A CORRECTION BY GEO. H. BURROWS
In a paper entitled Experiments on the Electrolytic Reduction of Potassium Chlorate,” I it was shown that potassium chlorate when electrolyzed in aqueous solution with copper electrodes gives rise to an amount of chloride far in excess of that calculated from the hydrogen equivalent of the current. In the analyses involved, the fact was overlooked that nitric acid containing oxides of nitrogen rapidly reduces potassium chlorate to chloride. Elimination of the error due to this oversight does not affect the nature of the results, but does decrease the numbers expressing the efficiencies, the true maximal efficiency found being 160-170 pct instead of 2 0 0 pct as stated. This correction made, it is found that the ratio between weight lost by the anode of the electrolytic cell and that gained by the copper voltameter cathode equals or exceeds in each case the ratio between the efficiency found and what we may call the theoretical efficiency. This is seen to be a necessary consequence of the partial explanation given. Two verbal errors also stand in the paper. Page 418, line 22, for 3 X 26.8, read 6 X 26.8 ; page 4 2 2 , line 7 from bottom, for cathode ’ read anode.’ Brocheta objects to the phrase electroly tic reduction of potassium chlorate’ being applied to the action described, and attributes the formation of chloride to the instability of copper chlorate in the presence of metallic copper. This he expresses as a side reaction and points out that if not interfered with, it would give an efficiency of 600 pct ; the main reaction, that between the caustic potash formed a t the cathode and the copper chlorate, prevents the realization of this and gives rise to reformation of potassium chlorate and precipitation of copper oxide. (‘
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Jour. Phys. Chem. 6, 417 ( 1 9 0 2 ) . Zeit. Elektrochemie, 9, 160 (1903).
A Correction
538
This view of the action at the anode appears reasonable and may be correct. It cannot be considered as proved, however, by the fact that metallic copper reduces copper chlorate in concentrated solution. Further, it would be expected that by preventing the mixing of the caustic potash of the cathode with the anode products, as, through use of a porous cup, the yield of 600 pct might be approximated. Such does not appear to be the case. In experiments tried, the efficiencies were well below xoo pct. Brochet states that potassium chlorate cannot be made to yield chloride by means of cathodic reduction and accounts for the non-appearance of hydrogen in the present case by assuming that it reduces the copper oxide formed to metallic copper. Part of the hydrogen, or its equivalent, taken up may be accounted for in this way, but not all. Gladstone and Triber have shown that hydrogen occluded by copper reduces potassium chlorate. If finely divided copper be deposited on a copper cathode and this, after washing with water, be introduced as cathode in a solution of potassium chlorate, under the conditions of temperature and concentration employed in niy experiments and using a platinum anode, reduction to chloride takes place with some readiness. An indirect reduction through copper chlorate is excluded. In the experiments on potassium chlorate, using copper anodes, a deposit of spongy copper is found on the surface of the cathode. It appears certain that this copper, either after the manner indicated by the theory of Binz or through its powerof occluding hydrogen, is instrumental in bringing about a direct reduction of potassium chlorate to potassium chloride. Cornell Udversity.
1
Jour. Chem. SOC.33, 306 (1878).
