HISTORY OF CHEMISTRY Chemistry as a science had its origin in Egypt (see ALCHEMY) —the product on the one hand of much practical experience of workers in metals, glass and pottery, of users of dyeing and tan ning materials ; and on the other of Greek and Eastern specula tion on the nature of the material world. The great school founded at Alexandria was the natural meeting place of the two streams, and from their union came in time the alchemy of the Arab con querors, the iatrochemistry (q.v.) of the medical chemists and finally our modern science. In all the older cosmogonies we find the idea that there was some primordial element or principle from which the visible universe was derived. Perhaps the oldest speculations assigned to water this elementary character; its teeming life, its vivifying power, its solid deposits all marked it as the origin of things. The doctrine that water was the prime element—associated with the name of Thales—exerted an im mense influence on scientific thought throughout the centuries. Van Helmont in the early I7th century thought he had proved it experimentally; it remained for Lavoisier in the late eighteenth to disprove it by more decisive experiment. But water was not the only "element" that was regarded as primordial by Greek philo sophers. That air could be condensed into clouds and clouds into rain was taught by Anaximenes ; water could be evaporated into air, leaving solid earth behind. Everything therefore sprang from air. That fire was the first principle of things would appeal to those who came in contact with the fire-worship of the Chaldeans, or with the religion of the ,Persians and Parsees, whom Zoroaster taught to look on fire as the symbol of goodness in creation. Heracleitus among the Greeks espoused the cause of fire, Phere cides that of earth; it was indeed easy to show that from com bustible solids fire, air and water could be derived. That all four were primal elements, and that the varieties of matter were made from intermixture of these, was the conception of Empedocles, who regarded each element as distinct and unchangeable. But the doctrine of the Four Elements which gave so powerful an impulse and direction to chemistry was that taught by Aristotle. The importance of his doctrine lay not so much in the nature he assigned to matter, or to the modes in which qualities might be affixed to it, but in the broad principle that one kind of matter could be changed into another kind—in a word, that transmuta tion was possible. Underlying all tangible bodies was an inde terminate matter-stuff (6X77) on which properties might be im pressed giving matter its particular form (Er6os).
If such fundamental qualities as hotness and dryness (or their opposite qualities, coldness and wetness) are impressed on the matter-stuff, we may conceive two qualities combining to give a primal form of matter. For instance, the combination of dryness with heat gives fire, with cold gives earth: the combination of wetness with heat gives air, with cold gives water. Moreover these qualities are not unalterable. If the coldness of water is overcome by heat, the water changes to steam or air; if its wet ness is overcome by dryness it leaves earth.
Aristotle's conception differed therefore not only from the unchangeable elements of Empedocles, but from the mechanical hypothesis of Democritus, who imagined the world built up by the fortuitous meeting of rapidly moving atoms—themselves of unalterable nature.
In Egypt the Aristotelian doctrine of the four elements readily took root. Working in metals had been practised for centuries not only along the Valley of the Nile, but in the Valleys of the Euphrates and the Indus, between which there had long existed intercourse.
How far the teaching of the Alexandrine school directly affected chemical practice among the Egyptians is doubtful. It is clear from the chemical writings that have been preserved—especially from the famous papyrus at Leyden—that the priests were well acquainted with methods for imitating gold and silver, and for covering metal vessels superficially with gold alloys so that the base metal could be removed and leave a pure gold surface which would "pass the test."