OBSERVATIONS.
Though Zinc be soluble in all the Acids, and when combined with those Acids exhibits some uncommon phenomena, yet M. Hellot is the first that ever gave a particular account of what happens in those dissolutions: so that all we have to say on this head is extracted from that Gentleman's Memoirs. If a solution of Zinc in the Vitriolic Acid, prepared according to the directions in the process, be distilled from a retort placed in a sand-bath with a graduated heat, almost half the liquor presently comes over in pure phlegm. A small quantity of a Sulphureous Acid Spirit rises next. A greater force of fire is now requisite: the retort must therefore be removed into a reverberatory, and the distillation continued with a naked fire. On the first impression of this heat an odour of Liver of Sulphur discovers itself, which becomes sharp and suffocating towards the end of the distillation. In two hours time white vapours begin to appear, as in the rectification of common Oil of Vitriol. If the receiver be then shifted, you will obtain an Oil of Vitriol, in quantity about the eighteenth part of the whole used in the distillation, which, though sulphureous, is yet so concentrated, that, if a few drops thereof be poured into a weak Oil of Vitriol, they fall to the bottom with as much noise as if they were so many bits of red-hot iron, and heat this Oil of Vitriol as much as common Oil of Vitriol heats water.
At the bottom of the retort there remains a dry, white, crystalline, saline mass, exceeding in weight the Zinc that was dissolved, about a twelfth part of the whole weight of the liquor. The increase of its weight is owing to a portion of the Vitriolic Acid that remains concentrated in the Zinc, and could not be expelled by the fire. This portion of Acid adheres to it most tenaciously: for, though M. Hellot kept the retort containing it during two whole hours in so violent a fire that the vessel began to melt, the smallest vapour did not rise from it.
This saline caput mortuum is in the form of needles, much like the Sedative Salt. It is caustic, grows considerably hot when water is poured on it, and gives in the air, but slowly. Spirit of wine, digested with this Salt for eight or ten days, acquires the same smell as that which is mixed with concentrated Oil of Vitriol in preparing Æther.
Zinc is dissolved by the Nitrous and Marine Acids, much in the same manner as by the Vitriolic; except that the Marine Acid does not touch a black, spungy, rarefied matter, which it separates from the Zinc. M. Hellot found upon trial that this matter is not Mercury, and that it cannot be reduced to a metallic substance.
That ingenious Chymist distilled likewise Solutions of Zinc in the Nitrous and Marine Acids. There came over at first, as there did from the solution made by the Vitriolic Acid, an aqueous, and then an acidulated liquor. At last, by exciting the fire with great violence, towards the end of the distillation, he obtained a small quantity of the Acid that hath been employed in the dissolution: but the small portion of Acid thus obtained was exceeding strong; and the quantity of the Nitrous much more considerable than that of the Marine Acid.
A solution of Zinc in the Marine Acid, being distilled to dryness, yields a Sublimate on applying a violent heat to it.
All the Acids dissolve with ease, not only Zinc, but its Flowers also; and that nearly in the same quantity, and with almost all the same phenomena. M. Hellot, observing that the residues of most of the solutions of Zinc have a great resemblance with its flowers, is of opinion that this semi-metal may be reduced, by the means of solvents, to the same state into which it is brought by the fire when sublimed in Flowers.