ADVANCED CHEMICAL PHYSIOLOGY 



287 



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 drops of a 1 per cent, solution of alizarin red to the TQ acid to act as 



indicator in case more ammonia is liberated than the amount of acid 

 used can absorb. Air is then made to pass rapidly through the urine 

 either by means of a blower or a good suction pump for one and a half 

 to two hours. The absorbing acid can then be titrated as usual with 



NaOH. 1 c.c. ~ 



The vacuum distillation methods of estimating ammonia in urine 

 are more accurate than Folin's and much more rapid. 



Many methods have been used. The method here described is the 

 one introduced by Shaffer. Place 50 c.c. urine in a round-bottom 

 | litre flask A (Fig. 199), add 20 gms. sodium chloride to prevent 



NaOH. 1 c.c. ~ H 2 SO 4 = 0-0017 gm. NH 3 . 



FIG. 199. Shaffer's method of estimating ammonia in urine. 



decomposition and 50 c.c. methyl alcohol to reduce the boiling point of 



N 

 the mixture. In flask B place 50 c.c. or less JQ acid and in C 10 c.c. 



N 



jQ-acid, diluted in both cases with a little water. The flasks may be 



tilted obliquely, and should be large enough to prevent loss of acid by 

 spraying during the violent commotion which is set up by the rapid 

 passage of steam. If such loss should occur, the acid may be recovered 

 by rinsing out the flask D. When the apparatus is ready, 1 gm. of 

 dry sodium carbonate is added to the liquid in the flask A, the stopper is 

 rapidly inserted and the suction started. The pump will quickly 

 reduce the pressure to about 30 mm., and the liquid in A, which is 

 warmed up to about 40 C. in a water bath, will begin to boil. The 

 temperature of the bath must be maintained and should not be allowed 

 to rise above 50 C. for fear of decomposing urea. When the boiling has 

 continued for fifteen minutes, all the ammonia will have been given off 

 and the operation is stopped by slowly letting in air by the stop-cock a. 



