1983 – 6(3)

III. – Original Latin works

The tradition of practical alchemy underwent an evolution in clarity with the pseudepigraphical Summa perfectionis of Geber, written in the late 13th c. [[ Gebri … Summa perfectionis magisterii in sua natura … , in Manget, J. J., Bibliotheca chemica curiosa, Genevae, 1702, vol. l. This is a reprint with slight variations of the edition published by Marcellus Silber, and edited by Fausto Sabeo et al., between 1523 and 1527 in Rome. I am presently working on a critical edition of the Summa, but until this task is accomplished, the reader may be advised to rely on the Sabeo edition and its reprints over the other available versions. ]]. The Summa spends three chapters simply describing the dimensions of a furnace to heat the aludel. The furnace is cylindrical, with an ash-box at the lowest level, a fire-box above this, and the hearth at the highest level. The latter space is partitioned off by a transverse iron rod driven into opposed walls of the cylinder, intended to support an aludel (or cucurbit). The oven is ventilated with ten air-holes; it is unspecified whether these and the doors to the ash – and fire-box have covers. The aludel, which is made of thick glass, is described in detail (fig. 3). The lower half is made from a rounded concha (rather like the « urinal » of medieval physicians) to whose neck Geber attaches a circular zona of glass, thus producing a collar. The upper half of the aludel, which is one span long, fits over the mouth of the concha and rests within the collar, which is fixed at the bottom : in this way a sealed joint is made. The conical upper end of the aludel is pierced; this allows the alchemist to insert some lint or cotton during sublimation: if powder collects on it, the process is not finished. The aludel also appears in another work ascribed to Geber, the L. Fornacum [[ The Liber fornacum, or Liber de fornacibus construendis has only been edited once, as is also the case with the Liber de inventione perfectionis attributed to Geber. These works were edited by a pseudonymous « Chrysogonus Polydorus »,and first printed in the ln hoc volumine de alchemia continentur haec … , (Nuremberg, 1541), printed by Johannes Petreius – the printer of Copernicus’s De revolutionibus orbium caelestium. Because of the extreme rarity of this edition and its reprints, I have been forced to use a modern German translation – Ernst Darmstaedter, Die Alchemie des Geber (Berlin, 1922). The L. fornacum occupies pp. 114-125 of this version. ]], along with separate furnaces for calcining, distilling (with a balneum mariae, a water bath), distilling per descensum (i.e. reduction by means of a descensory like the būt-bar-būt of Rhases), fusing, dissolving, and fixing (the conversion of a volatile reagent to a non-volatile compound). The cylindrical distillatory and dissolutory furnaces have separate fire-boxes and hearths; they are variants of the sublimatory furnace described above. The calcinatory and fusory ovens, however, are simple shaft furnaces, where the crucibles or cupels are set directly on the burning fuel. The fixatory furnace has a removable hearth set in an open shaft : hence it is a hybrid between the sublimatory and calcinatory types. The L. fornacum specifies that the calcinatory (and thus fixatory) oven should be rectangular- four feet long, three feet wide, and one half foot thick. The furnaces in general are made of clay, molded into sections which then form the component parts of the furnace.

Geber also departs from the Rhases tradition by incorporating assaying techniques into the Summa. Because these processes required a certain amount of specialized apparatus, it will be useful to describe them. As listed in the Summa perfectionis , they are cementation, cupellation, firing to the point of glowing, fusion, exposure to « the vapors of sharp things » (i.e. distilled vinegar and other vegetal acids), extinction (quenching), immersion of the hot metals in burning sulfur, the repetition of calcination (in modern parlance « oxidation ») and reduction, and attempted amalgamation of the metal to be tested with mercury. It is important to note that the Arabic Kitāb al-Asrār of Rhases mentions only color as a means of testing the respective metals’ purity (Ruska, 1937). The process of cementation, in which a laminated or filed metal was placed in a crucible with a variant mixture of vitriol (usually copper or iron sulfate), saltpeter (potassium nitrate), sal ammoniac (ammonium chloride), table salt, and/or brick dust, then heated at high temperature, caused the penetration of mineral acids in the form of vapor; these could be selected to decompose a specific metal while not attacking another. While cementation was known from antiquity both as an assaying technique and as a means of producing metal compounds for various applications, one can find many examples of the latter use in the K. al-Asrār and cognate texts, but none of the former. Only with the Summa perfectionis do we find a systematic description of cementation as one component in a battery of tests designed to ascertain the success of transmutation. The same may be said of the ancient technique known as cupellation, in which a porous cupel exposed to high heat is used to separate the base metals from gold and silver; when lead oxide (whose presence in the alloy to be tested is insured by the addition of metallic lead, followed by blasting) is formed, it sinks into the walls of the cupel, carrying other impurities with it. The production of cupels is carefully described in the Summa perfectionis: the author says to sift cinders, calces, or burnt animal bones, or a mixture of all three. These are then made into a kind of dough, with the addition of water, and that is shaped into the form of a small pot, whose base is sprinkled with powdered glass. When the cupels are dry, the metal to be tested is placed therein, and a fire of coals built upon it, whereupon the test may proceed. Although Geber does not take the step of quantifying this test, not even mentioning the analytical balance, his attempts nonetheless exhibit an incalculable superiority over the color tests of Rhases.