1. B. Brenner: Private communication.
2. R. S. Young: Cobalt. (1948) New York. Reinhold Pub. Corp.
3. R. Perrault: Le Cobalt. (1946) Paris. Duwod.
4. A. E. Van Arkel: Reine Metalle. (1939) Berlin. Julius Springer.
5. C. J. Smithells: Impurities in Metals. (1930) New York. John Wiley & Sons Inc.