But although the persistent and wonderfully energetic activities of the alchemists failed to find the philosophers’ stone, or to transmute the baser metals into silver and gold, they placed in the hands of man the key to a knowledge of chemistry, that branch of science which was destined in later years to play such an important part in pharmacy, in agriculture and in other industries. Thus we owe to alchemists the discovery of many processes and the invention of many apparatus which serve as the groundwork of modern chemistry. Some of the more important of these are the following: The use of the spirit lamp; the invention of tubular retorts; the production of potash and soda by burning the hard deposit which collects in wine casks as well as various marine plants; the oxidizing of certain metals (iron, lead, copper, quicksilver and antimony); the making of metallic arsenic, of wine of antimony, of sulphate of iron, of chloride of silver, of acetic acid and of many other chemical products; the purification of metals by the use of lead, etc. _Supplementary Data Relating to Balneotherapeutics._--I have referred to this subject on several occasions in the course of the earlier chapters of this history, but always without entering very much into details. This policy was adopted, partly because the facts upon which a satisfactory sketch of the growth of balneotherapeutics might be based were not very numerous, and partly because of the necessity of gaining space for more important matters. The principal facts to which I made reference were: First, that before the Christian era the employment of baths in a variety of different ways for therapeutic purposes was universal in the East; and, second, that in the city of Rome during the centuries immediately following the birth of Christ, facilities for this kind of treatment were provided on a most lavish scale--as in the baths of Agrippa (27 A. D.), of Titus (79 A. D.), of Caracalla (211 A. D.), and of Diocletian (302 A. D.). I may now add that the warm springs of Aachen (Aix-la-Chapelle), Baden-Baden and Wiesbaden, in Central Europe, and Bath, in England, were known to the ancient Romans, and were utilized by them to some extent for therapeutic purposes; but it was not until a much later period that they and the less well-known springs of Schwalbach, Driburg, Warmbrunn, Goeppingen and Gastein began to be actively frequented for remedial purposes. By the beginning of the sixteenth century it had become a very popular thing for sufferers from all sorts of ailments to resort to these and other European springs. The history of the therapeutic employment of mineral waters belongs, however, to the period of modern medicine rather than to that which I have been considering in the present volume. PART III MEDICINE DURING THE RENAISSANCE CHAPTER XXVI