'56 



of the urine in a test tube are rendered strongly alka- 

 line with ammonia. If the reaction be positive, the 

 solution assumes a carmine-red color, which on shaking- 

 must also appear in the foam. Upon standing 24 hours 

 a greenish precipitate is formed. The test must not be 

 considered positive unless a distinct coloration extends 

 to and includes the foam on shaking. 



VIII. 



VOLUMETRIC METHODS. 



Chlorides. Mohr's method. Principle: If silver nitrate be 

 added to a solution containing sodium chloride, neutral potas- 

 sium chromate, and an alkaline phosphate, the chloride is first 

 precipitated, then the chromaje, and lastly, the phosphate. The 

 formation of the red silver chromate indicates the complete pre- 

 cipitation of the chloride. 

 Sblutioijs required : 



. 1. Standard soluti'on o:^ silver nitrate : 

 Fused silver nitrate 29.075 grams. 

 Distilled water to make 1000 cc. 

 2., Saturated solution neutral potassium chromate: 

 • Neutral potassium chromate 10 grams. 



Distilled water to make 100 cc. 

 Process. The urine should not be high colored, 

 and should be free from aibumin or excess of uric acid 

 or mucus. Dilute" 10 cc. of the urine with 100 cc. of dis- 

 tilled water. Fill a burette with the silver solution to 

 the zero mark. Drop*it slowly into the urine, stir it well 

 and occasionally carry a drop of the mixture so as to 

 come in contact with a little of the chromate solution in 

 an evaporating dish. Test in this way until the first trace 

 of .orange color appears in the chromate solution. Make 

 sure that the precipitation of the chlorides is complete by 

 adding another drop of the silver solution from the 

 burette.* Read off the am£)unt of silver solution used and 

 calculate the result. 



