24 ON THE STUDY OF 



bodies, or substances of opposite qualities, have 

 an affinity for each other, and are brought to- 

 gether in union by attraction forming new com- 

 pounds, this constitutes what is understood to be 

 chemical attraction, the basis upon which all the 

 knowledge of the science is founded. 



Thus various combinations and changes arising 

 from chemical affinities, are constantly taking 

 place in nature, producing in some instances, 

 simple substances from precipitation ; in others, 

 new compounds from combination, by which the 

 material world is more or less in an uniform state 

 of decay and renovation. 



To imitate nature in these operations, whether 

 for the purpose of investigating her laws, or to 

 produce substances useful to man, constitutes the 

 practice of chemistry : to understand which, it is 

 requisite that we make ourselves acquainted not 

 only with the general principles of the science, 

 but also with the chemical affinities of each par- 

 ticular substance ; with the nature and laws of 

 heat and light, by the agency of which combina- 

 tions are produced ; with oxygen, the basis of 

 vital air, which forms a constituent part of most 

 substances ; and with each simple body through- 

 out nature, with the combinations of which it is 

 susceptible, and with the new substances which 

 those combinations may produce. 



To enter into all these particulars would be 

 foreign to my present purpose, which is only 



