1130 PHYSIOLOGY 



weighed as pyrophosphate. From the weight of this the amount of P 2 5 in 50 c.c. can 

 be calculated and the remainder of the solution can be diluted, so that 50 c.c. contain 

 O'l grm. P 2 O 5 . It is simpler to use acid potassium phosphate, KH 2 PO 4 , which can be 

 weighed directly and dissolved in water, so that 50 c.c. contain 0-1 grm. P 2 O 5 . Fifty 

 cubic centimetres of this solution are titrated with the uranium solution (36 grm. in 

 one litre) in the manner described below, and the uranium solution is then diluted so 

 that 1 c.c. = 5 mg. P 2 5 . 



The method of analysis is carried out as follows : Place 50 c.c. urine with a pipette 

 in a 100 c.c. beaker, add 5 c.c. acid sodium acetate solution and a few drops of cochi- 

 neal tincture. Heat the urine to boiling and run in slowly the standard uranium 

 acetate solution from a burette as long as a precipitate is formed. Again heat to 

 boiling and add the uranium solution drop by drop, until the red colour is changed to 

 green. This end-point can also be tested by taking out a drop and placing it in contact 

 with a drop of potassium ferro-cyanide solution or a little heap of finely powdered sub- 

 stance on a white piece of porcelain. A brown colour or precipitate is formed when 

 excess of soluble uranium salt is present in the solution. (A few more drops may be 

 required to reach this point than to turn the cochineal green.) 



The principle of the estimation of sulphates has already been described. It is not 

 advisable to attempt this volumetrically. 



