THE CARBOHYDRATES 63 



it yields first galactonic and then mucic acid; the latter, being in- 

 soluble, separates out as crystals. 



The Pentoses, C 6 H 10 5 , occur as the complex carbohydrates of 

 the vegetable world, known as pentosans. They also occur in the 

 constitution of certain nucleoproteins of the animal kingdom (see 

 p. 49). They are of interest as occurring in human urine in the rare 

 anomaly of metabolism known as pentosuria. 



Glycuronic acid, C 6 H 10 O 7 , 



CHO 



(CHOH) 4 



COOH, 



is a derivative of dextrose. It is found as a combined acid in the 

 blood, bile, and urine. It gives the same reduction tests as dextrose, 

 and also the special pentose reactions (q.v.). The osazone, which 

 resembles glucosazone, is difficult to obtain. With bromphenylhy- 

 drazine hydrochloride a glycuronate is formed characterized by its 

 insolubility in alcohol. Glycuronic acid itself is dextro: tatory, but 

 its compounds are levorotatory. 



Glucosamine, C 6 H 13 N0 5 , 



CH,OH 



(CHOH) 3 

 CHNH 2 



COH, 



also called chitosamine, is most readily prepared from chitin (e.g., 

 decalcified lobster shells) by the action of strong hydrochloric acid. 

 It is an amino sugar, and has been obtained from glucoproteins (mucins) 

 and other proteins. Glucosamine has reducing properties similar to 

 dextrose, yields the same osazone, but is not fermentable. 



SECTION II. 



The Disaccharides (C 12 H220 n ). The disaccharides cane-sugar, 

 maltose, and lactose, are to be regarded as the combination of two 

 molecules of monosaccharides with the elimination of a molecule of 

 water. 



CjjH^On + HgO = C 6 H 12 O 6 + C 6 H 12 6 



Cane-sugar-l- water= dextrose-t- levulose 

 Maltose + water = dextrose + dextrose 

 Lactose + water =dextrose+galactose 



Each disaccharide is readily split by boiling with weak mineral 

 acid into its component monosaccharides. Cane-sugar may also be 



