It is a regrettable fact that the majority of works dealing with the subject of Alchemy take a one-sided point of view. The chemists generally take a purely physical view of the subject, and instead of trying to understand its mystical language, often (I do not say always) prefer to label it nonsense and the alchemist a fool. On the other hand, the mystics, in many cases, take a purely transcendental view of the subject, forgetting the fact that the alchemists were, for the most part, concerned with operations of a physical nature. For a proper understanding of Alchemy, as I hope to make plain in the first chapter of this work, a synthesis of both points of view is essential; and, since these two aspects are so intimately and essentially connected with one another, this is necessary even when, as in the following work, one is concerned primarily with the physical, rather than the purely mystical, aspect of the subject. Now, the author of this book may lay claim to being a humble student of both Chemistry and what may be generalised under the terms Mysticism and Transcendentalism; and he hopes that this perhaps rather unusual combination of studies has enabled him to take a broad-minded view of the theories of the alchemists, and to adopt a sympathetic attitude towards them. With regard to the illustrations, the author must express his thanks to the authorities of the British Museum for permission to photograph engraved portraits and illustrations from old works in the British Museum Collections, and to G. H. Gabb, Esq., F.C.S., for permission to photograph engraved portraits in his possession. The author’s heartiest thanks are also due to Frank E. Weston, Esq., B.Sc., F.C.S., and W. G. Llewellyn, Esq., for their kind help in reading the proofs, &c. H. S. R. THE POLYTECHNIC, LONDON, W. _October, 1910._ CONTENTS PAGE CHAPTER I. THE MEANING OF ALCHEMY 1 § 1. The Aim of Alchemy 1 § 2. The Transcendental Theory of Alchemy 2 § 3. Failure of the Transcendental Theory 3 § 4. The Qualifications of the Adept 4 § 5. Alchemistic Language 5 § 6. Alchemists of a Mystical Type 7 § 7. The Meaning of Alchemy 7 § 8. Opinions of other Writers 8 § 9. The Basic Idea of Alchemy 10 § 10. The Law of Analogy 12 § 11. The Dual Nature of Alchemy 13 § 12. “Body, Soul and Spirit” 14 § 13. Alchemy, Mysticism and Modern Science 15 CHAPTER II. THE THEORY OF PHYSICAL ALCHEMY 17