URINE 499 



Standard acid and alkali solutions are best kept in paraffin-lined bottles. 

 The acid solution is the more permanent of the two. Alkali solutions must be 

 protected from the carbonic acid of the air, the solution being best drawn over 

 into the burette by means of a siphon tube leading from the top of the burette 

 to the interior of the alkali bottle. The air inlet through the stopper of the bottle 

 should be guarded by a tube containing soda lime. 



Acidity by Titration 



Folin's Method. Principle. The urine is titrated with standard 

 sodium hydroxide solution, using phenolphthalein as an indicator. 

 Potassium oxalate is added to precipitate the calcium which would 

 otherwise interfere with the end-point due to the precipitation of calcium 

 phosphate on neutralization of the urine. The acidity of the urine as 

 determined in this way is not a correct measure of the true acidity, which 

 is dependent upon the concentration of hydrogen ions. . The results 

 obtained do, however, ordinarily show a certain parallelism with the 

 hydrogen ion concentration and are of value for comparative purposes. 



Procedure. Place 25 c.c. of urine in a 200 c.c. Erlenmeyer flask and add 

 15-20 grams of finely pulverized potassium oxalate and 1-2 drops of a i per cent 

 phenolphthalein solution to the fluid. Shake the mixture vigorously for 1-2 

 minutes and titrate it immediately with N/io sodium hydroxide until a faint but 

 unmistakable pink remains permanent on further shaking. Take the burette 

 reading and calculate the acidity of the urine under examination. 



Calculation. If y represents the number of cubic centimeters of N/io sodium 

 hydroxide used and y' represents the volume of urine excreted in 24 hours, the 

 total acidity of the 24-hour urine specimen may be calculated by means of the 

 following proportion : 



25 : y : : y' : x (acidity of 24-hour urine expressed hi cubic centimeters of N/io 



sodium hydroxide). 



Each cubic centimeter of N/io sodium hydroxide contains 0.004 'gram of 

 sodium hydroxide, and this is equivalent to 0.0063 gram of oxalic acid. There- 

 fore, in order to express the total acidity of the 24-hour urine specimen in equiva- 

 lent jams__oijsKidiiim__h^ the value of x, as just determined, 

 by 0.004^ or multiply the value of x by 0.0063 if it is desired to express the total 

 acidity hi grams of oxalic acid._ 



Interpretation. (Under the heading "Interpretation" there will 

 be found, in connection with the various quantitative methods which 

 follow, brief notes as to the possible significance of the results ob- 

 tained. Fur some further points (and reference to literature) see the 

 chapters on the Normal and Pathological Constituents of Urine and 



to 27o-28o, but not above 300 C. Heat for half an hour, allow to cool in a dessicator, 

 but while still a little warm, transfer to a glass stoppered weighing bottle. Weigh out 

 rapidly o.i to 0.2 gm. portions of the sodium carbonate, dissolve in about 50 c.c. of water 

 in an Erlenmeyer flask, and titrate using methyl orange as an indicator. One hundred 

 c.c. of N/io acid are equivalent to 0.530 gm. of dried sodium carbonate. 



