153 On f^e Za'icis ofAffimty. 



ri^c latter, which ac% according to its mafs, eveii if it fiiouli 

 have an affinity inferior to that of the carbonic acid, may 

 fucceHivcly expel it from the combination until no more of it 

 n^mains, provided it be employed in a quantity fomewhat 

 t'uperior to that which would be neceflary to form its com- 

 bination immediately with the bafe. 



It refults from all the fac^s exhibited by the author, that 

 eladicity produces effects analogous to thofe of the force of 

 cohefion, by modifying, In a contrary manner, the effedls of 

 the afFmity proper to each fubftance. 



VII. Of the A^loH of CalortQ, 



Under this head Berthollet examines the a6lIon of caloric 

 on bodies, and the phcenomena it produces in the different 

 combinations or decompofitions. He alfo gives a great many 

 experiments on efflorefcence and on folvents. 



What the author underftands by efflorefcence is the pro- 

 perty which a fubftance has of rlfmg above the mafs, and of 

 thereby feparating Itfelf from the chemical aftion. 



" To make foda," fays he, *^ to rife by efflorefcence it 

 muft be combine J with carbonic acid, which it is able to take 

 up from the atmofphere ; but the action of carbonic acid, 

 tiirniOied in very fmall quantity, and in an elaftlc ftate, can- 

 not add fcnfibly to the force that produces the feparation of 

 the foda from the combination in which it exifts; itonly 

 withdraws the eliminated portion, and prevents it from con- 

 tinuing to act on the combination.'' 



In' regard to the employment of folvents, the author efta- 

 bliflics as a principle, that the objeft is to overcome the refift- 

 ancc arifing from the cohefion of the parts required to be put 

 in a<^ion, or from their elafticity, and to multiply their na- 

 tural contact. 



Solvents av5l on the fubftanccs they diffolve, by their af- 

 finity and by their quantity, as do all the fubftances which 

 tend to combine, and every thing that belongs to combina- 

 ation mult be applied to them : the author, for an example, 

 f*ikes water, which is ofteneft employed as a folvent. Ber- 

 thollet then examines thofe circumftances in which this aftioii 

 tan i'enfiblv chan«ji;e or modifv t^e refults. This leads him to- 



prefent 



