Absorption Spectra of Dyes. II. On Non-additivity of Absorption Spectra of Binary Mixtures of a Direct Dye and Some Acid Dyes in Aqueous Solution

Abstract 1. Absorption spectra of mixtures of Direct Sky Blue 6B with p-X-aniline → γ acid, in which the substituent X means H, CH3, OCH3, Cl or NO2, and the components in aqueous solution were observed in the visible and near ultraviolet regions. 2. All the absorption bands showed non-additive property, excepting the bands in the region of 400∼460 mμ of the mixtures of Sky Blue and X-β shown in Figs. 2 and 3. And optical densities of observed bands of a mixture were generally smaller than sums of the values of each component, but when the acid dyes made by α coupling were used as other components, increases were seen at the positions corresponding to wave lengths of the first bands of them. 3. An explanation for these non-additive properties was given by means of the interaction between the corresponding bands of components. 4. At the same time, in this connection, it is pointed out that the apparent single band of the first of p-X-aniline → γ acid in α coupling consists of two bands and similarly the first band of Direct Sky Blue 6B may also consist of two bands.