2 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



this second period the search for the PHILOSOPHER'S STONE, 

 a substance by which baser metals could be converted 

 into gold, led to an exhaustive study of all available 

 materials. Their actions upon one another were also studied, 

 and the effect of heat upon them both separately and in 

 mixtures of varying complexity. In this way, many new pro- 

 cesses and compounds were discovered. The physician 

 Geber, who lived in Spain at the close of the eighth century, 

 was perhaps the greatest of the alchemists ; the writings 

 that have been attributed to him afford a clear picture 

 of the progress which the science had made in the hands of 

 the earlier alchemistic workers. 



3. The Later Alchemistic Period extended roughly from 

 1500 to 1650 A.D. During this period the search for the 

 philosopher's stone (then regarded as a means of healing all 

 diseases) and for the equally imaginary ELIXIR OF LIFE 

 gradually gave place to deliberate investigations of the 

 action of drugs on the human body and to the preparation 

 of new substances for use in medicine. The writings of 

 Glauber (1603-1668) contain a description of many sub- 

 stances discovered during this period, and give a good idea 

 of the state of knowledge at the time when Boyle laid the 

 foundations of the modern science of Chemistry. 



The following pages contain an account of some of the 

 most important materials which became known during the 

 earlier part of these three periods, but large groups of 

 substances (including, for instance, the acids and alkalis) 

 are reserved for separate treatment in subsequent chapters. 

 The various materials may be classified conveniently under 

 the following headings : 



Soluble salts. Among the substances in common use 

 from very early times was the salt obtained by the evapora- 

 tion by the sun's rays of sea-water collected in shallow 

 pools along the sea-shore. The product was a mixture of 

 several substances, remarkable for their sharp taste and 



