, and thickened, and fixed by steaming. 
 If insoluble coerulein is used, it is previously rendered 
 soluble by the addition of sodium bisulphite. 
 
 In wool-dyeing, coerulein also gives excellent results. 
 It may be used for this purpose either in the form of the 
 bisulphite compound or as the paste. The most effective 
 mordant for wool is bichromate of potash (3%), and tar- 
 tar (2|%). The shades obtained resemble woaded greens. 
 Coerulein can also be used along with many of the 
 natural colouring matters and with the alizarins, by 
 which means a large variety of fast shades can be pro- 
 duced. 
 
 Detection on the -fibre. The colour is not removed by 
 
QUINOLINE-YELLOW. 245 
 
 boiling soap or caustic alkalies. Concentrated hydro- 
 chloric acid darkens the colour. The most characteristic 
 reaction is the action of a warm, acid solution of stannous 
 chloride, which turns the fibre brown-red, coerulin being 
 formed. On washing with water, or, better still, with 
 very dilute chloride of lime solution, the original colour 
 is restored. 
 
 Quinoline-yellow. 
 
 Quinoline-yellow is the sodium salt of^quinophthalondi- 
 sulphonic acid. 
 
 CH-C 9 H 4 N(S0 3 Na) 2 
 // 
 C 
 
 C 6 H 4 -CO-0. 
 
 It is obtained by treating quinaldine C 10 H 9 N with 
 phthalic anhydride in presence of zinc chloride, and sul- 
 phonating the product obtained. 
 
 It forms a bright-yellow powder, which dissolves easily 
 in water with an intense yellow colour, which is un- 
 altered by dilute sulphuric acid, but is turned somewhat 
 darker by ammonia. 
 
 Application. Quinoline-yellow is not applicable to 
 cotton. It is dyed on wool and silk in an acid-bath 
 (H 3 S0 4 ), and yields very pure shades of yellow, which 
 somewhat resemble those obtained with picric acid. It 
 stands light -fairly well, only becoming a trifle lighter after 
 a month's exposure, in which it differs materially from 
 picric acid, which becomes orange. 
 
 Quinoline-'blue, C 29 H 35 lS"oI is obtained by treating equal 
 molecules of quinoline and lepidine with amyl iodide and 
 subjecting the product obtained to the action of caustic 
 alkalis. 
 
246 COAL-TAR COLOURS. 
 
 It forms green crystals, which dissolve in boiling water 
 with a violet-blue colour, and is used for sensitising 
 photographic plates. 
 
 Quinoline-red, C 2 6-H 19 N 2 C1 is formed by. the action of 
 benzotrichloride on a mixture of quinaldine and isoquino- 
 line in presence of zinc chloride. It forms dark brown- 
 red needles with a bronze reflex, which dissolve in hot 
 water with a red colour. It is used like quinoline-blue 
 for sensitising photographic plates. 
 
 'V: 
 
AZO DYES. 247 
 
 III. THE Azo DYES. 
 
 THE azo dyes form a well-defined and well-studied group 
 of the coal-tar colours, Their chemical constitution has 
 been clearly proved in every case as far as possible iu 
 accordance with our present knowledge of chemistry. 
 All the azo dyes may be prepared according to one 
 general method, viz., by acting on diazo compounds with 
 phenoles or amines of the aromatic series. 
 
 Diazo compounds are formed (as stated on several pre- 
 vious occasions) when primary amines of the aromatic 
 series are treated with nitrous acid. In order to be able 
 to understand the manufacture of the azo dyes properly, 
 it will be necessary to know something of the properties 
 of these compounds. 
 
 If nitrous fumes, obtained by heating starch with 
 nitric acid possessing a specific gravity of 1'30 to 1'35, 
 are passed into an aqueous solution of nitrate of aniline, 
 the following equation is fulfilled : 
 
 C 6 H 5 NH 2 -HN]fi + HN0 2 - C ? H 6 - N : N'N0 3 + 2H 2 0. 
 Nitrate of aniline.^ Nitrate of diazobenzene. 
 
 A similar reaction takes place if a solution of aniline 
 hydrochloride is treated first with hydrochloric acid and 
 then with sodium nitrite, in the proportions indicated in 
 the equation : 
 
 C 6 H 5 NH 2 -HC1 + HC1 + NaNO a - 
 
 Aniline hydrochloride. 
 
 O a H 6 NH : N-01 + NaCl + 2H 2 0. 
 
 Diazobenzene chloride. 
 
 If nitrous fumes are passed into an alcoholic solutidtl 
 of aniline, a diazo compound is likewise formed, which 
 
248 COAL-TAR COLOURS. 
 
 is known as diazoamidobenzene, and has the formula 
 C 6 H 5 N:N-NH'C 6 H 5 . The formation of this compound 
 is easily explained by supposing the equation to be 
 fulfilled in two phases : 
 
 (1.) C 6 H 5 NH 2 + HO-NO - C 6 H 5 N:N-OH + H 2 0. 
 
 Aniline. Free diazobenzene. 
 
 The diazobenzene acts in the nascent state on a second 
 molecule of aniline, thus : 
 
 (2.) CgH 5 N : N-OH + C 6 H 5 NH 2 - 
 
 Diazobenzene. Aniline. 
 
 Diazoamidobenzene. 
 The formulae given in these equations for 
 
 Diazobenzene nitrate, C 6 H 5 N:N"'N0 3 , 
 
 Diazobenzene chloride, C 6 H 5 N:N'C1, 
 
 Diazoamidobenzene, C 6 H 5 N : N'NH'C 6 H 5 , 
 
 Diazobenzene, C 6 H 5 N : 
 
 are typical as representatives of this group, which latter 
 can therefore be characterised in the following manner : 
 
 " Diazo compounds are bodies which contain the 
 diatomic group N : N , which is bound on one side to a 
 carbon atom, the other bond being saturated with oxygen, 
 nitrogen, chlorine, bromine, etc." 
 
 Most of the diazo compounds crystallize well and are 
 colourless, with the exception of the diazoamido com- 
 pounds, which are either yellow or red. When heated, 
 they detonate with extreme violence. The diazo com- 
 pounds decompose very easily. Thus free diazobenzene 
 decomposes immediately when separated from its salts. 
 The stability of the compounds is, however, increased by 
 the introduction of electro-negative groups into the ben- 
 zene ring. Thus diazonitrophenol can be kept in the 
 free state without undergoing any change. 
 
AZO DYES. 249 
 
 If aqueous solutions of the salts of diazo compounds are 
 heated, decomposition ensues along with the evolution of 
 nitrogen gas and formation of resinous and other products. 
 If, however, the solution is acidulated before boiling, a 
 phenol is the chief product of the reaction ; e,g. : 
 
 + H 2 - C 6 H 5 OH + N 3 + HN0 3 . 
 Diazobenzene nitrate. Phenol. 
 
 The fact that the diazo compounds are so easily decom- 
 posed, along with the great danger of keeping large 
 quantities of such explosive substances, would render 
 their application in the manufacture of coal-tar colours 
 prohibitive, should it be necessary to prepare them in 
 the dry state. This can, however,be avoided by preparing 
 them in very dilute solutions, from which the azo bodies 
 can be separated directly without isolating the diazo 
 compounds. 
 
 The azo compounds also contain the diatomic group 
 N:N , which is, however, bound on either side to a 
 carbon atom. The simplest representative of this class of 
 bodies is known as azobenzene, and has the formula 
 
 Azobenzene and its homologues can be obtained by 
 reduction of the nitro derivatives of the corresponding 
 hydrocarbons. The most suitable reducing agents are 
 sodium amalgam, zinc and alcoholic potash, or an alkaline 
 solution of stannous hydrate. In the case of nitrobenzene, 
 the reaction takes place according to the equation 
 
 2C 6 H 6 1S"0 2 + 4H 2 - C 6 H 5 -N : N'C 6 H 5 + 4H 2 0. 
 Nitrobenzene. Azobenzene. 
 
 The simple azo compounds are for the most part 
 brightly- coloured bodies ; but they are no colouring 
 
250 COAL-TAR COLOURS. 
 
 matters, since they do not possess the property of com- 
 bining with either acids or bases. 
 
 The azo dyes are amido- or hydro xyl- derivatives of the 
 simple azo compounds, and are distinguished as amidoazo 
 and oxyazo dyes. From azobenzene, for instance, the 
 following representatives of these two groups may be 
 derived : 
 
 C 6 H 5 N : N C 6 H 4 NH 2 , Amidoazobenzene (aniline-yellow). 
 CgH.N : N C 6 H 4 OH~ Oxyazobenzene. 
 
 For dyeing, the amidoazo dyes can either be used as 
 such, or in the form of their sulphonic acids, while the 
 oxyazo dyes nearly always contain sulpho groups. It is 
 for this reason that the azo dyes have been divided below 
 into three groups. 
 
 The azo dyes are never prepared in practice from the 
 simple azo compounds, although this would be possible in 
 one or two cases. Thus, amidoazobenzene can be obtained 
 by nitrating azobenzene, which yields nitroazobenzene, 
 C 6 H 5 N":NC 6 H 4 ']SrO:,, and this, when reduced, yieWs 
 amidoazobenzene. The general method mentioned above, 
 i.e., allowing diazo compounds to act on phenols or 
 amines, has not only the advantage of being easily carried 
 out, but also allows a larger number of combinations to 
 be made. 
 
 The following example, the preparation of dimethyl- 
 amidoazobenzene, may serve to illustrate the reaction : 
 
 C 6 H 5 N : NCI + C 6 H 5 N(CH3) 2 = 
 Diazobenzene chloride. Dimethylaniline. 
 
 C 6 H 5 N : N C 6 H 4 N(CH 3 ) 2 + HC1. 
 Dimethylamidoazobenzene. 
 
 If aniline and diazobenzene hydrochloride are allowed 
 to act on each other in a similar manner, the reaction 
 
AMIDOAZO DYES. 251 
 
 is somewhat different, diazoamidobenzene being first 
 formed : 
 
 C 6 H 5 N : NCI + C 6 H 5 TH 2 - C 6 H 5 N : N NH C 6 H 5 + HC1. 
 Diazobenzene Aniline. Diazoamidobenzene. 
 
 chloride. 
 
 This latter product soon passes over, however, into the 
 isomeric amidoazobenzene, especially in the presence of a 
 small quantity of aniline hydrochloride : 
 
 C 6 H 5 N : N NH C 6 H 5 - C 6 H 5 N : N C 6 H 4 NH 2 . 
 Diazoamidobenzene. Amidoazobenzene. 
 
 In all cases hitherto noticed of amines or phenoles com- 
 bining with diazo compounds, the amido or hydro xyl 
 group invariably assumes the para position with respect 
 to the -N:N- group. 
 
 Of the general reactions of the azo compounds, we will 
 only mention here their behaviour towards energetic re- 
 ducing agents. The latter split up the azo compound into 
 two halves, and at the same time transform the -N : N- 
 group into two amido groups ; e.g. : 
 
 C fl H 5 N : N C 6 H 4 NH 2 + 2H 2 - C G H 5 NH 2 + C 6 H 4 (KH 2 ) 2 . 
 Amidoazobenzene. Aniline. Paraphenylene- 
 
 diamine. 
 
 ^(a) AMIDOAZO DYES. 
 
 Only three technical products belong to this group viz., 
 aniline-yellow, chrysoidine and phenylene-brown. The 
 colour-bases contained in them are all derived from azo- 
 benzene, C 6 H 5 -N : N- C 6 H 5 , and they form the following 
 series : 
 
 C 6 H 5 N : N C 6 H 4 NH 2 , Amidoazobenzene. 
 C 6 H 5 N" : N" C 6 H 3 (NH 2 ) 2 , Diamidoazobenzene. 
 NH 2 C 6 H 4 N" : N C G H 3 (NH 2 ) 2 , Triamidoazobenzene. 
 
252 COAL-TAR COLOURS. 
 
 The affinity of these bases to acids, and at the same 
 time their fastness on the fibre, is proportionate to the 
 number of amido groups they contain ; thus, phenylene- 
 brown is faster than chrysoidine, and this again is faster 
 than aniline-yellow. 
 
 It is a characteristic of these dyes that the aqueous 
 solutions of their hydrochlorides are precipitated by alka- 
 lies and ammonia, and reddened by strong acids. 
 
 1 Aniline-yellow. 
 
 Aniline-yellow, or amidoazobenzene hydrochloride, 
 C 6 H 5 N : N C 6 H 4 NH 2 HC1, can be obtained by mixing 
 dilute aqueous solutions of diazobenzene chloride and 
 aniline. 
 
 In the pure state it forms bluish- violet, lustrous needles, 
 which dissolve in acidulated water with a fine red colour. 
 If the solution is heated, the salt is decomposed and the 
 free base is precipitated. Free amidoazobenzene can be 
 completely precipitated from solutions of its salts by 
 ammonia. In the pure state it forms yellow crystals, 
 which melt at 127'5 , and can be volatilised without 
 decomposition. It is insoluble in water, but dissolves in 
 alcohol. 
 
 In acid solutions of aniline-yellow, silk is dyed red, the 
 salt itself being assimilated by the fibre. But on washing 
 with water, the salt is decomposed, and only the free base 
 remains on the fibre, to which latter it imparts a yellow 
 colour. 
 
 Aniline-yellow is at present not used on the large 
 scale, since it is not at all fast and easily volatilises when 
 steamed. 
 
 V' Chrysoidine. 
 
 Chrysoidine, or diamidoazobenzene hydrochloride, 
 C 6 H 5 N : N C 6 H 3 (NH 2 ) 2 HC1, is formed when an aqueous 
 
CHRYSOIDINE. 253 
 
 solution of metaphenylenediamine is poured into a very 
 dilute solution of diazobenzene chloride : 
 
 C 6 H 5 N : N 01 + 6 H 4 (NH 8 ) 3 = 
 Diazobenzene Phenylenediamine. 
 chloride. 
 
 C 6 H 5 N : N ' 6 H 3 (NH 3 ) 3 HC1. 
 Cbrysoidine. 
 
 Chrysoidine separates out as a sparingly soluble pre- 
 cipitate. 
 
 Metaphenylenediamine may be obtained in a compara- 
 tively pure state by first converting benzene by means of 
 concentrated nitric and sulphuric acids into dinitrobenzene, 
 C fi H 4 (NOo) 2 , and reducing this compound with iron and 
 hydrochloric acid. 
 
 The chrysoidine of commerce usually consists of dark 
 violet crystals, having a metallic reflex, which dissolve 
 easily and without decomposition in boiling water and in 
 absolute alcohol. From the orange-coloured solution 
 ammonia or caustic soda throw down a bright-yellow 
 precipitate, which consists of the free colour-base. Chry- 
 soidine contains two amido groups, and is therefore also 
 capable of combining with two equivalents of an acid. 
 The salts formed are, however, not at all stable. The 
 fact that solutions of chrysoidine are turned yellow by 
 excess of hydrochloric acid is due to the formation of 
 these abnormal salts. In very thin layers, these solutions 
 appear crimson. Concentrated sulphuric acid dissolves 
 chrysoidine with a yellowish-brown colour. 
 
 Stannous chloride decolourises in the cold. Basic lead 
 acetate produces an orange precipitate. 
 
 Cardinal is a mixture of magenta and chrysoidine. A 
 mixture of safranine and chrysoidine is sometimes sold as 
 cotton scarlet (Schulz & Julius). 
 
 Application. Silk is dyed in a neutral soap-bath, wool 
 
 r**^ 
 
 -- oi-rm'Sr \ 
 
254 COAL-TAR COLOURS. 
 
 in pure water. Cotton is mordanted with tannin and 
 tartar emetic. The solution of the dye should be filtered 
 before use. 
 
 Detection on the fibre. A solution of stannous chloride 
 in hydrochloric acid decolourises completely. Hydro- 
 chloric acid turns the colour red; ammonia, bright 
 yellow ; concentrated sulphuric acid is coloured yellow. 
 
 BismarcJc-brown, Phenylene-brown, Vesuvine, Cinnamon- 
 brown, Canelle, Manchester-brown. 
 
 Phenylene-brown is a hydrochloride of triamidoazo- 
 benzene, possessing the formula : 
 
 The colour-base is formed by the action of nitrous acid 
 on an aqueous solution of free metaphenylenediamine, 
 according to the equation : 
 
 Phenylenediamine. 
 
 /KH 2 
 C 6 H 4 -N:N-C 6 
 
 Triamidoazobenzene. 
 
 The precipitate, which still contains considerable quan- 
 tities of by-products, is washed, converted into the 
 hydrochloride, and purified. 
 
 The commercial product forms a dark powder. It 
 contains a certain amount of by-products insoluble in 
 water, which should be removed by filtration before use. 
 
 The free colour-base is somewhat soluble in boiling 
 water. It can be obtained by the addition of ammonia or 
 caustic alkali to the colour solution, in the form of a 
 brown voluminous precipitate ; when purified by recrystal- 
 lisation, it forms small crystals, which melt at 137. 
 Although it contains three amido groups, it will not com- 
 
AMiDOAZOSULPHONIC ACIDS. 255 
 
 bine with more than two equivalents of acid to form 
 stable salts. Bat if an excess of hydrochloric acid is 
 added to the solution it is coloured red, owing to the 
 formation of a salt containing three equivalents of acid. 
 Phenylene-brown dissolves in water and alcohol with a 
 brown colour ; the solution in sulphuric acid is yellow- 
 brown. 
 
 A mixture of stannous chloride and hydrochloric acid 
 decolourises the aqueous solution. Basic acetate of lead 
 produces a brown precipitate. 
 
 Application. Phenylene-brown is used largely for dye- 
 ing leather, under various names, as vesuvine, cinnamon- 
 brown, and Bismarck-brown. Wool is dyed without any 
 addition, or with some Glauber's salts. The inferior 
 qualities, which are generally used for dyeing leather, are 
 best dissolved with the addition of a few drops of sul- 
 phuric acid. Bismarck-brown is also used for cotton 
 which is mordanted either with tannin and tartar emetic 
 or with Turkey-red oil. ' 
 
 Detection on the Fibre. The red colouration produced 
 with hydrochloric acid is the best test for this colouring- 
 matter on the fibre. Ammonia produces but little 
 change, stannous chloride decolourises. 
 
