ATMOSPIIEUIC AIR AS THE TOOD OF PLANTS. 55 



1,000,000,000 parts of atinosplicric air contain of ammonia, according to 



Graeirer, at MiiliUiausen, Germany, averag:e, 333 parts. 



Fresenius, " Wiesbaden, " " 133 " 



Pierre, " Caen, France, 1851-52, " 3500 " 



" " " " 1852-53, " 500 " 



Bineau, " Lyons, " 1852-53, " 250 " 



" " Caliiire, " " wiuter, 40 " 



" " " " " summer, 80 " 



Ville, " Paris, " 1819-50, average, 24 " 



" Grenelle, " 1851, "" 21 " 



Graham lias shown by experhnent (Ville, Recherches 

 sur la Vegetation, Paris, 1S53, p. 5,) that a quantity of 

 ammonia like that found by Fresenius is sufficient to be 

 readily detected by its eifect on a red litmus pai»er, which 

 is not altered in the air. This demonstrates that the at- 

 mosphere where Graham experimented (London) contained 

 less than '"|j^„^^_^^^ths cf ammonia in the state of bicar- 

 bonate. The experiments of Fresenius and of Grager 

 were made with com[)aratively small volumes of air, and 

 those of the latter, as well as those of Pierre, and some of 

 Bineau's, were made in the vicinity of dwellings, or even 

 in cities, where the results might easily be influenced by 

 local emanations. Bineau's results were obtiuned by a 

 method scarcely ailmitting of much accuracy. 



The investigations of Ville {Recherches, Paris, 1853,) 

 are, perhaps, the most trustwoi'thy, having been made on 

 a large scale, and apparently with every precaution. We 

 may accordingly assume that the average quantity of am- 

 monia in the air is one part in fifty millions, altliough the 

 amount is subject to considerable fluctuation. 



From the circumstance that ammonia and its carbonate 

 are so readily soluble in water, we should expect that in 

 rainy weather the atmosphere would be washed of its am- 

 monia; while after prolonged dry weather it would con- 

 tain more than usual, since ammonia escapes from its 

 solutions with the first portions of aqueous vapor. 



The Absorption of Amnioiiia by Vej?etation. — The gen- 

 eral fact that ammonia in its compounds is appropriated 



