Quiz: Remember the definition of mal de mer?
acid dye n.
Any of a class of dyes that contain acidic groups, usually in the form of sodium or potassium salts, and are used in staining cytoplasm and various acidophilic structures of cells or tissues. Also called acid stain.
any bright-coloured synthetic organic compound whose molecule contains two groups of atoms-one acidic, such as a carboxylic group, and one colour-producing, such as an azo or nitro group. Acid dyes are usually applied in the form of their sodium salts, chiefly on wool but also on silk and, to a limited extent, in combination with a mordant, or fixing agent, on cotton and rayon. These dyestuffs produce bright, usually fast shades in a wide range of colours