80 METHODS FOR THE ANALYSIS OF URINE 



Determination of Calcium in Ash of Foods or Feces l 



Ignite the material in a crucible to a white ash and dissolve 

 the ash with the aid of a little hydrochloric acid. Bring the volume 

 of the ash solution to 75 to 150 c.c. Make just alkaline with strong 

 ammonia added drop by drop (using litmus paper or alizarin as 

 an indicator). Add concentrated HC1 drop by drop until just 

 acid to litmus. Then add 10 drops of concentrated HC1 (sp.gr. 

 1.20), and 10 c.c. of 2.5 per cent oxalic acid. Either of two pro- 

 cedures may then be followed, (a) The solution is boiled until the 

 precipitated calcium oxalate is coarsely crystalline, and then an 

 excess of 3 per cent ammonium oxalate is slowly added to the 

 boiling solution and the boiling continued until the precipitate is 

 coarsely crystalline. (If but little calcium is present, nothing will 

 precipitate at this point and it is not necessary to add oxalate.) Or 

 (6) the flask closed with a rubber stopper is shaken vigorously for 

 ten minutes. An excess of 3 per cent ammonium oxalate is then 

 added. Cool to room temperature. Add 8 c.c. of 20 per cent 

 sodium acetate solution. (In case of ash of feces add 15 c.c.) The 

 solution may either be (a) allowed to stand over night or (6) 

 stoppered and vigorously shaken for ten minutes. The calcium 

 oxalate is filtered off on a small ash free paper and washed free 

 from chlorides with 0.5 per cent ammonium oxalate solution. 

 Either of two procedures may next be followed, (a) The pre- 

 cipitate and filter are dried, burned in a platinum or porcelain 

 crucible to constant weight as CaO. (6) The precipitate is washed 

 three times with cold distilled water, as given under the method 

 for urine, and the oxalate titrated with potassium permanganate. 



Magnesium is determined in the nitrate from calcium just as 

 given above. 



IRON 



Method of Wolter 2 



Principle. The urine is ashed, the ash dissolved, and the iron 

 present oxidized to the ferric iron form by means of hydrogen 

 peroxide. The iron is then determined iodometrically. 



Procedure. The twenty-four-hour specimen of urine is treated 

 with 30 c.c. of concentrated iron-free nitric acid and then evapo- 



1 McCrudden: Jour. Biol. Chem., 1910, 7, 83; 1911, 10, 187. 

 * Wolter: Biochem. Zeit., 1910, 24, 103. 



