38 



CuOoHs ; and if the mixture were boiled this blue precipitate 

 would be reduced to a black precipitate of Cupric Oxide, CuO,. 

 The clear blue solution containing glucose, however, when boiled, 

 changes from transparent blue to opaque yellow, and speedily de- 

 posits a yellow, ultimately red, precipitate of cuprous oxide CuO. 

 When the quantity of sugar is large the change is immediate. 

 When small the reaction takes a few minutes for its completion. 



Fehling's Solution. Solution A. 34.64 grams of pure crys- 

 talline copper sulphate are powdered and dissolved in 500 cc. of 

 distilled water. Solution B. Sodio-potassium tartrate (Rochelle 

 Salts) 173 grams. Pure caustic potash 125 grams. Add enough 

 distilled water to make 500 cc. When using take equal parts of 

 Solutions A and B. (If diluted with 5-10 vols, of water the test 

 is said to be more sensitive). 



Place some Fehling's Solution in a test tube and boil 

 it. If no yellow discoloration takes place it is in good 

 condition. Add a few drops of the suspected urine and 

 boil. If the mixture suddenly turns to an opaque yellow 

 or red color, the presence of a reducing sugar is indicated. 

 Normal horse urine probably because of its pyrocatechin 

 usually changes the color of the copper solution, but this 

 does not indicate sugar. 



Benedict's Modification of Fehling's Test. Greater 

 delicacy and accuracy are claimed for this test. • There are 

 two solutions as in Fehling's. The first is prepared by 

 dissolving 34.65 grams of cupric sulphate in a small 

 amount of water and made up to 500 cc. The second by 

 dissolving 100 grams of anhydrous sodium carbonate and 

 173 grams of Rochelle salt dissolved in water and made up 

 to 500 cc. These solutions should be preserved separately 

 in rubber-stoppered bottles and mixed in equal volumes 

 when needed for use. This is done to prevent deteriora- 

 tion. 



To 2 cc. of Benedict's solution in a test tube add 6 cc. 

 of distilled water and not more than 7 to 9 drops of the 

 urine under examination. Boil the mixture vigorously for 

 15 or 30 seconds and allow it to cool to the room tempera- 

 ture. If sugar is present in the solution a precipitate will 

 form which is often hluish-green or green at first, especially 



