URINE AND ITS NORMAL CONSTITUENTS. 379 



placing a fragment of uric acid in a porcelain dish, adding a 

 drop of nitric acid, and carefully evaporating over a flame. To 

 the dry residue a drop of ammonia water is added, which pro- 

 duces a beautiful purplish-red color. This reaction occurs, how- 

 ever, also with a number of substances which are similar to, 

 but more complex in composition than, uric acid. 



The quantitative estimation of uric acid in urine is best accom- 

 plished by adding 10 c.c. of hydrochloric acid to 250 c.c. of 

 urine, setting aside for 24 hours in a cool place, and collecting 

 the crystals of uric acid on a small filter, which has been pre- 

 viously weighed. The crystals are washed with a little water, 

 and dried at 100. 



If the urine (to be tested for uric acid) be very dilute, it 

 should be evaporated to about one-half its bulk before adding 

 hydrochloric acid; if it contain albumin, this should be re- 

 moved by adding a drop of acetic acid, boiling, and filtering. 



Hippuric acid, C 9 H 9 N0 3 (Benzyl-glycocol, Benzyl-amido-acetic acid), 

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

 larger quantities in the urine of herbivora. Its constitution 

 may be considered as ammonia in which two hydrogen atoms 

 are replaced by the radicals of benzoic and acetic acid respec- 



/C 7 H 5 

 lively, thus, N C 2 H 3 2 . Hay, and especially aromatic herbs, 



contain benzoic acid, or compounds having a similar composi- 

 tion, and a portion of these compounds is eliminated in hip- 

 puric acid. Administration of benzoic acid also increases the 

 amount of hippuric acid in urine. 



When pure, hippuric acid crystallizes in transparent, color- 

 less, odorless prisms, which have a bitter taste, and are spar- 

 ingly soluble in water. 



Analytically hippuric acid is characterized : 



1. By giving a sublimate of benzoic acid, and an odor of 

 hydrocyanic acid, when heated in a dry test-tube. 



2. By giving a brown precipitate with ferric chloride. 



3. By giving off benzene and ammonia, when heated with 

 calcium hydrate. 



Other organic substances, such as kreatin, kreatinin, xanthin, 

 lactic acid, mucus, coloring matters, etc., occur in such small 



