On the solvent qualities of CALCINED MAGNESIA.

DR. Macbride, whose experimental researches have very justly acquired him a high degree of reputation in the philosophical world, supposes fixed air to be the combining principle of bodies, and has applied this ingenious theory to pharmaceutical improvements. He discovered that lime triturated with resinous gums, promotes their dissolution in water; which, he thinks, is thus enabled to take up the same parts of these substances, as are soluble in spirit of wine. These aqueous tinctures are transparent, not milky like the solutions made with yolk of egg, or gum arabic; but the lime communicates a highly disagreeable taste to them, and the action of lime water, which he used in some instances, is not sufficiently powerful to extract strong tinctures from these bodies. As calcined Magnesia has a great affinity with fixed air, I was desirous of trying whether it would contribute to render resinous substances soluble in water; for being itself insoluble, the solutions would consequently be free from any other impregnation than that of the resins.

EXPERIMENT X.

Five grains of camphor were rubbed for five minutes with an equal quantity of calcined Magnesia: after the camphor was reduced to powder, it united into a hard concrete with the Magnesia, but immediately dissolved on the addition of a small quantity of distilled water, of which an ounce was mixed with them, and immediately passed through filtering paper. The filtrated liquor was highly impregnated with the camphor.

EXPERIMENT XI.

Five grains of opium triturated in the same manner, yielded a transparent tincture, of as deep a colour as the tinctura Thebaica of the London Dispensatory, and tasting strongly of the opium.

EXPERIMENT XII.

Gum guaiacum and calcined Magnesia, of each a scruple, being rubbed with an ounce of water, and filtered, gave an elegant green tincture, quite transparent, and possessing, in a considerable degree, the taste of the gum.

Gum galbanum, storax, mastick, myrrh, assafÆtida, scammony and balsam of Tolu, being severally triturated with equal weights of calcined Magnesia, diluted with water and filtered, afforded neat tinctures, strongly impregnated with the different drugs.

EXPERIMENT XIII.

In order to determine the quantity of opium thus dissolved, half an ounce of crude opium, the same quantity of calcined Magnesia, and eight ounces of distilled water were rubbed for a quarter of an hour in a glass mortar, and having stood to infuse during two hours, the liquor was separated through paper. The tincture was of a darker colour than that before described, and was reduced by a gentle heat to a pilular consistence. This extract weighed sixty-eight grains, which, allowing for impurities, for what would be dissipated in evaporation, and for the air probably absorbed by the Magnesia, is a large proportion to be so soon dissolved. The residuum which was left in the filter was dried, and weighed six drachms.

EXPERIMENT XIV.

A drachm of Peruvian bark, twenty grains of calcined Magnesia, and four ounces of distilled water being rubbed together during fifteen minutes, the filtered infusion resembled in appearance the simple tincture of bark, and had an intensely bitter taste, but was not strongly impregnated with the peculiar aroma of the bark.

Thus then we have an easy and very elegant method of preparing aqueous tinctures from the gum resins, and administering them in a more convenient form and in larger doses than could be done when dissolved in a spirituous menstruum; and much more agreeably than in the half-dissolved state to which they are reduced by the aid of egg or gum arabic. The Magnesia does not impart any thing to them, whereas the lime will seldom be so saturated with air but that some part of it will remain soluble in the water: and as they may be given diluted to whatever degree the prescriber chuses, considerable advantages may be expected therefrom, it being probable that they will be better enabled to pervade the very small vessels; and the heating properties of the balsams be more effectually obviated than by any other mode of preparation.

Indeed, tinctures prepared by the above method, are not calculated for officinal compositions, but for extemporaneous prescription; as most of them, except camphor, deposite a sediment when they have been kept a week or two.