TIIK Xll'Urc ACID OF TUK SOIL. 205 



nitrification. As Ave have seen, this acid, according to 

 Mukler, passes into crenic acid by loss of oxygen, to be 

 reproduced from tlie latter by absorption of free oxygen. 

 The apocrenate of sesquioxide of iron, in wliicli both acid 

 and base are susceptible of this transfer of oxygen, 

 should thus exert great oxidizing power. (See p. 228.) 



The Conditions Influencing IVitrification 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 weatlier and in hot climates. 



h. Accordhig 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. 



c. 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. Boussingault found, however [Chimie Agri- 

 cole, III, 198), that caustic lime develo2:)ed ammonia from 

 the oi'ganic matters of his garden soil Avithout 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 eartli and 

 thus perfecting their exposure to the air, facilitated this 

 process. Boussingault's experiments on this point were 

 made by incloshig 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, \\ Inch 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. amiuouia and 

 0.482 grms. nitric acid. 



n. 1000 grms. of soil and 5500 grms. sand acquired 0.035 grms. ammonia and 

 0.545 gnus, nitric acid. 



12 



