The Collaborative International Dictionary
Phthalin
Phthalin \Phthal"in\, n. (Chem.) A colorless crystalline substance obtained by reduction from phthale["i]n, into which it is easily converted by oxidation; hence, any one of the series of which phthalin proper is the type.
Wiktionary
phthalin
n. 1 (context chemistry English) A colourless crystalline substance obtained by reduction from phthalein, into which it is easily converted by oxidation. 2 (context chemistry English) Any of the series of which phthalin proper is the type.