The Chemistry of Osmium

Abstract

AN important addition to our knowledge of the chemical nature of this interesting element is contributed by Prof. Moraht and Dr. Wischin, of Munich, to he current number of the Zeitschrift für Anoranische Chemie. Two years have scarcely elapsed since the position of osmium in the periodic system was finally decided by the painstaking re-detetmination of its atomic weight by Prof. Seubert. Previous determinations of the atomic weight of osmium had been made with material which Seubert subsequently showed to be impure, and in consequence the erroneous value, 198˙6, had been ascribed to it. Indeed previous to the year 1878 the order of precedence as regards atomic weight of the four metals of the platinum group—gold 196˙2, iridium 196˙7, platinum 196˙7, and osmium 198˙6—was entirely at variance with the order demanded by their chemical and physical properties, and a standing contradiction of the periodie law of Newlands and Mendeleef. In that year, however, Seubert attacked the case of iridium, and as the result of a series of determinations, made with the laborious care which has characterised all his work, the atomic weight of this metal, when obtained in a pure state, was shown to be 192˙5, a number very different to that previously assigned to it, and which was afterwards remarkably confirmed, even to the decimal place, by an independent investigation by Joly. Three years later Seubert made his celebrated re-determination of the atomic weight of platinum, which resulted in the number I94˙3 being finally derived for the true atomic weight of the perfectly pure metal. This value was likewise subsequently confirmed by Halberstadt. In the year 1887 the position of gold was decided by simultaneous independent re-determinations of its atomic weight by Thorpe and Laurie in this country and Krüss in Germany, the two values being practically identical, 196˙7. Lastly,' in 1891, Seubert completed his work by redetermining the atomic weight of osmium with a specimen of the metal of practically perfect purity, with the result that the old number, 198˙6, was found to be entirely erroneous, due to considerable quantities of impurities being present in the samples previously employed, and that the real value of this constant was 190 3, thus removing osmium from its former situation at the end of the series and placing it in its proper position at the head of it.