354 ANALYSIS OF URINE. [CH. XIII. 



Method of analysis. To i gram, of the charcoal in a dry 50 cc. 

 flask add 20 cc. of the urine. Shake vigorously and repeat the 

 shaking at intervals for 10 minutes. Filter through a small dry 

 paper into a dry tube. Measure 10 cc. of the nitrate by means of a 

 pipette and transfer it to a small beaker. Add 5 or 6 drops of the 

 chromate and titrate with the standard silver nitrate from a burette 

 until the end point is reached, as indicated by the appearance of a 

 reddish-brown colour. 



Calculation. I cc. of silver = o-oi gram. NaCl. 



Example. 10 cc. of the filtered urine required 10-6 cc. of silver. 

 So 10 cc. contain 10-6 x o-oi gram. NaCl. 

 So 100 cc. contain 1-06 gram. NaCl, 



J. Phosphates. 

 414. The estimation of phosphates. 



Principle. Urine is heated to boiling point, and titrated whilst hot with a 

 standard solution of uranium acetate, which gives a precipitate of (UO 2 )HPO 4 

 with phosphates in acetic acid solution. Cochineal tincture is used to indicate 

 by a change in colour when the uranium is in excess. 



Reagents required. 



1. Acetate solution. Dissolve 100 grams, of sodium acetate in a litre of 

 distilled water, and add 100 cc. of strong acetic acid. 



2. Cochineal tincture, prepared by extracting the insects with 30 per 

 cent, alcohol and filtering after two days. 



3. Standard potassium phosphate. Dissolve 7-672 grams, of pure re- 

 crystallised acid potassium phosphate in distilled water and make the volume 

 up to i litre. 25 cc. = o-i gram. P 2 O 6 . This solution can also be prepared by 

 measuring 28-17 cc. of the 0-2 M.KH 2 PO 4 described on page 24 into a TOO cc. 

 measuring flask and making the volume up to 100 cc. with distilled water. 



4. Standard uranium acetate. Dissolve by the aid of heat 36 grams, of 

 pure uranium acetate in a litre of distilled water. Allow the solution to cool 

 and then filter. Standardise the solution as follows : Into a beaker measure 

 25 cc. of the standard potassium phosphate, add about 25 cc. of distilled 

 water, 5 cc. of the acetate solution and about i cc. of the cochineal tincture. 

 Bring the mixture to the boiling point and titrate with the uranium acetate 

 solution from a burette till the red tinge just changes to a green, heating the 

 mixture to boiling just before the last few drops are added. If x cc. of the 

 uranium solution are used, then i cc. of the uranium corresponds to 



o-i 



gram. P 2 O 6 . 



If desired the solution can be diluted with water so that i cc. = 0-005 gram. 

 P a O 6 . To effect this add - cc. of distilled water to every 100 cc. 



