TRIPHENTL-CARBINOL DERIVATIVES. These rep resent the first discoveries in the aniline dyes, and some of them are still produced on the larg est possible scale. The fundamental compound of the class is triphenyl-earbinol and its derivatives are properly subdivided into rosanilines, rosolie acids, and phthaleins.
In the rosaniline group. two or three araido groups are introduced in place of hydro gen atoms of the phenyls The di-amido compounds are green; the tri-amido-eompounds are red, violet, or blue. Strictly speaking, the compounds thus obtained are not themselves dyes, but are bases which must first be combined with suitable acids, and thus brought into a soluble form. Their salts are beautifully crys talline bodies in the solid condition, showing colors quite different from those of the solutions, and having peculiar lustres like those of beetles' wings. The solutions have very intense colora tions and stain animal fibres readily and per manently, although they do not fix themselves easily upon cotton or linen. They are the most brilliant and lively dyes, but are strongly af fected by sunlight, and are consequently less use ful than some dyes of other classes. They are generally manufactured by oxidizing processes at a comparatively high temperature, whereby two or three simpler compounds are \v'elded, as it were, into compounds of complex molecular structure. Thus, in the manufacture of the well known magenta dye (a tri-amido-compound) ap proximately equal quantities of aniline, ortho toluidine, and para-toluidine arc heated from 8 to 10 hours with arsenic oxide to 1J0° C., in large iron kettles. A very thick mass results, which can he extracted with hot water, and the compound thus obtained is found to be made up of molecular of aniline. ortho-tolui dine, and para-toluidine, chemically combined.
Rosalie acid and its derivatives are made by the condensation of various phenols, three phenols being condensed into one compound of the rosolie acid group. just as three bases are
condensed into one compound of the rosauiline group. The comparatively few dyes of this group give various shades of red. '1'lle hydroxyl groups, and hence the acid character of the phenols, remain unchanged in the products of condensation; the latter therefore combine with bases, and then they readily go into solution.
The phthaleins differ from the rosolie acids in so far as one of the three phenyls of the triphenyl-carbinol is connected in them with a carboxyl group (MOH), the other two phenyls having one or more hydroxyls apiece, as in the rosolie acids. The phthaleins were discovered by Adolph Baeyer, and are chiefly remarkable for the fluorescence of their alkali salts in solution. They are prepared by heating phenols with plitlialic anhydride and a little sulphuric acid; when resorein is taken as the phenol, a very well-known compound is obtained, which has been called fluorescein, while its sodium salt is known as amain. Solutions of the latter are yellow by transmitted light, but bright green by reflected light. This fluorescence is so intense that it is distinctly noticeable in extremely dilute solutions; so that this salt has been used to trace subterranean watercourses supposed to connect two neighboring bodies of water, the dye being thrown into one of these and fluorescence being subsequently noticed in the other. The potassium salt of a brominated fluorescein is eosin, with a magnificent red and yellow fluorescence. These fluo•escences disap pear on the fibre, but eosin and analogous sub stances impart very brilliant flesh-tints to silk and wool.