286 PHYSIOLOGICAL CHEMISTRY 



25 c.c. N/10 acid. To make the alkali exactly N/10 it should 

 be diluted in the ratio of 23.2 :25. 



Measure the total volume of your alkali in a large cylinder 

 (first returning any of the solution remaining in the burette) 

 and calculate the amount of water necessary to dilute it to 

 tenth normal alkali. Add this amount of water from a cylinder, 

 shake well and allow to stand for a few minutes. 



Rinse out the burette with the diluted alkali, and repeat the 

 titration against standard acid. 



If your alkali does not check with the standard acid, correct 

 it again by adding the calculated amount of water, or the cal- 

 culated amount of sodium hydrate if the solution has been 

 made too dilute. 



Preserve your tenth normal solution for future use. 



(b) DETERMINATION OF ACIDITY OF URINE. 



(1) Preliminary Experiments. 



i. Measure out 10 c.c. of potassium dihydrogen phosphate 

 into each of 3 small beakers or Erlenmeyer flasks, and label 1, 

 2 and 3. 



To No. 2 add 3-4 drops sat. CaCl 2 soln. 



To No. 3 add 3-4 drops sat. CaCl 2 sol. + about 10 c.c. 15% 

 neutralized potassium oxalate solution. Titrate all 3 solutions 

 with N/10 NaOH, using phenolphthalein as indicator. Observe 

 that the presence of calcium increases the titration figure. The 

 phosphates of the alkaline earths precipitate in alkaline solu- 

 tion. On adding oxalate, however, the disturbing influence of 

 calcium is nullified, since it is precipitated as calcium oxalate. 



(2) Acidity of Urine. Folin's Method. 



i. Measure 25 c.c. of urine into an Erlenmeyer flask. Add 

 1-2 drops phenolphthalein and 10 c.c. neut. potassium oxalate 

 solution. Shake vigorously for 1-2 minutes and titrate at once 

 with N/10 NaOH to the first faint but permanent pink. From 

 the value obtained calculate the total acidity of the 24 hour 

 specimen in cubic centimeters of normal acid. 



ii. Repeat the process described in i, omitting the addition 



