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ELEMENTS OF MATERIA MEDICA.
Order 15. Compound of Aluminum.
Potas'sce Alumino-Sul'phas seu Alu'men. — Alu'mino-Sul'phate of Pot’ash
History. —Although the term alum ( alumen of the Romans— arv-mriptaof the Greeks) occurs in the writings of Herodotus {Euterpe, clxxx.),Hippocrates (He fistulis, De ulceribus, See.), Pliny {Hist. Nat. xxxv.i,Hioscorides (Lib. v. cap. 123), and other ancient writers, yet it is notsatisfactorily proved that our alum was the substance referred to. Onthe contrary, the learned Beckmann {Hist, of Invent, i. 288) has assertedthat the alum of the Greeks and Romans was sulphate of iron, and thatthe invention of our alum was certainly later than the 12th century.But Geber {Search of Perfection, ch. iii., and Invention of Verity, cli. iv.),who is supposed to have lived in the 8th century, was acquainted withthree kinds of our alum, and describes the method of preparing burntalum ; and it is not, I think, improbable, that even Pliny was acquaintedwith our alum, but did not distinguish it from sulphate of iron, for hetells us that one kind of alum was white, and was used for dyeing woolof bright colours.—[For further information, consult Parkes’s ChemicalEssays, i. 625, and Thomson’s Hist, of Chem. i. 125].
Natural History.— It is found native in the neighbourhood ofvolcanoes, and constitutes the mineral called native alum. Native alumoccurs in bituminous shale and slate clay, at Hurlett, near Paisley, andnear Whitby, in Yorkshire .
Preparation. —The method of preparing alum varies somewhat indifferent places. The mineral from which (in this country) it is procuredis called aluminous slate, aluminous shale, or aluminous schist (schistusaluminaris). This substance varies somewhat in its composition in dif-ferent localities, hut always contains sulphuret of iron, alumina, carbon,and sometimes a salt of potash. The most extensive alum manufactoryin Great Britain is at Hurlett, near Paisley. Here the aluminous schistlies between the stratum of coal and limestone (Williams, Nat. Hist, ofthe Mineral Kingdom, 2nd. ed. ii. 315). By the action of the air it under-goes decomposition, and falls down on the floor of the mine. The sul-phur attracts oxygen, and is converted into sulphuric acid, whichcombines partly with the iron (oxidized by the air), and partly with thealumina. The solution obtained by lixiviating the decomposed schist isevaporated, and the sulphate of iron allowed to crystallize: to themother liquor, which contains sulphate of alumina, sulphate of potashis added, by which crystals of alum are procured, which are purified bya second crystallization.
At Whitby, in Yorkshire , the method of making alum is somewhatdifferent. The schist is piled in heaps, and burnt by means of a slowsmothered fire. The calcined ore is lixiviated, and a salt of potashadded to the solution after it has deposited sulphates of lime and iron,and earthy matters (Winter, in Nicholson's Journal, vol. xxv )
Properties. —Alum crystallizes usually in regular octahedrons, fre-quently with truncated edges and angles, and sometimes in cubes. 'Theordinary alum of the shops consists of large crystalline masses, which do