A RESULT OF CHEMICAL AFFINITY. 27 



tion and swelling of it by a liquid, are effects in 

 which chemical affinity or attraction has a decided 

 share; and although we are accustomed to limit 

 the notion of affinity to such cases as exhibit a 

 change perceptible to our senses, in the properties 

 of the substances employed, as, for example, when 

 sulphuric acid and lime, or sulphuric acid and 

 mercury combine together, this limitation arises 

 from the imperfect apprehension of the essence of 

 a natural force. 



Everywhere, when two dissimilar bodies come in 

 contact, chemical affinity is manifested. It is a 

 universal property of matter, and by no means be- 

 longs to a peculiar class of atoms, or to a peculiar 

 arrangement of these. But chemical combination 

 is not, in all cases, the result of contact. 



Combination is only one of the effects of affinity, Affinity is 



everywhere 



and occurs when the attraction is stronger than all active 

 the obstacles which are opposed to its manifestation. bodLTin 

 When the forces or causes, which oppose chemical 

 combination, heat, cohesive attraction, electric at- 

 traction, or whatever they may be called, prepon- 

 derate, then chemical combination does not take 

 place ; and effects of another kind are manifested. 



Melted silver in a crucible, surrounded with red- 

 hot coals, in a place, therefore, where we should 

 hardly anticipate the presence of free oxygen, 

 absorbs as much as ten or twelve times its volume 

 of that gas. Metallic platinum exhibits the same 

 property in a far higher degree ; for from the 