 (b) AMIDOAZOSULPHONIC ACIDS. 
 
 The colouring matters of this class occur in commerce 
 as alkali- or ammonia- salts. The aqueous solutions are 
 precipitated by hydrochloric acid, in an excess of which 
 the precipitate re- dissolves with a red colour. Ammonia 
 and caustic soda do not produce any precipitates. Boiling 
 alcohol does not strip the colour. 
 
 Acid-yellow, Fast-yellow, Solid-yellow, New-yellow L. 
 
 Manufacture. Acid-yellow consists of the sodium salt 
 of the disulphonic acid of amidoazobenzene or aniline- 
 yellow along with some of the monosulphonic acid. 
 
256 COAL-TAR COLOURS. 
 
 It has the composition : 
 
 a 
 H 
 
 S0 3 Na 
 
 6 
 
 and is formed by the action of fuming sulphuric acid on 
 amidoazobenzene. 
 
 Acid-yellow forms a yellow powder, which dissolves 
 easily in water, but with difficulty in alcohol. On acidu- 
 lating the aqueous solution with hydrochloric acid, the 
 free amidoazobenzene-sulphonic acid is thrown down in. 
 the form of minute needles, which re-dissolve in excess of 
 hydrochloric acid with a reddish-yellow colour (in thin 
 layers crimson). 
 
 Ammonia and caustic alkalies do not effect any change, 
 nor is the colouring matter precipitated by basic acetate 
 of lead. Sulphuric acid dissolves acid-yellow with a 
 yellow colour. Zinc powder decolourises ; but if the 
 colourless solution is filtered and allowed to stand in the 
 air, the original colour is restored. 
 
 Application. Acid-yellow is not often used for dyeing 
 pure yellow, although it is comparatively fast as an 
 aniline dye, and will stand steaming. The shade obtained 
 with it is an almost pure yellow, and contains only a trace 
 of red; but it is not sufficiently brilliant to be used alone. 
 On the other hand, as its colour does not incline so much 
 towards the red, it is well adapted for dyeing compound 
 colours, such as olive, moss-green, or brown, in the place 
 of the natural yellow colouring matters hitherto used for 
 this purpose. It is dyed in an acid-bath, and can there- 
 fore be combined with acid-magenta, indigo extract, fast 
 red, etc. 
 
 Silk is dyed with boiled-off liquor, wool with sodium 
 bisulphate, or alum and sulphuric acid. An excess of acid 
 reddens the shade. 
 
 Large quantities of acid-yellow are used for the manu- 
 facture of diazo colours. 
 
HELIANTHIN. 257 
 
 When dyed on the fibre, fast-yellow is reddened by 
 hydrochloric acid ; ammonia has little action ; a boiling 
 solution of stannous chloride in hydrochloric acid de- 
 colourises. 
 
 Fast-yellow JR, Acid-yellow R, Yellow W, is the sodium 
 salt of amidoazotoluenedisulphonic acid. It produces a 
 reddish yellow on wool in an acid bath . 
 
 v 'Helianthin, Gold-orange, Orange III., Methyl-orange, Tro- 
 pceolin D. 
 
 This colouring matter is the sodium salt of dime- 
 fchylaniline-azobenzene-sulphonic acid, and possesses the 
 formula 
 
 It is obtained by the action of dimethylaniline on 
 diazobenzene-sulphonic acid. 
 
 Helianthin forms an orange-yellow powder, which 
 dissolves easily in hot water, but is only sparingly soluble 
 in alcohol. Concentrated sulphuric acid dissolves it with 
 a red-brown colour, which appears yellow in thin layers. 
 With hydrochloric acid, ammonia, caustic alkali, and 
 stannous chloride, it shows the same reactions as aniline- 
 yellow. Basic acetate of lead throws down all the 
 colouring matter as an orange-yellow precipitate. 
 
 If small quantities of solutions of sodium chloride or 
 magnesium sulphate are added to a dilute solution of 
 helianthin, the colouring matter is precipitated in the 
 form of minute crystals. 
 
 Application. Helianthin produces on silk and wool a 
 fiery orange. Both these materials are dyed in an acid 
 bath. 
 
 Helianthin, or methyl-orange, is frequently used as an 
 indicator in volumetric analysis. The light-yellow colour 
 
258 COAL-TAB COLOURS. 
 
 of the solution is immediately turned red by the addition 
 of a drop of hydrochloric acid. 
 
 Detection on the fibre. Hydrochloric acid turns it red, 
 concentrated sulphuric acid yellow, while alkalies have no 
 action. 
 
 V- Tropceolin 00, Orange IF., Orange M, Orange GS, Acid- 
 yellow D, New yelluiv, Diphenylamine orange. 
 
 This colouring matter is formed by the action of 
 diazobenzene-sulphonic acid on diphenylamine : 
 
 CgH 4 .N : N" i p TT -VT-TT r< TI 
 
 SO | + C 6 H 5 JNHC 6 H 5 = 
 
 3 
 
 Diazobenzene-sulphonic Diphenylamine. 
 acid. 
 
 /H 
 
 S0 3 H 
 
 Diphenylamine-azobenzene-sulphonic acid. 
 
 and is accordingly a phenylated acid-yellow. The com- 
 mercial product is the potassium or sodium salt. 
 
 Tropseolin 00 forms an orange-yellow crystalline 
 powder, which dissolves very easily in hot water, but is 
 only sparingly soluble in cold water and in alcohol. In 
 concentrated sulphuric acid it dissolves with a red- violet 
 colour. A hot aqueous solution is turned violet by hy- 
 drochloric acid, and on cooling a precipitate of the same 
 colour is formed. Caustic soda does not occasion any 
 change in the hot aqueous solution. 
 
 The colouring matter yields a very fine golden yellow 
 on silk or wool. 
 
 Fibres dyed with tropeeolin 00 are turned blue- violet 
 with sulphuric acid, red- violet with hydrochloric acid. 
 
 The other amidoazo dyes are described in the tables. 
 
OXYAZO DYES. 259 
 
 (c) OXYAZO DYES. 
 
 Since Peter Griess first published, in 1878, the results 
 of his scientific investigations on the diazo and azo com- 
 pounds, the manufacture of the oxyazo dyes has developed 
 to such an extent that it forms at the present day almost 
 the most important branch of the coal-tar colour industry. 
 New products are constantly being brought into the 
 market, which are as a rule superior to the older ones, 
 either in point of brilliancy or fastness. 
 
 The immense number of colouring matters belonging to 
 this group is easily accounted for if we consider that 
 every primary amine belonging to the aromatic series, 
 after having been converted into a diazo compound, will 
 combine with almost any phenol or derivative of a phenol 
 (in which the hydrogen atom standing opposite the 
 hydroxyl group is not substituted) to form an azo dye. 
 
 The oxyazo dyes yield different shades of yellow, orange, 
 red, claret, and brown. The names according to which 
 they are known in commerce usually correspond to the 
 colour e.g., orange (tropgeolin) , scarlet, claret-red, etc. 
 In order to distinguish between the shades, the capital 
 letters G, GG, R, RR, etc., are used. Two samples bearing 
 the same name and mark, but coming from different 
 works, are, however, not always identical, and the name 
 of a colouring matter is therefore not sufficient to prove 
 its chemical composition. Besides these names, which are 
 derived from the colour of the dye, there are many fancy 
 names in use. 
 
 The description of the azo dyes given in the following 
 pages is not a complete one, but contains all the more 
 important products. 
 
 Manufacture of the Oxyazo Dyes. 
 
 The general method according to which all these colour- 
 ing matters are prepared will be amply explained if we 
 take xylidine-red (scarlet R) as an example. It should 
 
260 COAL-TAR COLOURS. 
 
 be mentioned here that the proportions of the different 
 substances used correspond to the molecular weights shown 
 in the equations. 
 
 For the preparation of about 20 kilos, of colouring 
 matter 5 kilos, of xylidine are dissolved in 300 litres of 
 water and twice as much hydrochloric acid as would be 
 necessary to transform the xylidine into its hydrochloride' 
 An aqueous solution of the calculated quantity of sodium 
 nitrite is then gradually added, the liquid being kept in 
 constant agitation, in order to mix the liquids as rapidly 
 as possible. In many works the liquid is cooled with ice, 
 in order to prevent decomposition and the formation of 
 resinous products. In this manner a neutral solution 
 of diazoxylene chloride is obtained, according to the 
 equation : 
 
 + HC1 + 
 
 Xylidine hydrochloride. 
 C d H 3 |^ C : H ^ cl + NaCl + 2H 2 0. 
 Diazoxylene chloride. 
 
 The liquid is now allowed to flow into another vessel 
 of double the capacity, which contains beta-naphthol- 
 disulphonate of soda and ammonia dissolved in 300 litres 
 of water. Both liquids are mixed as rapidly as possible 
 during the operation. The colouring matter is formed 
 according to the equation : 
 
 r TT f (CH 3 ) 2 , p TT (OH 
 
 Diazoxylene chloride. Beta-naphthol-disulphonate of soda. 
 
 P TT f(CH 3 ) 2 (OH 
 
 CH 
 
 Xylidine-red. 
 
 After standing some time, the liquid is heated to the boil 
 with steam in order to separate some resinous impurities, 
 
OXYAZO DYES. 261 
 
 after which it is filtered and the colouring matter salted 
 out in the usual way. The precipitate is collected in a 
 filter-press, pressed and ground with a small quantity of 
 water, in order to remove the mother-liquors, after which 
 it is pressed again, dried and ground. 
 
 Compounds which contain the azo group N" : N 
 twice form a special branch of the oxyazo dyes. They 
 are known as tetrazo dyes, and are divided into three 
 classes viz., the " secondary azo compounds," the " dis- 
 azo compounds," and the tetrazo compounds proper. 
 
 Secondary azo compounds are obtained when amidoazo 
 compounds, such as aniline-yellow or acid-yellow, are used 
 in place of the simple amines. A colouring matter of this 
 kind would, for instance, be formed according to the 
 following equations : 
 
 1. C 6 H 5 - N : N - C 6 H 4 -NH,-HC1 + HC1 + 
 
 Amidoazobenzene hydrochloride. 
 
 C 6 H 5 -lSr : N-C 8 H 4 -N : N 
 
 Diazoazobenzene chloride. 
 
 2. C 6 H 5 -N : N-C 6 H 4 -N : N-C1 + C 10 H 6 
 
 Diazoazobenzene chloride. Naphthol sulphonate of soda. 
 
 Azobenzene-azonaphthol-sulphonate of soda. 
 
 Disazo compounds. Some of the polyatomic phenols, 
 like resorcin, C 6 H 4 (OH) 2 , and phloroglucin, C 6 H 3 (OH 3 ), 
 combine with more than one molecule of a diazo compound. 
 Thus, resorcin combines with two molecules of diazoben- 
 zene chloride to form a disazo compound having the 
 formula 
 
 OH 
 
 OH 
 
 -N:N-C 6 H 5 
 
 o 5" 
 
 3. What are usually known at present as tetrazo dyes 
 are those derived from benzidine, stilbene, etc. (see p. 278). 
 
262 
 
 COAL-TAR COLOURS. 
 
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OXYAZO DYES. 
 
 
 
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264 COAL-TAR COLOURS. 
 
 krfd 
 
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OXTAZO DYES. 
 
 265 
 
 ra 
 
 u 
 
 5 
 ox 
 
 
 
 
 OQ. 
 
 C 10 H 
 
 alene 
 
 0023 
 
 C 10 H 6 OH 
 
 -naplitho 
 
 M 
 
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266 
 
 COAL-TAR COLOURS. 
 
 flffs 
 
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OXYAZO DYES. 
 
 267 
 
 
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 Fast-red C. 
 Carmoisin. 
 
 Crocein 3 J3 
 
268 
 
 COAL-TAR COLOURS. 
 
 o tc'H 
 
 
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OXYAZO DYES. 
 
 269 
 
 
 6 
 
 c 
 
 , S3 
 1 
 
 S3 
 
 I 
 
 3 
 
 S 
 
 S a 
 
 
 
 
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 1^1 
 
 II 
 
 
 
270 COAL-TAR COLOURS. 
 
 The tables on pp. 262-269 contain all the most import- 
 ant oxyazo dyes which are or have been used on a large 
 scale in practice. 
 
 The first column contains the commercial names of the 
 colouring matters, while in the second column their 
 chemical constitution and scientific denomination is given. 
 In the third column are the amido compounds, which are 
 first diazotised in the ordinary manner, and are then 
 combined with' the phenols in the fourth column, produc- 
 ing the respective dyes. The last column gives the colour 
 reaction with strong sulphuric acid which is character- 
 istic, and frequently serves for the detection of the dye 
 either as such or on the fibre. 
 
 Properties of the Oxyazo Dyes. 
 
 The commercial products are yellow, orange, scarlet or 
 brown powders, which are either crystalline in themselves 
 or can generally be crystallised from water or alcohol, or 
 a mixture of the two. They are nearly all soluble in 
 water, and most of them will also dissolve in alcohol. 
 
 Their behaviour with concentrated sulphuric acid, in 
 which all azo dyes dissolve with very intense colours, is 
 especially characteristic. The colours of these solutions 
 differ so widely that they form for a practised eye one of 
 the most valuable means of distinguishing the colouring 
 matters. Thus, the scarlets R, RR, 3R, S and SS dissolve 
 in sulphuric acid with an orange colour, which appears 
 crimson in thin layers. 
 
 Scarlet G and tropaeolin yield yellow or orange-yellow 
 solutions. 
 
 Biebrich-scarlet colours the acid green ; 
 
 Crocein- scarlet, blue ; and 
 
 Tropceolin 3O, or fast-red, both yield a violet. 
 
 The reaction with concentrated sulphuric acid further 
 enables us in many cases to obtain an idea of the con- 
 
OXYAZO DYES. 271 
 
 stitution of a colouring matter. Thus the following 
 rule has been adopted for all tetrazo dyes which are 
 derived from beta-naphthol-azobenzene-azobenzene 
 
 C 6 H 6 -N:N-C 6 H 4 -N:N-C 10 H 6 OH:-- 
 
 " Colouring matters which contain the sulpho group 
 in the benzene ring only dissolve in concentrated 
 sulphuric acid with a green colour (Biebrich-scarlet). 
 
 " If the sulpho group is only contained in the naphthol 
 the solution in sulphuric acid will be red or violet 
 (Scarlet S). 
 
 " When, however, sulpho groups are contained both in 
 the benzene ring and in the naphthol, they are 
 coloured blue with sulphuric acid." 
 
 The aqueous solutions of the oxyazo dyes are either 
 not changed at all when acidulated with hydrochloric 
 acid, or a precipitate is formed. The latter is especially 
 the case when the colouring matter only contains one 
 sulpho group. The formation of a precipitate is due to 
 the fact that the free acid is insoluble in water, as in the 
 case of alkali-blue. The free acids of those colouring 
 matters, however, which contain two or more sulpho 
 groups are also soluble in the free state, and are there- 
 fore not precipitated by acids. Tropasolin 30 gives a 
 purple precipitate, which dissolves in excess of hydro- 
 chloric acid. Some of the Biebrich-scarlets show the 
 same reaction. 
 
 Ammonia and caus-tic alkalies do not, as a rule, cause any 
 precipitates in dilute solutions ; but they often change 
 the colour, owing to a saturation of the free hydroxyl 
 groups. 
 
 A dilute aqueous and only very light yellow solution 
 of tropseolin 30 No. 2 shows this change of colour very 
 readily ; the slightest trace of alkali suffices to turn the 
 colour of the liquid to a fine crimson. For this reason 
 
272 COAL-TAR COLOURS. 
 
 the product is useful as an indicator in volumetric 
 analysis. 
 
 Scarlets Gr and B, crocein-scarlet and Biebrich-scarlet 
 show a similar reaction, but are not nearly so sensitive as 
 tropeeolin 30 No. 2. Ammonia is almost without action 
 on the solutions of scarlet 2R and scarlet 3R. 
 
 Concentrated solutions of the oxyazo dyes are preci- 
 pitated by metallic salts ; most of the precipitates ob- 
 tained in this manner (as, for instance, those with alumina 
 and lead) are soluble in excess of water ; consequently 
 these colouring matters are not adapted for the prepara- 
 tion of lakes. 
 
 By energetic reducing agents, the oxyazo dyes are split 
 up like the amidoazo dyes, two or more amido compounds 
 being formed. Thus, if Biebrich-scarlet is treated with 
 stannous chloride and hydrochloric acid, it yields sul- 
 phanilic acid, phenylene diamine, and beta-amidonaph- 
 thol, according to the equation : 
 
 /S0 3 H /S0 3 H 
 
 Beta-naphthol-asobenzene sulphonic acid azobenzene-sulphonic 
 
 acid. 
 
 TT ( 
 
 S0 3 H 
 
 Sulphauilic acid. Phenylene diamine. Amidonaphthol-sulphonic 
 
 acid. 
 
 This reaction is of great value in the scientific exami- 
 nation of an azo dye for ascertaining the chemical com- 
 position ; but the separation, purification, and examination 
 of the decomposition products takes up so much time, and 
 is so difficult, that the work can only be carried out by 
 a competent chemist. The complete decolourisation by 
 means of stannous chloride and hydrochloric acid can, 
 however, be used for distinguishing the azo dyes from 
 other yellow and red dyes, especially the natural ones. 
 
OXYAZO DYES. 273 
 
 Alkaline reducing agents decompose most -of the oxyazo 
 dyes in the cold. In some cases, however, especially with 
 some of the tetrazo dyes, their action is not as energetic 
 as that of stannous chloride. 
 
 The tetrazo dyes derived from the azobenzene-sulphonic 
 acids (acid-yellow), such as Biebrich- scarlet and crocein- 
 scarlet, can easily be recognised by their behaviour towards 
 zinc powder, which rapidly decolourises the alkaline solu- 
 tion. If some of the decolourised liquid is poured on to a 
 watch-glass (in order to present a large surface to the action 
 of the air), it becomes intensely yellow, especially if diluted 
 with a little water. If the liquid is filtered and is then acidu- 
 lated with hydrochloric acid, a yellow crystalline precipi- 
 tate is formed, which dissolves in excess of hydrochloric acid 
 with a red colour, thus showing the reactions of acid-yellow. 
 
