Alumen Exsiccatum

Lond. Dried Alum. "Melt alum in an earthen vessel over the fire, and increase the heat until the ebullition cease."

Edinburgh.

"Melt the alum in an earthen or iron vessel, and let it be kept over the fire until it cease to boil; then rub it into a powder."

Alumen Siccatum, Dub. Burnt Alum.

"Take of alum, any quantity. Expose to the heat of a strong fire in an earthen vessel until it cease to boil; then pulverize it."

Syn. Sulphate d'Alumine Sec (F.), Gebrannter Alaun (G.), Alume cal-cinato (J.).

In these processes the alum, which is a sulphate of alumina and of potassa, loses its water of crystallization; but if the heat be too great, its acid is partly expelled, and it is partially decomposed. According to Kirwan, alum desiccated at 700° loses more than half its acid. By our experiments, English alum lost 0.48 in a moderate heat, and 0.46 in a red: Levant alum 0.41 in a moderate heat, and 0.44 in a red heat. Chaptal found that in a red heat alum of his own manufacture lost 0.67; Roman alum, 0.50; English, 0.47; and Levant alum, 0.40.

Qualities. - Dried alum has a more astringent taste than the crystallized salt. It is obtained in the form of a light, opaque, white, spongy, friable mass, 100 parts of which consist of 36.25 acid, and 63.75 bases, when it has been exposed to a heat of 700°: but in general, the desiccation being conducted at a lower temperature, the proportion of acid is greater. Dried alum consists of 1 eq. of alumina = 51.4+ 4 of sulphuric acid = 160.4+1 of potassa=47.15, making the equivalent 258.95.

Medical properties and uses. - It is chiefly used as an escharotic to destroy fungus in ulcers; but has also been given internally to the extent of Э j. for a dose in cases of cholic, the pain of which it is said to allay, while at the same time it gently opens the bowels.

Liquor Aluminis Compositus. Lond. Compound Solution of Alum

"Take of alum, sulphate of zinc, of each half an ounce; boiling water, three pints. Dissolve the alum and the sulphate of zinc in the water, and then filter."

This powerful astringent solution has been successfully used in gleets and leucorrhoea; and in some cases of ophthalmia. It requires to be diluted in all these cases, and to be employed with caution. Half an ounce of the solution and six and a half ounces of rose-water form an excellent collyrium in ophthalmia, after local bleeding.