THE NiTiiic Aciij oy t:ik soil. 255 



The nitrates accumulate near the surface when no rain 

 falls to dissolve and wash them down — when 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 ricli soils, but do not accumulate to any 

 extent, unless in caves or positions artificially sheltered 

 from the rain. 



Boussingault's examination of garden earth fiom Lieb- 

 frauenberg [Agvonomie, 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 lbs. of sifted and -well-mixed soil were 

 placed in a heap on a slab 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 Mas repeated four 

 times at various intervals. The subjoined statement gives 

 the per cent of nitiatcs 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.* 



The formation of nitrates proceeded rapidly during the 

 h' at of summer, but ceased by the middle of September. 

 T^hether this cessation was due to the lower temperature 

 or to the complete nitrification of all the matter existing 

 in the soil ca))able of this change, or to decomposition 

 of nitric acid by the reducing action of organic matters, 



• The fi^rures jrivpn above arc abhrpvitited fn^iu the originals, or reduced tO 

 Kuglisb dcnominatiouij witU a trifling loss of exactu^sij. 



