1. W. J. Traversy, Methods for Chemical Analysis of Water and Waste Waters, Water Quality Division, Department of Fisheries and Forestry. Ottawa. 1971.
2. J. Rodier, Analysis of Water, New York: Wiley. 1975. p. 216.
3. American Public Health Association, Standard Methods for Examination of Water and Waste Waters,12th Ed. New York. 1965. p. 154.
4. L. Meites, Editor, Hand Book of Analytical Chemistry, 1st Edition, New York: McGraw Hill. 1963, p. 6?26.
5. K. Kodama, Methods of Quantitative Inorganic Analysis, New York: Interscience. 1963. p. 256.