in Fluids. 347 



generally imagined ; and that no metal is ever dissolved 

 till it has first been melted. 



Perhaps it will be found, that the apparent violence 

 with which solid bodies of some kinds are attacked by 

 their liquid solvents and which has, I believe, been 

 considered as a proof of a strong chemical affinity is 

 not owing to any particular attraction, or election, but to 

 the considerable degree of heat, or of cold, which is pro- 

 duced in their union with their menstrua, or to a great 

 difference in the specific gravity of the menstruum in its 

 natural state, and that of the same fluid after it has been 

 changed to a saturated solution. 



If Fluids are non-conductors of Heat, it is evident 

 that, if any change of temperature takes place in chemi- 

 cal solution, it must necessarily produce currents in the 

 solvent, and that these currents must be the more rapid, 

 as the change of temperature is greater ; and as they 

 necessarily cause a succession of fresh particles of the 

 solvent to come into contact with the solid, it is evident 

 all other things being equal that the rapidity of the 

 process of solution will be as the rapidity of these cur- 

 rents, or as the change of temperature. 



But the currents produced by the difference in the 

 specific gravity of the fluid menstruum and of the sat- 

 urated solution, have perhaps, in general, a still greater 

 effect in bringing a rapid succession of fresh particles of 

 the menstruum into contact with the solid body that is 

 dissolved in it, than those produced by the change of 

 temperature. 



When these two causes conspire to accelerate the mo- 

 tion of -the same current, or when their tendencies are in 

 the same direction^ as is the case in the solution of common 

 sea-salt in water, the solution ought to be most rapid. 



