Derivatographisehe Untersuchung von Sulfaten

In splitting off water of crystallization from sulphates sometimes only 1/4, 1/2 or even 3/4 molecules of water are removed per one molecule of the salt. It is supposed that compounds like cadmium sulphate (3 CdSO4 · 8 H2O) are formed. Yet, generally the compounds correspond to the regular formulas with one or more molecules of water per one molecule of the salt. The last molecule of water is removed within a wider range of temperature then the preceding ones sometimes already together with products of desulphurization. This latter process may run (1) via basic sulphates to the oxides, (2) via sulphites to the oxides, (3) via basic sulphites to the oxides, and (4) via sulphate-sulphite double salts to the oxides. In case of the oxides corresponding to several stages of oxidation the final product depends on the temperature employed, the rate of heating, and the sample weight.