250 



PEACTICAL PHYSIOLOGY 



For quantitatively estimating urea two methods may be employed : 

 I. Precipitate from the urine all nitrogen-containing bodies except urea, 

 filter, then determine the amount of nitrogen in the filtrate, and from 

 this calculate the urea (see Advanced Course). II. By decomposing 

 urea with Sodium Hypobromite in the presence of free caustic alkali. 



FIG. 153. Dupr^'s urea apparatus. FJG. 154. Gerrard's urea apparatus. 



The alkali absorbs the liberated carbonic acid and the nitrogen is 

 collected in a graduated tube. From the amount of nitrogen evolved 

 the urea can be calculated by remembering that (H gramme urea con- 

 tained in urine, liberates 37'1 c.c. nitrogen. 1 There are various forms 

 of apparatus used for collecting the liberated nitrogen. The most 



1 0'1 gr. of pure urea really liberates, 37*27 c.c. of N. In urine only about 

 92 per cent, of the urea nitrogen is liberated by the hypobromide. This deficit 

 is, however, partly compensated for by a certain amount of nitrogen being simul- 

 taneously split off from the other nitrogenous bodies present. 



