258 THE URINE. 



On boiling with dilute mineral acids or alkalies hippuric acid is 

 decomposed into its components. The same result is reached if 

 ammoniacal decomposition is allowed to occur-, and in such urines 

 benzoic acid only is found. In traces, benzoic acid is said to occur 

 in every urine together with hippuric acid, and it is thought that its 

 presence under normal conditions may be due to the action of a 

 ferment, the so-called histenzyme of Schmiedeberg, which has been 

 found in the kidneys, and which is known to be capable of effecting 

 the decomposition of hippuric acid as outlined. 



On heating hippuric acid in a dry test-tube it melts, and is then 

 decomposed with the formation of benzoic acid, which sublimes in 

 the upper portion of the tube. The liquid mass at the same time 

 assumes a red color, and develops an odor which at first is suggestive 

 of hay, but subsequently resembles that of hydrocyanic acid. This 

 reaction, together with the form of the crystals and their insolubility 

 in petroleum-ether, serves to distinguish hippuric acid from benzoic 

 acid. But like this, it develops a marked odor of bitter almonds 

 when it is evaporated with nitric acid and the residue is then 

 heated. The reaction is due to the formation of nitrobenzol. 

 In the urine hippuric acid is, of course, not present in the free 

 state, but in combination with alkalies, and notably potassium and 

 sodium. 



Synthesis of Hippuric Acid. Hippuric acid can be formed syn- 

 thetically in vitro also from benzoic acid and glycocoll by heating 

 the two substances together at a temperature of 160 C. in a sealed 

 tube. In a similar manner it is obtained from benzamide and 

 monochlor-acetic acid. The reactions which take place may be 

 represented by the equations : 



C 6 H 5 .COOH -f CH 2 (NH 2 ).COOH = CH 2 .NH(C 6 H 5 .CO).COOH + H 2 O 

 Benzoic Glycocoll. Hippuric acid, 



acid. 



CgH5.CO.NH2 + CH 9 .C1.COOH = CH 2 .NH(C 6 H 5 .CO).COOH + HC1 

 Benzamide. Monochlor- ' Hippuric acid, 



acetic 

 acid. 



Isolation of Hippuric Acid. Hippuric acid is most conveniently 

 isolated from the urine of herbivorous animals, in which, as has 

 been stated, it is present in much greater amounts than in that of 

 man and the carnivorous animals. Tc Miis end, 1000 c.c. of fresh 

 urine are rendered feebly alkaline w iV h milk of lime and boiled for a 

 few minutes. The liquid is filtered while still warm, concentrated, 

 and on cooling acidified with hydrochloric acid added in moderate 

 excess. After twenty-four hours the crystals of hippuric acid which 

 have separated out are filtered off, and are freed from adhering pig- 

 ments as follows : they are dissolved in hot water, and treated with 

 alum and then with an amount of sodium carbonate sufficient to 

 cause the formation of an abundant precipitate ; the reaction, how- 

 ever, should remain still acid. The pigments are retained by the 

 aluminous precipitate. The filtrate is then strongly concentrated, 



