22 METHODS FOR THE ANALYSIS OF URINE 



twenty-four hour urine specimen may be calculated by means of 

 the following proportion: 



25 : y'-'.y' : x (acidity of twenty-four hour urine expressed in cubic 

 centimeters of N/10 sodium hydroxide). 



Each cubic centimeter of N/10 sodium hydroxide contains 

 0.004 gm. of sodium hydroxide, and this is equivalent to 0.0063 

 gram of oxalic acid. Therefore, in order to express the total 

 acidity of the twenty-four hour urine specimen in equivalent grams 

 of sodium hydroxide, multiply 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 in grams of oxalic acid. 



THE TITRATION OF ORGANIC ACIDS IN URINE 



Method of Van Slyke and Palmer l 



Principle. Interfering substances (carbonates and phos- 

 phates) are removed from the urine and the remaining weak acids 

 titrated. Creatinine is included and a correction for its presence 

 must be made. 



Procedure. 100 c.c. of urine, roughly measured, are thor- 

 oughly mixed with 2 gms. of finely powdered calcium hydroxide, 

 allowed to stand about fifteen minutes with occasional stirring, and 

 then passed through a dry folded filter. This treatment removes 

 carbonates and phosphates. To 25 c.c. of the filtrate in a 125 

 to 150 c.c. test-tube of clear glass (Pyrex, 30mm. X 200 mm.) one 

 adds 0.5 c.c. of 1 per cent phenolphthalein solution, and 0.2 N 

 hydrochloric acid from a burette (amount need not be measured) 

 until the pink color just disappears (pH = approximately 8). 

 5 c.c. of 0.02 per cent tropaeolin 00 solution are then added. As 

 the indicator solution is added it is thoroughly mixed with the 

 urine by shaking the tube; if this precaution is omitted some of 

 the tropaeolin 00 may be precipitated. Finally 0.2 N hydrochloric 

 acid is added from the burette until the red color equals that of a 

 standard solution containing 0.6 c.c. of 0.2 N HC1, 5 c.c. of tro- 

 paeolin 00 solution, and water to a total volume of 60 c.c. When 



1 Van Slyke and Palmer: Jour. Biol. Chem., 1920, 41, 567. 



