1. Dewan, J. T., and Allen, K. W., P.R. 76, 181 (1949).
2. Titterton, E. W. (unpublished experiments still in progress).
3. Hemmendinger, A., P.R. 73, 806 (1948), and erratum, P.R. 75, 1267 (1949).
4. Titterton, E. W., and Goward, F. K., P.R. 76, 142 (1949).