NITROGEN COMPOUNDS IN RAIN WATER. 331 



871. Nitrogen compounds in the atmosphere. The atmosphere 

 contains minute amounts l of combined nitrogen in the form of 

 ammonia, nitric acid, and nitrous acid. The ammonia is be- 

 lieved to exist (except where from local causes there is an escape 

 of free ammonia from some source) combined with either carbonic 

 or nitric acid. 



872. Nitrogen in rain-water. The nitrogen compounds are 

 more or less perfectly removable from the air by rain, and in 

 solution can be made available to plants through the soil. It 

 is now necessary to examine the results of analyses of rain- 

 water in order to ascertain the amount of nitrogen contained 

 in it. 



The following data are taken from the careful experiments 

 at Rothamsted, under the direction of Lawes, Gilbert, and War- 

 ington. The nitrogen existing as nitric acid and ammonia in 

 the rainfall of one year is not far from 3.3 pounds per acre. The 

 proportion of this calculated as ammonia is between 2.3 and 2.6 

 pounds per acre, the residue being given as nitric acid. Be- 

 sides the foregoing substances, there is also a small amount of 

 nitrogenous organic matter in the air which appears in the 

 analyses of rain-water, and amounts, according to Frankland, to 

 .19 parts per million parts of water. Taking a somewhat lower 

 estimate than this, Lawes, Gilbert, and Warington give the 

 quantity of nitrogen in the form of organic matter annually 



pounds of it under the influence of ozone, or to that of ammonia under the 

 influence of nascent hydrogen " (p. 540). 



But, as shown by Lawes, Gilbert, and Pugh, as well as by many other ex- 

 perimenters, leguminous crops appropriate from some source considerably more 

 nitrogen than do grasses ; for instance, under apparently similar circumstances 

 of supply of combined nitrogen. 



For an excellent treatment of the whole matter of appropriation of nitrogen, 

 the student should consult memoirs by Atwater, " On the Acquisition of Atmos- 

 pheric Nitrogen by Plants" (American Chem. Journ., vol. vi., 1885, no. 6). 



1 The following figures serve simply to indicate the wide range in results 

 obtained by different observers who have investigated the amount of ammonia 

 in the atmosphere. The data are from Proceedings of Am. Assoc. for Ad- 

 vancement of Science, 1857, p. 152. 



Observer Station Amount of ammonia in one million 



cubic meters atmosphere. 



Fresenius . Wiesbaden (during the day) .... 127.27 gr. 



" " (at night) 219.47 " 



Kemp . . Ireland 4423.00 " 



Ville . . Paris 27.39 " 



Horsford . Boston (in July) 640.70 " 



