88 CHEMICAL PHYSIOLOGY. 



11. Volumetric Process for Phosphoric acid, with Ferrocyanide of 

 Potassium as the Indicator. 



1 cc. of the SS. (Uranium acetate) = -005 gramme of phos- 

 phoric acid. 



(a.) Collect and carefully measure the urine passed during 

 24 hours. 



(b.) Place 50 cc. of the mixed and filtered urine in a 

 beaker. Do this with a pipette. Place the beaker under a 

 burette. 



(c.) To the urine add 5 cc. of the solution of sodium 

 acetate ; mix thoroughly. 



(d.) Fill a Mohr's burette with the SS. of uranium acetate 

 up to zero, or to any mark on the burette. See that the 

 Mohr's clip is tight, and that the outflow tube is filled with 

 the SS. Note the height of the fluid in the burette. Heat 

 the urine solution in the beaker to about 8u C. Drop 

 in the SS. (" Standard Solution ") of uranium acetate 

 from the burette. Mix thoroughly. Test a drop of the 

 mixture from time to time, until a drop gives a faint brown 

 colour when mixed with a drop of potassium ferrocyanide. 

 Do this on a white plate. 



(e.) Boil the mixture, and test again. If necessary, add a 

 few more drops of the SS., until the brown colour reappears 

 on testing with the indicator. [Paper may be dipped in 

 the indicator solution and tested with a drop of the mixture.] 

 Read off the number of cc. used. 



Example. Suppose 17 cc. of the SS. are required to precipitate 

 the phosphates in 50 cc. of urine; as 1 cc. of SS. = -005 gramme of 

 phosphoric acid, then -005 x 17 = -085 gramme of phosphoric acid 

 in 50 cc. of urine. Suppose the patient passed 1250 cc. of urine 



in 24 hours, then 50 : 1250 : : -085 : x 125 * ' 85 = 2-12 



50 

 grammes of phosphoric acid in 24 hours. 



12. Solutions Required. 



Sodium Acetate Solution. Dissolve 100 grammes of sodium 



