4Q8 



PHYSIOLOGICAL CHEMISTRY 



finally invert the tube and fix the stoppered end in the saucer-shaped vessel. By 

 means of the graduated pipette rapidly introduce i c.c. of urine 1 into the hypo- 

 bromite solution through the side opening of the bulbed-tube. Withdraw the 

 pipette immediately after the urine has been introduced. When the decomposition 

 of the urea is completed (10-20 minutes), gently tap the bulbed-tube with the finger 

 in order to dislodge any gas bubbles which may have collected on the inner surface 

 of the glass. The atmospheric pressure should 

 now be equalized by attaching the funnel-tube 

 to the bulbed-tube at the side opening and 

 introducing hypobromite solution into it un- 

 til the columns of liquid in the two tubes are 

 uniform in height. The graduated scale of 

 the bulbed-tube should now be read in order 

 to determine the number of cubic centimeters 

 of nitrogen gas evolved. By means of the ap- 

 pended formula the weight of the urea present 

 in the urine under examination may be com- 

 puted. 



FIG. 161. MARSHALL UREA APPARATUS. 



(Tyson.) 



a, Bulbed measuring tube; b, saucer- 

 shaped vessel; c, graduated pipette; d, 

 funnel-tube. 



FIG. 162. HUFNER UREA APPARATUS. 



Calculation.* By properly substituting in the following formula, the weight of 

 urea, in grams, contained in the volume of urine decomposed (i c.c. or more) may 

 readily be determined: 



1 Ordinarily i c.c. of urine is sufficient; more may be used, however, if its content of urea 

 is very low. 



2 0.003665 = coefficient of expansion of gases for iC. 354.5 = number of c.c. of nitrogen 

 gas evolved from i gram of urea. 



