=Alum, Ro′man.= _Syn_. RED ALUM*, ROACH A., ROCHE A., ROCK A.*; ALU′MEN ROMA′NUM, A. RU′BRUM, A. RU′PEUM, &c., L.; ALUN ROMAIN, A. DE ROCHE, Fr.; ALUME DI ROCCA, It. In small fragments, covered with a reddish powder (ALUMEN RUBRUM VE′′RUM); originally imported from Civita Vecchia, where it occurs native. It is much esteemed by dyers from being nearly free from iron-alum. That now sold for it in England is ordinary alum coloured with Venetian red, Armenian bole, or rose-pink (ALUMEN RUBRUM SPU′′RIUM). This is done by shaking the fragments in a sieve over a vessel of hot water, and then stirring them up with the colour, until the surface is uniformly tinged with it. In genuine roach-alum the colour not only covers the surface, but also partially pervades the substance of the crystals. The name was formerly also applied to a pure white variety of alum, prepared at Tolfa; but it is now, in English commerce, exclusively given to common alum artificially coloured. =Alum, Saccharated.= Alum, 6 oz., white lead 6 drms., sulphate of zinc 3 drms., sugar 1-1/2 oz. Mix the ingredients reduced to powder into a paste, with vinegar and white of egg. Used in eye waters and cosmetic washes. =Alum, So′da.= _Syn_. SULPHAS ALUMINÆ ET SODÆ, L. _Comp._ Na_{2}SO_{4} . Al_{2}(SO_{4})_{3} . 24Aq. An alum in which the potassium sulphate of common alum is replaced by a like salt of sodium. It does not occur in commerce. (Vide _suprà_ et _infrà_.) =ALUM-EARTH.= Alumina. =ALUM MOR′DANTS.= In _dyeing_, mordants having for their basis either common alum or the acetate or sulphate of aluminum. See ALUMS and MORDANTS. =AL′UM-ROOT.= _Syn._ AMER′ICAN SAN′ICLE; HEU′CHERA (Ph. U. S.), L. The root of _heuchera America′na_ (Linn.), a plant of North America. It is powerfully styptic and astringent; and is used chiefly as an external application in cancer. =ALUM-WHITE.= See WHITE PIGMENTS. =AL′UMS.= _Syn._ ALU′MINA (pl. of _alu′men_), L. In _chemistry_, a term applied to a series or group of salts having potassium alum for their type, which they resemble in crystalline form and constitution. It is found that the aluminum of common alum may be replaced by any other metal having a like nature, without affecting the leading characteristics of the salt; and further, that in the newly formed compound, as in potassium-alum, the second sulphate may also be replaced under the like conditions. All the alums crystallise in octahedrons or cubes, and they all contain the same number of molecules of water. The alums of commerce (or alums proper) all contain aluminum sulphate and an alkaline sulphate. _Prep._ All the alums may be made by mixing together solutions of the respective sulphates in equivalent proportions, when crystals may be obtained by evaporation in the usual manner. The presence of sulphuric acid, in slight excess, assists their crystallisation. =AL′UMED= (al′ŭmd). Mixed or impregnated with alum. In _dyeing_, mordanted with alum.