Prepn from sodium molybdate and CaSO4: Carosella, US 2460974 (1949 to U.S. Vanadium); by heating a stoichiometric mixture of CaO or CaCO3 and molybdic acid: Kroger, Nature 159, 674 (1947). Toxicity studies: L. T. Fairhall et al., “The Toxicity of Molybdenum,” U.S. Public Health Service Bulletin No. 293, Washington D.C. (1945) 36 pp.