THE NITRIC ACID OF THE SOIL. 255 
The nitrates accumulate near the surface when no rain 
falls to dissolve and wash them down—whien evaporation 
causes a current of capillary water to ascend continually 
in the soil, carrying with it dissolved matters which must 
remain at the surface as the water escapes into the atmos- 
phere. In regions where rain frequently falls, nitrates are 
largely formed in rich soils, but do not accumulate to any 
extent, unless in caves or positions artificially sheltered 
from the rain. 
Boussingault’s examination of garden earth from Lieb- 
frauenberg (Agronomie, etc., T. II, p. 10) conveys an idea 
of the progress which nitrification may make in a soil un- 
der cultivation, and highly charged with nitrogenous ma- 
nures, About 2.3 Ibs. of sifted and well-mixed soil were 
placed in a heap on aslab of stone under a glazed roof. 
From time to time, as was needful, the earth was moist- 
ened with water exempt from ammonia. The proportion 
of nitric acid was determined in a sample of it on the day 
the experiment began, and the analysis was repeated four 
times at various intervals. The subjoined statement gives 
the per cent of nitrates expressed as nitrate of potash in 
the dry soil, and also the quantity of this salt contained 
in an acre taken to the depth of one foot.* 
Per cent. Lbs. per acre. 
1857— 5th August, 0.01 34 
“Vth 0.06 222 
« — 2d September, 0.18 634 
‘_1%th 0.22 %60 
— 2d October, 0.21 728 
The Beuaon of nitrates proceeded rapidly during the 
heat of summer, but ceased by the middle of September, 
Whether this cessation was due to the lower temperature 
or to the complete nitrification of all the matter existing 
in the soil capable of this change, or to decomposition 
of nitric acid by the reducing action of organic matters, 
* The figures given above are abbreviated from the originals, or reduced to 
English denominations with a trifling loss of exactness. 
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