CHEMICAL BASIS OF THE ANIMAL BODY. 193 



4. Kynurenic acid. C 10 H 7 N0 3 . [C 9 H 5 N . OH . COOH.] Oxy- 

 chinolin-carboxylic acid. 



This acid occurs characteristically but in variable amounts in the 

 urine of dogs but does not appear to have been found normally in that 

 of man. It was first described by Liebig 1 . It is most readily separated 

 from fresh urine by precipitation with phosphotungstic acid after the 

 addition of hydrochloric acid ; it is then liberated from the precipitate 

 by the action of baryta 2 . It may also be obtained by concentrating 

 the urine to one-third of its bulk, acidulating with hydrochloric acid 

 and allowing it to stand in a cool place for several days until the 

 separation of the acid is complete 3 . It may be separated from 

 admixed uric acid by solution in dilute ammonia. It is practically 

 insoluble in cold water, slightly so in boiling water and readily soluble 

 in hot alcohol and in dilute ammonia. It crystallises in long brilliant 

 white needles which when kept under acidulated water are often 

 changed into long glittering foursided prisms. 



FIG. 33. CRYSTALS OF KYNURENIC ACID. (After Kiihne.) 



This acid forms salts of which that with barium crystallises readily 

 and in a very characteristic triangular form. 



Apart from its crystalline form and that of its barium salt this acid 

 may be readily recognised by the following reaction. When heated on 

 a water bath with hydrochloric acid and chlorate of potash and evapo- 

 rated to dryness a reddish residue is obtained which turns at first to a 



1 Liebig's Annalen, Bd. 86 (1853), S. 125, Bd. 108 (1858), S. 354. 



2 Hofmeister, Zt. f. physiol. Chem. Bd. v. (1881), S. 67. Cf. Brieger, Ibid. 

 Bd. iv. S. 89. 



3 Schmiedeberg u. Schultzen, Liebig's Annalen Bd. CLXIV. (1872), S. 155. 



F n 



