GEBER or JABIR, more fully Abu Musa Jabir ibn Hayyan, was the most celebrated chemist of mediaeval times. There is reason to believe that he belonged to the famous South Arabian tribe of Al-Azd, some members of which settled in the town of Kuf a shortly of ter its foundation by the Caliph Omar in A.D. 638. Jabir's father, Hayyan, was a druggist in KUfa and an ardent sup porter of the `Abbasid family, at that time plotting to secure the caliphate. It is probable that Jabir was born at the town of Tus (near the present Meshed) in the year A.D. 721 or 722, while his father was in Persia as an `Abbasid agent. Shortly afterwards, Hayyan was arrested and executed by 'Umayyad officers, and the younger Jabir was sent to Arabia, where he studied under Harbi at Himyari. As a youth, Jabir attached himself to the sixth Shiite Imam, Ja`Far a1-Sadiq, from whom he probably obtained his first introduction to occultism, though perhaps not to alchemy itself. He is said to have afterwards joined the Sufi order, then recently founded by Abu Hashim of Kufa (died A.D. In later life, Jabir became a friend of Harun al-Rashid's powerful minis ters the Barmakides, and, according to tradition, shared their ban ishment from Baghdad in A.D. 803. Retiring to Kufa, he spent the rest of his life in obscurity, though one authority maintains that he survived until the accession of the Caliph Al-Ma'mun in A.D. 813. His laboratory at Kufa came to light some two centuries later, during building operations in a quarter of the town known as the Damascus Gate.
Jabir was a voluminous writer, and fortunately made a list of the titles of his books, which was reproduced in part by Ibn Al Nadim in his Kitab al-Fihrist, a Muslim encyclopaedia of the loth century A.D. Many of these books are still extant, nearly zoo hav ing been reported as existing in manuscript or native lithographs in various European, Indian and North African libraries. They are, however, for the most part unedited (1928), and it is therefore impossible to express a final conclusion upon Jabir's scientific knowledge. In 1893, nine small works were edited and translated by O. Houdas and published by M. P. E. Berthelot in his La Chi mie au Moyen Age (Paris), but they are by no means the most important. Among the Latin alchemical manuscripts in the Biblio theque Nationale Berthelot found a mutilated treatise, entitled Liber de Septuaginta (Johannis), Translatus a Magistro Renoldo Cremonensi (Gerard of Cremona), which he considered was prob ably a translation from the Arabic Jabir. At that time (1893), the Arabic version was unknown ; it was, however, discovered in 1926 by Prof. Max Meyerhof, who found two separate manu scripts of it in the private libraries of Nureddin Bey Mustafa and Ahmad Pasha Taimur, at Cairo. Berthelot's conjecture was there fore well founded. Of the remaining extant treatises, the most noteworthy are the Great Book of Properties, the three Books of the Element of the Foundation, and a Book of Poisons, the last having been discovered in 1928 by Prof. Julius Ruska of Berlin.
Jabir's thought is often confused and superstitious, yet he has a two-fold importance for the history of chemistry. In the first place he was a skilled and ingenious experimentalist, and describes for the first time the preparation of nitric acid, the method of conducting certain essential chemical operations, and many other things of the same kind. Secondly, he suggested the comprehensive theory that all metals are composed of two principles resembling sulphur and mercury. This theory, which was a development of the Aristotelian conception of two "exhalations," persisted for many centuries and was at last modified into the phlogiston theory of Beccher and Stahl (17th and 18th centuries A.D.) Jabir ex plained the existence of different varieties of metals by assuming that the sulphureous and mercurial principles are not always pure and that they do not always combine together in the same pro portion. If they are perfectly pure and combine together in the most perfect natural equilibrium, then the product is the most per fect of metals, viz., gold. Defects in purity or proportion or both result in the formation of silver, lead, tin, iron or copper ; but since these metals are all essentially composed of the same constituents as gold, the accidents of combination may be removed by suitable treatment. Such treatment, which Jabir believed could be effected by means of elixirs, was the object of Alkisnia or alchemy.
Jabir's chemical theory was thus a development of Greek scien tific and occult philosophy. Etymological and other evidence ren ders it likely that his contact with Hellenism was made through Persian channels rather than through Syria and Egypt. The repu tation he acquired has never since been equalled in the whole de velopment of chemistry ; there is, indeed, scarcely a single later Arabic alchemical work in which he is not quoted, or at least men tioned. When, in the 12th and 13th centuries, Islamic science was transmitted to Latin Christianity, the fame of Jabir went with it; and, as we have seen, at least one of his books was translated into Latin. There are, however, several Latin treatises (Summa per fectionis, magisterii, De investigations perfectionis, De inventione veritatis, Liber f Testamentum Geberi) which pass under his name, but of which no Arabic original has hitherto come to light. These works, while their content as a whole can be fairly closely paralleled in the presumably authentic Arabic works, show a very much greater regard for systematic treatment and exposi tion than the latter ; hence several scholars, notably Kopp, Wiede mann, Berthelot and Darmstadter, have regarded them as Euro pean forgeries fathered upon the venerable name of Jabir. They are universally regarded as the most important of mediaeval chem ical works, and the problem of their authorship is in urgent need of solution. It is perhaps significant that a 13th-century man uscript of the Summa and De investigation perfectionis, discov ered at Florence in 1925 by Darmstadter, contains also a Latin version of the genuine Arabic work, The Book of Mercy.
See M. P. E. Berthelot, La Chimie au Moyen Age (3 vols., Paris, 1893) ; E. Darmstadter, Die Alchemie des Geber (Berlin, 1922) and Liber Misericordiae Geber (Archie. fur Geschichte der Medizin, xvii., 4, 181-197, 1925) ; J. Ruska, Uber des Schriftenverzeichnis des Gaber ibn Hajjan (Archie. f. Gesch. d. Med. xv., 53-67, 1923) and Die siebzig Bucher des Gaber ibn Hajjan (Lippmann Festschrift, Berlin, 1927, pp. ; E. J. Holmyard, "Jabir ibn Hayyan" (proc. Roy. Soc. Med., 1923, xvi., 46-57) ; An Essay on Jabir ibn Hayyan (Lippmann Fest schrift, 28-37), and The works of Geber (London, 1928). A complete edition of the Arabic works, with translation into English by E. J. Holmyard, is in course of publication (Paris, 1928) .