234 
On the nitrogen of plants. 
portion is absolutely inappreciable by the most delicate and 
best eudiometer ; it might be classed among the errors of ob- 
servation, even were its quantity ten thousand times greater. 
But the detection of ammonia must be much more easy, when 
a pound of rain-water is examined, for this contains all the 
gas that was diffused through 20,800 cubic feet of air. 
If a pound of rain-water contains only 1th of a grain 
of ammonia, then a field of 40,000 square feet, must 
receive annually upwards of 80lbs. of ammonia, or 6'5lbs. of 
nitrogen ; for, by the observations of Schubler, which were 
formerly alluded to, about 700,000lbs. of rain fall over this 
surface in four months, and consequently the annual fall must 
be 2,500,000lbs. This is much more nitrogen than is contain- 
ed in the form of vegetable albumen and gluten, in 2,650lbs. 
of wood, 2,800lbs. of hay, or 200 cvvt. of beet-root, which 
are the yearly products of such a field, but it is less than the 
straw, roots, and grain of corn, which might grow on the same 
surface, would contain. 
Experiments made in this laboratory (Giessen) with the 
greatest care and exactness, have placed the presence of am- 
monia in rain-water beyond all doubt. It has hitherto escaped 
observation, because no person thought of searching for it. 
All the rain-water employed in this inquiry was collected 
600 paces southwest of Giessen, whilst the wind was 
blowing in the direction of the town. When several hundred 
pounds of it were distilled in a Copper still, and the first two 
or three pounds evaporated with the addition of a little muria- 
tic acid, a very distinct crystallization of sal-ammoniac was 
obtained : the crystals had always a brown or yellow color. 
Ammonia may likewise be always detected in snow-water. 
Crystals of sal ammoniac were obtained by evaporating in a 
vessel with muriatic acid several pounds of snow, which 
were gathered from the surface of the ground in March, when 
the snow had a depth of ten inches. Ammonia was set free 
from these crystals by the addition of hydrate of lime. The 
inferior layers of snow, which rested upon the ground, con- 
