^ Inquiry ititc the Laws of Affinity. 4$ 



of pot-afli. I repeated the experiment feveral times, by adding nitric acid till nitrate of 

 pot-afli was no longer feparated. I then expofed the liquid to heat capable of making the 

 difengaged portion, of nitric acid evaporate, without altering the tartareous acid^ After 

 this the liquid had acquired an oily confidence ; it had no fmell, and did not announce the 

 exiftence either of the nitric acid or of pot-afli ; but on expofing it to a ftrong heat, much 

 nitrous gas was difengaged, the tartareous acid was reduced to coal, and its aflies afforded 

 a confiderablc quantity of carbonate of pot-afh. 



7. In this operation one portion of nitrate of pot-afli is feparated by the force of cryftallifa- 

 tlon in that fait, as far as that point at which that force is overcome by the fuperabundant 

 acid. The acidulous tartar is rendered foluble by the a£lioii of the nitric acid, which, at 

 the fame time, deprives it, by cryftallifation, of a part of the bafe neccflary to make it 

 infoluble. 



On the other hand, the tartareous acid, poured on a folutlon of the nitrate of pot-afli, 

 deprives it of its pot-afli to a certain degree, and forms an acidulous tartarite which is pre- 

 cipitated ; but as it has not the property of forming an acidulous tartarite of foda, of 

 fparing folubility, it does not produce any precipitate with thofe falts that have foda for 

 their bafe. 



In both circumftances, all that portion which cannot be feparated by the force of 

 cohefion, forms a liquid, in which the fubfl:ances acSl in proportion to their prefent 

 mafles. 



Nothing, therefore, can be concluded about the refpedive affinity from fuch feparations 

 as are cfFefted by precipitation or cryftallifation, fince by the mere change of proportions, 

 oppofite decompofitions may frequently be obtained. 



8. The precipitations which take place when, on comparing the affinities of bafes, one 

 of them forms an infoluble combination, has given rife to an error of the fame kind ; and 

 on this ground alone it has been efliablifhed that lime has a greater affinity than alkali for 

 the fluoric, phofphoric, and arfenical acids, or, in a word, with all thofe which form with 

 it an infoluble compound ; and that consequently it has the property of entirely decom- 

 pofing falts formed by the alkali and thefe acids. This precipitation is not the refult of 

 eledlive affinity, and it is not complete ; but its quantity is determined by the proportion 

 which the action of the fluid bears to the force of cohefion in the precipitate : hence it is 

 that the precipitate is frequently diflblved again on increafing the quantity of the liquid 

 fubftance oppofed to it. 



9. Although Bergman has well defcribed the changes which heat is capable of producing' 

 in chemical aftipn, when the fubftances have a tendency to become volatile, and has alfo 

 warned us againft employing too ftrong a heat in evaporation, the whole influence of heat 

 in thofe operations by which falts are feparated, in order to form a judgment of their affi- 

 nities, has not yet been ftiewn. 



It would not'have been concluded that the fulphuric acid has more affinity for the fixed 

 alkalis than the nitric or muriatic acids, from the fimple circumftance that, by a ftrong 



heat. 



