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2. Daesen, J.R. U.S. Patent No. 2,317,179, issued April 20,1943.
3. Boyle, E.J. U.S. Patent No. 2,472,402, issued June 7,1949.
4. Hydrometals Inc. British Patent No. 927,530, issued May 29, 1963; U.S. Patent No. 99.371.