In the case of anhydous salts, the weighing of the test portion is carried out directly into platinum crucible. Transfering of the crucible in a muffle furnace, maintained at (900 +- 50) °C. In case of hydrated sals, the weighing is also carried out directly; the test porion is previously heated in the flame of a Bunsen burner. Covering and placing of the crucible so that the Bunsen flame plys on its lid. Subsequent transfer of the covered crucible to the muffle furnace. Calculation of the loss in mass by difference after heating.