10 
ments of a number of chemical philosophers, both 
in this and in other countries ; and it forms a beau- 
tiful part of general chemistry ; it is too extensive 
to be treated of minutely ; but it will be necessary 
to dwell upon such parts of it, as afford practical 
inferences. 
If the organs of plants be submitted to chemical 
analysis, it is found that their almost infinite di- 
versity of form depends upon different arrange- 
ments and combinations of a very few of the 
elements \ seldom more than seven or eight belong 
to them, and three constitute the greatest part of 
their organized matter ; and according to the man- 
ner in which these elements are disposed, arise the 
different properties 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 derived from chemistry. The com- 
pounds in vegetables really nutritive as the food of 
animals, are very few ; farina or the pure matter 
of starch, gluten, sugar, vegetable gelly, oil, and 
extract. Of these the most nutritive is gluten, 
which approaches nearest in its nature to animal 
matter, and which is the substance that gives to 
wheat its superiority over other grain. The next 
in order as to nourishing power is oil, then sugar, 
then farina ; and last of all, gelatinous and ex- 
tractive matters. Simple tests of the relative nou- 
rishing powers of the different species of food, are 
the relative quantities of these substances that they 
