288 PRACTICAL PHYSIOLOGY 



The acid in B and C is titrated, after a few drops of a 1 per cent, 

 solution of alizarin red have been added as the indicator. Instead of 

 adding the alcohol all at once a side tube with stop-cock may be con- 

 nected with flask A so that alcohol can be added as required to keep 

 excessive frothing in check. 



Estimation of Amino Acids. Sorensen's Method. Measure 50 c.c. 

 urine into a 100 c.c. measuring flask, then add 1 c.c. phenolphthalein 

 solution (0-5 per cent.) and 2 gms. solid BaCl 2 . After shaking, add 

 a saturated solution of baryta until a definite red colour is produced 

 and then 5 c.c. in addition. Fill up to the mark with water, shake 

 well and allow to stand at least fifteen minutes before filtering 

 through a dry filter. 



80 c.c. ( = 40 c.c. urine) of the clear red filtrate are placed in another 



N 

 100 c.c. measuring flask and ^- HC1 added until the solution is definitely 



acid to litmus then filled up to the mark with water. Of this solution 

 two lots, A and B, of 40 c.c. are taken, A for estimation of the ammonia 

 either by Folin's method or preferably by the vacuum distillation 

 method, and B for the estimation of ammonia plus ami no acids. This 



N 

 estimation is carried out as follows: Add -g NaOH until the fluid is 



neutral, using phenolphthalein as indicator ; then add 20 c.c. neutral 



commercial formalin and titrate again with -= NaOH until a faint but 



o 



definite rose colour is developed. Then add 2 drops more of the alkali. 

 End point deep red. 



N 

 Calculation. c.c. -= NaOH required after the addition of the formalin 



X 2-8 = mgm. ammonia + amino acid nitrogen in 16 c.c. urine. Multiply 

 by 6-25 to convert to per cent. 



Then B result A result = amino acid nitrogen. 



Estimation of Chlorides. Volhard's Method. Pipette 10 c.c. albumin- 

 free urine into a 100 c.c. graduated flask, add 5 c.c. nitric acid and 



N 

 20-30 c.c. JTJ silver nitrate solution (17 gms. per litre) measured 



accurately with a pipette. The silver solution must be in excess. 

 Add distilled water to the 100 c.c. mark and mix thoroughly. Allow 

 to stand for a few minutes, then filter through a dry chloride-free 

 filter paper into a dry clean beaker and of the filtrate take 50 c.c. 

 into a flask, add 10-20 c.c. 10 per cent, iron alum solution and titrate 



N 

 with -J-Q potassium sulphocyanide (9-73 gms. per litre) until a permanent 



red colour results. 



1 c.c. N ^ AgNO 3 solution - 0-00585 gm. NaCl. 



In this method it is the amount of silver nitrate left uncombined 

 which is determined, and this amount subtracted from the amount 

 of silver nitrate originally added gives the amount of chloride present. 



Inorganic Phosphates. 10 c.c. urine are diluted to 40 c.c. with water, 

 an excess (10 c.c.) of magnesium citrate mixture added and the whole 

 made distinctly alkaline with ammonia. Stir well and allow to stand 

 overnight. Filter off the precipitate of ammonium magnesium phos- 



