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CHAPTER X. 



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TRANSITION FROM THE CHEMICAL TO THE CLASSI- 

 FICATORY SCIENCES. 



IT is the object and the boast of chemistry to 

 acquire a knowledge of bodies which is more 

 exact and constant than any knowledge borrowed 

 from their sensible qualities can be ; since it pene- 

 trates into their intimate constitution, and discloses 

 to us the invariable laws of their composition. But 

 yet it will be seen, on a little reflection, that such 

 knowledge could not have any existence, if we were 

 not also attentive to their sensible qualities. 



The whole fabric of chemistry rests, even at 

 the present day, upon the opposition of acids and 

 bases : an acid was certainly at first known by its 

 sensible qualities, and how otherwise, even now, do 

 we perceive its quality ? It was a great discovery 

 of modern times that earths and alkalies have for 

 their bases metals : but what are metals f or how, 

 except from lustre, hardness, weight, and the like, 

 do we recognize a body as a metal? And how, 

 except by such characters, even before its analysis, 

 was it known to be an earth or an alkali? We 

 must suppose some classification established, before 

 we can make any advance by experiment or obser- 

 vation. 



It is easy to see that all attempts to avoid this 



