274 PRACTICAL PHYSIOLOGY 



Reactions of Monosaccharides depending on the fact that they are 



aldehydes. 



/. Their Reducing Power. Dextrose is the aldehyde corresponding to 

 the hexatomic l alcohol, sorbite. 



CH 2 OH - (CHOH) 4 - CH 2 OH, CH 2 OH - (CHOH) 4 - CHO. 



Sorbite. Dextrose. 



It, therefore, manifests strong reducing powers on metallic oxides in 

 alkaline solution. 



EXPERIMENT III. Demonstrate the reducing power of a mono- 

 saccharide, such as dextrose on cupric salts in alkaline reaction. 



Trammer's Test. Place a few drops of a weak solution of cupric 

 sulphate in a test tube; add about 5 c.c. of a 1% solution of dextrose, 

 and then, drop by drop, a 20% solution of caustic soda until the 

 precipitate of cupric hydroxide, which at first forms, becomes re- 

 dissolved, and a clear blue solution is obtained. Boil. Reduction 

 is effected, a red precipitate of cuprous oxide resulting. 



Repeat experiment without the addition of dextrose. A black 

 precipitate of cupric oxide is obtained on boiling with excess of 

 caustic soda. 



EXPERIMENT IV. Fehling's Test. This differs from Trommer's test 

 in that tartrate of sodium and potassium (Rochelle salt) is added 

 to the mixture of CuS0 4 and NaOH. 2 Rochelle salt has the property 

 of dissolving cupric hydroxide forming a blue solution, which is 

 unaltered on boiling, and is therefore of especial value when the 

 solution to be tested contains only a small amount of dextrose or 

 other reducing substance. Boil a few c.c. of Fehling's solution in 

 a test tube. Add the dextrose solution drop by drop, with continued 

 boiling, until reduction results, as evidenced by the blue colour being 

 diminished and an orange red precipitate settling down. 



EXPERIMENT V. Nylander's Test. To about 5 c.c. of dextrose 

 solution in a test tube add about 1 c.c. of Nylander's reagent (a 

 solution containing 10% caustic soda, 4% Rochelle salt and 2% bismuth 

 subnitrate). Boil for two minutes. A black precipitate of bismuth 

 forms. Some substances (creatinin, uric acid) which reduce Fehling's 

 solution do not give this test. As regards the sugars, however, where 

 Fehling's test is positive this test will also be positive. 



1 A hexatomic alcohol is one which contains six OH groups. Glycerine is called 

 tri-atomic, because it contains three such groups. Ethyl alcohol is mon- atomic, 

 because it contains one. 



2 For the exact formula for Fehling's solution see p. 450. 



