334 PHYSIOLOGICAL CHEMISTRY. 



note the formation of crystals of a-crotonic acid which are soluble 

 in ether and melt at 72 C. In case very slight traces of /?-oxy- 

 butyric acid be present in the urine under examination the amount 

 of a-crotonic acid formed may be too small to yield a crystalline 

 product. In this event the distillate should be extracted with ether, 

 the ethereal extract evaporated and the residue washed with water. 

 Under these conditions the impurities will be removed and the a- 

 crotonic acid will remain behind as a residue. The melting-point 

 of this residue may then be determined. 



CONJUGATE GLYCURONATES. 



Glycuronic acid does not occur free in the urine but is found, for 

 the most .part, in combination with phenol. Much smaller quan- 

 tities are excreted in combination with indoxyl and skatoxyl. The 

 total content of conjugate glycuronates seldom exceeds 0.004 P er 

 cent under normal conditions. The output may be very greatly in- 

 creased as the result of the administration of antipyrin, borneol, 

 camphor, chloral, menthol, morphine, naphthol, turpentine, etc. 

 The glycuronates as a group are laevorotatory, whereas glycuronic 

 acid is dextrorotatory. Most of the glycuronates reduce alkaline 

 metallic oxides and so introduce an error in the examination of 

 urine for sugar. Conjugate glycuronates often occur associated 

 with dextrose in glycosuria, diabetes mellitus and in some other 

 disorders. As a class the glycuronates are non-fermentable. 



EXPERIMENTS. 



1. Fermentation-Reduction Test. Test the urine by Fehling's 

 test. - If there is reduction try Barfoed's test. If negative this 

 indicates the absence of monosaccharides. A negative fermentation 

 test would now indicate the presence of conjugate glycuronates 

 (or lactose in rare cases). 1 



If dextrose is present in the urine tested for glycuronates the 

 urine must first be subjected to a polariscopic examination, then 

 fermented and a second polariscopic examination made. The sugar 

 being dextrorotatory and fermentable and the glycuronates being 

 laevorotatory and non-fermentable the second polariscopic test will 

 show a laevorotation indicative of conjugate glycuronates. 



2. Tollens' Reaction. Make this test according to directions 

 given under Pentoses, page 37. 



1 If necessary to differentiate between lactose and glycuronates apply the mucic 

 acid test (see p. 337) or the phenylhydrazine reaction (see p. 306). 



