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THE NITRIC ACID OF THE SOIL. 265 
nitrification. As we have seen, this acid, according to 
Mulder, passes into crenic acid by loss of oxygen, to be 
reproduced from the latter by absorption of free oxygen. 
The apocrenate of sesquioxide of iron, in which both acid 
and base are susceptible of this transfer of oxygen, 
should thus exert great oxidizing power. (See p. 228.) 
The Conditions Influencing Nitrification have been 
for the most part already mentioned incidentally. We 
may, however, advantageously recapitulate them. 
a. The formation of nitrates appears to require or to be 
facilitated by an elevated temperature, and goes on most 
rapidly in hot weather and in hot climates. 
b. According to Knop, ammonia that has been absorbed 
by a soil suffers no change so long as the soil is dry; but 
when the soil is moistened, nitrification quickly ensues. 
Water thus appears to be indispensable in this process. 
ce. An alkali base or carbonate appears to be essential 
for the nitric acid to combine with. It has been thought 
that the mere presence of potash, soda, and lime, favors 
nitrification, “ disposes,” as is said, nitrogen to unite with 
oxygen. JBoussingault found, however (Chimie Agri- 
cole, III, 198), that caustic lime developed ammonia from 
the organic matters of his garden soil without favoring 
nitrification as much as mere sand. The caustic lime by 
its chemical action, in fact, opposed nitrification; while 
pure sand, probably by dividing the particles of earth and 
thus perfecting their exposure to the air, facilitated this 
process. Boussingault’s experiments on this point were 
made by inclosing an earth of known composition (from his 
garden) with sand, etc., in a large glass vessel, and, after 
three to seven months, analyzing the mixtures, which were 
made suitably moist at the outset. Below are the results 
of five experiments. 
I. 1000 grms. of soil and 850 grms. sand acquired 0.012 grms. ammonia and 
0.482 grms. nitric acid. 
iI. 1000 grms. of soil and 5500 grms. sand acquired 0.035 grms. ammonia and 
0.545 grms. nitric acid. 
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