What is "purpuric acid"

Murexan \Mu*rex"an\, n. [From Murexide.] (Chem.) A complex nitrogenous substance obtained from murexide, alloxantin, and other ureids, as a white, or yellowish, crystalline which turns red on exposure to the air; -- called also uramil, dialuramide, and formerly purpuric acid.

n. (context chemistry English) C₈H₅N₅O₆, a nitrogenous acid that yields alloxan and uramil when hydrolysed, known for its purple salts.