. Inquiry into the Laws of Affinity. €l 



A R T I C L E Xr. 

 On fame Errors ivhich proceed from afalfe Notion of EleElive Affinity. 

 t. I fliall here difcufs feveral opinions which have been adopted relative to eleftlve 

 affinity ; I fliall fhew how unfounded they are, and fliall oppofe to them the application of 

 the principles laid down in the preceding articles : 



Baume has obferved, that when the fulphate of pot-afli is diflblved by means of heat, In 

 ^n equal weight of nitric acid, cryftals of the nitrate of pot-afli are obtained by cooling: 

 he attributes this decompofition of the fulphate of pot-afli to reciprocal affinities which 

 produce oppofite combinations, but does not determine the caufe of this contrary effedt. 



2. The explanation of this remarkable fa£l has been contradi£led by Bergman. He 

 obferves, that there are fome falts which have a tendency for an excefs of acid, fuch for in- 

 ftance as the acidulous tartrite of pot-afli. He conceives that when thefe falts exifl: in a 

 ftate of neutralifation, it is iieceflary to confider their bafe as divided into two parts ; one 

 of which is particularly afFe£led by the whole a£lion of the acid, in order to form the aci- 

 dulous fait, while the other part only tends to fatisfy that portion of acidity which remains 

 in the acidulous fait. This part of the bafe is therefore only retained by a feeble acidity, 

 and may be carried off by an acid very inferior to that which enters into the firft combination. 

 Thus the acetous acid may carry ofi^ that part of the pot-afti which, in the tartrite of pot-afli, 

 is fuperfluous to the combination which confliitutes the acidulous tartrite of pot-afli, though 

 this acid has an affinity much weaker than that of the tartareous acid itfelf. 



Now, the fulphate af pot-afli is among the number of the falts which have a tendency to 

 form an acidulous fait. Nearly two thirds of its bafe enter into this combination, and it i* 

 this part alone that is fubje£l to the whole affinity of the fulphuric acid. The remaining 

 third may be feparated by an acid of an affinity inferior to that of the fulphuric acid, fuch as 

 the nitric acid, the muriatic acid, and the tartareous acid. When the decompofition is 

 carried to this point, it ceafes, whatever may be the quantity of the acid oppofed ; and if 

 the quantity be not too great to prevent the cryftalllfation, or if the excefs be expelled by 

 heat, an acidulous fulphate is obtained by folution and evaporation, which forms permanent 

 cryftals in the air. 



3. How could the illuftrious Bergman have deviated from the path traced out for him by 

 obfervation .' It is proved even by his own experiments, that the acid which is fuperabundant 

 to the acidulous fulphate of pot-afti exerts its affinity, that it exifts in combination, and 

 afts in proportion to its quantity. For he obferves, that if fulphuric acid be added to- 

 the acidulous fulphate of pot-afli, this fait is diffi)lved, and Jofesits property of cryftallifing ; 

 that this excefs of acid is expelled with difficulty, even by diftillatlon in a retort; and ra 

 order to obtain this efFeil, it is neceffary to fufe the faline combination ia a crucible, or ta 

 employ feveral times the repeated a6tron of very pure alcohol. 



4. The limit given by Bergman to the adtion of the acids upon the acidulous fulphate is 

 therefore imaginary. This fulphate ads hke all the falts which are capable of refifting, to 



a certala 



