HIPPURIC ACID. Gl 



(/) On warming uric acid with nitric acid and saturating it 

 with ammonia, we obtain murexid, C^^ Hg N. O^. 



(;«) On dissolving murexid in caustic potash and adding dilute 

 sulphuric acid, we obtain murexan, C^ H^ N„ O.. 



14. Hipjmric Acid. 



Hipjmric, or urobenzoic acid, is an ordinary, although not a 

 constant, ingredient of the urine of the graminivora. It has 

 been observed by Lehmann, Ambrosiani, and Reich, in the 

 lu'ine of diabetic patients, and Bouchardat has found it in the 

 same secretion in certain anomalous cases to which he has ap- 

 plied the term " hippime." Liebig has recently asserted that 

 it is a constant ingredient of healthy human urine ; and even 

 if this statement be too general, there can be no doubt that it 

 does very frequently occur in minute quantity in this secretion. 



Hippuric acid is readily obtained by evaporating the urine 

 of the horse or cow to about one tenth of its volume, and adding 

 sufficient hydrochloric acid to give it a decidedly acid reaction. 

 Yellow or brown crystals of hippuric acid are almost immedi- 

 ately deposited, which must be collected, dissolved in a hot 

 solution of carbonate of soda, and filtered through animal char- 

 coal. By the addition of hydrochloric acid to this solution, 

 (which must be concentrated, if requisite,) we obtain tolerably 

 pure crystals of hippm'ic acid. 



This acid forms long transparent four-sided prisms, acumi- 

 nated at the extremities; it is destitute of odour, and has a 

 faintly bitter, but not an acid taste. It dissolves in about 400 

 parts of cold water, and in a much larger proportion in hot 

 water, from which it recrystallizes on cooling. It is freely 

 soluble in alcohol, less so in ether. A cold aqueous solution 

 strongly reddens litmus. At a moderate heat, hippuric acid 

 melts (without yielding water) into a colourless oily fluid, which, 

 on cooling, solidifies into a crystalline milk-white mass. At a 

 higher temperature the acid undergoes decomposition, and yields 

 a crystalline sublimate composed of benzoic acid and benzoate 

 of ammonia, while, at the same time, some red oily di-ops are 

 produced, which develop a peculiar odour, resembling that of 

 the Tonquin bean. Hydrocyanic acid is subsequently formed, 

 and the previous odour is replaced by a bitter-almond smell. 

 The action of perchloride of iron on this acid is worthy of 

 notice. On the addition of this reagent to a solution of hip- 



