Читать книгу The Fontana History of Chemistry - William Brock J. - Страница 10

Although it is possible to argue that modern chemistry did not emerge until the eighteenth century, it has to be admitted that applied, or technical, chemistry is timeless and has prehistoric roots. There is conclusive evidence that copper was smelted in the Chalcolithic and early Bronze Ages (2200 to 700 BC) in Britain and Europe. Archaeologists recognize the existence of cultures that studied, and utilized and exploited, chemical phenomena. Once fire was controlled, there followed inevitably cookery (gastronomy, according to one writer, was the first science), the metallurgical arts, and the making of pottery, paints and perfumes. There is good evidence for the practice of these chemical arts in the writings of the Egyptian and Babylonian civilizations. The seven basic metals gave their names to the days of the week. Gold, silver, iron, mercury, tin, copper and lead were all well known to ancient peoples because they either occur naturally in the free state or can easily be isolated from minerals that contain them. For the same reason, sulphur (brimstone) and carbon (charcoal) were widely known and used, as were the pigments, orpiment and stibnite (sulphides of arsenic and antimony), salt and alum (potassium aluminium sulphate), which was used as a mordant for vegetable dyes and as an astringent.

The methods of these early technologists were, of course, handed down orally and by example. Our historical records begin only about 3000 BC. With the aid of techniques derived ultimately from the kitchen, these artisans extracted medicines, perfumes and metals from plants, animals and minerals. Their goldsmiths constructed wonderful pieces of jewellery and their metallurgists worked familiarly with the common metals and their alloys, associating them freely with the planets. Jewellers were particularly interested in the different coloured effects of the various alloys that metallurgists prepared and in the staining of metallic surfaces by salts and dyes, or the staining of stones and minerals that imitated the colours of precious minerals. In fact, throughout the east we find an emphasis upon colour, and the establishment of what Needham describes as the industry of aurifiction. Clearly there existed a professional class of artisans, metallurgists and jewellers who specifically designed and made imitation jewellery from mock silver, gold or artificial stones. The Syrians and Egyptians appear to have developed a particular talent for this work, and written examples of their formulae or recipes have survived in handbooks that were compiled centuries later in about 200 BC. For example, to prepare a cheaper form of ‘asem’, an alloy of gold and silver:

Take soft tin in small pieces, purified four times; take four parts of it and three parts of pure white copper and one part of asem. Melt, and after casting, clean several times and make with it whatever you wish to. It will be asem of the first quality, which will deceive even the artisans.

Or, in the equivalent of nineteenth-century electroplating, to make a copper ring appear golden so that ‘neither the feel nor rubbing it on the touchstone will discover it’:

Grind gold and lead to a dust as fine as flour; two parts of lead for one of gold, mix them and incorporate them with gum, coat the ring with this mixture and heat. This is repeated several times until the object has taken the colour. It is difficult to discover because the rubbing power gives the mark of an object of gold and the heat [test] consumes the lead and not the gold.

In one sense this aurifictional technology can be described as simple empiricism. To say that, however, does not mean that its practitioners were devoid of ideas about the processes they worked, or that they had no model to underpin their understanding of what was happening. Given that these technologies were evidently closely bound up with magic, ritual and trade secrecy, this was equivalent to a theoretical underpinning. Although these artisans may not have had any sophisticated chemical theory to explain or guide their practices, that experience was undoubtedly bound up with ritualistic beliefs concerning the objects that were handled. We need only notice the more than obvious connection of the names of metals with the planets, and

TABLE 1.1 The ancient associations of metals and the heavens.

from them the names of the week (table 1.1), as well as beliefs that metals grew inside the earth, to conclude that myth and analogy played the equivalent role of chemical theory in these technologies. Moreover, it seems highly likely from later written records that metallurgists believed that, while metals grew normally at a slow pace within the earth, they could accelerate this process within the smithy, albeit an appropriate planetary god or goddess had to be propitiated by ritual purification for the rape of mother earth. It was this element of ritual, albeit in a Christianized form in the Latin west and a Taoist form in China, that was handed on to the science of alchemy.

