718 PHYSIOLOGICAL CHEMISTRY. 



acid), is a normal constituent of human urine, but is found in much 

 larger quantities in the urine of herbivora. Its constitution is 

 CH 2 .NH CO 2 H, 



| and is the result of the combination of glycocoll 



C 6 H 5 CO 



and benzoic acid. This synthesis occurs in the kidney. Hay, and 

 especially aromatic herbs, contain benzoic acid, or compounds having 

 a similar composition, and a portion of these compounds is eliminated 

 in hippuric acid. Administration of benzoic acid increases the amount 

 of hippuric acid in urine. 



When pure, hippuric acid crystallizes in transparent, colorless, 

 odorless prisms, which have a bitter taste, and are sparingly soluble 

 in water. 



Experiment 98. (Preparation of hippuric acid.} To 400 c.c. of horse's urine 

 add some milk of lime, heat, filter, evaporate the filtrate to a small volume, 

 and acidify with hydrochloric acid. The calcium hippurate which had been 

 formed is decomposed and the liberated hippuric acid separates either at once 

 or on standing. If too highly colored, dissolve crystals in hot water contain- 

 ing some ammonia, decolorize solution with boneblack, filter, acidify with 

 hydrochloric acid, and recrystallize. Examine crystals microscopically and 

 chemically. 



Tests for hippuric acid. 



1. Heat in a dry test-tube : a sublimate of benzoic acid is formed 

 and the odor of hydrocyanic acid is noticed. 



2. To solution add ferric chloride : a brown precipitate is formed. 



3. Heat the dry acid with calcium hydroxide in a test-tube : ben- 

 zene and ammonia are evolved. 



4. Evaporate to dryness with a few drops of nitric acid : an intense 

 odor of nitrobenzene is evolved. 



Chlorides in urine. Chlorides are present in larger amount than 

 any other inorganic constituent. As sodium chloride is the most 

 abundant, the total quantity is usually expressed in terms of sodium 

 chloride, and normally amounts to 10 to 15 grammes in twenty-four 

 hours. While the origin of the chlorides is in the ingested food, they 

 bear some relation to the body metabolism, which as yet is not un- 

 derstood. In nephritis there is a retention of chlorides, particularly 

 with the development of oedema. In pneumonia there is a great 

 decrease in the chlorides, with a return to normal amounts at, or even 

 slightly before, the crisis. The significance of these facts is not 

 known. 4 



Qualitative test for chlorides. To a few c.c. of urine, acidified with 

 nitric acid, add a few c.c. of 5 per cent, silver nitrate solution. A 



