URINE AND ITS CONSTITUENTS. 719 



white precipitate of silver chloride forms. By comparing the result 

 with that obtained with a known normal urine, a rough estimate 

 can be gotten as to the amount of chlorides present. 



Estimation of chlorides. The chlorides in a measured amount of 

 urine are precipitated by the addition of an excess of silver nitrate 

 solution of known strength. The silver chloride is removed and the 

 amount of silver nitrate remaining in solution is determined by the 

 method given on page 427. The following solutions are used : (1) 

 Silver nitrate of such strength that 1 c.c. corresponds to 0.01 gramme 

 of sodium chloride. (2) Potassium sulphocyante of such strength that 

 1 c.c. corresponds to 1 c.c. of the silver solution. (3) Ammonio- 

 ferric alum, saturated solution. 



To 10 c.c. of urine in a 100 c.c. graduated flask add 4 c.c. of con- 

 centrated nitric acid and 50 c.c. of distilled water. Add 15 c.c. of 

 the silver solution and dilute the mixture to the 100 c.c. mark, shak- 

 ing well. Filter off 50 c.c. and titrate with the sulphocyanate solu- 

 tion, after adding 3 c.c. of ammonio-ferric alum. The result multi- 

 plied by 2 shows the number of cubic centimeters of silver nitrate 

 which was in excess. The difference between this number and 15 

 is the number of cubic centimeters of silver nitrate which corresponds 

 to the chloride content of the 10 c.c. of urine. 



Phosphoric acid is found in urine, in part (about two-thirds) com- 

 bined with alkalies, and in part (about one-third) with lime and 

 magnesia. These phosphates have in acid or neutral urine the com- 

 position NaH 2 PO 4 , CaH 4 (PO 4 ) 2 , MgH 4 (PO 4 ) 2 ; in amphoteric urine, 

 in addition to the above, there occur Na 2 HPO 4 , CaHPO 4 , MgHPO 4 ; 

 in alkaline urine compounds of the composition Na 2 HPO 4 , CaHPO 4 , 

 MgHPO 4 , Na 3 PO 4 , Ca 3 (PO 4 ) 2 , Mg s (PO 4 ) 2 , MgNH 4 PO 4 may be pres- 

 ent. A small quantity is present as glycerin-phosphoric acid. 



The phosphates in urine amount normally to about 3 grammes of 

 P 2 O 5 in twenty-four hours. They are derived mainly from the food, 

 and to a much smaller amount from the body protein. They are in- 

 creased in certain cases of diabetes, and are decreased in most of the 

 fevers. The determination of the phosphatic output has little clinical 

 importance. 



On adding any alkali the phosphates of calcium and magnesium 

 (generally termed earthy phosphates) are precipitated ; the phosphates 

 of sodium or possibly potassium remain dissolved, and may be pre- 

 cipitated as magnesium ammonium phosphate by the addition of 

 magnesia mixture. 



