FORM IN WHICH AMMONIA IS PRESENTED. 99 



containing nitrogen is added to it than has been 

 taken from it in the form of grass, herbs, or seeds. 

 By means of manure, an addition only is made to 

 the nourishment which the air supplies. 



In a scientific point of view, it should be the care 

 of the agriculturist so to employ all the substances 

 containing a large proportion of nitrogen which his 

 farm affords in the form of animal excrements, that 

 they shall serve as nutriment to his own plants. 

 This will not be the case unless those substances 

 are properly distributed ypon his land. A heap of 

 manure lying unemployed upon his land would serve 

 him no more than his neighbors. The nitrogen in 

 it would escape as carbonate of ammonia into the 

 atmosphere, and a mere carbonaceous residue of 

 decayed plants would, after some years, be found in 

 its place. 



All animal excrements emit carbonic acid and 

 ammonia, as long as nitrogen exists in them. In 

 every stage of their putrefaction an escape of am- 

 monia from them maybe induced by moistening them 

 with a potash ley; the ammonia being apparent to 

 the senses by a peculiar smell, and by the dense 

 white vapor which arises when a solid body moist- 

 ened with an acid is brought near it. This ammonia 

 evolved from manure is imbibed by the soil either 

 in solution in water, or in the gaseous form, and 

 plants thus receive a larger supply of nitrogen than 

 is afforded to them by the atmosphere. 



But it is much less the quantity of ammonia, 

 yielded to a soil by animal excrements, than the 

 form in which it is presented by them, that causes 

 their great influence on its fertility. Wild plants 

 obtain more nitrogen from the atmosphere in the 

 form of ammonia than they require for their growth, 

 for the water which evaporates through their leaves 

 and blossoms, emits, aft^r some time, a putrid smell, 

 a peculiarity possessed only by such bodies as con- 

 tain nitrogen. Cultivated plants receive the same 

 quantity of nitrogen from the atmosphere as trees, 



