1. F. A. Forward and I. H. Warren:Met. Rev., 1960, vol. 5, pp. 137–64.
2. F. Pawlek: German Patent 888,929,1953.
3. 0. C. Ralston:AIME Trans., 1924, vol. 70, pp. 447–70.
4. F. A. Forward: Fifth International Mineral Processing Congress, Paper No. 40, Inst. of Mining and Metallurgy, London 1960.
5. L. S. Getskin, V. V. Yatsuk, and A. P. Panteleeva:Tsvetnye Metaly, English Ed.,May 1965, pp. 24–26.