20 THE CHEMISTRY OF THE FARM 



The atmosphere also contains a very small and 

 variable quantity of ammonia. Schloesing found near 

 Paris an average of 1 lb. of ammonia in 26,000,000 

 subic yards of air. Miintz and Aubin found at 

 the top of the Pic du Midi 1 lb. of ammonia in 

 44,000,000 cubic yards. According to Schloesing, the 

 quantity is greatest in warm southerly winds. The 

 ammonia of the air is directly absorbed by plants to a 

 small extent ; it is chiefly rendered available through 

 absorption by the soil, and by means of rain, which 

 brings it in solution to the earth. 



The atmosphere also furnishes a small amount of 

 nitrous and nitric acid. The nitrogen and oxygen of 

 the atmosphere combine under the influence of electric 

 discharges, nitrous acid being formed; this is con- 

 verted into nitric acid by the action of ozone, or 

 peroxide of hydrogen. Nitric acid may also be formed 

 in the atmosphere by the oxidation of ammonia by 

 ozone and peroxide of hydrogen. 



The amount of nitrogen in the form of ammonia and 

 nitric acid annually carried to the soil by rain, varies 

 in different years and places. At Kothamsted, in Hert- 

 fordshire, the amount of nitrogen as ammonia in the 

 rain, mean of eighteen years, is 2-6 lbs. per acre ; the 

 nitrogen as nitrates and nitrites about I'l lbs. ; the 

 organic nitrogen a nearly similar quantity. The total 

 nitrogen is about 4*7 lbs. per acre.^ In tropical rain 

 the proportion of nitrogen as nitrates is generally in- 

 creased, while the ammonia is diminished. The total 

 nitrogen found in the rain in New Zealand, Barbadoes, 



'The rain incjucies the snow, hail, and dew dep<ibit.cd on the ruiu» 

 gaugo. 



