the Lazvs of Affinity * 151 



be Surmounted by the acSlion of the fubftance that tends to 

 combine with thefe parts, or to decompofe their combination. 

 It is well known that argil, the parts of which, by deficca- 

 tion, have acquired a ftrong adhefion, is no longer attacked' 

 by an acid which has the property of diflblving it when it is 

 in another (late. 



It is this reciprocal affinity, alfo, of the faline parts that 

 produces cryftallifation, and the latter in chemical action has 

 elTe^ls which deferve attention. On this fubje6t the author 

 prefents fome confiderations, as well as on the force produced 

 by cryftallifation in a faline folution. " It eftabliflies,*' fays 

 lie, *^ a boundary to the degree of the faturation with a fait 

 to which the water can attain ; fo that, if it does not diflblve 

 a larger quantity, it is not becaufe its affinity for it is fatisfied, 

 but becaufe it has no longer fufficient power to overcome the 

 rcfiftance of the cryftalliiiuion/' From thefe and other con- 

 fiderations Berthollet concludes, that the force of coheiion, 

 which had been confidered only as an obltacle to folution, 

 determines the quantities of the fubftances which can be 

 put in action in a liquid, and thereby modifies the conditions 

 of the chemical aAion : it is that alfo which caufes thofc fc- 

 parations that take place either by cryllallifation or precipita- 

 tion, and which eftablidies the proportions of the combina- 

 tions which are formed in feparating from the liquid when 

 the property of being infoluble depends on thefe proportions. 



VI. Of the FJaJlic'ity of thofe Suhjlances iL'bijh cxcrclfe a 

 Chemical Afiion, 



When afubftance efcapes in the form of gas, in proportion 

 as it is difengaged from an intimate combination, the whole 

 portion which alFumes the elaftic ftate does not contribute to 

 the refiftance ; fo that this fubftance no longer aiSts according 

 to its mafs : the fubftance oppofed to it may then render the 

 dccompofition complete, and it will be fufficient to employ 

 the quantity which would have been necelTary to form imme-» 

 diately the combination into which it ought to enter, or, at 

 Jcaft, a fmall excels only will be required. ** This is what 

 happens,** favs JkTthollet, " in regard to carbonic acid when 

 it forms a carbonat, ^nd when another acid is oppofed to it > 



the 