 The reduction with zinc powder in alkaline solution, 
 therefore, only effects a partial decomposition. Taking 
 Biebrich-scarlet as an example, the following equation 
 would be fulfilled : 
 
 /S0 3 H /S0 3 H 
 
 C 6 H 4 -N:N-C 6 H 4 -N:N-C 10 
 
 Biebrich-scarlet. 
 /S0 3 H /S0 3 H 
 
 H H 
 
 Amidohydrazobenzene-disulphonic Amidonaphthol. 
 acid. 
 
 The colourless hydrazo compound is oxidised in ths air 
 to the corresponding azo compound (fast-yellow). 
 
 Application of the Oxyazo Dyes. 
 
 Among the tropgeolins, tropaeolin B and tropseolin 30 
 No. 2 are used to a considerable extent for dyeing silk 
 orange. The scarlets have replaced cochineal to a con- 
 siderable extent in wool-dyeing, while some (crocein- 
 scarlet, etc.) are used very largely in cotton- dyeing. 
 
274 COAL-TAR COLOURS. 
 
 As a rule the fastness of the azo dyes increases with the 
 molecular weight. Most of them are pretty fast to light, 
 but they cannot be used for dyeing the Turkish fez, the 
 colour of which must be so fast that several months' 
 exposure to the direct sunlight will not bleach it. 
 
 Thus xylidine-scarlet (scarlet R) when exposed for 
 eight months to direct sunlight is changed to a light and 
 dull pink ; but it stands the action of diffused sunlight very 
 well. The azo dyes do not stand washing with soap as well 
 as cochineal, nor are they as fast to milling as the latter. 
 This is explained by the fact that cochineal-scarlet is an 
 alumina-tin lake, insoluble in water, while the compounds 
 of the azo dyes with alumina and tin dissolve in water. 
 
 Silk is dyed in a bath containing boiled-off liquor, or in 
 a soap-bath acidulated with sulphuric acid. 
 
 Wool is dyed in an acid bath. The colouring matters 
 dye more evenly and are more completely extracted from 
 the solution when certain salts are added to the dye- 
 bath, in order to decrease their solubility. Glauber's 
 salts and sulphuric acid, or sodium bisulphate and acetic 
 acid, are generally used for this purpose. Some of the 
 azo dyes are used with alum or stannic chloride and tartar ; 
 the shades obtained in this matter are purer and more 
 brilliant than when dyed according to the ordinary method. 
 
 Cotton can be prepared with an oil mordant or with 
 stannate of soda and alum. It is then dyed in a con- 
 centrated solution of the colouring matter, and dried 
 without being washed. The Biebrich- an dcrocein- scar lets 
 can also be dyed on unprepared cotton by padding or 
 otherwise treating the fabric with a concentrated solution 
 of the colouring matter and alum at a moderate temper- 
 ature. The colours do not stand washing. 
 
 For cotton- warp dyeing and in calico printing, Holliday's 
 and Graessler's patents are of importance ; in both pro- 
 cesses the formation of the colouring matter is effected 
 directly on the fibre. According to Holliday's method 
 
AZO DYES. 275 
 
 cotton may be dyed orange, scarlet, maroon, etc., according 
 to the amido compound and phenol used. The material 
 is first prepared with Turkey-red oil, then passed through 
 an alkaline solution of the phenol (e.g., beta-naphthol), 
 after which it is squeezed and passed through a solution 
 of a diazo compound prepared in the ordinary way (e.g., 
 diazoxylene chloride), when the colouring matter is pre- 
 cipitated directly on the fibre. As no sulpho compounds 
 are used in this process, the colouring matters precipitated 
 on the fibre are as a rule very fast, owing to their insolu- 
 bility in water, dilute acids, and alkalies. The scarlets 
 produced in this manner are as brilliant as Turkey-red, 
 but are not quite as fast as the latter, especially to heat, 
 which destroys or volatilises the colour. The goods can- 
 not therefore undergo the operation of " hot pressing." 
 
 The following example will serve to illustrate Graessler's 
 patent. In order to produce xylidine-red, C 6 H 3 (CH 3 ) 2 
 IS" : N C 10 H 6 OH, on the fibre a mixture of beta-naphthol, 
 xylidine, sodium nitrite and ammonium chloride, thick- 
 ened with starch-paste, is printed and steamed. The heat 
 causes the xylidine to decompose the ammonium chloride, 
 when ammonia is liberated and xylidine hydrochloride 
 is formed, which latter reacts with the sodium nitrite so 
 as to form sodium chloride and diazoxylene chloride 
 
 This combines in the nascent state with the naphthol to 
 form xylidine-red. The whole reaction is expressed by the 
 following equations : 
 
 C 6 H 3 sa + C 10 H 7 OH + NaN0 2 + ISTH 4 C1 - 
 
 Xylidine. Beta-naphthol. 
 
 - N : N ' C 10 H 6 OH + NaCl + 2H 2 
 Scarlet. 
 
276 COAL-TAR COLOURS. 
 
 According to Dawson*s patent, the azo colours may be 
 fixed on the fibre in one operation. For this purpose 
 an aromatic amine (for example, naphthylamine) is dia- 
 zotised in the usual manner, after which it is completely 
 neutralised by the addition of chalk. To the solution 
 obtained in this manner the equivalent of naphthol is 
 added in a very finely divided state, along with acetate of 
 soda and a slight quantity of acetic acid. Cotton immersed 
 in such a bath acts catalytically, and induces the gradual 
 formation of the colour upon its surface or within the 
 fibre, thereby becoming gradually and effectively dyed. 
 Wool and silk may be similarly treated. 
 
 Detection on the Fibre. 
 
 When dyed on the fibre, all orange, red, claret-red, and 
 brown oxyazo dyes are completely and permanently 
 decolourised * when the material is boiled with tin or zinc 
 powder and hydrochloric acid. When treated with con- 
 centrated sulphuric acid they yield characteristic intense 
 colourations, which have already been described in the 
 tables. 
 
 Bisulphite Compounds of the Azo Dyes. 
 Several patents have been taken out for the production 
 of soluble compounds from the insoluble azo dyes by treat- 
 ment with alkaline bisulphites. The preparation of these 
 compounds is either effected like that of coerulein S, or 
 alizarin-blue S, by treating the finely divided colouring 
 matter with a concentrated solution of an alkaline bisul- 
 phite, or by treating the azo dye with a bisulphite in a 
 solvent common to both (alcohol). The compounds are 
 not affected by dilute acids, but under the influence of 
 heat they are decomposed into the original dye-stuff and 
 a neutral sulphite. It has been proposed to utilise this 
 
 * In one or two cases the liquid, after filtering, is turned yellow in 
 the air. 
 
AZO DYES. 277 
 
 latter property in calico-printing, for which purpose the 
 bisulphite compound, suitably thickened, is printed on the 
 fabric and subsequently steamed. During the steaming 
 the decomposition takes place, and the insoluble azo dye 
 is fixed on the fibre. The colours produced in this manner 
 are said to stand washing. 
 
 The most important commercial product of this class 
 which has hitherto been brought out is known as Azarin. 
 
 Azarin possesses the formula 
 
 C 6 H 2 C1 2 (OH)-N : N-C 10 H 6 OH + NH 4 'H- S0 3 , 
 
 by which it is represented as a molecular compound of 
 naphthol-azo-dichlor-phenol and ammonium bisulphite. 
 It forms an orange-paste, which resembles ordinary 
 alizarin-paste in appearance. The colouring matter is 
 not easily soluble in water, but dissolves readily in 
 alkalies with a deep bluish-violet colour. If the paste is 
 heated, a copious disengagement of sulphur dioxide takes 
 place and the colour turns to a scarlet. 
 
 Azarin is chiefly applied to cotton. The material is 
 first prepared with Turkey-red oil and aluminium acetate, 
 after which it is dyed in a neutral bath of azarin. A 
 brilliant red inclining to a crimson can be obtained in this 
 manner, which stands the action of soap tolerably well. 
 
 The same principle has recently been applied (and 
 patented) for rendering soluble the colours produced from 
 diazotised primuline (see p. 28lS^Land the phenols. The 
 great advantage possessed by the dyes obtained in this 
 manner is that they may be applied in one bath. 
 
 Azo Dyes derived from Benzidine, Tolidine, and Stilbene. 
 A. Colours derived from Benzidine and Tolidine. 
 
 If benzidine, 
 
 C 6 H 5 -NH 2 
 
 C 6 H 5 -NH 2 , 
 
278 COAL-TAR COLOURS. 
 
 is treated with nitrons acid, it yields a tetrazo compound, 
 the hydrochloride of which would be represented by the 
 formula 
 
 C 6 H 5 -N : NCI 
 
 C 6 H 5 -N" : NCI. 
 
 When combined in the ordinary way with the aromatic 
 amines or phenols, or their derivatives, the salts of tetrazo- 
 diphenyl yield a series of colouring matters which possess 
 the peculiar but valuable property of dyeing vegetable 
 fibres in a neutral or alkaline bath without the inter- 
 vention of a mordant. 
 
 v' Congo-red is obtained according to the patent specifica- 
 tion by the action of tetrazo-diphenyl chloride on naph- 
 thylamine-sulphonate of soda, and possesses the formula 
 
 The commercial product is a brown-red powder, which 
 dissolves easily in water with a fine red colour. The 
 aqueous solution is so sensitive to acids that a single drop 
 of very dilute sulphuric acid suffices to convert the whole 
 of the liquid to a beautiful blue; in strong solutions a 
 precipitate of the free sulphonic acid is formed. This 
 property makes Congo-red valuable as an indicator in 
 volumetric analysis. 
 
 Application. Cotton is either dyed in a neutral bath or 
 in a weak soap-bath at a boiling temperature. A fine 
 scarlet is produced in this manner ; but although fast 
 to soap, it possesses the fatal property of being changed 
 by the slightest trace of acid to a violet or even to a 
 blue. Washing restores the original shade. Wool can 
 be dyed in a neutral bath. Another method is to dye in 
 an acid bath, and subsequently brighten the colour in a 
 weak alkali. 
 
CHRYSAMIN, 279 
 
 Brilliant Congo G is formed by the action of one mole- 
 cule each of /3-naphthylamine disulphonic acid and J3- 
 naphthylamine monsulphonic acid on tetrazobenzene 
 chloride. Brilliant Congo R is formed in a similar manner, 
 tolidine being substituted for benzidine. Congo 4 B is the 
 product of the reaction of equal molecules of naphthionic 
 acid and resorcin on one molecule of diazotised tolidine. 
 
 Benzopurpurin 4 B is formed from diazotised tolidine 
 (1 mol.) and naphthionic acid (2 mol.). Benzopurpurin 
 6 B is the product of the action of Laurent's a-naph- 
 thylamine monosulphonic acid (2 mol.) on diazotised 
 tolidine (1 mol.). Deltapurpurin 7 B is formed from 
 diazotised tolidine (1 mol.) and /3-naphthylamine mono- 
 sulphonic acid S (2 mol.). Eosazurin B is formed by the 
 action of methyl -/?-naphthylamine sulphonic acid (2 mol.) 
 on diazotised tolidine (1 mol.). 
 
 All these colouring matters are applied like Benzo- 
 purpurin, and produce various shades of red. Phosphate 
 of soda, stannate of soda, or Turkey-red oil, are some- 
 times added to the dye-bath in order to obtain more 
 brilliant colours. The dye-bath should be as concentrated 
 as possible. 
 
 Chrysamin is a yellow dye obtained by the action of 
 tetrazo-diphenyl chloride on salicylate of soda. It pos- 
 sesses the formula 
 
 Chrysamin forms a yellow powder, which is sparingly 
 soluble in cold water, but dissolves easily on boiling, with 
 an orange colour. An addition of caustic soda turns the 
 colour of the solution to an orange-red, from which 
 sulphuric acid precipitates the colouring matter (the free 
 acid) in orange flakes. Concentrated sulphuric acid dis- 
 solves chrysamin with a deep magenta colour. 
 
280 COAL-TAR COLOURS. 
 
 Application. Cotton is dyed with the addition of soap 
 and phosphate of soda at a boiling temperature. The 
 shades obtained are fast to light. 
 
 Chrysamin R is the corresponding compound from 
 tolidine. 
 
 Benzopurpurin is obtained by the action of tetrazo- 
 ditolyl chloride on naphthylamine sulphonate of soda, and 
 possesses the formula 
 
 Benzopurpurin forms a dark-red powder, which dis- 
 solves easily in water with a red-orange colour, on which 
 caustic soda is without action. Dilute sulphuric acid 
 precipitates the colouring matter from its solutions as 
 a brown-red precipitate, resembling ferric hydrate in 
 appearance. Concentrated sulphuric acid dissolves the 
 colouring matter with a pure blue colour. 
 
 Application. Cotton is dyed with the addition of potas- 
 sium carbonate at a boiling temperature. A very fine 
 scarlet may be obtained in this manner, which differs 
 materially from the red obtained with Congo-red in not 
 being changed by dilute acids and in being faster to light. 
 
 Azo-blue is formed by the action of tetrazo-ditolyl 
 chloride on beta-naphthol sulphonate of soda, and pos- 
 sesses the formula 
 
 a 
 C 7 H 6 -N : N . 10 C 5 H ^ SOsNa 
 
 Azo-blue forms a dark-blue powder, which dissolves 
 easily in water, with a rich violet colour. Caustic soda 
 turns the colour of the solution to a fine crimson, which is 
 restored to the original colour by the addition of dilute 
 sulphuric acid. 
 
AZO-VfOLET. .. 281 
 
 Concentrated sulphuric acid dissolves azo-blue with a 
 pure blue colour. 
 
 Application. Cotton is dyed with the addition of soap 
 and phosphate of soda at a boiling temperature. A 
 reddish blue is thus obtained, which is fast to soap and 
 acids, but is not very brilliant. 
 
 Azo-violet is the product of the reaction of equal mole- 
 cules of naphthionic acid and a-naphthol monosulphonic 
 acid NW on one molecule diazotised dianisidine. Helio- 
 trop is produced from methyl-/:?-naphthylamine sulphonic 
 acid S (2 mol.) and diazotised anisidine (2 mol). Benza- 
 zurin Gr is the purest shade of blue hitherto produced in 
 this series. It is formed from a-naphthol monosulphonic 
 acid NW (2 mol.) and diazotised dianisidine (1 mol.). 
 The application of these colouring matters in dyeing re- 
 sembles that of azo-blue. 
 
 The colouring matters of this group may be used along 
 with each other for the production of mixed shades on 
 cotton. They are also applicable to wool and silk under 
 the same conditions, and may therefore be found useful in 
 the dyeing of mixed fabrics. 
 
 B. Colours derived from Stilbene. 
 By diazotising diamidostilbene disulphonic acid, 
 
 CH C 6 H 3 | g S H 
 II ( N H 
 
 CeH 3 1 S0 3 H, 
 
 and combining the product formed with various phenols, 
 or aromatic amines, a series of colours is obtained which 
 resemble in their properties those derived from benzidine 
 and tolidine. 
 
 The diazotised diamidostilbene disulphonic acid (1 mol.) 
 yields with 
 
 /3-naphthylamine (2 mol.), Hessian-purple IS" ; with naph- 
 thionic acid (2 mol.), Hessian-purple P; with /3-naphthyl- 
 
282 COAL-TAR COLOURS. 
 
 amine monosul phonic acid Br, Hessian-purple B ; and with 
 /3-naphthylamine nionoaulphonic acid D, Hessian-purple D. 
 All these dyes yield blue shades of red, and are applied 
 on cotton either with soap or with salt and acetic acid. 
 
 With salicylic acid (2 mol.) the diazotised diamido- 
 stilbene disulphonic (1 mol.) acid yields Hessian-yellow, 
 and with phenol (2 mol.) Brilliant-yellow is obtained. 
 By ethyl ating brilliant-yellow Chrysophenin is formed, 
 which will probably, by reason of its superiority, take the 
 place of the older dye Chrysamin. 
 
 Hessian-violet is formed from diazotised diamidostilbene 
 disulphonic acid (1 mol.) and equal molecules of a-naph- 
 thylamine and /2-naphthol. 
 
 Mikado-orange is formed by the action of glycerin in 
 alkaline solution on paranitrotoluene sulphonic acid. Its 
 exact composition is not yet known, but it probably also 
 belongs to the stilbene colours. The other so-called 
 mikado colours are obtained in a similar way, other oxidis- 
 able substances being used in place of glycerin. 
 
 / 
 
 Primuine. 
 
 f\ 
 
 This colouring matter, which was first brought out by 
 Messrs. Brooke, Simpson & Spiller, is formed by the action 
 of sulphur on paratoluidine and subsequent sulphonation. 
 It is the monosulphonic acid of the base, C 28 H 18 N 4 S 3 . 
 
 The commercial product forms a lemon-yellow powder, 
 soluble in water with a yellow colour ; in strong sul- 
 phuric acid the solution has a yellow colour and a strong 
 green fluorescence. 
 
 Application. If cotton, wool, or silk are boiled in a 
 solution of primuline, a canary-yellow is obtained, which 
 is in itself not of much interest. If, however, the material 
 dyed with primuline is passed into a bath containing 
 nitrous acid (nitrite of soda and sulphuric acid),, and then 
 into an alkaline solution of a phenol,* various shades are 
 
FLAVANILINE. 283 
 
 produced on the fibre which range from yellow to red and 
 brown, and which are perfectly fast to acids and alkalies, 
 but not to light. As is the case with the benzidine colours, 
 primuline is .more readily absorbed by the vegetable fibres 
 from an alkaline bath, while the presence of a weak acid 
 favours its absorption by the animal fibres. In dyeing 
 with primuline, it is necessary to preserve the diazotised 
 fibre from the action of light, since an exposure of less 
 than half a minute to direct sunlight is sufficient to destroy 
 the diazo compound, and thus to produce uneven results. 
 
 Detection. Treated with an alkaline solution of hypo- 
 sulphite of soda (ISTaSOo), all the primuline colours are 
 converted back again into the original canary-yellow 
 shade, which, when diazotised and passed into an alkaline 
 solution of /3-naphthol, is turned scarlet. 
 
 Primuline also comes into the market as Sidphine, 
 Polychromine, and Carnotine. 
 
 DERIVATIVES OF QUINOLINE AND ACEIDINE. 
 Flavaniline. 
 
