390 PHYSIOLOGICAL CHEMISTRY. 



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 has 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 

 gram of sugar; this quantity must, therefore, be contained in 

 the number of c.c. of urine used. Suppose 30 c.c. of urine, di- 

 luted with 9 parts of water, or 3 c.c. of pure urine have been re- 

 quired to decompose the 10 c.c. of Fehling's solution, then 3 c.c. 

 of urine contain of grape-sugar 0.05 gram, or 100 c.c. of urine 

 1.666 gram, according to the equation : 



3 : 0.05 : : 100 : x 



x = 1.666. 



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

 rectly 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. 



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. 



The further detection of bile depends upon the reactions of the 

 biliary coloring matters or biliary acids; it frequently happens, 

 however, that the pigments are present, whilst the acids are not. 



Gmelin's test for biliary coloring matters has been already 

 considered, and may be applied to urine either by allowing a 

 small quantity of nitric acid, containing some nitrous acid, 

 to flow down the sides of a test-tube (containing the urine) in 

 such a manner that the two fluids do not mix, or by placing 

 upon a porcelain plate a few drops of the urine, near it a few 

 drops of nitric acid, to which one drop of sulphuric acid has 

 been added, and allowing the two liquids to approach gradually. 

 In both cases (if bile pigment is present) a play of color is seen 

 at the point of union between the two fluids, the colors changing 



