270 HOW CROPS FEED. 
ibility of nitrates and nitrites (p. 73). According to 
Goppelsréder (Dingler’s Polytech. Jour., 164, 388), certain 
soils rich in humus possess in a high degree the power to 
reduce nitrates to nitrites. It is not unlikely that further 
reduction may occur—that, in fact, the deoxidation may 
be complete and free nitrogen be disengaged. This isa 
question eminently worthy of study. 
Loss of Nitrates may occur when the soil is saturated 
with water, so that the latter actually flows through and 
away from it, as happens during heavy rains, the nitrates 
(those of sesquioxide of iron, perhaps, excepted) being 
freely soluble and not retained by the soil. Boussingault 
made 40 analyses of lake and river water, 25 of spring 
water, and 35 of well water, and found nitric acid in ev- 
ery case, though the quantity varied greatly, being largest 
in cities and fertile regions. Thus the water of the upper 
Rhine contains one millionth, that of the Seine, in Paris, 
six millionths, and that of the Nile four millionths of ni- 
tric acid. The Rhine daily removes from the country 
supplying its waters an amount of nitric acid equivalent 
to 220 tons of saltpeter. The Seine carries daily into the 
Atlantic 270 tons, and the Nile pours 1,100 tons into the 
Mediterranean every twenty-four hours. 
In the wells of crowded cities the proportion of nitrates 
is much higher. In the older parts of Paris the well wa- 
ters contain as much as one part of niter (or its equiva- . 
lent of other nitrates) in 500 of water. 
The soil may experience a loss of nitrates by the com- 
plete reduction of nitric acid to gaseous nitrogen, or by 
the formation of inert compounds with humus, as will be 
noticed in the next section. 
Loss of assimilable nitrogen by the washing of nitrates 
from the soil may be hindered to some extent in compact 
soils by the fact just noticed that nitric acid is liable to be 
converted into ammonia, which is at once rendered com- 
paratively insoluble. 
