The Urine. 



215 



The colour of healthy filtered ■ urine is yellowish-red or 

 yellow ; but a great deal depends on its age. It always 

 turns brown on standing a few hours, the brown colour 



Fig. 12.— Crystals of Nitrate of Urea (Funke).* 



commencing on its surface and extending downwards, due 

 to the oxidation of pyrocatechin. This substance reduces 

 salts of copper (see Sugar). 



Urea, if in excess, may be precipitated by strong nitric 



Fig. 13.— Crystals of Impure 

 Hippuric Acid. 



Fig. 14. — Crystals of Purified 

 Hippuric Acid (Funke). 



acid. If the normal bulk of urine is being excreted, urea is 

 not precipitated until after gently evaporating the urine to 



* ' Atlas of Pathological Chemistry.' Supplement to Lehmann's 

 Physiological Chemistry ' (Cavendish Society). 



