1) Wool-coloring agent 
An acid dye is a dye which is a salt of a sulfuric, carboxylic or phenolic organic acid. The salts are often sodium or ammonium salts. Acid dyes are typically soluble in water and possesses affinity for amphoteric fibers while lacking direct dyes` affinity for cellulose fibers. When dyeing, ionic bonding with fiber cationic sites accounts for fix....
any bright-coloured synthetic organic compound whose molecule contains two groups of atoms—one acidic, such as a carboxylic group, and one ... [2 related articles]
An anionic dye characterised by substantivity for protein fibres and often applied from an acid dyebath.
[n] - dye in which the chromophore is part of a negative ion
noun dye in which the chromophore is part of a negative ion
any of a class of dyes containing one or more acidic groups, as the sulfo group: used in acid solution chiefly for dyeing wool and silk.