Dr. W. Gregory on the Preparation ofHippuric Acid. 127 



acting in a different direction withdraws the oxygen and 

 allows the potassium to unite with the compound radical fer- 

 rocyanogen ; thus Fe^ Cyg 3K + KO + PbO = Fcg Cyg 4K 

 + Pb02, the decomposition being of the same kind when an 

 organic matter is substituted for the oxide capable of further 

 oxidation. Soda and ammonia may be substituted for potash 

 in the above decomposition, producing the oxidation or dis- 

 charging the indigo. This is curious in the case of ammonia, 

 for it cannot be explained by any other than by the ammo- 

 nium theory, and shows the complete analogy between the 

 oxide of ammonium and the oxide of the simple metallic ra- 

 dicals, potassium and sodium. It is interesting also to ob- 

 serve that the last member in the formula Fe^ Cyg 4R, may 

 be substituted by any alkaline base. Thus, that it may either 

 be Fe^ Cyg 3K K, or Fe^. Cyg 3K Na,or Fe^ Cyg 3K NH4. This 

 circumstance points to important theoretic^ considerations 

 in the atomic constitution of the prussiates, which would be 

 foreign to the present paper, the principal object of which is 

 to furnish a means of discharging indigo, and thus supply 

 a process much wanted in the art of calico-printing, and which 

 I have followed for many years with success. 



XXVI. On the Preparation of Hippuric Acid. 

 By William Gregory, M.D."^ 



SINCE the discovery of hippuric acid by Liebig, that body 

 has at all times attracted much attention. Its composition 

 and the products of its decomposition, among which were ben- 

 zoic acid and benzamide, rendered it interesting, and various 

 ingenious views were entertained of its constitution. Its 

 detection in human urine by Liebig gave it additional im- 

 portance. 



The beautiful discovery of Dessaignes, that hippuric acid, 

 when heated with strong acids, is resolved into benzoic acid 

 and glycocoU, has greatly increased the interest already at- 

 tached to hippuric acid, which now affords the best means of 

 obtaining glycocoll, and has enabled Horsford, in his elabo- 

 rate researches on that substance, to fix its formula in a very 

 satisfactory manner. 



If to hydrated hippuric acid . Cjg N Hg Og, 

 we add 1 equiv. water ... HO, 



and from the sum Cjg N H,q O7, 



subtract 1 equiv. glycocoll . . C4 N H4 O3, 



there remain C14 Hg O4, 



which is hydrated benzoic acid. 



* Communicated by the Chemical Society; having been read March 15, 

 1847. 



