The Occurrence of Dwi-Manganese (At. No. 75) in Manganese Salts

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As the present writer is responsible for the polarographic investigations of solutions containing dwimanganese (see letter by Dolejěsk and Heyrovský, NATURE, 116, p. 782), he alone replies to the criticism of the above letter by Mr. A. N. Campbell (NATURE, 116, p. 866). This criticism shows a misunderstanding of what the polarographic-electro-analysis with the dropping mercury cathode really means. First of all, the present author's potentials refer, as expressly stated, to the calomel—not absolute—zero, and thus, of course, do not agree with those obtained by Mr. Campbell, since the present author's special electrolytic method is based on an almost currentless reversible electrolysis which differs widely from ordinary electrolytic methods (see, for example, Tran. Far. Soc., 19, p. 692, 1924; Rec. Trav. Ch. Pays-Bas, 44, p. 488, 1925). The over-voltage on the pure mercury cathode beads is so large that hydrogen begins to be deposited from a deci-normal hydrionic concentration at —1.20 v. from the calomel electrode (Rec. Trav. Ch. Pays-Bas., 44, p. 503, 1925), and at the acidity of the solutions used in the dwi-manganese investigations, at —1.3 v. to —1.4 v., i.e. far behind the point of deposition of element “75. Variation of hydrion concentration from 0.1 n. to neutral solution produced no effect upon the “75” hump, neither was its shape or position affected by polarising the sulphate or the chloride. Solutions of manganese sulphate which were freed from the two impurities by means of the electro-chemical deposition described in the first letter showed no hump whatever before the deposition potential of manganese at —1.35 v.

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