1. J. R. Boldt and P. Queneau, ed.:The Winning of Nickel, Van Nostrand, N. Y., 1967.
2. H. R. Comwall:U.S.G.S. Bull. 1223, 1966.
3. N. Zubryckyj, D. J. I. Evans, and V. N. Mackieu:J. Metals, AIME, 1965, vol. 17, p. 478.
4. F. E. Joyce:Bureau of Mines, USA, Report of Invest. RI6644, 1965.
5. A. W. Fletcher and M. Shelef:Trans. TMS-AIME, 1964, vol. 230, p. 1721.