HIPPURIC ACID. 191 



we must seek to ascertain the reason why the fixed acid is freed from 

 the adjunct. This adjunct of hippuric acid might be regarded, in 

 reference to its composition, as an amide of fumaric acid (C 4 H 3 NO 2 =r 

 H 2 N.C 4 HO 2 ), and we should thus arrive at the reverse of Fehling's 

 view of the subject. The question therefore now remains Ts it 

 more probable that in hippuric acid benzamide is combined with 

 fumaric acid, or fumaramide with benzoic acid ? or is it more pro- 

 bable that in the action of peroxide of lead the benzoic acid is 

 converted into benzamide by the oxidation of the fumaramide, or 

 that by the action of concentrated acids the benzamide is decom- 

 posed and fumaramide formed ? No satisfactory answer to these 

 questions can be deduced either from the laws of stoichiometry or of 

 affinity; since most unquestionable observations show in both cases 

 the remarkable fact of the alternating substitution of 1 atom of amide 

 and 1 atom of oxygen, (for in the conversion of benzoic acid into 

 benzamide the former takes in exchange 1 equivalent of amide for 1 

 atom of oxygen, and a similar substitution occurs in the conversion 

 of fumaric acid into fumaramide.) If, however, we regard benzoic 

 acid as existing preformed in hippuric acid, we are by no means 

 constrained to assume that the adjunct is fumaramide, or indeed 

 any amide-compound. If we represent the formula of hippuric acid 

 =C 4 H 3 NO 2 .C 14 H 5 O 3 .HO, this view is supported in the first 

 place by the circumstance that hippuric acid has many physical and 

 chemical properties in common with benzoic acid, which lead to 

 the assumption that benzoic acid exists preformed in it, but afford 

 no presumption in favour of the pre-existence of benzamide or 

 fumaric acid in it. Secondly, we are indebted to the labours of 

 Strecker for our knowledge of another conjugated acid, in whose 

 analogous decomposition by acids glycine is also separated, which 

 here also can only be produced by the assimilation of water ; this 

 acid being the biliary acid presently to be considered, where the 

 same adjunct is combined with the cholic acid which we have 

 already described. Thirdly, the fact discovered by Wohler that 

 benzoic acid, in its passage through the animal organism, is con- 

 verted into hippuric acid, affords a certain amount of support to 

 this view. 



Recently, however, Strecker* has been led to yet another view 

 regarding the constitution of hippuric acid from its behaviour with 

 nitric oxide, and from the formation of the acid whose formula 

 = C 18 H 7 O 7 .HO. He looks upon hippuric acid as an amide-com- 

 pound of this acid, and=H 2 N.C 18 H 7 O 7 ; but the amides never 

 have acid properties (besides which this only represents the 

 * Ann. d. Ch. u. Pharm. Bd. 68, S. 53. 



