ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 55 
1,000,000,000 parts of atmospheric air contain of ammonia, according to 
ooo 
Graeger, at Mihlhausen, Germany, average, 333 parts. 
Fresenius, ‘‘ Wiesbaden, 7 om tours * 
» Pierre, “Caen, France, 1851-52, os 3500 = “* 
‘73 a3 ce ae 1852-55, cc 500 ce 
Bineau, ‘Lyons, ‘ 1852-55, Ze Zu 
SaCarare'* “© winter, ais 
“ce ce cc ‘a9 «c summer, SO ec 
Ville, ‘Paris, “1849-50, average, 24 ‘ 
os ‘““Grenelle, “ 1851, “ LS oi 
Graham has shown by experiment (Ville, Recherches 
sur la Vegetation, Paris, 1853, p. 5,) that a quantity of 
ammonia like that found by Fresenius is sufficient to be 
readily detected by its effect on a red litmus paper, which 
is not altered in the air. This demonstrates that the at- 
mosphere where Graham experimented (London) contained 
less than **| | ooo.o0.ths of ammonia in the state of bicar- 
bonate. The experiments of Fresenius and of Griiger 
were made with comparatively 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 obtained by a 
method scarcely a lmitting of much accuracy. 
The investigations of Ville (Recherches, Paris, 1853,) 
are, perhaps, the most trustworthy, 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, although 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 Ammonia by Vegetation.—The gen- 
eral fact that ammonia in its compounds is appropriated 
