470 PHYSIOLOGICAL CHEMISTRY. 



(copper, bismuth, silver, mercury) in the presence of alkalies ; 2, to 

 produce a yellow or brown color, when in contact with alkalies, 

 slowly in the cold, rapidly on heating ; 3, to give a deep red color 

 with picrates in alkaline solution, and a number of different colors 

 with certain phenols in the presence of sulphuric acid ; 4, to ferment 

 with yeast ; 5, to unite with phenyl-hydrazine to a crystalline com- 

 pound ; 6, to have the power of rotation to the right of the plane of 

 polarization. 



The tests for sugar should always be preceded by tests for albu- 

 min, which latter, if present, should be removed by coagulation and 

 filtration. Earthy phosphates also interfere with the copper tests 

 sometimes, because they are precipitated by the alkali, and this 

 precipitate may be mistaken either for precipitated cuprous oxide, 

 when no sugar is present, or it may cover the precipitated cuprous 

 oxide to such an extent that this is not recognized, when sugar is 

 present. 



To avoid these errors, it is well to render slightly alkaline the 

 urine by a few drops of potash solution, filter after a few minutes, 

 and use this urine for the tests. 



Trommers 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.) 



As various organic substances (other than sugar) have a tendency 

 to reduce cuprous oxide at a temperature of 100 C. (212 F.), it is 

 well to set aside a test-tube prepared as above (without heating it) 

 for from six to twenty-four hours. If sugar be present, the forma- 

 tion of cuprous hydroxide will gradually take place, whilst most 

 other orgonic matters do not act upon cupric oxide at ordinary 

 temperature. 



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 ; 



