1. Kihlborg, L. (to be published).
2. Tridot, G., Tudo, J., Leman-Delcour, G., and Nolf, M., C.R. Acad. Sci., Paris, 260, 3410 (1965).
3. Kierkegaard, P., and Westerlund, M., Acta Chem. Scand., 18, 2217 (1964).
4. Magnéli, A., and Blomberg, B., Acta Chem. Scand., 5, 585 (1951).
5. Freundlich, W., and Pailleret, P., C.R. Acad. Sci., Paris, 261, 153 (1965).