the Laws of Affinity . 345 



combined portion from that which is not, and to say that the 

 barytes has more affinity for the former than for the latter. 

 This, however, is what is really said when it is affirmed that 

 the sulphuric acid has more affinity for the barytes than any 

 other acid has, because a sulphat of barytes is formed by pre- 

 cipitation ; and thus an effect, which depends in particular 

 on the force of cohesion peculiar to the sulphat of barytes, 

 is ascribed to elective affinity. 



It is manifest, therefore, that the elective affinity of two 

 substances in regard to a third, cannot be determined by a 

 direct experiment even when trial is made on two substances 

 which are in a liquid, and which may become neutralised 

 by saturation ; sines, in order to ascertain the saturation, it is 

 necessary to employ the intervention of foreign forces. 



5th, We have shown in articles II. and III. that the affi-* 

 nity of a substance may be compensated by its quantity. 



From this consideration it would appear that it is sufficient 

 to ascertain the capacities of saturation of different bases for 

 an acid, or of different acids for a base, in order to establish 

 the ratio of their affinity ; for it ought to be in the inverse 

 ratio of the quantities necessary to produce the same degree 

 of saturation. 



This consequence, however, is erroneous when we are de- 

 sirous of applying it to the elective affinities; because, as soon 

 as the two substances are put in circumstances to combine 

 with a third, new forces are established, which not only de- 

 termine other results, but even change the constitution of 

 these substances. Thus, if we compare the sulphuric acid 

 with carbonic acid, it is certain, that if a quantity of potash 

 be brought to the term of neutralisation by carbonic acid, 

 it exercises a force as great as the quantity of sulphtiric acid 

 which would be necessary to produce the same effect : and 

 yet if sulphuric acid be poured on the combination thu» 

 formed, all the carbonic acid is disengaged; because^ not 

 being retained by an equal force, it resumes the elastic state ; 

 and even if it be retained by a sufficient quantity of water, 

 it will no longer be in the same state of compression ; it will 

 no more have the same constitution 5 it will no longer be the 

 same substance in regard to chemical action. In a word, we 



Vol. IX. X X " must 



