in Chemistry, a clear and transparent saline matter, usually found in large masses, of a very agreeable and aromatic taste, useful in medicine and in various arts.

Most of the alum to be met with is artificially prepared by the methods related in their proper place under the article Chemistry, or by others similar to them; though sometimes a small quantity is produced naturally. This native alum is mixed with heterogeneous matters, or efflorescences in various forms upon the ores during calcination. It rarely occurs in a crystallized state, though thus it is said to be met with in Egypt, Sardinia, Spain, Bohemia, and other places. It is also found in waters impregnated with fixed airs, but very seldom in fountains or hot medicated waters.

There are several kinds of alum to be met with; but these differ from one another only in being mixed with some salts which are not of the aluminous kind. That called the Roman alum has been considered as preferable to any other. This is usually met with in small crystals, and has a reddish colour, most probably owing to a small quantity of calx of iron, which, however, does not in the least impair its qualities. The other kinds of alum contain a portion either of vitriolated tartar or sal ammoniac, according to the nature of the alkali used in its preparation. Mr Bergman informs us, that the vegetable alkali, if pure, does not hurt the alum, though it be added in the preparation; but that the volatile alkali, by adulterating it with a portion of vitriolic sal ammoniac, renders it unfit for some purposes. The alum, made by adding a portion of clay to the liquor at the beginning of the boiling, he considers as equal, if not superior to Roman alum. He informs us also, that a kind of alum some time ago began to be manufactured at Brunswick, which was equal in quality to the Roman alum. On a chemical analysis of this alum he found it mixed with cobalt.

This fact is extremely useful in the art of dyeing; as by means of it a great number of colours are fixed and rendered permanent upon cloth, which otherwise would either not adhere in any degree, or only for a very short time. In what manner this is accomplished, we are very much ignorant; the conjectures and theories on this subject are related under the article Dyeing. It constitutes the basis of crayons, which generally consist of the earth of alum finely powdered and tinged for the purpose. In the preparation of Prussian blue, it prevents the basis of martial vitriol, which is soluble in acids, from being precipitated by the superfluous alkali employed in the preparation of the pigment; that is, the alkali which is not coloured by the saturating matter. As this basis adheres more strongly than the clay to the vitriolic acid, and would form a green by the mixture of its yellowness, the white earth of alum likewise, according to its quantity, dilutes the darker colours, even black itself, and produces an infinite number of shades. It is also of use in the making of candles: for, being mixed with the tallow, it gives it a hardness and consistence which it has not naturally. Wood sufficiently soaked in a solution of alum does not easily take fire; and the same is true of paper impregnated with it; which, for that reason, is very properly employed in preserving gunpowder, as it also excludes the moisture of the air. Paper impregnated with alum is useful in whitening linen, and silvering bras without heat. Alum is also of use in tanning, where it affords in retorting the cohesion of the skins almost entirely destroyed by the lime. Vintners fine down their wines, &c., with alum; fishers use it to dry cod fish with; and bakers have mixed it with the flour to make their bread compact and white: to this last use of it great objections have been made; but unjustly, for it is entirely innocent. It is now seldom used.

In medicine it is of considerable use as an astringent and tonic. It is reckoned particularly serviceable for restraining hemorrhages, and immoderate secretions from the blood; but less proper in intestinal fluxes. In violent hemorrhages, it may be given in doses of 15 or 20 grains, and repeated every hour or half hour till the bleeding abates: in other cases, smaller doses are more advisable; large ones are apt to nauseate the stomach, and occasion violent constipations of the bowels. It is used also externally, in astringent and repellent lotions and collyria. Burnt alum taken internally has been highly extolled in cases of colic. In such instances, when taken to the extent of a scruple for a dose, it has been said gently to move the belly, and give very great relief from the severe pain. Its officinal preparations are, for internal use, pulvis hydropis, and aqua hydropica; for external applications, the aqua aluminae, and coagulum aluminae et alumen stylum; which last is no other than the alum dried by fire, or freed from the watery moisture, which, like other salts, it always retains in its crystalline form. By this loss of water it becomes sharper, so as to act as a slight emetic; and it is chiefly with this intention that it is employed in medicine, being very rarely taken internally. For these preparations, see Pharmacy.

