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CHEMISTRYferenee between the total cathodic diffusion current and the anodic diffusion current.The rate of accumulation of the chloro cuprous complex is shown by curve C in Figure 14. The data in this figure were obtained at a pH of 5.3 at 25°. From the difference between curve A (the total cathodic diffusion current) and curve B (the cathodic counterpart of curve C) the equilibrium concentration of the cupric tartrate complex is calculated to be 1.13 millimolar compared to its initial value of 2.66 millimolar, and the equilibrium concentration of the chloro cuprous complex was 1.53 millimolar -i.e., 57.5% reduction. At a higher pH value the reduction proceeds more rapidly and more completely, and when the copper concentration is greater than about 5 millimolar cuprous chloride precipitates.From the observed diffusion currents the id/Cm2 /3P /6 value for the cupric tartrate complex under the conditions of Figure 14 is 2.38 and that of the chloro cuprous complex is 1.75. Correspondingly, from these data and the Ilkovic equation, the diffusion coefficient of the cupric complex is 0.39 X 10 ~5 and that of the cuprous complex is 0.83 X 10-5 sq. cm. per second. The much larger diffusion coefficient of the cuprous complex accounts for about a third of the greatly enhanced current observed when copper is deposited on a platinum cathode from a solution containing both hydrazine and chloride. SUMMARYThe optimum conditions for the separation and successive determinations of copper, bismuth, lead, and tin from a tartrate solution by controlled potential deposition onto a platinum cathode have been established. The influence of such important variables as pH, total tartrate concentration, temperature, and cathode potential have been investigated systematically. All four metals may be determined without any intermediate treatment of the solution, except acidification for the determination of tin, in a total elapsed time of about 4 hours (1 hour actual operator time). Very few other elements interfere.The beneficial effect of hydrazine and hydroxylamine as addition agents has been investigated, and their oxidation products at a platinum anode have been identified. Hydrazine in the presence of chloride ion is a much more efficient anodic depolarizer than hydroxylamine, and it plays an even more important role by reducing +2 copper to a chloro cuprous complex which greatly accelerates the copper deposition.

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