On the Composition of Watcis of Land-Drainage. 141 



grains of nitric acid ; the adjoining Plot, No. 7, to which 400 lbs. 

 of ammonia-salts had been applied, 5"86 grains ; and the next 

 Plot, No. 8, manured with 600 lbs. ammonia-salts, contained 

 6*93, or nearly 7 grains of nitric acid per gallon. 



It appears from these experiments that salts of ammonia in 

 contact with soil permeated by air suffer decomposition, and that 

 the ammonia is gradually oxydised into nitric acid, which makes 

 its appearance in land-drainage in combination with lime, and 

 likewise, as we shall see further on, with magnesia. The oxy- 

 dation of ammonia proceeds slowly but steadily ; hence the 

 ammonia-salts which had been applied early in spring gave rise 

 to the formation of nitric acid, a considerable proportion of which 

 continued in the soil for some months, as the drainage-waters 

 collected in December contained more nitric acid the larger the 

 proportion of ammonia-salts which had been applied to the plots 

 in spring. 



It may be inferred fi'om these observations that, in all proba- 

 bility, nitric acid, and not ammonia, is the source from which 

 plants derive their nitrogen as far as their supply is dependent 

 upon the nitrogenous constituents of the soil. 



12. It is a well-established fact that soils have not the power 

 to retain either soda or nitric acid, and that, in consequence, the 

 beneficial effects which usually result from the application of 

 top-dressings with nitrate of soda to cereal crops in propitious 

 seasons, are lost in a great measure when nitrate of soda is 

 applied to the land early in spring, and continuous wet weather 

 sets in. 



The drainage from Plot 9, manured in spring every year with 

 550 lbs. of nitrate of soda per acre, presents a striking illus- 

 tration of the effect of rain on soils top-dressed with nitrate 

 of soda. The drainage-water taken in December from this plot 

 contained only 1*91 of nitric acid, or scarcely more than that 

 from the continuously unmanured portions of the same field, 

 which shows plainly that soils have not the power of retaining 

 nitric acid for any length of time. 



On Plot 7, 400 lbs. of ammonia-salts, containing the same 

 amount of nitrogen which is present in 550 lbs. of nitrate of 

 soda, had been applied. The drainage from that plot contained 

 in December 5*86 grains of nitric acid, or about 3 times as much 

 as that from Plot 9 top-dressed with nitrate of soda. Whilst 

 the nitric acid from the latter plot was removed in the course of 

 the season, the ammonia-salts on Plot 7 appear to have become 

 gradually oxydised and changed into nitrates. The land on 

 Plot 7 contained, in consequence, considerable quantities of 

 nitrates at a period of the year when the nitrate of soda applied 

 to Plot 9 had drained away to a much greater extent. 



