70 PHYSIOLOGY FOB THE LABORATORY. 



Carbohydrates in Foods The Sugars. 



V. TEST FOR DEXTROSE, GRAPE SUGAR FEHLING'S 



SOLUTION. 



Materials. 15c.c. of Fehling's solution, which is a solution of 

 alkaline potassio-tartrate of copper K 2 Cu(C 4 H 4 O 6 ) 2 . Three grapes. 

 Water, 



Apparatus. Test-tubes. Bunsen burner. Mortar, and pestle. 

 Funnel and filter-paper. 



Experiment : 



1. Boil 15 c.c. of Fehling's solution in a test-tube. 



If no yellow color appears, the solution is in 

 good condition. 



2. Thoroughly mix with water in a mortar three or 



four grapes. 



3. Filter. 



4. Test the nitrate for a reducing sugar as follows : 



5. Add 1 c.c. of the filtrate to the Fehlirig's solu- 



tion and boil. What color is the precipitate 

 cuprous* oxid, Cu 2 O ? The sugar acts as a 

 reducing agent and changes the cupric salt 

 to a cuprous salt. This is characteristic of 

 dextrose, but there are other sugars, as maltose 

 and lactose (milk-sugar), that reduce metallic 

 salts, although in a less degree. 



VI. TEST FOR DEXTROSE BARFOED'S SOLUTION. 



Materials. 15 c.c. of Barfoed's solution, which is a solution of 

 acetate of copper in water acidulated with acetic acid. 5 c.c. of a 

 solution of dextrose. 



Apparatus. Test-tubes. Bunsen burner. 



