Mines and mineral resources. Operating regulations to govern methods of mining and safety and welfare of employees on leased lands on public domain under mineral leasing acts, potash, Oct. 2, 1917 (40 Stat., 297) and Feb. 7, 1927 (44 Stat., 1057), oil shale, sodium, phosphate, Feb. 25, 1920 (40 stat., 437), sulphur, Apr. 17, 1926 (44 Stat., 301), gold, silver, and quicksilver, June 8, 1926 (44 Stat., 710); approved June 2, 1927.