Phthalic \Phthal"ic\, a. [Naphthalene + -ic.] (Chem.)
Pertaining to, or designating, a dibasic acid obtained by the
oxidation of naphthalene and allied substances.
[1913 Webster]
{Phthalic acid} (Chem.), a white crystalline substance,
{C6H4.(CO2H)2}, analogous to benzoic acid, and employed in
the brilliant dyestuffs called the phthaleins.
[1913 Webster]