Antimonii Oxysulphuretum. U. S. - Kermes Mineral.

If, in the process for preparing the sulphurated antimony, the liquor obtained by boiling together sulphuret of antimony and the alkaline solution be allowed, after filtration, to stand until it becomes cool, without the addition of sulphuric acid, a powder is slowly deposited, which, when washed and dried, is the preparation in question, as formerly made. in this case, the precipitation takes place simply because the oxide and sulphuret of antimony are less soluble in the liquor cold than hot; but, as the oxide is more soluble in the alkaline liquid than the sulphuret, the latter is deposited in larger relative proportion than in the last preparation; and the kermes thus obtained, though an oxysulphuret, yet contains but a small proportion of the oxide.

The French Codex directs it to be made with the carbonate of soda, instead of one of the caustic alkalies; the process being in other respects the same; but, as the carbonate is not capable of holding so much of the oxide in solution when cold as the caustic alkali, more of the oxide is precipitated on cooling. The resulting kermes is, therefore, richer in oxide than as procured by the former method; and, as the efficacy of the preparation depends on the oxide, it is proportionably more efficient. This process was adopted at the recent revision of the U. S. Pharmacopoeia.

Properties

Kermes mineral is distinguished from the precipitated sulphuret by its darker colour, which is ordinarily some shade of dark-brown; but it loses its colour by exposure to air and light, and becomes ultimately yellowish-white. its chemical relations are similar to those of the sulphurated antimony or precipitated sulphuret.