2136. MARSH, D. W. (Mineral Pigments Corp.). Wet-Process Iron Oxide. United States Patent 2,633,407, Mar. 31, 1953. Chem. Abs., vol. 47, 1953, p. 7173.

Metallic Fe is oxidized in an acid solution of colloidal ferrous hydrate and ferric salt. An alkali is added to a solution of ferrous salt to produce a colloid at about pH 11. The mixture is heated to 130° F., and ferric ion added to about pH 4. The optimum ratio of ferrous to ferric ion is 1.67:1. After 1-4 hr. aeration, the temperature is raised to 180° F. and scrap Fe added. When the desired color is obtained (after about 90 hr.), the product is separated and dried to yield unhydrated red Fe oxide of low Mn and low Cu content with low oil-absorption characteristics.

MARSHALL, W. H., Jr. See abs. 2788.