ATMOSPHERIC Ain AS THE FOOD OF PLANTS. !)6 



combine to a solid salt, llie 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 camphoi-, 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. At. wH. Pbr cent. 



NH3 17 21.5 



H2O 18 23.8 



CO2 44 55.7 



NH3. H2O. CO2. 79 100.0 



Tests for Amiuoiiia. — «. If salts of ammonia are rubbed to- 

 gether with slaked lime, ^)e^^t witli the addition of a few drops of water, 

 tht: ammouia is liberated in the gaseous st:-.te, and betrays itself (1) by 

 its charaeteristic odor ; (2) by its reaction on moistened test-papers; and 