 If acetanilid, C 6 H 5 NHC 2 H 3 0, is heated for several hours 
 with zinc chloride to 250-270, a brown melt is obtained, 
 which yields when purified a yellow powder, soluble in 
 water. The free base has the composition C 16 H 14 N 2 , and 
 melts at 97. The combination, with one equivalent of 
 hydrochloric acid, forms the colouring matter flavaniline 
 a-para-amido phenyl-y-lepidine hydrochloride, C 16 H 14 N 2 
 HC1, or 
 
 CH 3 
 I 
 
 Application. ^Flavaniline is a basic colouring matter, 
 
 and is applied in dyeing like the other basic coal-tar 
 
 * Phenol yields a yellow, resorcin an orange, and j3-naphthol a red. 
 
284 COAL-TAR COLOURS. 
 
 colours. Wool and silk are dyed in neutral baths ; cotton 
 is previously prepared with, tannin and tartar emetic. 
 The shades obtained are bright yellow with a slight cast 
 of green. On silk the colouring matter shows a beautiful 
 moss-green fluorescence. 
 
 Flavaniline S is the sulphonic acid of flavaniline. 
 
 Phosphine Aniline-orange, Chrysaniline, Philadelphia- 
 yellow (impure). 
 
 Preparation. In the manufacture of phosphine, the 
 resinous bye-products obtained in the manufacture of 
 magenta by the arsenic-acid process are used. These 
 contain, as has already been mentioned, violaniline, mauv- 
 aniline and chrysaniline, a little rosaniline, and bodies 
 of a resinous character. 
 
 To separate these, a very tedious process has to be 
 adopted. It consists in first boiling the mass with dilute 
 hydrochloric acid. The violaniline and resins remain 
 insoluble. By fractional precipation, first the mauv- 
 aniline, then the rosaniline, and finally chrysaniline, are 
 thrown down. 
 
 Another source of chrysaniline are the arsenical mother- 
 liquors which remain after precipitating the magenta 
 with salt. Salt and lime are added to these, the precipi- 
 tate is dissolved in nitric acid, and the sparingly soluble 
 nitrate of chrysaniline precipitated with excess of nitric 
 acid, and then converted into the hydrochloride. 
 
 A base of higher molecular weight, corresponding to 
 chrysaniline, is obtained by heating arseniate of toluidine 
 to 130-150, and is known as chrysotoluidine. 
 
 Properties. Phosphine, C 19 H 15 N 3 HN0 3 , is the nitrate 
 of chrysaniline or diamidophenylacridine : 
 
 /N\ 
 
 C 6 H 4 C 6 H 3 NH 2 HN0 3 
 \C/ 
 
 C 6 H 4 -NH 
 
PHOSPHINE. 285 
 
 It comes into commerce as a yellow or orange powder, 
 easily soluble in water and alcohol. 
 
 If concentrated hydrochloric acid is added to an 
 aqueous solution of phosphine, a precipitate of the diacid 
 salt is produced, which is easily soluble in water. 
 
 The reaction of phosphine solutions with nitrates is 
 especially characteristic. If a solution of saltpetre con- 
 taining 1 part per 100 is added, a red crystalline preci- 
 pitate of nitrate of chrysaniline is immediately produced. 
 In warm solutions the precipitate is only produced on 
 standing ; under the microscope it is seen to consist of 
 needles. 
 
 In solutions of phosphine, ammonia, and caustic alkalies 
 precipitate chrysaniline, C 20 H 17 N 3 H 2 0, as an amorphous 
 yellow powder, soluble in alcohol and ether. 
 
 Phosphine is easily reduced by stannous chloride and 
 hydrochloric acid, but the colour is quickly reproduced on 
 exposure to air. This reaction is useful in the detection 
 of phosphine. 
 
 Application. Phosphine is not much used, but finds 
 some application in silk-dyeing and in woollen-printing. 
 
 Silk may be dyed in a pure soap bath, and the colour 
 brightened with acetic acid. A mixture of magenta and 
 phosphine gives a fine scarlet on silk. In wool-dyeing 
 an addition of acid is necessary. 
 
 On cotton, mordanted with aluminium acetate (red 
 liquor) it gives a nankin-yellow, which resists the action 
 of soap. 
 
 Detection on the fibre. Acids redden the colour, but 
 on standing it is stripped. Ammonia turns it to a 
 greenish yellow, which is lighter than the original colour. 
 Stannous chloride and hydrochloric acid decolourise it 
 gradually. 
 
286 COAL-TAR COLOURS. 
 
 IV. ARTIFICIAL INDIGO. 
 
 Ox the 1st of May, 1880, a patent was taken out by 
 Professor Baeyer, of Munich, for the " Preparation of 
 Derivatives and Homologues of Ortho-nitro-cinnamic Acid, 
 and their conversion into Indigo-blue and allied Dye-stuffs." 
 Thus indigo-blue, or indigotine, belongs to the coal-tar 
 colours. In spite of the endeavours of the " Badische 
 Anilin und Soda Fabrik," this synthesis has not yet 
 become a practical success, since the artificial indigo is 
 much more expensive than the natural product. If the 
 cost of artificial indigo could be reduced below that of 
 natural indigo, its introduction into commerce would 
 cause as great a revolution in dyeing as that of alizarin 
 in place of madder. 
 
 Of more practical importance than artificial indigo is 
 the " propiolic acid," which, in itself colourless, may be 
 converted into indigo-blue on the fibre. 
 
 Propiolic Acid. 
 (Ortho-nitrophenyl-propiolic Acid.) 
 
 Preparation. The starting-point for the manufacture is 
 ortho-nitro-cinnamic acid 
 
 which is obtained from cinnamic acid. 
 
 Ginnamic acid, C 6 H 5 - CH : CH - COOH, may be obtained 
 by heating benzaldehyde with acetic anhydride : 
 
ARTIFICIAL INDIGO. 287 
 
 Benzaldehyde. Acetic anhydride. 
 
 2C 6 H 5 -CH:CH-COOH + H 2 0. 
 
 Cinnamic acid. 
 
 On a [large scale, benzal chloride is heated to 180-200 
 with anhydrous sodium acetate : 
 
 C 6 H 5 CHC1 2 + 2CH 3 COONa = 
 Benzal chloride. Sodium acetate. 
 
 C 6 H 5 - CH : CH - COOH + 2NaCl + CH 3 COOH. 
 Cinnarnic acid. 
 
 The cinnamic acid is treated with fuming nitric acid, 
 which converts it into two isomeric mononitro acids. The 
 ortho acid (which alone is used) is separated from the 
 para acid by a method based upon the different solubility 
 of the two products. 
 
 Another method is to heat ortho-nitro benzaldehyde with 
 acetic anhydride : 
 
 Ortho-nitro Acetic acid, 
 
 benzaldehyde. 
 
 N 2 - TT O 
 
 -CHiCH-COOH^ 
 
 Ortho-nitro-cinnamic acid. 
 
 Ortho-nitro-cinnamic acid unites with bromine to form a 
 dibromide : 
 
 Ortho-nitro-cinnamic acid. 
 
 C6H M -CHBr-CHBrCOOH. 
 
 Ortho-nitro-cinnamic acid dibromide. 
 
288 COAL-TAR COLOURS. 
 
 This dibromide is boiled with alcoholic potash : 
 
 r TT { tfO' 
 
 ^6^4 [ CHBr- CHBr- COOH 
 
 Ortho-nitro-cinnamic dibromide. 
 
 Ortho-nitrophenyl-propiolate 
 of potash. 
 
 The free acid is separated by means of hydrochloric acid. 
 
 From ortho-nitrophenyl-propiolic acid and its ethers 
 certain intermediate products may be obtained. These 
 are indogenic acid and its ethers, and indogene, both of 
 which are converted by dilute acids and alkalies, in 
 presence of air, into indigo-blue (not indcin), thus being 
 suitable for calico-printing. 
 
 Properties. The pure acid forms colourless needles or 
 leaflets, which become brown on heating, and swell up 
 and decompose at 155 to 160. It is soluble in boiling 
 water, but is decomposed by long boiling. Its alkali 
 salts are easily soluble in water, but are precipitated by 
 excess of alkali. 
 
 The acid comes into commerce as "propiolic acid," in a 
 paste containing 25 per cent, of solid substance. 
 
 By boiling with reducing agents, such as potash and 
 grape-sugar, indigo-blue is formed : 
 
 2C 9 H 5 (N0 2 )0 2 + 2H a = 18 H 10 N S 3 + 2C0 2 + 2H 2 0. 
 Propiolic acid. Indigo-blue. 
 
 If propiolic acid, in sulphuric-acid solution, is treated 
 with reducing agents, like ferrous sulphate, metallic iron, 
 zinc, tin, lead, copper, etc., or is reduced with sulphurous 
 acid, potassium sulphocya.nide, etc., indigo-blue is not pro- 
 duced, but a very similar colouring matter, known as 
 indo'in, is formed. If, for instance, propiolic acid is mixed 
 with sulphuric acid and ferrous sulphate, the solution 
 
ARTIFICIAL INDIGO. 289 
 
 turns blue and indom separates as a flocculent pre- 
 cipitate. Indo'in may be distinguished from indigo by the 
 following reactions : 
 
 It dissolves in cold sulphuric acid, but does not easily 
 yield a sulphoriic acid on heating. With sulphurous acid 
 or bisulphites, a blue solution is produced, from which a 
 colouring matter soluble in water may be salted out. On 
 warming, this double compound is decomposed, yielding 
 sulphurous acid and the original colouring matter. 
 
 Application. Propiolic acid is used exclusively for 
 calico-printing. 
 
 The printer's colour consists of a solvent, a reducing 
 agent, and a thickening. The most suitable combination 
 is borax, xanthate of soda or zinc, and starch. 
 
 The colour does not stand steaming well. It is developed 
 like aniline-black. In this operation the unpleasant 
 smell of mercaptan, C 2 H 5 SH, is produced, which adheres 
 very tenaciously to the material, but can be removed by 
 treatment with weak alkalies and soap-baths. 
 
 The blue obtained in this manner is not pure, but 
 slightly grey. 
 
 The production of propiolic-acid blue is thus very 
 simple. On the other hand, the production of blue with 
 natural indigo is very complicated, as the following 
 example will show : 
 
 A tin-indigo compound is first prepared by reducing 
 indigo with stannous chloride and soda, and precipitating 
 with hydrochloric acid. This indigo-white compound is 
 thickened, and printed, and the pieces passed through 
 milk of lime, which dissolves the indigo- white and allows 
 it to penetrate the fibre. They are then immersed in 
 running water, which effects the oxidation and the 
 fixation of the blue. Then follows an acid bath #> re- 
 move the lime, and finally a soap bath. The colour is 
 never very intense, and the operation must be carried out 
 with great care and rapidity, in order to prevent the 
 
 u 
 
290 COAL-TAR COLOURS. 
 
 indigo-white becoming oxidised before it has had time to 
 be absorbed by the fibre. 
 
 Propiolic-acid blue, however, possesses the disadvantage 
 that it cannot be used along with other colouring matters 
 which require steaming, since it is turned grey by this 
 operation. 
 
 It may be printed along with aniline-black, and also 
 with iron and alumina mordants, which are afterwards 
 dyed in alizarin. 
 
 Detection on the fibre. It is unaltered by hydrochloric 
 acid and caustic soda. Stannous chloride first turns it 
 green, and then decolourises it. When warmed with an 
 alkaline solution of hyposulphite of soda, the colouring 
 matter is first reduced and then removed from the fibre. 
 If this solution is exposed to the air, it becomes blue, the 
 indigo being regenerated. Concentrated nitric acid turns 
 it yellow. Boiling alcohol is not coloured, but chloro- 
 form becomes blue. 
 
 On heating a small piece of the material purple vapours 
 are given off. 
 
ANTHRACENE. 291 
 
 V. THE ANTHRACENE COLOURING-MATTERS. 
 
 ALTHOUGH the number of colouring matters obtained from 
 anthracene is very limited, they all resemble each other 
 so closely in their chemical properties, and at the same 
 time differ so widely from the other coal-tar colours, that 
 they form a natural group of the latter. 
 
 In the free state they are almost insoluble in water, but 
 are easily soluble in ammonia and caustic alkalies. With 
 the alkaline earths and most metallic oxides they yield 
 richly coloured, insoluble lakes. This behaviour towards 
 bases indicates the acid nature of these colouring matters, 
 and a more thorough examination will show that they 
 contain free hydroxyl groups, and therefore belong to the 
 phenols. 
 
 The anthracene colouring-matters can only be dyed 
 with the help of mordants ; they are invariably adjective, 
 The shades produced with them are much faster to soap, 
 chloride of lime, dilute acids, and in most cases also to 
 light, than those obtained with the other coal-tar colours, 
 while at the same time they are faster than most of the 
 natural colouring- matters. 
 
 Manufacture of Commercial Alizarin. 
 
 The method usually adopted for the transformation of 
 anthracene into alizarin is effected in three distinct opera- 
 tions. Anthracene is first oxidised to anthraquinon, 
 which is then treated with sulphuric acid, and thereby 
 transformed into sulphonic acids. These are melted in 
 the third operation with caustic soda$ when alizarin is 
 
292 COAL-TAE COLOURS. 
 
 formed. The following anthracene derivatives are formed 
 during the process : 
 
 /CH\ 
 
 ^6^4 | C 6 H 4 . 
 
 \CH/ 
 
 Anthracene. 
 
 Anthraquinon. 
 
 3 S0 3 H. 
 
 Anthraquinon-monosulpbonic acid. 
 
 S0 3 H-C 6 H 3 <>C 6 H 3 SO S H. 
 
 Alpha- and beta-anthraquinon-disulphonic acids. 
 
 Alizarin. 
 
 OHC 6 H 3 <^>C 6 H 3 (OH) 2 . 
 
 Flavopurpurin, and Anthrapurpurin. 
 
 In order to prepare alizarin, anthrapurpurin, or flavo- 
 pnrpurin from this product, it is necessary to introduce 
 two or more hydroxyl groups ; and this is effected by 
 means of a well-known reaction based upon the behaviour 
 of the sulpho groups towards molten caustic alkali, which 
 is also used, for instance, in the manufacture of resorcin. 
 In melting the anthraquinon-sulphonic acids with alkali, 
 however, the sulpho groups are not simply replaced by 
 hydroxyl, but an oxidation invariably takes place simul- 
 taneously, 
 
 Thus when anthraquinon-monosulphonic acid is melted 
 with caustic soda in the manufacture of alizarin, the re- 
 action does not take place according to the equation * 
 
ANTHRAQUINON. 293 
 
 OglSTa + 2NaHO = 
 
 C 14 H 7 2 ONa + Na 2 S0 3 + H 3 0, 
 Oxyanthraquinon, 
 
 but according to the following equation : 
 
 C U H 7 ' S0 8 Na + 3NaHO = 
 
 C 14 H 6 3 (ONa) 2 + Na 2 S0 3 + H 3 + H 2 0. 
 Alizarin. 
 
 The hydrogen formed according to this equation does 
 not make its appearance in the gaseous condition, but acts 
 as a reducing agent on the anthraquinon-monosulphonic 
 acid and on the alizarin formed. This would diminish 
 the yield considerably ; but it is checked by adding to the 
 melt some oxidising substance, such as chlorate of potash. 
 
 Melting with caustic soda. In this operation anthra- 
 quinon-monosulphonic acid yields alizarin ; the alpha- 
 disulphonic acid, flavopurpurin ; and the beta acid, an- 
 thrapurpurin. 
 
 The operation is carried out under a high pressure in 
 strong boilers provided with stirring gear. From 3 to 4 
 parts of solid caustic soda are first heated with a small 
 quantity of water, until the whole becomes liquid, after 
 which the chlorate of potash is added along with 1 part of 
 anthraquinon-monosulphonate of soda. The boiler is then 
 closed, and the contents heated for twenty-four hours to 
 180-200. The melt is then allowed to cool, and is dis- 
 solved in a large quantity of water arid neutralised with 
 hydrochloric acid. According to a more recent patent, this 
 neutralisation is effected with sulphurous acid, in order 
 to effect a regeneration of the caustic soda. The alizarin 
 is precipitated in a very finely divided flbcculent state. 
 The whole is now pumped through filter-presses, well 
 washed, and the cakes of alizarin obtained in this manner 
 ground with water to a homogeneous paste containing a 
 known percentage. The latter contains alizarin, flavo- 
 purpurin, and anthrapurpurin in varying proportions. 
 
294 
 
 COAL-TAR COLOURS. 
 
 Alizarin, C 14 H 6 2 (OH) 2 . 
 
 For the preparation of pure alizarin, pure anthraqui- 
 non-monosulphonic acid is melted with caustic soda. It 
 can also be obtained from the blue shade of commercial 
 alizarin in the following 1 manner : 
 
 The paste is dissolved in dilute caustic soda, and the 
 solution is filtered from the anthraquinon and other in- 
 soluble impurities. A solution of barium chloride is 
 then added, and the whole is heated to the boil, when 
 alizarate of barium separates out in a crystalline state. 
 The precipitate is collected on a filter, washed, and decom- 
 posed with an acid. The washing is then continued, in 
 order to remove the barium and free acid. The product 
 obtained in this manner is almost chemically pure, but it 
 can be purified still further by sublimation or crystal- 
 lisation from glacial acetic acid. 
 
 Alizarin has also been obtained synthetically by heating 
 phthalic anhydride with pyrocatechin : 
 
 C 6H 4 < C Q>0 +C 6 H 4 <Qjg- = 
 
 Phthalic anhydride. Pyrocatechin. 
 + H0. 
 
 Alizarin. 
 
 The position of the hydroxyl groups is shown in the 
 following constitutional formula : 
 
 CO.H 
 
ALIZARIN. 295 
 
 Sublimated alizarin forms splendid orange-red crystals, 
 which melt at about 280. It is almost insoluble in cold 
 water and but sparingly soluble in boiling water, one 
 litre of which takes up O31 grm. of alizarin. In cold 
 alcohol it does not dissolve easily, but boiling alcohol and 
 glycerin dissolve it. Sulphuric acid dissolves alizarin 
 with a reddish-brown colour, but on diluting with water 
 the alizarin is reprecipitated in the unchanged state. In 
 solutions of alum or aluminium sulphate alizarin is almost 
 insoluble. 
 
