102 Chemistty. [Lecture 27. 



chemists. The food we eat, the medicines we 

 apply as remedies for diseases, have all been, if 

 I may repeat the figure employed in the first of 

 these chemical lectures, anatomized and dis- 

 sected. Hence we are the better enabled to 

 judge of the salutary nature of each. All the 

 productions of art and nature have, in short, 

 been investigated, and their composition fully 

 explained. This is the true practical, I might 

 say the really philosophical use, of chemistry ; 

 and to this every student ought, in the first in- 

 stance, and as the first object, to apply. 



TTo cmiyoio of bodies io effected, as was for- 

 merly stated, partly by the agency ot heat, still 

 more, perhaps, by that of mixture, and still 

 more by the united effects of both judiciously 

 applied. It is of the utmost importance, there- 

 fore, that the student should render himself 

 master of the affinities of different substances, 

 and know with what bodies they will unite in 

 solution, &c., and what bodies they will dislodge. 

 The acids are the most powerful agents as men- 

 strua, or in the liquid state, and with their affini- 

 ties for the different solid matters it is necessary 

 to be well acquainted ; for by their means alone 

 many of the most important facts in natural 

 philosophy may be investigated and explained. 

 But in a state of fusion, which may commonly 

 be effected by the means of heat, most bodies 

 may be brought to act upon each other. 



In the subsequent lectures the action of the 



