560 PHYSIOLOGICAL CHEMISTRY 



Lyman has suggested a nephelometric method for the determination 

 of calcium in urine and feces. 1 



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. i. 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 concentrated 

 hydrochloric acid are added. Then add 10 c.c. of 2.5 per cent oxalic acid. Run 

 in slowly with stirring 8 c.c. of 20 per cent sodium acetate. Allow to stand over 

 night at room temperature or shake vigorously for ten minutes. Filter off the 

 precipitate of calcium oxalate on a small paper and wash free from chlorides 

 with 0.5 per cent ammonium oxalate solution. The precipitate may then be 

 dried, ignited to constant weight and weighed as calcium oxide or it may be 

 manipulated volumetrically as described below. 



Volumetric Procedure. If free from uric acid the calcium oxalate precipitate 

 may be washed three times with distilled water, filling the filter about two- 

 thirds full and allowing it to drain completely before adding more. A hole is 

 made in the paper and the calcium oxalate washed into the flask. The volume 

 of the fluid is brought up to about 50 c.c. and 10 c.c. of concentrated sulphuric 

 acid added. Titrate with standard potassium permanganate solution to a pink 

 color which endures for at least a minute. 



Calculation. One c.c. of N/io permanganate solution is equivalent to 2.8 

 mg. of CaO. Calculate the daily output of calcium expressed as CaO. 



Interpretation. The average urinary excretion of calcium by normal 

 adults lies between o.i to 0.4 gram (expressed as CaO) per day. It is 

 dependent very largely upon the amount of calcium in the diet. From 

 10 to 40 per cent of the ingested calcium ordinarily is excreted by this 

 channel, the greater part being eliminated by the feces. The pro- 

 portion is dependent particularly on the amount of calcium in the food. 

 If the calcium ingestion is very high the per cent of the total excretion 

 taking place by way of the kidneys will be low, and vice versa. As ex- 

 cretion takes place by way of the intestine as well as by the kidneys no 

 conclusions can be drawn from urinary analyses alone. The excretion 

 of calcium may be greatly increased in certain bone disorders as osteo- 

 malacia. In others as in rickets the urinary excretion may be very 

 low. 



Procedure for Magnesium. Transfer the filtrate from the determination 

 of calcium as above to a porcelain dish, add about 20 c.c. of concentrated nitric 

 acid and evaporate to dryness. Heat the residue over a free flame until the 

 ammonium salts are destroyed and the residue fuses. After cooling take the 

 residue up with water and a little hydrochloric acid and filter if necessary. 

 Dilute to about 80 c.c., nearly neutralize with ammonia and cool. Add a slight 

 excess of sodium acid phosphate and then ammonia drop by drop with constant 

 stirring until the solution is alkaline and then add enough more slowly with 



1 Lyman: Jour. Biol. Chem., 21, 551, 1915. 



