CHEMICAL AFFINITY. 179 



Another class of saline compounds has been derived from 

 wood-spirit, of which the basyle is methyle, C 2 H 3 O, equally 

 numerous, and closely analogous in properties to the alcoholic 

 series. Many other classes of organic compounds besides are 

 found to correspond with that series, and the order of saline 

 compounds is likely to undergo a vast expansion. It thus ap- 

 pears that conclusions respecting salts are of a wide and general 

 application. Indeed the great question respecting the constitu- 

 tion of an oxygen-acid salt, is the pivot upon which the whole 

 body of chemical theory turns at this moment. 



SECTION II. 



CHEMICAL AFFINITY. 



In the preceding section, compound bodies have been viewed 

 as already formed, and existing in a state of rest. The arrange- 

 ment, weights and other properties of their atoms, have also 

 been examined, with the relations and classification of the 

 compounds themselves. But chemistry is more than a des- 

 criptive science ; for it embraces, in addition to views of com- 

 position, the consideration of the action of bodies upon each other 

 which leads to the formation and destruction of compounds. 

 Certain bodies, when placed in contact, exhibit a proneness to 

 combine with each other, or to undergo decomposition, while 

 others may be mixed most intimately without change. The 

 actual phenomena of combination suggest the idea of peculiar 

 attachments and aversions subsisting between different bodies, 

 and it was in this figurative sense that the term affinity was 

 first applied by Boerhaave to a property of matter. A specific 

 attraction between different kinds of matter must be admitted 

 as the cause of combination, and this attraction may be con- 

 veniently distinguished as chemical affinity. 



The particles of a body in the solid or liquid state exhibit an 

 attraction for each other, which is the force of cohesion, and 

 even different kinds of matter have often an attraction for each 

 other, which is probably of the same nature, although distin- 

 guished as adhesion. This force retains bodies in contact, 

 which are once placed in sufficient proximity to each other. 

 It is exhibited in the adhesion of two smooth pieces of lead 

 pressed together, or perfectly flat pieces of plate-glass, which 



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