URINE 433 



used tests for sugars are based. When whitish-blue cupric hydroxide in 

 suspension in an alkaline liquid is heated it is converted into insoluble 

 black cupric oxide, but if a reducing agent like certain sugars be present 

 the cupric hydroxide is reduced to insoluble yellow or red cuprous 

 oxide. These changes are indicated as follows: 

 OH 



/ - 

 Cu ->Cu 



V Cupric oxide 



OH 



Cupric hydroxide 



(whitish-blue). 

 Reaction in absence 

 of a reducing agent. 



OH 



2Cu -> Cu 2 0+2H 2 0+0. 



Cuprous oxide 

 (yellow to red). 



V Cuprous oxide 



N (yello 



OH 



Cupric hydroxide. 

 Reaction in presence 

 of a reducing agent. 



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 or 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 oxide. 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 



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 tartate 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's 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. 



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