1. Gmelin, Handbuch der Anorganischen Chemie: Vanadium, 8th ed., Part A, No. 1, 1968, pp. 2 ff
2. Gmelin, Handbuch der Anorganischen Chemie: Niobium, 8th ed., Part A, No. 1, 1969, pp. 1–8
3. Gmelin, Handbuch der Anorganischen Chemie: Tantalum, 8th ed., Part A, No. 1, 1969, pp. 1–6.
4. M.E. Weeks, H.M. Leicester, Discovery of the Elements, 7th ed., 1968, Chapter 8, pp. 322–382.
5. N.N. Greenwood, A. Earnshaw, Chemistry of the Elements, 2nd ed., Butterworths/Heinemann, Oxford, 1997, Chapter 22, pp. 976–1001.