1. Coward, H. F., and Jones, G. W., U.S. Bur. Mines 1938, Bull. 279 (Revised)
2. See, e.g., Rice, G. S., Grcenwald, H. P., and Howarth, H. C., U.S. Bur. Mines 1933, Bull. 363;
3. Mason, T. N., and Wheeler, R. V., Safety in Mines Research Board 1931, Paper 64
4. Greenwald, H. P., U.S. Bur. Mines 1939, Rcpt. Invest. 3462
5. Rcpt. Invest. 1932, Bull. 365