COMPOUNDS OF CAEBON WITH OXYGEN AND NITROGEN 407 



distinguished by such characteristic peculiarities as the cyanogen com- 

 pounds. 



The reactions and properties of the amides and nitriles of the 

 organic acids are described in detail in books on organic chemistry ; we 

 will here only touch upon the simplest of them, and to clearly explain 

 the derivative compounds will first consider the ammoniacal salts and 

 amides of carbonic acid. 



As carbonic acid is bibasic, its ammonium salts ought to have the 

 following composition : acid carbonate of ammonium, H(NH 4 )CO 3 , and 

 normal carbonate, (NH 4 ) 2 CO 3 ; they represent compounds of one or 

 two molecules of ammonia with carbonic acid. The acid salt appears 

 in the form of a non-odoriferous and (when tested with litmus) neutral 

 substance, soluble at the ordinary temperature in six parts of water, 

 insoluble in alcohol, and obtainable in a crystalline form either without 

 water of crystallisation or with various proportions of it. If an aqueous 

 solution of ammonia be saturated with an excess of carbonic anhydride, 

 and then evaporated over sulphuric acid in the bell jar of an air-pump, 

 crystals of this salt are separated. Solutions of all other ammonium 

 carbonates, when evaporated under the air-pump, yield crystals of this 

 salt. A solution of this salt, even at the ordinary temperature, gives 

 off carbonic anhydride, as do all the acid salts of carbonic acid (for 

 instance, NaHC0 3 ), and at 38 th6 separation of carbonic anhydride 

 takes place with great rapidity. On losing carbonic anhydride and 

 water, the acid salt is converted into the normal salt, 2(NH 4 )HC0 3 

 = H 2 + C0 2 + (NH 4 ) 2 C0 3 ; the latter, however, decomposes in solu- 

 tion, and can therefore only be obtained in crystals, (NH 4 ) 2 C0 3 ,H 2 O ; at 

 low temperatures, and from solutions containing an excess of ammonia, 

 as the product of dissociation of this salt : (NH 4 ) 2 CO 3 = NH 3 

 + (NH 4 )HC0 3 . But the normal salt, 34 according to the general type, is 



acids or alkalis. Under the action of alkalis the amides naturally give off ammonia, 

 through the combination of water with the amide, when a salt of the acid from which the 

 amide was derived is formed : ENH 2 + KHO = RKO + NH 3 . 



The same reaction takes place with acids, only an ammoniacal salt of the acid is of 

 course formed whilst the acid held in the amide is liberated: RNH 2 +HC1+H 2 O 



Thus in the majority of cases amides easily pass into ammoniacal salts,' but they 

 differ essentially from them. No ammoniacal salt sublimes or volatilises unchanged, and 

 generally when heated it gives off water and yields an amide, whilst many amides vola- 

 tilise without alteration and frequently are volatile crystalline substances which may be 

 easily sublimed. Such, for instance, are the amides of benzoic, formic, and many 

 other organic acids. 



34 The acid salt, (NH 4 )HC0 3 , on losing water ought to form the carbamic acid t 

 OH(CNH 2 O) ; but it is not formed, which is accounted for by the instability of the acii 

 salt itself. Carbonic anhydride is given % off and ammonia is produced, which gives 

 4jajamonium carbamate., 



