THE URINE. 375 



ties in human urine as coupled combinations with indoxyl, skatoxyl, 

 and phenols. It is also found in the artists' color " jaune indien," 

 which contains the magnesium -salt of euxanthonic acid. On heat- 

 ing this acid with water to 120-125 C. it splits into euxanthin and 

 glycuronic acid. 



This acid may pass into the urine in larger quantities as coupled 

 glycuronic acids after the administration of various medicines or 

 other substances (see below). Thus after the administration of 

 chloral hydrate, naphthalin, camphor, and turpentine, respectively, 

 urochloralic acid, naphthol-glycuronic acid, campho-glycuronic 

 acid, and terpen-glycuroriic acid appear in the urine. The coupled 

 glycuronic acids turn the plane of polarization to the left, while 

 glycuronic acid itself is dextro-gyrate. With the absorption of 

 water they may split into glycuronic acid and other coupled bodies. 

 A few of the coupled glycuronic acids, such as the urochloralic 

 acid, reduce copper oxide and certain other metallic oxides in al- 

 kaline solution, and therefore they may interfere with the detection 

 of sugar in the urine. 



Glycuronic acid is not crystalline, but is obtained only as a syrup. 

 It dissolves in alcohol and is easily soluble in water. If the watery 

 solution is boiled for an hour, the acid is in part (20$) converted 

 into the anhydride GLYCUROtf,C 6 H 8 6 , which is crystalline, soluble 

 in water but insoluble in alcohol. The potassium-salt of this acid 

 crystallizes in fine needles. The neutral barium-salt is amorphous, 

 soluble in water, but is precipitated by alcohol. If a concentrated 

 solution of the acid is saturated with barium hydrate, the basic ba- 

 rium-salt separates. The neutral lead-salt is soluble in water, but 

 the basic salt is, on the contrary, insoluble. The acid is dextro- 

 gyrate, reduces copper, silver, and bismuth salts. It gives a crys- 

 talline combination with phenylhydrazin. 



Glycuronic acid may be prepared from urochloralic acid or cam- 

 pho-glycuronic acid by boiling with a mineral acid. It may be 

 prepared more easily by heating euxanthonic acid with water in 

 PAPIN'S digestor to 120 b -125 C. for an hour and evaporating the 

 watery solution at+40 C. The anhydride which crystallizes grad- 

 ually is removed, the mother-liquor diluted with water and boiled 

 for a time to convert a second portion of acid into anhydride, and 

 then evaporated at about -j- 40 C. This is continued until nearly 



