( 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.