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Thymol blue (thymolsulphonephthalein) is a brownish-green or reddish-brown crystalline powder that is used as a pH indicator. It is insoluble in water but soluble in alcohol and dilute alkali solutions.
T 1736 (OTTO) Thymol blue solution Cas 76-61-9 - used to determine the acidity or basicity of solutions.