240 ELEMENTARY PHYSIOLOGY. [XXIII. 



7. Uric Acid. 



a. Place a few crystals of uric acid on a slide, 

 and add a little liquor potassse to dissolve 

 them; then add nitric acid just to excess. 

 Examine with a high power the crystals of 

 uric acid formed. They are generally rhombic 

 plates with obtuse angles, but they vary 

 greatly in form. Note the star-shaped and 

 dumb-bell crystals. 



b. Make a saturated solution of uric acid in 

 strong sodium hydrate, mount a drop and 

 place it aside for some time. Crystals of 

 sodium urate will crystallise out. Note the 

 spheres covered with small thin projecting 

 prisms ; hexagonal prisms and thick tablets 

 may also be seen. 



c. To a little uric acid in an evaporating dish 

 add a little fairly strong nitric acid, the uric 

 acid will be split up and gases given off. 

 Evaporate to dryrtess on a water-bath at 

 a temperature not above 40 C. A reddish 

 residue will be left, to this add a drop or 

 two of weak ammonia; a red-purple colour 

 will be formed; this is the murexide test 

 for uric acid. Add then a drop of strong 

 sodium or potassium hydrate, the colour will 

 turn to a blue-purple. 



8. To 100 c.c. of urine (best evaporated to a third 

 of its bulk) add about 1 c.c. of pure strong 

 hydrochloric acid. Place aside for a day or two 



