Inquiry into the Laws of AJlmf J. 67 



5. When, therefore, water is evaporated, In which feveral falts have been put in a ftate 

 of folution, they will be found to feparate according to the order of their folubiiity, and it 

 is from this property that we are able to afcertain the changes of bafc which may 

 be efFe£led. 



But the folubiiity of falts varies according to the temperatures. It is, therefore, the 

 folubiiity relative to the difFefent temperatures which ought to be confidcred. The nitrate 

 of pot-alh, mixed with the muriate of foda, will cryftallife at a low temperature ; but the 

 muriate of foda will feparate even during the time of evaporation. No exchange of bafes 

 will be efFedted, becaufe the nitrate of foda is a little more foluble in cold than the nitrate 

 of pot-afh, and on the contrary, the muriate of pot-afli is rather more foluble in heat than 

 the muriate of foda. 



6. I here attend only to the principal refult, arifing from a force of cohefion fo great, 

 that it caufes the effe£t of the forces oppofed to it to difappear. But when this power is 

 not confiderable in the combinations that may be formed, the mutual a£lion of the fub- 

 ftances which remain in the liquid ftate, that of the folvent, and the proportions which 

 vary by the cryftallifation of a combination that is feparated, muft produce different efi"ccts. 

 The experiments I have began will not fail to elucidate this fubjedl. 



7. Another circumftance may change the a£Hon of the complex affinities ; namely, the 

 formation of a triple fait which precipitates ; but by knowing the degree of folubiiity of 

 this combination, we may ftill foretel the decompofitlon that will take place. The fame 

 confideratlon is applicable to the affinities called eUHlve. 



8. A precipitate is fometlmes efFedled by the mixture of two faline fubftances which have 

 the fame acid ; for Inftance, by a mixture of the muriate of magneCa and the muriate of 

 lime. It Is probable that two combinations are then formed, one with an excefs of acid 

 and a fmall part of the two bafes, the other with the greateft part of the two bafes and a 

 fmall portion of acid. 



This elFed Is analogous to what we have obferved in Art. IX. No. 3 ; but here it is the 

 mutual affinity of the two bafes which determines the precipitation. 



9. We have feen in Art. VII. that heat, by increafing the volatility of a fubftance, 

 weakens Its combination. This caufe a£ls no lefs in the complex than in the eleftive 

 affinities. It is a force added to thofe which aft, and determines the union and the 

 reparation of thofe fubftances which have the greateft tendency to form a volatile com- 

 bination. 



Whenever, therefore, it is defired to know what will happen, by expofing two falts to 

 the a£tion of heat, it is only neceflary to examine whether one of the two bafes and one of 

 the two acids poflefs a greater degree of volatility than the remaining bafe and acid, and 

 we may be aflured that, on applying a fufficient degree of heat, the combination of the 

 moft volatile bafe and acid will be formed and fublimed, while the more fixed bafe and 

 acid will alfp remain combined. Among the bafes, ammonia and the oxide of mercury, 

 and among tlie acids, the carbonic and muriatic, affisrd feveral illuftrations of this truth. 



K 2 10. Efilorefcence 