For a science alchemy was. Theory controlled and exploited the empirical. Alchemy became a science when the masses of technical lore connected with dyeing and metallurgy became confronted by and amalgamated with Greek theories of matter and change. Greek philosophers with their strong sense of rationality and logic contributed a theory of matter that was able to order, classify and explain technological practice. The pre-Socratic philosophers of the sixth century BC had conjectured that the everyday substances of this material world were generated from some one primary matter. Both Plato (c 427–c 347 BC) and Aristotle (384–322 BC), teaching in the fourth century BC, had also written of this prime matter as a featureless, quality-less stuff, rather like potter’s clay, onto which the various qualities and properties of hotness, coldness, dryness and moistness could be impressed to form the four elements that Empedocles (d. c. 430 BC) had postulated in the fifth century BC. This quartet of elementary substances, in their turn, mixed together in various proportions to generate perceptible substances. Conversely, material substances could, at least in principle and often in practice, be analysed into these four components:

Although Aristotle seems not to have articulated a theory of cohesion, we may assume that the four elements were ‘bound together’ by the moist quality. Expressed in rectangular diagrammatic form, which became the basis for later geometrical talismans and symbols, each adjacent element can be seen to possess a common quality; hence all four of the elements are, in principle, interconvertible. Thus, by changing the form or forms (transformation) of bodies, Nature transmutes the underlying basic, or primary, matter into different substances. Despite pertinent criticisms by Theophrastus (371–286 BC), Aristotle’s pupil and successor at the Lyceum, that fire was different from other elements in being able to generate itself and in needing other matter to sustain it, the theory of the four elements was to remain the fundamental basis of theoretical chemistry until the eighteenth century.

For Aristotle there was a fundamental distinction between the physics of the heavens, which were eternal, perfect, unchanging and endowed with natural circular motion, and the sublunar sphere of the earth, which was subject to change and decay and where movement was either upwards or downwards from the centre of the universe. This sublunar region was composed from Empedocles’ four elements. Aristotle had rejected the atomic theory introduced in the fifth century BC by Democritus. The claim that the apparent differences between substances arose from differences in the shapes and sizes of uncuttable, homogeneous particles, while ingenious, seemed to Aristotle pure invention, whereas the four elements lay close to human sensory experience of solids and liquids and of wind and fire, or of hot and cold, wet and dry objects. How could atomism account for the wide variety of shapes and forms found in minerals in the absence of a formal cause? Moreover, to Aristotle, the postulation of a void meant that there was no explanation for motion, and without motion there could be no change. Atomism also failed to distinguish between physical and mathematical division – a problem that was overcome after Aristotle’s death by Epicurus (341–270 BC), who allowed that, although atoms were the unsplittable physical minima of matter, because an atom had definite size, it could be said to contain mathematically indivisible parts. Epicurus also explained the compounding of atoms together as they fell with equal speeds through the void as due to sudden ‘swerves’ or deviations. These unpredictable swerves are a reminder that atomism, as popularized in Epicurean philosophy, had more to do with the establishment of a moral and ethical philosophy than as an interpretation of the physics and chemistry of change. Swerving atoms allowed for human free will. Atomism for the Epicureans, as well as for its great poetic expositor, the Roman Lucretius in De rerum natura (c. 55 BC), was a way of ensuring human happiness by the eradication of anxieties and fears engendered by religions, superstitions and ignorance. Ironically, in the sixteenth century, atomism began to be used as a way of eliminating the superstitions and ignorance of Aristotelianism.

The other great post-Aristotelian system of philosophy, Stoicism, because it adopted and adapted considerable parts of Aristotelianism, was more influential. Founded by the Athenian, Zeno (342–270 BC), during the fourth century BC and refined and developed up to the time of Seneca in the first century AD, Stoicism retained Aristotle’s plenistic physics and argued for the indefinite divisibility of matter. Stoics laid stress on the analogy between macrocosm and microcosm, the heavens and the earth, and distinguished between inert matter and a more active form, the latter being called the pneuma, or vital spirit. Pneuma pervaded the whole cosmos and brought about generation as well as decay. Ordinary substances, as Empedocles and Aristotle had taught, were composed from the four elements, albeit hot and dry, fire and air were more active than passive wet and cold, water and earth. From this it was but a short step to interpreting air and fire as forms of pneuma, and pneuma as the glue or force that bound passive earth and water into cohesive substances. The concept was to have a profound effect on the interpretation of distillation.

