AbstractMixtures of thorium and uranyl perchlorates and sulfosalicylic acid have been studied by potentiometric titration with sodium and ammonium hydroxides, respectively, using glass electrode as indicator electrode. No precipitation was observed in these titrations up to pH 8 in the presence of an excess of sulfosalicylic acid. The reaction between thorium and sulfosalicylate ions has been studied spectrophotometrically, using 1:1 uranyl sulfosalicylate complex as an indicator. The latter complex was reinvestigated at pH 3.7 for comparison. By employing Job's method of continuous variations, it was found that thorium and sulfosalicylate ions reacted in a 1:1 ratio at pH 3.7, showing that an exchange reaction had taken place between thorium salt and uranyl sulfosalicylate.