SB bflfl 
 
GIFT OF 
 
 . W . E. VU^X 
 
for % $iraropwnt of &rf8, IpTOfacfttm, anto Cmnnuw. 
 
 CANTOR LECTURES. 
 
 ON THE 
 
 [LINE OR COAL TAR COLOURS. 
 
 THKEE LECTURES, DELIVERED BEFORE THE ABOVE SOCIETY, 
 
 BY W. H. PBRKIN, ESQ., F. E. S 
 
 Reprinted from the "Journal of the Society of Arts." 
 
 LONDON : 
 
 W. TROUNCE, PRINTER, 9, CURSITOR-STREET, CHANCERY-LANE. 
 
 1869. 
 
ON THE MILINE OE COAL TAR COLOURS, 
 
 LECTURE I. DELIVERED MONDAY, DECEMBER TTH, 1868. 
 
 COAL TAR, BENZOL, NITROBENZOL, ANILINE, AND ANILINE PURPLE OR MAUVE, 
 
 In this short course of lectures it is my desire to bring 
 before you a somewhat condensed history of the artificial 
 colouring matters, generally known as the " Coal Tar 
 Colours." By this designation it is not meant to imply 
 that colouring matters actually exist in coal tar, and may, 
 therefore, be extracted from it, but that coal tar is the 
 source of certain products which, when changed by 
 various chemical processes, are capable of yielding 
 coloured derivatives. You will thus perceive that it is 
 important for us to consider the various means employed 
 to obtain the raw materials before giving our attention 
 to the colouring matters themselves. We will, therefore, 
 at once proceed to the consideration of "coal tar;" its 
 formation and constitution. 
 
 Coal tar consists of the oily fluid formed by the destruc- 
 tive distillation of coal, and is obtained as a secondary 
 product in the manufacture of coal gas. Originally, 
 coal tar was a great nuisance to the gas manufacturer, 
 and it was often a problem to him what he should do 
 with it. I need scarcely say that this state of things is 
 now changed. In the gas works the coal is distilled in 
 large retorts, sometimes 25 or 30 feet in length. They 
 are made of fire-clay or iron, and several are arranged 
 in one furnace, or oven, as it is usually termed. Each 
 retort is fitted with an iron mouth-piece, from which a 
 vertical tube rises, the mouth-piece also having a door 
 fastened with a cross-bar and screw. 
 
 When in use these retorts are rapidly filled with coal 
 by means of a proper scoop, and then the doors luted 
 and fixed so as to be air-tight. Distillation commences 
 immediately, as the retorts are constantly kept red hot. 
 The gas and other products which form pass up the 
 front vertical pipe (connected with the mouth piece), 
 through a bend, and down into a long horizontal tube, 
 called the " hydraulic main." Here most of the oily 
 products condense, and as they accumulate pass on with 
 the gas down the general main, and flow into a tank 
 provided for their reception. These oily products 
 constitute "coal tar." The coal gas, leaving this tar 
 behind, passes on to the condensers, and deposits a 
 second but smaller quantity of tar, and is then purified 
 and stored in the gas holders. The gas, however, does 
 not interest us now. 
 
 I am here distilling some coal in a small glass retort, 
 the beak of which is inserted into one of the openings of 
 a three-necked receiver. The second opening is con- 
 nected with the tube, so that the gaseous products 
 may be examined, whilst the third and lower one is 
 fitted to a small bottle, in which you see we have 
 already obtained a quantity of an oily fluid. This is our 
 coal tar. 
 
 242941 
 
 Having now seen how coal tar is produced, we will 
 consider of what it consists. Coal tar is by no means a 
 definite body, but contains a great number of different 
 substances, as a glance at the following table will show : 
 
 TABLE I. PRODUCTS OF THE DISTILLATION OF COAL. 
 
 Name. 
 
 Formula. 
 
 Boiling 
 point. 
 Centigr. 
 
 
 HH 
 
 t 
 
 Marsh gas (hydride of methyl) 
 Hydride of hexyl 
 
 (CH 3 )H 
 (C 6 H 13 >H 
 
 65 
 
 Hydride of octyl 
 
 'C 8 H 17 >H 
 
 106 
 
 
 m T-T >TT 
 
 (^ 10 1 21 J-tl 
 
 158 
 
 Olefiant gas (ethylent:) 
 
 C.& 4 
 
 
 Propylene (tritylene) 
 
 cX 
 
 
 Caproylene (hexylene) 
 
 
 55 
 
 OEnanthylene (heptylene) 
 Paraffin . 
 
 H? 
 
 99 
 
 
 C 2 H, 
 
 . . 
 
 Benzol 
 
 oX 
 
 80-8 
 
 
 oX 
 
 97-5 
 
 Toluol 
 
 C 7 H 8 
 
 110 
 
 Xylol 
 
 OX 
 
 139 
 
 
 oX 
 
 148-4 
 
 
 Ci n-H-l 4 
 
 1707 
 
 Naphthalene 
 
 c X 
 
 212 
 
 Paranaphthalene (anthracene). . 
 
 n TT 
 
 %fe; 
 
 
 
 
 C 15 H 4 
 
 
 Water 
 
 {I} 
 
 100 
 
 
 I H ) 
 / H U 
 
 { TT > O 
 
 
 
 IHJ 
 
 ( H \q 
 
 < /nxr\ 4 " 
 
 
 
 I (9 ) J 
 
 CO 
 
 1 1 
 
 
 COj 
 
 . . 
 
 
 CS 2 
 
 47 
 
 
 S0 2 
 
 10 
 
 
 l fC* TT C\\ 1 
 
 120 
 
 
 \ (C 2 H 3 O) J 
 H J Q 
 
 188 
 
 
 \ (C 6 H 5 ) j 
 
 (,AJ 
 
 203 
 
 Phlorylic alcohol (phlorol) 
 
 I (C,H,) i 
 
 {C<&)} 
 
 
 
 
 
 
 
Name. 
 
 Formula. 
 
 Boiling 
 
 point. 
 (Viiti.::r. 
 
 
 (H) 
 H N 
 
 33 
 
 
 (H) 
 
 I (C ^MN 
 
 182 
 
 
 ( H ) 
 
 (C.H.)'"N 
 
 115 
 
 
 (LH, 
 
 131 
 
 
 (CLHJ"^ 
 
 154 
 
 
 (C.H'irN 
 
 170 
 
 
 O!H"Y"N 
 
 188 
 
 
 c'rf! a Y"N 
 
 211 
 
 
 C^H,, '"N 
 
 230 
 
 Viridine 
 
 c "H ;>N 
 
 251 
 
 
 011,'% 
 
 235 
 
 
 C 10 H S )'"N 
 
 260 
 
 
 oiXiHB 
 
 256 
 
 
 C*H>N 
 
 133 
 
 
 HCN 
 
 26-5 
 
 This list, however, does not indicate all the constituents 
 of coal tar, but only those which chemists have tip to 
 the present time succeeded in separating from it ; more- 
 over, when we consider how greatly coal differs in 
 composition, and also that the products vary according 
 to the temperature to which the coal has been submitted, 
 it is evident that coal tar must be an almost endless 
 source of chemical products. Many would perhaps 
 consider this list a perfectly hopeless jumble of names 
 impossible to impress upon the memory ; but, fortun- 
 ately, chemists are able to classify their products, so that 
 this formidable array of substances may be grouped 
 under three or four different heads only, and, therefore, 
 their relationship being once understood, little difficulty 
 is experienced in remembering their names. 
 
 Amongst these products, and at the lower part of this 
 table, you will observe a substance called "aniline." 
 This substance is of great interest to us, being one of 
 the principal sources of the coal-tar colours. Aniline 
 was discovered by Unverdorben, in 1826, amongst the 
 products of the distillation of indigo, and from its pro- 
 perty of forming crystalline compounds with acids was 
 called " crystalline." Afterwards Runge obtained it from 
 the distillation of coal, and, because it gave a blue coloura- 
 tion with a solution of chloride of lime, called it "kyanol " 
 or blue oil. Fritzsche, still later, obtained aniline by the 
 distillation of indigo with hydrate of potassium, and gave 
 it its present name, derived from anil, the Portuguese for 
 indigo. A.bout this time Zinin discovered a remarkable 
 reaction, by which ho obtained aniline from a substance 
 called nitrobenzol ; he called it, however, benzidam. The 
 products obtained by these different chemists were not 
 at first known to be identical ; and it was not until Dr. 
 Hofmann investigated the subject that they were all 
 shown to be the same body, aniline. 
 
 Zinin' s process for the conversion of nitrobenzol into 
 aniline consisted in treating the nitrobenzol with an 
 alcoholic solution of sulphide of ammonium ; this was 
 greatly improved upon by Bechainp, who employed a 
 mixture of finely-divided iron and acetic acid, in place 
 -of sulphide of ammonium. 
 
 This is a brief sketch of the history of aniline up to 
 the time of the discovery of the mauve dye ; it was then 
 purely a laboratory product, and was prepared in very 
 small quantities at the time, and only when required for 
 scientific research. Chemists have always been desirous 
 of producing natural organic bodies artificially, and have 
 in many instances been successful. It was while trying 
 to solve one of these questions that I discovered the 
 " mauve." I was endeavouring to convert an artificial 
 base into the natural alcaloid quinine, but my experi- 
 ment, instead of yielding the colourless quinine, gave a 
 reddish powder. With a desire to understand this 
 peculiar result, a different base of more simple construc- 
 
 tion was'selected, viz., aniline, and in this case I obtained 
 a perfectly black product; this was purified and dried, and 
 when <li-;-' sted with spirits of wine gave the mauve dye. 
 
 You will perceive that this discovery did not in any 
 way originate from a desire to produce a colouring 
 mattiT, as is sometimes stated, but in experiments of a 
 purely theoretical nature. 
 
 After showing this colouring matter to several friends, 
 I was advised to consider the possibility of manufac- 
 turing it upon the largo scale, and was, eventually, 
 induced to make the experiment, though, I must confess, 
 not without considerable fear of the result, especially as 
 my chemical advisers set before me anything but en- 
 couraging prospects. In starting this manufacture, the 
 first difficulty was to decide upon the source from which 
 aniline could be obtained at a sufficiently low price. It 
 was at once evident that indigo was by far too costly a 
 product for this purpose. Attention was therefore 
 directed to the extraction of aniline from coal-tar, but 
 after very numerous experiments, it was found that the 
 difficulty of purifying it was so great, that it was not 
 practicable to prepare it at a reasonable price from this 
 product. There was, therefore, but one source left, 
 namely, nitrobenzol ; but to prepare aniline from this 
 body necessitated the establishment of a now manufacture; 
 nitrobenzol at that time not being a commercial article, 
 and although it could be produced in small quantities 
 without much difficulty, yet when tons were required at 
 a limited cost many obstacles presented themselves. 
 
 Having spoken of nitrobenzol, it will be necessary, 
 before proceeding further, to tell you something of the 
 body it is prepared from, and also how it is made 
 in quantity. Nitrobenzol is produced from a derivative 
 of coal-tar called benzol you will see it mentioned in 
 the list of coal-tar products. It is composed exclusively 
 of carbon and hydrogen, and is therefore called a hydro- 
 carbon. 
 
 Benzol was discovered by Faraday, in 1825, ono 
 year before aniline by Unverdorben. Its existence in 
 coal-tar was first pointed out by Dr. Hofmann, in 1845 
 and afterwards Mansfield showed that an almost un- 
 limited supply might be obtained from this source. 
 Benzol is a volatile oil, boiling at a temperature of 
 8 8 C . , nearly twenty degrees lower than water, and is also 
 very inflammable, burning with a smoky flame. When 
 ignited it cannot be extinguished by water, as it floats 
 upon its surface. Its vapour, when mixed with air, is 
 explosive. It is also very dense. This I can easily 
 show you by decanting a small quantity of benzol 
 vapour several times from one vessel into another, and 
 then igniting it. Instances have been known, when 
 distilling benzol in large quantities, and some leak in 
 the apparatus has occurred, so that its vapour has 
 escaped, that it has run along the ground, and been 
 ignited by a furnace situated thirty or forty feet distant, 
 and instantly run back to the apparatus. To illustrate 
 this I will pour some benzol vapour into the top of a 
 slightly inclined trough, fourteen feet long, at the lower 
 end of which is placed a lamp. The vapour will be seen to 
 run gradually down till it reaches the lamp, where it 
 ignites and instantly rushes back to the top of tho 
 trough. One of the most remarkable properties of ben- 
 zol is, that when cooled down to nearly the freezing 
 point of water, it solidifies to a beautiful crystalline 
 mass. This property of benzol is sometimes taken 
 advantage of when it is required in a very pure state, as 
 the impurities which accompany it are fluid, and do not 
 freeze when cooled with ice. 
 
