THE AMMONIA OF THE SOIL. 239 
to agricultural vegetation only a‘ter their incorporation 
with the soil. 
Rain and dew are means of collecting them from the 
atmosphere, and, as we shall shortly see, the soil is a 
storehouse for them and the medium of their entrance into 
vegetation. | 
This is therefore the proper place to consider in detail 
the origin and formation of ammonia and nitric acid, so 
far as these points have not been noticed when discussing 
their relations to the atmosphere. 
Ammonia is formed in the Soil either in the decay of 
organic bodies containing nitrogen, as the albuminoids, 
ete., or by the reduction of nitrates (p. 74). The former 
process is of universal occurrence since’ both vegetable 
and animal remains are constantly present in the soil; the 
latter transformation goes on only under certain condi- 
tions, which will be considered in the next section (p. 
269). , 
The statement that ammonia is generated from the free 
nitrogen of the air and the nascent hydrogen of decom- 
posing carbohydrates, as cellulose, starch, ete., or that set 
free from water in the oxidation of certain metals, as iron 
and zine, has been completely disproved by Will. (Ann. 
d. Ch. u. Ph., 45, pp. 106-112.) 
The ammonir encountered in such experiments may have been, Ist, 
that pre-existing in the pores of the substances, or dissolved in the wa- 
ter operated with. Faraday (Researches in Chemistry and Physics, p. 145) 
has shown by a series of exact experiments that numerous, we may say 
all, porous bodies exposed to the air have a minute amount of ammonia 
adhering to them; 2d, that which is generated in the process of testing 
or experimenting (as when iron is heated with potash), and formed by 
the action of an alkali on some compound of nitrogen occurring in the 
materials of the experiment; or, 3d, that which results from the reduc- 
tion of a nitrite formed from free nitrogen by the action of ozone (pp. 
77-83). 
The Ammonia of the Soil.—a. Gaseous Ammonia as 
Carbonate.—Boussingault and Lewy,in their examination 
of the air contained in the interstices of the soil, p. 219, 
