The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918
Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.
The Butea frondosa, also called Dhak or Pulas, is a fine tree, 30-40 feet high, belonging to the order Leguminosæ. It is common throughout India and Burma, and is found in the North-West Himalaya, as far as the Jhelum River. The flowers, which in the dried condition are known as tísu, késú, kesuda or palás-képpúl, have a bright orange colour, and, although they are much larger, closely resemble in appearance the common gorseflower (Ulex europæus) with which, indeed, they are botanically allied. Large quantities of the flowers are collected in March and April, and employed by the natives to produce a yellow dye, much used during the "Holi" festival. The dyeing operation, which consists in steeping the material in a hot or cold decoction of the flowers, is virtually a process of staining, because the colour can be readily washed out. On the other hand, a more permanent result is sometimes produced either by first preparing the cloth with alum and wood ash or by adding these substances to the dye-bath.
From the Butea frondosa is also obtained the so-called "Butea gum" or "Bengal kino," employed by the natives for tanning leather, and the tree is of additional interest because in many parts of India the lac insect (Coccus lacca) is reared upon it. This latter, as is well known, causes the formation of stick lac, from which shellac and lac dye are prepared.
Butin, C15H12O5. The flowers are extracted with water, and the extract digested boiling with a little sulphuric acid. A light viscous precipitate devoid of dyeing property separates, and this is removed while hot and the filtrate left over-night. The clear liquid is now decanted from a small quantity of tarry substance, and partially evaporated on the water-bath. A further quantity of a black viscous precipitate thus separates, and when this has been removed the filtrate, after some days, deposits crystals of the colouring principle. For purification the product is dissolved in a little alcohol, the mixture poured into ether, and the solution well washed with water. The liquid is evaporated, and the residue repeatedly crystallised from dilute alcohol (Perkin and Hummel, Chem. Soc. Trans., 1904, 85, 1459).
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* This result has been criticised by Goschker and Tambor, who by the employment of mordanted calico obtained from butin very weak shades. It is, however, certain that by the use of mordanted wool a conversion of butin into butein occurs.Butin and butein dye mordanted woollen cloth identical shades, though as butin gives with an alcoholic lead acetate a practically colourless precipitate, it is not to be regarded as a colouring matter. In other words, butin is merely a colouring principle, and is converted during the dyeing operation by the action of the mordant into the colouring matter butein.*
The following shades are obtained: Chromium. Reddish-brown,
Aluminium. Brick-red
Tin. Full-yellow
Iron. Brownish-black,
and these are strikingly similar to those yielded by some of the hydroxybenzylidenecoumaranones artificially prepared by Friedlander and Rüdt (Ber., 1896, 29, 879) (see above).
The butea flowers contain but a trace of free butin or butein, and the glucoside present, which has not yet been isolated, is probably that of butin. This glucoside does not decompose readily during the dyeing process, hence the flowers do not dye mordanted cotton. In wool-dyeing, where acid-baths are employed, a better result is obtained, although in this case the shades possess but little strength. If the glucoside is first hydrolysed by boiling the flowers with dilute hydrochloric acid, or if sulphuric acid is employed, and the acid then neutralised with sodium carbonate, on evaporation a material is obtained which readily dyes by the usual methods. Such products give the following shades: with chromium, deep terra-cotta; with aluminium, a bright orange; with tin, bright yellow; and with iron, a brownish-olive. The chromium colour is characteristic, and is much redder in tint than that yielded by any known natural yellow dye.
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