URINE. 



289 



is present in the urine of the dog and has recently been detected 

 by Swain in the urine of the coyote. To isolate it from the urine 

 proceed as follows : Acidify the urine with hydrochloric acid in 

 the proportion i : 25. From this acid fluid both the uric acid and 

 the kynurenic acid separate in the course of 24-48 hours. Filter 

 off the combined crystalline deposit of the two acids, dissolve the 

 kynurenic acid in dilute ammonia (uric acid is insoluble) and re- 

 precipitate it with hydrochloric acid. 



Kynurenic acid may be quantitatively determined by Capaldi's 

 method. 1 



COOH. 



BENZOIC ACID, 



Benzoic acid has been detected in the urine of the rabbit and dog. 

 It is also said to occur in human urine accompanying renal disor- 

 ders. The benzoic acid probably originates from a fermentative 

 decomposition of the hippuric acid of the urine. 



EXPERIMENTS. 



i. Solubility. Test the solubility of benzoic acid in water, alco- 

 hol and ether. 



FIG. 94. 



BENZOIC ACID. 



2. Crystalline Form. Recrystallize some benzoic acid from hot 

 water, examine the crystals under the microscope and compare 

 them with those reproduced in Fig. 94, above. 



1 Zeitschrift fur physiologische Chcmie, 1897, xxiii, p. 92. 



