Opium appears to consist of about five parts in twelve of gummy matter, four of resinous matter, and three of earthy or other indiffolu-ble impurities (a). From these laft it has been purified, in the (hops, by softening the opium with boiling water, in the proportion of a pint to a pound, into the consistence of a pulp, with care to prevent its burning; and whilst it remains quite hot, strongly pressing it from the feces through a linen cloth: the (trained opium is then infpiffated in a water-bath, or other gentle heat, to its original consistence. When thus softened with a small quantity of water, the gummy and refinous parts pass the drainer together; whereas, if dissolved by a larger quantity, they would separate from one another. * A more perfect method of purification is now directed by the London college, which consists in dissolving one pound of opium in twelve pints of proof spirit, draining the solution, and then distlling the spirit from it, till it be reduced to a due consistence. This preparation is ordered to be kept in a soft form, for making pills, and a hard one, for powdering.

(a) Alston, Edinburgh medical essays, vol. v. art. 12.

Opium puri-ficat. Ph. Lond.

It has been disputed, whether it is in the gummy or in the refinous parts of opium, that its activity resides. From the experiments of Hoffman (a) and Neumann (b), it seems to be neither in the direct gum, nor in the direct resin, but in a certain subtile part of the resinous matter, somewhat analogous to essential oils, but of a much less volatile kind: they report, that on boiling the opium in water, there arises to the surface a frothy, viscid, unctuous, strong-fcented substance, to the quantity of two or three drams from sixteen ounces: that this substance, in the dose of a few grains, has killed dogs that could bear above a dram of crude opium; that in dislillation with water, though it does not rife itself, it gives over, at least in part, the active principle of which it is the matrix; impregnating the distilled liquor with its scent and its soporific power; as essential oils exhale their odoriferous principle in the air, without being dissipated themselves. What this subtile and highly active principle really is, in essential oils, in odorous vegetables that yield no oil, and in opium, is equally unknown.

Both water and rectified spirit extract, difficultly, by maceration or digestion, the active matter of opium, and receive from it a yellow or brownish tincture. The watery solution is found to contain great part of the resin along with the gum; and the spirituous, a smaller proportion of the gum along with the resin. Such part of the gum as is left by spirit, and such part of the resin as is left by water, seem to be equally inert.

(a) Difs. de opii correctione genuina & ufu, Oper. supple-pent. ii. P. i. p. 645. Not. ad Poterium, p. 437.

(b) Chymia medica, vol. i. p. 996. Chemical works, p. 308,

Tinctures of opium in water, wine, and proof spirit, have the same effects as the opium in substance; with this difference, that they exert themselves sooner in the body, and are less disposed to leave a nausea on the stomach. Tinctures made in rectified spirit are said to act with greater power than the others: Geoffroy relates, from his own observation, that while the watery and vinous tinctures occasioned quiet sleep, the spirituous brought on a phrenzy for a time. It is said likewise, that alkaline salts di-minish the soporific virtue of the opium; that fist alkalies render it diuretic, whilst volatile ones determine its action to the cutaneous pores; and that acids almost entirely destroy its force.

The officinal tinctures of opium are made in wine or proof spirit. The college of London directs ten drams of drained opium, dried and powdered, to be macerated without heat for ten days in a pint of proof spirit; the college of Edinburgh orders two ounces of crude opium to be digested for four days in a pound and a half of spirituous cinnamon water: a mixture of wine and proof spirit has been sometimes made choice of, in order to prevent in some measure an inconvenience which both of them separately, con-sidered as officinals, are liable to, being apt to throw off in long standing a part of the opium, which in wine falls to the bottom, and forms a crust on the surface of spirit. Of the first of the above tinctures twenty drops, and of the latter twenty-five drops are reckoned to contain one grain of opium: * but as these quantities of the menstrua do not easily dissolve all the active matter of so large a proportion of the opium, those doses are generally observed to have some-what less effect than a grain of the drug in sub-stance. As drops also, according to different circumstances, vary in quantity, though in number the same, it were to be wished that the shops were furnished with a solution of this drug, made in a quantity of menstruum large enough not only for the complete extraction of the active parts, but to admit of the dose being exactly determined by weight or measure.

* (a) This calculation refers to the preceding editions pf the dispenfatories. The London college have apparently much diminished the quantity of opium in their tinctures as it was formerly made with two ounces of strained opium to the pint. But it is probable that they have found by experiment that the loss of weight in drying the opium to powder is equivalent to the difference. By using this drug in powder, the difference of strength resulting from the unavoidable difference of consistence in various parcels of the crude or strained opium, is obviated.

Tinctur. opii Ph. Lond.

Tinctura the-baica vulgo laudanum liquidum Ph. Ed.

In a solid form, independently of such materials as may be subservient to the other indications of cure, it is sometimes mixed with spo-naceous or gummy substances which promote its dissolution in the stomach, and sometimes with resinous ones, which render its dissolution and operation more gradual and flow: to these is commonly superadded some aromatic ingredient, to prevent its occasioning a nausea.

*The London and Edinburgh colleges have now, however, preserved only a single form each of opiate pills, in which the promotion of its solubility seems the only subject considered. The former unites two drams of hard drained opium with one ounce of extract of liquorice. The latter directs the combination of one part of opium, four of extract of liquorice, three of Spanifh soap, and two of powdered Jamaica pepper.

Pil. ex opio Ph. Lond.

Pil. thebaicae vulgo pacificae Ph. Ed.

Many have endeavoured to correct certain ill qualities, which they suppose opium to be pos-sessed of, by roasting it, by fermentation, by long continued digestions, or boiling, by repeated dissolutions and distillations. These kinds of processes, though recommended by several late writers, do not promise any singular advantage. That they weaken the opium is indeed very probable; but this intention is answered as effectually, and with far greater certainty, by diminishing the dose of the opium itself: for the ill effects, which opium produces in certain cir-cumstances, do not depend on any distinct property or principle, and appear to be no other than the necessary consequences of the same power, by which in other circumstances it proves so beneficial: the only rational way of improving or correcting this valuable drug seems to be, by joining or interposing such medicines, as may counteract or remove those particular effects of it, which in particular cases may be injurious.