CHAMBERS'S INFORMATION FOR THE PEOPLE. 



aniline ; and colouring-matters are prepared from 

 naphthylamine precisely as rosaniline, &c. are 

 prepared from aniline. Thus, Magdala red is 



N 3 I (CiqHeJs and gives violet and blue products, 



when one, two, or three of the ammonia hydrogen 

 atoms are replaced by ethyl, amyl, phenyl, &c. 



Anthracene is a crystalline solid obtained from 

 the least volatile part of the oil of coal-tar that is, 

 from the part which comes over at the very end of 

 the distillation. It has the composition C U H 10 . 

 By oxidation it is converted into anthraquinone 

 (C 14 HgO 2 ), from which, by means of various re- 

 actions, which cannot be detailed here, two colour- 

 ing-matters are obtained namely, alizarine and 

 anthrapurpurine (C 14 H 8 O 4 and C^HgOg). The 

 first of these is identical with the alizarine, and 

 the second isomeric with the purpurine obtained 

 from madder. 



2. Natural Colouring-matters. We shall de- 

 scribe first the colouring-matters obtained from 

 plants. 



Madder is the root of various species of Rubia, 

 especially Rubia tinctorum, Rubia cordifolia, and 

 Rubia peregrina. It is imported from Smyrna 

 and Cyprus, and is also grown near Avignon, in 

 Alsace, and in Holland. Madder contains, besides 

 woody tissue, a bitter extractive matter, and sugar, 

 two substances which give it its value as a dye- 

 stuff; these are ruberythric acid (C so H 22 O n ) and 

 Purfurine (C^HgOg). In the presence of the ni- 

 trogenous substances contained in the madder, 

 ruberythric acid undergoes a kind of fermentation, 

 by which it is converted into a kind of sugar, and 

 alizarine (C 14 H 8 O 4 ). As dyes, the alizarine and 

 purpurine themselves may be used, but more 

 frequently preparations of madder containing them, 

 and known as ' flowers of madder ' and garancine 

 (from garance, the French name for madder), are 

 employed. 



Flowers of madder consist simply of powdered 

 madder, from which the soluble substances have 

 been removed by the action of slightly acidulated 

 water. The water removes the sugar originally 

 present in the madder, and also that produced by 

 the decomposition of the ruberythric acid, and 

 leaves undissolved the woody tissue, the alizarine, 

 and purpurine. The sweet solution thus obtained 

 is sometimes allowed to ferment, and then dis- 

 tilled, thus yielding alcohol. The washed residue, 

 pressed, dried, and again ground, amounts to one- 

 half of the weight of the original madder ; as it 

 contains very nearly all the alizarine and pur- 

 purine, it is therefore nearly twice as powerful a 

 dye-stuff, and besides, gives better colours, as the 

 water has removed various yellow substances 

 which affect the purity of the colour. Garancine 

 is prepared by acting upon madder by means of 

 sulphuric acid. The acid partially destroys the 

 woody matter, and sets free colouring-matter, 

 which in the madder itself is combined and inactive. 

 Thus, 100 parts of madder yield 40 parts of garan- 

 cine, and these 40 parts of garancine have the tinc- 

 torial value of 200 parts of madder. It is this gain 

 of colouring-matter which renders it profitable to 

 manufacture garancine, although the colours pro- 

 duced are not so pure as those obtained from the 

 'flowers.' We have mentioned above that part 

 of the colouring-matter (about one-half) remains 

 combined and inactive in the madder, and can be 

 set free by the action of sulphuric acid. This 



342 



may be done either at once, as in the manufacture 

 of garancine ; or, the woody residue, remaining in 

 the dye-vats after the cloth has extracted all the- 

 colouring-matter that it can from the madder or 

 flowers of madder, may be treated with sulphuric 

 acid, and thus converted into what is called 

 garanceux, an inferior kind of garancine. 



Alizarine and purpurine unite with some me- 

 tallic oxides or hydrated oxides, forming coloured 

 insoluble compounds called ' lakes.' Thus, the- 

 compound of alizarine or purpurine with hydrate 

 of alumina is red, that with hydrated ferric 

 oxide is violet, or, when seen in mass, black. 

 This character, which alizarine and purpurine 

 share with many vegetable colouring-matters, is,, 

 as we shall see, of great importance in dyeing. 



Indigo. This very valuable blue colouring- 

 matter is obtained from a considerable number of 

 plants, belonging to different natural families. 

 By far the most of the indigo of commerce is. 

 derived from plants belonging to the genus- 

 Indigofera natural order, Leguminosce. The 

 most important are Indigofera tinctoria, Indigo- 

 fera disperma, Indigofera Anil, and Indigofera 

 argentea. These indigo plants are chiefly culti- 

 vated in Bengal, Java, China, Egypt, Mexico, and 

 the West Indies. The colouring-matter is mainly- 

 derived from the leaves, so that those varieties- 

 which have most leaves and least wood are pre- 

 ferred. 



In some localities, the leaves are pulled, but 

 usually the entire plant is cut down. The follow- 

 ing is a description of the manufacture of indigo 

 in Bengal. 



The factory contains filters, presses, a boiler, a 

 drying-house, tanks for water, and from 30 to 40 

 vats. These vats are built of brick cemented in* 

 the inside. They are about 20 feet square, by two 

 and a half to three feet in depth. They are 

 arranged in two rows, one behind the other, and 

 on a higher level, so that the contents of a vat of 

 the upper row can be emptied by a tap into one of" 

 the lower row. The plants cut in the morning are 

 packed before evening in the upper row of vats. 

 When the vats are well packed with plants, water 

 is run into them, so as to cover the plants. Fer- 

 mentation then sets in, and lasts from 9 to 14. 

 hours. When this is completed, the liquid, now 

 more or less bright yellow in colour, is allowed to- 

 run into the lower vats. It is then thoroughly 

 stirred by naked workmen with long bamboo- 

 canes. During this agitation, which is continued 

 for two or three hours, the liquid becomes green, 

 and the indigo collects in flocculent particles. It 

 is allowed to settle, and the clear brown liquid is 

 run off by opening holes at different levels in the 

 vat. The precipitate is then boiled in a copper 

 vessel, in order to prevent a second fermentation,, 

 which would injure the quality of the product ;. 

 it is left to settle for twenty hours, and again 

 boiled for two or three hours. It is then run into- 

 a large filter, consisting of a vat, over which are 

 placed bamboos covered with rushes, and over all 

 a stout linen cloth. Most of the indigo remains 

 on the cloth, and what runs through with the- 

 liquid settles in the vat, and is recovered. The 

 indigo collected on the cloth is pressed into- 

 wooden moulds. The bricks so formed are care- 

 fully dried in the drying-house, which is protected 

 from the direct rays of the sun. 



The rationale of this process will be understood 



