DOCTRINE OF ACID AND ALKALI. 127 



position to unite. They combine, often with vehe- 

 mence, and produce neutral salts ; they exhibit, in 

 short, a prominent example of the chemical attrac- 

 tion, or affinity, by which two ingredients are formed 

 into a compound. The relation of acid and base 

 in a salt is, to this day, one of the main grounds of 

 all theoretical reasonings. 



The more distinct developement of the notion of 

 such chemical attraction, gradually made its way 

 among the chemists of the latter part of the seven- 

 teenth and beginning of the eighteenth century, as 

 we may see in the writings of Boyle, Newton, and 

 their followers. Beccher speaks of this attraction 

 as a magnetism ; but I do not know that any writer 

 in particular, can be pointed out as the person who 

 firmly established the general notion of chemical 

 attraction. 



But this idea of chemical attraction became 

 both more clearer and more extensively applicable, 

 when it assumed the form of the doctrine of elective 

 attractions, in which shape we must now speak 

 of it. 



