DYEING. 



221 



> Substantive 



I Colouring 

 Matters. 



Tests of the 

 goodness of 

 tedigo. 



Composi- 

 tiuii of indi- 

 go. 



Green indi- 

 go. 



Baratat rer- 

 te. 



Ixajninnl 

 by I)r Ban- 



errfu 



ed. When the first of these, he adds, sells at 9s. a 

 pound, the second is commonly thought to be worth 

 7s. and the third 5s. 6d. The finest blue indigo from 

 the East Indies commonly sells 20 per cent, higher 

 even than the finest glowing, (though the last probably 

 contains nearly as much colouring matter as the first) ; 

 and 70 or 80 per cent, higher than the best copper- 

 coloured. 



72. Berthollet has proposed a method of determining 

 the relative values of different specimens of indigo, by 

 dissolving equal portions of each in sulphuric acid, and 

 afterwards destroying their colour by means of oxy- 

 muriatic acid ; that specimen being considered as the 

 most valuable which required the greatest quantity of 

 oxymuriatic acid to destroy its colour. Dr Bancroft 

 has suggested another method of ascertaining the same 

 thing, wliich is more simple, and perhaps not less ac- 

 curate. He proposes to mix equal portions of different 

 solutions in sulphuric acid, and, after diluting these 

 witli a certain quantity of water, to compare the shades 

 of colour possessed by the several mixtures. 



73. According to the experiments of Bergman, one 

 part in nine of indigo is soluble in water by boiling ; 

 and this part appeared to consist of mucilaginous, as- 

 tringent, and saponaceous particles. The astringent 

 particles are precipitated by solutions of alum, sulphate 

 of iron, and sulphate of copper. M. Quatramere also 

 has separated the soluble parts by means of water. He 

 mentions, that their quantity is greater in proportion 

 as the indigo is inferior in quality, and that the n-i- 

 duum, after this operation, is equal to the finest indigo. 

 He accordingly proposes to purify indigo of inferior 

 quality by boiling il in a bag, renewing the water till 

 it acquires no more colour. For the chemical proper- 

 ties and composition of indigo, see CHEMISTRY, vol. vi. 

 p. 112. 



7*. About the year 1790, Mr Alderman Prinsep, 

 who had then lately returned from India, presented Dr 

 Ham-reft with a specimen of indigo which he had pro- 

 cured in that country, and to which he gave the name 

 of green indigo. Dr Bancroft at first entertained the 

 hope of its proving the s:;im- kind of colouring matter 

 as that obtained by the inhabitants of Cochin-china from 

 a plant called tai, which, when macerated and ferment- 

 ed like indigo, yields a green fecula capable of dyeing 

 a beautiful and lasting emerald green. The specimen 

 was too small, however, to enable Or Bancroft to exa- 

 mine its properties with sufficient precision ; but he as- 

 certained, that it differed in several respects from com- 

 mon indigo, and particularly that it did not produce, 

 like that (ubctAQOe, a fixed colour on linen or cotton by 

 topical application. See Bancroft, i. 26' 1. 



7.5. Al*>ut three years afterwards, considerable at- 

 tention was excited, among those who took an interest 

 in the improvements of dyeing, to another species of 

 indigo which had been sent from Calcutta, under the 

 name of Lanital verle. It was described to be a simple 

 uce, and to have been prepared witli water and 

 fire only, " from an indigoferous plant, an ever green, 

 with leaves somewhat resembling those of the laurel, 

 bearing large clusters of small yellow (lowers, ;md pro- 

 ducing seeds in large pods pointed at the end ;" and it 

 was added, " that the seed did not vegetate in Bengal." 

 It was also represented as giving a durable light green 

 colour, without any mordant or basis, to silk and wool. 

 Dr Bancroft soon procured a specimen of this colour- 

 ing matter, and, with his usual zeal, set utxmt an ex- 

 aininatui.: of it* properties. After making a few ex- 

 periments upon it, he discovered that it was a species 



of impure indigo, and that it owed its green colour to Substantive 

 the presence of an olive- coloured matter, which, on be- Colouring 

 ing burnt, appeared to consist chiefly of jcarbon. The ^ ^, 

 manufacture of this dye was therefore abandoned. 



76. Pastel, or woad, also affords a blue colouring pastel or 

 matter, which possesses properties somewhat analo- woad. 

 gous to those of indigo. Two species of plants are dis- 

 tinguished under this name, the isatis tinctoria, and 

 the isatis Ltisitardca. The former is chiefly cultivated 

 in Languedoc, Provence, and Normandy ; and also in 

 some parts of England. The plant, after being cut 

 down, is washed in a running stream, and then dried 

 in the sun as speedily as possible. When it is dried 

 slowly, it is in danger of being spoiled by the colour 

 becoming black. It is next carried to the mill to be 

 ground, and reduced to a paste. In this state it is 

 formed into heaps, which are covered to secure them 

 from rain. At the end of a fortnight these heaps are 

 opened, and beaten, to produce a thorough intermix- 

 ture of the crust formed on the surface with the inter- 

 nal part. It is then made into round balls, and placed 

 in a situation where it may be freed from the moisture 

 which still adheres to it. The balls are afterwards 

 heaped above one another, to undergo the process of 

 fermentation, and evolve the blue colour yielded by 

 the plant. As the process advances, the smell of am- 

 monia is exhaled, and the balls are gradually reduced to 

 a coarse powder ; the state in which woad occurs in 

 commerce. 



77- Pastel affords, without the assistance of indigo, a Extractiea 

 blue colour of considerable permanency, but little lus- of indigo 

 tre. As it yields a, small quantity of colouring matter from wo ^- 

 in comparison of indigo, and of inferior beauty, the 

 use of woad, as a dye, is now almost totally abandoned. 

 As,truc aHirms, that pastel treated like indigofera yields 

 a colouring matter which greatly resembles indigo ; and 

 Chaptal states, that, from experiments which he made 

 in 1795, with the view of adding some vegetables to 

 the list of those which furnish blue colours, he disco- 

 vered that goals rue, sain foin, chick peas, and lucern,^ 

 yielded a blue colour when treated like indigo, which 

 he did not, however, succeed in precipitating. D'Am- 

 bourney also attempted to procure indigo from pastel. 

 He succeeded by letting fresh leaves of pastel ferment 

 in a certain quantity of water ; taking out tlie leaves, 

 and pouring solution of caustic alkali into the liquor, 

 and afterwards filtering. The fecula which remained 

 on the filter, he says, resembles Carolina indigo. Thirty- 

 five pounds of fresh ripe pastel leaves yielded eight 

 ounces of fecula. 



78. Turmeric is enumerated by Dr Bancroft among Turmeric 

 the vegetable colouring matters which he calls substan- 

 tive ; though the little durability which it possesses, as 



a dye, scarcely entitles it to that epithet. Turmeric 

 is the root of the curcuma, of which there are two spe- 

 cies, the rotunda and the longa The former is chiefly 

 cultivated for the use of the dyer. Turmeric is of a 

 very rich colour, and surpasses every other yellow 

 colouring matter in beauty ; but it has a very slight 

 attraction either to stuffs, or the mordants which are 

 iiMi.-illy employed to give fixity to colours. The root 

 must be reduced to powder to be fit for use. It is 

 sometimes employed to give the yellows made with 

 weld a golden cast, and to communicate an orange tint 

 to scarlet ; but its effects soon disappear. 



79. Mr Bayley, who, in 179-% was extensively en- 

 gaged in dyeing silk handkerchiefs to imitate those of 

 India, informed Dr Bancroft that the yellow spots were 

 produced solely by a tincture of turmeric made by di- 



