Schweitzer and Stephens have recently suggested that the hydration numbers of Al3+and Ga3+and Ga3+in aqueous solutions containing a considerable excess of chloride ion are probably less than six. Hydration numbers as low as 4.64 (in 1.44 M AlCl3+ 2.15 M CaCl2) or 4.61 (in 0.645 M GaCl3+ 3.32 M CaCl2) were obtained.1That Ga3+forms chloro-complexes under these conditions is well known though interaction between Al3+and chloride is considered unlikely in aqueous solution.2–4