1. Data and curves are presented on the absorption spectra of various phthalein derivatives of pyrogallol, hydroxyhydroquinol and phloroglucinol. Correlations are drawn with data previously obtained for phthaleins of the mono-and dihydroxybenzenes.2. The effect on the chemical properties and absorption spectra of the phthaleins, due to the introduction of hydroxyl groups, is discussed.3. Gallein, which is colored in both the solid state and in neutral solution, is shown to be primarily lactoid in structure, but probably in equilibrium with a small amount of the quinoid modification. 4. The unusual behavior of hydroxyhydroquinolphthalein in weakly alkaline solutions both as regards its absorption and fluorescence is described and a possible explanation is advanced.
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