Prepd by coupling diazotized o-tolidine with 5-amino-4-hydroxy-2,7-naphthalenedisulfonic acid in sodium carbonate soln: Lewers, Lowy, Ind. Eng. Chem. 17, 1289-1290 (1925); Colour Index vol. 4 (3rd ed., 1971) p 4198. Toxicity study: Anderson et al., Proc. Soc. Exp. Biol. Med. 31, 825 (1934). Review of teratogenicity studies: R. L. Cahen, Clin. Pharmacol. Ther. 5, 480 (1964).