100 Chemistry. [Lecture 27 



fluid. The terms for these operations are solu- 

 tion, fusion, and evaporation. 



II. When we would dissolve a solid in a 

 fluid, divide the solid mechanically, or by 

 other means increase its surface. If a brittle 

 body, by pulverizing ; if a metallic, by beating 

 it into leaves. The reason is plain, viz. that 

 the fluid only acts on the surface with which 

 it is in contact. 



III. The action of one body on another is 

 promoted by moderate heat, which performs the 

 solution sooner in the action of a fluid on a so- 

 lid ; for, on removing the heat, the additional 

 quantity which the heat had enabled it to dis- 

 solve will be deposited. This is particularly the 

 case in salts and water. In general, the action 

 of bodies on each other is more languid as the 

 heat is less, and the contrary. From these facts 

 it appears that the attraction the particles of one 

 body have for those of another is increased by 

 heat; and, on the contrary, the attraction be- 

 tween the particles of the same body is dimi- 

 nished by heat, as is evident in the formation of 

 vapour. 



Digestion is the continued action of bodies on 

 each other, one or all of which are in a fluid 

 state, This operation may be performed with or 

 without the employment of additional heat, and 

 in an ordinary vessel when the bodies are not 

 volatile ; when they are, a reflecting vessel is 



