HYDROGEN AND NITROGEN. 415 



Carbonates of ammonium. The neutral carbonate of oxide of 

 ammonium appears not to exist in a free state, but by distilling 

 the sesquicarbonate of ammonia of the shops, by a gentle heat. 

 Rose obtained a volatile crystalline salt, which may be viewed 

 as a compound of carbonate of ammonia with carbonate of 

 ammonium : N H 3 , C O 2 -f N H 4 O, C O 2 . When the commer- 

 cial salt is exposed to the air, it loses its pungent odour, and a 

 white friable mass remains, which is the bicarbonate of am- 

 monium, or carbonate of water and oxide of ammonium : 

 H O, C O 2 + N H 4 O, C O 2 . This is a stable salt, and may be 

 dissolved and crystallized without change. 



The sesquicarbonate of ammonia of the shops is a crystalline 

 transparent mass, which Rose finds to have generally, but not 

 always, the composition assigned to it by Mr. Phillips, or to 

 contain 3CO 2 with 2N H 3 and 2H O. Rose is disposed to 

 consider it a compound of carbonate of ammonia and bicarbonate 

 of oxide of ammonium, or N H 3 C O 2 + (H O, C O 2 + N H 4 O, C O 2 ) . 

 Mr. Scanlan has shown that a small quantity of water dissolves 

 out the carbonate from this salt, and leaves the bicarbonate, 

 which is the least soluble. This observation does not prove 

 the commercial salt to be a mechanical mixture of the two salts 

 derived from it, as many undoubted compounds of two salts 

 are decomposed by water, when one of the constituent salts is 

 much more soluble than the other. Another salt was obtained 

 by Rose, in well formed crystals, of which the ammonia and 

 carbonic acid are in the proportions of the sesquicarbonate, but 

 with three additional atoms of water. No less than twelve 

 different carbonates of ammonia are described by that chemist, 

 (Scientific Memoirs, ii, 98). 



Sulphate of ammonium, N H 4 O, S O 3 -f H O.- This is a highly 

 soluble salt, which possesses an atom of water of crystallization, 

 in addition to the atom which is essential to its constitution. 

 The salt may be deprived of the former by a gentle heat. 



It is to be observed that salts of this class are still generally 

 named as salts of ammonia, although admitted to contain ammo- 

 nium. 



Compounds of ammonia and metallic salts, supposed to resemble 

 the ammonium compounds. The whole or a portion of the am- 

 monia absorbed by certain anhydrous salts is retained with 

 great force, and cannot be separated from them by heat. An- 

 hydrous chloride of copper, for instance, absorbs a single equi- 



