CH. XXXIX.] SALTS OF URINE 597 



In neutral urine, in addition, disodium hydrogen phosphate, 

 Na 2 HP0 4 , calcium hydrogen phosphate, CaHP0 4 , and magnesium 

 hydrogen phosphate, MgHP0 4 , are found. In alkaline urine there 

 may be instead of, or in addition to, the above, the normal phosphates 

 of sodium, calcium, and magnesium [Na 3 P0 4 , Ca 3 (P0 4 ) 2 , Mg 3 (P0 4 ) 2 ]. 



The earthy phosphates are precipitated by rendering the urine 

 alkaline by ammonia. In decomposing urine, ammonia is formed 

 from the urea: this also precipitates the earthy phosphates. The 

 phosphates most frequently found in the 

 white creamy precipitate which occurs 

 in decomposing urine are : 



(1) Triple phosphate or ammonio- 

 magnesium phosphate (NH 4 MgP0 4 + 

 6H 2 0). This crystallises in " coffin-lid " 

 crystals (see fig. 384) or feathery stars. 



(2) Stellar phosphate, or calcium 

 phosphate ; this crystallises in star-like 

 clusters of prisms. 



As a rule normal urine gives no 

 precipitate when it is boiled ; but some- 

 times neutral, alkaline, and Occasionally 



faintly acid urines give a precipitate of 



Calcium phosphate When boiled : this JJ undergone alkaline fer- 



precipitate is amorphous, and is liable 

 to be mistaken for albumin. It may be distinguished readily from 

 albumin, as it is soluble in a few drops of acetic acid, whereas 

 coagulated protein does not dissolve. 



The phosphoric acid in the urine chiefly originates from the phos- 

 phates of the food, but is partly a decomposition product of the phos- 

 phorised organic materials in the body, such as lecithin and nuclein. 

 The amount of P 2 5 in the twenty-four hours' urine varies from 2 '5 

 to 3*5 grammes, of which the earthy phosphates contain about half 

 (1 to.1'5 gr.). The urine also contains minute quantities of organic 

 phosphates, for instance, glycero-phosphates. 



Tests for the Inorganic Salts of Urine. 



Chlorides. Acidulate with nitric acid and add silver nitrate ; a white precipitate 

 of silver chloride, soluble in ammonia", is produced. The object of acidulating with 

 nitric acid is to prevent phosphates being precipitated by the silver nitrate. 



Sulphates. Acidulate with hydrochloric acid, and add barium chloride. A 

 white precipitate of barium sulphate is produced. Hydrochloric acid is again added 

 first, to prevent precipitation of phosphates. 



Phosphates. i. Add ammonia; a white crystalline precipitate of earthy (that 

 is, calcium and magnesium) phosphates is produced. This becomes more apparent 

 on standing. The alkaline (that is, sodium and potassium) phosphates remain in 

 solution, ii. Mix another portion of urine with half its volume of nitric acid ; add 

 ammonium molybdate, and boil. A yellow crystalline precipitate falls. This test is 

 given by both classes of phosphates. 



