1. Kollonitsch, J., Fuchs, O., and Gábor, V., Nature, 173, 125 (1954).
2. Carrara, G., Pace, E., and Cristiani, G., J. Amer. Chem. Soc., 74, 4949 (1952).
3. Baltazzi, E., and Robinson, R., Chem. and Indust., 22, 540 (1953).
4. Paul, R., and Joseph, N., Bull. Soc. Chim. France, 550 (1952). Chaikin S. W., and Brown, W. G., J. Amer. Chem. Soc., 71, 125 (1949).
5. Grassmann, W., Hörmann, H., and Endres, H., Chem. Ber., 86, 1477 (1953).