Geber’s furnaces, on the other hand, show a greater tendency toward specificity when compared to those of the Rhases tradition: this tendency becomes ever more pronounced during the culmination of the Middle Ages. The specialization of furnaces did not so much produce new inventions as it did alterations – frequently of a radical nature – on older types. The late Middle Ages witnessed the dispersion and perhaps the earliest development, for example, of a specific genus of alchemical oven – the covered, cylindrical « disgesting » furnace later called an « athanor » [[ The L. fornacum (Darmstaedter, op. cit., 116) calls the fixatory furnace an athanor. If the L. fornacum is really by the author of the 13th c. Summa perfectionis, we may then see an early, transitional usage of the term « athanor, we may then see an early, transitional usage of the term « athanor » here, which is similar to the Arabic tannūr in that it relates to a high temperature oven. By the 14th c., however, such texts as the L. de multiplicatione and the L. lucis had restricted the term « athanor » to the low temperature version of the domed furnace.]] . The term « athanor » is derived, of course, from the Arabic at-tānnur, a bread baker’s oven – the Latin version came to mean a specific furnace for low, constant heat, however, while its Arabic namesake was a high-temperature roasting oven, evolving from the ancient glass-maker’s kiln (Ruska, 1937). Although the athanor and at- tānnur were both dome shaped, the former was highly insulated, in keeping with its goal of supplying constant heat. The need for such an oven may have resulted from the increasing interest in amalgams allowed to digest for long periods of time; the 14th c. De multiplicatione of ps. Thomas Aquinas, for example, prescribes that an amalgam be heated twenty six weeks in an athanor. This furnace receives a good description in the appendix to John of Rupescissa’s L. lucis (the L. lucis is a fourteenth or fifteenth c. text, but it is unclear to me wether the appendix formed part of the original text – at any rate, the athanor’s description in the main body of the text is consonant with the appendix). This furnus physicus (fig. 4) is 3,5 feet tall, and 1,5 feet wide; it has four sections and three compartments. The lowest space, the ash-box, is 1 foot high, and separated from the focus by an iron grate. 9 fingers above the grate is an iron plate, separating the vented focus from the hearth. The plate has a central, circular hole, 4 fingers wide. 3 iron slats (« A » in illustration), each with a hole of different size, can be slid in from a slot in the furnace wall to partially cover the central hole, thus varying the heat. A tripod fits over the perforated slat, and upon this sits the ovum philosophicum (« B »), a split globe 7 fingers in diameter, into which a « certain small clay vessel » is packed to be heated. The illustration shows a conical, capped vessel being heated in place of the egg. The hearth and its cover, which are luted inside and out for insulation, comprise 1 foot, 9 fingers in height; the center of the removable cover is bored so that the interior heat may be judged.
IV. – Latin works depending on non-alchemical sources
The late 15th and early 16th c. saw the birth of two independent genres which quickly outpaced the developments made in apparatus by alchemists – the printed metallurgical treatise and distillation book. The advances made in these texts were partially re-absorbed by the alchemists of the period, leading to a dependency which can be seen in the Alchemia (1597) and Commentarii I (1606) of Andreas Libavius, one of the great systematizers of Renaissance alchemy. The Commentarri I gives pictures of over 189 furnaces, most of them drawn from purely metallurgical texts such as those of G. Agricola and L. Ercker. Libavius divides his furnaces into nine main types-athanors, reverberatory furnaces, assaying furnaces (fornaculae), baths (of water, ash, sand, or steam), distilling furnaces (vesicariae, cacabariae), crucible furnaces, descensories, « wind-ovens » (anemiae), and self-feeding furnaces (furni acesiae).
The fornax anemiae is not a blast furnace in the modern sense (a shaft furnace where air is forced directly into the mixture of fuel and ore), but rather an open hearth built outside, receiving the prevailing wind, and equipped with built – in bellows : such a design is quite ancient. The furnus acesiae, commonly known in the 15th c. as the piger Henricus, had an attached, vertical, covered chute, in which one packed charcoal or other fuel. The tube fed directly into the fire-box; as fuel was consumed, gravity would carry more down to replace it. Libavius’s Alchemia also describes numerous fornaces conjunctae, which employed a central tower- oven to heat surrounding water-baths and the like. Libavius’s description of industrial cupellation- and muffel-furnaces were also culled from the technical writers, especially Agricola. The same reliance occurs in Libavius’s depiction of glassware; his illustration of the caput Aethiopicum, for example, a stillhead enclosed in a glass, water-cooled unit, derives directly or indirectly from the L. de arte distillandi de compositis of H. Brunschwig (1512), a medical work. In like manner, he includes high, conical still-heads similar to the Rosenhut of Puff van Shrick’s nueczliche materi von manigerley ausgeprânten wasser (1478).
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