The Concepts of Substance and Chemical Element

Abstract

IN one of his dialogues, Plato discusses the Pythagorean theory of the formation of bodies in space by arrangements of two kinds of triangles, and points out that gold should have such a constitution. But he then adds, It is better to call it gold. This distinction between the theoretical view of the philosopher and the outlook of the worker with materials runs through the history of the concept of substance. The subject is rather complex, and it may be well to state the main topics I have chosen, and the order in which they will be introduced. I shall, in the first place, indicate rapidly the views on the nature of matter and its changes, and the theory of the primary matter, held by the Greek philosophers, and particularly by Aristotle, and this review will show the greater difficulty of the concept of substance as compared with mathematical, dynamical, and physical concepts. I shall then deal with the beginnings of chemistry early in the Christian Era, and the blending of Greek ideas of matter with experimental results on the treatment of various substances, which led to the early chemical the ories. This subject will be taken up again in the form it had reached in the seventeenth century, when the concept of the chemical element as a substance, as distinct from a philosophical, or Aristotelean, ele ment, which was rather a general property of substance, appears dis tinctly with Robert Boyle. We shall also see a revival of atomism, a branch of early Greek philosophy which had been rejected by Plato and Aristotle. The atomic theory then took its place as one of the foundations of chemistry. In the fourth and final section, the atomic theory of Dalton will be the central theme, and it will be shown how the new experimental knowledge of our own time has led to a return to the idea of primary matter, and has made it necessary, in defining chemical composition and combining proportions, to do so with reference to the atomic the ory, the descriptive definitions based on the properties of substances being incomplete and insufficient to comprehend the cases which are