126 HISTORY OF CHEMISTRY. 



which all supposed acids conformed. Yet the general 

 conception of such a combination as that of acid 

 and alkali was supposed to be, served so well to 

 express many chemical facts, that it kept its ground. 

 It is found, for instance, in Lemery's Chemistry, 

 which was one of those in most general use before 

 the introduction of the phlogistic theory. In this 

 work (which was translated into English by Keill, 

 in 1698) we find alkalies defined by their effer- 

 vescing with acids 4 . They were distinguished as 

 the mineral alkali (soda), the vegetable alkali (po- 

 tassa), and the volatile alkali (ammonia). Again, 

 in Macquer's Chemistry, which was long the text- 

 book in Europe during the reign of phlogiston, we 

 find acids and alkalies, and their union, in which 

 they rob each other of their characteristic pro- 

 perties, and form neutral salts, stated among the 

 leading principles of the science 5 . 



In truth, the mutual relation of acids to alkalies 

 was the most essential part of the knowledge which 

 chemists possessed concerning them. The import- 

 ance of this relation arose from its being the first 

 distinct form in which the notion of chemical at- 

 traction or affinity appeared. For the acrid or 

 caustic character of acids and alkalies is, in fact, a 

 tendency to alter the bodies they touch, and thus 

 to alter themselves ; and the neutral character of 

 the compounds is the absence of any such proclivity 

 to change. Acids and alkalies have a strong dis- 

 4 Lemery, p< 25. * Macquer, p. 19. 



