URINE 345 



Measure 50 c.c. of urine into a flask, add 3 c.c. pure HC1 and 

 boil gently for 15 minutes to decompose the ethereal sul- 

 phates. From a burette run in standard barium chloride solu- 

 tion (1 c.c. = 0.01 gm. S0 3 ) as long as a precipitate forms, 

 the mixture being kept hot. After running in the first 3-4 

 c.c. of barium chloride, allow the precipitate to settle and 

 with a glass rod remove a drop of the liquid. Place it on a 

 watch glass over a black surface and add a few drops of the 

 BaCl 2 solution. If there is a precipitate, return the whole 

 to the flask, rinsing in the last traces with water, and add 

 more BaCl 2 . Again allow to settle and test as before. Pro- 

 ceed until no more BaS0 4 is precipitated. Excess of BaCl 2 

 must be avoided. When the minimal excess has been added, 

 a drop of the clear fluid removed from the flask will give only 

 a cloudiness with a drop of dilute H 2 S0 4 . If more than a 

 cloudiness appears, excess has been added and the whole 

 operation must be repeated. Calculate the amount of S0 3 

 present in 50 c.c. urine and in the 24 hour sample. 



44. Phosphates. 



When a solution of disodium phosphate acidified with acetic 

 acid is treated with a solution of uranium acetate, a white 

 precipitate of uranium phosphate is formed. To determine 

 the end point, a drop of the liquid is brought in contact with 

 a drop of potassium ferrocyanide on a white tile. Any excess 

 of uranium causes a brown color to appear. 



To 50 c.c. of urine in a small beaker, add 5 c.c. of a special 

 sodium acetate mixture (100 g. sodium acetate dissolved in 

 800 c.c. water plus 100 c.c. 30% acetic acid and the volume 

 made up to 1 liter). This changes any acid phosphate into 

 diacid sodium phosphate. Heat to boiling and from a burette 

 run in drop by drop a standard uranium acetate mixture 

 (1 c.c. is equivalent to 0.005 g. of P 2 5 ). Keep the mixture at 

 the boiling point. From time to time remove a drop with a 

 glass rod or dropper and bring it in contact with a drop of 

 potassium ferrocyanide on a white tile. If a glass rod is 

 used it should be rinsed before replacing it in the beaker. It 



