OF THE NITROGEN OF PLANTS. 75 



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 0.000000048 

 of a grain. This extremely small proportion 

 is absolutely inappreciable by the most delicate 

 and best eudiometer ; it might be classed among 

 the errors of observation, even were its quan- 

 tity ten thousand times greater. But the de- 

 tection 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 contain only ^th of a 

 grain of ammonia, then a field of 40,000 square feet 

 must receive annually upwards of 80 Ibs. of ammo- 

 nia, or 65 Ibs. of nitrogen ; for, by the observations 

 of ScMbler, which were formerly alluded to, about 

 700,000 Ibs. of rain fall over this surface in four 

 months, and consequently the annual fall must be 

 2,500.000 Ibs. This is much more nitrogen than 

 is contained in the form of vegetable albumen and 

 gluten, in 2650 Ibs. of wood, 2800 Ibs. of hay, or 

 200 cwt. of beet-root, which are the yearly produce 

 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. 



