Acid dyes are sodium salts of sulphonic acid and a few
carboxyl groups present. They are soluble in water. Acid dyes are so called due
to:
The original number of the class are applied in a bath
containing mineral or organic acid.
As they are sodium salts of organic acids and active color
component is anion.
The acid dyes have a direct affinity towards protein fibres
and polyamide fibres.
The first acid dye was made by Nicholson in 1862, when he
sulphonated aniline blue, it was known at that time as Blue De Lyons. Other
basic dyes were subsequently sulphonated to convert them into acid dyes, making
them more easily applicable to wool than the present basic dyes.Acid
Magenta(C.I. Acid Violet 19) is obtained by the sulphonation of magenta.