€o Jfiguify into the Laws of Affinity, 



But the changes would be much more confiderable, if barytes were to ferve as a compa- 

 rifon with either pot-afli or foda ; the force of cohefion pofleffed by the fulphate of barytes 

 would then operate in fuch a manner, that it would leave the alkali only a very fmall 

 quantity of fulphuric acid, which would be much nearer to a meafure of the force of cohe- 

 fion of the fulphate of barytes, compared with that of the folvent, than of the affinity of the 

 barytes compared with that of the alkali. 



This is fo true, that if, in order to compare the affinity of the acids for barytes, we 

 were to begin by treating barytes with an excefs of fiilphuric acid, it would be almoft in- 

 tirely precipitated, unlefs the acid were extremely concentrated ; we could not diftinguifli 

 the combined portion from that which is not, and affert, that barytes has a greater affinity 

 for the former part than for the latter. This however is really ftated, when it is affirmed, 

 that the fulphuric acid has-a greater affinity for barytes than any other acid, becaufe a ful- 

 phate of barytes is formed by precipitation. That effect is attributed to cle£live affinity, 

 which depends more particularly upon the force of cohefion peculiar to the fulphate of 

 barytesi^ 



It is therefore manifeft that the ele£live affinity of any two fubftances, with regard to a 

 third, cannot be determined by a direiS: experiment, even when the trial is made with two 

 fubftances in a liquid Hate, and which can be neutralifed by faturation; fince it is neccflary 

 to introduce foreign powers in order to afcertain the faturation. 



5. It has been feen in articles II and III, that the affinity of a fubftance may be com- 

 penfated for by its quantity. 



From this confideration, it would appear to be fufficient if we were to difcover the capacities 

 of faturation which different bafes have for an acid, or different acids for a bafe, in order to 

 afcertain the proportion of their relative affinity: for this fhould feem to be in the inverfe 

 proportion of the quantities neceffary for producing the fame degree of faturation. 



This confequence is erroneous, when we wifll''to apply it to the eledtive affinities, be- 

 caufe as foon as two fubftances are prefented in order to combine with a third, new forces 

 are eftablifhed, which not only determine other refults, but even change the conftitution 

 of thofe fubftances. 



I compare the fulphuric and carbonic acids. It is certain that if I bring a quantity of 

 pot-afli to a term of neutralifation by the carbonic acid, it exerts a force as great as the 

 quantity of fulphuric acid which would be neceffary to produce the fame effe£t ; and yet if I 

 pour the fulphuric acid upon the firft mentioned combination, the whole of the carbonic 

 acid will be difengaged j becaufe, being no longer retained by an equal force, it again 

 affumes the elaftic ftate; and even if it be abforbed and retained by a fufficient quantity of 

 water, it will no longer be in the fame ftate of compreffion; it will not have the fame 

 conftitution; it will no longer be the fame fubftance relative to chemical action. And 

 laftly, we muft apply the obfervations made in the preceding numbers to the action of 

 fubftances unequally faturated. 



The comparifon between the capacities of faturation, though it may lead to importank 

 confidcrationsi cannot therefore be applied to the determination of elettive affinities. 



ARTICLE 