Chemical compounds (an anachronism, of course) were mixtures of these four elements in varying proportions – albeit Aristotle’s and the Stoics’ views were rather more sophisticated than this bald statement suggests. The central theorem of alchemy, transmutation, could be seen in one of two ways, either as what we would call chemical change caused by the different proportions of elements and their rearrangement, or as a real transmutation in which the qualities of the elements are transformed. Alchemy allowed far more ‘transmutations’ than later chemistry was to allow, for it permitted the transmutation of lead or other common metals into gold or some other precious metal. A real transmutation of lead and gold was to be achieved by stripping lead of its qualities and replanting the basic matter that was left with the qualities and attributes of gold. Since lead was dense, soft and grey, while gold was dense, soft and yellow, only a change of colour seemed significant. However, although alchemy is usually taken to be the science of restricted metallic transmutations, it is worth emphasizing that it was really concerned with all chemical changes. In that very general sense, alchemy was the basis of chemistry.

One of the most important geographical areas for the creation of alchemy was Egypt during the Hellenistic period from about 300 BC to the first century AD. Egypt was then a melting pot for Greek philosophy, oriental and Christian religions, astrology, magic, Hermeticism and Gnosticism, as well as trade and technology. Hermeticism, which took its title from Hermes, the Greek form of the Egyptian deity, Thoth, the father of all book learning, was a blend of Egyptian religion, Babylonian astrology, Platonism and Stoicism. Its vast literature, the Hermetic books, supposedly written by Hermes Trismegistus, was probably compiled in Egypt during the second century BC. Gnosticism, on the other hand, was an ancient Babylonian religious movement, which stressed the dualism between light and darkness, good and evil. Gnosis was knowledge obtained only through inner illumination, and not through reason or faith. Humankind was assured of redemption only from this inner enlightenment. Gnosticism both competed with early Christianity and influenced the writing of the Gospels. As its texts show, however, Gnosticism was as much influenced by contemporary alchemy as it influenced alchemical language. For example, in the Gnostic creation story, chemical expressions referring to sublimation and distillation are found, as in the phrase ‘the light and the heavy, those which rise to the top and those which sink to the bottom’. The most important of the Gnostics, Theodotos, who lived in the second century AD, used metaphors of refining, filtering, purifying and mixing, which some historians think he may have drawn from the alchemical school of Mary the Jewess. When Gnostic language is met in alchemical texts of the period, such as the Dialogue of Kleopatra and the Philosophers, however, it is difficult to know whether the author is referring to the death and revivification of metals or to the death and regeneration of the human soul. Exoteric alchemy had become inextricably bound with esoteric alchemy.

Most historians have seen three distinctive threads leading towards the development of Hellenistic alchemy: the empirical technology and Greek theories of matter already referred to, and mysticism – an unsatisfactory word that refers to a rag-bag of magical, religious and seemingly irrational and unscientific practices. Undoubtedly this third ingredient left its mark on the young science, and it in turn has left its mark on ‘mysticism’ right up until the twentieth century. In Hellenistic Egypt, as in Confucian China, there was a distinctive tendency to turn aside from observation and experiment and the things of this world to seek solace in mystical and religious revelations. It was the absorption of this element into alchemy that splintered its adherents into groups with different purposes and which later helped to designate alchemy as a pseudo-science.

Recent studies have shown the considerable extent of pharmacological knowledge within the Arabic tradition. This tradition was to furnish the Latin west with large numbers of chemical substances and apparatus. It was clearly already well established in Greek alchemy, and it is to medicine that the historian must also look for another of alchemy’s foundation stones. For it was the Greek pharmacists who mixed, purified, heated and pulverized minerals and plants to make salves and tinctures. In Greek texts the word for a chemical reagent is, significantly, pharmakon.

