THE URINE. 429 



tals can only be mistaken for small, not fully-developed crystals of 

 ammonium-magnesium phosphate. They differ from these by 

 their insolubility in acetic acid. The oxalate may also occur as 

 flat, oval, or nearly-circular disks with central cavities which from 

 the side appear like an hour-glass. Calcium oxalate may occur as 

 a sediment in an acid as well as in a neutral or alkaline urine. 

 The quantity of calcium oxalate separated from the urine as 

 sediment depends not only upon the amount of this salt present, 

 but also upon the acidity of urine. The solvent for the oxalate in 

 the urine seems to be the double-acid alkali phosphate, and the 

 greater the quantity of this salt in the urine the greater the 

 quantity of oxalate in solution. When, as above mentioned (page 

 427), the simple-acid phosphate is formed from the double-acid 

 phosphate, on allowing the urine to stand, a corresponding part of 

 the oxalate may be separated as sediment. 



Calcium .carbonate occurs in considerable quantities as sediment 

 in the urine of herbivora. It only occurs in small quantities as a 

 sediment in human urine, and indeed only in alkaline urines. It 

 has either almost the same appearance as amorphous calcium 

 oxalate, or it occurs as somewhat larger globules with concentric 

 bands. It dissolves in acetic acid with the generation of gas, which 

 differentiates it from calcium oxalate. It is not yellow or brown 

 like ammonium urate and does not give the murexid test. 



Calcium sulphate occurs very rarely as a sediment in strongly-acid urines. 

 It appears as long, thin, colorless needles, or generally as plates grouped 

 together. 



Calcium phosphate. The CALCIUM TRIPHOSPHATE, Ca 3 (P0 4 ) 2 , 

 which only occurs in alkaline urines, is always amorphous and 

 occurs partly as a colorless, very fine powder and partly as a mem- 

 brane consisting of very fine granules. It differs from the amor- 

 phous urates in that it is colorless, dissolves in acetic acid, but 

 remains undissolved on warming the urine. CALCIUM DIPHOS- 

 PHATE, CaHPO -\- 2H 2 0, occurs in neutral or only in very faintly, 

 acid urine. It is found sometimes as a thin film covering the 

 urine, and sometimes as a sediment. In crystallizing the crystals 

 may be single, or they may cross "one another, or they may be ar- 

 ranged in groups of colorless, wedge-shaped crystals whose wide end 

 is sharply defined. These crystals differ from crystalline alkaline 



