78 METHODS FOR THE ANALYSIS OF URINE 



cubic centimeters of silver nitrate solution used multiplied by 0.01 

 gin. will give the weight of sodium chloride in the 5 c.c. portion of 

 urine used. The weight of chlorine may be computed by using 

 the factor 0.006 instead of 0.01. 



Calculate the weight of sodium chloride and chlorine in the 

 twenty-four-hour urine specimen. 



A "short cut" method of calculating the twenty-four-hour 

 output of sodium chloride consists in subtracting the burette 

 reading from 20 c.c., multiplying this value by the total urine 

 volume and pointing off three places. 



CALCIUM AND MAGNESIUM 



Me Crudden's Methods 1 



Principle. Urine contains magnesium, phosphates, and a 

 small amount of iron, each of which will interfere with the accurate 

 determination of its calcium content if proper conditions of acidity 

 are not maintained during the precipitation. In the following 

 method the proper acidity is attained through the use of sodium 

 acetate and hydrochloric acid, and this with slow addition of the 

 ammonium oxalate reduces the danger of occlusion of magnesium 

 oxalate, calcium phosphate, or ferric phosphate in the calcium 

 oxalate precipitate. 



The calcium oxalate precipitate is either ignited and weighed 

 as CaO or determined volumetrically by titration with potassium 

 permanganate. Magnesium is determined in the filtrate from the 

 calcium determination after destruction of the organic matter. 

 It is determined in the usual way by ignition of the magnesium 

 ammonium phosphate precipitate and weighing as the pyrophos- 

 phate. 



Lyman has suggested a nephelometric method for the determi- 

 nation of calcium in urine and feces. 



Procedure for Calcium. If the urine is alkaline, make it neutral 

 or slightly acid and filter. Take 200 c.c. of the filtered urine for 

 analysis. If it is only faintly acid to litmus paper, add 10 drops of 

 concentrated hydrochloric acid (sp.gr. 1.20). If the urine is 

 strongly acid, it may be made just alkaline with ammonia and 

 then just acid with hydrochloric acid after which the 10 drops of 



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



