135 mg of Pb (NO3)2, 86 mg of CdCO3 and 134 mg of CrCl3 were each dissolved in 20 ml of distilled water in separate 100 ml flasks. The solutions were made up to the mark with distilled water to 5 mM solutions of the salts. Buffer solutions for pH range of 1 – 8 were prepared as described by Lange (1973).