Much of the common alum, especially that prepared on the Continent, contains both potassium and ammonium; and recently enormous works for its manufacture have been established in England. As an astringent, and as a source of alumina in dyeing, it resembles potash-alum (_i. e._ ordinary alum). It may, however, be readily distinguished from the latter by the fumes of ammonia which are evolved when it is moistened and triturated, or heated, with caustic potassa or quick-lime; and by the residuum of its exposure to a white heat being pure alumina. See ALUM (_antè_). =Alum, Basic.= A variety of alum found native at Tolfa. On calcination and subsequent lixiviation it yields ordinary alum. A like substance falls as a white powder, when newly precipitated alumina is boiled in a solution of alum. =Alum, Baumé’s.= Alum-white. See WHITE PIGMENTS. =Alum, Dried; Alum, Burnt.= _Syn_. ALU′MEN US′TUM, A. EXSICCA′TUM (B. P.); ALUN SEC, Fr.; GEBRANNTER ALAUN, Ger.; ALUME CALCINATO, Ital. Alum deprived of its water of crystallisation by heat. _Prep._ Take of alum, 4 oz. Heat the alum in a porcelain dish or other suitable vessel, till it liquefies, then raise and continue the heat, not allowing it to exceed 400°, till aqueous vapour ceases to be disengaged, and the salt has lost 47 per cent. of its weight. Reduce the residue to powder, and preserve it in a well-stopped bottle. _Prop., &c._ Similar to those of common alum, but it is rather more astringent, and is less soluble. When moistened, or placed in contact with water, it resumes its water of crystallisation with evolution of heat.——_Dose_, 10 to 20 gr.; in colic (especially painters’ colic), hæmoptysis, &c. It is chiefly used as an escharotic, to destroy ‘proud flesh,’ &c. It must be kept in a stoppered bottle. =Alum, Chrome.= See ALUMS (in Chemistry). =Alum, I′ron= (-ŭrn). _Syn_. ALU′MEN FER′RICUM, SUL′PHAS FER′RI ET POTAS′SÆ, FER′RI PEROX′IDI POTASSIO-SUL′PHAS, &c., L. _Comp._ K_{2}SO_{4} . Fe_{2}(SO_{4})_{3}.24Aq. _Prep._ Take of peroxide of iron, 9 lbs.; sulphuric acid 14 lbs.; dissolve, dilute the mixture with water, q. s., and add of potassium sulphate, 10 lbs.; evaporate, and crystallise. _Prop., &c._ Crystals, beautiful octahedrons of a pinkish or pale violet colour. It is strongly recommended, by Dr Tyler Smith, as a chalybeate tonic, and has been used by him, at St. Mary’s Hospital with marked success. It has also been used as a mordant, in dyeing black.——_Dose_, 1/2 gr. to 5 gr.