cently made clear
that nitric acid, rather than ammonia, is the form of nitrogenous food
which is most serviceable to vegetation, and the one which is most
abundantly supplied by the air and soil. The value of ammonia is however
positive, and not to be overlooked.

When peat, properly prepared by weathering or composting, is suitably
incorporated with a poor or light soil, it slowly suffers decomposition
and wastes away. If it be wet, and air have access in limited quantity,
especially if _lime_ be mixed with it, a portion of its nitrogen is
gradually converted into ammonia. With full access of air _nitric acid_
is produced. In either case, it appears that a considerable share of the
nitrogen escapes in the free state as gas, thereby becoming useless to
vegetation until it shall have become converted again into ammonia or
nitric acid. It happens in a cultivated soil that the oxygen of the air
is in excess at the surface, and less abundant as we go down until we
get below organic matters: it happens that one day it is saturated with
water more or less, and another day it is dry, so that at one time we
have the conditions for the formation of ammonia, and at another, those
favorable to producing nitric acid. In this way, so far as our present
knowledge warrants us to affirm, organic matters, decaying in the soil,
continuously yield portions of their nitrogen in the forms of ammonia
and nitric acid for the nourishment of plants.

The farmer who skillfully employs as a fertilizer a peat containing a
good proportion of nitrogen, may thus expect to get from it results
similar to what would come from the corresponding quantity of nitrogen
in guano or stable manure.

But the capacity of peat for feeding crops with, nitrogen appears not
to stop here. Under certain conditions, _the free nitrogen of the air
which cannot be directly appropriated by vegetation, is oxidized in the
pores of the soil to nitric acid, and thus, free of expense to the
farmer, his crops are daily dressed with the most precious of all
fertilizers_.

This gathering of useless nitrogen from the air, and making it over into
plant-food cannot go on in a soil destitute of organic matter, requires
in fact that vegetable remains or humified substances of some sort be
present there. The evidence of this statement, whose truth was maintained
years ago as a matter of opinion by many of the older chemists, has
recently become nearly a matter of demonstration by th