THE AROMATIC OXY-ACIDS. 263 



in diseases which are associated with a high grade of polyuria, such 

 as diabetes insipidus, diabetes mellitus, in chronic interstitial neph- 

 ritis, etc. 



To demonstrate its presence in the urine large amounts are con- 

 centrated to a syrup, which is then extracted with four times its 

 volume of alcohol by boiling. On cooling, this extract is treated 

 with an excess of ether, when the inosit gradually crystallizes out 

 and may be recognized by its special tests (see page 360). 



The remaining aromatic substances which have been found in the 

 urine are the kynurenic acid and urocaninic acid of the urine of 

 dogs, and the so-called lithuric acid, which has been obtained from 

 the urine of the ox. The two latter have thus far been found in 

 only one instance and need not be considered at this place. Their 

 formulae are given as : 



C 12 H 12 N 4 O 4 , urocaninic acid. 

 C, 5 H 19 NO 9 , lithuric acid. 



The so-called damalic acid and damalunc acid, which are obtained 

 from the urine of the horse and the cow, probably represent a mixt- 

 ure of benzoic acid and volatile fatty acids. 



Kynurenic Acid. Kynurenic acid is said to be a constant con- 

 stituent of the urine of dogs, and is supposedly formed during the 

 process of intestinal putrefaction. Its mother-substance is mani- 

 festly an albuminous derivative, as the amount which appears in the 

 urine is largely dependent upon the quantity of albuminous food 

 ingested. Of its chemical nature and immediate antecedents, how- 

 ever, nothing is known. 



Kynurenic acid is now regarded as oxyquinolin-carbonic acid, and 

 is decomposed by heat, with the formation of carbon dioxide and a 

 basic substance, kynurifn. On reduction the latter is transformed 

 into quinolin. These changes are represented by the equations : 



(1) CH.C 9 H 5 N.COOH = C 9 H 9 NO -f CO 2 . 



Kynurenic acid. Kynurin. 



(2) C 9 H 7 NO + 2H == C 9 H 7 N + H 2 O. 

 Kynurin. Quinolin. 



Isolation. To isolate kynurenic acid from the urine, 500 c.c. are 

 treated with hydrochloric acid in the proportion of 4 c.c. for every 

 100 c.c. of the urine. On standing for forty-eight hours the sub- 

 stance in question crystallizes out together with uric acid. To sepa- 

 rate it from the latter, dilute ammonia is added to the crystalline 

 precipitate. The uric acid remains, and from its ammoniacal solu- 

 tion the kynurenic acid is then precipitated by acidifying with hydro- 

 chloric acid. 



The crystals are soluble in alcohol and melt at 253 C. On 

 evaporating a bit of the material with hydrochloric acid and potas- 

 sium chlorate on a porcelain plate a reddish residue is obtained, 



