ELECTROLYTIC PRECIPITATION O F LEAD FROM ACETATE SOLUTIONS
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BY RALPH C. SNOWDON,
Under ordinary conditions the electrolysis of lead acetate solutions gives large feathery crystals of lead which fall from the cathode to the bottom of the cell. Even if an excess of acetic acid be added, there is no marked change in the size of the crystals or in the quality of the deposit. This solution seemed therefore an admirable one on which to try the methods which had previously proved successful with silver nitrate‘. It had been shown that rapid motion of the electrolyte, produced either by rotating the cathode or by stirring, tends to make the deposit smoother and to re’duce the size of the crystals. It was also shown that the size of the crystals of deposited metal decreases with increasing current density until conditions are reached where the speed of the rotating cathode is not sufficient to burnish the rapidly precipitated masses of metal. Following out the “chemistry” conception of electrolytic precipitation I used a solution of lead acetate and acetic acid, normal with respect to each. Knowing from much previous experience that a satisfactory deposit of lead could not be obtained without stirring, I tried a rotating cathode made of a copper tube having a wetted surface of I O cm2. This was speeded to about 2 500 revolutions per minute. A lead anode was used. At a low current density, 0.j amp/dm2, the metal deposited from this solution in a crystalline and adherent form, almost entirely without the ‘‘ flaky ” appearance which is so noticeable with a stationary cathode. At higher current densities, however, the deposit kept growing worse and worse, falling off in leafy crystals. This was probably because the speed of rotation of the cathode was not high enough for the speed of precipitation, the two always being interdependent to a greater or lesser extent . Snowdon : Jour. Phys. Chem., 9, 392 (1905).
Pyecz@2ation of Lead f ~ o mAcetate Solutions
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Since it was not feasible to increase the speed of rotation of the cathode, I next tried the addition of gelatine to the solution. One gram of gelatine per liter was added; the temperature was kept at 30'; the cathode density was 1.5 amp/dm2; and the other conditions were as in the preceding runs. A matte deposit of lead was obtained, very adherent and entirely satisfactory in every way. It is not claimed that a lead acetate solution would be a desirable one to use in precipitating lead. There are other solutions, notably the fluosilicate, which give an adherent deposit of lead over a much wider range of conditions. The object of the paper was to show that it is quite possible to get a good plating deposit of lead even from an acetate solution and that the favorable conditions are the same for lead as for other metals. This work was suggested by Prof. Bancroft and carried out under his direction. Cor?aell Universiiy.
