41 6 PHYSIOLOGICAL CHEMISTRY 



Cu 

 Cu OH 



0+H 2 0. 

 Cu OH 



Cu 



Cuprous hydroxide Cuprous oxide 

 (yellow). (brownish-red). 



The chemical equations here discussed are exemplified in Trommer's 

 and Fehling's tests. 



(a) Trommer's Test. To 5 c.c. of urine in a test-tube add one-half its volume 

 of KOH or NaOH. Mix thoroughly and add, drop by drop, agitating after the 

 addition of each drop, a very dilute solution of copper sulphate. Continue the addi- 

 tion until there is a slight permanent precipitate of cupric hydroxide and in conse- 

 quence the solution is slightly turbid. Heat, and the cupric hydroxide is reduced 

 to yellow cuprous hydroxide or to brownish-red cuprous oxide. 



If the solution of copper sulphate used is too strong, a small brownish-red pre- 

 cipitate produced in the presence of a low percentage of glucose may be entirely 

 masked. On the other hand, if too little copper sulphate is used a light-colored 

 precipitate formed by uric acid and purine bases may obscure the brownish-red 

 precipitate of cuprous oxide. The action of KOH or NaOH in the presence of an 

 excess of sugar and insufficient copper will produce a brownish color. Phosphates 

 of the alkaline earths may also be precipitated in the alkaline solution and be mis- 

 taken for cuprous hydroxide. Trommer's test is not very satisfactory. 



Salkowski 1 has proposed a modification of the Trommer procedure which he 

 claims is a very accurate sugar test. 



(b) Fehling's Test. To about i c.c. of Fehling's solution 2 in a test-tube add 

 about 4 c.c. of water, and boil. 3 [The cupric hydroxide is held in solution by the 

 sodium potassium tartrate (Rochelle salt).] This is done to determine whether 

 the solution will of itself cause the formation of a precipitate of brownish-red 

 cuprous oxide. If such a precipitate forms, the Fehling's solution must not be 

 used. Add urine to the hot Fehling's solution, a few drops at a time, and heat the 

 mixture to boiling after each addition (never add more urine than the original 

 volume of Fehling's solution). The production of yellow cuprous hydroxide or 

 brownish-red cuprous oxide indicates that reduction has taken place. The 

 yellow precipitate is more likely to occur if the urine is added rapidly and hi large 

 amount, whereas with a less rapid addition of smaller amounts of urine the 

 brownish-red precipitate is generally formed. 



This is a much more satisfactory test than Trommer's, but even 

 this test is not entirely reliable when used to detect sugar in the urine. 



1 Salkowski: Zeit. physiol. Chem., 79, 164, 1912. 



2 Fehling's solution is composed of two definite solutions a copper sulphate solution 

 and an alkaline tartrate solution, which may be prepared as follows: 



Copper sulphate solution = 34.65 grams of copper sulphate dissolved in water and made 

 up to 500 c.c. 



Alkaline tartrate solution = 125 grams of potassium hydroxide and 173 grams of Rochelle 

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



These solutions should be preserved separately in rubber-stoppered bottles and mixed 

 in equal volumes when needed for use. This is done to prevent deterioration. 



3 More dilute Fehling solution should be used in testing urines containing small amounts 

 of sugar. In case of urines containing a high concentration of sugar it may sometimes be 

 desirable to use a larger volume of Fehling's solution. 



