1. Rüdorff, W. Z., Anorg. Allgem. Chem., 245, 383 (1941).
2. Bloc, F., and Herold, A., C.R. Acad. Sci. Paris, 251, 2038 (1960).
3. Ubbelohde, A. R., and Lewis, F. A., Graphite and its Crystal Compounds, 121 (Oxford Univ. Press, 1960).
4. Nelson, J. B., and Riley, D. P., Phys. Soc. Proc., 57, Pt. 6, 477 (1945).