1. Über die Darstellung des amorphen Bors.
2. W. J. Kroll, Germ. Pat. 381,577, 1916 and 386,602, 1916; W. J. Kroll, U.S. Pat. 1,707,059, 1929.
3. W. J. Kroll, Germ. Pat. 382,077, 1923; 381,049, 1920; 399,399, 1924; W. J. Kroll, U.S. Pat. 1,359,813, 1921.
4. W. J. Kroll, Germ. Pat. 410,533, 1917; 615,566, 1930; 622,135, 1930; W. J. Kroll, U.S. Pat. 1,428,041, 1922.