Originally introduced as an antisyphilitic. Initially characterized as 4,4′-(1,2-diarsenediyl)bis[2-aminophenol] dihydrochloride; composition was later determined to be of a mixture of cyclic 3-amino-4-hydroxyphenylarsenic species. Prepn: P. Ehrlich, A. Bertheim, US 986148 (1911 to Hoechst); eidem, Ber. 45, 756 (1912); W. A. Christiansen, J. Am. Chem. Soc. 42, 2402 (1920). Toxicity data: J. F. Schamberg et al., Am. J. Syph. Neurol. 18, 37 (1934). Review of structure: A. S. Levinson, J. Chem. Educ. 54, 98-99 (1977). MS determn of chemical composition: N. C. Lloyd et al., Angew. Chem. Int. Ed. 44, 941 (2005).