ADVANCED PHYSIOLOGICAL CHEMISTRY 



469 



The technique of the method is as follows : 25 c.c. urine are placed 

 in a large test-tube a (2J-3 cm. diam. and 20-30 cm. long) and are mixed 

 with 8-10 gr. sodium chloride and 5-10 c.cm. petroleum (to prevent 

 excessive frothing), arid lastly with 1 g. sodium carbonate. The test- 

 tube is closed by an indiarubber stopper through which pass two 

 tubes, the one for the air inlet passing to the bottom of the test- 

 tube, the other connecting the top of the test-tube with a wide tube 

 (U tube) b containing a loosely packed cotton-wool plug (to catch 

 any particles of fixed alkali which might be sucked over with the 

 air current). This safety tube is connected with a second test-tube G 

 (of the same size as the first) containing 5 c.c. n/W H 2 S0 4 + 5 c.c. H 2 0, 

 the tubing being so arranged that the air bubbles through the acid. 

 A third tube or bottle d arranged as the second and also containing 

 10 c.c. fi/20 acid follows this, otherwise all the ammonia would not 

 be caught by the acid. The tubing connected with this tube 'goes 

 to a Bunsen's air pump e attached to a tap /. A quick stream of 

 air (600-700 litres per hour) is made to pass through the apparatus 

 for li hours. The acid in the two last test-tubes is then washed 

 into an Erlenmeyer's flask and titrated with n/10 or n/'20 alkali. For 

 titrating Folin recommends 2 drops of a 1% solution of Alizarin red 

 (for 200-300 c.c. fluid), the titration being carried just till a pink 

 (not a violet) colour appears. This indicator is not so easily affected 

 by C0 2 , ammonia salts, etc., as others are. 



Jb Svuetian/Pojmp 



FIG. 275. Shaffer's method of estimating ammonia in urine. Bectdard's modification. 



Shaffer's vacuum distillation method of estimating ammonia in urine 

 is as accurate as Folin's and much more rapid. 



