Abstract
IN a letter to NATURE of November 28 bearing the above title, the authors, Messrs. Dolejšek and Heyrovsky, deduce the existence of element 75 from measurements of the potential of a cathode immersed in saturated manganese sulphate solution. Their conclusion is supported by an examination of the X-ray spectrum, with which I have nothing to do. I do not think, however, that their deductions from the potential-current curves are necessarily valid. They find for the deposition potential of manganese 1.34 volt (abs.), a figure in substantial agreement with my own (Trans. Faraday Soc. (1924), 19, 559 and 20, 1). Below that potential they find two humps in what should normally be a very flat curve. The first and smaller hump they show to be due to some common impurity removable by hydrogen sulphide. The second, commencing at a voltage of 1.00 volt, they attribute to the discharge of the new element, dwi-manganese. I see no reason why this potential should not represent the potential of incipient hydrogen discharge: the actual deposition of manganese at 1.3 volt is accompanied by violent hydrogen discharge. Assuming their manganese sulphate solution to be neutral, the equilibrium potential of hydrogen should be about 0.13 volt, which requires an overvoltage of 0.87 volt, a readily realisable figure if the cathode were smooth platinum. The oscillatory nature of the potential curve in the neighbourhood of the manganese deposition potential may be due to the simultaneous discharge of hydrogen and manganese.
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CAMPBELL, A. The Occurrence of Dwi-manganese (At. No. 75) in Manganese Salts. Nature 116, 866 (1925). https://doi.org/10.1038/116866a0
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DOI: https://doi.org/10.1038/116866a0
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