1. A. PACZ, US Pat. 1387900 (1921), Br. Pat. 158 827.
2. R. C. PLUMB and J. E. LEWIS, J. Inst. Metals
86 (1957) 393.
3. V. DE L. DAVIES and T. M. WEST, ibid.
92 (1963) 175.
4. C. B. KIM and P. W. HEINE, ibid.
92 (1963) 367.
5. H. FREDRIKSSON, M. HILLERT and N. LANGE, ibid.
101 (1973) 285.