The Geber Problem
The Origin of Liber Fornacum
Introduction: The literature on Jabir’s Latin works is extensive. In this and later Brief Notes we intend now and then to direct the attention of historians of science to some revealing materials that can help in illuminating the path of research into what is called the Geber Problem. Briefly, the question is the following: Who wrote the five disputed Latin alchemical works that are ascribed to Geber? Were they written by Jabir ibn Hayyan or by a Latin writer who ascribed them to him? 
Liber Fornacum The longest and best known of the writings of Geber is the summa perfetionis magisterii. The Summa makes reference to two other books, De investigatione perfectionis , and Liber fornacum . The first of these accompanies the Summa in a thirteenth-century manuscript, but the second (Liber fornacum) is extant in a fifteenth century manuscript in Venice and in two seventeenth century manuscripts in London and Glasgo, and the three mention the name of the translator. It was printed in a sixteenth-century edition of Geber's works and the name of the translator was given.  There may be more manuscripts also. De investigatione, De inventione, and Liber fornacum  all cite the Summa. The Testamentum is mentioned in the Liber fornacum (which is itself mentioned in the Summa).
From this maze of citations it is evident that the Liber Fornacum is a main work among this group of Geber’s Latin works. It is mentioned in the Summa and the Summa is mentioned in it.
The oldest known extant MS of Venice mentions Rodericum Yspanensem as the translator. The two other manuscripts from the seventeenth century in the British Library and in Glasgow give the name of Rodogero Hispalensi as the translator. The details of these manuscripts are as follow :
- Venice, Biblioteca Marciana MS. Lat. VI. 215. [3519.] 297 folios. Parchment. Octavo
Geber. Liber de inventione perfectionis. Liber Fornacum translatum. per Rodericum Yspanensem.
This manuscript was written by 'Theodoricum Ghysiberti de Luneborg de Saxonia, anno 1475'.]
- Ferguson MS. 232.
78 folios. 285x208mm. 17th Century. In Latin.
f72v-76 Geberi Arabis Philosophi sollertissimi rerumque naturalium peritissimi, liber fornacum ad exerienda [...] pertinentium interprete Rodogero Hispalensi.
- British Library MS. Sloane 1068.
Paper, 389 folios. 17th Century
6. Ejusdem 'liber fornacum, ad exercendam chemiam pertinentium; interprete Rodogero Hispalensi'. f.369. [Printed Basiliae, 1561, p.193.
There is also a manuscript at Wellcome Institute which has to be investigated:
London, Wellcome Institute MS. 384.
16 + 338 folios. 245x175mm. 16th Century [c.1565.]
18. ff111-117v Geber. Liber fornacum.
Conclusion: From the preceding information we learn that the Liber Fornacum was translated from Arabic by a known translator. And since it mentions the Summa, we can safely conclude that the Summa was translated also from Arabic. Therefore the assumption that the Latin works of Jabir (Geber) were written by a Latin author cannot be accepted and it is based on conjecture and not on concrete evidence. And despite some voluminous recent published works the question is far from being settled as some historians of science like us to believe. 
 The basic information given in this note was presented in Science and Technology in Islam, UNESCO, 2001, ed. A.Y. al-Hassan et al. Part I, pp.156-157. Further new information on the Geber Problem is given in a paper in the articles section of this site.
 Russell,Richard (translator), The Alchemical Works of Geber, introduction by E. J. Holmyard, Weiser, Maine, USA, 1994, Chapter IV p. 153
 Russell, op. cit., Chapter VI p.157
 See below British Library MS. Sloane 1068
 Russell, op. cit, Chapter III, OF Furnaces, p. 232.
 This information occurs in a listing of alchemical manuscripts in world libraries that is given in the Alchemy web site http://www.levity.com/alchemy/home.html published by Adam McLean.
 A voluminous work trying to give credibility to the assumption of a Latin author is The Summa Perfectionis of Pseudo Geber by William R.Newman, Leiden, 1991.