THE CHEMICAL AND NATURAL SCIENCES
IN the sciences which we have hitherto considered, observation and practice have, up to a certain point, guided theory. It was not the same with chemistry, the theories of which were closely connected with metaphysics and had no great influence on the technical processes. The first gropings, of chemical technique are very ancient. They seem to go back to a prehistoric epoch, to the time when metals were first used for manufacturing weapons, and when certain alloys were perceived to be advantageous. Amongst these alloys, that of tin and copper was specially important. From the most remote antiquity Egypt was an important centre of the trade in tin; which in later times was supplied by Phœnician traders.1 Other metals were afterwards discovered and alloyed. In Egypt, the method of treating them was preserved by tradition in the form of short and probably mysterious receipts whose secret was jealously guarded by the priests. Certain hieroglyphic signs, completed by oral instructions, were sufficient to ensure the transmission of the methods of manufacture.
As to the Greeks, the sum of their practical knowledge amounts approximately to the following: "They knew how to prepare certain salts of copper, of____________________