ON DYES AND DYE-STUFFS OTHER THAN ANILINE.

LECTURE I.—DELIVERED TUESDAY, FEBRUARY 7TH, 1871.

RED COLOURING SUBSTANCES.— MADDER.

This well-known tinctorial substance may still be con-sidered as the most important of all the dye-stuffs em-ployed by calico printers, owing to the brilliancy of the colours, and their permanence under the action of light and soap, and the wear and tear which fabrics so died can sustain, as well as on account of the variety of shade and colour that can be obtained ; one dyeing operation being sufficient to produce pinks, reds, purples, violets, puce, and black ; and, notwithstanding the compétition that madder colours have met with of late years from aniline dyes, I believe the quantity of madder consumed in England is quite as great at the présent day as ever it was.

The employment of madder-root as a dye dates from the most ancient times, as is proved by the Egyptians using madder-dyed fabrics to wrap round their mummies. The Greeks and Romans were acquainted withit under the names of Erythrodanon and Rubia, and their modes of fixing it on cotton fabrics were the same as those now employed, namely, aluminous salts for producing reds, and salts of iron for purples and blacks.

The plant which produces madder is an herbaceous one, and is called Rubia tinctorium. It bears a yellow flower, and a dark red berry fruit. The red colour-ing matter exists almost entirely in the cortical part of the root, little or no colour being found either in the epidermis or in the ligneous or centre part of the root. M. Decaisne and M. Edouard Koechlin have shown that the colouring matter in the fresh root is yellow, and becomes red under the oxidising influence of the atmosphère. The same process goes on, to a certain extent, in the roots of the plant when they are allowed to remain Several yoars in the ground, especially in chalk formations. In France, the roots are allowed to remain in the ground two or three years ; in Turkey and the East, from five to seven. In the latter countries and in Naples, they are dried in the open air, but in Holland and France stoves are employed foi’ this purpose. Naples and Turkey madders are imported in the root, and are known in commerce as Naples and Turkey roots, while those from France and Holland are ground, and sold under the name of French and Dutch madder.

One hundred parts of fresh root yield on perfect desic-cation twenty parts of dried substance. The roots as im-Ported always contain sixteen or eighteen per cent. of water ; the fresh roots, therefore, give 24 or 25 per cent, of commercial madder. Dutch and Alsacian madder, after being ground, is stored in large casks, and kept for two or three years, when the colouring

matter is developed, and its tinctorial power is much increased ; if, however, it is kept five or six years, further changes ensue, and its value seriously decreases. French Avignon madder can be employed at once, although the quality is much improved by keeping it one or two years. The best Avignon madders are grown on lime formations. The roots that have a red colour are called palus, and those that are pink rosées ; the former being considered the finest. The value of these madders is in ratio to the fineness of their powder, the finer powder containing the most colouring matter.

The nature of the Chemical changes occurring in madder during the time it is stored, and which so much improves its commercial value, was entirely un-known until the elaborate and interesting researches of Dr. Ed. Schunck, F.R.S., published in the year 1851. He succeeded in isolating a peculiar ferment called Erythrozym, which possesses the property of de-composing a substance called by him Rubian. Rubian may be considered as a glucoside (this name being given by chemists to compounds of sugar with other organic principles), and is decomposed by erythrozym into a peculiar sugar and Alizarine. Whether there are in the rubia-root several glucosides which unfold themselves respectively into sugar and one of the colour-giving principles, or there is only one glucoside, and its colour-giving principle as it is liberated gets successively oxidised into alizarine, purpurine, &c., is not y et satisfactorily deter-mined. Still, this valuable discovery of Dr. Schunck has thrown much light on the subject, and has led to several important commercial improvements, to which I shall call your attention as I proceed. One hundred parts of dried madder-root consist of—

Soluble in cold water........................ 55 parts.

Soluble in boiling water, and which contains the greater part of the colour-giving principles........................................ 3 J »

Soluble in alcohol ............................ 1:5 „

Fibrous matter .............................. 40-85 „

I shall make no remark on the gum, mucilage, pectine, pectic acid, and pectates which the rubia-root contains, but state that the water extract contains also the yellow colouring-matter discovered by Kuhlmann in 1824, and called by him Xanthine; but this colour bas never received any commercial application, from its want of brilliancy. Water also dissolves another colouring principle called Chlorogenine, which is decomposed by weak acids into sugar and a brownish green matter. Both these

---

Le texte affiché peut comporter un certain nombre d'erreurs. En effet, le mode texte de ce document a été généré de façon automatique par un programme de reconnaissance optique de caractères (OCR). Le taux de reconnaissance estimé pour cette page est de 99,19 %.

La langue de reconnaissance de l'OCR est le Français.

---