URINK 155 



(2) Earthy phosphates that is, phosphates of calcium (abundant) 

 and magnesium (scanty). 



The composition of the phosphates in urine is liable to variation. 

 In acid urine the acidity is due to the acid salts. These are chiefly 

 sodium dihydrogen phosphate, NaH 2 PO 4 , and calcium dihydrogen 

 phosphate, Ca(H 2 P0 4 ) 2 . 



In neutral urine, in addition, disodium hydrogen phosphate 

 (Na 2 HP0 4 ), calcium hydrogen phosphate, CaHPO 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 (PO 4 ) 2 , 

 M g3 (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 MgPO 4 -f 6H 2 O). This crystallises 

 in ' coffin-lid ' crystals (see fig. 45) or feathery stars. 



(2) Stellar phosphate, or calcium phosphate, 

 which crystallises in star-like clusters of prisms. 



As a rule, normal urine gives no precipitate when 

 it is boiled ; but sometimes neutral, alkaline, and 

 occasionally faintly acid urines give a precipitate of 

 calcium phosphate when boiled ; this 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 phosphate, 

 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 thephos- 

 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.). 



