BY DR. LAUDER BRUNTON. 



we have the primary form so modified that the cr3 r stals resemble 

 hcxMgon.il plates. Experience gained by a frequent comparison 

 with accurate drawings of the various forms of crystals of uric 

 acid, can alone enable the observer rapidl} r to identity uric acid. 

 When any doubts exist as to the identity, it is well to dissolve 

 the suspected crystals in liquor potassre, and to proceed as 

 directed above, for by neutralizing an alkaline urate with acid, 

 some of the commoner, and therefore easily identified shapes of 

 uric acid crystals, are obtained. 



2. Place a very small quantity of the reddish crystalline 

 deposit in a watch glass ; add four or five drops of nitric acid 

 and heat very cautiously over a small spirit-lamp flame. The 

 uric acid will dissolve, and on evaporating to dryness, a red- 

 dish-yellow residue is obtained. On exposing this residue to 

 the vapor of ammonia, or adding, by means of a thin glass rod, 

 a small quantity of solution of ammpnia, a beautiful purple- 

 red color is developed, which, on the subsequent 'addition of a 

 little solution of caustic potash, assumes a violet tint. This 

 reaction has received the name of the Murexide Test. ^i-uxv 



*187. Separation of Hippuric Acid (C !) IT iJ NO ! )._Afterfl fA ^ u 

 urea, hippuric acid is the organic compound present in largestr,i 

 quantity in the urine of man, the mean quantity excreted pei 

 diem amounting at least to one gramme. The difficulties 

 tending the separation of hippuric acid from the urine of man 

 are, however, great, and it is therefore advisable that the stu- 

 dent should learn to isolate this substance when it is present in 

 larger quantities than normal in the urine. As the urine of 

 herbivora contains large quantities of hippuric acid, it may be 

 advantageous to use for the experiment to be described cows' 

 or horses' urine, or the urine of men in whom an excessive 

 excretion of hippuric acid has been Induced ; this maybe done 

 by administering to a man ten or fifteen grammes of benzoic 

 acid ten or twelve hours before the urine is collected. 



It is a fact worthy of remembrance that when benzoic acid is 

 administered to healthy men, large quantities of hippuric (gty- 

 co-benzoic) acid are excreted. There appears to be always in 

 the system a quantity of glycocine (C. 2 H.,(NH 2 ) 2 ). which al- 

 though it is never excreted as such, is capable of being seized 

 upon by the radical of benzoic acid, so as to yield hippuric acid. 

 By comparing the formula? of glycocine and hippuric acid, ex- 

 hibited below, it will be seen that the latter can be represented 

 as derived from the former by the substitution of (C 7 H 5 0) for 

 H, thus: 



Glycocine C 2 H,(NHJO 2 



Hippuric acid C 2 II 2 (NH 2 )(C.H 5 0)O 2 . 



Take 200 cubic centimetres of the fresh urine of the cow 

 and concentrate it, by heating on the water-bath, to forty cubic 



