1. F. Sutton andJ. Grant, Systematic Handbook of Volumetric Analysis. London: Butterworths Scientific Publication. 1955. p. 314.
2. E. B. Sandell, Colorimetric Determination of Traces of Metals. New York; Interscience Publishers Inc. 1950. p. 260.
3. L. Wilkinson, Analyst83, 390 (1958).
4. G. Schwarzeribach, Complexometric Titrations. London: Methuen & Co. 1957.
5. R. F. Cellini andE. A. Valiente, An. real soc. españ. fisica quim., Ser. B 51, 47 (1955).