which, despite its esoteric title and hint of great promises, was a straightforward manual of chemical practice. Rhazes classified substances into metals, vitriols, boraxes, salts and stones on the grounds of solubilities and tastes, and added sal ammoniac (ammonium chloride), prepared by distilling hair with salt and urine, to the alchemists’ repertory of substances. Sal ammoniac was soon found to be most useful in ‘colouring’ metals and in dissolving them.
A rationalist and systematist, Rhazes seems to have been among the first to have codified laboratory procedures into techniques of purification, separation, mixing and removal of water, or solidification. But although he and other Arabic authorities referred to ‘sharp waters’ obtained in the distillation of mixtures of vitriol, alum, salt, saltpetre and sal ammoniac, it is doubtful whether these were any more than acid salt solutions. On the other hand, it was undoubtedly by following the procedures laid down by Rhazes and by modifying still-heads that Europeans first prepared pure sulphuric, hydrochloric and nitric acids in the thirteenth century.
The Secret of Secrets was divided into sections on substances – a huge list and description of chemicals and minerals – apparatus and recipes. Among the apparatus described and used were beakers, flasks, phials, basins, crystallization dishes and glass vessels, jugs and casseroles, candle and naphtha lamps, braziers, furnaces (athanors), files, spatulas, hammers, ladles, shears, tongs, sand and water baths, hair and linen filters, alembics (stills), aludels, funnels, cucurbits (flasks), and pestles and mortars – indeed, the basic apparatus that was to be found in alchemical, pharmaceutical and metallurgical workshops until the end of the nineteenth century. Similarly, Rhazes’ techniques of distillation, sublimation, calcination and solution were to be the basis for chemical manipulation and chemical engineering from then onwards. We must be careful, however, not to take later European artists’ representations of alchemical workshops at face value.
A few of the techniques described by Rhazes deserve further comment. Calcination originally meant the reduction of any solid to the state of a fine powder, and often involved a change of composition brought about by means of strong heat from a furnace. Only later, say by the eighteenth century, did it come to mean specifically the reduction of a metal to its calx or oxide. There were many different kinds of furnace available and they varied in size according to the task in hand. Charcoal, wood and straw were used (coal was frowned upon because of the unpleasant fumes it produced). The temperature was raised blacksmith-fashion by means of bellows – hence the derogatory names of ‘puffers’ or ‘workers by fire’ that were applied to alchemists. Direct heat was often avoided in delicate reactions by the use of sand, dung or water baths, the latter (the bain-marie) being attributed to the third-century BC woman chemist known as Mary the Jewess. Needless to say, because heating was difficult to control, apparatus broke frequently. Even in the eighteenth century when Lavoisier found need to distil water continuously for a period of months, his tests were continually frustrated by breakages. By the same token, since temperature conditions would have been hard to control and replicate, the repetition of processes under identical conditions was difficult or impossible. However, whether alchemists were aware of this is doubtful.
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. Already in 3000 BC there is archaeological evidence 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 being 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 a variation of this, no holes were drilled and the distillate was collected directly in the trough around the rim, from where it was probably removed from time to time by means of a dry cloth. In the Mongolian or Chinese still, the distillate fell from a concave roof into a central catch-bowl from which a side-tube led to the outside. Modern experiments, using working glass models of these stills, have shown that5:
the preparation of strong spiritous liquor was, from a technological point of view, a rather simple matter and no civilisation had a distillation apparatus which gave it an advantage.
Even so, although the Chinese probably had distilled alcohol from wine by the fourth century AD, it was several centuries later before it was known in the west. Even earlier, in the second century of our era, 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 not 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 notion that ‘earths’ contained a fatty material was still to be found in Stahl’s theory of phlogiston in the eighteenth century.
An improvement on distillation techniques was apparently first made by Alexandrian alchemists in the first century AD – though, in the absence of recorded evidence, it is just as likely that these alchemists were merely adopting techniques and apparatus from craftsmen and pharmacists. This is particularly evident in the ‘kerotakis’, which took its name from the palette used by painters and artists. This wedge-shaped palette was fitted into an ambix (still-head) as a shelf to contain a substance that was to be reacted with a boiling liquid, which would condense, drip or sublime onto it. These alchemists made air cooling in the distillation process more efficient by separating the distillate off by a continuous process and raising the ambix well above the bikos or cucurbit vessel embedded in the furnace or sand bath. (In 1937 the word Ambix was adopted by the Society for the History of Alchemy and Early Chemistry as the title of the journal that ever since has played an important role in the history of chemistry.) In the Latin west the word alembic (from the Arabic form of ambix, ‘al-anbiq’) came to denote the complete distillation apparatus. By its means, rose waters, other perfumes and, most importantly, mineral acids and alcohol began to be prepared and explored in the thirteenth century.
Continuous distillations were also made possible in the ‘pelican’, so-called because of its arms, which bore resemblance to that bird’s wings. Such distillations were believed to be significant by alchemists, who were much influenced by Jābir’s reputed success at ‘projection’ (the preparation of gold) after 700 distillations. The more efficient cooling of a distillate outside the still-head appears to have been a European contribution developed in the twelfth century. Alchemists and technologists referred to these as water-cooled stills or ‘serpents’. This more efficient cooling of the distillate probably had something to do with the preparation of alcohol in the twelfth century, some centuries after the Chinese. This became an important solvent as well as beverage in pharmacy. By then chemical apparatus was becoming commonly made of 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’ or ‘aqua ardens’ (the water that burns), and only in the sixteenth century was it renamed alcohol. It had also been 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 produce ‘potable gold’. John’s advocation of the quintessence was extremely important since it encouraged pharmacists to try and extract other quintessences from herbs 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.
The sixteenth century saw great improvements in
