742 



PHYSIOLOGICAL CHEMISTRY. 



by acetic or hydrochloric acid, but dissolves on the addition of caustic 

 potash and burns on platinum foil without leaving a residue ; it is 

 recognized by the murexide test. Uric acid crystallizes in many forms, 

 usually in rhombs with rounded corners, the so-called "whetstone 

 crystals." The crystals are usually brow 7 n. The sediment has a 



FIG. 77. 



Calcium oxalate crystals. (Finlayson.) 



red crystalline appearance (" brick-dust "), and occurs in any concen- 

 trated, strongly acid urine. 



Add urates (Na, K) form a voluminous sediment, amorphous under 

 the microscope, of a yellowish-brown or reddish color. This is the only 

 sediment which dissolves on heating. 



FIG. 78. 



Crystalline phosphates. (Finlayson.) 



Calcium oxalate is rarely found in more than microscopic amounts. 

 The crystals are peculiarly clear, and have a double envelope, or 

 sometimes a dumb-bell appearance. 



Magnesium-ammonium phosphate, or triple phosphate, MgNH 4 .- 

 PO 4 .6H 2 O, is found generally in triangular prisms with bevelled. 



