CARBOHYDRATES 21 



with dilute mineral acids. They reduce metallic oxides in alkaline 

 solution, are optically active and extremely soluble. With phenyl- 

 hydrazine they form characteristic osazones. 



CH 2 OH 

 GLUCOSE (CHOH) 4 



CHO 



Glucose, also called dextrose or grape sugar, is present in the blood 

 in small amount and also occurs in traces in normal urine. 1 After 

 the ingestion of large amounts of sucrose, lactose or glucose, causing 

 the assimilation limit to be exceeded, an alimentary glycosuria may 

 arise. In diabetes mellitus very large amounts of glucose are excreted 

 in the urine. The following structural formula has been suggested by 

 Victor Meyer for d-glucose: 



CHO 



I 

 H C OH 



HO C H 



H C OH 



I 

 H C OH 



I 

 CH 2 OH 



(For further discussion of glucose see section on Hexoses, page 20.) 



EXPERIMENTS ON GLUCOSE 



The following tests are made on glucose as a typical carbohydrate 

 and are not specific for this sugar. A specific test for glucose is the 

 Phenylhydrazine Reaction (3) in the absence of a positive Resorcinol- 

 Hydrochloric Acid Reaction (see page 35). 



1. Solubility. Test the solubility of glucose in the "ordinary solvents" and 

 in alcohol, (in the solubility test 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. a-Naphthol Reaction (Molisch). 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 Mo- 

 lisch's reagent (a 15 per cent alcoholic solution of a-naphthol) has been added, 

 so that the sugar solution will not mix with the acid. A reddish-violet zone 

 is produced at the point of contact. 



1 See Folin's test for sugar in normal urine (Jour. Biol. Chem., 22, 327, 1915). 



