CHEMISTRYThe four elements: c.450 BC

The philosopher Empedocles, a native of Sicily, introduces a theory which will be accepted in Europe until the 17th century. He states that all matter is made up, in differing proportions, of four elemental substances – earth, air, fire and water. Not until the arrival of a ‘sceptical chemist’ (the title of a book by in 1661) is there a serious threat to this Greek theory of the elements.

Soon an equivalently simple notion is put forward to account for the make-up of living creatures, in the theory of the four humours.

Democritus and the atom: c.420 BC

In the late 5th century BC Democritus sets out an interesting theory of elemental physics. Notions of a similar kind have been hinted at by other Greek thinkers, but never so fully elaborated.

He states that all matter is composed of eternal, indivisible, indestructible and infinitely small substances which cling together in different combinations to form the objects perceptible to us. The Greek word for indivisible is atomos. This theory gives birth to the atom.

Aristotle’s variable atoms: 4th century BC

Aristotle, practical as ever in his determination to get things worked out in detail, proposes a new theory to explain how the four elements of Empedocles and the atoms of Democritus produce the wide range of substances apprehended by our senses.

He suggests that there are two pairs of alternatives – hot and cold, moist and dry – which provide the exact nature of matter. In broad terms the four possible combinations are the four elements: earth (cold and dry), air (hot and moist), fire (hot and dry), water (cold and moist). But it is the infinitely variable balance between these qualities which creates the different atoms of stone or wood, bone or flesh.

Greek science in Alexandria: from the 3rd century BC

Classical Greece has produced a brilliant tradition of theorists, the dreamers of science. Attracted by the intellectual appeal of good theories, they are disinclined to engage in the manual labour of the laboratory where those theories might be tested.

This limitation is removed when the centre of the Greek world transfers, in the 3rd century BC, to Alexandria. In this bustling commercial centre, linked with long Egyptian traditions of skilled work in precious metals, people are interested in making practical use of Greek scientific theory. If Aristotle says that the difference in material substances is a matter of balance, then that balance might be changed. Copper might become gold.

Among the practical scientists of Alexandria are men who can be seen as the first alchemists and the first experimental chemists. Their trade, as workers in precious metals, involves melting gold and silver, mixing alloys, changing the colour of metals by mysterious process.

These are the activities of . The everyday items of a chemical laboratory – stills, furnaces, flasks – are all in use in Alexandria.

There are strong mystical influences in Egypt, some of them deriving from Babylonian astrology, and this tradition too encourages experiment. Astrologers believe in many hierarchies, among the planets in the heavens but also among metals in the earth. Lead is the lowest of the metals, gold the highest. Left to itself, out of sight in the earth, lead may slowly be transformed up the scale to achieve ultimate perfection as gold.

If this process could be accelerated, in the back of a jeweller’s shop, there would be certain immediate advantages. In the early centuries, the experiments of chemistry and alchemy go hand in hand.

Alchemy in Asia: 8th – 10th century AD

There are two important centres of alchemical experiment in medieval Asia. One is Baghdad under the caliphate, where from the 8th century there is enthusiastic translation and study of Greek scientific texts. Arab alchemists, in their pursuit of synthesized gold, make practical advances in techniques of distillation. And they identify several chemical substances.

The other great centre is China, where alchemical experiments have a slightly different purpose. The quarry is still gold, but as an elixir of eternal life. This is the pursuit of the Daoists (one of whom describes, with gentle irony, an Experiment which goes wrong in the 9th century). It is Daoists who make the most startling chemical discovery of the period – gunpowder.

Gunpowder: 10th century

In about 1040 a Chinese manual on warfare is issued under the title Compendium of Military Technology. It is the first document to describe gunpowder. This black powder, formed by pounding a mixture of saltpetre, charcoal and sulphur (a dangerous process if the pounding is overdone), seems to have been developed in the small chemical laboratories attached to the temples of Daoists where research is conducted mainly on the secret of eternal life.

At this early stage in China the military use of gunpowder is limited to grenades and bombs lobbed at the enemy from catapults. Its real destructive force will only emerge when the explosion is confined, in the development of artillery.

Science’s siesta: 8th – 15th century AD

In the profoundly Christian centuries of the European Middle Ages the prevailing mood is not conducive to scientific enquiry. God knows best, and so He should – since He created everything. Where practical knowledge is required, there are ancient authorities whose conclusions are accepted without question – Ptolemy in the field of astronomy, Galen on matters anatomical.

A few untypical scholars show an interest in scientific research. The 13th-century Franciscan friar Roger Bacon is the most often quoted example, but his studies include alchemy and astrology as well as optics and astronomy. The practical scepticism required for science must await the Renaissance.

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