PHYSIOLOGICAL CHEMISTKY 435 



solution (9-73 grm. per litre), until on stirring the liquid assumes 

 a permanent slight red colour. Take the reading on the burette. 

 Let this be a c.c. Then the amount of chloride ( - Cl.) in the 10 c.c. 

 urine employed is equal to (30 - a) 0-00355 grm. The sulphocyanide 

 solution must be exactly equivalent to, or standardised in terms of, 

 the silver nitrate solution. 



Phosphate. 



EXPERIMENT II. Boil some solution of ammonium molybdate in 

 nitric acid in a test tube, and add drop by drop boiling urine acidified 

 with nitric acid. A yellow precipitate indicates the presence of 

 phosphate. 



EXPERIMENT III. Make urine alkaline by the addition of ammonia. 

 A white precipitate of calcium and magnesium phosphate forms. 

 Filter off this precipitate and prove that it contains phosphate by 

 the molybdate test. 



Estimation of Phosphate. Standard uranium nitrate solution is 

 added to urine in the presence of sodium acetate and acetic acid 

 until all the phosphate is precipitated, as shown by the presence of 

 slight excess of uranium in the solution. Sodium acetate is added 

 so as to prevent the liberation of nitric acid, in which uranium 

 phosphate is soluble. The acetic acid serves to prevent the pre- 

 cipitation of other uranium compounds than the phosphate and to 

 dissolve any calcium phosphate present. 



Place 50 c.c. urine in a porcelain basin. Add 5 c.c. of a solution 

 containing 100 grm. sodium acetate and 100 c.c. glacial acetic per 

 litre. Heat the basin and run in from a burette a standard solution 

 of uranium nitrate, until a drop of the solution, placed on a small 

 heap of powdered potassium ferrocyanide on a white tile gives an 

 immediate brown colour, due to the formation of uranium ferro- 

 cyanide. The most convenient standard solution of uranium nitrate 

 contains 35 '5 grm. per litre. 1 c.c. of this solution is equivalent to 

 0'005 grm. phosphoric acid (P 2 5 ). 



Sulphates and Neutral Sulphur. There are two varieties of 

 sulphates in the urine, each of which has a special significance of its 

 own. These varieties are : 



1. Inorganic sulphates (sodium sulphate, potassium sulphate, etc.). 



OK 



2. Ethereal sulphates (phenyl sulphate of potassium) S0 2 <^QQ g 



OK 



(indoxyl sulphate of potassium) SO 2 <^Qp TT -^ 



Under ordinary conditions the ethereal sulphates constitute only 



