162 HEALTHY URINE. 



3. Schiff's test. Place a crystal of urea in a porcelain capsule, 

 pour upon it a drop of concentrated furfurol solution 

 in water and add a drop of HC1, a play of colours 

 changing through yellow, green, blue to violet, and in 

 a few minutes to a purple-violet. The change is some- 

 what slow, the purple colour being the best marked. 

 Old furfurol solutions colour red on the addition of 

 HC1. 

 To a solution of the crystals apply the following tests : 



1. Add acetic acid and a few drops of a solution of mercuric 



nitrate a white pp (the basis of Liebig's volumetric 

 method). 



2. Add a solution of sodium hypobromite effervescence 



occurs. 



Quantitative Estimation of Urea. 



Knop-Hufner } s process (or some modification as that now 

 given). Depends upon the decomposition of urea by a hypo- 

 bromite or hypo-chlorite. Reaction : 



-. 



remain in the solution. 



Theoretically l g urea yields 046666 g nitrogen. The volume 

 of this at O C. and 760 mm Hg = 372-7 cc . Practically 

 354 cc are obtained at the ordinary temperature (18C.) and 

 pressure. If in a preliminary trial more than 2 pc - is found 

 to be present, the urine should be diluted. 



Process. Do this first with a 2 p - c - solution of urea in 

 water, then with urine. 



1. Preparation of sodium hypobromite solution (Knop). Dis- 

 solve 100 g NaOH in 250 cc distilled water; when cool, 

 add 25 cc of bromide (in the open air or a draught 

 closet). 



