216 THE CARBOHYDRATES. 



certain conjugated glucuroric acids (see Chapter XV) synthetically, 

 among them being euxanthic acid. The most abundant source of glucu- 

 ronic acid is the artist's pigment " Jaune indien," which contains the 

 magnesium salt of euxanthic acid (euxanthon-glucuronic acid). 



Glucuronic acid is not crystalline, but is only obtainable as a syrup. 

 It dissolves in alcohol and is readily soluble in water. If the aqueous 

 solution is boiled for an hour the acid is partly (20 per cent) converted 

 into the crystalline lac tone, glucurone, CeHgOe, which is soluble in water 

 and insoluble in alcohol, and which has a melting-point of 175-178 C. 

 The alkali salts of the acid are crystalline. If a concentrated solution 

 of the acid is saturated ' with barium hydroxide the basic barium salt is 

 obtained as a precipitate. The neutral lead salt is soluble in water, 

 while the basic salt is insoluble. The readily crystallizable cinchonine 

 salt can be used in isolating glucuronic acid (NEUBERG *). Glucuronic 

 acid is dextrorotatory, while the conjugated acids are levorotatory ; 

 they behave like dextrose with the reduction tests, and do not ferment 

 with yeast. They give the pentose reactions with phloroglucin or orcin 

 and hydrochloric acid, and also a good reaction with naphthoresorcinol 

 and hydrochloric acid (see page 211). The product produced herewith 

 is soluble in ether with a blue, bluish-violet or reddish-violet color, and 

 the solution shows an absorption band somewhat to the right and on the 

 D-line. According to MANDEL and NEUBERG 2 this reaction is not 

 characteristic of glucuronic acid, as many aldehyde and ketone acids 

 give the same reaction; still, it is important in the differentiation of 

 the pentoses. With the phenylhydrazine test it gives crystalline com- 

 pounds which are not sufficiently characteristic (THIERFELDER, P. 

 MEYER 3 ). By the action of 3 mol. phenylhydrazine and the necessary 

 amount of acetic acid upon 1 mol. glucuronic acid at 40 for a few days, 

 NEUBERG and NEIMANN obtained the glucuronic-acid osazone, which 

 was very similar to glucosazone and melted at 200-205. With p-brom- 

 phenylhydrazine hydrochloride and sodium acetate, glucuronic acid gives 

 p-bromphenylhydrazine glucuronate, which is characterized by its insolu- 

 bility in absolute alcohol and by a very prominent levorotatory action. 

 This compound is very well suited for the detection of glucuronic acid. 4 

 Dissolved in a mixture of alcohol and pyridine (0.2 gram substance in 4 cc. 

 pyridine and 6 cc. alcohol) the rotation is 7 25', which corresponds to 

 ( n )*}= 369. On distillation with hydrochloric acid, glucuronic acid 

 yields furfurol and also carbon dioxide, and on this behavior TOLLENS 



1 Ber. d. d. chem. Gesellsch., 33. 



2 Biochem. Zeitschr., 13. 



3 Thierf elder, Zeitschr. f. physiol. Chem., 11, 13, 15; P. Mayer, ibid., 29. 



4 See Neuberg, Ber. d. d. chem. Gesellsch., 32; and Mayer and Neuberg, Zeitschr. 

 f . physiol. Chem., 29. 



