NITROGENOUS COMPOUNDS 57 



to which great historical interest attaches with which it is 

 isomeric, NH 4 OCN -> CO(NH 2 ) 2 . It may also be formed by 

 hydrolysis of cyanamide 



CN.NH 2 + H 2 O -> CO(NH 2 ) 2 



Further, hydrolytic treatment converts it first into ammonium 

 carbamate, and this finally into ammonium carbonate 



CO(NH 2 ) 2 + H 2 O -> NH 4 .O.CO.NH 2 

 NH 4 .O.CO.NH 2 + H 2 -> (NH 4 ) 2 CO 3 



Guanidine occurs in small quantity both in animal and 

 vegetable products, but it is of interest chiefly on account of 

 its relation to urea on the one hand and to uric acid, creatine, 

 and creatinine on the other. 



Uric acid, a white crystalline substance, practically 

 insoluble in water, is the chief nitrogenous constituent of the 

 excrement of birds and reptiles. It is found also in the 

 muscular juices, in blood and in the urine of mammals, especially 

 the carnivora. In the urine of herbivorous animals, hippuric 

 acid forms a considerable proportion of the nitrogenous matter. 

 This compound is easily resolved into glycocine and benzoic 

 acid, C 6 H 5 COOH. 



Alkaloids. Xanthine is important chiefly because of its 

 close relationship to theobromine and caffeine. These 

 compounds are usually referred to a special class of amino 

 bodies called alkaloids or vegetable bases. 



Apart from their chemical composition and reactions, 

 considerable interest attaches to these substances by reason of 

 their pronounced physiological effects. Theobromine occurs 

 in cocoa, and caffeine or theine in coffee and tea ; and it is to 

 the presence of these alkaloids that the stimulating effects 

 of the beverages are due. Other alkaloids exert a sedative 

 influence. They are largely used in medicine. The great 

 majority are more or less poisonous to animals, and are distin- 

 guished by their extremely bitter taste. The presence of 

 alkaloids in certain herbs, e.g. lupines, renders them distaste- 

 ful to cattle, and it is said that they have been known to cause 

 death. 



