Medieval Alchemy - Distillation
|Rhazes was a rationalist and very systematic in
his laboratory procedures. He identified techniques of purification,
separation, mixing and removal of water, or solidification. Although
he and other Arabic alchemists referred to 'sharp waters' obtained in the
distillation of mixtures of vitriol, alum, salt, saltpetre and sal ammonia
it is very likely that these were nothing more than acid salt solutions.
It was the Europeans who really made inroads into distillation. By modifying the still-heads the Europeans first prepared pure sulphuric, hydrochloric and nitric acids by the 13th century. Distillation, one of the most important procedures in practical chemistry, gave rise to a diversity of apparatus, all of which are the ancestors of today's oil refineries. There is archeological evidence from 3000 BC of extraction pots being used in the Mesopotamian region. These pots were used by herbalists and perfume makers. A double-rim trough was percolated with holes, the trough itself was filled with perfume-making flowers and herbs in water. When fired, the steam condensed in the lid and percolated back onto the plants below. In the Chinese or Mongolian still, the distillate fell from a concave roof into a central catch-bowl from which a side-tube led to the outside.
The Chinese probably had distilled alcohol from wine by the fourth century AD, and it was several centuries later before it was known in the west. Even earlier, in the second century, the Chinese had discovered how to concentrate alcohol by a freezing process, whereby separation was achieved by freezing water and leaving concentrated alcohol behind.
The observation of distillation also provided a solution to the theoretical problem of what made solid materials cohere. The binding material could no be Aristotelian water since this patently could not be extracted from a heated stone. Distillation of other materials showed however, that an 'oily' distillate commonly succeeded the 'aqueous' fraction that first boiled off at a lower temperature. It could be argued, therefore, that an 'unctuous', or 'fatty', moisture was the cohesive binder of solid bodies. This theory that 'earths' contained a fatty material was still to be found in the 18th century.
An improvement on distillation techniques was apparently made by the Alexandrian alchemists in the 1st century AD. A wedge shaped palette used by artists and painters was fitted into an ambix (still-head) like a shelf to contain a substance that was to be reacted with a boiling liquid, which would condense, drip or sublime onto it. They also introduced air-cooling in the distillation making the process more efficient and allowing them to draw the distillate off in a continuous process.
In the Latin west the word alembic came to denote came to denote the complete distillation apparatus. By distilling rose waters, other perfumes and, most importantly, mineral acids and alcohol began to be prepared and explored in the 13th century. Alcohol became an important solvent for pharmacists and as a beverage. By this time more of the chemical apparatus was being made from glass. It should be noted that, although 'alcohol' is an Arabic word, it had first meant antimony sulphide, 'kohl'. In the Latin west, alcohol was initially called 'aqua vitae' o 'aqua ardens' (the water that burns), and only in the 16th century did it become named 'alcohol'.
It was even named the 'quintessence', or fifth essence, by the fourteenth-century Spanish Franciscan preacher, John of Rupescissa, in an influential tract, De consideratione quintae essentiae. According to John, alcohol, the product of the distillation of wines, possessed great healing powers from the fact that it was the essence of the heavens. An even more powerful medicine was obtained when the sun, gold, was dissolved in it to make 'potable gold'. John's advocation of the quintessence was extremely important since it encouraged pharmacists to try and extract other quintessences from herb and minerals, and thus to usher in the age of iatrochemistry in the sixteenth century. here was the parting of the ways of alchemy and chemistry.