ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 53 
combine to a solid salt, the carbonate of ammonia, which 
appears. as a white cloud where its ingredients come in 
contact. 
Carbonate of ammonia occurs in commerce under the 
name “salts of hartshorn,” and with the addition of some 
perfume forms the contents of the so-called smelling-bot- 
tles. It rapidly vaporizes, exhaling the odor of ammonia 
very strongly, and is hence sometimes termed sal volatile. 
Like camphor, this salt passes from the solid state into 
that of invisible vapor, at ordinary temperatures, without 
assuming intermediately the liquid form. 
In the atmosphere the quantity of carbonic acid greatly 
preponderates over that of the ammonia; hence it is im- 
possible that the latter should exist in the free state, and 
we must assume that it occurs there chiefly in combination 
with carbonic acid. The carbonate of ammonia, whether 
solid or gaseous, is readily soluble in water, and like free 
ammonia it evaporates from its solution with the first 
portions of aqueous vapor, leaving the residual water rel- 
atively free from it. : 
In the guano-beds of Peru and Bolivia, carbonate of 
ammonia is sometimes found in the form of large trans- 
parent crystals, which, like the artificially-prepared salt, 
rapidly exhale away in vapor, if exposed to the air. 
This salt, commonly called bicarbonate of ammonia, con- 
tains in addition to carbonic acid and ammonia, a portion 
of water, which is indispensable to its existence. Its com- 
position is as follows: 
Symbol. Al. w't. Per cent. 
NH; V7 21.5 
HO 18 22.8 
CO, +4 55.7 
NH3. H,0. CO.g. 79 100.0 
Tests for Ammonia.—a. If salts of ammonia are rubbed to- 
gether with slaked lime, best with the addition of a few drops of water, 
the ammonia is liberated in the gaseous state, and betrays itself (1) by 
its characteristic odor ; (2) by its reaction on moistened test-papers ; and 
