346 Researches respecting 



must apply to the action of substances unequally saturated 

 the observations made in the preceding articles. 



A comparison, then, of the capacities of saturation, though 

 it may conduct to important considerations, cannot be ap- 

 plied to the deternfiination of elective affinities. 



XL Of some Errors which arise from a false Idea of 

 Elective Affinity, 



1st, I shall here discuss some opinions adopted respecting 

 elective affinities i I shall show how little foundation they 

 have, and shall oppose to them the application of principles 

 established in the preceding articles. 



Baume observed that when the sulphat of potash was dis- 

 solved by means of heat, in an equal weight of nitric acid, 

 crystals of nitrat of potash were obtained by cooling, He 

 ascribes this decomposition of the sulphat of potash to reci* 

 procal affinities, which produce opposite combinations with- 

 out determining the cause of this contrary effect. 



2d, The explanation of this remarkable fact has been con- 

 tradicted by Bergman. He observes that there are salts which 

 tend to have an excess of acid, such as the acidulous tartrite 

 of potash. He is of opinion that, when these salts are in a 

 state of neutralisation, we must consider their base as divided 

 into two parts ; one upon which the whole action of the acid 

 is particularly exercised to form an acidulous salt, while the 

 other part only tends to satisfy the excess of acidity in the 

 acidulous salt. This part of the base is retained then only 

 by a weak acidity, and it may be taken away by an acid very 

 inferior to that which enters into the first combination. Thus 

 the acetous acid may take away part of the potash, which in 

 the tartrite of potash is superfluous, to the combination that 

 constitutes the acidulous tartrite of potash, though this acid 

 has a much weaker affinity than the tartareous acid. 



But the sulphat of potash is among the number of those 

 vsalts which tend to form an acidulous salt; nearly two-thirds 

 of its base enter into this combination, and it is only this 

 portion which is subject to all the affinity of the sulphuric 

 acid; the other third may be separated by an acid of an affi- 

 nity inferior to thai of the sulphuric acid^ such as the nitric, 



Uiuriatic^ 



