or Alumen, in natural history, a peculiar kind of salt, sometimes found pure, but often separated from several substances, as a soft reddish stone in Italy, several kinds of earth, and, in England, from a whitish or bluish stone, called Irish slate. Alum, in medicine, is a powerful astringent. In dying, it fixes the colours upon the stuff. See Chemistry.

Process of making Alum. At Whitby, in Yorkshire, alum is made thus: Having burnt a quantity of the ore with whins, or wood, till it becomes white, then they barrow it in a pit, where it is steeped in water for eight or ten hours. This liquor, or lixivium, is conveyed by troughs to the alum-house, into cisterns, and from them into the pans, where it is boiled about 24 hours. They add a certain quantity of the lye of kelp; the whole is drawn off into a settler; where having remained about an hour, that the sulphur and other drugs may have time to settle to the bottom, it is conveyed into coolers. This done, to every tun of the liquor they add about eight gallons of urine; and having stood four days and nights, till quite cool, the alum begins to crystallize on the sides of the vessel, from which being scraped off, it is washed with fair water, and then thrown in a bing, to let the water drain off. After this it is thrown into a pan, called the roching pan, and there melted; in which state it is conveyed by troughs into tuns, where it stands about 10 days, till perfectly condensed. Then flaving the tuns, the alum is taken out, chipped, and carried to the store-houses.

This is what we commonly call roche or rock alum, as being prepared from stones cut from the rocks of the quarry; and stands contradistinguished from the common alum, or that prepared from earths.

Artificial Alum, that prepared by art, in contradiction from the native alum. It is also used for alum produced by causing burnt earthen vessels imbibe a large quantity of oil of vitriol; the effect of which is, that they are thereby reduced to a mucilage, which, being exposed to the open air, affords crystals of pure alum. Tobacco-pipes, wetted with spirit of sulphur, likewise afford beautiful crystals of plumose alum.

Burnt Alum, is that melted in a fire-shovel, or crucible, where it is allowed to bubble till it becomes a white hard substance.

The watery part of the alum being thus expelled, the remainder is left poffefted of all its acids, lefs clogged, and more in a condition to exert its effects. It proves a gentle efcharotic, and is used in small quantities, mixed with other ingredients, in tooth-powders.

Crude Alum, that which has undergone no other refinement than what it receives at the alum-works.

Native Alum, or Fossil Alum, that formed by nature, without the affistance of art.

There are still mines of native alum in the island of Chio, consisting of a kind of vaults, or apartments crufted over with alum, which may be looked upon as exfoliations from the rock.

Plumose Alum, or Plume Alum, a kind of natural alum, compofed of a fort of threads, or fibres, refebling feathers; whence it has its name.

Prepared Alum, or Purified Alm, that which is difolved in hot rain-water, and afterwards made to crystallize, by evaporating the water.

Rock-Alum, or Rock-Alum. See the article, Process of making Alum, fupra.

Roman Alum, a fort of rock-alum, of a reddifh colour, made in the country near Rome.

Saccharine Alum, is a composition of common alum with rofc-water, and the whites of eggs, which being boiled to the confiftence of a patte, is formed in the shape of a sugar-loaf; it is ufed as a cosmetic.

Scifile Alum, the fame with plumose alum.

Alumen, the Latin name of alum.

Alumen catini, a name fometimes ufed for the falt of the keli.

Alumen faglioide, a name fometimes ufed for lapis specularis.

Aluminous, an epithet for things that partake of the nature of alum.

Alumta, in botany. See Luteola.

Alus, or Alum, in botany, an obfolute name of the symphytum. See Symphytum.

Alvus, in anatomy, a term ufed for the belly in general, but more frequently applied to the bowels.

Alwaiddi, a fect of Mahometans who believe all great crimes to be unpardonable.

Alypias, the name of a kind of white turbitb. See Turbitb.

Alpum, in botany, a synonyme and likewife the trivial name of a species of globularia. See Globularia.

Alyssoides, in botany, a synonyme of the alyffum. See Alyffum.

Alyffum, or Alysson, in botany, a genus of the tetradynamia filiculosa. The flowers of the alyffum confift of four leaves in the form of a crofs: The capsule is short and smooth, and contains a number of roundifh seeds. There are 14 species of the alyffum, none of which are natives of Britain.

Alytarcha, a priest of Antioch in Syria, who, in the games instituted in honour of the gods, prefided over the officers who carried rods to clear away the crowd, and keep order.

In the Olympic games, the alytarches had the fame command, and obliged every person to preferve order and decency.

Alzachi, in botany, an obfolute name of the anguria. See Anguria.

Alzagi, or Alzegi. See Zegi.

Alzarac, the Arabian name of a coarfe kind of camphor.

Alzira, a town of Spain, in the province of Valencia, situated on the river Xucar, about 18 miles S of the city of Valencia, W. long. 20°, N. lat. 39° 10'.

Alziz, among Arabian physicians. See Ziz.

Alzum. See Bdelium.