1276 



KYNURENIC ACID. 



Piria?s reaction. If tyrosine is moistened on a watch-glass 

 with concentrated sulphuric acid and warmed for five or ten 

 minutes on a water bath, it turns pink owing to the formation of 

 tyrosine-sulphonic acid C 9 H 10 (SO 2 OH) NO 3 + 2H 2 O. This 

 is then diluted with water, warmed, neutralized with barium 

 carbonate, and filtered while hot. The filtrate yields a violet 

 colour on the careful addition of very dilute perchloride of iron. 

 The colour is readily destroyed by any excess of the iron salt. 



4. Kynurenic acid. C 10 H 7 NO 3 . [C 9 H 6 N . OH . COOH.] 

 (Hydroxyquinoline-carboxylic acid.) 



This acid occurs characteristically but in variable amounts 

 in the urine of dogs, but does not appear to have been found 



FIG. 227. CRYSTALS OF KVNUREXIC ACID. (After Kiibue.) 



normally in that of man. It is practically insoluble in cold 

 water, slightly so in boiling water and readily soluble in hot 

 alcohol and in dilute ammonia. It cr}'stallizes in long brilliant 



FIG. 228. CRYSTALS OF BARILAI KYNURENATE. (After Ktihne.) 



white needles which when kept under acidulated water are 

 often changed into long glittering four-sided prisms. 



