49&

DYEING AND CALICO PRINTING.

case of red woods, logwood, and aniline black. M. Kcechlin thinks that thesal-ammoniac adts by double decomposition, causing the formation of chlorideof copper, which in its turn is converted into protochloride by the catechuin,and together kept in solution by the sal-ammoniac. The last-named salt, bybecoming again oxidised by contad of air, is again capable of ading upon afresh portion of organic matter: the sal-ammoniac cannot be replaced by anyother ammoniacal salt; and although M. Kcechlin states that chloride ofsodium ads in a similar manner, this is denied by Schlumberger, who pur-posely tried it experimentally. Recently it has been found that sulphuret ofcopper can be advantageously used instead of the oxy-salts of that metal.

About the year 1832 the fixation of cutch by means of the bichromate wasfirst applied by MM. Kcechlin Freres, at Mulhouse. The deeper-colouredgoods are steamed before they are padded in the chromate solution, whichshould be sufficiently strong to prevent the colour running, while the solutionis made warm. For bright-coloured goods the steaming is simply replaced byan exposure to air.

The oxidation of the catechuin in the bichromate solution is instantaneous,producing at once a brown colour; the chromate solution itself is reduced tosesquioxide.

M. Schlumberger thinks that there is a kind of chrome-lake formed alongwith the oxidised catechu, the oxide entering into combination and modifyingthe colour produced. M. Heckmann* states that some of the oxide is onlymechanically mixed with the colour, and this is the generally admittedopinion.

Oxidation by means of passing the goods through milk of lime is anotherprocess, which, although less satisfactory, is employed whenever catechu isprinted on along with such colours as are fixed by means of lime, as is thecase with fast blue. The presence of an alkali or of an alkaline earth aidsthe absorption of oxygen by the catechuin, but this operation is usuallycarried out along with the employment of salts of copper and of sal-ammoniac,and also with the ageing process.

Catechu serves for dyeing bright and deep brown, fawn, drab, and woodcolours, and also for printing. Catechu colours are often associated withgarancin colours, by mordanting with alumina and dyeing up in garancin andcutch, the hue produced is modified, and turned to brownish-red.

The cutch dyes are remarkable on account of their fastness ; they resistalkalies, soap, acids, and even chlorine, in a high degree, and do not admit ofthe application of the discharge process.

Catechu is used either in aqueous deco&ion or hot infusion, or vinegar oracetic acid are mixed therewith, or a solution in caustic soda is used. Thefollowing are instances of the mode of mixing the ingredients:—

Catechu. . 6 kilos.

Soda-lye, at io° Baume (sp. gr. 1*070, containing about)

7*75 per cent of dry caustic soda).J ® h tres *

Water . 8 „

Thicken with gum ; steam, and next oxidise by passing through a bath ofbichromate (containing from 5 to 7 grms. of that salt to the litre of water), ata temperature of from 75 0 to 88° for two minutes.

* “ Bulletin de la Societc Industrielle de Mulhouse,” vol. xiv., pp. 186 and 197.