56 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



Groups containing Nitrogen.— The simplest compound of 

 nitrogen is of course ordinary ammonia, which has the com- 

 position NH3. Each of these three atoms of hydrogen is 

 capable of being replaced by complex groups of various kinds ; 

 moreover, just as ammonia, NH3, combines with acids, e.g., HCl, 

 to form ammonium chloride, NH3HCI (or NH4CI as it is gener- 

 ally written), so organic derivatives of ammonia also are capable 

 of acting as bases in this way. Ordinary sulphate of quinine 

 is a case in point. Ammonia derivatives are possessed of 

 different properties according, on the one hand, to the number 

 of hydrogen atoms replaced or, on the other, to the character 

 of there placing groups. E.g., if one of the hydrogen atoms is 

 replaced by a hydrocarbon residue we have what are known 

 as amino derivatives, thus :— 



CH3NH2 is methyl-amine. 



CeHjNHg is phenylamine or amino-benzene, commonly 

 known as aniline. 



CH2NH2 

 I is ammo-acetic-acid, glycocol or glycin, a 



COOH 

 very important member of the series of amino acids. 



If the replacement is effected by an acid residue an acid 

 amide results ; thus CH3CONH2 is known as acetamide. 

 The well-known substance urea is an amide of carbonic 



acid,CO<^QjJ, and has the formula C0<^^^^ 



The group NHg, which is thus seen to be formed by the 

 replacement of one hydrogen in ammonia by a complex group, 

 is known as the amino group, and like other well-defined 

 groups it can be recognised in a compound by its specific re- 

 actions ; one of the most important of these is its reaction with 

 nitrous acid, which results in the elimination of nitrogen and 



