XX.] 



URIC ACID, ETC. 



129 



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 pur_ple-red colour of murexide, 

 CsHs(NH,)N,0„ appears. It 

 turns violet on adding caustic 

 potash. 



{h.) 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 (CgH^N^Oy) is 

 formed, which, on being 

 further heated, yields alloxan 

 (C4H2N2O4) ; the latter strikes 

 a purple colour — murexide— 

 with ammonia. 



(r \ PlnPA ^^r^o t\n\c\ nr» a ^^0- 68.— Uric kc\(\. a. Rhomboidal, truncated, 



y.) riace uric acia on a hexahedral.an.llan.in.ited crystals; 6. Rhom- 



micrOSCOpiC slide, and dissolve biu prism, horizontally truncated angles of 



if iv^ li'o,,-./^-- •»%/^4-r.r,r,^ TJ"^«4- ^^6 rhoinbic prism ; c. Prism with a hexa- 



It m liquor potaSSae. Heat, hedral basic surface, barrel - shaped figure, 



prism with a hexahedral basal surface ; d. 

 Cylindrical figure, stellate and superimposed 

 groups of crystals. 



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. 



{(1.) 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. 



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

 off the smell of burnt feathers. 



{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 



