26 
MANURES. 
salts df potash, of soda, of lime; these are the most 
abundant and active. Then we have salts of iron ; 
manganese, of clay, and magnesia. These last, exist¬ 
ing in small proportion, may be thrown out of the 
account, bearing in mind, however, that, though we 
set these aside, a plant does not; they enter equally 
with the others into its composition. 
Let us begin with the salts of potash. It is found 
combined in cattle dung, first, with a vegetable acid, 
the acid of mould. It is a nourisher of plants. 
Secondly, with sulphuric acid, or the acid of sulphur, 
called oil of vitriol. This is one of the poisoners, 
existing only in small proportion in cow dung; it min¬ 
isters to the wants of a healthy plant. The same is 
true of the common salt, or the muriate of soda of 
dung. If it existed in larger quantities, it would 
poison the plants to which it might be applied. 
The next salts are. those of lime, phosphate and 
sulphate of lime, or lime united to sulphuric and phos¬ 
phoric acid, forming plaster and bonedust. The acids 
here, if abundant, would have a decided bad influence, 
they are poisoners; but the carbonic acid, in the car¬ 
bonate of lime, is a nourisher. Now, from the small 
quantity in which these all exist in cattle dung, they 
act only beneficially. But if you apply a great excess, 
even of cattle dung, you may be sure of an unfavor¬ 
able result. It will be produced by the acids of those 
salts which we have called poisonous. 
To continue our remarks on the acids of salts of 
dung, it is to be observed, that they act also upon the 
soil. They decompose that. That is, they extract 
from the soil alkalies, or other substances, like those 
in the original salt. Now though applied, as they 
must be, in very small doses in cattle dung, yet, be¬ 
cause of their decomposing action on soil, they 
continually renew themselves, they last till all their 
acid is taken up to supply the wants of growing 
plants. 
Let us now, reader, if you understand how the 
