XIX.] 



VOLUMETRIC ANALYSIS FOR UREA. 



121 



3. Apparatus and Solutions required. 



( i. ) A 40 per cent, solution of caustic soda. 



( ii.) Tubes containing 2 and 4 cc. of bromine. This is far more con- 

 venient than the fluid bromine, 

 (iii. ) A strong glass cylinder with a glass stopper, 

 (iv.) A 5 cc. pipette. 

 ( v. ) Urea apparatus, e.g., of Dupre, or Gerrard. 



4. Make, the hynobromite solution : Place 23 cc. of the caustic soda solution 

 in the glass-stoppered cylinder, drop into it 



gently a tube containing 2 cc. of bromine. 

 Shake the cylinder so as to break the 

 bromine tube ; the soda combines with the 

 bromine. These bromine tubes can be 

 purchased. The solution spoils by keeping, 

 so that it should be made fresh for each 

 estimation. 



5. Dupre's Apparatus. 1 In this 

 apparatus (fig. 62) the graduation on 

 the collecting tube represents either 

 the percentage of urea or cc. of N". 

 The collecting tube, which is clamped 

 above, is placed in a tall vessel con- 

 taining water, and connected with a 

 small glass flask containing a short 

 test-tube. 



(a.) Remove the short test-tube 

 from the flask, and in the latter 

 place 25 cc. of the hypobromite 

 solution. 



(b.) With a pipette measure off 5 

 cc. of the clear filtered urine, and 

 place it in the short test-tube attached 

 to the india-rubber stopper, and seen 

 on the left side of fig. 62. This 

 is preferable to the pipette shown 

 in the fig. Place the caoutchouc 

 stopper in the flask. 



(>:.) Test to see if all the connec- 

 tions are tight. Open the clamp at 

 the upper end of the collecting tube, 

 depress the tube in the water until 

 the water inside and outside the tube 

 is at zero of the graduation. Close the clamp, and raise th 

 collecting tube. If the apparatus be tight, no air will pass in 



FIG. 62. Dupre"'s Urea Apparatus. 



1 Made by George J. Smith, 73 Farringdon Street. 



