THE ATMOSPHERE. 17 



The atmosphere also contains a very small and variable 

 quantity of ammonia. Schloesing found near Paris an 

 average of 1 Ib. of ammonia in 26,000,000 cubic yards 

 of air. Miintz and Aubin found at the top of the Pic du 

 Midi 1 Ib. of ammonia in 44,000,000 cubic yards. Accord- 

 ing 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 atmo- 

 sphere combine under the influence of electric discharges, 

 nitrous acid being formed ; this is converted 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 Rothamsted, in Hertford- 

 shire, the amount of nitrogen as ammonia in the rain, 

 mean of five years, is 2'4 Ibs. per acre; the nitrogen as 

 nitrates and nitrites about 1 Ib. ; the organic nitrogen a 

 similar quantity. The total nitrogen is thus about 4'4 Ibs. 

 per acre.* The average of many experiments on the conti- 

 nent (excluding Paris) gives 10' 18 Ibs. of nitrogen per 

 acre. The continental average is above the truth for the 

 open country, many of the determinations having been 



* The quantities here given are those obtained in recent experiments 

 with improved methods. The rain includes the snow, hail and dew 

 deposited on the rain gauge. 



3 



