Alumen Pharm. Lond. & Edinb. Alum: a semitransparent, austere, styptic salt; com-posed of the vitriolic acid, and a certain earth; which earth is either the pure argillaceous earth, or else is contained, in great quantity, in all the argillaceous fossils that have been examined.

The greatest quantities of this salt are artificially produced from different kinds of minerals, whose nature and composition are little known. A bluish slate found in the hills near Scarborough and in some other parts of England (a), and a whitish stone at Tolfa near Rome (b), become richly aluminous, by calcination; and a bituminous earth near Hall in Saxony, by exposure to the air: this last, if laid in large heaps, grows hot, like the pyritas, and at length bursts into flame (c). There are, in Sweden, ferrugineous pyritae, from which alum, as well as vitriol, obtained (d); and most, if not all, of the aluminous dates, participate also largely of vitriol: it is probable that in all the matrices of this salt, the part, which becomes alum, differs from that which in the pyritae becomes vitriol, only in the former having an argillaceous earth in the place of the metallic calx of the latter.

(a) Colepress, philosoph. transact. No. 142.

(b) Mercatus, metalloibec. armarium iii. cap. 2.

(c) Hoffman, observ. physico-chym. lib. iii. obs. 8.

(d) Leopold, relatio de itinere suo suecico, p. m. 84, & seqq.

The alum, produced in the mineral, some-times shoots upon the surface into fibrous efflorescences, called by the antients, from their form, alumen plumosum; though later times have applied that name to a substance of a very different kind. The salt is extracted from the earthy matter by elixation with water; and afterwards brought to a crystalline form, by evaporating the solution to a proper pitch, and then fetting it to shoot, with the addition of a little alkaline lye or putrefied urine, without which the crystallization does not succeed. Even when the pure earth, separated from alum, is redissolved in the vitriolic acid, the solution does not easily shoot into perfect cry-stals, till some alkaline salt, fixt or volatile, is added; this acid seeming not to fully satiate itself with the aluminous earth, and the unsa-tiated part preventing the crystallization of the reft (a). The alkaline liquor is to be dropt in by degrees, till a white precipitation begins to appear; a mark, that all the redundant acid is now saturated, and that a further addition would decompose more and more, proportion-ably to its quantity of the alum itself.

The English alum is colourless, and commonly in large mattes; into which it is formed, by melting the crystals over the fire, with the addition of a little water, and pouring the fluid matter into wooden tubs, in which it concretes and assumes the figure of the vessel: the Roman is of a reddish hue, and in smaller crystal-lized masses. The name roch or rock alum is applied among us to the English, on account of the hardness and fize of its masses; and by foreign writers to the Roman, on account of the hard stone or rock from which it is extracted. The Roman is thought to be somewhat less styptic and less nauseous than the English, and is supposed by some to have for its basis a somewhat different kind of earth.

(a) Marggraf, mem. de l'acad. des science. de Berlin, ann. 1754.

The purification of alum for medical pur-poses is now directed by the London college, which is effected by boiling a pound of it in a pint of water, with the addition of a dram of chalk, and then chrystallizing the drained liquor.

Alum is a strong astringent; one of the strongest of the substances of that class. It is in common use for external purposes; against relaxations of the uvula; in gargarisms for spongy scorbutic gums; in epithems and col-lyria for inflammations and defluxions of the eyes, etc. In this last intention, we have scarcely any application more effectual than the coagulum recommended by Riverius, made by agitating the white of an egg with a lump of alum, till it acquires the consistence of an unguent, which is to be spread on tow, and applied warm to the eyes at bed-time; proper evacuations, if the inflammation is considerable, being premised.

Internally, it is given in small doses, of half a grain or less, as a mild corroborant; and in larger ones, as ten, fifteen, and sometimes twenty grains, for restraining immoderate haemorrhages. These large doses are never ad-visable, but in profuse and threatening evacuations; as they are apt to nauseate the stomach, occasion gripes, and leave obstinate constipations of the bowels. The first dose or two sometimes purge a little.

Aluminis pu-rificatio Ph. Load.

Coagulum aluminis Ph.

Lond.

* Pulvis helvetii.

Pulvis styp-ticus Ph. Ed.

It has been customary to mix alum, for internal use, with an equal* or with half its quantity of dragons blood; which serves to disguise the alum, and render it, especially when the mixture is made by melting them together*, more flow of solution in the stomach, in consequence of which it fits easier and may be given with less inconvenience in considerable doses: this is, perhaps, the only advantage of the addition of dragons blood to alum. The Edinburgh college, in their last edition, have in place of dragons blood substituted the gum kino, in the proportion of three drams to one ounce and a half of alum; an alteration which much improves the medicine; as this astringent gum is perfectly soluble in watery menstrua. Dr. Thompson, in the medical essays pub-lished by a society at Edinburgh, gives an account of the good effects of the former compound in uterine haemorrhages; and assures us, that he had never found any medicine so much to be depended on, whether for correcting the too frequent return of the menses or their too great abundance, for flopping the floodings which women with child are subject to, or moderating the flow of the lochia. In violent bleedings, he gave half a dram, of a mixture of equal parts of the two, every half hour; and seldom failed to suppress the discharge before three or four drams had been taken. The success of this medicine in these disorders induced him to prescribe it in the fluor albus, and in this also it had excellent effects.