C 10 ], 



more than seven or eighr belong to them, and three con- 

 stitute the greatest part of their organized matter ; and 

 according to the manner in which these elements are 

 disposed, arise the different proper ties of the products 

 of vegetation, whether employed as food, or for other 

 purposes and wants of life. 



The value and uses of every species of agricul- 

 tural produce, are most correctly estimated and applied 

 when practical knowledge is assisted by principles de- 

 rived from chemistry. The compounds in vegetables 

 really nutritive as the food of animals, are very few ; 

 farina or the pure matter of starch, gluten, vegetable 

 jelly, and extract. Of these the most nutritive is 

 gluten, which approaches nearest in its nature to ani- 

 mal matter, and which is the substance that gives to 

 wheat its superiority over other grain. The next in 

 order as to nourishing power, is sugar, then farina ; 

 and last of all gelatinous and extractive matters. Sim- 

 ple tests of the relative nourishing powers of the differ- 

 ent species of food, are the relative quantities of these 

 substances that they afford by analysis ; and though 

 taste and appearance must influence the consumption 

 of all articles in years of plenty, yet they are less at- 

 tended to in times of scarcity, and on such occasions 

 this kind of knowledge may be of the greatest impor- 

 tance. Sugar and farina or starch, are very similar 

 in composition, and are capable of being converted 

 into each other by simple chemical processes. In the 

 discussion of their relations, I shall detail to you the 

 results of some recent experiments which will be 

 found possessed of applications both to the ceconomy 



