730 PHYSIOLOGICAL CHEMISTRY. 



Tests. 



1. Trommer's test. A few drops (2-4) of a 5 per cent, solution of 

 cupric sulphate are added to about 5 to 8 c.c. of urine in a test-tube 

 and then an equal volume of potassium (or sodium) hydroxide solu- 

 tion is added. The alkaline hydroxide precipitates both earthy phos- 

 phates and cupric hydroxide, the latter, however, dissolving (espe- 

 cially if sugar be present) in the excess of the alkali, producing a 

 beautiful blue transparent liquid. (If no sugar is present, the color 

 is less blue, but more of a greenish hue.) The liquid is now heated, 

 when, if sugar be present, a yellow precipitate of cuprous hydroxide 

 is formed which subsequently loses its water and becomes the red 

 cuprous oxide, which falls to the bottom or adheres to the sides of 

 the test-tube. (Plate VIII., 5.) 



In drawing conclusions from the above test, it should be remem- 

 bered that a change of color does not indicate sugar ; that a precipi- 

 tate of earthy phosphates must not be mistaken for cuprous oxide ; 

 and that substances other than sugar may deoxidize cupric oxide at 

 the temperature of 100 C. (212 F.). 



A disadvantage of Trommer's test is the formation of black cupric 

 oxide whenever too much copper solution is used in proportion to the 

 sugar present. The formation of the black oxide, which may mask 

 a small quantity of cuprous oxide, is avoided in the next test. 



2. Fehling's test differs from Trommer's test in merely using a pre- 

 viously mixed reagent instead of producing this reagent, as it were, 

 in the urine by adding to it cupric sulphate and an alkaline hydroxide 

 successively. This reagent, known as Fehling's solution, or as alkaline 

 cupric tartrate volumetric solution, is made by mixing exactly equal 

 volumes of the below-mentioned copper solution and the Rochelle 

 salt solution at the time required. 



Copper solution : 



Crystallized cupric sulphate 34.64 grammes. 



Water, sufficient quantity to make .... 500 c.c. 



Rochelle salt solution : 



Potassium sodium tartrate 173 grammes. 



Potassium hydroxide . . . . . . .125 " 



Water, sufficient quantity to make .... 500 c.c. 



Both solutions are preserved in small well-stoppered bottles, and 

 mixed only at the time needed, because the mixture is apt to decom- 

 pose when kept some time. 



The addition of sodium-potassium tartrate in Fehling's solution prevents the 

 precipitation of cupric hydroxide by the alkaline hydroxide. This action is anal- 



