Elements and Chalcogenides

Abstract

Among the minerals occurring in elementary form, only sulfur (S) and graphite (C) are to be determined by DTA. The metals silver, gold, platinum, copper or bismuth can be recognized differential thermal analytically at their temperatures of melting (e.g., Ag melts at 960° C), but for one thing the identification of such expensive minerals by means of melting temperature determinations in DTA would be paradoxical, secondly these metals occur very seldom in chemical pure substances. Sulfur shows a weak endothermic reaction at 130° C (melting point, after Kopp and Kerr, 1957), and a very strong exothermic deflection with a peak at 380° C (oxidation of S to SO₂).The author’s DTA runs of greater sensibility show the endothermic peak caused by melting at 120° C (melting point, after D’ANS-LAX : 119° C), and at 96° C another weak endothermic peak occurs reflecting the structural transformation from orthorhombic to monocline. The oxidation peak, occurring at 380° C for 50 mg in our runs, is the most important DTA characteristic for elementary sulfur as well as for sulfides, but in the last case it appears without exception at higher temperatures (see 1.2). This very intensive oxidation deflection (peak) allows very small quantities of sulfur in a rock sample to be determined. Grim and Johns heated some hundreds of grams to find small traces of sulfur. It would be more simple to heat the amount of 150 mg, finely ground, consisting of 50 mg sulfur containing rock sample mixed with 100 mg of inert material (compare with 1.2).