Chap. II.] Chemical Philosophy. 105 



among the most importaut e\ ents recorded in the 

 history of chemistry. The explanation which they 

 have afforded to the principles of coinbustioiiy re^ 

 spiration, aciditij, &c. places their value in a very 

 interesting point of light. To this discovery, and 

 these investigations, we may trace the commence- 

 ment of that grand revolution in chemical science, 

 which was soon afterwards established. 



Paracelsus believed that there was only one acid 

 principle in nature, which communicated taste and 

 solubility to the bodies with which it was combined. 

 Becher embraced the same opinion, and added to 

 it, that this acid principle was a compound of earth 

 and zvater, which he considered as two elements. 

 Stahl, as we have seen, adopted the theory of Be- 

 cher, and endeavoured to prove that the acid prin- 

 ciple is sulphuric acid, of which, according to him, 

 .all the other acids are mere compounds; but his 

 proofs were only conjectures or vague experiments, 

 from which nothing could be deduced. Neverthe- 

 less, his opinion, like every other wiiich he advanced 

 in chemistry, continued to have supporters for a 

 long time, and was even sanctioned by Macquer. 

 At last its defects began to be perceived. Kcrg- 

 man and Scheele declared openly against it ; and 

 their discoveries, together with those of Lavoisier, 

 demonstrated the falsehood of both parts of the 

 theory, by showing that sul})huric acid does not 

 exist in the other acids, and that it is not com- 

 posed of water and earth, but ol sulphur aiici 

 oxygen. 



The opinion, however, that acidity is owing to 

 some principle common to all the salts, w^as not 

 abandoned, YV^allerius, Meyer, and Sage, had ad- 



