CH. vil. GEBER DISCOVERS ACIDS. 45 



carefully noticed the fact, though he could not explain it. 

 But the discovery which most of all gives Geber the right to 

 be called the 'founder of chemistry' was that of strong 

 acids. Most of the chemical experiments we make now 

 would be impossible without acids, but before Geber's time 

 vinegar seems to have been the strongest acid known. He 

 found, however, that by heating copperas (or sulphate of 

 iron) with saltpetre and alum, he could distil off a vapour 

 which cooled down into a very strong acid, now called 

 nitric add. He used this to dissolve silver, and by mixing 

 it with sal-ammoniac he found it would even dissolve gold. 

 Sal-ammoniac was a kind of salt which was known to the 

 Arabs before Geber's time. They made it by heating the 

 dung of camels, and the name ammoniac was given to it 

 because they made it first in the desert near the temple of 

 Jupiter Ammon. Geber also made sulphuric acid by dis- 

 tilling alum. When we remember that all these experiments 

 were made more than a thousand years ago, we must 

 acknowledge that Geber deserves great honour for the dis- 

 coveries which he made. 



Albategnuis, 879. We have seen that in chemistry the 

 Arabs learned very little from the Greeks, but in mathe- 

 matics and astronomy they found a great deal written, and 

 the Arabian astronomers spent much of their time in trans- 

 lating Greek works. Unfortunately they mixed up astronomy -, 

 or the study of the heavenly bodies, with astrology ', a kind of 

 magic art, by which they imagined they could foretell what 

 was going to happen by studying the stars. In spite of this, 

 however, there were several very celebrated Arabian astro- 

 nomers, one of whom, called Albategnuis, born A.D. 879, 

 made a great many good observations. He calculated the 

 length of the year more exactly than Ptolemy had done, 



