102 CHEMICAL PHYSIOLOGY. 



dissolve it in liquor potassae. Heat if necessary; add: 

 hydrochloric or nitric acid just to excess, and examine with 

 the microscope the crystals of uric acid which form. They 

 may be transparent rhombs with obtuse angles, dumb-bells y 

 or in rosettes. 



(d.) Dissolve some uric acid in caustic soda, add a drop or 

 two of Fehling's solution or dilute cupric sulphate and 

 caustic soda and boil = a white precipitate of cupric urate, 

 which after a time becomes greenish. 



(e.) Schiff s Test. Dissolve some uric acid in a small 

 quantity of sodic carbonate. Place, by means of a glass rod, 

 a drop of solution of silver nitrate on filter-paper, and on 

 this place a drop of the uric acid solution. A dark brown 

 or black spot of reduced silver appears. 



(/) Garrod's Microscopic Test. Add 6 to 8 drops of 

 glacial acetic acid to 5 cc. urine in a watch-glass, put into it 

 a few silk threads, and allow the whole to stand for twenty- 

 four hours, taking care to prevent evaporation by covering 

 it with another watch-glass or small beaker. Examine the 

 threads microscopically for the characteristic crystals of uric 

 acid, which are soluble in KHO. A similar reaction may 

 be done on a microscopic slide. 







(g.) Heat some uric acid in a test-tube. It blackens and 

 gives off the smell of burnt feathers. 



4. Uric Acid Salts (Urates). Uric acid forms salts (chiefly 

 acid), with various bases, which are soluble with difficulty in cold, 

 but readily soluble in warm water. HC1 and acetic acid decom- 

 pose urates, when the uric acid crystallises. 



Urates form one of the commonest and least important deposits 

 in urine. There is usually a copious precipitate, varying in 

 colour from a light pink or brick-red to purple. They occur in 

 catarrhal affections of the intestinal canal, after a debauch, in 

 various diseases of the liver, in rheumatic and feverish conditions. 

 They frequently occur as the " milky " deposit in the urine of 

 children. Urates constitute the "lateritious" deposit, or "critical" 

 deposit of the older writers. Urates frequently occur even in 

 health, especially when the skin is very active (in summer), or 

 after severe muscular exercise ; when much water is given off by 

 the skin, and a small quantity by the kidneys. 



