The Fontana History of Chemistry. William Brock J.
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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