110 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



are excreted. This amount is made up of alkaline and 

 earthy P 2 5 in decidedly varying proportions; of the alkaline 

 P 2 5 about 60 per cent consists of the dihydrogen (acid) 

 phosphate and the remaining 40 per cent as the monohydrogen 

 phosphate. 



TOTAL P 2 5 . 



The procedure is based upon the quantitative precipita- 

 tion of all the phosphates in the urine with uranium nitrate, 

 as uranium phosphate, using potassium ferrocyanide as 

 indicator. The phosphates must be present as acid salts. 



Quantitative Estimation. 

 Reagents necessary: 



1. A uranium nitrate solution 1 c.c. of which equals 0.005 

 grm. P 2 5 (35.461 grms. in a liter). How is this calculated? 



2. An accessory solution (100 grms. of sodium acetate and 

 300 grms. of acetic acid in a liter). 



3. A solution of potassium ferrocyanide. What is the 

 reaction which indicates the absolute precipitation of all 

 the P 2 5 ? 



Method: Place 25 c.c. of urine in a large evaporating-dish, 

 add 5 c.c. of the accessory solution (why?), and warm gently 

 over an asbestos board. Keeping the solution warm, add the 

 known uranium nitrate solution from a burette, from time to 

 time removing a drop of the urine on the end of a glass rod 

 and adding it to a drop of the potassium ferrocyanide which 

 has been placed upon a white porcelain dish. When all the 

 P 2 5 has been precipitated by the uranium and the first ex- 

 cess of the latter appears in the urine solution, the drop of 

 indicator on the plate when tested as above will take on a 

 faint reddish-brown color. The test should be repeated after 

 a minute; if it again causes a color, the titration is complete, 



