Synonyms: 2,7-Naphthalenedisulfonicacid, 4-[(2-arsonophenyl)azo]-3-hydroxy- (9CI); 2,7-Naphthalenedisulfonic acid,4-[(o-arsonophenyl)azo]-3-hydroxy- (8CI); Benzenearsonic acid,o-(2-hydroxy-3,6-disulfo-1-naphthylazo)- (6CI);1-[(2-Arsonophenyl)azo]-2-hydroxy-3,6-naphthalenedisulfonic acid;2-(2-Hydroxy-3,6-disulfo-1-naphthylazo)benzenearsonic acid; ARANS; Naphtharson;Thoron; Thoron (reagent); Thoron free acid