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The toxic effects ofmanganese in various industries have become important from the point of view of industrial medicine. This has led us to seek a more sensitive method for determining this. toxic element in industrial environments. Industries concerned are the metallurgical and iron and steel, and also those engaged in the manufacture of glass, paint, varnish, and electric batteries; the soldering industry can be included since the rods used often contain manganese. Most of the analyses carried out nowadays for this purpose use colorimetric methods, which consist in oxidizing manganese to the permanganate state and comparing the resulting characteristic coloration with that of previously prepared standards. Among these methods we may mention that of Willard and Oreathouse-r", in which the oxidation is carried out with sodium or potassium periodate; others use ammonium persulphate as the oxidizing agent in the presence of silver ions as catalyst35• Considering the great accuracy and sensitivity of the polarographic method, we, for our part, have looked for, and, we think, found, a method which gives greater precision, working at low concentrations, than colorimetric methods. Various studies of the polarographic behaviour of manganese exist; some authorsvs used alkaline and alkaline-earth chlorides as supporting solutions with small quantities of gelatine to suppress maxima; others recommended ammonium salts 911 as supporting solutions; others again used potassium sulphocyanidev-P or potassium cyanide-". In all these cases, when great sensitivity is desired, the oxygen in the working solutions must be eliminated in order to avoid possible interference by the cathode reduction waves of oxygen. . In a previous publication-s we pointed out that manganese exhibited a cathodic reduction wave at very low concentrations when using O·IN sodium sulphite as a supporting solution. This procedure avoids the necessity of eliminating the oxygen in the test solutions by means of a current of purified hydrogen or nitrogen; the sulphite, acting as a strong reducing agent, eliminates the oxygen in the solutions, and at the same time acts as a support favouring the diffusion currents of the ions under study. In the experiments reported here' we used accordingly O·IN sodium

A new polarographic method for determining traces of manganese suspended in industrial atmospheres