 Alizarin crystallised from moist ether contains three 
 molecules of water of crystallisation. When precipitated 
 by acids from alkaline solutions, it also contains water, 
 which is given off at 100. 
 
 The behaviour of alizarin towards alkalies is that of a 
 weak acid. It dissolves in caustic alkalies and in am- 
 monia with a blue-violet colour, but is precipitated from 
 these solutions by acetic acid. If, however, alizarin is 
 boiled with sodium acetate, it dissolves and is separated 
 out unchanged on cooling. But if the boiling is con- 
 tinued for some time, acetic acid is given off and the 
 alizarin remains permanently dissolved. 
 
 The compounds of alizarin with calcium and barium are 
 thrown down as violet precipitates when salts of lime or 
 baryta are added to an alkaline solution of the colouring 
 matter. The peculiar behaviour of the calcium compound 
 towards free carbonic or acetic acids is described on 
 p. 304. (Rosenstiehl's method of dyeing.) 
 
 With all other bases alizarin yields sparingly soluble 
 or insoluble permanent lakes. The alumina and tin lakes 
 are red, the others mostly dark-coloured. The behaviour 
 of alizarin towards these bases is that of a strong acid; so 
 strong, indeed, that it is capable of decomposing chlorides 
 and nitrates in dilute solutions, thus replacing hydro- 
 chloric and nitric acids, 
 
296 COAL-TAR COLOURS. 
 
 unn. 
 
 Pure anthrapurpurin (also called isopurpurin) is best 
 obtained by melting pure beta-anthraquinon-disulphonic 
 acid with caustic soda and chlorate of potash. Nothing 
 more is known of the position of the hydroxyl groups 
 than that they are contained in both benzene rings : 
 
 OH-C 6 H 3 <>C 6 H 3 (OH) 2 . 
 
 Anthrapurpurin sublimates with partial decomposition, 
 and melts at 360. It is somewhat soluble in boiling 
 water ; easily soluble in boiling alcohol and glacial acetic 
 acid. 
 
 Its solutions in caustic alkalies are redder than those 
 of alizarin. It is somewhat soluble in a solution of barium 
 hydrate. Sulphuric acid dissolves it with a dull violet 
 colour, but the addition of a trace of sodium nitrite to 
 the solution turns it a splendid red-violet. A boiling 
 solution of alum dissolves a trace of anthrapurpurin with 
 an orange colour, which on cooling separates out again. 
 (Distinction from purpurin.) 
 
 Flavopurpurin. 
 
 With respect to formula and preparation, the same 
 applies as for anthrapurpurin, except that in the pre- 
 paration, instead of the beta acid, alpha-anthraquinon- 
 disulphonic acid is used. Flavopurpurin forms yellow 
 needles, which melt above 330 and can be sublimated 
 It is almost insoluble in water, but dissolves easily in cold 
 alcohol. 
 
 Its solutions in alkalies are redder still than those of 
 anthrapurpurin ; the solution in ammonia is yellowish- 
 red, while that of anthrapurpurin is violet. A boiling 
 solution of alum does not dissolve it. 
 
PURPURIN. 
 
 297 
 
 Purpurin. 
 
 Purpnrin, C u H 5 2 (OH) 3 , is isomeric with anthrapur- 
 purin and flavopnrpurin, and was the first trioxyanthra- 
 quinon known. Although it is not a constituent of 
 artificial alizarin, it will be described here, since after 
 alizarin it is the most important constituent of madder, 
 aud the results obtained in dyeing with artificial alizarin 
 and with madder are often compared with each other. 
 
 Purpurin differs from its two isomers in having all the 
 three hydroxyl groups in one benzene ring. Their rela- 
 tive position is shown in the formula : 
 
 Lalande has devised a method for the preparation of 
 purpurin from alizarin. Alizarin is dissolved in concen- 
 trated sulphuric acid, and is oxidised by the introduction 
 of dry arsenic acid, and heating to 150-160. When 
 the reaction is over, the colouring-matter is precipitated 
 by dilution with water, and washed with a concentrated 
 solution of alum, which dissolves the purpurin, while un- 
 changed alizarin remains behind. The liquid is filtered 
 and the purpurin precipitated by the addition of hydro- 
 chloric acid. Pure purpurin is obtained by crystallising 
 the precipitate obtained in this manner from alcohol. 
 
 It forms red needles, which begin to sublimate at 150, 
 and melt at 253, In boiling water it dissolves with a 
 
298 COAL-TAR COLOURS. 
 
 dark-red colour. When crystallised from aqueous alcohol, 
 it is obtained in the form of orange needles, of the formula 
 
 Purpurin dissolves in caustic alkalies with a purple 
 colour ; but if the solution is exposed to the light for 
 some time, the colouring-matter is destroyed and the 
 liquid is decolourised. 
 
 The most characteristic property of purpurin is, that it 
 dissolves in a boiling solution of alum with a yellowish- 
 red colour and green fluorescence. The purpurin-alumina- 
 lake also shows this property. 
 
 If a solution of alizarin in alkalies or alum is treated 
 with an excess of acid, purpurin hydrate is thrown down, 
 which dissolves in tepid alcohol much more easily than 
 purpurin. When heated, it parts with its water of hydra- 
 tion and passes over into ordinary purpurin. The artifi- 
 cial purpurin-paste is supposed to consist chiefly of this 
 hydrate. 
 
 Commercial Alizarin. 
 
 Alizarin is always sold in commerce in the form of a 
 paste, which contains the hydrates of the colouring 
 matters in an exceedingly fine state of division. The 
 amount of dry colouring-matter is usually 20 per cent., 
 but pastes are sometimes sold which contain as much as 
 60 per cent, of dry substance. These concentrated 
 pastes are not so advantageous as the thinner ones, as 
 they do not divide as evenly in the dye-baths and in 
 printer's colours. According to an agreement lately made 
 among the German alizarin manufacturers, no other than 
 20 per-cent. alizarin is brought into the market. 
 
 If alizarin-paste is dried and afterwards ground to a 
 paste again with water, it is found to have lost its slight 
 solubility altogether, and has become totally unfit for 
 dveing. The reason of this change is, that it is very 
 
COMMERCIAL ALIZARIN. 299 
 
 difficult to obtain the original fine state of division by 
 grinding; and besides that, the colouring matters give up 
 their water by hydration on drying. 
 
 The two most important commercial varieties are 
 alizarin-blue shade, or alizarin V, and alizarin -yellow 
 shade, or alizarin G. 
 
 The blue shade of alizarin is obtained by melting crude 
 anthraquinon-monosulphonic acid with caustic soda, and 
 consists chiefly of alizarin. In dyeing it yields with an 
 alumina mordant a bluish but not very brilliant shade of 
 red; with a small percentage of mordant, however, 
 beautiful shades of pink can be obtained. It is used 
 besides along with an iron mordant for dyeing and 
 printing fast violets. 
 
 Alizarin-yellow shade contains a large percentage of 
 anthrapurpurin and flavopurpurin, and little alizarin. 
 Anthrapurpurin yields with alumina mordants an almost 
 neutral red; flavopurpurin, however, yields a fiery red 
 which contains a considerable proportion of yellow. The 
 larger the proportion of flavopurpurin the yellower the 
 shades. The violets obtained with flavopurpurin, and 
 anthrapurpurin, and iron mordants are of no use. 
 
 The chief impurities which alizarin-blue shade contains 
 are anthraquinon and oxyanthraquinon. 
 
 PO 
 
 Oxyanthraquinon, C 6 H 4 < ~~ > C 6 H 8 OH, is the mono- 
 
 hydroxyl derivative corresponding to anthraquinon-mono- 
 sulphonic acid ; and it would be the only product of the 
 alizarin melt, were it not that a simultaneous oxidation 
 takes place and alizarin is formed. 
 
 In a similar manner alizarin-yellow shade contains two 
 dioxyanthraquinones, C U H 6 2 (OH) 2 , which are isomeric 
 with alizarin. 
 
 AntJvraflavic acid is produced from the alpha-disulphonic 
 acid of anthraquinon; flavopurpurin can be regarded as 
 an oxyanthraflavic acid. Similar relations exist between 
 
300 COAL-TAR COLOURS. 
 
 beta-anthraquinon-disulphonic acid, isoanthraflavic acid, 
 and anthrapurpurin. 
 
 The oxyanthraquinones which occur as imparities in 
 alizarin may be detected by boiling with lime and 
 filtering. If the filtrate is coloured brown, the sample 
 contains oxyanthraquinon, anthraflavic acid, or isoanthra- 
 flavic acid, all of which can be precipitated by the addi- 
 tion of an acid. None of these impurities are of any 
 value in dyeing, and therefore only diminish the value of 
 the alizarin. 
 
 The different colouring matters contained in commercial 
 alizarin can be recognised in the following manner : 
 
 A small sample of the alizarin in question is dissolved 
 in sodium carbonate, and the solution filtered from the 
 undissolved anthraquinon and oxyanthraquinon, which 
 latter can be separated from each other by means of caustic 
 alkali or quicklime. The filtrate is then acidified with 
 hydrochloric acid, and the precipitate boiled with milk of 
 lime in order to remove anthraflavic and isoflavic acids. 
 The undissolved lime-lakes are stirred to a paste with 
 water, decomposed with hydrochloric acid, and the residue 
 collected on a filter, washed, and dried. 
 
 The residue obtained in this manner is a mixture of 
 alizarin, flavopurpurin, and anthrapurpurin ; but the quan- 
 titative separation of these three products is very difficult 
 to carry out. According to the following method of 
 Schunck and Bomer, they can easily be detected when 
 present simultaneously : - 
 
 A small sample is dried at 100, and then placed be- 
 tween two glass plates separated from each other by a 
 leaden ring some millimetres in thickness. The whole is 
 heated in an air-bath to 140-150, at which temperature 
 the alizarin sublimates and is carried away : if the tem- 
 perature is now raised to 170, a mixed sublimate of 
 flavopurpurin and anthrapurpurin is obtained. These 
 two colouring-matters are most readily detected under the 
 
ALIZARIN. 301 
 
 microscope ; flavopurpurin forms reddish-yellow needles, 
 while anthrapurpurin forms thick crystals. The -quanti- 
 tative separation of the two might be effected by boiling 
 with benzene, in which flavopurpurin dissolves, anthra- 
 pui-purin not. 
 
 The valuation of the alizarins is usually effected by 
 estimating the percentage of dry substance and the ash, 
 and by carrying out comparative dye-trials. 
 
 In estimating the percentage of dry substance, it should 
 be borne in mind that the temperature should not be 
 allowed to rise much above 100, since alizarin begins to 
 sublimate at 110. The residue should appear yellow, 
 and not dark brown. Alizarin pastes sometimes contain 
 glycerin, Turkey-red oil, etc., which have been added in 
 order to thicken the paste. These can be separated from 
 the colouring-matters by diluting with water and filtering. 
 The nitrate may contain besides, small quantities of salts 
 which have not been properly removed in the manufacture. 
 It should neither have a brown nor a reddish tinge, but 
 should be perfectly colourless. 
 
 The ash should not weigh more than 1 per cent, of the 
 dry alizarin, and should be free from iron. 
 
 Application of Alizarin. 
 
 The alizarin colouring-matters are adjective in their 
 behaviour towards all textile fibres. The shades produced 
 with the help of different mordants are characterised by 
 their fulness, brilliancy, and fastness. They are used 
 principally for dyeing and printing cotton, and to some 
 extent in wool-dyeing. On silk they yield fine shades of 
 red, brown, black, etc. ; but they are not used much in 
 silk-dyeing, on account of the great advantages which the 
 substantive coal-tar colours possess over alizarin. Their 
 fixation with the help of mordants not only necessitates a 
 much longer and more difficult process of dyeing, but has 
 
302 COAL-TAR COLOURS. 
 
 besides the disadvantage of causing the silk to lose some 
 of its gloss and pliability, on account of the alumina 
 deposited on the fibre. 
 
 COTTON. The mordants used in cotton- dyeing and 
 calico-printing are salts of alumina, iron, chromium, and 
 tin, besides lime, tannic acid, and oil mordants. 
 
 Alizarin-red and pink. Alizarin- red is the alumina lime- 
 lake of the yellow shade, alizarin-pink the alumina lime- 
 lake of the blue shade of alizarin. These lakes can be 
 obtained as such by dissolving the colouring-matter in 
 an alkali and adding a solution of alum, in the form of 
 red flocculent precipitates. The combination of pure 
 alizarin with alumina is the most stable ; and the affinity 
 which these two bodies have for each other is so great 
 that if alizarin is boiled with a dilute solution of alumi- 
 nium sulphate, the latter is decomposed, aluminium 
 alizarate being formed. An additional proof of the 
 affinity of these two substances is rendered by the fact 
 that alizarin is precipitated from its alkaline solutions 
 when agitated with aluminium hydrate. 
 
 When dyed on cotton, alizarin is not present in the 
 form of pure alumina lake, but in a much more corn-, 
 plicated combination, which contains besides alumina two 
 other inorganic bases viz., lime and stannic oxide. The 
 compound contains besides, tannic acid, fatty acids, and 
 in some cases phosphoric and arsenic acids, which, along 
 with the alizarin, form the acid constituents. Alizarin- 
 red thus offers a very striking example of the rule that 
 the stability of a colour is proportionate to the number of 
 the different constituents of the lake. 
 
 Alizarin can be fixed on the fibre in two ways viz,, 
 either by dyeing or by steaming. In dyeing, the material 
 is first prepared with the mordant (alumina, iron, etc.), 
 and then dyed in a hot bath of alizarin ; while in steam- 
 ing, the alizarin and mordant are printed simultaneously 
 on the fabric and the colour developed by means of steam, 
 
ALIZARIN-KED. 303 
 
 In Turkey-red dyeing the only mordant base which is 
 applied is a salt of alumina, the lime and stannic oxide 
 contained in the finished lake being introduced during 
 the different operations of dyeing and clearing. 
 
 Yarn is mordanted with solutions of alum or alumi- 
 nium sulphate neutralised with soda or chalk. The same 
 mordant can be used for dyeing calico or other cotton 
 fabrics. For the production of coloured designs on a 
 white ground, it is necessary to print the mordant on 
 those places which must subsequently appear coloured. 
 In printing, a special mordant for red is commonly used, 
 which is obtained by adding to a solution of alum a 
 quantity of acetate of lead insufficient to effect a total 
 double decomposition, along with some soda. The solu- 
 tion obtained in this manner contains basic acetate and 
 basic sulphate of alumina. Acetate of alumina alone 
 would not give good results, as it renders the material 
 impervious, and difficult to wet out. The mordant is 
 thickened with starch for printing. 
 
 The following operations effect the precipitation of the 
 alumina imbibed by the fibre in a more or less granular 
 but not gelatinous condition. The material is first hung 
 up in a large chamber heated to 32-40 C., in which the 
 degree of moisture is carefully regulated. It remains 
 here until a considerable proportion of the acetic acid has 
 been given off, which renders the alumina- salts more basic 
 and almost insoluble. 
 
 In the next operation, the " dunging," the material is 
 passed through a hot bath containing cow's (or pig's) 
 dung and chalk. The chalk removes acetic and sulphuric 
 acids from the printed material, while the action of the 
 cow's dung is chiefly a mechanical one ; it prevents any 
 detached mordant from settling on the white parts of the 
 fabric. 
 
 The pieces are now thoroughly washed and passed into 
 the dye-bath, where they are dyed with alizarin, bes^in- 
 
304 COAL-TAE COLOURS. 
 
 ning at a low temperature, and raising gradually to the 
 boil. 
 
 The analysis of materials dyed with madder, therefore, 
 with a mixture of natural alizarin and purpurin, appears 
 to show that the red contains alumina and lime in the 
 proportion of two molecules of A1 3 3 to three of CaO. 
 According to the more recent investigations of Liechti 
 and Suida, the most probable formula for the normal 
 alizarin-red lake (before soaping) is : 
 
 A1 2 3 CaO (C U H 6 3 ) 3 H 2 0. 
 
 The subsequent operation of soaping, however, disturbs 
 the ratio of the lime to the alumina, some of the latter 
 being removed. The material contains, previous to dye- 
 ing, a small quantity of lime, which has become assimi- 
 lated during the bleaching process from the chloride of 
 lime used. But the greater part of the lime is taken 
 from the calcareous water used in preparing the dye-bath. 
 According to Rosenstiehl, it is necessary for this reason 
 that the water should contain a certain amount of lime. 
 Although the alizarin lime-lake is insoluble in pure 
 water, it dissolves easily in carbonic acid; and as the 
 natural waters usually contain bicarbonate of lime as 
 well as free carbonic acid, a considerable proportion of 
 the alizarin is dissolved as lime-lake, which is taken up 
 as such by the alumina on the fibre. But as the dyeing 
 is always carried out at a high temperature, carbonic 
 acid is gradually evolved, and the lime-lake which is thus 
 caused to fall accumulates at the bottom of the vessel, and 
 causes a loss of alizarin. In order to counteract this evil, 
 Rosenstiehl recommends an addition of calcium acetate 
 to the dye-bath, or in case the water contains much lime, 
 simply an addition of acetic acid. At first the bath is 
 kept slightly acid. The alizarin dissolves in the calcium 
 acetate, which it gradually decomposes as the temperature 
 rises, Acetic acid is thus set free, while the alizarin 
 
ALIZARIN-RED. 305 
 
 lime-lake formed is taken up along with free alizarin by 
 the alumina. 
 
 After dyeing, the red has a dull appearance, and must 
 pass through the operation of clearing in order to obtain 
 its full brilliancy. 
 
 This is effected by boiling with soap and stannous 
 chloride. The action of the latter is rather complicated. 
 In the first place, it removes part of the soda from the 
 soap, and yields sodium chloride and stannous hydrate. 
 The soap is thus rendered more neutral and more fitted 
 to give up fatty acid to the colour-lake, which is proved 
 by the considerable quantity of fatty acid taken up during 
 this operation. The stannous hydrate reduces and there- 
 by decolourises the brown impurities fixed on the fibre 
 along with the alizarin. It is thereby gradually oxidised 
 to stannic hydrate, which combines with part of the 
 alizarin to form an orange lake, and thus brightens the 
 colour. 
 
