A PRIZE ESSAY, 
11 
which form it. This may be done by a very particu¬ 
lar and minute, or by a more general division. It 
may be done for our present purpose, by separating 
the several substances of a plant into classes of com¬ 
pounds. You are already chemist enough to under¬ 
take this mode of analysis; in truth you have already 
done it, again and again. For our purpose, the an¬ 
cient chemists had a very good division of all matter 
into four elements; fire, air, earth, and water. Now, 
by fire you separate plants into the other three ele¬ 
ments. You are, reader, though perhaps you do not 
know it, somewhat of a practical chemist. Whenever 
you have burned a charcoal pit, what did you? You 
separated the wood into air, water, and earth. 
You drove off by heat or fire the airy or volatile 
parts of the plant: you left its carbon, or coal; if you 
had burnt this, you would have left ashes. Now these 
ashes are the earthy parts of plants. If you burn a 
green stick of wood, you drive off first its water and 
volatile parts, which form soot. You burn its carbon, 
and leave its ashes, or salts. So that by simply burn¬ 
ing, you reduce the substance or elements of plants to 
water, carbon, salts. All plants then, without excep¬ 
tion, contain the several substances in our list above, 
as water, carbon, and salts. To apply this knowledge 
to manure, we must say a word on the form in which 
some of these, which we call the elements of plants, 
exist in them. The sap is water; it holds dissolved 
in it some salts of the plant. This sap, or juice, forms 
a pretty large proportion of the roots, say seventy-five 
to eighty parts in one hundred, of potatoes, turnips, 
beets, &c. This may be called the water of vegeta¬ 
tion. If we dry beet root, or any othei plant, we 
merely drive off this water of vegetation. Now what 
have we left ? To go back to our process cf analysis, 
let us char the dried root. We drive off more water 
and volatile parts. This water did not exist, as such, 
in the plant. It existed there as hydrogen and oxy* 
