URINE 305 



tinge can be detected. Observe over a white paper. Do not 

 look through the liquid at the blue sky. The volume of urine 

 required to reduce the 20 c.c. of Fehling's will contain 0.1 gm. 

 dextrose or 0.134 gm. lactose. Perform duplicate analyses. 

 Time may be saved by running through a trial titration before 

 the actual determination, in order to find roughly the volume 

 of urine required to reduce the Fehling's solution. 



Calculate the weight of sugar in 100 c.c. of urine. If the 

 sugar content of the urine is so high that less than 2 c.c. are 

 required to reduce 20 c.c. of Fehling's solution, the urine must 

 be further diluted. 



(b) Benedict's Method. The greater accuracy of this method 

 is due to several facts: the solution is less strongly alkaline, so 

 that the decomposition of the sugar on boiling is less, and the 

 end point is perhaps sharper than in the original Fehling 

 method. 



Standard Copper Solution. Eighteen grams pure crystalline 

 CuS0 4 ; 200 grams crystalline Na 2 C0 3 ; 200 grams sodium or 

 potassium citrate; 125 grams KCNS; 5 c.c. of a 5% solution of 

 K 4 Fe(CN) 6 ; distilled water to make a total volume of 1 liter. 

 Dissolve the carbonate, citrate and thiocyanate in about 700 

 c.c. of water and filter if necessary. Dissolve the copper sul- 

 phate in 100 c.c. of water, and add slowly, stirring constantly, 

 to the 700 c.c. Add the ferrocyanide and make up to exactly 

 1 liter. The only ingredient which need be weighed exactly 

 is the copper sulphate. 



Analysis. Measure 25 c.c. (pipette) of the reagent into a 25-30 

 cm. evaporating dish. Add 10-20 grams crystalline Na 2 C0 3 , or 

 1/2 this amount of the anhydrous salt, some talcum or powdered 

 pumice and heat to boiling over a free flame until the carbonate 

 has dissolved. 



Accurately dilute 10 c.c. of urine to 100 c.c. unless the 

 amount of sugar in it is small, when it can be used without 

 dilution. Fill a burette with the urine, and run it into the 

 boiling copper solution, rapidly at first and then, more slowly 

 as the color grows less, then a few drops at a time until the 



