URINE 



461 



differentiated from other crystalline urinary sediments from the fact 

 that it is soluble in alkalis, alkali carbonates, boiling glycerol, concen- 

 trated sulphuric acid, and in certain organic bases such as ethylamine 

 and piperidin. It also responds to the murexide test (see page 380), 

 SchifFs reaction (see page 381) and to Folin's phosphotungstic acid 

 reaction (see page 381). 



Urates. The urate sediment may consist of a mixture of the urates 

 of ammonium, calcium, magnesium, potassium, and sodium. The 

 ammonium urate may occur in neutral, alkaline, or acid urine, whereas 

 the other forms of urates are confined to the sediments of acid urines. 

 Sodium urate occurs in sediments more abundantly than the other 



FIG. 136. VARIOUS FORMS OF URIC ACID. 



i, Rhombic plates; 2, whetstone forms; 3, 3, quadrate forms; 4, 5, prolonged into 

 ints; 6, 8, rosettes; 7, pointed bundles; 9, barrel forms precipitated by adding hydro- 



points 



chloric acid to urine. 



urates. There are two sodium urates, the mono and the di, which may 



Nfl +\ Na +\ 



be expressed thus jj + ^C 5 H 2 N 4 O3~ and +CsH^Os". Both 



salts dissociate with the production of an alkaline reaction, the alka- 

 linity being stronger in the case of the di-sodium urate. The so-called 

 quadriurate or hemiurate have no existence as chemical units. 1 The 

 urates of calcium, magnesium, and potassium are amorphous in 

 character, whereas the urate of ammonium is crystalline. Sodium 

 urate may be either amorphous or crystalline. When crystalline it 

 forms groups of fan-shaped clusters or colorless, prismatic needles (Fig. 



1 Taylor: Jour. Biol. Chem., i, 177, 1905. 