 Benzol is often sold under the name of benzine collas, 
 for the purpose of removing grease from wearing ap- 
 ]>ar<l. But let us consider how benzol is separated 
 from the great number of products with which it is asso- 
 ciated in coal-tar. The first operation consists in dis- 
 tilling the coal-tar, just as it comes from the gas-works, 
 in large stills, holding one or two thousand gallons each; 
 these arc often made of old steam-boilers ; at first very 
 volatile and light oily products come over, and arc col- 
 
lected until their density increases to such an extent 
 that they no longer float upon water. These constitute 
 crude coal-tar naphtha. The distillation is then carried 
 on, and heavy, or, as they are technically termed, "dead" 
 oils, are collected, a residue of common pitch being left 
 in the still. This pitch is generally run out, and cast 
 into blocks ; but sometimes the distillation is carried on 
 after the dead oils have been obtained, when a mixture 
 of solid oily products distils, nothing but a kind of cake 
 being left behind. These latter substances, however, do 
 not interest us now. 
 
 The light oil, or crude coal tar naphtha, is then puri- 
 fied by one or two alternate distillations with steam and 
 treatments with concentrated sulphuric acid. It is thus 
 rendered a colourless fluid. Thus purified, coal tar 
 naphtha contains, besides benzol, at least four or five 
 other bodies. These, however, mostly differ from benzol 
 in being less volatile ; therefore, the naphtha is again 
 distilled, the first, or more volatile, portions only being 
 collected for benzol. By repeating this process of 
 fractional distillation several times commercial benzol is 
 obtained. Some manufacturers employ stills of a peculiar 
 construction, which enable them to obtain a good pro- 
 duct by a smaller number of distillations. Benzol, 
 when treated with fuming nitric acid or aquafortis, 
 undergoes a remarkable change. At first the two fluids 
 mix and become of a dark brown colour and slightly 
 warm, in the course of a few moments red fumes appear, 
 and the mixture enters into ebullition. During this 
 violent action the colour of the liquid becomes lighter 
 and ultimately changes to orange. If water be now 
 added to this product, the benzol, which is such a light 
 body, will be seen to have completely changed into a 
 dense yellow oil sinking in water. This oil is nitro- 
 benzol. Nitrobenzol was discovered in 1834, by 
 Mitscherlich. It solidifies into a crystalline mass at a 
 temperature of about 3 C. ; its odour is like that of the 
 oil of bitter almonds, and before the introduction of coal 
 tar colours it was made in small quantities, and sold 
 under the name of essence de Myrbane, for the purpose 
 of scenting soap. 
 
 From the energy with which benzol is attacked by 
 fuming nitric acid, nitrobenzol at first appeared to be a 
 most difficult product to manufactuie on the large scale, 
 and this difficulty seemed the greater when it was found 
 necessary that it should be made at a moderate cost. 
 Moreover, at the time I am now referring to, fuming 
 nitric acid, sp. gr. 1.5, could not be obtained in the 
 market, or only at such a cost as almost to preclude its 
 use. Under these circumstances, two mixtures were 
 experimented with instead of the nitric acid in a very 
 concentrated condition. The first was a mixture of 
 nitrate of sodium and sulphuric acid, the second a 
 mixture of ordinary nitric acid, sp. gr. 1.3, and sulphuric 
 acid. The mixture of sulphuric acid and nitrate of sodium 
 was preferred, and employed on the large scale. 
 
 The first apparatus used in the manufacture of nitro- 
 benzol, for the preparation of aniline for the mauve 
 dye, is shown in Fig. 1. It consisted of a large cast-iron 
 
 FIG. 1. 
 
 cylinder, a, fitted with a stirrer, b, and closed with a 
 door, c, fastened by a cross-bar and screw, d. This 
 cylinder was capable of holding between thirty and forty 
 gallons. It was provided with two necks, e e, one for the 
 introduction of the benzol and sulphuric acid, which 
 were supplied through a syphon tube ; the other for the 
 exit of nitrous fumes. This last was connected with an 
 earthenware worm, to condense any benzol which might 
 be volatilised by the heat of the re-action. The nitrate 
 of sodium was always introduced into the cylinder before 
 the door was fastened up and luted. Until the prepara- 
 tion of nitrobenzol was understood, there was a great 
 amount of uncertainty in its manufacture, and several 
 explosions occurred, but fortunately without causing any 
 injury to the workmen attending the apparatus. These 
 explosions originated generally from the liberation of 
 too much nitric acid from the nitrate of sodium, by the 
 sulphuric acid, before the formation of nitrobenzol had 
 begun, so that when it started, the chemical action set in 
 with such energy that an explosion ensued. After a few 
 of these unpleasant occurrences, however, sufficient 
 experience was obtained to get the manufacture under 
 control. Apparatus of a much more extensive character 
 has since been substituted for the cylinders. In Figs. 2 
 and 3 you get a view of the apparatus now used in 
 England for the manufacture of nitrobenzol. 
 
 This apparatus consists of large cast-iron pots, a a a, 
 about 4 feet 6 inches deep, and 4 feet 6 inches wide ; they 
 are arranged in rows, and provided with stirrers, worked 
 from a shafting by means of bevel wheels. This arrange- 
 ment will be seen from the section, fig. 3 ; the covers of 
 these vessels are also made of cast-iron, and are in two 
 pieces b b' (Fig. 3) of unequal size, provided with a tall rim, 
 and so arranged that cold water may be kept circulating 
 over their surface ; this assists in condensing the benzol, 
 which would otherwise distil away by the heat of the 
 reaction. Through the larger half of the cover the 
 spindle of the stirrer, c, passes, and on account of the 
 difficulty of keeping a stuffing-box in order when using 
 the powerful chemicals necessary in this manufacture, a 
 kind of water-joint has been substituted. It is necessary 
 that it should be deep and rather capacious, as seen at d. 
 Instead of filling this joint with water, which would 
 absorb the nitrous fumes, and produce an acid solution, 
 which would soon destroy the apparatus, the joint is filled 
 with nitrobenzol ; a cast-iron tube, e, passes through 
 the lid to carry nitrous fumes ; this is also cooled, so as 
 to condense any benzol vapour which may have escaped 
 the cooling action of the lid ; small pipes are introduced 
 through another opening for the purpose of supplying the 
 necessary chemicals. Besides these, there is a large 
 opening, /, in the smaller half of the lid, for the purpose 
 of introducing any of the products, which may be added 
 in large quantities at a time. At the bottom of these 
 large vessels are openings for running out the finished 
 product. 
 
 The process of preparing nitrobenzol with a mixture 
 of sulphuric acid and nitrate of sodium in place of nitric 
 acid, may be carried on very well in this apparatus, pro- 
 vided sufficient sulphuric acid be employed to produce 
 an acid sulphate of sodium, as this will be found quit ; 
 fluid at the close of the operation, and can be freely run 
 out at the small outlet. A mixture of strong nitric acid 
 and sulphuric acid is now usually employed for the con- 
 version of benzol into nitrobenzol. In working by 
 this latter method the entire charge of benzol is first 
 introduced though the large opening in the lid ; this is 
 then closed and the stirrer set moving ; the nitric and 
 sulphuric acids are then cautiously run in through the 
 small pipes, care being taken not to add too much nitric 
 acid, until the red fumes begin to appear. After all the 
 charge of acids has been added, and the reaction has 
 perfectly ceased, the product is drawn off. At first a 
 mixture of sulphuric and nitric acids runs out, and 
 then the nitrobenzol; this is collected separately and 
 purified, first by agitation with water, and then rendered 
 perfectly neutral by means of a dilute solution of soda. 
 
FIG. 2 
 
 Should it contain any unconverted benzol this may bo 
 distilled off by means of steam. On the Continent 
 manufacturers do not appear to have succeeded well 
 in manufacturing nitrobenzol ; when it first became 
 a commercial article, their difficulty appears to 
 have arisen from the fact that they experimented 
 in earthenware vessels, which are both dangerous 
 and unsuitable, and it was not until information 
 was obtained from England, I believe, that they 
 were able to produce this body at a moderate price. 
 
 We will now pass on to the processes for converting 
 nitrobenzol into aniline. I have already mentioned 
 that Zinin was the first who discovered that nitrobenzol 
 could be converted into aniline, or, as he termed it, 
 benzidam. His process consisted in treating an alcoholic 
 solution of nitrobenzol with ammonia and sulphuretted 
 hydrogen ; but, although the discovery of this process 
 was one of great importance from many points of view, 
 still it was very tedious. Bechamp, however, found 
 that by employing a mixture of acetic acid and finely 
 divided iron instead of ammonia and sulphuretted 
 hydrogen, the nitrobenzol was very rapidly converted 
 into aniline, and this process has been found the best 
 yet proposed for manufacturing aniline in large quan- 
 tities. Many other rea gents have been suggested, as 
 arsenite of sodium, powdered zinc, &e., but none of 
 them have been found so advantageous as iron and 
 acetic acid. 
 
 In carrying out Bechamp's process, cylinders like those 
 used for nitrobenzol (Fig. 1) were originally employed. 
 The cylinder was set in brickwork, and heated by means 
 of a small furnace, iron borings were first introduced, 
 and the door fixed in its place air-titiht. One neck was 
 connected to the upper extremity of a cast-iron worm by 
 means of a pipe called an adapter ; the second neck being 
 fitted with a .'-yplion-tuLe. for the introduction of the 
 nitrolicnzol and ac>lic acid. In working on tin; largo 
 scale it is necessary to add the nitrobenzol and ace tit- 
 acid in small quantities at a time, otherwise the re- 
 action is so violent as to almost burst the apparatus : by 
 working carefully, however, there is no need to fear any 
 
difficulties, especially if the stirrer is well used. By the 
 time all the charge has been introduced, a quantity of fluid 
 will have distilled orer ; this is returned into the cylinder 
 and the fire lit, and the aniline distilled off. 
 
 The principal change which has taken place in this 
 process consists in using high pressure or superheated 
 steam for the distillation instead of fire, and working the 
 apparatus by means of a steam-engine instead of by 
 hand. In Fig. 4 is shown a sketch of the apparatus 
 now generally employed for the preparation of aniline. 
 
 You will observe that the stirrer, which is worked by 
 bevel wheels, has a hollow shaft or spindle, , as seen in 
 the section. This is ground to an elbow, , connected 
 to the steam main, e, and held down by a screw, so that 
 when the steam is turned on, it passes through the hollow 
 elbow down the shaft, and then blows out at the bottom, 
 d, among the products ; and in this manner the aniline 
 is volatilized, and passes with the steam through the 
 neck, , and is condensed by a worm, not shown in this 
 drawing. Aniline thus obtained is generally redistilled, 
 and sometimes with a little lime or caustic soda, for the 
 purpose of decomposing a body called acetanilide, which 
 is often produced in the manufacture of aniline, especially 
 if the operation is conducted over a fire instead of with 
 steam. 
 
 Commercial aniline generally appears of a pale sherry 
 colour ; when chemically pure, it is colourless, but if kept 
 long it becomes quite brown. It possesses a peculiar 
 odour, which is slightly vinous when the aniline is pure. 
 It burns with a smoky flame, but is not very inflammable ; 
 its boiling point is 182 C. One of its most characteristic 
 re-actions is its power of producing a blue or blue violet 
 colouration with chloride of lime, to which I shall again 
 have occasion to refer. Aniline differs entirely from 
 
 benzol and nitrobenzol, being perfectly soluble in dilute 
 acids. This is owing to its being an organic base, and 
 forming compounds with acids. Thus with hydro- 
 chloric acid, it forms hydrochlorate of aniline ; with 
 sulphuric acid, sulphate of aniline, &c. 
 
 We will now, in a very rapid and general way, glance 
 at the chemical changes which take place in converting 
 benzol into nitrobenzol and aniline. 
 
 Benzol, as I have already stated, is a hydrocarbon, 
 i.e., a body composed of hydrogen and carbon only ; it 
 is represented by 
 
 6 H 6 
 
 This is treated with nitric acid, which contains 
 HNO, 
 
 The nitric acid acts upon the benzol and introduces its 
 nitrogen and part of its oxygen, at the same time 
 removing hydrogen and forming water. 
 
 ?j^ + 2^2 = SlEt^IP.! + H 2 O 
 
 Nitric acid. Benzol. Nitrobenzol. Water. 
 
 Nitrobenzol, when treated with iron and acetic acid, is 
 converted into aniline by the influence of hydrogen gas, 
 in what is termed the nascent state, or the peculiar 
 condition in which it is when being liberated from a 
 compound. 
 
 This hydrogen unites with the oxygen of nitrobenzol 
 and removes it as water, and at the same time two atoms 
 of hydrogen combine with the deoxygenated nitrobenzol, 
 forming aniline. 
 
 C 6 H 5 N0 2 + H 6 = C 6 H,N + 2H 2 
 
 Nitrobenzol. 
 
 Aniline. 
 
 FlG. 4. 
 
8 
 
 Having now seen the various operations which require 
 to be performed for the production of aniline from coal 
 tar, AVC are prepared for the consideration of its coloured 
 derivatives. We will, therefore, commence at once with 
 the first of the coal tar colours, " the mauve dye." I have 
 already t;iven you the history of its discovery; I will now 
 tell you how it is made. 
 
