1. The Chemistry of Hydrometallurgical Processes;Burkin,1966
2. Analytical Chemistry, Volumetric Methods, Marmara University, Publ. Number455, Istanbul;Dolen,1988
3. The recovery of tungsten from South African low-grade scheelite concentrates;Fieberg,1986
4. Forward, F.A., Vizsolyi, A.I., 1965. Process for the production of tungstic acid, U.S. Patent 3,193,347.