Alum Mines are said to have been first found in Italy in the year 1465; and in 1506 King Henry VII. made a monopolizing grant of this commodity to Augustin Chigi, a merchant of Sienna. In the year 1668, the manufacture of alum was first invented, and successfully practised in England, meeting with great encouragement in Yorkshire, where it was first made, from Lord Sheffield, and the other gentlemen of that county. King James I. by advice of his ministry, assumed the monopoly of it to himself, and therefore prohibited the importation of foreign alum; and in 1625 the importation of it was further prohibited by the proclamation of Charles I.

Alum Works, places where alum is prepared, and manufactured in quantities for sale. They differ from Alypius, one of the seven Greek writers on music, which Meibomius has industriously collected and published, with a commentary and explanatory notes. The time in which he flourished cannot be precisely determined. He is said to have wrote before Euclid and Ptolemy; and Caiiodorus arranges his work, entitled, "Introduction to Music," between that of Niconachus and Gaudentius. In this work is to be found the most complete nomenclature of all the sounds of the different scales and modes of the ancient Greek music, which have escaped the wreck of time. So complex was the science of music in Greece at this period, that the characters used for sounds were 1620 in number. The 24 letters of the alphabet furnished these notes, sometimes in an entire, sometimes in a mutilated, and sometimes in an altered form; and numerous discriminations of these took place by means of the accents and varied positions of letters.

From the MS. of Joseph Scaliger, Meurinus first published this tract in 1616; but according to the testimony of Fabricius, it is by no means correct. Extracts have been published from Alypius, by Kircher, in his Musurgia, 1650, alleging that he translated the whole into Latin; but this table of ancient musical notation is so inaccurate, which he has inferred from him, that Meibomius, who consulted not only the Greek MS. of Scaliger, but that of Belejanus, Barocci, Barberitti, and Selden, affirms, that he found in it more than 200 errors. The learned Meibomius, with incredible industry, deciphered these characters, which previous to his time were so much confounded, disfigured, and corrupted, either through the ignorance or inattention of the transcribers of ancient MSS. This advantage resulted to the science of music, chiefly by his commentaries on Greek musicians, and particularly on the works of Alypius.

Alypius of Tagaste, a Christian divine who flourished in the fourth century. In the year 388, he was baptized along with Augustine, and, in consequence of a similarity of dispositions and religious sentiments, they became strongly attached to each other. In quest of information and improvement, he took a journey into Palestine; and returning home, he soon acquired such general esteem, that he was appointed bishop of his native city. He had adopted in the early part of his life the opinions of the Manichaeans; but in consequence of farther information and matured experience, he became a powerful advocate for the Catholic faith. The Donatists flourished about this period, and arrogantly claimed the exclusive honour of being the true church; but he, along with his friend Augustine, united his exertions in opposing the tenets of that sect. In the council of Carthage in the year 403, the erudition and talents of Alypius, along with several other eminent divines, were unsuccessfully employed in endeavouring to reclaim them, and to bring them again into the bosom of the church. In 411 Alypius was one of the seven who held a friendly and theological conference with seven of the Donatist bishops. But all the eloquence and strength of argument made use of by these divines, although seconded by the penal decrees of the emperor Honorius, were unsuccessful in producing a recantation of their errors, or a peaceful union with their brethren. In support of the Catholic faith, Alypius appears to have vigorously exerted erted his talents; and it is much to be regretted that the means he employed for that purpose were not at all times the most honourable; for in the violence of his zeal he went as deputy from the churches of Africa to the emperor Honorius, in order to obtain severe decrees against the sect of the Pelagians. Although Alypius failed in his attempts to reclaim the Donatists from error, yet he was successful with the emperor in obtaining penal decrees against the Pelagians; in consequence of which their ministers were banished, their churches demolished, and their assemblies discontinued. Alypius died about the year 430, and his dispositions appear to have participated more of the violence of zeal, than of the meekness of charity. (Gen. Biog.)