PHYSIOLOGICAL CHEMISTRY. 



v(p-T) 



354.5 X 760(1 +0.0036650 

 w = weight of urea, in grams. 



1} = observed volume of-nitrogen expressed in cubic centimeters. 

 p = barometric pressure expressed in mm. 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 vol- 

 ume of urine used and w denotes the weight of the urea contained 

 in the volume 3; : 



y:w:: 100 : x (percentage of urea) . 



Sodium hypobromite solution may also be employed for the de- 

 termination of urea in the apparatus devised by Hufner which is 

 pictured in Fig. 119, page 377. 



2. Knop-Hiifner Hypobromite Method (using the Doremus- 

 Hinds Ureometer). In common with the method already de- 

 scribed this method depends upon the measurement of the volume 

 of nitrogen gas liberated when the urea of the urine is decomposed 

 by means of sodium hypobromite solution. The Doremus-Hinds 

 'ureometer (Fig. 120, p. 378), is one of the simplest and cheapest 

 forms of apparatus in general use for the determination of urea by 

 the hypobromite process. In using this apparatus proceed as fol- 

 lows : Fill the side tube B and the lumen of the stopcock C with the 

 urine under examination. Carefully wash out tube A with water 

 and introduce into it sodium hypobromite solution 2 being careful to 

 fill the bulb sufficiently full to prevent the entrance of air into the 



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

 following table : 



Tension in Tension in 



Temp. Mm. Temp. Mm. 



15 C 12.677 21 C 18.505 



16 C I3-5I9 22 C 19-675 



17 C 14.009 23 C 20.909 



18 C 15.351 2 4 C 22.211 



19 C 16.345 25 C 23.582 



20 C 17.396 



2 For directions as to the preparation of this solution see page 375. 



