ON THE NITROGEN OP PLANTS. 
233 
times contain ammonia, though not always in equal quantity. 
It must be greater in summer than in spring or in winter, be- 
cause the intervals of time between the showers are in sum- 
mer greater; and when several wet clays occur, the rain of 
the first must contain more of it than that of the second. The 
rain of a thunder-storm, after a long protracted drought, 
ought for this reason to contain the greatest quantity, which 
is conveyed to the earth at one time. 
But all the analyses of atmospheric air, hitherto made, have 
failed to demonstrate the presence of ammonia, although, ac- 
cording to our view, it can never be absent. Is it possible 
that it could have have escaped our most delicate and most 
exact apparatus ? The quantity of nitrogen [of the the am- 
monia] contained in a cubic foot of air is certainly extremely 
small, but notwithstanding this, the sum of the quantities of 
nitrogen from thousands and millions of dead animals, is 
more than sufficient to supply all those living atone time with 
this element. 
From the tension of aqueous vapor at 15°C.(59° F.) = 6.98 
lines (Paris measure,) and from its known specific gravity at 
0° C. (32° F.) it follows, that when the temperature of the air 
is 59 F., and the height of the barometer 28," 1 cubic metre, 
or 64 Hessian cubic feet of aqueous vapor, are contained in 
487 cubic metres, or 31,158 cubic feet or air ; 64 feet of 
aqueous vapor weigh about l^lb. Consequently, if we sup- 
pose that the air, saturated with moisture at 59° F., allows all 
the water which it contains in the gaseous form to fall as rain; 
then 1 Hessian pound* of rain-water must be obtained from 
every 20,800 cubic feet of air. 
The whole quantity of ammonia contained in the same 
number of cubic feet will also be returned to the earth in this 
one pound of rain-water. But if the 20,800 cubic feet of air 
contain a single grain of ammonia, then ten cubic inches, the 
quantity usually employed in an analysis, must contain 
only 0.00000004S of a grain. This extremely small pro- 
*l.llbs. avoirdupois. 
Vol. vii,— No. hi. 30 