The modern conspectus is, therefore, that practical alchemy was the bastard child of medicine and pharmacy, as well as of dyeing and metallurgy. By applying Aristotelian, Neoplatonic, Gnostic and Stoic ideas to the practices of doctors and artisans, Greek alchemists reinterpreted practice as transmutation. This point is especially clear in a seventh-century AD text by Stephanos of Alexandria, ‘On the great and sacred art, or the making of gold’, in which he attacked goldsmiths for practising aurifiction. If such craftsmen had been properly educated in philosophy, he commented, they would know that gold could be made by means of an actual transformation.

For one group of such-minded alchemical philosophers, astrology, magic and religious ritual grew at the expense of laboratory and workshop practice. Alchemical symbolism and allegory appealed strongly to the early Gnostics and Neoplatonists. The ‘death’ of metals, their ‘resurrection’ and ‘perfection’ as gold or purple dyes were symbolical of the death, resurrection and perfection of Christ and of what should, ideally, happen to the human soul. This esoteric alchemy is more the province of the psychologist and psychiatrist, as Jung claimed, or of the historian of religion and anthropology, than of the historian of chemistry. Nevertheless, as in the case of Isaac Newton, the historian of science must at all times be aware that, until the nineteenth century at least, most scientific activities were, fundamentally, religious ones. The historian of chemistry must not be surprised to find that even the most transparent of experimental texts may contain language that is allegorical and symbolical and which is capable of being read in a spiritual way.

Exoteric alchemists continued their experimental labours, discovered much that was useful then and later, and suffered the indignities of bad reputation stemming from less noble confidence tricksters. Another group became interested in theories of matter and promoted discussion of ideas of particles, atoms or minima naturalis. Finally, the artisans and technologists continued with their recipes, uninterested in theoretical abstractions.

The primitive notion that metals grew inside the earth had been supported by Aristotle in his treatise Meteorologica – the title referred to the physics of the earthly, as opposed to the celestial, sphere, and had nothing to do with weather forecasting. Less perfect metals, it was supposed, slowly grew to become more noble metals, like gold. Nature performed this cookery inside her womb over long periods of time – it was for this reason that, during the middle ages, mines were sometimes sealed so as to allow exhausted seams to recover, and for more metals to grow. If one interpreted the artisans’ aurifictions as aurifactions, then it appeared that they had successfully succeeded in repeating Nature’s process in the workshop in a short time. Perhaps further experimentation would bring to light other techniques for accelerating natural alchemical processes.

Although Aristotle had never meant by ‘prime matter’ a tangible stuff that could be separated from substances, this was certainly how later chemists came to think of it. Similarly the tactile qualities became substantialized (substantial forms) and frequently identified with the aerial or liquid products of distillation, or pneuma.

In gold-making, much use of analogy was made. Since there is a cycle of death and regrowth in Nature from the seed, its growth, decay and regeneration as seed once more, the alchemist can work by analogy. Lead is taken and ‘killed’ to remove its form and to produce the primary matter. The new substance is then grown on this compost. In the case of gold, its form is impressed by planting a seed of gold on the unformed matter. To grow this seed, warmth and moisture were requisite, and to perform the process, apparatus of various kinds – stills, furnaces, beakers and baths – was required, much of it already available from artisans or readily adapted from them.

A secret technical vocabulary was developed in order to maintain a closed shop and to conceal knowledge from the uninitiated, a language that through its long history became more and more picturesque and fanciful. In Michael Maier’s Atalanta fugiens (1618), we read that ‘The grey wolf devours the King, after which it is buried on a pyre, consuming the wolf and restoring the King to life.’ All becomes clear when it is realized that this refers to an extraction of gold from its alloys by skimming off lesser metal sulphides formed from a reaction with antimony sulphide and the roasting of the resultant gold – antimony alloy until only gold remains. As Lawrence Principe has noted, this incomprehension on our part is surely little different from today’s mystification when the preparative organic chemist issues the order, ‘dehydrohalogenate vicinal dihalides with amide ion to provide alkynes’. In other words, although alchemists undeniably practised deliberate obfuscation, much of our incomprehension stems from its being in a foreign language, much of whose vocabulary has been lost. On the other hand, we must recognize that obscurity also suited the rulers and nobility of Europe, who patronized alchemists in the hope of solving their monetary problems.