 First of all aniline and sulphuric acid, in the proper 
 proportions for the formation of sulphate of aniline, are 
 mixed in a large vat with water, and boiled until perfectly 
 dissolved. Bichromate of potassium is then dissolved in 
 a second largo vat. These two solutions, when cold, are 
 mixed in a third and still larger vessel, and allowed to 
 stand one or two days. In this way a large quantity of 
 a fine black precipitate is formed ; this is collected upon 
 shallow filters, well washed with water, and then dried. 
 When dry it is a most unpromising sooty -black powder, 
 and contains various products besides the mauve ; the most 
 troublesome of these is a brown, resinous product, 
 soluble in most of the solvents of the colouring matter 
 itself. 
 
 At first this resinous substance was removed by 
 digestion with coal tar naphtha previously to the extrac- 
 tion of the colouring matter, which was afterwards 
 effected with methylated spirits of wine, and the solution 
 thus obtained when distilled left the mauve as a fusible 
 bronze-coloured mass. 
 
 When digesting the black precipitate with naphtha 
 or strong spirits of wine, the operation had to be 
 performed in closed vessels under pressure or in 
 connection with a condensing arrangement, otherwise 
 large quantities of these valuable solvents would have 
 been lost, and great difficulty was experienced in getting 
 apparatus perfectly tight, on account of the " searching" 
 character of these fluids. Substitutes had also to be 
 found for the ordinary materials employed by engineers 
 for making good manhole joints, and a number of other 
 matters which are apparently of but small importance, 
 but it is remarkable the amount of difficulty and annoy- 
 ance they caused. The method of extraction has, 
 however, been materially improved upon by substi- 
 tuting dilute methylated spirits of wine for strong, as 
 this weaker spirit dissolves only a small quantity ol 
 resinous matter but all the colouring matter, so that the 
 digestion with coal tar naphtha is now found unnecessary. 
 The solution of the colouring matter in dilute spirit 
 is placed in a still and the spirit distilled off, the colour- 
 ing matter remaining behind in aqueous solution ; this 
 is filtered and then precipitated with caustic soda. It is 
 afterwards collected on a filter, washed with water, and 
 drained until of a thick pasty consistence, and, i: 
 necessary, dried. 
 
 The solid mauve dissolves very freely in spirits o 
 wine, forming an intensely coloured solution ; it is also 
 soluble to a small extent in water, but the aqueous 
 solution on cooling forms a kind of jelly. 
 
 The formation of the mauve or aniline purple by th< 
 action of bichromate of potassium upon sulphate o 
 aniline is a process of oxidation, and since the pub 
 lication of the original specification at the Paten 
 
 Office a great number of patents have been taken 
 out for the preparation of this colouring matter, 
 in which the bichromate has been replaced by 
 ther oxidizing agents, as peroxide of lead, permanga- 
 late of potassium, peroxide of manganese, chloride of 
 ime, ferricyanide of potassium, chloride of copper, &c. ; 
 ut I need not make any special remarks upon these 
 various processes, as experience has shown that bichro- 
 mate of potassium and a salt of aniline, the reagents first 
 roposed, possess advantages over all others, and are 
 low nearly universally employed for the preparation of 
 iniline purple. The next best process appears to bo 
 ,hat of Dale and Caro, in which chloride of copper is 
 jmployed. 
 
 The affinity of aniline purple for silk or wool is very 
 remarkable, and if I take some wool and pass it through 
 i solution of mauve, you will see how rapidly it absorbs 
 .t, even from a very dilute solution. Aniline purple is 
 sent into the market in three different conditions, in 
 paste, in solution, and in crystals ; but the latter are 
 very rarely employed, as they are very expensive and do 
 not offer corresponding advantages to the consumer. 
 
 The mauve is the most permanent coal-tar purple 
 mown, especially with respect to its power of resisting 
 Lhe action of light. 
 
 I will now endeavour to give you some idea of the 
 approximate amount of the various products we have 
 considered obtainable from lOOlbs. of coal, and for this 
 purpose I have arranged them in the following table 
 with their respective weights : 
 
 Iba. ozs. 
 
 Coal 100 
 
 Coal-tar 10 12 
 
 Coal-tar naphtha 
 
 Benzol 
 
 Nitrobenzol 
 
 Aniline 
 
 Mauve 
 
 You see the smallness of the amount of colouring 
 matter obtainable from coal or coal tar; but there is 
 fortunately one thing which, to some extent, compensates 
 for this, and that is the wonderful intensity of this 
 colouring matter. I will illustrate this remarkable fact. 
 I have here a large carboy containing nine gallons of 
 water, and will now add to this a solution containing 
 one grain of rnauve, and illuminate the liquid with the 
 magnesium lamp, and you see the single grain has 
 coloured this large bulk of water. A gallon of water 
 contains 70,000 grains, therefore nine gallons contain 
 630,000 grains. This solution, then, contains only one 
 part of mauve to 630,000 of water. 
 
 I have now shown you the manifold operations which 
 have to be performed before we can derive the mauve 
 from coal tar, and have also mentioned a few of the 
 obstacles which had to be overcome before its manufac- 
 ture on the large scale could be accomplished. We have 
 thus laid the ground work of our subject, and in our 
 next lecture I hope to tell you a little more about mauve, 
 and then give an account of the many other colouring 
 matters of which it may be considered the parent. 
 
 LECTURE II. DELIVERED MONDAY, DECEMBER MTU, 1868. 
 
 MAUVE, MAGENTA, AND SOME OF THEIR DERIVATIVES. 
 
 You will rcmcmLcr that in my last lecture we went 
 over all the various steps between coal and colour. . We 
 saw how coal tar was produced from coal ; how coal tar, 
 
 naphtha, and benzol were separated from coal tar; 
 how nitrobenzol and aniline were made from benzol, 
 and concluded with an account of the preparation of 
 
aniline purple, or mauve from aniline. We will now 
 proceed to the study of some of the most remarkable 
 properties of aniline purple. 
 
 This colouring matter is sometimes supplied to con- 
 sumers in a pure and beautifully crystalline condition. 
 This product is found to be a salt of a compound, 
 chemically termed an organic base. This base has been 
 called " mauveine ;" it is composed exclusively of 
 carbon, hydrogen, and nitrogen, in the following pro- 
 portions : 
 
 C 27 H 24 N 4 
 
 Mauveine, although the base of aniline purple, when in 
 solution is not of a purple but of a dull violet shade, and 
 in the solid state is a nearly black crystalline powder. 
 The moment, however, mauveine is brought in contact 
 with an acid so as to form a salt, its solution changes to 
 a purple colour. This takes place even with that feeble 
 acid cai'bonic. I have here a dilute solution of mauveine ; 
 you will observe the dull violet colour it possesses, but 
 if my assistant only breathes through it a few moments 
 the carbonic acid of his breath will combine with it, and 
 it will acquire the ordinary colour of aniline purple. 
 
 Mauveine is a most powerful chemical body, and will 
 easily decompose ammoniacal salts. This may be readily 
 seen if some mauveine be heated with chloride of 
 ammonium and a little water, when an abundance of 
 ammonia gas will be evolved, which can be distin- 
 guished not only by its odour, but by the white fumes it 
 produces with hydrochloric acid. 
 
 The salts of mauveine are beautifully crystalline, and 
 possess a splendid green metallic lustre. The crystal- 
 lised commercial product consists of the acetate. 
 Mauveine possesses one of the peculiar properties of 
 indigo, indigo, when treated with reducing agents, 
 such as a mixture of sulphate of iron and lime, is rendered 
 nearly colourless and soluble, but this colourless indigo, 
 when subjected to the oxidising influence of the atmo- 
 sphere, rapidly becomes blue again. I here refer to the 
 indigo vat so much used by dyers. Mauveine, when treated 
 in a similar manner, is also nearly decolourised, changing 
 to a pale brownish yellow fluid, but the moment this is 
 exposed to the air it assumes its original colour far more 
 quickly than indigo. This remarkable fact may be 
 strikingly illustrated by boiling an alcoholic solution of 
 salt of mauveine with a few strips of zinc in a sealed 
 tube from which the air has been previously removed. 
 The dark purple solution will gradually lose its colour, 
 and change to a very pale-yellowish brown shade. 
 
 I have a tube containing some aniline purple decolour- 
 ised in this manner, and now if I open it, the air rushes 
 in and the solution instantly assumes the ordinary purple 
 colour. 
 
 Ordinary indigo is quite insoluble in water, and, 
 therefore, its property of becoming soluble, as well as 
 colourless, when treated with reducing agents, is of great 
 practical value, as the dyer, by immersing his goods in 
 this solution of indigo, and then exposing them to the 
 oxidising influence of the air, gets the colouring matter 
 firmly fixed in the fibre of his materials. But as the 
 mauve is always soluble in water, this property has not 
 been found of any practical value. 
 
 Aniline purple, when introduced as a dye, being the 
 first colour of its kind, had to encounter many prejudices, 
 and, on account of its peculiar nature, required the 
 adoption of new or modified processes for its application. 
 These difficulties, however, once overcome, its progress 
 was very rapid. At first it was principally employed by 
 the silk dyer and printer, its application to silk being 
 comparatively easy, but it was not used by the calico- 
 printer till a few years afterwards. 
 
 I distinctly remember, the first time I induced a calico- 
 printer to make trials of this colour, that the only report 
 I obtained was that it was too dear, and it was not until 
 nearly two years afterwards, when French printers put 
 aniline purple into their patterns, that it began to interest 
 British printers. 
 
 It will be seen that to introduce a new coal-tar colour 
 
 after the mauve was a comparatively simple matter. 
 The difficulty in the manufacture of all the raw mate- 
 rials had been overcome, as well as the obstacles in the 
 way of the practical applications of an aniline colour tc 
 the arts. 
 
 We will now turn our attention to a colouring matter 
 which has often been confounded with aniline purple. 
 I have designated it as "Runge's blue," as it was first 
 observed by Hunge. I have mentioned that Runge, when 
 he first obtained aniline, termed it "kyanol," or blue oil, 
 on account of the blue-coloured solution it gave with 
 chloride of lime. 
 
 After discovering the mauve, I naturally made experi- / 
 ments with this coloured product of Runge's, to see if its 
 contained aniline purple, but my experiments answered 
 the inquiry in the negative. A few years afterwards, 
 however, I was puzzled by finding that French manu- 
 facturers were beginning to produce aniline purple by 
 the agency of chloride of lime and a salt of aniline ; being 
 much occupied at that time, I was unable to look care- 
 fully into the matter ; and it was not until investigating 
 these apparently opposite results a short time since that I 
 was able to understand them. I will perform Runge's 
 experiments, and for that purpose will take a solution of 
 hydrochlorato of aniline, and add to it a very dilute 
 solution of chloride of lime (taking care not to add too 
 much). The solution is now changing, and getting 
 slightly opaque ; by daylight it has an appearance like 
 indigo, but if I render it clear by the addition of alcohol, 
 and place it before the magnesium lamp, it is seen to 
 be of a brilliant colour, and nearly pure blue, quite 
 unlike aniline purple. 
 
 I have lately succeeded in obtaining this blue product 
 in the solid condition, by treating a solution of hydro - 
 chlorate of aniline with a dilute solution of chloride of 
 lime, and precipitating the resulting colouring matter 
 with common salt; it is thus obtained in an impure con- 
 dition, and may be collected upon a filter ; by treatment 
 with cold ether or benzol, a large quantity of brown im- 
 purities are separated, the colouring matter being left in 
 the solid condition. This substance dissolves in alcohol, 
 forming a nearly pure blue solution, and is capable of 
 dyeing silk a blue or blue-violet colour. 
 
 An alcoholic solution of Runge's blue behaves with 
 caustic potash quite differently to aniline purple, forming 
 a brownish red-coloured solution instead of a violet. 
 Therefore, there can no longer be any reason for con- 
 founding this body with aniline purple, it being entirely 
 different, both in colour and chemical properties. But 
 as this colouring matter is produced by oxidising hydro- 
 chlorate of aniline with chloride of lime, how is it that 
 manufacturers have succeeded in preparing aniline purple 
 with the same re-agents ? This question I find is very 
 easy to answer ; the manufacturer has gone a step further 
 and boiled his product. Now, if I take a piece of silk 
 dyed with Runge's blue, and, instead of boiling it, which 
 would wet it, and make it difficult to manipulate, do 
 that which is equivalent steam it a very remarkable 
 change takes place Runge's blue being changed 
 into the mauve. So, here we have cleared up the 
 mystery, and find that by the action of chloride of 
 lime on hydrochlorate of aniline, we first get Runge's 
 blue, and then, by heating this blue, we change it 
 into mauve. Runge's blue is a very unstable body, 
 and of no practical value, its alcoholic solution changing 
 into mauve in a day or two. This change takes place 
 directly by boiling. 
 
 We must now pass on to another colouring matter, 
 in name well-known to all of you, I mean magenta, 
 also called roseine, fuchsine, aniline red, and various 
 other names. The discovery of this body and its 
 manufacture were strangely dependent upon the source 
 which had been selected for the preparation of aniline 
 for the mauve. Had the aniline contained in coal tar, 
 or the aniline obtained from indigo, been employed for 
 the preparation of the mauve, instead of that prepared 
 from commercial benzol, magenta and its train of 
 
10 
 
 coloured derivatives would in all probability have 
 remained unknown to this present day, from the simple 
 fact that magenta cannot be produced from pure aniline, 
 a second body being also required. 
 
