The classical method for the determination ot rhodium involves its separation from all other heavy metals and final weighing as metal 1. Other gravimetric methods using organic precipitants have been proposed. WATANABE~ used I-nitroso-2-naphthol, with subsequent ignition of the precipitate to the oxide. HAINES AND RYAN 3 precipitated rhodium with 2-mercaptobenzoxazole or 2-mercaptobenzothialoze, finally igniting to the metal. DUVAL et al. 4 recommended the 2-mercaptobenzoxazole precipitate as a weighing form, and the 2-mercaptobenzothiazole precipitate was used as the weighing form by UBALDINI~. DUVAL 4, and also PSI~ENITSrN~, precipitated rhodium with thionalide and used the precipitate as the weighing form; CURRAH et al. 7 used the precipitate formed by reaction of rhodium with thiobarbituric acid.
A titrimetric determination using thionalide, described by KIENITZ AND ROMBOCK 8, is subject to many interferences. Polarographic determination of rhodium has been made in solution as fluoride 9, cyanide or thiocyanate 1~ or pyridine 11. Rhodium can be determined spectrographically 12. Spectrophotometric determination of rhodium has been made with hypochlorite la, and with tin(II) in hydrochloric acid14,15. RYAN 16 proposed 2-mercapto-4,5-dimethylthiazole and 2-mercaptobenzoxazole as spectrophotometric reagents, and WATANABE 17 showed that the precipitate obtained with i-nitroso-2-naphthol could be dissolved in acetone for spectrophotometric measurement.