2T0 HOW CROPS FEED. 



ibility of nitrates and nitrites (p. 73). According to 

 Goppelsroder {Blngler's Polytech. Jour.^ 164, 388), certain 

 soils rich in liumus possess in a high degree the power to 

 reduce nitrates to nitrites. It is not unlikely that further 

 reduction may occur — that, iu fact, the deoxidation may 

 be complete and free nitrogen be disengaged. This is a 

 question eminently worthy of study. 



Loss of Nitrates may occur when the soil is saturated 

 with Avater, 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 Avater, 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 countiy 

 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 Avill 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 li;d)le to be 

 converted into ammonia, which is at once rendered com- 

 paratively insoluble. 



