URINE AND ITS CONSTITUENTS. 



733 



The following table shows the tests for distinguishing dextrose 

 from other reducing agents occurring in the urine : 



Quantitative estimation of sugar. By far the best method is 

 the decomposition of a copper solution of a known strength, and 

 Fehling's solution prepared as stated above, answers this purpose 

 well. 



1000 c.c. of Fehling's solution, containing 34.64 grammes of crys- 

 tallized cupric sulphate, CuSO 4 .5H 2 O, are decomposed by 5 grammes 

 of grape-sugar, or 1 c.c. of solution by 0.005 of grape-sugar. 



To make the quantitative determination, operate as follows : 10 c.c. 

 of Fehling's solution are poured into a porcelain dish of about 200 c.c. 

 capacity, placed over a flame. The copper solution is diluted with 

 about 40 c.c. of water, and heated to boiling ; to the boiling liquid, 

 urine (which has been previously diluted with 9 parts of water) is 

 added from a burette very gradually, until the blue color of the solu- 

 tion has disappeared, and there remains, upon subsidence of the 

 cuprous oxide, an almost colorless, clear liquid. A filtered portion 

 of this liquid, acidified with hydrochloric acid, should not give a 

 reddish-brown precipitate with potassium ferrocyanide (a precipitate 

 would show that all copper had not been precipitated, and that more 

 urine was needed), while a second portion of the filtered fluid should 

 not produce a red precipitate on boiling with a few drops of Fehling's 

 solution (a precipitate would indicate that too much urine had been 

 added, in which case the operation has to be repeated). 



The calculation of the amount of sugar present is easily made. 

 10 c.c. of Fehling's solution are decomposed by 0.05 gramme of 

 sugar ; this quantity must, therefore, be contained in the number of 