 According to another method, stannic oxide is intro- 
 duced into the colour-lake by passing the pieces through 
 a moderately warm bath containing nitromuriate of tin. 
 The latter is a stannic salt, and is obtained by adding 
 stannous chloride to an equal weight of nitric acid. 
 
 The fastness of alizarin-red is due to a great extent to 
 the presence of fatty acids or of oxidised fatty acids. The 
 amount of fatty acid introduced during the operation of 
 soaping is insufficient, and special operations are therefore 
 necessary in order to charge the fibre with this substance. 
 Turkey-red, which is the fastest and most permanent 
 colour obtained with alizarin, contains the maximum 
 amount of fatty acids. 
 
 The oil which yielded the fatty acids in the old method 
 of Turkey-red dyeing was known as Jiuile tournante, or 
 rancid Gallipoli. It is a species of olive oil which contains 
 free ole'ic acid, and possesses the property of forming an 
 emulsion with alkaline carbonates. The yarn or fabric 
 
306 COAL-TAB COLOURS. 
 
 was passed through, or padded, with an emulsion of this 
 kind and then exposed to the air, whereby part of the oil 
 was oxidised to a compound insoluble in alkaline carbon- 
 ates. The operation required, however, a great deal of 
 time and trouble. 
 
 At present rancid Gallipoli is not used at all, or only 
 in a few special cases. It has been replaced by the so- 
 called Turkey-red oil (see p. 51), with which the same 
 results can be obtained more simply and more rapidly. 
 The operation of oiling can either take place before mor- 
 danting with alumina, or after dyeing, in which latter 
 case the action is assisted by steaming. In some cases 
 Turkey-red oil is added to the dye-bath. 
 
 Sumach, or some other form of tannin, is usually added 
 to the dye-bath. It combines with part of the alumina, 
 and thus yields fuller shades. Glue is frequently added 
 besides, in order to render the tannic acid insoluble, and 
 thus to prevent it from becoming attached to those parts 
 which must remain white. On heating, the alumina on 
 the fibre decomposes the finely divided compound of tannic 
 acid and glue, and becomes saturated with tannic acid. 
 
 In printing it is often desirable to use a strongly alka- 
 line mordant in place of the ordinary mordant for red. 
 Aluminate of soda is generally used for this purpose. 
 The fixation of the mordant is effected by means of a 
 weak solution of ammonium chloride, according to the 
 equation : 
 
 Na 6 Al 4 9 + 6NH 4 C1 + H 2 = 2H 4 A1 2 5 
 
 Aluminate Aluminium 
 
 of soda. hydrate. 
 
 From this it follows that the alumina is not thrown 
 down in the form of ordinary gelatinous aluminium 
 hydrate, A1 2 (OH) 6 , but in a more granular condition, 
 containing less water of hydration. The printer's colours 
 for steam reds and pinks invariably contain, besides 
 
ALIZARIN-RED. 307 
 
 thickening, alizarin and a salt of alumina, acetate of lime. 
 The salt of alumina must be one which will be decom- 
 posed by the heat of the steaming chamber, and usually 
 consists of acetate or sulphocyanide of alumina. 
 
 The acetate of alumina (prepared from acetate of lead 
 and alum, or by dissolving aluminium hydrate in acetic 
 acid) is decomposed on heating, and the acetic acid liber- 
 ated helps to dissolve the alizarin, and thus enables it to 
 penetrate the fibres and combine with the alumina. The 
 acetate of lime also helps to dissolve the alizarin, and 
 yields besides the lime necessary for the formation of the 
 alizarin-lake. When acetate of lime is used, the acetate 
 of alumina is usually replaced by nitrate of alumina ; the 
 colours are thus rendered brighter. 
 
 The slightest trace of ferric oxide suffices to change 
 the fine red or pink shades of the alumina-lake to a dull 
 red or even a brown. The printer must therefore take 
 special precautions to keep his colour free from iron. But 
 as the latter is in continuous contact with the steel 
 " doctors " of the printing-machine during the operation 
 of printing, traces of iron are always taken up by the 
 colour. Now, the presence of small quantities of iron is 
 no disadvantage as long as it is prevented from entering 
 into the alizarin-lake in the ferric state, and this can be 
 prevented in several ways. 
 
 Thus an addition of stannous chloride or stannous 
 hydrate reduces all the iron to the ferrous state. Arse- 
 nious acid is more effective ; it combines with the ferric 
 oxide to form an insoluble salt, which is not decomposed 
 by alizarin. An addition of sulphocyanide of potassium 
 to the colour is very serviceable. The iron is oxidised to 
 the ferric state by the nitrate of alumina, and then com- 
 bines with the sulphocyanide of potassium to form ferric 
 sulphocyanide. In some cases sulphocyanide of potassium 
 is dispensed with, and the whole of the alumina contained 
 in the colour replaced by sulphocyanide of alumina. 
 
308 COAL-TAR COLOURS. 
 
 The colours containing sulphocyanide of alumina are at 
 the same time excellent resists under other colours which 
 contain strong acids or oxidising agents. If, for instance, 
 alizarin-red is printed and steamed, it can be printed over 
 with aniline-black (of course without being previously 
 washed). The oxides of chlorine which are evolved 
 during the development of the black act on the hydro- 
 sulphocyanic acid and on the surplus of sulphocyanide 
 of alumina, and form persulphocyanogen, while the red 
 remains intact. 
 
 After steaming, the material must be passed through a 
 slightly alkaline bath, containing chalk, soluble glass, 
 etc., in order to remove the thickening, the acetic acid 
 produced in steaming, as well as any colour-lake not 
 attached to the fibre, etc. The material can then be 
 soaped, oiled, cleared, etc. 
 
 Alkaline solutions of alizarin produce a violet precipi- 
 tate with ferrous salts, while with ferric salts they yield 
 an almost black precipitate. 
 
 The production of alizarin-violet on cotton is quite 
 similar to the process of Turkey-red dyeing. The blue 
 shade of alizarin is used for this purpose ; the yellow 
 shade cannot be used, since anthrapurpuriii yields greyish- 
 violet shades, while flavopurpurin yields a reddish violet. 
 
 Ferrous acetate is usually employed as a mordant. 
 It is decomposed in the drying chamber into acetic acid 
 and ferrous hydrate. The material is then passed through 
 cow's dung and chalk, after which it is washed and dyed 
 with alizarin. Arsenite of soda is frequently added to the 
 dye-bath, in order to produce faster and brighter shades. 
 It reduces part of the ferric oxide fixed on the fibre to 
 ferrous oxide, and thus gives rise to a compound lake 
 containing ferric and ferrous oxides. The ferrous oxide 
 may be supposed to play the same part in the violet as 
 lime in the red. Arsenious acid also enters into com- 
 bination in the colour. 
 
ALIZARIN. 309 
 
 The steam colours for fast violet contain ferrous ace- 
 tate, acetate of lime, alizarin, and a thickening. Arsenite 
 of soda is frequently added besides. 
 
 Brown. Mixtures of iron and alumina mordants pro- 
 duce fine shades of brown. Alizarin-red can also be 
 changed to a brown by an admixture of Prussian-blue. 
 In order to produce a brown in this manner, ferrocyanide 
 of potash is mixed with the colour, which is decomposed 
 in steaming by the action of the free acid, and yields 
 Prussian-blue. 
 
 Puce. A very fine steam puce can be produced with 
 nitro-acetate of chromium as a mordant. 
 
 WOOL. Alizarin, anthrapurpurin, and flavopurpurin 
 can be used with advantage in wool-dyeing when it is 
 necessary to produce shades fast to light and milling. 
 They may all be applied in a similar manner and yield 
 similar shades. The colours produced may be varied 
 considerably according to the mordant used. 
 
 Wool mordanted with potassium bichromate and dyed 
 in alizarin yields different shades of maroon, which 
 are characterised by their fulness of colour and their 
 " bloom." If in place of alizarin alone mixtures of 
 alizarin and other artificial or natural colouring-matters 
 are used, a great variety of shades can be obtained. 
 Wool may also be dyed by boiling it with alizarin and 
 bichromate in one bath. 
 
 Wool mordanted with alum and tartar yields on dyeing 
 with alizarin, or better with anthrapurpurin, a very fine 
 red or scarlet. The addition of chalk or calcium acetate 
 to the dye-bath is essential in order to obtain bright 
 colours. It is also necessary, in order to obtain even 
 colours, to dye very gradually ; first cold, then raising 
 the temperature slowly to the boiling-point. No good 
 results have hitherto been obtained with alizarin and 
 alum in one bath. 
 
 Stamious chloride and oxalic acid used as a mordant 
 
310 COAL-TAE COLOURS. 
 
 yields shades which range from orange to a yellow shade 
 of scarlet. < Good results are obtained with stannous 
 chloride, oxalic acid and alizarin in one bath. The 
 colours obtained with tin as a mordant, although fast to 
 light, are rendered dull by milling with soap. 
 
 By mordanting the wool with copperas and tartar dull 
 violets are obtained. If much colouring matter is used, 
 the violet is so dark as to be almost a black. Alizarin 
 can also be dyed with copperas and oxalic acid in one 
 bath. 
 
 Nickel ammonium sulphate and uranium acetate have 
 also been proposed as mordants for alizarin on wool. 
 
 SILK. Alizarin and allied colouring-matters may also 
 be applied to silk mordanted with various metallic salts. 
 After dyeing, the silk is usually brightened by boiling it 
 in a soap-bath. The colours obtained are full and fast, 
 but are only applied in exceptional cases, where fastness 
 is an absolute necessity. 
 
 Regeneration of alizarin from spent baths. It has been 
 mentioned above that the fabrics printed with alizarin 
 are passed through a chalk-bath after steaming. In this 
 operation the surplus alizarin is removed from the fabric, 
 and settles at the bottom of the bath in the form of a lake, 
 or lakes, along with the chalk and impurities. In order 
 to regenerate the alizarin, the mud is collected, dissolved 
 in dilute hydrochloric acid, the residue washed with 
 water, dissolved in dilute soda, filtered and precipitated 
 again with hydrochloric acid. 
 
 If the colour contains iron, the alizarin may be re- 
 generated by treating with warm, dilute sulphuric acid, 
 which dissolves all the impurities, but leaves the alizarin 
 behind. 
 
 Reactions of A lizarin when Dyed on Textile Fabrics. 
 Fabrics dyed or printed with alizarin do not part with 
 any of their colour when boiled with solutions of caustic 
 
ALIZARIN. 311 
 
 alkalies, moderately concentrated. Dilute acids have like- 
 wise no action. Concentrated acids, however, decompose 
 the colour-lakes and simultaneously remove the metallic 
 base either wholly or partially. The different alizarin 
 colours do not possess the same power of resisting the 
 action of acids ; thus the violet is decomposed more easily 
 than ordinary red, while Turkey-red offers the greatest 
 resistance. 
 
 In concentrated sulphuric acid cotton fabrics dissolve 
 at the ordinary temperature along with the alizarin 
 colours fixed to the fibre. If the solution thus obtained 
 is diluted with water, the alizarin is thrown down as a 
 flocculent precipitate, which may be collected in a filter, 
 washed, dried, and sublimated, or at least recognised as 
 alizarin by the violet colour it imparts to solutions of the 
 alkalies. 
 
 Some organic, non-volatile acids are known to possess 
 the property of preventing the precipitation of the sesqui- 
 oxides (ferric oxide, alumina, etc.) from their solutions 
 by means of alkalies or ammonia. These acids have a 
 comparatively strong action on the alizarin colours. If, 
 for instance, Turkey-red cloth is printed with oxalic acid 
 and steamed, the alumina-lake is partially decomposed, 
 and a pink design on a red ground is the result. 
 
 Strong acid oxidising agents, like nitric acid or ferric 
 chloride, destroy alizarin. 
 
 A dilute solution of chloride of lime has scarcely any 
 action on Turkey-red, but it gradually destroys the ordi- 
 nary alizarin-red. Turkey-red will, however, not with- 
 stand the simultaneous action of chloride of lime and an 
 acid. 
 
 This property has found some application in the pro- 
 duction of white designs on a Turkey-red ground. 
 
 One method, for instance, of producing designs of this 
 kind is to print the red fabric with tartaric acid, and then 
 pass it through a solution of chloride of lime. Wherever 
 
312 COAL-TAR COLOURS. 
 
 tartaric acid has been printed the colouring-matter is 
 destroyed by the action of the chlorine liberated, while 
 at the same time the alumina is dissolved by the excess 
 of tartaric acid. 
 
 Potassium bichromate does not attack alizarin, but free 
 chromic acid destroys it. White designs or discharges 
 can therefore also be produced with this compound by 
 passing the fabric through a solution of the bichromate, 
 drying, and subsequently printing with tartaric (or 
 oxalic) acid, which liberates chromic acid and simul- 
 taneously dissolves the mordant. 
 
 Red prussiate of potash in alkaline solution, otherwise 
 one of the most powerful oxidising agents, is without 
 action on the colours produced with artificial alizarin. 
 Dilute solutions of permanganate of potash are likewise 
 without action. 
 
 Nitrous fumes convert alizarin-red into alizarin-orange. 
 
 The alizarin colours are very fast to light and air. The 
 red is, however, temporally affected by heat. When the 
 fabrics are dried in the usual manner, over cylinders 
 heated by steam, it parts with some of its brilliancy and 
 acquires a slight cast of brown. The original colour is, 
 however, almost completely restored by exposing the 
 goods to the air. It is probable that the alizarin-red 
 lake contains some water of hydration, which is partly 
 given off in drying, but is taken up again in a moist 
 atmosphere. 
 
 Detection on the fibre. In order to detect the presence 
 of alizarin in red, brown, violet, or black cotton fabrics, 
 the above reaction with concentrated sulphuric acid will 
 suffice. But in case the sample of material is too small, 
 or the colours too light (containing only a small per- 
 centage of alizarin), the following characteristic reactions 
 are resorted to : 
 
 Ammonia and soda have no action on the colour, neither 
 has a dilute solution of chloride of lime. The material is 
 
PURPURIN. 
 
 decolourised by boiling it with a mixture of two parts 
 alcohol and one part concentrated hydrochloric acid. 
 This latter reaction is of value in distinguishing between 
 alizarin-black and logwood-black, which latter is de- 
 stroyed even by dilute acids, colouring the solution red. 
 It also serves to distinguish between alizarin-black and 
 aniline-black, which latter is not affected, or at least only 
 turned to a greenish shade. 
 
 Alizarin-red is turned violet when boiled with barium 
 hydrate. 
 
 Materials dyed with alizarin can be distinguished from 
 those dyed with madder or with preparations of madder 
 by boiling them with a solution of aluminium sulphate. 
 The latter yield a fluorescent solution (see Purpurin, 
 p. 295). 
 
 The spectroscope may render good services in the 
 detection of alizarin and alid colouring-matters, as they 
 all give in ammoniacal solution (aqueous or alcoholic) 
 characteristic bands of absorption. 
 
 Alizarin is used at present pretty largely in wool- 
 dyeing. But as it is seldom used as a self-colour, and is 
 nearly always mixed with one or more natural or artificial 
 colouring-matters, its detection is often very difficult and 
 tedious. 
 
 Application of Purpurin. 
 
 Almost all colours which are at present obtained with 
 artificial alizarin were formerly produced with madder, 
 or preparations of madder. The latter contains very little 
 anthra or flavopurpurin, but in place of these we find 
 purpurin. 
 
 It might therefore be inferred that a mixture of the 
 blue shade of alizarin and Lalande's artificial purpurin 
 would yield the best substitute for madder. Nevertheless, 
 purpurin is not used in the large scale. When used in 
 the form of the crude product, it gives an inferior steam 
 
314 COAL-TAR COLOURS. 
 
 red verging into a brown. But in the purified state it is 
 said to yield a most brilliant scarlet. 
 
 The colours produced with artificial alizarin are faster 
 than those produced with purpurin. The latter are 
 destroyed by alkaline solutions of red prussiate and by a 
 1 per cent, solution of permanganate. 
 
 In order to estimate the amount of pure purpurin in a 
 sample of the commercial product, a weighed quantity is 
 boiled with a solution of aluminium sulphate, filtered from 
 the undissolved alizarin, etc., and the purpurin precipi- 
 tated in the filtrate by the addition of an acid. The 
 precipitate is collected in a filter, washed, dried and 
 weighed. 
 
 For the detection of small quantities of alizarin in a 
 sample of purpurin an alkaline solution is prepared and 
 exposed to the light until all the purpurin is destroyed. 
 The unchanged sodium alizarate is then decomposed with 
 dilute sulphuric acid, the liquid extracted with ether, 
 evaporated to dryness, and the residue tested in the 
 usual way for alizarin. 
 
 Alizarin-carmine. Alizarin S or W S. 
 
 The preparation of an alizarin sulphonic acid is effected 
 by acting on 1 part of alizarin with 3 parts of concentrated 
 sulphuric acid containing 20 per cent, of anhydride, at 
 100-150 C. The heating is continued until a sample 
 dissolves completely in water, The product is then 
 dissolved in water and the excess of sulphuric acid 
 precipitated by barium hydrate or milk of lime. The 
 filtrate is neutralised and evaporated down. 
 
 The product of the reaction is alizarin monosulphonic 
 acid, C 14 H 5 2 (OH) 2 S0 3 H. The free acid is soluble in 
 water and yields three series of salts. Those of the 
 general formula, C 14 H 5 2 (OH) 2 S0 3 M, are yellow or 
 orange, and are soluble in water. The sodium-salt, 
 C 14 H 5 2 (OH) 2 S0 3 Na, is the commercial product; it is 
 
ANTHRACENE-BROWN. 
 
 315 
 
 decomposed by sulphuric acid, but not by hydrochloric 
 acid. 
 
 The alkali-salts corresponding to the general formula, 
 C U H 3 2 (OH)(OM)S0 3 M, are reddish violet ; those of the 
 alkaline earths, reddish yellow. 
 
 The salts of the general formula, C U H 5 2 (OM) 2 S0 3 M, 
 are the most easily soluble, and are coloured intensely 
 violet. 
 
 In spite of the advantages which alizarin-carmine pre- 
 sented as a strongly acid colouring-matter, soluble in water, 
 it has nevertheless not until recently met with much 
 success in wool-dyeing. The free acid does not dye wool 
 directly, and it is necessary in order to obtain a red to 
 mordant with alumina. A good scarlet can be obtained 
 in one bath with alizarin S, alum, and oxalic acid. 
 
