CONSTITUENTS OF URINE. 277 



Hippuric acid, benzoylamido-acetic acid, C 9 H 9 N0 3 , or 

 C H 5 .CO.NH.CH 2 .COOH. This substance is found (to the 

 amount of about 2 %) in the urine of horses, cattle, and many 

 herbivora ; it is also present in human urine (usually about 

 5%), and, during starvation, in that of carnivora. 



Hippuric acid readily decomposes (under hydrolysis), giving 

 benzoic acid and amido-acetic acid (glycocoll), C C H 5 CO.NH. 

 CH 4 .COOH + H a O - C 6 H 5 .COOH+CH 2 (NH 2 ).COOH. 



It is probably from the phenyl derivatives present in hay, 

 grass, and many fruits and berries that hippuric acid is formed 

 in the animal. Moreover, the putrefaction of proteids yields 

 certain phenyl derivatives which may produce benzoic acid and 

 thus hippuric acid on oxidation. 



Other derivatives of benzene occur in the urine, especially of 

 herbivora, thus, phenyl sulphuric acid, C C H 5 .O.SO 2 .OH, occurs 

 as potassium salt. Cresyl sulphuric acid, C (J H 4 (CH 3 X ).O.SO 2 .OH, 

 and pyrocatechin sulphuric acid, C C H 4 (OH).O.S0 2 .OH, also 

 occur in the urine of horses. Indoxyl sulphuric acid, 

 C 8 H 6 N.O.SO 2 .OH, or indican, is also found in urine, especially 

 of herbivora. By warming with acids, its potash salt yields 

 indoxyl and potassium sulphate 



' C 8 H B N.O.SO a .OK + H a O = C 8 H 6 N(OH) + KHSO 4 . 



On oxidation, e.g., by bleaching powder, indoxyl yields 

 indigo 



2C 8 H N.OH + O a = C 16 H 10 N 2 2 +2H 2 0. 



