URIC ACID, URATES, ETC. 



101 



(c.} The crystals are soluble in caustic soda or potash. 

 Observe this under the microscope. 



(d.) Take some serpent's urine which is solid, and con- 

 sists chiefly of ammonium urate dissolve it in a 10 per cent, 

 solution of caustic soda 

 with the aid of heat. 

 Add water, and allow it 

 to stand. Pour off the 

 clear fluid, and precipi- 

 tate the uric acid with 

 dilute hydrochloric 

 acid. Collect the de- 

 posit, and use it for 

 testing. 



3. Reactions and Tests. 



(a.) Murexide Test. 

 Place some uric acid in 

 a porcelain capsule, add 

 nitric acid, and heat 

 gently, taking care that 

 the temperature is not 

 too high not above 

 40 C. 'Very disagree- 

 able 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, 



Fig. 26. Uric acid. a, Rhomboiclal, 

 truncated, hexahedral, and laminated 

 crystals ; b, rhombic prism, horizon- 

 tally truncated angles of the rhombic 

 prism, imperfect rhombic prisms ; c, 

 prism with a hexahedral basic surface, 

 barrel-shaped figure, prism with a hexa- 

 hedral basal surface ; d, cylindrical 

 figure, stellate and superimposed groups 

 of crystals. 



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 discharged 

 by heat is obtained. When uric acid is acted on by nitric 

 acid, alloxantin (C 8 H 4 N 4 O 7 ) is formed, which on being further 

 heated yields alloxan (C 4 H 2 N 2 O 4 ), which strikes a purple 

 colour murexide with ammonia. 



(c.) Place some uric acid on a microscopic slide, and 



