A PRIZE ESSAY. 
49 
lent as many fifty pounds as lie employs cords of cow 
dung. But, however prepared, nitre affords, by its 
elements, nourishment to plants. All its parts act. 
Its alkali acts, and its acid acts. 
SECTION XII. 
ASHES. 
It is easy to see that salts, whatever be their name 
or nature, which are likely to be of any service to 
the‘farmer, are those only which either enter into and 
form part of the plants, or which, by the action of 
their acid or base, act on the earthy parts of soil, or 
upon the mould. Salts either poison or nourish 
plants. The first, like the medicines we take, are 
good in small doses; the second can hardly injure, 
even by their excess. If we recur to the principle, 
with which we set out early in this essay, that the 
ashes of plants contain all their salts, then, rightly to 
know what salts are likely to produce good effects as 
manure, we should first study the composition of 
ashes. We have, in ashes, a great variety of sub¬ 
stances. They come from the soil. They form a 
part of plants. The dead plant returns them again to 
their mother earth, or we, losing the volatile parts of 
a plant, its mould and ammonia, by burning, collect 
its salts as ashes. Let us see what these salts are made 
of. In the first place, you know, all salts are com¬ 
posed of an acid and a base. 
The bases are, The acids are, 
Potash and soda, 
lime, 
Carbonic, or carbon united to 
oxygen, 
Phosphoric, or phosphorus, do. 
3 
