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DIVISION II.

CHAPTER I.

THE GENERAL PRINCIPLES OF THE FIXATION OF COLOURING MATTER UPONFIBROUS TEXTURES. CLASSIFICATION OF DYE-MATERIALS.

/ T'' HE substances employed industrially to impart colours to textile fabrics

"*• are of very various origin and different charaders. Some of them playonly a subsidiary part, and are removed as soon as the colouring-matter isdefinitely fixed—such are, for instance, thickeners, acids used as discharges,resists or solvents, oxidising and reducing agents, substances employed only onaccount of their hygroscopic properties, and some others which, of greatutility, have their adion unexplained. Other substances, again, concur eitherwholly or partly to constitute the colour remaining upon the cloth. Indigotineis integrally fixed, while acetate of alumina and chromate of potash are sub-stances employed as agents for the fixing of madder-red and chrome-yellow,deriving their powers from the alumina and chromic acid they contain. Allthese substances are, therefore, dyes or tindorial matters, because for theprodudion of madder-red alumina is as necessary as alizarine itself,which is naturally of a pale yellow-red colour. It is clear, however, thatin a restrided sense alumina cannot be called a tindorial or colour-givingmatter, considering that it does not impart to tissues, nor is itself possessedof, any colour. Colours likewise exist that diredly impart to cloth their owntinge, such as indigotine, carthamic acid, bixine. There also belong to thisclass the oxides of iron and chromium, and ultramarine. A rather too familiarinstance of the tindorial power of oxide of iron occurs in the “ iron-moulding”of linen. But a large number of dyes require the intervention of a mordant.When a substance is dyed red with madder the alumina is the mordant andthe alizarine contained in the madder the colouring matter ; whilst in the caseof chrome-yellow the chromic acid is the colouring matter and the oxide oflead maybe called the mordant. Taking the widest limit of this view, it mustbe admitted that the colour yielded by catechu is the result of the union ofcatechine with oxygen, the latter ading really as a mordant. But the termmordant is now limited in its application to substances in the solid state-There must be no confusion between the colouring matters and mordantsof commerce, and the produce fixed upon the woven fabric; madder,