VOLUMETRIC ANALYSIS FOR UREA. 97 



beakers, filter paper, glass rod, plate of glass, and three pipettes, 

 10, 15, and 20 cc. 



6. Estimation of Urea by the Hypobromite Method. 



The principle of this method rests on the fact that urea is 

 decomposed by alkaline solution of sodic hypobromite. The 

 urea yields CO 2 (which is absorbed by the caustic soda), and N, 

 which is disengaged in bubbles and collected in a suitable 

 apparatus. 



Sodic Carbon Sodic 



Urea. flypobromite. Dioxide. Nitrogen. Water. Bromide. 



CON 2 H 4 + SNaBrO = CO 2 + N 2 + 2H 2 O + SNaBr 



Every 0*1 gramme of urea yields at the ordinary temperature 

 and pressure 3 7 '3 cc. of nitrogen ; the calculation, therefore, is 

 simple. Many different forms of apparatus have been devised, 

 including those of Knop and Hiifner, E/ussel and West, Graham 

 Steele, Simpson, Dupr4, Charteris, &c. 



(a.) Study these forms of apparatus, but make the experi- 

 ment with the apparatus of Dupre or Steele. 



7. Dupre's Apparatus. In this apparatus the graduation on 

 the collecting tube represents the percentage of urea, and not cc. 

 of N. The collecting tube, which is clamped above, is placed in 

 a tall vessel containing 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. 



(6.) With a pipette measure off 5 cc. of the clear filtered 

 urine, and place it in the short test-tube. With a pair of 

 forceps carefully introduce the tube with the urine into the 

 flask, and place the caoutchouc stopper in the latter. 



(c.) Test to see if all the connections 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 

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

 pass in, and on lowering the collecting tube the water will 

 stand at zero inside and outside the tube. 



