1. E. S. Shedd, J. S. Marchant, and T. A. Henrie: US Bureau of Mines Report of Investigations 6362 (1964).
2. E. Morrice, C. Wyche, and T. A. Henrie: US Bureau of Mines Report of Investigations 6075 (1962).
3. D. G. Kesterke, D. C. Fleck, and T. A. Henrie: US Bureau of Mines Report of Investigations 6436 (1964).