PATENTS

      169.            BENNETCH, L. M.  (Reconstruction Finance Corp.).  Black Oxide of Iron.  United States Patent 2,631,085, Mar. 10, 1953.  Chem. Abs., vol. 47, 1953, p. 7172.

Yellow oxide of Fe(Fe₂O₃·H₂O) is combined with FeO·H₂O in an aqueous slurry to yield black magnetic oxide of Fe(Fe₃O₄).  FeSO₄ solution is treated with just enough NaOH to precipitate approximately 65% of the Fe as FeO·H₂O.  The slurry is oxidized at room temperature with air to form Fe₂O₃·H₂O from the precipitate, and the slurry is then made slightly alkaline by adding NaOH to precipitate the balance of the Fe in solution as FeO·H₂O.  The mixture of hydrates is filtered, washed, and heated for 2 hr. at 200° F. to produce the black oxide.