EXAMINATION OF THE URINE. 121 



color becomes more violet. Aldehyde gives the same reac- 

 tion. 



3. Gunning's Test. Add to some of the distillate a few 

 drops of mercuric chloride solution, then some sodium hydrox- 

 ide solution and an equal volume of alcohol. Shake thor- 

 oughly and filter through a close filter. The filtrate must be 

 quite clear. Acidify the filtrate faintly with hydrochloric 

 acid and float on it some ammonium sulphide solution, so as 

 to form two layers. At the surface of contact a grayish- 

 black ring of mercuric sulphide will appear. The reaction 

 depends upon the solubility of mercuric hydroxide in ace- 

 tone. Aldehyde also possesses this property (v. Jaksch). 



The confusion with aldehyde is not especially to be feared, 

 since this substance has not hitherto been found in urine 

 and could only be present if the acidified urine should be 

 carelessly distilled too far. Aldehyde may be readily detected 

 in the distillate by the following reactions : 



1. If we add to a small portion some ammoniacal silver 

 solution (to prepare this add to about 5 cc. of silver nitrate 

 solution some drops of ammonia and then half the volume of 

 sodium hydroxide solution), blackening quickly takes place. 



2. If we warm a small portion after the addition of some 

 sodium hydroxide solution, a yellow color appears (eventually 

 turbidity also) and a characteristic odor develops (formation 

 of aldehyde resin). 



XIX. DETECTION OF BILE-PIGMENT. 



1. Gmelin's Test. Float some icteric urine by means of a 

 pipette on a few cubic centimeters of nitric acid, which con- 

 tains a very small amount of nitrous acid (fuming nitric acid) : 

 colored rings where the two liquids meet and in the follow- 

 ing order from top to bottom: green, blue, violet, red. 



2. Rosenbach's Modification of Gmelin's Test. Filter a 

 quantity of the urine, partly dry the filter by pressing between 