 You will observe, by reference to the table of coal tar 
 products, that next to benzol there is a substance 
 named toluol, a substance having a boiling point not 
 very much above that of benzol. On this account 
 toluol is always contained in commercial benzol, and 
 possesses most of its properties. With nitric acid it 
 forms nitrotoluol, very similar to nitrobenzol ; with iron 
 and acetic acid it is converted into a base, toluidine, very 
 similar to aniline, except that it is solid instead of liquid, 
 when pure. Therefore, aniline prepared from com- 
 mercial benzol always contains a little toluidine, and 
 this is the second body requisite for the formation of 
 magenta. 
 
 An apparatus for the fractional distillation of coal 
 tar naphtha has been devised, so that its constituents 
 may be almost completely separated from each 
 other, and thus pure benzol or pure toluol may be 
 obtained.* Having obtained these hydrocarbons, pure 
 aniline and pure toluidine may be prepared and then 
 mixed in the most suitable proportions for manufacturing 
 magenta. This process is not very generally employed, 
 however, but the quality of the mixture of aniline and 
 toluidine is determined by distillation, noting the 
 quantities which come over at different temperatures. 
 The necessity of toluidine as well as aniline for the 
 production of magenta was discovered by Dr. Hofmann, 
 who found that it could not be produced by 
 perfectly pure aniline, nor perfectly pure toluidine, 
 but that a mixture of these two bases yielded it 
 in quantity. Magenta was apparently first observed 
 by Natanson, in 1856, when examining the action 
 of chloride of ethylene on aniline, and afterwards 
 by Dr. Hofmann, in 1858, when studying the action 
 of tetrachloride of carbon on aniline, but industrially 
 the discovery of magenta was made by M. Virguin, of 
 Lyons, in 1859, three years after the mauve. M. 
 Virguin' s process consisted in treating commercial 
 aniline with a fuming liquid, called tetrachloride of tin, 
 and was first carried out by Messrs. Renard Brothers, 
 of Lyons. Since 1859 patents have been taken out for 
 the production of this colouring matter with aniline, and 
 almost all chemicals known, whether capable or incapable 
 of forming magenta. I may mention one process which 
 was extensively employed, and is still used to some 
 extent in Germany, and that is the method of making 
 magenta with commercial aniline and nitrate of mercury. 
 With care this process works very well, and the colour- 
 ing mutter produced is of good quality. When first 
 introduced, mngenta prepared by this method was not 
 purified, but sent into the market in a crude form, so 
 that before using it the dyer had to extract it with water. 
 In the preparation of magenta by this process, all the 
 mercury of the nitrate of mercury employed is recovered 
 in the metallic state, but although this process may 
 possess some advantages, vet the use of mercury salts 
 is most undesirable, on account of their fearfully 
 deleterious influence upon the workmen. 
 
 The process, which has almost superseded all others, 
 is that for the use of arsenic acid, as proposed by Med- 
 lock, and patented by him in January, I860. This 
 patent is notorious for the amount of litigation it has 
 caused, showing that a patentee should not only be a 
 discoverer but a lawyer, and even more, and able to 
 discover precisely how much to claim and disclaim in 
 his patent, and also to arrange his specification so that 
 the intellects of the whole world may not be able to dis- 
 cover a single flaw in his description ; and it is a com- 
 mon misfortune to inventors who wish to thoroughly 
 protect themselves, to find that they have claimed too 
 much. 
 
 The manufacture of magenta, as now carried on, is a 
 
 * See " Clarke's Specification," A.D. 1863. June 5th, No. 1,405. 
 
 very simple process ; it is conducted in an apparatus 
 somewhat similar to that represented by fig. 5. 
 
 FIG. 5, 
 
 This apparatus consists of a large iron pot, a, about 4ft. 
 diameter, set in a furnace of brick-work ; it is provided 
 with a stirrer, b, worked by hand. All the gearing for 
 this stirrer is fixed to the lid, so that stirrer, lid, and ail 
 may be lifted away by means of a crane, or other suit- 
 able apparatus. There is also a bent tube fixed into the 
 lid, and connected to a condensing worm, fl, by means of a 
 joint, which can be made or broken at pleasure. In 
 preparing magenta, a quantity of aniline, containing 
 about 25 per cent, of toluidine, and a nearly-saturated 
 solution of arsenic acid, is introduced into this appara- 
 tus, and well mixed by working the stirrer ; the pro- 
 portions of the materials are in aboxit the ratio of 1 of 
 aniline to 1'5 of a 75 per cent, solution of arsenic acid. 
 When these are well mixed the fire is lighted. After the 
 product has been heated for some time water begins to 
 distil over, then aniline and water, and lastly nearly pure 
 aniline. 
 
 This operation requires some hours for completion, and 
 this is determined by inserting an iron rod, from time to 
 time, and drawing out a portion of the product for 
 examination, as well as by the amount of aniline which 
 distils over. When the heating has been completed, a 
 steam-pipo is introduced into the apparatus, and steam 
 blown through the fused mass ; by this means an addi- 
 tional quantity of aniline is separated. The lid is then 
 liberated and lifted, with the stirrer, from the apparatus, 
 and the product left to cool before it is removed. A 
 more elaborate and larger apparatus is sometimes used, 
 which possesses considerable advantages over the smaller 
 one. The iron pot is larger, and is provided with 
 an outlet at the side, which is closed during the opera- 
 tion, and the shaft of the stirrer is hollow (as in the 
 aniline apparatus described last lecture, fig. 4), and 
 worked by sl':mi. When the operation of heating is 
 concluded, steam is blown down the shaft, and after the 
 addition of water the product is boiled and run out 
 of the outlet in the side of the pot; by this arrangement 
 it is unnecessary to disconnect the lid of the apparatus, 
 and the product does not require to be removed by me- 
 chanical me;m<, as with the apparatus previously de- 
 scribed. 
 
 The crude product obtained by heating aniline and 
 arsenic acid, is next transferred to vats, boiled with 
 water and filtered. Common salt is then added, which 
 precipitates the crude magenta; this is collected and 
 dissolved in boiling water, again filtered, and the solution, 
 on cooling, deposits the colouring matter in the crystal- 
 lino condition. This, when recrystallised, constitutes 
 commercial magenta. 
 
11 
 
 Commercial magenta consists of brilliant crystals, 
 sometimes half-an-inch in length, having a beautiful 
 golden green metallic appearance ; these dissolve in warm 
 water almost entirely, forming an intense purplish red 
 solution. Dr. Hofmann has carefully studied the chemical 
 nature of magenta, and has found it to consist of the 
 salt of an organic base, which he has called rosaniline. 
 This base may be obtained from the commercial product, 
 by dissolving it in water and boiling it with an alkali, 
 or alkaline earth, such as ammonia, potash, or lime ; it 
 is thus rendered nearly colourless, and after filtration 
 rosaniline separates from the clear solution, on cooling, 
 in colourless crystals. It is composed of carbon, hydro- 
 gen, and nitrogen when anhydrous, but generally 
 contains un equivalent of water also. The anhydrous 
 base has the formula 
 
 C 20 H 19 N 3 
 
 This colourless base immediately becomes dark red 
 upon combining with an acid, as I can show you by 
 heating some with acetic acid, when the colour is 
 immediately developed. The magenta produced by 
 heating commercial aniline with nitrate of mercury 
 is the nitrate of rosaniline ; that produced with arsenic 
 acid is the arseniate, but in the process of purifica- 
 tion this latter salt becomes converted into hydro- 
 chlorate, which is the salt most generally found in the 
 market. Other salts are also commercially manufac- 
 tured, such as the oxalate and acetate, especially when 
 a very pure product is required; these salts are generally 
 prepared from pure rosaniline, by combining it with the 
 required acid, and crystallising from water. 
 
 The acetate of rosaniline crystallises in magnificent 
 octahedra, possessing the ordinary golden green metallic 
 lustre to a very high degree ; it is also the most soluble 
 salt of rosaniline known. The affinity of rosaniline 
 salts for animal fibres is very great ; it does not, however, 
 resist the action of light nearly to the same extent as 
 the mauve. All the derivatives of rosaniline also possess 
 a very great affinity for animal fibres, in most cases quite 
 equal to that of magenta itself. 
 
 When speaking of aniline purple, I showed you that 
 by reducing agents it became colourless, or nearly so, 
 but that the original colour was developed when it was 
 exposed to the oxygen of the air. Salts of rosaniline 
 or magenta are also decolourised by reducing agents, 
 but, unlike aniline purple, the colour is not restored by 
 exposure to the air. Dr. Hofmann has found that 
 in this case a new organic base is produced which he 
 has called leucaniline. This substance differs only from 
 rosaniline in containing an additional quantity of hydro- 
 gen. It may be reconverted into rosaniline by oxidising 
 agents such as bichromate of potassium, Sec. 
 
 There is another very peculiar reaction of rosaniline. 
 This base, when brought in contact with hydrocyanic 
 acid, instead of forming a coloured hydrocyanate of 
 rosaniline, yields a perfectly colourless body, which is 
 not a salt but a base. This remarkable fact was dis- 
 covered by Dr. Hugo Muller, and he has called this 
 new body hydrocyanrosiline. We shall have occasion to 
 refer again to this substance and leucaniline. 
 
 In the formation of magenta, a second product is 
 obtained, commercially called phosphinc. This substance 
 was first introduced by Mr. E. Nicholson. Dr. Hofmann 
 has investigated it, and found it also to contain an organic 
 base, which he has called chrysaniline. 
 
 Phosphinc or chrysaniline is not capable of being pro- 
 duced at will, and the quantity formed in the manu- 
 facture of magenta is variable. In shade it is of rather 
 a yellow orange. This colouring matter differs from 
 rosaniline, the base of magenta, in exactly the opposite 
 direction to leucaniline, containing two atoms less of 
 hydrogen. Leucaniline, rosaniline, and chrysaniline, are 
 thus related : 
 
 Leucaniline C 20 H 21 N 3 
 
 Eosaniline C 20 H 19 N 3 
 
 Chrysaniline C ZO TL 1 7 N_ 
 
 The principal use of phosphine is for the formation of 
 a scarlet with magenta. It is not converted into 
 magenta, nor decolourized with reducing agents or 
 hydrocyanic acid, and therefore does not seem to be of 
 the same class of colouring matters as rosaniline. 
 
 From the residues obtained in the manufacture of 
 magenta three new colours have been obtained by Messrs. 
 G-irard and Delaire, but, I am sorry to say, my time will 
 not allow me to enter into the particulars of these pro- 
 ducts. I believe they have not been commercially intro- 
 duced as yet. 
 
 Magenta is now more used as a source of other colours 
 than as a dye. This has caused its manufacture to be 
 conducted on a very extensive scale, and it is now looked 
 upon by the manufacturer as a raw material much in 
 the same way as aniline was regarded in the early days 
 of aniline purple. 
 
 We will next consider some of the derivatives of 
 magenta, and the first we will study is aniline blue 
 or bleu de Lyon. If aniline be treated with a salt 
 of rosaniline or magenta, a remarkable change takes 
 place ; at first the colour gradually becomes purple, biit 
 afterwards gets quite blue, ammonia being evolved at the 
 same time. This peculiar reaction was observed by 
 MM. Girard and Delaire, who found that this change 
 of colour was due to the formation of a new body, which 
 they termed the bleu de Lyon ; intermediate products were 
 likewise obtained, to which we shall refer presently. 
 MM. Girard and Delaire patented their process in 
 January, 1861. This new aniline blue is one of the most 
 important of the artificial colouring matters, and its v 
 manufacture has been very much improved upon since 
 its discovery. There are several circumstances which 
 materially influence the beauty of its tint, such as the 
 quality of the aniline and the particular salt of rosaniline 
 employed in its manufacture. It is found by experience 
 that the aniline should be as pure and free from toluidine 
 as possible, and that the salt of rosaniline should contain 
 a feeble acid, such as the acetate, valerate, oleate, or 
 benzoate ; but why the latter is necessary chemists are 
 unable to understand at present. Practically, the various 
 salts of rosaniline required for the manufacture of the 
 blue are not prepared separately, but are produced in the 
 operation by double decomposition, which is simply a 
 process of exchange ; thus, if acetate of rosaniline is 
 required, a mixture of hydrochlorate of rosaniline and 
 acetate of sodium is employed ; these re-act on each 
 other, and change into acetate of rosaniline and chloride 
 of sodium. 
 
