Archive image from page 110 of Cytological technique; the principles underlying. Cytological technique; the principles underlying routine methods cytologicaltechn00bake Year: 1960 THE CHEMICAL COMPOSITION OF DYES 91 Beyond auxochromes and chromophores, dyes often possess atoms or groups of atoms that are called modifiers. Thus rosani- NH NH, + Rosaniline line differs from pararosaniline only in the possession of a single methyl group; this modifies the colour, making it very slightly bluer. (Basic fuchsine is a mixture of these two closely related dyes.) The methyl group is here a modifie
Archive image from page 110 of Cytological technique; the principles underlying. Cytological technique; the principles underlying routine methods cytologicaltechn00bake Year: 1960 THE CHEMICAL COMPOSITION OF DYES 91 Beyond auxochromes and chromophores, dyes often possess atoms or groups of atoms that are called modifiers. Thus rosani- NH NH, + Rosaniline line differs from pararosaniline only in the possession of a single methyl group; this modifies the colour, making it very slightly bluer. (Basic fuchsine is a mixture of these two closely related dyes.) The methyl group is here a modifier. It has been mentioned that the hydrogens of basic auxochromes may also be replaced by methyl or ethyl or aryl groups; this again modifies the colour. Each replacement of one of these hydrogens in pararosaniline by methyl makes a bluer dye, and cr)stal violet, in which all six are replaced, is nearly blue. Ethyl and particularly aryl groups have even more blueing effect, and purely blue dyes such as methyl blue (p. 94) may be obtained in this way. Dyes are classified into groups by their chromophores. Most of these groups contain both cationic and anionic dyes, possessing the auxochromes mentioned above; many of them in all groups have modifiers (frequently methyl or ethyl). The great majority of the dyes used in microtechnique owe their colour either to the quinonoid ring or to the azo-group, -N=N- (p. 96). The quinonoid dyes, however, are so diverse that it is necessary to divide them into sub-groups, each characterized by a particular chromophore that can be represented in a skeleton formula. The principles of dyeing in microtechnique can be explained by the use of only a few dyes, belonging to a small number of groups.
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