The electrolytic production of lead chromate using periodically reversed direct current and superimposed alternating current on direct current

It was the purpose of this investigation to study the effect of varying the direct to reverse time ratio of periodically reversed direct current from 1.0 to 20.0 on the electrolytic production of lead chromate at an average anode current density of 0.0059 amperes per square centimeter, and to study the effect of 60 and 502.3 ± 7.7 cycles per second from 0.00113 to 0.01546 amperes per square centimeter of peak superimposed alternating current on direct current on the yield of lead chromate prepared by the electrolysis of a bath containing potassium chromate and sodium nitrate between lead electrodes. Electrolysis of a bath containing 3.60 grams of potassium chromate, 11.62 grams of sodium nitrate, end 1000 grams of water with simple direct current yielded 6.07 grams of lead chromate per ampere-hour, the purity being 92.7 percent lead chromate. The anode current density was 0.0049 amperes per square centimeter, and the current efficiency was 98.1 percent. During the electrolysis, by maintaining the ph of the electrolyte at 6.0, by adding a solution to 2.0 weight percent chromic acid, the purity of the product was increased. Electrolysis of the same bath using periodically reversed direct current yielded 4.53 grams of lead chromate per ampere-hour, the purity being 93.9 percent lead chromate. The time ratio was 20.0, the anode current density was 0.0049 amperes per square centimeter, and the current efficiency was 66.75 percent. Decreasing the direct to reverse time ratio gave lower yields and purities. Apparently, there is no advantage in using periodically reversed direct current over the use of direct current for this reaction under the above conditions. Electrolysis of the same bath with alternating current superimposed on direct current yielded 5.49 grams of lead chromate per direct current ampere-hour, at a purity of 99.4 percent lead chromate, when using 494.7 cycle alternating current. The alternating and direct current densities were 0.0078 and 0.0048 amperes per square centimeter, respectively. This was the purest product obtained in this investigation. Use of 60 cycle alternating current yielded 3.83 grams of lead chromate per direct current ampere-hour, at a purity of 93.9 percent lead chromate. The alternating and direct current densities were 0.00141 and 0.00484 amperes per square centimeter. Further experiments were made using direct current and periodically reversed direct current on a bath containing 6.80 grams of potassium chromate, 8.14 grams of sodium nitrate, and 1000 grams of water. Results from these electrolytes were much poorer than those obtained with the previous bath, so no experiments with superimposed alternating current on direct current were carried out with this latter bath.