 On the large scale, the process of making aniline 
 blue is carried out in various ways, but many employ 
 the apparatus shown in fig. 6. This apparatus con- 
 sists of an oil bath, a, set in a brick furnace ; it has 
 a cover, b, perforated with large holes ; into these holes 
 are placed small enamelled cast-iron pots, <?, provided 
 with a flange, on which they rest. These pots will hold 
 from three to five gallons, and are fitted with lids held 
 down with clamps ; each lid is provided with a small 
 stuffing-box, through which the rod of a stirrer, d, passes. 
 In the lid are also two other perforations ; one of these 
 is fitted with a wooden plug, <?, for the purpose of testing 
 the progress of the operation ; the other is connected 
 with a bent, movable tube,/, united to a long central main, 
 to collect any aniline vapour which passes over. This main 
 is connected at one end with a worm, #, to condense the 
 vapours. The oil bath by which these pots are heated 
 is provided with a thermometer, so that the temperature 
 may be properly regulated. In preparing the blue a 
 mixture of magenta, acetate of sodium and aniline is 
 introduced into the pots, the aniline being employed in 
 excess. When charged the oil bath is heated up to 190 Q C., 
 and kept near that temperature. At first the red colour of 
 the mixture changes slowly, but afterwards with rapidity. 
 The progress of the operation is ascertained by removing 
 the wooden plug, and withdrawing a small quantity of 
 the product upon the end of an iron or glass rod, and 
 it is considered complete when a good blue colour lias. 
 
12 
 
 Fro. G. 
 
 been obtained ; to ascertain this point with precision, 
 considerable experience is necessary. The excess of 
 aniline distils during this operation, and is condensed | 
 by the worm, and collected in a suitable receiver, so that 
 it may be used again. 
 
 From the crude blue product thus obtained, which is 
 a fluid of the consistency of treacle, all the different 
 qualities of blues found in the market are prepared. 
 The cheaper qualities are obtained by simply treating 
 the crude product several times with hydrochloric 
 acid. This removes all the free aniline, and most of the 
 red and purple impurities. Another similar but more 
 effective process is employed for the preparation of the 
 
 is effected by subjecting indigo to the action of con- 
 centrated sulphuric acid, whereby a sulpho acid is 
 produced. 
 
 Mr. Nicholson has found that aniline blue, when 
 treated by a similar process, also forms a sulpho acid, 
 perfectly soluble in water, and forming with alkalies 
 nearly colourless solutions. These, however, when 
 decomposed by acids, change back to the original blue. 
 
 This soluble blue is now much used for silk dyeing, 
 but by dyers it is not thought to be so fast as the 
 normal compound. By some modification of the process 
 just described, Mr. Nicholson has obtained another 
 soluble blue, commercially known as "Nicholson's blue.' 
 
 better qualities, and consists in mixing the crude product I This is now very extensively employed in Great Britain 
 with methylated spirits of wine, and pouring it into ' for wool dyeing, but its application does not appear to be 
 water acidulated with hydrochloric acid, and then ! well understood in France and Germany, so that its 
 thoroughly washing the colouring matter which it pre- 
 cipitates with water. But for the purest kinds of blue there 
 are several processes employed ; these arc based upon 
 the difficult solubility of some of its compounds in 
 alcohol. In preparing these very pure qualities of blue, 
 instead of starting with the crude product, one of the 
 
 purified blues is taken. 
 
 Aniline blue, or "bleu de Lyon," is supplied to con- 
 sumers ^as a coarse powder having a coppery lustre, or in 
 alcoholic solutions ; it is nearly insoluble in water, and 
 has to be dissolved in alcohol before it is added to the 
 dye bath. 
 
 The nature of this blue has been determined by Dr. 
 Hofmann. It is found to contain, like magenta, a colour- 
 less base, becoming blue only upon combining with acids. 
 Dr. Hofmann has shown this base to contain 
 
 and has called it "triphenylrosaniline." Like rosaniline, 
 it becomes colourless when treated with nascent hydro- 
 gen, forming a new base, giving colourless salts, as leuc- 
 uniline. The composition ' 
 
 use there is not so great as in our own country. 
 
 If a salt of rosanilino and aniline be heated together, 
 and the process stopped before aniline blue is produced, 
 the resulting product when treated with dilute acid gives 
 a colouring matter, which has been called "violet 
 imperial." This was at first supposed to consist of a 
 mixture of blue and magenta, but recent research has 
 
 shown it to consist of intermediate products. Very large 
 quantities of this colouring matter have been used, but 
 its consumption is now rapidly falling off, owing to the 
 introduction of new violets, about to be described. A 
 few months after the discovery of aniline blue, another 
 colouring matter, called the "bleu de Paris," was 
 obtained by M. M. Persoz De Luynes and Salvetat. 
 These chemists found that when aniline was heated with 
 tctrachloride of tin for thirty hours to ISO'-C. in a 
 scaled tube, neither a red nor a violet, but a very pure 
 blue was produced. This colouring matter is generally 
 described as being identical, or probably identical, with 
 the bleu de Lyon. These blues are, however, widely 
 different in their chemical nature, as the bleu do Paris 
 
 is easily soluble in water, and crystallizes freely in 
 : needles of a blue colour, with a coppery reflection. It 
 
 The insolubility of aniline blue in water has bc-n consists of the hydrochlorate of an organic base, which 
 found a great drawback to its use, because when employed is precipitated from its solution by alkalies as a purplish 
 for dyeing it t is thrown out of solution in the dye bath, blue powder ; it dyes silk readily, and retains its blue 
 and then mechanically adheres to the goods, so that it colour by artificial light. It is" remarkable that the 
 aiterwards rubs off. discoverers of the bleu de Paris do not seem to have 
 
 Mr. Nicholson has, however, discovered a process for ) observed its difference from the bleu de Lyon. 
 rendering this blue perfectly soluble in water. His j I have prepared some of this product with a view to 
 process closely corresponds to that employed to render | its examination, but hitherto have been prevented from 
 indigo permanently soluble, This, it will be'remembered, j determining its composition. I hope to do so soon. 
 
13 
 
 The bleu de Paris is, unfortunately, difficult to prepare 
 in large quantities, and has never been introduced com- 
 mercially. 
 
 The recognition of the nature of the bleu de Lyon, 
 by Dr. Hofmann, led him to study the action of a 
 class of substances upon rosaniline, known to chemists 
 as the iodides of the organic radicals ; this investigation 
 resulted in the discovery of the brilliant colours known 
 as the Hofmann violets, and of which so many shades 
 can be obtained, from a very red purple to a nearly 
 pure blue. 
 
 The substances generally used for the preparation of 
 the Hofmann violets from rosaniline are the iodides of 
 methyl and ethyl ; the iodide of methyl differs from that 
 of ethyl in a practical point of view, in being rather 
 quicker in its action; it is also more volatile. Both 
 these substances contain a remarkable element called 
 iodine. This body is found in sea- water and sea-weed ; 
 its aspect is very similar to that of a metal ; one of its 
 characteristii properties is that when heated it volatilizes 
 and produces a beautiful purple coloured vapour, and 
 here we find how dangerous a little knowledge is when 
 relied upon. When the iodide of ethyl, which, as I have 
 told you, contains iodine, was introduced for the prepara- 
 tion of the Hofmann violets, it was stated in some of our 
 periodicals or daily papers, I do not remember which, 
 that chemists had at last succeeded in fixing the colour 
 of iodine, whereas, the iodine has nothing whatever to 
 do with the colours produced with the iodides of ethyl and 
 methyl, but is simply an instrument in bringing about 
 the change which takes place in their formation ; more- 
 over, these colours can be equally produced without 
 using iodine at all. It is unfortunate that the popular 
 reports upon scientific matters are generally so utterly 
 untrustworthy. One of the most remarkable reactions 
 of iodine is the blue violet colour it gives with a 
 solution of starch ; this is used as a test for its pre- 
 sence when in the free condition, and is remarkably 
 delicate ; it is of no use as a colour, as it is instantly de- 
 composed when heated. To prepare iodide of ethyl, 
 ordinary alcohol is treated with iodine and phosphorus ; 
 the operation has to be conducted with care, as iodine 
 reacts upon phosphorus with great energy ; iisually the 
 alcohol and phosphorus are placed in a retort, and the 
 iodine added very carefully, and in small quantities at 
 the time. The mixture is then distilled, and the distillate 
 mixed with water, which causes the iodide of ethyl to 
 separate as a colourless heavy oil. Iodide of ethyl is 
 very volatile, boiling at 70C. ; it has an ethereal odour, 
 and when pure is colourless and transparent ; it contains 
 no less than 81 per cent, of iodine. Iodide of methyl is 
 prepared in exactly the same manner as that of ethyl, 
 substituting wood naphtha, or methylic alcohol, for 
 ordinary alcohol ; it contains a still larger quantity of 
 iodine than the iodide of ethyl, viz., 89 per cent. 
 
 For the preparation of these substances on the large 
 scale special apparatus has been devised, and sometimes 
 amorphous or red phosphorus is substituted for the 
 ordinary kind ; but I shall not have time to enter more 
 fully into this subject. To produce the violets, Dr. 
 Hofmann heats pure rosaniline with iodide of ethyl, or 
 methyl and methylated spirits of wine, in a cast-iron 
 digester, closed air-tight, with a lid fastened down with 
 screws. A process very similar to this is sometimes 
 employed, and consists in using a salt of rosaniline, caustic 
 alkali, iodide of ethyl, and alcohol. But in Germany the 
 ordinary hydrochlorate of rosaniline is employed with 
 alcohol, or wood spirit and iodide of ethyl, and is found 
 to work very successfully. By employing the rosaniline 
 itself a lower temperature is required for the formation 
 of violet, than when using its salts ; in fact, I have found 
 that a mixture of iodide of ethyl and rosaniline re-act 
 even at the ordinary temperature if left in contact for 
 a few days, and produce a red shade of violet. 
 
 On the large scale Hofmann's violet is generally 
 prepared in deep cast-iron vessels, surrounded with a 
 steam jacket, and provided with a lid having a perfora- 
 
 ion, closed with a screw plug. This lid can be firmly 
 
 ^astened down with screws, the joint being made with a 
 vulcanised indiarubber washer. This apparatus is charged 
 
 with a mixture of hydrochlorate of rosaniline dissolved 
 n alcohol or wood spirit, and iodide of ethyl or methyl, 
 n proportion according to the shade required. After the 
 
 apparatus is closed the steam is allowed to enter the steam 
 acket, and the heating continued for five or six hours ; 
 .he plug is then removed from the lid of the apparatus, 
 
 and the alcohol or unused iodide of ethyl distilled off. 
 Che resulting product is dissolved in water, filtered, and 
 >recipitated with chloride of sodium, but sometimes it is 
 irst treated with caustic alkali, to remove all the iodine, 
 o that it may be recovered. Thus obtained, the colour- 
 
 ing matter is of a golden lustre if of a blue shade, and of 
 greenish if of a red shade. 
 
 Like all the other colours we have considered, the 
 EEofmann violets are nearly white organic bases, their 
 
 composition differing according to the shade of colour, 
 ;hus : 
 
 A red shade is composed of .. C 22 H 23 N 3 
 A red violet shade, of ...... C 24 H 2 ,N 3 
 
 A very blue shade .......... C 2 6 H 3 1 N 3 
 
 The colours of the Hofmann violets are remarkable for 
 ;heir brilliancy, but, unfortunately, they do not resist 
 the action of light so well as might be desired ; it is re- 
 markable, however, that the regard for fastness seems 
 ;o have given way to the desire for brilliancy. 
 
 In the early days of coal-tar colours fastness was so 
 much talked about, that when magenta was first intro- 
 duced it was thought by some that it would not be 
 .argely used how different has it proved to be. ^ Al- 
 though not very fast upon cotton, the Hofmann violets 
 are sufficiently so for woollen and silk goods, as colours 
 always resist the light better when applied to animal 
 fibres. 
 
 In the formation of Hofmann violets we see that 
 rosaniline, when treated with iodide of ethyl, becomes 
 blue, the red being converted into violet; but with 
 mauveine, the base of the mauve, exactly the reverse 
 takes place, the mauveine being converted into a much 
 redder shade with iodide of ethyl. The colouring matter 
 produced from mauveine and iodide of ethyl is com- 
 mercially known as ' dahlia ;" the colour is intermediate 
 in shade between aniline purple and magenta. This 
 colouring matter possesses the same character for fast- 
 ness as the mauve, and also gives the same reactions 
 with acids; unfortunately it is rather expensive, and 
 has therefore not been very extensively used. 
 
 Lastly, there has been a process proposed for the pro- 
 duction of colouring-matters similar to the Hofmann 
 violets, by first converting the aniline into ethyl- 
 aniline, a base previously discovered by Dr. Hofmann. 
 It is found that by substituting this base for aniline, in 
 some of the processes which have been employed for the 
 manufacture of magenta, the ethyl-aniline yields purple 
 or violet colouring-matters. 
 
 This process has been patented by M.M. Poirier and 
 Chappat, but the reaction appears to have been first ob- 
 served by M. E. Kopp. From the great similarity of 
 these colouring matters to the Hofmann violets, I need 
 not enter into any lengthened description of their pro- 
 perties. 
 
 Sea- water contains, besides iodine, another remarkable 
 element called bromine ; it is a liquid giving off very 
 irritating orange-coloured vapours. This remarkable 
 body yields, with many hydro- carbons, a great variety 
 of compounds. With ordinary turpentine, it acts 
 with great violence ; but if the action be moderated by 
 the presence of a large quantity of water, a thick viscid 
 oil is obtained. This body was examined by Mr. C. 
 Greville Williams, who found it to possess the formula 
 
 I have found that this substance, when heated with a 
 solution of magenta in methylated spirits, produces a 
 
purple colouring matter of great beauty, commonly known 
 as the Britannia violet ; it is very extensively employed 
 for dyeing and printing, and can be produced of any shade, 
 from purple to a blue violet. 
 
