304 PHYSIOLOGICAL CHEMISTRY 



2. Quantitative Estimation of Sugar. The quantitative esti- 

 mation of sugar in urine is attended by some difficulty, and a 

 variety of methods have been proposed. Only two titration 

 methods will be included here, first the Fehling method, because 

 it is the standard method upon which most later and more ac- 

 curate methods are based, and second Benedict's method, which 

 is perhaps the best for general use, all things considered. 



(a) Fehling Method. The Fehling test may be made quan- 

 titative by making up the copper sulphate solution accurately. 

 A given amount of dextrose will reduce a definite amount of 

 copper. As long as copper sulphate remains unreduced the 

 solution will have a blue color. A measured volume of Feh- 

 ling 's solution may thus be titrated with the dextrose urine 

 until the color has completely disappeared. From the volume 

 of urine necessary to reduce the given volume of Fehling 's 

 solution, the amount of dextrose in the urine may be calculated. 



The quantitative Fehling solution is made up of such a 

 strength that 10 c.c. of the copper solution (20 c.c. of the 

 mixed Fehling 's) will be reduced by 0.1 gm. glucose or 0.134 

 gm. lactose. 



Before starting the experiment read through the entire direc- 

 tions for the process. 



With a pipette measure 10 c.c. of each part of the quantita- 

 tive Fehling 's solution into an Erlenmeyer flask (or evaporat- 

 ing dish). Add 80 c.c. of water measured with a graduate. 

 Dilute 5 c.c. of urine (measured with a pipette) with 20 c.c. 

 distilled water (also measured with a pipette). Diluting in a 

 volumetric flask is preferable, but the method described is 

 satisfactory. 



Fill a burette with the diluted urine. Heat the diluted 

 Fehling 's solution in the Erlenmeyer with a small flame, and 

 run in the urine, first a few drops at a time, boiling a few 

 seconds after each addition. If the liquid remains blue after 

 the addition of 2 c.c. of urine, continue the process, adding the 

 urine in 0.2 -0.3 c.c. portions until the blue or green color has 

 almost disappeared, then drop by drop until no blue or green 



