CARBOHYDRATES. 23 



an important hexose. These three hexoses are fermentable by 

 yeast, and yield Isevulinic acid upon heating with dilute mineral 

 acids. They reduce metallic oxides in alkaline solution, are optically 

 active, and extremely soluble. With phenylhydrazine they form 

 characteristic osazones. 



CH 2 OH 



DEXTROSE, (CHOH) 4 . 



CHO 



Dextrose, also called glucose or grape sugar, is present in the 

 blood in small amount and may also occur in traces in normal urine. 

 After the ingestion of large amounts of sucrose, lactose or dex- 

 trose, causing the assimilation limit to be exceeded, an alimentary 

 glycosuria may arise. In diabetes mellitus very large amounts of 

 dextrose are excreted in the urine. The following structural for- 

 mula has been suggested by Victor Meyer for J-dextrose : 



OOH 



H - C - OH 

 HO - C - H 

 H - C - OH 



.A. 



H - C - OH 

 ,OH 



CH, 



(For further discussion of dextrose see section on Hexoses, 

 page 22.) 



EXPERIMENTS ON DEXTROSE. 



i. Solubility. Test the solubility of dextrose in the "ordinary 

 solvents" and in alcohol. (In the solubility tests throughout the 

 book we shall designate the following solvents as the "ordinary 

 solvents": H 2 O; 10 per cent NaCl; 0.5 per cent Na 2 CO 3 ; 0.2 per 

 cent HC1; concentrated KOH; concentrated HC1.) 



2. Molisch's Reaction. Place approximately 5 c.c. of concen- 

 trated H 2 SO 4 in a test-tube. Incline the tube and slowly pour down 

 the inner side of it approximately 5 c.c. of the sugar solution to 

 which 2 drops of Molisch's reagent (a 15 per cent alcoholic solution 



