AROMATIC OXYACIDS. 697 



This acid crystallizes in leaves which melt at 165, and on strongly heating 

 it yields skatol with the splitting off of carbon dioxide. The solution, acidified 

 with hydrochloric acid, when treated with a little ferric chloride solution, becomes 

 cherry red on boiling. With some acid and a little nitrite as well as with hydro- 

 chloric acid and chloride of lime the solution becomes red, then cloudy, and a 

 red pigment precipitates. This pigment is soluble in amyl alcohol and gives the 

 above-mentioned absorption bands between D and E. This red pigment is 

 urorosein. 



Urorosein is the name given by NENCKI l to a red pigment which occurs in 

 the urine under the conditions mentioned under indol acetic acid. This pig- 

 ment is not preformed in the urine, but is produced from its chromogen (indol 

 acetic acid) when the urine is treated with hydrochloric acid alone. The urine 

 becomes red. According to HERTER this does not occur in perfectly fresh urine, 

 but only after a formation of nitrite by bacterial action which acts in the reaction 

 as an oxidizing agent. Urorosein differs from indirubin essentially by the same 

 properties as skatol, with which, according to some, it is identical (see above). 



Aromatic Oxyacids. In the putrefaction of proteins in the intes- 

 tine, paraoxyphenyl-acetic acid and paraoxyphenyl-propionic acid are 

 formed from tyrosine as an intermediate step, and these in great part 

 pass unchanged into the urine. The quantity of these acids is usually 

 very small. They are increased under the same conditions as the phenols, 

 especially in acute phosphorus poisoning, in which the increase is con- 

 siderable. A small portion of these oxyacids is also combined with 

 sulphuric acid. 



Besides these two oxyacids which regularly occur in human urine 

 we sometimes have other oxyacids in urines. To these belong homo- 

 gentisic acid in alcaptonuria, oxymandelic acid, found by SCHULTZEN and 

 RIESS ki urine in acute atrophy of the liver, oxyhydroparacoumaric acid, 

 found by BLENDERMANN in the urine on feeding rabbits with tyrosine, 

 gallic acid, which, according to BAUMANN, 2 sometimes appears in horse's 

 urine, and kynurenic acid (oxyquinolincarboxylic acid), which up to the 

 present time has been found only in dog's urine. Although all these 

 acids do not belong to the physiological constituents of the urine, still 

 they will be treated in connection with these. 



/OH 



Paraoxyphenylacetic Acid, C 8 H 8 O 3 , C 6 H 4 <f , and p-Oxyphenylpropionic 



\CH 2 .COOH 



/OH 

 Acid (Hvdroparacoumaric Acid), C 9 H 10 O 3 , C 6 H 4 \ ,are crystalline 



\CH 2 .CH 2 COOH 



and are both soluble in water and in ether. The one melts at 148 C. and the 

 other at 125 C. Both give a beautiful red coloration on being warmed with MIL- 

 LON'S reagent. 



To detect the presence of these oxyacids proceed in the following way (BAU- 

 MANN) : Warm the urine for a while on the water-bath with hydrochloric acid 

 in order to drive off the volatile phenols. After cooling shake three times with 



1 Nencki and Sieber, Journ. f. prakt. Chem., (N. F.), 26. 



2 Schultzen and Riess, Chem. Centralbl., 1869; Blendermann, Zeitschr. f. physiol. 

 Chem., 6, 267; Baumann, ibid., 6, 103. 



