DOCTRINE OF ACID AND ALKALI. 265 



CHAPTER III. 



DOCTRINE OF ELECTIVE ATTRACTIONS. GEOFFKOY. BERGMAN 



npHOUGH the chemical combinations of bodies had already been 

 -*- referred to attraction, in a vague and general manner, it was im- 

 possible to explain the changes that take place, without supposing the 

 attraction to be greater or less, according to the nature of the body. 

 Yet it was some time before the necessity of such a supposition was 

 clearly seen. In the history of the French Academy for 1718 (pub- 

 lished 1*719), the writer of the introductory notice (probably Fonte- 

 nelle) says, " That a body which is united to another, for example, a 

 solvent which has penetrated a metal, should quit it to go and unite 

 itself with another which we present to it, is a thing of which the 

 possibility had never been guessed by the most subtle philosophers, 

 'and of which the explanation even now is not easy." The doctrine 

 had, in fact, been stated by Stahl, but the assertion just quoted shows, 

 at least, that it was not familiar. The principle, however, is very 

 clearly stated 1 in a memoir in the same volume, by Geoffrey, a French 

 physician of great talents and varied knowledge. " We observe in 

 chemistry," he says, " certain relations amongst different bodies, 

 which cause them to unite. These relations have their degrees and 

 their laivs. We observe their different degrees in this ; that among 

 different matters jumbled together, which have a certain disposition 

 to unite, we find that one of these substances always unites constantly 

 with a certain other, preferably to all the rest." He then states that 

 those which unite by preference, have "plus de rapport," or, ac- 

 cording to a phrase afterwards used, more affinity. "And I have 

 satisfied myself," he adds, " that we may deduce, from these observa- 

 tions, the following proposition, which is very extensively true, though 

 I cannot enunciate it as universal, not having been able to examine 

 all the possible combinations, to assure myself that I should find no 

 exception." The proposition which he states in this admirable spirit 

 of philosophical caution, is this : " In ali cases where two substances. 



1 Mem. Acnd. Par. 1718, p. 202. 



