474 PHYSIOLOGICAL CHEMISTRY. 



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), whilst 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 

 c.c. of urine used. Suppose 30 c.c. of urine, diluted with 9 parts of 

 water, or 3 c.c. of pure urine, have been required to decompose the 10 

 c.c. of Fehling's solution, then 3 c c. of urine contain of grape-sugar 

 0.05 gramme, or 100 c.c. of urine 1.666 grammes, according to the 

 proportion : 



3 : 0.05 : : 100 : x 



3 = 1.688. 



If the urine contains but very little sugar, it may be used directly 

 without diluting it, or instead of diluting it with 9 parts of water, it 

 may be diluted with 4 volumes or with an equal volume of water. 



Determination by fermentation. The fermentation test above described can be 

 used for quantitative determination of sugar, provided the quantity present is 

 not less than 0.5 per cent., when the results are fairly accurate. The determi- 

 nation is made by observing carefully the specific gravity of the urine at the 

 same temperature before and after fermentation. The decomposition of the 

 sugar causes the specific gravity to become less, and every degree of the urin- 

 ometer indicates 0.219 per cent, of sugar. If, for instance, urine showed a spe- 

 cific gravity of 1032 before, and 1022 after fermentation, the quantity of sugar 

 present is 10 times 0.219, or 2.19 per cent. The yeast to be used for the experi- 

 ment should be well washed upon a filter with pure water, and the urine 

 quickly filtered before taking its specific gravity after fermentation has taken 

 place. 



Experiment 77. Determine the amount of sugar in urine by the methods 

 described above. If no suitable urine is to be had, add some glucose to urine 

 and use this solution. 



Detection of bile. The presence of bile in urine is generally 

 indicated by a decided color, which varies from a deep brownish-red 

 to a dark brown ; the foam of such urine (produced by shaking) has 

 a distinct yellow color, and a piece of filtering-paper or a piece of 

 linen dipped into the urine assumes a yellow color, which does not 

 disappear on drying. 



