CHEMICAL BASIS OF THE ANIMAL BODY. 1C7 



By similar treatment uric acid is ivadily obtained from fowl's 

 excrement, a convenient source of the acid. 



ititication of uric acid. The crystalline forms afford some 

 clue, luit are so numerous that some forms which may at any 

 tiiin' present themselves are scarcely characteristic. The rhombic, 

 tables, dumb-bell,' and 'whetstone' crystals are on the whole 

 most characteristic. 



i. Murcxid test. The suspected substance is treated in a por- 

 celain dish with a few drops of strong nitric acid ami evaporated 

 on /til/I/ to dry ness, by preference on a water-bath. The residue 

 thus obtained will, if uric acid is present, be of a yellow or more 

 frequently red colour, which turns to a brilliant reddish purple on 

 exposure to the vapours of ammonia. On the subsequent addition 

 of a drop of caustic soda the colour is changed to a reddish blue. 

 This di>ap pears on warming, whereas the similar colour obtained 

 by the above process from guanin does not. This is an important 

 means of distinguishing between the two substances. 



Tin- te.-t depends on tin- formation of murexid, which is the arid 



UDinonilUn >alt f purpuric acid, the ai-id it-elf l>ein<f unknown in the 



-tate. Uric acid is decomposed when heated with nitric arid, 



yielding alloxan and then alloxantin ; by the action of ammonia the 



latter is converted into imin-xid (NH 4 ) C 8 H 4 N 6 O 6 -f- H 2 0. 



The murexid test is so striking and characteristic that it suf- 

 fices completely for the identification of uric acid. The following 

 tests may be applied in confirmation if required, but not for the 

 purposes of initial detection. 



ii. ^'Jiiff's reaction. 1 The substance is dissolved in sodium 

 carbonate, and a drop is then placed on filter paper previously 

 moistened with nitrate of silver. A yellow or almost black 

 colouration, due to the formation of metallic silver by reduction 

 of its nitrate, is at once obtained. 



iii. When a solution of urie aeid in eau-tic soda is boiled with 

 a small amount of Fehlinu's fluid, reduction occurs with produc- 

 tion of a greyish precipitate of urate of cuprous oxide. If the cop- 

 per salt is in excess red cuprous acid is obtained. 



ni'itinn <>f iirir iif'nl iii xuliitioii* (i/fiif). The accurate 

 quantitative determination of uric acid is a matter of some dif- 

 ficulty: for details some standard work- (quoted sub urea) 

 should be consulted. It will suffice to indicate here the princi- 

 ple- of the more usually employed methods. 



i. ,sW/.-<;//W. /-/,/' '//</.- When an ammoniacal solution 



' An,,. ,/. ('/,. ii. rhnrm. \\>\ < i\ 



H /. Jahrb. 1884, S. 597. Cf < 'aiii-r.-r. /. 1 Diol. Bd. XXVII. 



(1890 - 



