XX.] URIC ACID, ETC. I3I 



of small spheres covered with spines, and the ammonium urate, of 

 spherules often united together (fig. 77). 



(c.) Make a saturated solution of uric acid in caustic soda. Place a drop 

 of the mixture on a slide, allow it to evaporate. Examine it microscopically, 

 when the urate of soda in the form of spheres covered with spines will be 

 obtained. 



(/.) The same result as in {e.) is obtained by dissolving the ordinary deposit 

 of urates with caustic soda, and allowing some of it to evaporate on a slide. 



6. Uric Acid from Serpent's Excrement. — Heat the powdered excrement 

 in a porcelain vessel with 15-20 vols, of water just to boiling, add carefully 

 small quantities of caustic potash or soda until the whole is dissolved and 

 there is no further odour of ammonia given off. Filter, and saturate the 

 filtrate with CCV>, which causes at first a gelatinous and tlien a finely-granular 

 precipitate of acid alkaline urate. Separate the latter b}^ syphoning off the 

 fluid, wash it with small quantities of iced water, place it in a boiling dilute 

 solution of hydrochloric acid, and boil the mixture for some time. After it 

 cools, uric acid crystallises out, the latter is washed with cold water and dried. 



7. Hippuric Acid, C^H^NOg (benzoyl -amido- acetic acid or 

 benzoyl-glycin). — This substance is so called because it occurs in 

 large quantity in the urine of the horse and many herbivora, 

 chiefly in the form of alkaline hippurates (sodium hippurate). It 

 belongs to the aromatic series. It dissolves readily in hot alcohol, 

 but is sparingly soluble in water. 



Quantity in man .5 to i gram daily. It is a conjugate acid, which, when 

 boiled with alkalies and acids, takes up water and splits into benzoic acid and 

 glycin. It occurs in colourless four-sided jjrisms, usually with two or four 

 bevelled surfaces at their ends. It has a bitter taste. Benzoic acid, oil of 

 bitter almonds, benzamid, cinnamic acid, and toluol reappear in the urine as 

 hippuric acid. The benzoic acid unites with the elements of glycocoll (glycin), 

 and is excreted as hippuric acid in the urine. 



Benzoic Acid. Glycocoll. Hippuric Acid. Water. 



C7H0O., + C.HsNO., = CyHyNOa -f H,0. 



The amount is increased by eating pears, a])ples with their skins, cranberries, 

 and plums. Nothing is known of its clinical significance. It seems to be 

 formed chiefly from the husks or cuticular structures. 



Tests and Reactions. 



(a.) Heat some crystals in a dry tube. Oily red drops are 

 deposited in the tube, while a sublimate of benzoic acid and 

 ammonium benzoate are given off. The latter is decomposed, 

 giving the odour of ammonia, while there is an aromatic odour of 

 oil of bitter almonds. 



{h.) Examine the colourless four-sided prisms with the micro- 

 scope (fig. 69). 



(r.) Boil with HNO3, and heat to dryness ^ odour of nitrr»- 

 benzene. Benzoic acid gives a similar reaction. 