 The Britannia violet possesses the golden green lustre 
 so common to all, the aniline colours. It is easily fusible, 
 amorphous, and very soluble in water. 
 
 In my last lecture I showed you the great intensity of 
 the mauve dye. I will now make a few experiments, to 
 illustrate the great intensity of some of the colouring 
 matters we have been considering this evening. 
 
 I have here some screens of white paper, on which I 
 have dusted a very small quantity of the solid colouring 
 matters, so small a quantity that I dare say you can 
 scarcely discover its presence. If I now project spirits 
 of wine upon these screens, so as to dissolve the colours, 
 you will see their remarkable intensity. 
 
 Let us now consider for a moment the great rapidity 
 with which the discovery of new coal-tar colours followed 
 that of the mauve or aniline purple. 
 
 Aniline purple was discovered in 1856 ; tlirce years 
 afterwards, in 1859, the magenta was introduced. In 
 1861 we had the aniline blue; in 1863 the Hofmann 
 violet; and in 1865 the Britannia violet. Thus we see 
 that all these colours have not only been discovered, 
 but introduced commercially, in a period of less than 
 ten years. 
 
 We have now reviewed the principal coal-tar colours, 
 but there still remain some important ones for our con- 
 sideration next lecture ; and although some of these 
 are not at present largely used, yet it is to them, per- 
 haps, that we may look for the future development of 
 this branch of industry. 
 
 LECTURE III. DELIVERED MONDAY, DECEMBER 21sT, 1868. 
 
 VARIOUS ANILINE, PHENOL, AND NAPHTHALIN COLOURS -APPLICATION OF THE COAL 
 
 TAR COLOURS TO THE ARTS. 
 
 Last lecture we considered, among other subjects 
 magenta and some of its coloured derivatives, as the' 
 blues and violets. This evening we commence with 
 some of the green colouring matters which have also 
 been produced from magenta. The first green colouring 
 matter we shall consider is the "aldehyd green," which 
 owes its name to a substance called "aldehyd" being 
 employed in its preparation. I must, therefore, first tell 
 you what aldehyd is. 
 
 Aldehyd is a product of the oxidation of alcohol ; it is 
 a volatile liquid possessing a very peculiar odour, and 
 was discovered by a chemist named Dobereiner, but 
 analysed by Liebig. It is obtained by treating alcohol 
 with a mixture of bichromate of potassium and sulphuric 
 acid, and was generally prepared in glass retorts, but, 
 now that it is required for colour making, the glass 
 apparatus is replaced by copper or leaden vessels. 
 
 Towards the end of 1861, M. Lauth described a 
 reaction by which rosaniline could be made to produce a 
 blue colouring matter ; but this product was found to be 
 useless as a dye, on account of its instability. It was 
 produced by the action of aldehyd upon a solution of 
 rosaniline and sulphuric acid. This useless colour was 
 afterwards experimented upon by a dyer named Chirpin, 
 who, after a number of fruitless attempts at fixing it, 
 told his difficulties to a photographic friend, who 
 evidently thought if it was possible to fix a photograph 
 it was possible to fix anything else. He, therefore, 
 advised his confidant to try hyposulphite of sodium. 
 On making this experiment, however, the dyer did not 
 succeed in fixing his blue, but found ic converted into a 
 splendid green dye, now known as aldehyd green. 
 
 To prepare this colouring matter, a cold solution of 
 magenta, consisting of one part of colouring matter 
 dissolved in a mixture of three parts of sulphuric acid. 
 and one part of water, is employed ; about on" and a -hall 
 parts of aldehyd arc added by degrees to this solutim. 
 and when the whole is mixed it is heated on a water 
 bath, until a drop of the product diffused in water 
 produces a fine blue colouration. It is then poured into 
 n. Large quantity of boiling water, containing three or 
 four times as much hyposulphite of sodium as the 
 magenta employed. After boiling a short time the 
 product is filtered off from a greyish insoluble residue 
 which forms, The filtrate contains the green. This process 
 
 I being a very simple one, a great number of dyers now 
 I prepare the colouring matter as they require it. It may, 
 however, be precipitated by means of tannin or acetate 
 of sodium, collected on filters and drained to a paste, and, 
 if necessary, dried. In both these forms it is found in 
 the market. 
 
 The aldehyd green is principally employed in silk 
 dyeing. It is a splendid colour, and very brilliant both 
 by day and artificial light. The chemistry of this green 
 is at present hidden in obscurity, as it is very difficult to 
 obtain in a chemically pure condition. But like the 
 colouring matter previously described, it is undoubtedly 
 the salt of an organic base apparently containing sulphur. 
 
 This base is colourless, or nearly so, and becomes 
 changed to the normal colour of aldehyd green upon 
 absorption of carbonic acid. 
 
 It will also decompose ammonia salts, combining with 
 the acid and becoming green. I have here a solution 
 containing the colourless base of this green, an ammonia 
 salt and a little free ammonia. If I pour it upon a 
 piece of white blotting-paper it does not stain it, but if I 
 heat it the ammonia salt is decomposed, and we get the 
 green developed with its ordinary intensity. 
 
 There is another green of an entirely different nature 
 to the aldehyd green; it is called the iodine green. 
 This colouring matter is always produced, but in variable 
 quantities, in the preparation of the Hofmann violets, 
 from magenta and iodide of ethyl or methyl. Of late 
 much attention has been directed to this colouring 
 matter, and by making a few alterations in the process 
 for preparing the Hofmann, from forty to fifty per cent, 
 of product can now be obtained from the magenta used. 
 The iodine green is much used for cotton and silk dyeing ; 
 its colour is Uuer than that of aldehyd green, and it is, 
 therefore, more useful, as it yields, with the addition of 
 yellow, a greater variety of green shades. 
 
 Iodine green contains an organic base which is not 
 precipitated by alkaline carbonates. With picric acid 
 it forms <i difficultly-soluble- pi crate, and is generally 
 prepared on the Continent as a paste consisting of this 
 colour precipitated with picric acid and drained on a 
 filter. In England it is, however, sold in alcoholic 
 solution. It is a good green by gaslight. 
 
 The next green I have to bring before you is a magenta 
 derivative, commercially called " Perkin's green." In its 
 
properties it resembles more closely the iodine than the 
 aldehyd green, but differs from this in its solubility, and 
 in being- precipitated by solutions of alkaline carbonates, 
 as carbonate of sodium. It is an organic base which is 
 nearly colourless, and is by no means a chemically 
 powerful body. Like the iodine green, it is precipitated 
 by picric acid, forming a picrate which crystallises from 
 alcohol in small prisms with a golden reflection. This 
 colouring matter is principally employed for calico 
 printing, and is now extensively used. Thus you see 
 we have three aniline greens, some useful for one, and 
 some for another purpose, so that the silk and cotton 
 dyer, and the calico-printer, as well as others can be 
 supplied. For fastness these greens are, I think, quite 
 as good as the violets ; the aldehyd green, however, I 
 believe, resists light the best. 
 
 S In the formation of the mauve, or aniline purple, there 
 is always a small quantity of a second colouring matter 
 i produced, of a rich crimson colour, similar to that of 
 v safflower. Several years ago I examined this substance, 
 ', and found it to dye silk a remarkably clear colour, but 
 owing to the press of other matters, and the very small 
 quantities in which it could be obtained, I did not give 
 it any further attention. By a new process, however, 
 it can now be produced in somewhat larger quantities, 
 and endeavours are being made to introduce it to the 
 arts, as it produces beautiful tints of pink upon silk 
 and cotton, and, moreover, can be used for printing 
 cotton, silk, and wool processes, to which safflower cannot 
 be applied as it will not bear steaming. This aniline 
 pink or crimson is a beautiful chemical body, crystal- 
 lising in small prisms, possessing a golden green lustre. 
 It is soluble in alcohol, and also in water ; it produces 
 solutions remarkable for their fluorescence, so much so, 
 that by certain lights they appear as if filled with a pre- 
 cipitate. In colour and fastness it is equal to safflower, 
 and should it be found possible to manufacture it at a 
 moderate price, I should imagine it would entirely 
 supersede that colouring matter, especially as it is not 
 affected by alkaline solutions. 
 
 There is a product in the English market supposed to 
 be an aniline colour called "Field's orange," after its dis- 
 coverer Mr. Frederick Field. Its properties are those 
 of a nitro-acid, but as its preparation has not been 
 described, of course I cannot tell you anything about it. 
 With alkalies it forms a rich orange-coloured solution, 
 but by the addition of an acid it is precipitated as a pale 
 yellow powder. 
 
 Field's orange is a very useful colouring matter, 
 having a great affinity for animal fibres, and is ex- 
 tensively used for wool-dyeing, as it resists the action of 
 light very well. 
 
 We now come to a colouring matter of a very indefinite 
 nature. I refer to aniline black. This substance appears 
 to be closely allied to the insoluble part of the black 
 precipitate formed in the manufacture of the mauve. 
 This precipitate, however, always contains oxide of 
 chromium, which cannot exist in the aniline black 
 generally employed, as no chromium compound is used 
 in its preparation, but as copper compounds are used, it 
 may be that aniline black represents the black precipi- 
 tate with the oxide of chromium replaced by the oxide 
 of copper, or it may even be that in either case the 
 metallic oxide is not an essential part of this black 
 substance. 
 
 Aniline black is perfectly insoluble, and has, therefore, 
 to be formed upon the fibre when employed for calico 
 printing. As we shall have to refer to its application to 
 dyeing and printing, I will not make any further remarks 
 upon it just now. 
 
 From mauve and magenta, chocolate maroons and 
 browns are prepared, but, as they are of secondary 
 importance as yet, I will only just mention one or two 
 of the methods of preparing them. 
 
 One of the processes for preparing chocolate from 
 magenta is by the action of nitrous acid, but care has to 
 be taken to watch the progress of the operation, and to 
 
 stop it when the required shade has been obtained. 
 Another process consists in heating magenta with hydro- 
 chlorate of aniline to a temperature a little above 200 0, 
 The product, when purified, produces a maroon colour. 
 Browns are generally obtained from the residue of 
 magenta making. 
 
 All the colouring matters we have considered up to the 
 present time are derivatives of aniline and toluidine, and 
 constitute nearly all the colours of the rainbow. 
 
 By the action of nascent hydrogen upon dinitrobenzol, 
 Mr. A. H. Church and myself obtained, in 1857, a 
 crimson colouring matter, which was named nitroso- 
 phenyline. I have lately made a few new experiments 
 upon this remarkable body, and find that it has an affinity 
 for pure cotton, dyeing it of a clear cerise colour, con- 
 siderably less blue in tint than safflower. With very 
 dilute acids, this colouring matter forms a blue solution ; 
 with less dilute acid, a crimson colour ; and with con- 
 centrated sulphuric acid, a green colour. It is difficult to 
 judge of the probable utility of this colouring matter, as 
 it is so difficult to obtain in quantity by the present 
 process. I may mention that my new experiments with 
 this substance have caused me to doubt the purity of the 
 product examined by Mr. Church and myself ; and this 
 is not remarkable when we consider how few methods of 
 purifying artificial colouring matters were known at the 
 date of our experiments, as well as the small amount of 
 substance at our disposal. 
 
 We now turn to a product very different from aniline, 
 though related to it in some respects very closely. On 
 the table you will see a coal-tar product called "phenol" 
 or " carbolic acid." It was discovered, along time since, 
 by Kunge, and afterwards studied by a great number of 
 chemists. It is only, however, during the last few years 
 that it has been introduced into commerce in a pure condi- 
 tion, thanks to Dr. Grace Calvert, so well known to the 
 Society of Arts. 
 
 Phenol or carbolic acid is a splendid crystalline body, 
 possessing many most interesting properties ; but I must 
 confine myself to a short account of its coloured deriva- 
 tives only. 
 
 Carbolic acid, when treated with nitric acid, yields a 
 yellow acid, known as picric acid. This substance can 
 be produced from many other bodies besides carbolic 
 acid, and when first employed for dyeing purposes was 
 generally prepared from the resin of the Xanthorrhea 
 hastilis, but now, owing to the cheapness and purity of 
 carbolic acid, I believe it is exclusively used in its manu- 
 facture. Picric acid requires care in its preparation, if 
 phenol and strong nitric acid be employed, as the action 
 is very violent. Pure picric acid is of a very pale yellow 
 colour ; it is employed principally for silk dyeing, the 
 colour it produces on silk being much darker than that 
 of the acid itself. Picric acid has a very bitter taste, and 
 by some it is said to be a great improvement upon hops, 
 in the manufacture of bitter beer, especially as it has 
 been proposed as a tonic in place of quinine. Picric acid 
 forms beautiful yellow salts, the most interesting being 
 that of potassium. This salt is extremely insoluble in 
 water, and very explosive ; it has been proposed as a 
 substitute for gunpowder for charging shells. Picric 
 acid, under the influence of cyanide of potassium, is 
 perfectly decomposed, and changed into a new compound 
 called isopurpuric acid, a substance isomeric with 
 murexide. The potassium salt of this compound is very 
 explosive, and, to avoid danger, it is generally supplied 
 in a moist condition, and mixed with glycerine. It pro- 
 duces a kind of maroon colour upon wool, but I do not 
 think it has been extensively used up to the present. 
 
