THE VOLATILE PART OF PLANTS. 115 



CH S COOH + NH S C 



Acetic acid. Ammonia. Ammonium acetate. 



Amides. This term is often used as a general desig- 

 nation for all the bodies of this section which result from 

 the substitution of the hydrogen of ammonia by any 

 atom or group of atoms. In a narrower sense amides 

 are those ammonia-derivatives containing "acid-radi- 

 cals " which are indicated in their systematic names. 



Acetamide, CHgCONH^ Many ammonium salts, 

 when somewhat strongly heated, suffer decomposition 

 into amides and water. 



CH S COONH 4 = CHjCONH, + H,O 



Ammonium acetate. Acetamide. Water. 



The above equation shows that acetamide is ammonia, 

 NH 8 , or HNH 2 , one of whose hydrogens has been re- 

 placed by the group of atoms, CH 3 CO, the acetic acid 

 radical, so called. Acetamide is a white crystalline body. 

 The simple amides, like acetamide, are as yet not known 

 to exist in plants. They readily unite with water to 

 produce ammonium salts. 



Carbamide, or Urea CO(NH 2 ) 2 . This substance 

 the amide of carbonic acid CO(OH) 2 naturally occurs 

 in considerable proportion in the urine of man and mam- 

 malian animals. It is a white, crystalline body, with a 

 cooling, slightly salty taste, which readily takes up the 

 elements of water and passes into ammonium carbonate. 

 Urea has not been found in plants, but derivatives of it 

 in which acid radicals replace a part of its hydrogen are 

 of common occurrence. (Guanin, allantoin.) 



Amidoacids are acids containing the NH 2 group as a 

 part of the acid radical. 



Amidoacetic Acid, C 2 H 5 N0 2 , or CH 2 (NH 2 )COOH, 

 is derived from acetic acid, CH 8 COOH, by the replace- 

 ment of H in CH 8 by NH 2 . The amidoacids have not a 

 sour, but usually a sweetish taste, and, like the amides, 

 act both as weak acids and weak bases. Amidoacetic 



