Jabir or Geber, fl. 8th cent., Arab alchemist and physician, originally named Jabir ibn Hayyan. He is believed to have lived at Kufa and at Baghdad. A great number of works on alchemy, many of them unpublished, have been attributed to him, but scholars disagree as to their authenticity. Recent studies indicate that many of the extant works in Arabic were written in the 9th and 10th cent. by later Arab alchemists and issued under Jabir's name. The works influenced the development of medieval alchemy and indicate the use of laboratory experiments. They perpetuated the theory that metals are composed of mercury and sulfur and can be transmuted into gold. In the early 14th cent. a Spanish alchemist wrote under the Latinized form of the name, Geber; his works are considered the clearest expression of alchemical thought to appear before the 16th cent. Several of the Arabic works were translated by E. J. Holmyard and published in 1928.