Geber (flourished 14th century) was the unknown author of several books that were among the most influential works on alchemy and metallurgy during the 14th and 15th centuries.
The name Geber, a Latinized form of Jābir, was adopted because of the great reputation of the 8th-century Arab alchemist Jābir ibn Ḥayyān. A number of Arabic scientific works credited to Jābir were translated into Latin during the 11th to 13th centuries. Thus, when an author who was probably a practicing Spanish alchemist began to write in about 1310, he adopted the westernized form of the name, Geber, to give added authority to his work, which nevertheless reflected 14th-century European alchemical practices rather than earlier Arab ones.
Four works by Geber are known: Summa perfectionis magisterii (The Sum of Perfection or the Perfect Magistery, 1678), Liber fornacum (Book of Furnaces, 1678), De investigatione perfectionis (The Investigation of Perfection, 1678), and De inventione veritatis (The Invention of Verity, 1678). They are the clearest expression of alchemical theory and the most important set of laboratory directions to appear before the 16th century. Accordingly, they were widely read and extremely influential in a field where mysticism, secrecy, and obscurity were the usual rule.
Geber accepted most of the Arabic alchemical theories and spread them throughout western Europe. He assumed that all metals are composed of sulfur and mercury and gave detailed descriptions of metallic properties in those terms. He also explained the use of an elixir in transmuting base metals into gold.
Geber’s rational approach, however, did much to give alchemy a firm and respectable position in Europe. His practical directions for laboratory procedures were so clear that it is obvious he was familiar with many chemical operations. He described the purification of chemical compounds, the preparation of acids (such as nitric and sulfuric), and the construction and use of laboratory apparatus, especially furnaces. Geber’s works on chemistry were not equaled in their field until the 16th century with the appearance of the writings of the Italian chemist Vannoccio Biringuccio, the German mineralogist Georgius Agricola, and the German alchemist Lazarus Ercker.