134 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



A 



Estimation. 



Urea is hydrolysed by water, acids, or alkalies into carbonic acid 

 and ammonia ; it is decomposed by nitrous acid or alkaline hypobrom- 

 ite into carbon dioxide and nitrogen. These reactions are made use 

 of in order to determine the amount of urea in a given solution. 



* (i) Hypobromite Method. 



The most simple and rapid method is the decomposition by alkaline 

 hypobromite ; the carbon dioxide is absorbed by the 

 alkali and the evolved nitrogen is collected and 

 measured. This method is the one suggested by 

 Hiifner and most frequently employed in medical 

 practice. The estimation is generally carried out in 

 the apparatus designed by Dupre and known as 

 Dupre's ureometer (Fig. 26). 



The estimation is earned out as follows : 

 25 c.c. of freshly-prepared hypobromite solution 1 

 are placed in the bottle of about 120 c.c. capacity. 

 5 c.c. of urea solution are measured out with a 

 pipette into a small tube which is placed in the 

 bottle, taking great care not to upset the solution 

 into the hypobromite. The bottle is closed with 

 an india-rubber stopper and placed in cold water 

 to cool. Through the india-rubber stopper a ^lass T-piece passes. 

 One end of this is connected by rubber tubing to a graduated burette 

 which is placed in a jar of water. The rubber tubing is of such a length 

 that the burette can be lifted out of the water without stretching. The 

 other end of the T-piece is closed by a piece of rubber tubing and a small 

 clip. The burette is filled with water by opening the screw clip ; and it 

 is raised or lowered until the water stands at the uppermost graduation 

 and at the same level outside and inside. The clip is closed and leak- 

 age in the system is tested for by raising and lowering the burette in 

 the water for at least a minute and then seeing whether the level of 

 the water returns to the top graduation when the water inside and 

 outside the tube are again made to stand at the same level. When 

 the system has been tested to see that it is air-tight the analysis can 

 be commenced. The reading of the top graduation is noted. The 

 bottle is tilted so as to upset the urea solution in the little tube into 

 the hypobromite solution and it is thoroughly washed out with the latter. 

 Nitrogen is rapidly evolved and displaces the water in the burette. 



1 ioo gm. caustic soda are dissolved in 250 c.c. water and to the cold liquid 25 c.c* 

 Bromine are added. 



FIG. 26. 



