COHESION. 277 



693. RELATION OF COHESION AND AFFIN- 



What is said 



of the relation iTY. The chemical affinity of potassa for 

 "/ndaffinit ? carbonic acicl , is evidently greater than that 

 of lime. The former base retains the acid 

 so firmly, that no degree of heat can effect it, while 

 the latter gives up its acid with readiness, under the 

 influence of a high temperature. Notwithstanding the 

 superior affinity of potassa, lime will take from it, its 

 carbonic acid, if added to a solution of carbonate of 

 potassa, in water. The mixture being made, the par- 

 ticles in this and in all similar cases, tend to re-arrange 

 themselves in the solid form. They seem to do this 

 without reference to their chemical affinities, in such a 

 manner as best to resist the solvent action of the water, 

 or other liquid. Carbonate of lime resists such action 

 better than carbonate of potassa. The former is there- 

 fore produced. The cohesion of carbonate of lime, 

 using the term, in the sense of capacity to resist the 

 separating power of water, has therefore determined 

 the production of this substance, in opposition to or- 

 dinary chemical affinities, 



694. The above case illustrates a gene- 



Statc and il- 

 lustrate the ral law. Two substances, which when 

 general law? Qn it e( j form an insoluble compound, gen- 

 erally unite and produce it, when they meet in so- 

 lution. To illustrate by another example : phos- 

 phate of lime, or bone ash, is insoluble. Then 

 we may be sure that phosphoric acid and lime, if 

 brought together by mixing two solutions, will de- 

 sert any substances with which they were before 

 combined, and unite to form insoluble phosphate of 



12* 



