LESSON XXIV 

 ESTIMATION OF PHOSPHATES AND SULPHATES IN URINE 



ESTIMATION OF PHOSPHATES 



The phosphoric acid in the urine is combined with soda, potash, lime, and 

 magnesia. 



(<i) Estimation of t lie total phosphates. 



For this purpose the following reagents are necessary : 



i. A standard solution of uranium nitrate. The uranium nitrate solution 

 contains 35*5 grammes in a litre of water ; 1 c.c. corresponds to 0*005 gramme 

 of phosphoric acid (Po0 5 ). 



ii. Acid solution of sodium acetate. Dissolve 100 grammes of sodium 

 acetate in 900 c.c. of water ; add to this 100 c.c. of glacial acetic acid. 



hi. Solution of potassium ferrocyanide. 



Method. Take 50 c.c. of urine. Add 5 c.c. of the acid solution of sodium 

 acetate. 1 Heat the mixture to 80 C. 



Eun into it while hot the standard uranium nitrate solution from a 

 burette until a drop of the mixture gives a distinct brown colour with a drop 

 of potassium ferrocyanide placed on a porcelain slab. Kead off the quantity 

 of solution used and calculate therefrom the percentage amount of phosphoric 

 acid in the urine. 



Another indicator which may be used is cochineal tincture, a few drops of 

 which may be added to the mixture. A change of colour from red to green 

 is the sign of the end of the reaction. 



(6) Estimation of the phosphoric acid combined with lime and maynexia 

 (alkaline earths). 



Take 200 c.c. of urine. Bender it alkaline with ammonia. Lay the mixture 

 aside for twelve hours. Collect the precipitated earthy phosphates on a filter ; 

 wash with dilute ammonia (1 in 3). Wash the precipitate off the filter with 

 water acidified by a few drops of acetic acid. Dissolve with the aid of heat, 

 adding a little more acetic acid if necessary. Add 5 c.c. of the acid solution 

 of sodium acetate. Bring the volume up to 50 c.c., and estimate the phos- 

 phates in this volumetrically by the standard uranium nitrate as before. 

 Subtract the phosphoric acid combined with the alkaline earths thus obtained 

 from the total quantity of phosphoric acid, and the difference is the amount 

 of acid combined with the alkalis, soda and potash. 



1 In using uranium nitrate it is imperative that sodium acetate should 

 accompany the titration in order to avoid the possible occurrence of free nitric acid 

 in the solution. If uranium acetate is used, it may ba omitted. 