 Tin mordants yield orange shades. 
 
 The shades obtained on wool with chromium and iron 
 mordants resemble those produced with ordinary alizarin. 
 
 Anthracene-brown. Anthragallol. 
 
 Anthragallol, C 14 H 5 2 (OH) 3 , is formed by heating gallic 
 acid either with phthalic anhydride and zinc chloride or 
 with benzoic acid and strong sulphuric acid. It is 
 isomericwith anthrapurpurin, flavopurpurin and purpurin, 
 and its constitution is represented by the formula 
 
 C.OH 
 
 C - CO - 
 
 C.OH 
 
 The commercial product forms a dark-brown paste, 
 which dissolves in caustic alkalies with a greenish-blue 
 colour. 
 
316 
 
 COAL-TAB COLOURS. 
 
 Anthragallol yields with the usual metallic mordants 
 various shades]of brown. On wool mordanted with bichro- 
 mate of potash a fine brown is obtained, which is charac- 
 terised by its great fastness both to light and to milling. 
 
 A lizar in- orange. 
 
 Hitherto, two mono-nitro derivatives of alizarin have 
 been produced, which are distinguished as a and /3-nitro- 
 alizarin. The ft compound is the chief constituent of 
 commercial alizarin- orange. 
 
 For the preparation of this colouring- matter, alizarin 
 (blue shade) is treated in solution or in a finely divided 
 state with nitrous fumes. The raw product is purified by 
 dissolving it in sodium carbonate, filtering and precipita- 
 ting again with an acid. 
 
 If /?-nitro-alizarin is reduced, an amido- alizarin is 
 formed, which, when treated with nitrous acid, can be 
 transformed into purpurin C U H 5 2 (OH) 3 . The consti- 
 tutional formula of /3-iiitro-alizarin must therefore be 
 
 .OH 
 
 C.O.H 
 
 Purpurin. 
 
ALIZARIN-ORANGE. 
 
 317 
 
 Pure nitre-alizarin forms yellow needles or leaflets, 
 which melt at 244. At a higher temperature it subli- 
 mates with partial decomposition. It possesses stronger 
 acid properties than alizarin. 
 
 Nitro-alizarin is almost insoluble in water, but will 
 dissolve in glacial acetic acid. In concentrated sulphuric 
 acid it dissolves with a golden-yellow colour. 
 
 The alkali-salts dissolve in water with a red colour, but 
 they are insoluble in strong alkaline lyes. Nitro-alizarin 
 can therefore only be dissolved in dilute alkalies. The 
 other metallic salts are insoluble in water. 
 
 Alizarin-orange is brought into commerce in the form of 
 a paste containing 10-20 (usually 15) per cent, of dry sub- 
 stance, or as an orange-coloured powder. The latter 
 consists of the acid sodium salt C u H 5 3 (N0 2 )(OH)(ONa), 
 and is easily soluble in water. The colouring-matter is 
 not in such a fine state of division as those of the alizarin 
 pastes, and if allowed to stand, it settles to the bottom. 
 
 In order to detect impurities or unchanged alizarin, a 
 sample is dissolved in dilute caustic soda, filtered (if 
 necessary), and treated with an excess of concentrated 
 caustic soda. The nitro-alizarin is thereby completely 
 precipitated as the sodium salt, and the filtrate can easily 
 be tested for alizarin. 
 
 With alumina mordants, nitro-alizarin yields an orange; 
 with iron mordants, a red shade of violet. 
 
 Application. Alizarin-orange is used chiefly in calico- 
 printing as a steam-colour, and is fixed just like alizarin. 
 The colour for printing contains besides alizarin-orange alu- 
 minium nitrate, calcium acetate, and a thickener. It does 
 not keep so well as that prepared with alizarin, since nitro- 
 alizarin is a much stronger acid, and has a great tendency 
 to form lakes, even in the cold. This may be checked to 
 some extent by the addition of some acetic acid ; neverthe- 
 less, the colour must be used as soon as prepared, otherwise 
 it becomes red, and does not yield an orange, but a dull yellow. 
 
318 COAL-TAR COLOURS. 
 
 This rapid change is a great drawback in the applica- 
 tion of alizarin-orange. 
 
 According to Kielmeyer, the addition of calcium hypo- 
 sulphite in place of calcium acetate will make the colour 
 keep for at least a day. The introduction of aluminium 
 sulphocyanide in place of aluminium nitrate will no doubt 
 further the application of alizarin-orange. The colours 
 prepared with this mordant are said to keep very well. 
 
 The material is invariably oiled before printing. After 
 steaming, the colour is dull, and is only developed into a 
 bright shade after treatment with a boiling soap solution. 
 
 If red prussiate of potash is added to the colour before 
 printing, some Prussian-blue is formed along with the 
 nitro-alizarin alumina-lake. Fine shades of brown can be 
 produced in this manner. 
 
 Alizarin- orange is exceedingly fast ; it is not attacked 
 by solutions of chloride of lime, but it is destroyed by the 
 joint action of chloride of lime and acids. 
 
 Alizarin-orange is used to some extent in wool-dyeing 
 on account of the fastness of the shades produced. With 
 an alumina mordant it yields bright shades of orange ; 
 with bichromate of potash, brown shades of orange. It is 
 generally applied on wool along with other colouring- 
 matters for the production of mixed shades. Thus when 
 used along with coerulein, alizarin -blue, or alizarin, very 
 beautiful effects can be obtained. 
 
 Detection on the fibre. The colour is brightened by 
 boiling with soap, but it is stripped with an orange cojour 
 by ammonia or caustic soda. If boiled with barium 
 hydrate the sample is turned violet. An acid solution of 
 stannous chloride strips with a yellow colour. 
 
 Alizarin-blue. 
 (Anthracene-blue.) 
 
 Alizarin-blue is prepared in the following manner: 
 One part of dry and finely pulverised nitro-alizarin is 
 
ALIZARIN-BLUE. 
 
 319 
 
 heated, with 5 parts of dehydrated glycerin, and 5 parts 
 concentrated sulphuric acid, to 150. After the reaction 
 is over, the melt is boiled with an excess of water, when 
 the colouring- matter passes into solution in the shape of 
 its sulphuric acid compound. On cooling it falls in the 
 form of a brown flocculent precipitate, which when washed 
 with water loses its acid and becomes blue. 
 
 Alizarin-blue occurs in commerce as a dark- violet paste 
 containing 10 per cent, of dry substance. The pure 
 colouring-matter can be obtained from the dried paste by 
 crystallising repeatedly from glacial acetic acid and 
 naphtha. In the pure state it forms brown-violet needles, 
 which melt at 270, and may be partially sublimated. It 
 is insoluble in water, and only sparingly soluble in benzene 
 and alcohol. 
 
 The empirical formula of alizarin-blue is C 17 H 9 NO^. It 
 is closely allied to quinoline, C 9 H 7 N, which is obtained in 
 a similar manner by heating nitro-benzene and glycerin 
 with concentrated sulphuric acid. 
 
 CHoOH 
 
 + CHOH 
 
 CH 2 OH 
 
320 COAL-TAR COLOURS. 
 
 Alizarin-blue is formed according to the equation 
 
 CH 8 OH 
 
 C.OH | 
 
 + CHOH- 
 CHoOH 
 
 C.OH 
 
 O CO 
 
 c 
 
 Alizarin-blue is, therefore, the quinoline of alizarin. It 
 contains both hydroxyl groups of alizarin unchanged, and 
 is therefore an acid. On the other hand, however, the 
 quinoline complex imparts basic properties to the com- 
 pound, and alizarin-blue will therefore combine with 
 acids to form unstable compounds. Thus it will crystal- 
 lise from glacial acetic acid, and from dilute sulphuric 
 acid as a brown salt containing one equivalent of acid. 
 But these compounds are so loose that they are decom- 
 posed by washing with water. In concentrated sulphuric 
 acid alizarin-blue dissolves with a red colour, while in 
 arsenic acid and phosphoric acid it dissolves with a red- 
 yellow colour. 
 
 With dilute caustic alkalies it yields a green -blue solu- 
 tion, from which it is precipitated by excess of alkali. 
 
ALIZARIN-BLUE. 321 
 
 All the other salts are insoluble in water. They are ob- 
 tained by precipitating the alkaline solutions of alizarin- 
 blue with the corresponding metallic salts. Alizarin-blue 
 yields with lime, baryta, and ferric oxide, greenish-blue, 
 with nickel, blue, and with alumina and chromium, bluish- 
 violet lakes. 
 
 The affinity of alizarin-blue for some bases is so great 
 that in some cases it will expel even sulphuric acid from 
 its compounds (e.g., from copper sulphate). 
 
 In alkaline solution it may be reduced with zinc 
 powder to a red liquid, which, when exposed to the air, 
 resumes its original colour, and therefore forms a vat like 
 indigo. 
 
 Application. The application of alizarin-blue for 
 dyeing on the large scale is somewhat restricted. Its 
 insolubility in water and its tendency to form insoluble 
 lime-lakes are not in its favour. In vat- dyeing it cannot 
 compete with indigo, on account of its high price. 
 
 For printing similar methods may be employed as those 
 used for indigo. The colour for printing can be made up 
 with st anno us oxide and caustic soda, which reduces, and 
 at the same time dissolves, the colouring matter. After 
 printing, the colour is developed by exposure to the air 
 and washing in running water. The results obtained by 
 this method have, however, not been very satisfactory. 
 
 The best steam colour is obtained with chromium 
 acetate. An addition of magnesium chloride or calcium 
 chloride produces a faster, and at the same time a purer, 
 blue. 
 
 The greatest drawback in alizarin-blue fixed in this 
 manner is that it is not so fast to light as indigo. 
 
 If the colours printed or dyed 011 calico are exposed to 
 sunlight, they become yellowish, and, after soaping, pale 
 violet. 
 
 Alizarin-blue stands the action of oxidising agents 
 better than indigo ; it is not so easily attacked by chloride 
 
 Y 
 
322 COAL-TAR COLOURS. 
 
 of lime, chromic acid, and alkaline ferricyanide of 
 potash. 
 
 Alizarin -blue S. Like coerulein, alizarin-blue can be 
 transformed into a dry powder soluble in water. For 
 this purpose, the commercial paste is mixed with a con- 
 centrated solution of sodium bisulphite, and after standing 
 for 8-14 days, the liquid is filtered, and the solid com- 
 pound is isolated by evaporating down or salting out. 
 
 Alizarin-blue S is a dark-purple powder, which is easily 
 soluble in water. The brown-red solution is decomposed 
 by strong acids and by soda; it is also decomposed if 
 heated above 70. The colour can, however, be mixed 
 without undergoing any change with salts of chromium, 
 lime, or magnesia, as well as with acetic or tartaric acid. 
 The decomposition only takes place on steaming. 
 
 Alizarin-blue S is not only distinguished from ordinary 
 alizarin-blue by its solubility and easier application, but 
 also by its greater fastness to light. It has consequently 
 replaced ordinary alizarin-blue to a great extent in print- 
 ing and dyeing. 
 
 In wool-dyeing, alizarin-blue S promises to be a great 
 success as a substitute for indigo. The wool is first 
 mordanted with bichromate of potash and tartar, and 
 afterwards dyed in alizarin-blue S. In the dyeing it is 
 necessary to observe certain precautions. In the first 
 place, the water should contain no lime, or, if lime is pre- 
 sent, it should be neutralised with acetic acid. Secondly, 
 it is necessary, in order to obtain full and even shades, to 
 dye very gradually, working first for some time in the 
 cold, and then gradually raising the temperature to a boil. 
 In case the water contains bicarbonate of lime in solution, 
 it should be neutralised before dyeing with acetic acid. 
 Beautiful deep-blue shades can be obtained in this man- 
 ner, which are as fast as indigo to light and milling, and, 
 besides, possess a characteristic bloom. 
 
 Alizarin-blue 8 W is a cheaper form of soluble alizarin- 
 
ALIZARIX-GREEN. 323 
 
 blue, consisting simply of a strong solution of the bisul- 
 phite compound. It has replaced the powder to a great 
 extent. 
 
 Detection on the fibre. Alizarin-blue is turned bluish- 
 green by alkalies, while dilute hydrochloric acid turns it 
 violet. Nitric acid decolourises, or, in case the blue is dyed 
 on wool with a mordant of bichromate, it produces an 
 orange spot. An acid solution of stannous chloride turns 
 the colour to a brownish-yellow. Solutions of soap, soda, 
 and chloride of lime are without action. 
 
 Phosphoric acid (sp. gr. 1*435) gives an orange solution, 
 which, when diluted with water, is turned blue again by 
 ammonia. 
 
 The spectroscope may also be used for detecting 
 alizarin-blue. 
 
 Alizarin-green S. 
 
 This colouring-matter is formed in the following man- 
 ner : By treating alizarin-blue with a large excess of 
 fuming sulphuric acid, a product is obtained which by 
 the action of alkalies or acids is converted into " alizarin- 
 blue-green." If this latter product is heated with con- 
 centrated sulphuric acid to 120-130, alizarin -green is 
 formed, which after separating and washing with water 
 is obtained in the form of fine bluish-grey needles. The 
 commercial product forms a red-brown liquid, which smells 
 strongly of sulphurous acid, and when boiled yields a blue 
 precipitate. On wool mordanted with bichromate of 
 potash it produces greenish shades of blue, resembling in 
 appearance dull shades of indigo extract. The colour 
 stands milling. 
 
 Detection on the fibre. Boiling with dilute sulphuric 
 acid removes the greater part of the colour. Stannite of 
 soda turns the colour to a dull violet ; the original colour 
 is restored by washing and exposure to the air. Nitric 
 acid produces a yellow spot with a violet border. 
 
324 COAL-TAR COLOURS. 
 
 Alizarin-Hack S. 
 
 This colouring-matter is the sodium bisulphite com- 
 pound of naphthazarin or dioxynaphthoquinon. Its com- 
 position is represented by the formula C 10 H 4 (X (OH).,+ 
 NaH S0 3 . 
 
 Naphthazarin is formed by the action of zinc and strong 
 sulphuric acid on dinitronaphthalene. 
 
 The commercial product forms a black-coloured paste, 
 which dissolves in boiling water with a reddish-brown 
 colour, which is turned to a fine blue on the addition of 
 caustic soda. 
 
 Application. On wool mordanted with bichromate of 
 potash alizarin-black produces reddish shades of black. 
 Dead blacks can be obtained by the addition of a little 
 coerulein. With small percentages of the colouring 
 matter, various shades of slate are obtainable, which are 
 considerably faster to light than logwood shades. On 
 calico, alizarin-black may be printed with a chrome 
 mordant. 
 
 Galloflavin. 
 
 Galloflavin is formed by passing a limited quantity of 
 air through an alkaline solution of gallic acid in water or 
 alcohol at a low temperature. The empirical formula, 
 C 13 H 6 9 , is assigned to the new dyestuff produced in this 
 manner ; the constitution is not known. 
 
 The commercial product forms a dull -yellow paste, 
 which dissolves in caustic soda with a brown-orange 
 colour. 
 
 On wool mordanted with bichromate of potash, gallo- 
 flavin yields shades resembling those obtained with 
 fustic. It is also employed with a chrome mordant in 
 calico printing. 
 
 The shades obtained with galloflavin on wool are not 
 very fast to light. 
 
ADDENDUM. 
 
 Tartrazine. 
 
 This colouring-matter is the sodium salt of disulpho- 
 diphenylizine-dioxytartaric acid, the constitution of which 
 is represented by the formula 
 
 COOH 
 
 C: 
 
 I 
 
 COOH 
 
 It is formed by acting (in aqueous solution) with 
 phenylhydrazine monosulphonic acid on dioxytartaric 
 acid. 
 
 The commercial product forms an orange-yellow 
 powder, easily soluble in water, with an orange-yellow 
 colour. In concentrated sulphuric acid it dissolves with 
 a yellow colour. Tartrazine dyes wool yellow in an acid 
 bath. The colour produced is fast to light, and also 
 stands soaping fairly well. 
 
INDEX. 
 
 Absorption spectra, 13, 18. 
 
 of mixtures, 22. 
 Acetanilide, 96. 
 Acid brown G, 262. 
 
 colouring-matters, 31. 
 
 green, 146, 147. 
 S.O.F., 147. 
 
 magenta, 160. 
 
 violet 6 B, 175. 
 
 yellow, 255, 266. 
 R, 257. 
 D, 258, 267. 
 Acridin, 106. 
 Adjective dyeing, 48. 
 Albumen, 56. 
 Aldehyde green, 185. 
 Alizarin, 294. 
 
 absorption spectra of, 16. 
 
 black S, 324. 
 
 blue, 318. 
 S, 322. 
 shade, 299. 
 
 carmine, 314. 
 
 G, 299. 
 
 green S, 323. 
 
 manufacture of commercial, 
 291. 
 
 orange, 316. 
 
 pink, 302. 
 
 red, 302. 
 
 S, 314. 
 
 V, 299. 
 
 violet, 308. 
 
 W.S., 314. 
 
 yellow shade, 299. 
 
 Alkali^blue, 166. 
 
 green, 148. 
 Alpha -napthol, 123. 
 
 sulphonic acids of, 125. 
 Amaranth, 156, 268. 
 Amido-azo dyes, 251. 
 
 sulphonic acids, 112. 
 Amines, 31. 
 
 formation of, 94. 
 Aniline, 94. 
 
 black, 201. 
 
 blue, 161. 
 
 dyes, 140. 
 
 orange, 284. 
 
 red, 148. 
 
 salt, 96. 
 
 yellow, 252. 
 Anisol, 118. 
 Azodiphenyl-blue, 187. 
 Anthracene, 86. 
 
 brown, 315. 
 
 blue, 318. 
 
 oil, 72. 
 
 Anthraflavic acid, 299. 
 Anthragallol, 315. 
 Anthrapurpurin, 296. 
 Anthraquinon, 133. 
 
 sulphonic acids of, 135. 
 Archil red A, 265. 
 Aromatic acids, 135. 
 
 aldehydes, 129. 
 Artificial indigo, 286. 
 Auramine, 181. 
 Aurantia, 223. 
 Aureosin J, 235. 
 Aurin, 227. 
 Azaleme, 156. 
 
