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Hafnium(IV); Effect of Acidity on the Degree of Polymerization1b2Polymerization of zirconium and hafnium (ca. 0.05 M ) has been investigated by equilibrium ultracentrifugation. Hf (IV) a t this concentration is probably polymerized in 5 M HC1.In the range 0 j-2 M HCl, Hf(1V) is probably either a trimer or tetramer and the degree of polymerization is relatively independent of Hf(IV) and HC1 concentrations.Polymerization of Zr(1V) is similar. The principal difference is that Zr(1L') is more highly aggregated than Hf(I\.') at the lower acidities. Centrifugation of solutions containing varying concentrations of Zr( 11') and of supporting electrolyte in 1 Jf HC1 indicate that the polymers, like those of hafnium, are trimeric or tetramericat this acidity and carry charges of G Q . plus one per monomer unit. The same degree of polymerization was found for Zr(1Y) in 1 -11 HClOd Decrease of temperature from ca. 25' to ca. 5" markedly lowers the degree of polymerization in 0.08 M HC1, in contrast to the small effect observed in 1 M HCl. Aging of ZrOCll solutions, or heating, increased the degree of polymerization signihcantly but did not produce very large polymers.There is definite polymerization in 3 M HC1.At acidities 0.2 M and less, Hf(1V) is more highly polymerized and polydisperse.(1) This document is based on work performed for the U. S. Atomic , ibid., 76. 5769 (1953). This paper reviews zirconium literature and has a more complete set of references than presented here. Earlier literature is reviewed by F. P. Venable, "Zirconium and Its

experiments designed to test the effect of carrier on the separation.Chemistry of Aqueous Uranium(V) Solutions. I. Preparation and Properties.Analogy between Uranium(V), Neptunium(V) and Plutonium(V)1