146 



ESSENTIALS OF CIIF.M ICAL I'll YSK'U x ;y 



water, and is converted into ammonium carbonate [CON 2 H 4 

 = (NH 4 ) 2 C0 3 ]. Hence the ammoniacal odour of putrid urine. 



By means of nitrous acid, urea is broken up into carbonic acid, 

 water, and nitrogen, CON 2 H 4 + 2HN0 2 ==C0 2 + 3H 2 + 2N 2 . This 

 may be used as a test for urea. Add fuming nitric acid (i.e. nitric acid 

 containing nitrous acid in solution) to a solution of urea, or to urine ; 

 an abundant evolution of gas bubbles takes place. 



Hypobromite of soda decomposes urea in the following way : 



CON 2 H 4 + SNaBrO = CO 



[urea] 



[sodium 

 hypobromite] 



[carbonic 

 acid] 



- N 2 



[nitro- 

 gen] 



2H 2 



[water] 



3NaBi 



[sodium 

 bromide] 



This reaction is important, for on it one of the readiest methods for 

 estimating urea depends. There have been various pieces of appa- 

 ratus invented for rendering the analysis easy ; but the one described 



0,0 



FIG. 44. a, nitrate ; 6, oxalate of urea. 



in the practical exercise at the head of this lesson is the best. If 

 the experiment is performed as directed, nitrogen is the only gas that 

 comes off, the carbonic acid being absorbed by excess of soda. The 

 amount of nitrogen is a measure of the amount of urea. 



The quantity of urea excreted is somewhat variable, the chief cause 

 of variation being the amount of protein food ingested. In a man 

 taking the usual Voit diet containing about 100 grammes of protein 

 (which will contain about 16 grammes of nitrogen) the quantity of 

 urea excreted daily averages 33 grammes (500 grains). The per- 

 centage in human urine would then be 2 per cent. ; but this also 

 varies, because the concentration of the urine varies considerably in 

 health. The excretion of urea is usually at a maximum three hours 

 after a meal, especially after a meal rich in protein. 



Muscular exercise has but little effect on the amount of nitrogen 



