URINE 331 



the water bath. If the blue color disappears, the alkaline reac- 

 tion is due to ammonia. If it persists, to fixed alkalies. 



For purposes of diagnosis of kidney disorders, it is some- 

 times advisable to determine both the freezing point and the 

 electrical conductivity of the urine. The technique of these proc- 

 esses, is, however, beyond the scope of this course. 



Quantitative Analysis (Make All Determinations in Duplicate) 

 Total Solids. In order to make an accurate determination 

 of total solids, it is necessary to evaporate a measured quantity 

 of urine in a vacuum at room temperature, as the temperature of 

 the boiling water bath causes decomposition of urea and loss of 

 ammonia and C0 2 . By acidifying slightly with acetic acid it. is 

 possible partially to avoid this source of error. The residue is 

 weighed quantitatively, and the total solids calculated from the 

 result. 



DETERMINATION OF ACIDITY OF URINE. 



31. Preliminary Experiments. 



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. 



32. Acidity of Urine. Folin's Method. 



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. 



