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

Abstract

IN investigations of the electrolytic deposition potentials of manganese solutions by the use of the dropping mercury cathode and the automatically registering “polarograph”, comparatively large impurities (1:20,000) were detected even in the purest samples, e.g. Kahibaum's or Merck's “pro analysi”. (Cf. Rec. Trav. Chim. Pays-Bas, 44, 1925, 488-600.) From the position of the hump on the current-voltage curve (Fig. 1), the impurity was at first thought to be zinc (l.c. p. 520). However, on closer examination, the “saw-like” character of the undulations showed that this increase of current must be due to the deposition of a metal or metals not alloying with mercury (l.c.). At the potential at which the manganese impurity is distinctly shown, i.e. at 1.0 volt (from the calomel zero), zinc, nickel, cobalt, and iron may be deposited from their 10⁵ molar solutions (cathodic potentials 1.00, 1.06, 1.20, and 1.27 volts respectively). From the different heights of the humps on the polarographic curves, the impurity in the manganous solutions can be estimated as 0.54.0 × 10⁵ equiv. per litre. varying in different specimens within these limits. As analytical tests for zinc, nickel, cobalt, and iron in these solutions give negative results, these metals cannot be present in concentrations greater than 10⁵ equiv. per litre. Hence the persistent impurity was suspected to be analogues of manganese—eka-manganese (43) and dwi-manganese (75).