Phthalein

[Sarah]

One of a series of artificial organic dyes made as condensationproducts of the phenols with phthalic acid, and well represented byphenol phthaleïn. Their alkaline solutions are fluorescent. Phenolphthalein, a white or yellowish white crystalline substance made fromphthalic acid and phenol. Its solution in alkalies is brilliant red,but is decolorized by acids, and as this reaction is exceedinglydelicate it is used as an indicator.