ANILYTICAL EDITIOS
XIARCH 15. 1940
163
-4cknowledgment I
The authors gratefully acknowledge a grant from the Faculty Research Committee of the University of Pennsylvania, and wish to thank A. Kenneth Graham and H. J. Read for discussing the results of this paper with them.
Literature Cited
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FIGURE2. EFFECTO F TEMPERATURE O S V.4LUE O F FREE SODIUM CYANIDE AS OBTAINED BY TITRATION METHOD AT PH 10.8 complexes of copper exist, such as NaCu(CK’)?, XazCu(CK),, and Na3Cu(CN), (,$,It?). The principal effect of a n increase in temperature of the brass plating solution is to dissociate these complexes progressively into simpler compounds and sodium cyanide. Therefore, a t least two and possibly all three of these complexes must be present together in brass plating baths. On the other hand, we are not certain that an increase in temperature will cause Na?Zn(CN)r to dissociate into NaZn(CN), and NaCN, since there is little if any evidence that the latter complex exists. However, a n increase in temperature raises the p H by increasing the hydrolysis of the free sodium cyanide and carbonate present, and this in turn, due to the amphoteric nature of zinc, increases the free sodium cyanide in the manner pointed out above.
(1) Blum, IT., Trans. Electrochem. Soc , 60, 143 (1931); Metal I d . ( N . Y . ) , 29, 284-5 (1931). (2) Blum, W., and Hogaboom, G. W., “Principles of Electroplating and Electroforming”, p. 384, New York, McGraw-Hill Book Co., 1930. (3) Ibid., p. 387. (4) Glasstone, S., J . Chem. Soc., 1929, 702-13. (5) Graham, A. K., Metal I n d . ( N . Y . ) 36, ~ 279-83 (1938). (6) Heiman, S., and McNabb. W. M., IND.ENQ. Camf., Anal. Ed., 10, 698-701 (1938). (7) Hogaboom, G. B., Proc. Convention Am. Electroplaters’ SOC., pp. 181-90 (1937). (8) Kolthoff, I. hl., and Sandell, E. B., “Textbook of Quantitative Inoreanic Analvsis”. KI. 545. New York. Macmillan Co.. 1936. (9) M e t a l h d u s t r y Publishing Co., New York, “Plating and Finishing Guidebook 1939”, p. 62. (IO) Morris, S., and Lilly, V. G., IND.ESG. CHEM.,Anal. Ed., 5, 407-8 (1933). (11) Pagel, H. A.. and Carlson, W., J . Am. Chem. SOC.,54, 4487-9 (i932). (12) Pan, L. C., Metal Ind. ( N . Y . ) , 30, 4 0 2 4 (1932). (13) Ibid., pp. 438-9. (14) Pan, L. C., Trans. Electrochem.Soc.. 62, 63-9 (1932). (15) Springer, R., Metal I n d . ( N . Y . ) ,35, 174-5 (1937). (16) Wagner, R. M., and Beckwith, M.M., Proc. Convention Am. Electroplaters’ Soc., pp. 147-63 (1938).
Separation of Cadmium from Zinc I
By the Use of Granular Aluminum
Summary Of the many methods reported in the literature for the analysis of free sodium cyanide in brass plating solutions, the method investigated by Pan is the most satisfactory. This will yield reproducible and useful values only if the limits imposed by the sodium carbonate and ammonia concentrations are realized and if the dilution, temperature, and p H are carefully controlled It is true that the titration, when carried out under certain arbitrary conditions-i. e., dilution to 70 ml., p H of sample 10.8, and a t 12’ C.-gives a value of free cyanide which may be mathematically and arbitrarily considered as the amount in excess of the compounds Na2Cu(CN)3 and NaZn(CN)3. However, this is not valid evidence that such a compound as NaZn(CN)3 exists, as Pan contends (14). The authors’ results indicate that a brass plating solution is a mixture of NaCu(CN)*, Na2Cu(CK)3, Na2Zn(CN)(, lJazZnOz, and possibly other complexes such as zinc ammine. The equilihrium among these complexes, and consequently the value of the free sodium cyanide, is shifted by changes in the concentrations of the constituents of the solution, the temperature, and the pH. As Blum (1) has indicated in general for all cyanide plating baths, i t is better to consider this method as giving a quantity which can be readily measured for control purposes. Experimental work is necessary to establish the quantitative relationships between the free cyanide as determined by this method and the various properties of the plating solution and of the brass deposits, which the free cyanide concentration is known to influence.
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F. E. TOWNSEND AND GEORGE N. CADE, JR., National Zinc Company, Inc., Bartlesville, Okla.
T
HE determination of cadmium in the complex materials encountered in metallurgical analysis is usually a lengthy task, mainly because cadmium undergoes almost no specific characteristic reactions on which a quantitative determination can be based. It must therefore be separated from almost all the other metals before its chemical determination can be attempted. Probably the most tedious of these separations is the separation of cadmium from zinc. The method described here does not, entirely replace the conventional hydrogen sulfide method in all cases, but i t does reduce the number of separations often necessary. I n addition, the time required for one separation using aluminum is much less than that required for one using hydrogen sulfide. Reagents Granular aluminum (
