280 



PRACTICAL PHYSIOLOGY 



originally taken gives the amount of ammonia (or nitrogen) distilled 

 over. 



EXAMPLE. If 50 c.c. ^ H 2 SO 4 be taken in the first instance 



N 

 and if at the final_titration 25 c.c. -^ NaOH are required, then 



N 

 50 c.c. - 25 c.c. = 25 c.c. ^ H 2 SO 4 neutralised by the NH 3 evolved. 



25 c.c. 



^ H 2 S0 4 = 25 c.c. ^ NH 3 = 25 c.c. ^ N 



and as 1 c.c. JQ N = 0-0014 gm. N 



then in 5 c.c. urine there is 25 x 0-0014 = 0-035 gm. N, and therefore 

 in 1,500 c.c. 10-5 gms. N. 



FIG, 195, 



Preparation of Urea from the Urine. Take about 50 c.c. urine in 

 a porcelain basin and evaporate to dryness on the water bath. As soon 

 as it is dry turn out the flame heating the bath, add about 10 c.c. acetone 

 and allow the extraction to continue on the warm water bath for several 

 minutes. Pour off the hot acetone extract, filtering through glass wool, 

 into a large dry clock glass or glass evaporating basin. Urea crystallises 

 out in long silky needles. It can be purified if desired by recrystallisa- 

 tion from alcohol. The yield obtained is about 1 grm. per 50 c.c. urine. 



Estimation o! Urea. Urease Method. Soy beans contain a specific 

 enzyme urease which rapidly and quantitatively decomposes urea at a 

 low temperature into carbonic acid and ammonia. 



Method of Estimation. The following modification of the ordinary 

 urease method, devised by Wishart, has been found to give reliable 

 results. 



