Jabir ibn Hayyan

Something close to three thousand works were attributed to Jabir, which was already suspicious to medieval Arabic bibliographers, Ibn al-Nadim, in the tenth century, records that some of his contemporaries doubted Jabir had existed at all.

The dating was settled philologically by Paul Kraus in a two-volume study published in Cairo in 1942-43. Kraus showed on internal evidence, technical terms not coined until the mid-ninth century, and citation of Greek works that had not been translated into Arabic when the supposed author died, that the corpus cannot be the work of a single eighth-century author, and belongs instead to a school writing over roughly a century between about 850 and 950. That conclusion has held. His further identification of the authors with Ismaili circles has not: the Shi'ism of the texts has since been shown to differ substantially from Isma'ilism, and it should not be repeated as current scholarship.

What remains genuinely open is narrower than it is usually made to sound. The dispute among specialists, Fuat Sezgin, Pierre Lory and Syed Nomanul Haq against the strong form of Kraus, is not about the corpus's overall date but about whether an authentic eighth-century core survives underneath the later redaction. The traditional birth year of about 721 is itself an inference from the date of his father's execution rather than a record.

The authorship problem does not diminish the work.

It sets out the sulphur-mercury theory of metallic composition, which structured alchemical thinking in Arabic and then in Latin for the better part of a millennium; a doctrine of mizan, the balance of the four qualities in a substance, worked out numerically; and a great deal of genuine laboratory procedure, distillation, crystallisation, sublimation, and the preparation of strong acids.

The Latin Geber is a further complication and a common source of error. The most influential Latin text under that name, the Summa perfectionis, is not a translation from the Arabic Jabir at all; it is a Latin composition of around 1300, which William Newman has argued in detail was written by Paul of Taranto. So the figure who stood for the whole art in medieval Europe, to the point that his Latinised name became a byword for obscure language, is at two removes from any historical person: a Latin author writing under an Arabic name that was itself the pen-name of a school.