Elements of the Theory and Practice of Chymistry, 5th ed.

by Pierre Joseph Macquer

This method of separating Arsenic from Sulphur hath two advantages over that in which a Fixed Alkali is the medium. The first is, that by this means all the Arsenic contained in the mixture is extracted out of it; and the second, that, as Mercury doth not absorb Arsenic, we are not put to the trouble of groping out, as it were, by trials the quantity necessary to be added; and that, though more be added than is necessary to absorb all the Sulphur, it will be of no prejudice to the operation. But then it is attended with the inconvenience of being much more tedious and more laborious than the other. For, in the first place, it requires previously a very tiresome trituration, in order to procure an union between the Sulphur and the Mercury, and so to form an Æthiops; without which the Mercury and the sulphurated Arsenic will sublime separately, so that no decomposition will be effected. Secondly, though the Mercury be sufficiently united with the Sulphur of the Arsenic by the long trituration that precedes the sublimation, this doth not prevent, as we took notice above, the sublimed Arsenic and Cinabar from being in some measure blended together; so that each requires a second separate sublimation to render it very pure.

These inconveniencies cause a Fixed Alkali to be used preferably to Mercury; the loss of a small quantity of the Arsenic, which remains united with the Alkali, being little regarded; as that metallic substance is neither scarce nor precious.

When Arsenic is united with a great quantity of Sulphur, it may be freed from a part thereof without the intervention of any third body: it is sufficient for the purpose to sublime it with a very gentle fire, increased by insensible degrees. The most sulphureous part ascends first; what rises afterwards is more Arsenical, and less sulphureous; and the last flowers of all are pure Arsenic, or at least nearly so.

PROCESS III.

To give Arsenic the Metalline Form. Regulus of Arsenic.

Take two parts of white Arsenic in fine powder, one part of the black flux, half a part of Borax, and as much clean iron filings. Rub the whole together, in order to mix them thoroughly. Put this mixture into a good crucible, and over it put Sea-salt three fingers thick. Cover the crucible; set it in a melting furnace; and begin with a gentle fire to heat the crucible equally.

When arsenical vapours begin to ascend from the crucible, raise the fire immediately so as to melt the mixture. Examine whether or no the matter be thoroughly melted, by introducing an iron wire into the crucible; and if the fusion be perfect, take the crucible out of the furnace. Let it cool; break it; and you will find in it a Regulus of a white and livid metallic colour, very brittle, scarcely hard, but rather friable.

OBSERVATIONS.

White Arsenic is, as hath been said, a metallic calx; and consequently wants no more, in order to its acquiring the metalline properties, than to be combined with the phlogiston: this is effected by the operation before us.

The Iron added doth not serve here, as in making the Regulus of Antimony, to precipitate the Regulus of Arsenic, by separating it from some other substance with which it was united: on this occasion it does nothing but join the Regulus of Arsenic, to which it gives solidity and consistence. This is the only reason of its being made an ingredient in the mixture; as the Regulus of Arsenic, without it, would have such a tender consistence, that it could scarce be handled without falling asunder into little bits. The Iron procures a further advantage in this process; which is, that it prevents a great quantity of Arsenic from being lost in vapours: for the Arsenic, with which it combines, is restrained, and, in some measure, fixed by it.