Stannioxalic Acid

It was shown by Hansemann and Lowenthal that freshly precipitated stannic hydroxide is freely soluble in oxalic acid solution, and that when this solution is evaporated a gummy mass remains; and Pechard, by dissolving stannic hydroxide in potassium hydrogen oxalate solution obtained monoclinic crystals, to which he attributed the formula K₂O.SnO₂.2C₂O₃.7H₂O. Rosenheim and Platsch isolated, however, in the same way, crystals having the composition 3K₂O.2SnO₂.7C₂O₃.5H₂O, and showed that a solution of this substance gives the reactions neither of tin nor of oxalic acid. It is, therefore, the potassium salt of a complex stannioxalic acid. The barium salt, 2BaO.SnO₂.4C₂O₃.2H₂O, obtained by adding barium chloride to a solution of the potassium salt, forms insoluble white needles. The free acid could not be obtained; attempts to isolate it yielded mixtures of colloidal stannic acid and oxalic acid. This power of stannic tin to combine with oxalic acid furnishes a means for the analytical separation of the metal.