CH. VI. ARABIAN ALCHEMISTS. 41 



also how to extract many beautiful colours out of rocks and 

 earths. But the chief thing which interested them in the 

 books of the Egyptians, Chaldeans, and Greeks, was the 

 attempts these nations had made to turn other metals into 

 gold, a discovery which tradition said had been made by Her- 

 mes Trismegistus about 2,000 years before Christ. We know 

 very little of this Hermes, and indeed we are not sure 

 whether he is not altogether an imaginary person ; but the 

 alchemists, as the people were called who tried to make gold, 

 considered themselves followers of Hermes, and often called 

 themselves Hermetic philosophers. To melt the mouth of a 

 glass tube so as to close it was called securing it with ' Her- 

 mes, his seal,' and even to this day a bottle or jar which is 

 closed so that it is air-tight is said to be hermetically sealed. 



The Arabs were a very superstitious people, and believed 

 in all kinds of charms ; and this idea of making gold in a 

 mysterious way took a great hold of them. Many thousands 

 of clever men occupied themselves in the supposed magic 

 art of alchemy. We need not study it here, but only observe 

 how very useful it was in teaching the first facts of chemistry. 

 These men, who were many of them learned, clever, and 

 patient, spent their lives in melting up different substances 

 and watching what changes took place in them. In this 

 way they learnt a great deal about the materials of which 

 rocks, minerals, and other substances are made. 



One of the first things they discovered was that by 

 heating some substances, such as nitre or saltpetre, they 

 drove something out of them which was invisible, and yet 

 that they could collect this invisible something in bottles; 

 and in some cases, if they put a light to it, it exploded 

 violently, breaking the bottle to atoms. Now, because this 

 was invisible and yet so powerful, they thought it must be 



