the Laws of Affinity, 343 



not mean the absolute saturation at which all reciprocal 

 action would cease ; but a degree of saturation whicli it is 

 easy to ascertain, and which is common to all combinations : 

 it is that of neutralisation, when the properties of neither of 

 the constituent parts predominate. The term of the crystal- 

 lization of salts does not always coincide with neutralisation : 

 for example, m regard to alkaline carbonats, which still give 

 signs of alkalinity, and in regard to the acidulous tartrite of 

 potash, which, on the other hand, retains an excess of acid. 

 The last combination, however, may be taken at the term at 

 which it is neutral, because it still has the property of cry- 

 stallization : it is even this tartrite that is necessarily obtained 

 when in the experiment there is present an excess of the base; 

 but when there is an excess of acid, the degree of saturation 

 of the acidulous tartrite of potash may be determined by the 

 quantity of potash necessary to neutralise it. 



3d, A consideration which seems to deserve some atten- 

 tion is, that in comparing affinities it would be necessary to 

 employ in all the experiments the same proportions of all the 

 substances successively subjected to operation; because, if the 

 proportions vary, the result of the action not being the same, 

 the affinity could no longer be represented by the same 

 number. I shall render this observation more sensible by an 

 example: 



Let 1 00 represent the potash, which ought to be saturated 

 by 100 parts of sulphuric acid, and let 100 parts of soda be 

 opposed to it. Let us suppose that after the action it is found 

 that the potash has taken up 60 parts of acid, and the soda 40^ 

 I should thence conclude that the affinities of these two bases 

 for the sulphuric acid are in the ratio of 60 to 40 : but there 

 remain 40 parts of potash uncombined, which really continue 

 to act, and which by their action Contribute to divide the 

 acid ; so that, if this quantity be varied, the result cannot be 

 the same ; for, if, instead of 100 parts of potash and 100 parts 

 of soda, we take 80 parts of each, we shall have for the un- 

 combined portion 20 parts of potash and another quantity 

 of soda ; so that the forces exercised by these two parts are no 

 longer in the former ratio : hence it results that the two satu- 

 rations cannot be in the ratio of 60 to 40, 



4th, 