 Eunge, when experimenting with the products of the 
 distillation of coal, obtained two compounds, called by 
 him rosolic and brunolic acids, which he regarded 
 as products existing in coal-tar ; I think it most pro- 
 bable, however, that these bodies were produced in his 
 process of purification, and did not exist ready formed 
 in coal-tar. 
 
 Rosolic acid was afterwards examined by Dr. Hugo 
 
16 
 
 Miiller, who obtained it from crude carbolate of calcium, 
 which had been exposed to the oxidising action of the 
 air. This process, however, does not yield rosolic acid 
 in quantity, but in 1861, Kolbe and Schmitt described a 
 method of producing this substance, by heating a mixture 
 of oxalic, carbolic, and sulphuric acids. It is stated, 
 however, that this process was discovered by M. Jules 
 Persoz, in 1859. It is by this method that rosolic acid is 
 now manufactured. 
 
 Commercial rosolic acid, commonly called aurine, is a 
 beautiful brittle resinous substance, having a slight 
 green metallic lustre ; when pure it may be crystallised, 
 and if pulverised forms a scarlet orange powder. Its 
 solutions are of an orange colour, but change with 
 alkalies to a most magnificent crimson. It has not 
 been found capable of very many applications in dyeing 
 and printing, although it produces very good orange 
 shades, and with magenta it makes a very good scarlet. 
 
 The great difficulty in applying rosolic acid to the 
 arts is owing to the easy solubility of its salts in water. 
 It appears to be closely allied to rosaniline, as it has 
 lately been found possible to obtain it from this colouring 
 matter. 
 
 When heated with ammonia, in a closed vessel, 
 to 120 or 140 C., rosolic acid permantly changes into 
 a new colouring matter of a crimson shade, called 
 "peonine" or "coralline." It forms beautiful tints 
 upon silk, similar to safflower, provided it is kept slightly 
 alkaline, but if treated with the least quantity of acid 
 the freshness of its colour is destroyed. When heated 
 with aniline this colouring matter undergoes a similar 
 change to magenta, being converted into a blue called 
 azuline. This colouring matter, as well as coralline, was 
 discovered by M. Jules Persoz, and patented by M. M. 
 Guinon Mamas and Bonnet in 1862. Azuline, when in 
 the solid state, presents a coppery coloured surface, it is 
 soluble in alcohol, but difficultly so in water. It is not 
 manufactured now, having been replaced by the more 
 brilliant blues obtained from rosaniline, and described in 
 our last lecture. 
 
 We must now turn our attention to another series of 
 coal-tar colours, derived from a beautiful product called 
 naphthaline. You will see it on the table of coal tar 
 products, it is a hydrocarbon containing 
 
 and may be obtained in any quantity. It is remarkable 
 for the readiness with which it sublimes, and, like benzol 
 and toluol, it yields with nitric acid a nitro-compound 
 called " nitronaphthaline," a beautifully crystalline 
 body, and this, with iron and acetic acid, yields an 
 organic base called " naphthylamine." This base is 
 solid, and beautifully crystalline, but possesses a very 
 disagreeable odour. 
 
 Mr. Church and myself obtained from a salt of 
 "naphthylamine " and a mixture of nitrite of potassium 
 and potash, a beautiful substance crystallising in orange 
 needles with a green lustre. It is called by a rather 
 long name " azodinaphthyldiamine." 
 
 This substance is a feeble organic base, and dissolves 
 in alcohol, forming an orange-coloured solution, which 
 changes to a splendid violet colour upon the addition of 
 hydrochloric acid. It has, however, been found useless 
 as a dye, because the purple colour only exists in the pre- 
 sence of free acid, and the orange-colour of the base 
 itself is liable to turn brown when exposed to the light. 
 It would appear probable, however, that azodinapthyl- 
 dinmine may become useful as the starting-point for new 
 colouring matters, as I have lately succeeded in producing 
 from it a very promising crimson substance, possessing 
 a considerable affinity for animal fibres. 
 
 A very beautiful yellow colouring matter has been 
 obtained by Dr. Martius from napthylamine, somewhat 
 similar to picric acid, but of a much more intense colour. 
 It is prepared by treating hydrochlorate of naphthylamino 
 with nitrite of potassium; by this means a Mibstnnco 
 known as diazonaphthol is obtained ; this is then heated 
 
 with nitric acid, and is transformed into the new 
 yellow, chemically known as dinitronaphthol. This sub- 
 stance is commercially called Manchester yellow. It 
 possesses the properties of an acid. The commercial 
 compound consists of a beautifully-crystalline calcium 
 salt, soluble in water, and dyeing silk or wool a mag- 
 nificent golden yellow colour. 
 
 Owing to an increasing demand for bonzoic acid, ex- 
 periments have lately been made, with a view of obtain- 
 ing it from naphthaline instead of gum benzoin, &c. For 
 this purpose experiments were made with an acid derived 
 from naphthaline, called phthalic acid, which, when care- 
 fully heated with lime, is found capable of yielding 
 benzoate of calcium, from which benzoic acid can be 
 prepared. But as in these processes secondary compounds 
 are formed, which interest us this evening, I will briefly 
 describe the process employed for obtaining these various 
 substances. 
 
 First of all, naphthaline is heated with a mixture of 
 chlorate of potassium and hydrochloric acid ; in this way 
 a mixture of chloronaphthalineandbichloronaphthaline is 
 obtained. These products are then heated with nitric 
 acid, and yield a mixture of phthalic acid, and a substance 
 called the chloride of chloroxynaphthyl. The phthalic 
 acid is converted into the calcium salt, and heated with 
 slaked lime to a temperature of 350 or 370 C., to con- 
 vert it into a benzoate. 
 
 It is, however, the chloride of chloroxynaphthyl which 
 interests us now. This substance, when heated with an 
 alkali, yields the salts of an acid called chloroxynaphthalic 
 acid, which may be obtained in a free state by means of 
 hydrochloric acid. When pure, chloroxynaphthalic acid 
 is a pale yellow crystalline powder, forming beautiful 
 compounds with baryta, zinc, and copper. It dyes wool 
 a scarlet colour. The great interest of this substance 
 consists in its stipposed relationship to alizarine, the 
 colouring matter of madder, the only difference in 
 composition of chloroxynaphthalic acid and alizarine 
 being in the former containing an equivalent of chlorine 
 in place of hydrogen, thus : 
 
 C 10 H 6 3 Alizarine. 
 
 C 10 (H 6 C1.)0 3 Chloroxynaphthalic acid. 
 
 Many endeavours have been made to remove this 
 chlorine, and to put hydrogen in its place, with the 
 hopes of producing alizarine ; but, up to the present 
 time, no definite results have been obtained. 
 
 I am inclined to think that, although this relationship 
 of composition exists between these bodies, yet that their 
 chemical nature is quite dissimilar. We generally find 
 that chlorinated bodies have similar properties to those 
 from which they are derived or represent. Chloroxy- 
 naphthalic acid, however, does not appear to possess 
 properties similar to alizarine. This acid dyes wool 
 readily without a mordant ; alizarine only slightly 
 stains it. When boiled with cloth prepared with alu- 
 mina or iron mordants, it scarcely produces any change, 
 while alizarine yields intense colours. 
 
 This process of preparing benzoic and chloroxynaph- 
 thalic acids is carried out on the large scale in France, by 
 MM. P. and E. Depouilly, to whom I am indebted for the 
 specimens of these products shown in this lecture. Some 
 of the chloroxynaphthalates are beautifully-coloured salts, 
 and are used as pigments. 
 
 Laurent in his researches obtained a body from 
 naphthaline called carminaphtha. This product is now 
 claiming the attention of manufacturers, and is said to 
 produce very fine shades of colour upon fabrics. 
 
 llrfuro making any further remarks upon the coal 
 tar colours, I wish to draw your attention to some of 
 their applications to the arts. 
 
 I Inve told you that most of the coal tar colours 
 contain carbon, hydrogen, and nitrogen, and that they 
 are generally organic bases. They differ essentially 
 from most of the vegetable colouring matters, which 
 contain, with but few exceptions, only carbon, hydrogen, 
 and oxygen, and are weak acids. You will thus under- 
 
17 
 
 stand that many difficulties had to be encountered in 
 their application for dyeing and printing, because they 
 would not combine with the ordinary mordants used for 
 the colouring matters of woods, as alumina and oxide 
 of tin. These observations refer .to the dyeing and 
 printing of vegetable fibres, and not to silk or wool, as 
 these materials absorb the coal tar colours without the 
 intervention of a mordant. 
 
 In silk dyeing, the principal difficulty experienced in 
 applying the coal-tar colours was owing to their great 
 affinity for the fibre, thus preventing the dyer from 
 obtaining an even colour, especially when dyeing light 
 shades. After a time, however, it was found that this 
 obstacle could be overcome by dyeing the silk in a weak 
 soap lather, to which the colour had been added. This 
 not only caused the dyeing to proceed with less rapidity, 
 but also kept the face of the silk in good condition. 
 Silk dyed by this process is left soft, but may afterwards 
 be rendered hard or "scroop" by rinsing in a bath of 
 slightly acidulated water. 
 
 This process was first used for dyeing silk with the 
 mauve or aniline purple. It has, however, been since 
 found suitable for nearly all the aniline colours, as 
 magenta, Hofraann, and Britannia violets, &c. For 
 dyeing silk with coal-tar colours of an acid nature, such 
 as picric acid, dinitronaphthol, &c., the silk is simply 
 worked in a cold aqueous solution of the colouring 
 matter, sometimes slightly acidulated, as when using the 
 sulpho-acids of aniline blue or soluble blue. The 
 process of printing silk with aniline colours is com- 
 paratively simple. An aqueous or alcoholic solution of 
 the colouring matter is thickened with gum Senegal, 
 printed on with blocks, and, when dry, exposed to the 
 action of steam for about half-an-hour. The gum is then 
 washed off, and the goods finished. 
 
 In my last lecture I referred to the formation of two 
 colourless products from magenta, the one called 
 leucaniline, and the other hydrocyanrosaniline. 
 
 Some few years since, it was found that if silk dyed 
 with magenta has the reagents necessary for the for- 
 mation of these colourless products printed upon it, 
 what is called a discharge style can be produced. One 
 of the substances used for effecting this change is 
 powdered zinc mixed with gum. This process also 
 applies to all the coloured derivatives of magenta, and 
 yields better results than can be obtained by printing on 
 the colouring matter and leaving the white parts, 
 because the colours are always clearer when dyed than 
 when printed. But this is not all. "When printing two 
 colours on silk, say a pattern with a green ground and 
 purple spots, two blocks have to be used, the one for the 
 ground and the other for the spots ; and, when removing 
 the first block, the silk often moves slightly, therefore 
 when the spots are put in by the second block they do 
 not exactly register, and thus an imperfect result is 
 obtained. This difficulty, however, can be avoided by 
 taking silk dyed with any of the derivatives of magenta, 
 and printing it with the discharge previously mixed 
 with the colour it is desired to introduce, of course 
 employing 'a colouring matter which is not affected by 
 the discharge, as aniline purple, aniline pink, &c. 
 This discharge style has only been employed for silk at 
 present. 
 
 We will now turn our attention to the methods of 
 dyeing wool. These methods, as a rule, are very simple, 
 the wool being merely worked in a hot aqueous solution 
 of the desired colouring matter, no mordant being 
 required. Acids are generally found to be injurious, a 
 neutral bath being preferred, and the operation finished 
 by bringing the temperature nearly up to that of boiling 
 water. 
 
 With the^blue known as Nicholson's blue, the process 
 of dyeing is different to that just given, and consists of 
 two distinct operations, the wool being first worked in an 
 alkaline solution of the colour, which gives it a kind of 
 grey or slate shade, and then in an acid bath, which 
 developes the colour. 
 
 The printing of wool is similar to that of silk, the 
 colouring matter being simply thickened with gum, 
 printed on the goods, steamed, and then washed. 
 
 The dyeing of cotton with aniline purple at first 
 presented many difficulties. This colouring matter was 
 found to be capable of producing a very beautiful colour 
 without a mordant, and it was proposed to employ it in 
 this manner, but the colour thus obtained would not bear 
 washing, being nearly all removed with hot water and 
 soap. Mordants, such as alum, were then experimented 
 with, but these gave no results. After some time Mr. E. 
 Pullar and myself found a method of applying this 
 colouring matter to cotton, which is based upon the 
 insolubility of the compounds it forms with tannin. In 
 using this process the cotton is first soaked in a decoction 
 of sumac or some other tannin agent, then in a solution 
 of stannate of soda, and, lastly, in water, slightly acidu- 
 lated with sulphuric acid. The cotton thus prepared 
 contains an insoluble compound of tin and tannin, and 
 which possesses a great affinity for aniline purple. The 
 stannate of soda may be replaced by alum, or a solu- 
 tion of tin salt. This method of preparing cotton has 
 been found suitable for nearly all the aniline colours dis- 
 covered since the mauve, and is now almost universally 
 employed in Great Britain for cotton dyeing. Other 
 processes have been proposed for cotton dyeing, but are 
 not so generally employed as the one just described. 
 
