URINE: QUANTITATIVE ANALYSIS. 369 



a small beaker add from 2.5 grams to 5 grams of anhydrous sodium 

 carbonate 1 and heat the mixture to boiling over a wire gauze until 

 the carbonate has been brought into solution. 



Place the urine under examination in a burette and run it into 

 the hot Benedict solution rather rapidly 2 until the formation of a 

 heavy chalk-white precipitate is noted and the blue color of the solu- 

 tion lessens perceptibly in its intensity. From this point in the de- 

 termination from 2 to 10 drops 3 of the urine should be run into 

 the boiling Benedict solution at one time, boiling the solution vig- 

 orously for about 15 seconds after each addition. Complete re- 

 duction of the copper is indicated here as in Fehling's original 

 method, by the complete disappearance of all blue color. The end- 

 point here, however, is very sharply defined, contrary to the condi- 

 tions in the older method. 



To prevent the annoying bumping which often interferes with 

 the titration, a medium-sized piece of washed absorbent cotton 4 

 may be introduced into the solution. This cotton may be stirred 

 about through the solution as the titration proceeds and the bump- 

 ing thus eliminated. 



Calculation. Thirty cubic centimeters of Benedict's solution 

 is completely reduced by 0.073 gram of dextrose. If y represents 

 the number of cubic centimeters of urine necessary to reduce the 30 

 c.c. of the solution we have the following proportion: 



y : 0.073 : : TOO : x (percentage of dextrose) . 



solution are the same as those already described in connection with Benedict's 

 qualitative test, see p. 309. The third solution is made up as follows : 



Potassium ferro-thiocyanate solution = 15 grams of potassium ferrocyanide, 

 62.5 grams of potassium thiocyanate and 50 grams of anhydrous sodium carbo- 

 nate dissolved in water and made up to 500 c.c. 



These three solutions should be preserved separately in rubber-stoppered 

 bottles and mixed in equal volumes when needed for use. This is done to 

 prevent deterioration. 



^he amount added depends upon the dilution to which the solution is to be 

 subjected in titration. For this reason the maximum amount of sodium car- 

 bonate should be added when titrating urines containing a very low percentage 

 of sugar. 



2 Not rapidly enough, however, to interfere in any marked degree with the 

 continuous vigorous boiling of the solution. 



3 The exact amount to run in depends upon the intensity of the remaining blue 

 color, as well as upon the sugar content of the urine. The 10 drops should be 

 added at one time only when urines containing a very low percentage of sugar 

 are under examination. 



4 Glass wool may be substituted if desired. 



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