The Story of Alchemy and the Beginnings of Chemistry

By asserting, and to some extent experimentally proving, the existence of one principle in many apparently very different substances (or, as would be said to-day, one property common to many substances), the phlogistic theory acted as a very useful means for collecting, and placing in a favourable position for closer inspection, many substances which would probably have remained scattered and detached from one another had this theory not been constructed. A single assumption was made, that all combustible substances are alike in one respect, namely, in containing combined fire, or phlogiston; by the help of this assumption, the theory of phlogiston emphasised the fundamental similarity between all processes of combustion. The theory of phlogiston was extraordinarily simple, compared with the alchemical vagaries which preceded it. Hoefer says, in his Histoire de la Chimie, "If it is true that simplicity is the distinctive character of verity, never was a theory so true as that of Stahl." The phlogistic theory did more than serve as a means for bringing together many apparently disconnected facts. By concentrating the attention of the students of material changes on one class of events, and giving descriptions of these events without using either of the four alchemical Elements, or the three Principles, Stahl, and those who followed him, did an immense service to the advancement of clear thinking about natural occurrences. The principle of phlogiston was more tangible, and more readily used, than the Salt, Sulphur, and Mercury of the alchemists; and to accustom people to speak of the material substance which remained when a metal, or other combustible substance, was calcined or burnt, as one of the elements of the thing which had been changed, prepared the way for the chemical conception of an element as a definite substance with certain definite properties.