INTRODUCTION. XVU 



to decomposition ; for, according to the laws of elective 

 affinity, one constituent of a compound body will forsake 

 another, for which it has a certain degree of affinity, to 

 unite itself with a third, for which its affinity is stronger. 

 We thus see how important it is, for those who wish to 

 study the operations of art and nature, to be acquainted 

 with the degrees of affinity that exist amongst the various 

 elementary bodies which enter into combination. Whilst 

 the chymist influences, according to his will, nearly all 

 the agents which are employed by nature, she can follow 

 him in her labors, even when she cannot imitate him in 

 her productions. She knows the materials which the 

 chymist employs, and can often furnish them to him, and 

 facilitate his operations. She can foresee his mistakes, 

 and cautiously turn aside the causes which would pro- 

 duce them. In a word, the mutual action exercised by 

 bodies is constantly regulated by the immutable laws of 

 nature. But the chymist can at pleasure dispose of these 

 same bodies of which he knows the respective affinities. 

 He can combine them in all their proportions, submit 

 them to all degrees of heat, and subject them to the 

 action of external agents, the energy of which he can 

 increase or diminish to almost any extent, and thus 

 produce results which nature, in her constant and unde- 

 viating march, cannot give rise to. It is by means of 

 this power, that chymistry forms, every day, new com- 

 positions, and that she has enriched industry and econo- 

 my with a vast variety of productions, which, without 

 the assistance of this science, would have been for ever 

 unknown. 



Rude and inorganic matter obeys no other laws than 

 those of which I have spoken. All the changes which it 



B 



