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 Chemistry is the black or Egyptian art, having taken its rise out of the searches made by the Alchemists to discover the philosopher’s stone. Aristotle had no notion whatever of the rich field of knowledge and power which lay in the analysis of substances. He had no idea of the composition of water or air. The crucible and the retort had never been worked in Athens; the most superficial guess-work, as to what we should call the chemical properties of bodies, contented the philosophers of the day. Aristotle’s work ‘On Generation and Corruption’ would have been the appropriate place for enunciating some of the laws of Chemistry; but he does not go beyond a resolution of the “Four Elements” into the ultimate principles of the Hot, the Cold, the Wet, and the Dry—the first pair being “active” and the second “passive” principles. Hot and Wet, we are told, form Air; Hot and Dry, Fire; Cold and Wet, Water; Cold and Dry, Earth. From these principles Aristotle deduces the generation and destruction of physical bodies; but on the details of a theory which now seems puerile we need not dwell.