( v ) Phthalein dye e . g ., phenolphthalein , fluorescein , eosin , mercurochrome . ( vi ) Triarybnethane dye , e . g ., malachite green , rosaniline .
Classification of Dyes on the Basis of Application
( i ) Direct dyes These dyes applied directly to fibre and are more useful to the fabrics containing H-bonding like cotton , rayon , wool , silk and nylon , e . g ., martius yellow , congo reu / etc .
( ii ) Acid dyes These are water soluble and contain porar / acidic groups which interact with the basic group of e . g ., Orange-I , congo red , methyl orange , etc . These dyes does not have affinity for cotton but are used for silk , wool , etc .
( iii ) Basic dyes These dyes contain basic group ( like NHz group ) and react with anionic sites present on the fabric . These are used to dye nylons and polyester , e . g ., butter yellow , magenta ( rosaniline ), aniline yellow , etc .
( iv ) Vat dyes Being water insoluble , these cannot be applied directly . These are first reduced to a colourless soluble form by a reducing agent in large vats and then , applied to fabrics . After applying , these are oxidised to insoluble coloured form by exposure . to air or some oxidising agents , e . g ., Indigo , tyrian purple , etc .
( v ) Mordant dyes These are applied with the help of a binding material ( e . g ., metal ion , tannic acid or metal hydroxide ) called mordant . Depending upon the metal ion used , the same dye can give different colours . Alizarin is an important example of such dyes .
( vi ) Ingrain dye These dyes are synthesised directly on the fabric . These are water insoluble and particularly suitable for cotton fibres . Azo dyes belong to this group of dye .
Chemistry in Cosmetics Cosmetics are used for decorating , beautifying or improving complexion of skin . Some of the cosmetics of daily use are as
1 . Creams These are stable emulsions of oils or fats in water and contain emmollients ( to prevent water loss ) and humectants ( to attract water ) as two fundamental components .