 We now pass on to the application of coal-tar colours 
 to the art of calico printing. The mauve, when first 
 introduced, was applied to printing in a very simple 
 manner ; the colouring matter was merely mixed with 
 gum and albumen, printed on the goods and steamed ; by 
 this process the albumen became insoluble, and fixed the 
 colour. Caseine and gluten were sometimes used as 
 substitutes for albumen. Being dissatisfied with this 
 mechanical mode of applying aniline purple, in conjunc- 
 tion with Mr. Grey, I made a number of experiments 
 with a view of obtaining some more chemical method 
 of fixing this colouring matter, and at last succeeded. 
 The process proposed consisted in printing the pattern 
 with a salt of lead, then converting this into the 
 oxide or a basic salt, by passing the goods through 
 an alkaline solution. Thus prepared, they were 
 worked in a boiling solution of aniline purple in 
 soap. In this way a very pure colour was obtained 
 on the mordanted parts, the soap keeping the whites 
 pure. This process, however, was of very limited 
 application, as it could only be applied for single-colour 
 patterns. After this, several processes were patented for 
 the use of tannin for fixing the mauve ; these were based 
 upon the method of dyeing cotton previously mentioned, 
 and some very fast results were obtained, but as these 
 methods are now out of use, I will not describe them 
 further. 
 
 The process now nearly universally employed in the 
 north was discovered by M. Alexander Schultz and 
 myself; in consists in printing the colouring matter with 
 a mordant composed of a solution of arsenite of alumina 
 in acetate of alumina. On steaming the cloth printed 
 with this mixture for about half-an-hour, the colour is 
 firmly fixed in the fibre. After steaming, the goods are 
 generally soaped, and then finished. One of the great 
 advantages of this process is that it can be worked in 
 patterns with a great variety of colours, and is also suit- 
 able to nearly all the aniline colours, as well as the 
 mauve, yielding shades of great brilliancy. 
 
 ^ During the last few years, much attention has been 
 given to the application of aniline black to calico printing. 
 This substance is not prepared in the separate condition, 
 but formed on the fabric ; it is produced by printing a 
 mixture of a salt of aniline, chlorate of potassium, and 
 sulphide of copper, thickened with starch, upon the goods, 
 and in this manner a dull grey impression is obtained ; 
 but, after three or four days ageing, this changes to a 
 dark olive, and is then rendered perfectly black by 
 passing the goods through a dilute solution of carbonate 
 of soda. This colour is very fast, but is inclined to acquire 
 
18 
 
 a slightly green shade by long exposure to the air. 
 Unfortunately, it cannot be printed on with other ,'colours, 
 because when steamed the cotton is destroyed by the acid 
 character of the mixture employed for its formation. It 
 can, however, be printed on at the same time as madder 
 mordants, and these can be afterwards dyed with a 
 lead mordant, so that when passed through bichromate 
 of potassium, a pattern with black and yellow or orange 
 can be obtained. 
 
 The aniline colours have produced quite a revolution 
 in the arts of dyeing and printing, and have made these 
 processes far simpler than they were, and there is such 
 a variety of shades of colour now sent into the market, 
 that the dyer or printer has little else to consider than 
 the intensity of the colour required ; and, in fact, if a 
 dyer has a large order to execute of a particular shade 
 of colour not in the market, he will not trouble about 
 matching it himself, but sends to the colour manufacturer 
 to supply him with a product capable of yielding the 
 required shade. 
 
 Besides dyeing and calico-printing, several other 
 branches of industry have benefited by the coal-tar 
 colours, such as the arts of lithography, type-printing, 
 paper-staining, and colouring, &c. Before they could, 
 however, be used for these various purposes, it was 
 necessary that they should be made into lakes or pig- 
 ments, by union with alumina or other suitable base; 
 but as most of the aniline colours are of a basic nature, 
 it was found impossible to combine them directly with a 
 metallic oxide like alumina ; advantage was, therefore, 
 taken of their affinity for starch granules, and some very 
 brilliant products were obtained by dyeing powdered 
 starch with the cold aqueous solution of these colouring 
 matters. These starch powders, however, are wanting 
 in covering power or body, so that other processes had 
 to be sought for, and now these lakes are made upon an 
 alumina base, by the intervention of tannin or benzoic 
 acid. 
 
 Many attempts have been made to prepare a pigment 
 from rosolic acid or aurine, and this, to some extent, has 
 been accomplished by precipitating a solution of the 
 colouring matter with alumina ; by this process, a bright 
 orange-scarlet coloured product can be obtained ; it is, 
 however, only suitable for paper-staining. I have, 
 therefore, lately been further experimenting in this 
 direction, and have succeeded in forming a very brilliant 
 scarlet pigment, which can be used for printing inks and 
 a variety of other purposes. 
 
 Upon the table there are some specimens of magenta, 
 Britannia violet, aniline blue, green and orange lakes, 
 and also some very beautiful and intense-coloured prepa- 
 rations of coal-tar colours, now generally called carmines. 
 These lakes, when ground with printers' varnish, pro- 
 duce printing inks of very great brilliancy, and are 
 extensively used for this purpose, and Mr. Hanhart, 
 whose name is so intimately connected with the art of 
 lithography, has most kindly furnished me with the 
 various illustrations of the application of these products 
 to lithographic printing for this lecture. 
 
 These lakes in a wet condition are being largely 
 used for paper- staining, and also for paper colouring, 
 as well as for a variety of other less important pur- 
 poses. 
 
 The peculiar bronze surface produced by evaporating 
 a solution of an aniline colour, has been taken advantage 
 of by the manufacturer; and all the bronze bonnets, 
 hats, flowers, and feathers, so much worn in the autumn 
 of last year, derived their lustre from aniline colours. 
 When first employed for this purpose, no fixing agent 
 was used with them, and as they are mostly soluble in 
 water, a shower of rain was often found to cause 
 beautiful purple drops to fall from these bronzed bonnets 
 and hats, and produce a kind of mottled pattern upon 
 the white collars, and sometimes even upon the face of 
 the wearer. 
 
 Aniline colours are used for writing inks, colouring 
 soap, &c., but as these applications are only of small 
 
 importance in a commercial point of view, I will not 
 spend time in speaking about them. 
 
 I have in these lectures brought before you in a rapid 
 I fear too rapid manner, an account of most of the 
 coal-tar colours ; but, before concluding, I should like 
 to show you the close relationship which exists between 
 some of them, especially between those derived from 
 rosaniline or magenta. 
 
 I have endeavoured to show you that the derivatives 
 of magenta closely agree in properties, all of them con- 
 taining colourless organic bases, the colour being de- 
 veloped upon their combining with acids. But I 
 now wish to show you more than this, by briefly 
 explaining their chemical structure. To describe this 
 thoroughly it would be necessary for me to enter fully 
 into the chemical theory of substitution ; but as this would 
 occupy a great deal of time, I must content myself with 
 just mentioning a few facts connected with that subject. 
 
 Rosaniline and its derivatives contain carbon, hydro- 
 gen, and nitrogen, as I have told you on a previous 
 occasion. Chemical substances containing hydrogen 
 often hold it in what is turned a replaceable condition, 
 that is, in such a condition that it may easily be removed, 
 and another substance of equal value (either simple 
 or compound) introduced in its place. A compound 
 substance, capable of replacing hydrogen, is called a 
 "radical/' and I want to speak about two of these 
 radicals, one called ethyl, and contained in iodide of 
 ethyl, the other called phenyl, and contained in aniline. 
 
 Ethyl contains C 2 H 5 
 Phenyl C 6 H 5 
 
 I will first mention a familiar instance of the replace- 
 ment of hydrogen by a radical. Water is composed of 
 two equivalents of hydrogen and one of oxygen, thus 
 
 Now, it is quite easy to remove an equivalent of this 
 hydrogen and replace it by ethyl. 
 
 H 
 
 H 6 ) 
 
 
 
 This is water with hydrogen replaced by ethyl, a replace- 
 ment compound by some very much preferred to water 
 itself ; it is alcohol. 
 
 Rosaniline contains three equivalents of hydrogen, 
 replaceable by radicals. This is the formula of the 
 hydrochlorate of rosaniline, the three separate H's being 
 replaceable : 
 
 (C 20 H 16 ) 
 H 
 H 
 H 
 
 N 3/ HC1. 
 
 Now, what takes place upon boiling this salt with 
 aniline ? The phenyl of the aniline simply takes the 
 place of the replaceable hydrogen, producing what is 
 called triphenylrosaniline. The result of this replace- 
 ment is that the rosanilino salt has been changed from 
 red into blue the bleu do Lyon which is represented 
 thus: 
 
 C,H ) 
 
 y2"l \N 3 ,HC1 
 
 Dr. Hofmann, on observing this relationship, was 
 induced to try whether he could replace the hydrogen 
 in rosaniline by other radicals than phenyl. Ho tried 
 to introduce ethyl by digesting rosaniline with iodide of 
 ethyl, and succeeded in introducing three molecules of 
 the radical ethyl in the place of the three replaceable 
 hydrogens. I will endeavour to show you how this 
 takes place, by the following equation : 
 
19 
 
 N 3 ,HC1. = 
 
 Three molecules of iodide of ethyl. Hydrochlorate of rosaniline. 
 
 HI 
 HI 
 HI 
 
 Three of iodide of hydrogen 
 or hydriodic acid. 
 
 Hydrochlorate of triethylrosaniline. 
 
 Here we see the iodine has simply exchanged its ethyl 
 for the replaceable hydrogen of rosaniline, and the result 
 is a blue shade of the Hofmann violet. 
 
 Now it is not necessary to replace the three hydrogens ; 
 two may be replaced, and we get a less blue violet. 
 Represented thus : 
 
 0, H le ) 
 
 H 
 
 N 3 ,HC1. 
 
 Hydrochlorate of diethylrosaniline. 
 
 Or one may be replaced, and we get a red violet. 
 Represented thus : 
 
 H 
 
 N 3 ,H 01. 
 
 Hydrochlorate of ethylrosaniline. 
 
 When speaking of the violet imperial, I mentioned 
 that it consisted of products intermediate between ros- 
 aniline and the bleu do Lyon. These intermediate 
 substances consist of rosaniline with one or two equivalents 
 
 of hydrogen replaced by phenyl. 
 Up to the pr 
 
 present moment it has only been found 
 possible to replace one equivalent of hydrogen in 
 mauveine, or the mauve dye, and, as I previously men- 
 
 tioned, it is curious that the result of this replacement 
 is perfectly opposite to that which takes place in the case 
 of rosaniline, the replacement of hydrogen by ethyl 
 in rosaniline causing it to become bluer in shade, and the 
 replacement of hydrogen by ethyl in mauveine causing 
 it to become redder in shade. The following is the 
 formula of the hydrochlorate of ethyl-mauveine or 
 dahlia : 
 
 But although I have tried to explain the relationship 
 of these colouring matters as simply as I can, 
 yet, this part of my lecture assumes much of the 
 character of a lecture on theoretical chemistry. 
 Here we are talking about substitution products of 
 bodies, a branch of the highest theoretical chemistry, 
 and it must strike us as remarkable, when we find 
 that these considerations have been pressed upon 
 us, by the discussion of bodies which may now be 
 said to be common dye-stufis. We have also been talk- 
 ing quite in a familiar manner about nitrobenzol, 
 aniline, iodide of ethyl, aldehyd, &c., substances which 
 were, only a few years since, the recherche compounds of 
 the laboratory. In fact, the coal-tar colour industry is 
 entirely the fruit of theoretical chemistry. Let us con- 
 sider the enormous rapidity with which this industry 
 has developed. It only dates from 1856, and now we 
 have large factories for the production of coal-tar colours, 
 not only in Great Britain, but in Germany, France, 
 Switzerland, America, and other countries. I had hoped 
 to have been able to give you a statistical account of 
 this industry, but have not had sufficient time for this 
 purpose. Dr. Hofmann, however, in his report on the 
 coal-tar colours, shown at the Paris Exhibition of 1867, 
 remarks that, "in 1862, the value of these manufactures 
 had risen from nothing to 10,000,000 of francs, or more 
 than 400,000 sterling. At the present day this sum is 
 trebled, which would make it about one million and a- 
 quarter pounds sterling, although the products are 
 much cheaper than they were before." And, now, when 
 you hear of these results, do not forget that they are the 
 truly practical fruits of theoretical chemistry, not studied 
 for the purpose of producing commercial products, but 
 simply for its own sake. 
 
I.\i\ KUSITV OK CA1.1KOUN1A L1BKAKY 
 
 THIS BOOK IS DUE ON THE LAST DATE 
 STAMPED BELOW 
 
 OCT 22 i*/ 
 NOV 7 1917 
 
 MOV 21 1917 
 
 APR 
 
 REC'D LD 
 
 > 1957. 
 
 30i 6,'14 
 

 '-/