4 8 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



however, and the plants are unable to absorb any appreciable 

 quantity directly from the atmosphere. 



Combined Nitrogen in Rain Water. The atmospheric ammonia 

 and nitric acid are chiefly of importance from the fact that they 

 are brought to the soil in rain, dew or snow, and thereby afford 

 nourishment for plants. 



The quantity of combined nitrogen in the rain has been ascer- 

 tained at a number of Experiment Stations, 1 by determining the 

 quantity and composition of each rainfall. The results of a 

 number of series of observations, each extending over a period of 

 a year or longer, are summarized in the following table : 



COMBINED NITROGEN IN RAINFAU, PER YEAR IN POUNDS PER ACRE. 



There appears to be considerable variation in the quantity of 

 combined nitrogen brought to the earth by the rain; the average 

 for the temperate zone is 8 pounds per acre. This is sufficient 

 to produce approximately 5.3 bushels of corn, leaves and stalk 

 included. But it is probable that the water which percolates 

 through the soil, in humid regions, takes out more combined 

 nitrogen than is brought down by the rain. 



Hydrogen Peroxide. Country and sea air contains a small 

 quantity of a powerful oxidizing agent, which, according to 

 1 Miller, Jour. Agr. Sci., 1905, p. 280. 



