A PRIZE ESSAY. 
25 
poison, in a small dose become medicines, so, in 
plants, a small dose is not only good, but truly essen¬ 
tial. Now if we divide the acids into two classes, the 
nourishers and the poisoners, such will also be the 
nature of the salts. When we therefore attempt such 
a general division of the salts, it may be said that all 
the acids derived from the vegetable kingdom are 
harmless; so are the acids called mineral, yet whose 
components are, in part, like those of the vegetable 
acids; for instance, aqua-fortis, or nitric acid. But 
the true mineral acids are poisonous; such are oil of 
vitriol and spirits of salt. One thing is here to be 
borne in mind. It must never be out of sight, in try¬ 
ing to understand how salts make plants grow. You 
cast your salt upon the ground; it lies there ; no action 
occurs. It rains; your salt is dissolved and disap¬ 
pears ; it seems to do no good. Cast your salt now 
among sprouting seeds and growing roots; here is life. 
Well now, life is just as much a power or force as 
electricity is. It exerts its force, no matter how; that 
is quite another consideration. I say, life exerts its 
force here to separate the acid and the base of a salt, 
just like a chemical force. We can and do separate 
the components of salts by other substances ; nay, we 
do it by electricity alone. 
Now this is all which it is necessary for you to 
know, and to understand about this action of plants 
upon salts; it does disunite the components of the 
salts. What is the consequence? The alkali, earth, 
and metal act as such, the same as if no acid was 
present. The acid also acts by itself: if it is a nour¬ 
ishes it helps the plant; if it is a poisoner, it hurts it. 
It produces either a healthy, green crop, the effect of 
alkali, or a stunted, yellow, sickly plant, the effect of 
acids. Now neutralize this acid, kill it. You see 
/our crops start into luxuriance, and reap where you 
have strewed. So much for illustration. Let us now 
apply this view of the action of salts to those con¬ 
tained in cattle dung. In the first place, we have 
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