324 GLYCURONIC ACID 



In a general way we may suspect a given urine of con- 

 taining conjugate glycuronic acid if it polarizes to the left 

 without showing fermentescibility and reducing power, the 

 laBVOgyratory power changing to dextrogyratory and coin- 

 cidently a marked reducing power developing after boiling 

 for a long time with dilute acid. 



C. Neuberg recommends in the determination of glycur- 

 onic acid to first concentrate it by lead precipitation, after 

 hydrolytic cleavage of the urine. After decomposing the 

 lead precipitate by means of sulphuretted hydrogen or sul- 

 phuric acid one sometimes succeeds in obtaining the beau- 

 tiful crystalline cinchonin salt of the acid. The p-brom- 

 phenylhydrazine compound of glycuronic acid may also 

 prove of important service, according to Neuberg ; it can be 

 distinguished from the bromphenylosazones of sugar by its 

 almost complete insolubility in warm alcohol, but is espe- 

 cially characterized by the fact that its optical rotating 

 power in a pyridinalcoholic solution is much more marked 

 than that of any of the analogous sugar compounds. 



The brilliant colors produced in the orcin- and phloro- 

 glucin-tests may also serve for the detection of glycuronic 

 acid. According to Neuberg, these tests are not to be at- 

 tributed to the separation of furfurol, and to speak of them 

 as "furfurol reactions " is a mistake. They are, however, 

 not at all characteristic of glycuronic acid, but are well 

 known reactions also of the pentoses. It seems, moreover, 

 that they respond to any sugar with an uneven number of 

 carbon atoms in its molecule. 



The naphtho -res orcin reaction of B. Tollens 61 offers dis- 

 tinct advantages over these reactions. It depends on the 

 fact that naphtho-resorcin [1.3 dioxynaphthalin, C 10 H ( . 

 (OH) 2 ] changes the glycuronic acid, on boiling with hydro- 



W B. Tollens (Gottingen), Ber. d. deutsch. chem. Ges., Ifl, 1783, 1908; 

 Zeitschr. f. physiol. Chem., 56, 115, 1908; C. Tollens (Kiel), Munchener med. 

 Wochenschr., 1909, 652; C. Neuberg and O. Schewket, Biochem. Zeitschr., M, 

 502, 1912. 



