284 URINE. [CH. XII. 



A certain amount of phosphorus is found in the urine 

 in an organic form, not as a phosphate. It may be present 

 as glycero-phosphoric acid. The average daily amount is 

 about 50 mgms. 



For method of estimation see Ex. 414. 



327. Test for chlorides by adding to about 3 cc. of urine a 

 few drops of pure nitric acid and 3 cc. of a 3 per cent, solution of 

 silver nitrate. An abundant curdy precipitate of silver chloride 

 appears at once. If the chlorides are less in quantity, the solution 

 merely becomes milky or opalescent. 



NOTE. If nitric acid is not added, urates might be precipitated by silver 

 nitrate, especially if the urine be ammoniacal. 



328. To a test-tube nearly full of urine add a little strong 

 ammonia and boil. A white flaky precipitate of the phosphates 

 of calcium and magnesium is formed. Filter off the precipitate, 

 wash with water, and dissolve in 5 cc. of dilute acetic acid. Divide 

 the solution into two parts. To one part add a solution of potassium 

 oxalate. A white precipitate is produced, showing the presence of 

 calcium in the urine. 



329. To the other portion of the solution add an equal bulk 

 of strong nitric acid and about 5 cc. of ammonium molybdate. 

 Boil : a yellow crystalline precipitate is produced, showing the 

 presence of phosphates. 



NOTE. Neutral urine is very apt to yield a precipitate of earthy phos- 

 phates on boiling, owing to the change of reaction due to the evolution of 

 CO 2 (see notes to Ex. 28). 



330. To demonstrate the presence of acid-phosphates in 

 urine. Treat 5 cc. of urine with an equal volume of 5 per cent, 

 solution of barium chloride. Filter repeatedly through a small 

 filter paper till the filtrate is clear. Treat the filtrate with a little 

 baryta mixture and boil. Filter; dissolve the precipitate in 

 nitric acid and boil the solution obtained with ammonium molybdate. 

 The yellow precipitate shows the presence in the urine of acid 

 phosphates, such as NaH 2 PO 4 . 



