URINE 499 



w = 



354.5X760(1+0.0036650 

 w = weight of urea, in grams. 



v = observed volume of nitrogen expressed in cubic centimeters. 

 p = barometric pressure expressed in millimeters of mercury. 

 T = tension of aqueous vapor 1 for temperature t. 

 t = temperature (Centigrade). 



If we wish to calculate the percentage of urea we may do so by means of the 

 following proportion in which y represents the volume of urine used and w denotes 

 the weight of the urea contained in the volume y: 



y : w :: x : (percentage of urea). 



Sodium hypobromite solution may also be employed for the determination of 

 urea in the apparatus devised by Htifner, which is pictured in Fig. 162. 

 Interpretation. See page 493. 



Ammonia 



i. Folin's Method. Principle. The ammonia of the urine is set 

 free by the addition of an alkali and this ammonia is then carried over 



FIG. 163. FOLIN AMMONIA APPARATUS. 



by an air current into a flask containing a measured amount of standard 

 acid. The excess acid is then titrated. The necessity for distillation 

 is avoided. 



1 The values of T for the temperatures ordinarily met with are given in the following 

 table: 



Temp. Tension in mm. Temp. Tension in mm. 



i5C 12.677 2iC 18.505 



i6C I3-5I9 22 c 19-675 



i7C 14.009 23C 20.909 



i8C I5.35I 24C 22.211 



i9C 16.345 25C 23.582 



20C 17.396 



