URINE 541 



ence in the result (at the most i per cent) if the boiling period be prolonged to 

 8 or 9 minutes, provided that the boiling be gentle enough to prevent excessive 

 concentration. The volume of the solution in the test tube should not become 

 less than 6 to 7 c.c. 



Calculation. Divide 2.5 by the volume of urine taken (whether this is 

 several c.c. or a fraction of i c.c.) to get the per cent of sugar in the urine. 



TIME OF BOILING REQUIRED FOR COMPLETE REDUCTION OF COPPER 

 SOLUTION BY AN EXCESS OF GLUCOSE 



Interpretation. See page 539. 



4. Fehling's Method. Principle. Diluted urine is run into a 

 measured amount of Fehling's solution at the boiling-point until all 

 of the copper it contains is reduced as indicated by the loss of blue color. 

 This method has several disadvantages over Benedict's method. The 

 end point is difficult to determine and the mixed solution is unstable. 

 It gives less accurate results. 



Procedure. Place 10 c.c. of the urine under examination in a 100 c.c. volu- 

 metric flask and make the volume up to 100 c.c. with distilled water. (If the 

 urine contains less than 0.5 per cent of sugar it may be used without dilution. A 

 concentration of about 0.5 per cent is the most satisfactory for this titration.) 

 Thoroughly mix this diluted urine by pouring it into a beaker and stirring with 

 a glass rod, then transfer a portion of it to a burette which is properly supported 

 in a clamp. 



Now place 10 c.c. of Fehling's solution 1 hi a small beaker, dilute it with approxi- 

 mately 40 c.c. of distilled water, heat to boiling, and observe whether decomposi- 

 tion of the Fehling's solution itself has occurred as indicated by the production of 

 a turbidity. If such turbidity is produced the Fehling's solution is unfit for use. 

 Clamp the burette containing the dilute urine immediately over the beaker and 

 carefully allow from 0.5-1 c.c. of the diluted urine to flow into the boiling Fehl- 

 ing's solution. Bring the solution to the boiling-point after each addition of 

 urine and continue running the urine from the burette, 0.5-1 c.c. at a tune, as in- 

 dicated, until the Fehling's solution is completely reduced, i.e., until all the cupric 

 oxide in solution has been precipitated as cuprous oxide. This point will be 

 indicated by the absolute disappearance of all blue color. When this end point 



1 Directions for the preparation of Fehling's solution are given in a note at the bottom 

 of p. 25. 



