06 Chemistry. [Lecture 27. 



this attraction, the mixture is much more diffi- 

 cult to evaporate than either the solid or fluid in 

 their separate state. Heat produces vapour by 

 lessening the attraction between the particles 

 of a body ; it enlarges the dimensions of a solid 

 till it becomes fluid; if continued, it enlarges 

 the dimensions of a fluid to vapour. According 

 to Sir Isaac Newton, this attraction is equal at 

 equal distances, and at unequal distances un- 

 equal. 



When the volatility of a body is repressed by 

 mixture, and the two cannot be separated by 

 heat, the separation is produced by the addition 

 of a third body, which has a stronger attraction 

 for one of the two bodies than they have for one 

 another. This kind of attraction, from the cir- 

 cumstance of certain bodies uniting with a kind 

 of preference to certain other bodies, was at first 

 named elective attraction ; and afterwards, for a 

 similar reason, affinity, which is the term at 

 present in most general use. 



Many of the hardest bodies are very quickly 

 separated by mixture. Metals require a very 

 great force to divide them mechanically, but this 

 division is easily effected by chemical solvents. 

 But the following observations will serve more 

 fully to explain the nature of elective attraction 

 or affinity. 



1 . This sort of attraction differs from that of 

 gravitation, electricity, and magnetism, in not 

 obtaining between large and sensible parts of 



