URINE: QUANTITATIVE ANALYSIS. 405 



Shake the mixture vigorously for 1-2 minutes and titrate it im- 

 mediately with T ^j- 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 

 YQ- sodium hydroxide used and y' represents the volume of urine 

 excreted in twenty- four hours, the total acidity of the twenty- four 

 hour urine specimen may be calculated by means of the following 

 proportion : 



25 : y : : y' : x (acidity of 24-hour urine expressed in cubic centimeters 

 of 1% sodium hydroxide). 



Each cubic centimeter of T \ sodium hydroxide contains 0.004 

 gram 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 ^ it is desired to express the 

 total acidity in grams of oxalic acid. 



XIX. Purine Bases. 



i. Kriiger and Schmidt's Method. This method serves for the 

 determination of both uric acid and the purine bases. The principle 

 involved is the precipitation of both the uric acid and the purine 

 bases in combination with copper oxide and the subsequent decom- 

 position of this precipitate by means of sodium sulphide. The uric 

 acid is then precipitated by means of hydrochloric acid and the 

 purine bases are separated from the filtrate in the form of their 

 copper or silver compounds. The nitrogen content of the precipi- 

 tates of uric acid and purine bases is then determined by means of 

 the Kjeldahl method (see p. 381) and the corresponding values for 

 uric acid and purine bases calculated. The method is as follows: 

 To 400 c.c. of albumin-free urine 1 in a liter flask, 2 add 24 grams 

 of sodium acetate, 40 c.c. of a solution of sodium bisulphite 3 and 

 heat the mixture to boiling. Add 40-80 c.c. 4 of a 10 per cent solu- 



1 If albumin is present, the urine should be heated to boiling, acidified with 

 acetic acid and filtered. 



2 The total volume of urine for the twenty-four hours should be sufficiently 

 diluted with water to make the total volume of the solution 1600-2000 c.c. 



3 A solution containing 50 grams of Kahlbaum's commercial sodium bisulbhite 

 in 100 c.c. of water. 



4 The exact amount depending upon the content of the purine bases. 



