XX.] 



URIC ACID, ETC. 



I2 9 



is not too high not above 40 C. Very disagreeable fumes are 

 given off, while a yellow or reddish stain remains. Allow it to 

 cool, and bring a rod dipped in ammonia near the stain, or moisten 

 it with strong ammonia, when a purple-red colour of murexide 

 C 8 H 8 (NH 4 )N 5 O 6 , appears. It 

 turns violet on adding caustic 

 potash. 



(6.) Repeat the experiment, 

 but act on the residue with 

 caustic soda or potash, when 

 a violet-blue colour dis- 

 charged by heat is obtained. 

 The latter distinguishes it 

 from guanin. When uric acid 

 is acted on by nitric acid, 

 alloxantin (C 8 H 4 N 4 7 ) is 

 formed, which, on being 

 further heated, yields alloxan 

 (C 4 H 2 N 2 4 ) ; the latter strikes 

 a purple colour murexide 

 with ammonia. 



(c.) Place uric acid on a 

 microscopic slide, and dissolve 

 it in liquor potassse. Heat, 

 if necessary; add hydro- 

 chloric 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, or in 

 rosettes. 



(d.) Dissolve 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 uric acid in a small quantity of 

 sodium carbonate. Place, by means of a glass rod, a drop of solu- 

 tion 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. 



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

 off the smell of burnt feathers. 



Fl 68. Uric Acid, a. Rhomboidal, truncated, 

 hexahe.lral. and laminated crystals ; fc. Rhom- 

 biu prism, horizontally truncated angles of 

 the rnoml)i c prism; c. Prism with a hexa- 

 hedral basic 8Urface) barrel - shaped figure, 

 prism with a hexahedral basal surface ; d. 

 Cylindrical figure, stellate and superimposed 

 groups of crystals. 



(g.) 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 



I 



