THE NITKK' ACID OF TIIK SOIt. 251 



question — " IIow groat is the ammonia-content of good 

 manured soil lying fallow ?" — made repeated determina- 

 tions of ammonia (17 in all) in the same soil (well-ma- 

 nured, sandy, calcar(>ous loam exposed to all rains and 

 dews but not washed) during five months. The moist 

 soil varied in its proportion of ammonia with the greatest 

 irregularity between the extremes of 0.0008 and 0.0003" |^. 

 Similar observations were made the same summer on the 

 loamy soil of a field, at first bare of vegetation, then cov- 

 ered with a vigorous potato crop. In this case the fluctu- 

 ations ranged from 0.0009 to 0.0003" |„ as iiregularly as in 

 the other instance. 



Knop and WollF examined the soil last mentioned at 

 various depths. At 3 ft. the proportion of ammonia was 

 scarcely less than at the surface. At 6 ft. this loam, and 

 at a somewhat greater depth an underlying bed of sand, 

 contained no trace of ammonia. This observation ac- 

 cords with the established fact tliat deep well and drain- 

 waters are destitute of ammonia. 



Boussingault has discovered [Agrononiie, 3, 195) that 

 the addition of caustic lime to the soil largely increases its 

 content of ammonia — an effect due to the decomposing ac- 

 tion of lime on the amide-like substances already noticed. 



NITRIC ACID (NITRATES, NITROUS ACID, AND NITRITES) OF 

 THE SOIL. 



Nitric acid is formed in the atmospliere by the action 

 of ozone, and is brought down to the soil occasionally in 

 the free state, but almost invarial)ly in combination with 

 ammonia, by rain and dew, as has been already described 

 (p. 86). It is also produced in the soil itself by processes 

 whose nature — considerably obscure and little understood 

 ■ — will be discussed presently. 



