ACTION OF SOLIDS ON DISSOLVED MATTERS. 31 



the French missionaries we know that alum is uni- 

 versally employed in Pekin to clear it. In fact, if a 

 crystal of alum be held in such a water only for a 

 few seconds, we observe the sediment separating 

 in large thick flocculent masses, the water becomes 

 transparent, and hardly a trace of dissolved alum is 

 to be detected by the most delicate re-agents. 

 Chemistry is acquainted with a number of similar 

 means for causing the separation from liquids of 

 suspended precipitates. 



In these cases we see, that by an alteration of 

 the quality of the water, produced by what we call 

 mere mixture with a foreign body, its -power of 

 combining with others is destroyed or weakened. 



It is well known that the force with which, in a Action of 

 solution, the particles of the liquid and those of the dissolved 

 dissolved body attract each other, is very unequal in 

 different cases ; and in this point of view the action 

 of many solid bodies on saline solutions is very 

 remarkable ; inasmuch as it is thereby demon- 

 strated, that the molecular force, which deter- 

 mines the phenomena of cohesion, and the moist- 

 ening of solid bodies by liquids appears to be 

 identical with chemical affinity, since chemical com- 

 pounds can be decomposed by means of it. Pro- 

 fessor GRAHAM has shewn that common charcoal, 

 deprived by acids of all soluble ingredients, com- 

 pletely removes the metallic salts or oxides from 

 solutions of salts of lead, tartar emetic, ammoniated 

 oxide of copper, chloride of silver in ammonia, and 