 327 
 
328 
 
 INDEX. 
 
 Azarin, 277. 
 Azo-black, 269. 
 
 blue, 280. 
 
 compounds, 108. 
 
 dyes, quantitative determina- 
 tion of, 65. 
 
 violet, 281. 
 
 B. 
 
 Bases in coal-tar, 70. 
 Basic colouring-matters, 30. 
 Basle-blue, 195. 
 Bavarian-blue, D.S.F., 167. 
 Benzal chloride, 87. 
 
 green, 144. 
 Benzaldehyde, 130. 
 Benzene, 80. 
 
 sulphonic acids of, 111. 
 Benzidme, 100. 
 
 sulphonic acid of, 114. 
 
 azo dyes derived from, 277. 
 Benzoic acid, 136. 
 Benzophenon, 132. 
 Benzopurpurin, 280. 
 4 B, 279. 
 6 B, 279. 
 
 Benzotrichloride, 88. 
 Beuzoyl-green, 144. 
 
 chloride, 87. 
 
 Benzylrosaniline-violet, 173. 
 Beta-napthol, 123. 
 
 sulphonic acids, 126. 
 Biebrich-scarlet, 269. 
 Bismarck brown, 254. 
 Bisulphite compounds of (he azo 
 
 dyes, 276. 
 Bleu fluorescent, 225. 
 
 de nuit, 161. 
 
 lumiere, 161. 
 Blackley-blue, 188. 
 Blue-black B, 269. 
 Boiled off liquor, 42. 
 Brilliant cotton blue, 168. 
 
 Congo G., 279. 
 
 crocein, 265. 
 
 green, 146. 
 
 orange, 262. 
 
 pcarlet, 26-S. 
 
 yellow, 222, 282. 
 
 C. 
 
 Canelle, 254. 
 Carbolic acid, 118. 
 Cardinal, 253, 156. 
 Carrmn-naphtha, 265. 
 Carmoisin, 267. 
 Carnotine, 283. 
 Casein, 43. 
 Cellulose, 43. 
 Cerise, 156. 
 Cbestnut-brown, 184. 
 China-blue, 168. 
 Chrome violet, 196. 
 Chroinophorous groups, 29. 
 Chrysauiiu, 279. 
 
 K, 280. 
 
 Chrysaniline, 284. 
 Chrysaurein, 266. 
 Chryseolin, 266. 
 Chrysoidine, 252. 
 Chrysolin, 234. 
 Cinnamic acid, 286. 
 aldehyde, 130. 
 Cinnamon-brown, 254. 
 Cloth-red B, 2H5. 
 G-, 265. 
 S, 268. 
 
 Coal-tar colours, history of. 2. 
 quantitative determination 
 
 of, 64. 
 
 classification of, 139. 
 Coal-tar, formation of, 69. 
 distillation of, 71. 
 constituents of, 74. 
 raw products of, 75. 
 Coccinin B, 264. 
 Cochineal red A, 268. 
 Coerulem, 242. 
 Colorimetry, 64. 
 
 Colouring-matters, general chemi- 
 cal properties of the, 27. 
 optical properties of the, 5. 
 methods of dissolving, 35. 
 marks used for distinguish- 
 ing, 7. 
 
 as mordants, 56. 
 testing of, 60. 
 impurities in, 66. 
 Coloured inks, 36. 
 
INDEX. 
 
 329 
 
 Coloured varnishes, 38. 
 Comparative dye-trials, 60. 
 Complementary colours, 6. 
 Corallin, 229. 
 Congo-red, 278. 
 Constitutional formula, 28. 
 Cotton, 43. 
 
 blue, 168. 
 
 E. 197. 
 
 Coupler's blue, 186. 
 Cresorcin, 121. 
 Cressols, 121. 
 Cressol-red, 265. 
 Crocem 3 B X, 267. 
 
 orange, 262. 
 
 scarlet, 3 B, 268. 
 7 B, 269. 
 6 B, 265. 
 Crystal -violet, 174 
 
 quantitative determination 
 
 of, 66. 
 
 Cumidines, 99. 
 Cumidine-red, 264. 
 
 scarlet, 264. 
 Cyanosin, 237. 
 
 D. 
 
 Dahlia, 170. 
 Dark green, 226. 
 Ddtapurpurin 7 B, 279. 
 Diamido-benzenes, 96. 
 Dianthine B, 235. 
 Diazo compounds, 106, 261. 
 Dichroistic solutions, 17. 
 Diethylaniline, 104. 
 Dimethylaniline, 103. 
 Dinitrobenzenes, 90. 
 Dinitrotoluenes, 91. 
 Dioxybenzenes, 119. 
 Dioxytoluenes, 122. 
 Diphenyl, 83. 
 Diphenylamine, 102. 
 
 blue, 162. 
 
 orange, 258, 266. 
 Discontinuous spectra, 12. 
 Distillation of coal-tar, 71. 
 Dyeing, general principles of, 45- 
 57. 
 
 E. 
 
 Empirical formulas, 75. 
 
 Eosins, 234. 
 
 Eosin, absorption spectrum of, 14. 
 
 A, 234. 
 
 A extra, 234. 
 
 B, 234. 
 
 B. B., 236. 
 
 B. N., 235. 
 
 G.G.F., 234. 
 
 5 G, 235. 
 
 J, 235. 
 
 orange, 235. 
 
 soluble in spirit, 236. 
 
 yellowish, 234. 
 Erythrosin, 235. 
 
 B, 237. 
 
 Essence de Mirbane, 90. 
 Ethyl-blue, 163. 
 
 eosin, 236. 
 
 green, 14H. 
 
 violet, 174. 
 Ethylene-blue, 212. 
 Eurhodines, 196. 
 
 F. 
 
 Fat colours, 39. 
 Fast and loose colours, 57, 
 Fast-green, 144. 
 blue E, 188. 
 B, 188. 
 2B, 196. 
 
 E, for cotton, 196. 
 red A, 267. 
 
 B, 265. 
 
 C, 267. 
 
 D, 268. 
 
 E, 268. 
 scarlet B, 269. 
 yellow, 255. 
 
 E, 257. 
 
 Fibres, chemistry of the, 39. 
 Flavaniline, 283. 
 
 S, 284. 
 
 Flavopurpurin, 296. 
 Fluorescein, 232. 
 Fluorescence, 25. 
 Fluorescent resorcin-blue, 225. 
 
330 
 
 INDEX. 
 
 Fuchsin, 156. 
 V, 156. 
 
 G. 
 
 Gallein, 242. 
 Gallic acid, 137. 
 Gallocyanin, 198. 
 Galloflavin, 324. 
 Gallotannic acid, 137. 
 Gambine, 226. 
 Gentian-blue 6 B, 161. 
 Girofle, 195. 
 Gold-orange, 257, 266. 
 Golden yellow, 266. 
 Green grease, 72. 
 Guernsey-blue, 188. 
 Guinea-green, 147. 
 
 H. 
 
 Heat, action of on dyed fabrics. 
 
 58. 
 
 Heavy oil, 72. 
 Helianthin, 257, 266. 
 Heliochysin, 222. 
 Helvetia-green, 146. 
 Hessian-purple B, 282. 
 
 D, 282. 
 
 N, 281. 
 
 P, 282. 
 
 Hessian- violet, 282. 
 Hoffman's violet, 170. 
 Homogeneous light, 9. 
 Huile Lournaute, 305. 
 Hydrazines, 108. 
 Hydrocarbons in Coal-tar, 69. 
 Hydrocarbons, the, 80. 
 Hydroquinon, 120. 
 Hydroxyl group, 33. 
 
 I. 
 
 Indigen, 186. 
 
 Indigo substitute, 188. 
 
 Indophenol, 199. 
 
 white, 200. 
 Induline, 186. 
 Imperial scarlet, 269. 
 Impurities, estimation of in 
 
 colouring-matters, 6. 
 Iso-butylphenol, 122. 
 Isomeric compounds, 79. 
 Isopurpuhc acid, 215. 
 
 Ketons, 132. 
 
 K. 
 
 L. 
 
 Lakes, 34. 
 
 Lauth's violet, 212. 
 
 Leuco bases, 142. 
 
 Light, action of on dyed fabrics, 
 
 59. 
 Light, decomposition of by the 
 
 prism, 7. 
 Light-green, 147. 
 Light oil, 72. 
 Liquid toluidine, 99. 
 Line spectra, 12. 
 Lutecienue, 236. 
 
 M. 
 
 Magdala-red, 193. 
 
 Magenta, absorption spectrum of, 
 
 14. 
 Magenta, 148. 
 
 manufacture of, 153. 
 
 detection of, 158. 
 
 S, 193. 
 Malacbite-green, 144. 
 
 soluble in spirit, 145. 
 Manchester-yellow, 219. 
 Mandarin, 266. 
 
 G B, 267. 
 Maroon, 184. 
 Martius-yellow, 219, 
 Mauvein, 196. 
 Metaxylene, 83. 
 
 toluidine, 98. 
 Metallic sulphides as mordants, 
 
 51. 
 
 Metanil-yellow, 267. 
 Meldola's blue, 197. 
 Methyleue-blue, 2C8. 
 Methyl-blue, 163. 
 
 B I, 168. 
 Methyl water- blue, 168. 
 
 violet, 170. 
 6 B, 173. 
 
 green, 175. 
 
 eosin, 236. 
 
 orange, 257, 266. 
 
INDEX. 
 
 331 
 
 Methyl-violet, absorption spec- 
 trum of, 14. 
 
 Methyldiphenylamine, 104. 
 Mesitylene, 83. 
 Mikado-orange, 282. 
 Milling, 58. 
 
 action of, on dyed fabrics, 58. 
 Monoethylanaline, 102. 
 Monomethylaniline, 102. 
 Muscarin, 197. 
 
 N. 
 
 Naphthamein, 207. 
 Naphtliionic acid, 114. 
 Napbthols, 123. 
 
 sulphonic acids, 124. 
 Napbthol-yellow, 219. 
 
 S, 221. 
 
 quantitative estimation of ,65. 
 Naphthol-green, 227. 
 
 (alpha) orange, 266. 
 
 (beta) orange, 266. 
 
 orange, 266. 
 
 black, 269. 
 
 Naphthylamines, 100. 
 Naphthylamine, sulpbonic acids 
 
 of, 114. 
 Naphthalene, 84. 
 
 tetra chloride, 88. 
 Naphthylene-blue E, 
 
 red, 193. 
 
 violet, 207. 
 Neutral colouring-matters, 35. 
 
 oils, 81. 
 
 blue, 195. 
 
 violet, 196. 
 
 red, 196. 
 New coccin, 268. 
 
 E, 265. 
 New green, 144. 
 
 red, 156. 
 
 red L, 269. 
 
 blue, 196. 
 
 yellow, 259, 267. 
 
 L, 255. 
 
 Nicholson's blue, 166. 
 Night-blue, 184. 
 
 application of, for quantita- 
 tive determination of acid 
 
 colours, 65. 
 
 Nigrosine, 186. 
 Nile-blue, 197. 
 Nitro-alizarin (/3), 316. 
 Nitro-sulphonic acids, 112. 
 
 benzene, 89, 
 
 toluenes, 91. 
 
 xylenes, 92. 
 
 naphthalenes, 92. 
 Nitroso-dimethylaniline, 104. 
 
 0. 
 
 Oil mordants, 51. 
 Opal-blue, 161. 
 Orange, 266. 
 
 L, 2fi6. 
 
 II., 266. 
 
 III., 257, 266. 
 
 IV., 258, 267. 
 
 G, 262. 
 
 G S, 258. 
 
 No. 3, 262. 
 
 G T, 263, 267. 
 
 M, 258, 267. 
 
 M N, 267. 
 
 T, 267. 
 
 E, 267. 
 Orcein, 122. 
 Orcin, 122. 
 
 Orchil substitute, Poirrier's, 262. 
 Orthoxylene, 83. 
 Orthotoluidine, 98. 
 Orthonitrophenyl-propiolic acid, 
 
 286. 
 
 Oxyanthraquinon, 299. 
 Oxyazo dyes, 259. 
 
 compounds, 108. 
 Oxytoluenes, 121. 
 
 P. 
 
 Para-rosaniline, constitution and 
 
 synthesis of, 149. 
 Paratoluidine, 98. 
 Paraxylene, 83. 
 Paris violet, 170. 
 Perspiration, action of, on dyed 
 
 fabrics, 58. 
 Phenol, 118. 
 Phenols in Coal-tar, 70. 
 
 formation and behaviour of, 
 116. 
 
332 
 
 INDEX. 
 
 Phenicienne, 218. 
 Phenol phthalein, 231. 
 Phenosafranine, 189. 
 Phenyl-brown, 218. 
 
 violet, 169. 
 Phenylene-brown, 254. 
 
 diamine, 97. 
 
 Philadelphia-yellow, 284. 
 Phloroglucin/121. 
 Phloxin, 237. 
 
 P, 237. 
 
 T A, 237. 
 Phosphine, 284. 
 Phthalems, 230. 
 Phthalic acid, 138. 
 Picoline, 105. 
 Picric acid, 213. 
 
 absorption spectra of, 14. 
 
 quantitative determination 
 
 of, 65. 
 Pink, 190. 
 Pitch, 72. 
 Polychromine, 283. 
 Primary colours, 6. 
 
 amines, 31, 94] 
 Primrose, 236. 
 Prirrmline, 282. 
 Propiolic acid, 286. 
 Prune, 198. 
 Ppeudocumene, 83. 
 Purpurin, 297. 
 Pyrocatechin, 119. 
 Pyrogallic acid, 120. 
 Pyridine, 105. 
 Pyrosin, 235. 
 
 Q- 
 
 Quinaldine, 106. 
 Quinoline, 105. 
 
 sulphonic acid, 115. 
 
 blue, 245. 
 
 red, 246. 
 
 yellow, 245. 
 
 E. 
 
 Eancid Gallipoli, 305. 
 Red corallin, 229. 
 Ked-violet 4 E S, 175. 
 5 E extra, 170. 
 
 Eegina purple, 173. 
 Eesorcin, 119. 
 
 brown, 264. 
 
 green, 226. 
 
 yellow, 266. 
 Ehodaraine, 241. 
 Eoccellin, 267. 
 Eosaniline, 149. 
 
 group, 140. 
 
 salts, properties of the, 155. 
 Eopazurin B, '279. 
 Eose B, soluble in water, 235. 
 
 J B soluble in spirit, 236. 
 Eose bengale, 237. 
 Eosein, 156. 
 Eosolan, 196, 
 Eosolic acid, 227. 
 Eosonapthylamine, 193. 
 Eosophenolin, 230. 
 Eubidin, 267. 
 Eubine, 156. 
 
 S, 156. 
 Eubeosin, 236. 
 
 S. 
 
 Safranine, 190. 
 
 B extra, 189. 
 Safrosin, 235. 
 Salicylic acid, 136. 
 Salt-forming groups, 30. 
 Saturated colours, 6. 
 Scarlet G, 263. 
 
 2 G, 262. 
 
 4GB, 262. 
 
 G E, 263. 
 
 G T, 263. 
 
 E, 263. 
 
 2 E, 264. 
 
 3 E, 264. 
 6 E, 268. 
 
 3 E B, 269. 
 
 4 E B, 268. 
 6 E B, 269. 
 E T, 263. 
 
 Scroop silk, 42. 
 
 Secondary amines, 31, 101. 
 
 Secondary azo compounds, 261. 
 
 Shades, 6. 
 
 Silica as a mordant, 53. 
 
INDEX. 
 
 333 
 
 Silk, 40. 
 
 Soap as a mordant, 51. 
 Solid-green, 144. 
 J, 146. 
 
 violet, 198. 
 
 yellow, 261. 
 Soluble-blue, 168. 
 
 eosin, 234. 
 
 primrose, 235. 
 Solvents fur colouring-matters, 
 
 36. 
 
 Souple silk, 42. 
 Spectra, 11. 
 Spectroscope, 10. 
 Spectrum, 9. 
 Spirit-blue O, 161. 
 
 soluble -blue, 161. 
 
 primrose, 236. 
 
 violet. 169. 
 Stilbene, 83. 
 
 azo dyes derived from, 277. 
 
 colours derived from, 281. 
 Substantive dyeing, 45. 
 Sulphauilic acid, 113. 
 Sulphiue, 283. 
 Sulpho group, 33. 
 Sulphonic acids, 34, 109, 
 Sulphur as a mordant, 50. 
 Sun-gold, 222. 
 
 T. 
 
 Tannin mordants, 54. 
 Tartar emetic, 54. 
 Tartrazin, 325. 
 Tetrabromfluorescem, 234. 
 Tetramethyldiamidobenzophe- 
 
 non, 132, 133. 
 Tetraiodnuores,;ein, 235. 
 Tetrazo compounds, 261. 
 Tertiary amines, 31, 102. 
 Thionin, 212. 
 Tintometer, The, 64. 
 Tolidine, 101. 
 Tolidines, azo dyes derive J from, 
 
 277. 
 Toluene, 81. 
 
 Butler Tanner, The Selwood 
 
 Tolui.lines, 97. 
 
 Toluidine, sulphonic acids of, 
 
 113. 
 
 Tolylenediamiues, 99. 
 Trioxybenzenes, 120. 
 Triphenyltnethane, 149. 
 Tropaeolin D, 257, 266. 
 
 O, 266. 
 
 O 0, 253, 267. 
 
 O O No. 1, 266. 
 
 O No. 2, 266. 
 . K, 266. 
 Turkey-red oil, 52. 
 
 U. 
 
 Uranin, 234. 
 
 V. 
 
 Vesuvine, 254. 
 Victoria-blue, 183. 
 
 green, 144. 
 
 yellow, 219. 
 Violaniline, 186. 
 Violet 5 E, 170. 
 
 6 B, 174. 
 Viridine, 148. 
 
 \V. 
 
 Water-blue, 168. 
 Wool. 42. 
 
 scarlet K, 263. 
 
 X. 
 
 Xanthoprote'ic aciJ, 43. 
 Xylenes, 81. 
 Xylenols, 122. 
 Xylidine, 99. 
 
 sulphonic acids, 113. 
 
 red, 264. 
 
 scarlet, 264. 
 
 Yellow corallin, 229. 
 T, 266. 
 W, 257. 
 
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