CONSTITUTION OP HIPPURIC ACID. 39 



(39.) Our actual knowledge, then, of the constitution of hip- 

 puric acid amounts to this, that it contains the residues of three 

 distinct molecules, which by an absorption of water are capable 

 of being obtained separate from one another. When any one of 

 these residues is destroyed or removed, the other two residues are 

 left in combination ; and accordingly by treating hippuric acid 

 with different reagents, we may obtain the benzoic and ammoniacal 

 residues in the form of benzamide, or the benzoic and glycolic 

 residues in the form of benzogly colic acid, or the glycolic and 

 ammoniacal residues in the form of sugar of gelatin. To this 

 much, which is certain, a something may be added which is pro- 

 bable. From many considerations into which I cannot at present 

 enter, it seems, at any rate, that the ammoniacal constituent of hip- 

 puric acid is actually in more intimate association with the gly- 

 colic than with the benzoic residue, so that the composition of 

 hippuric acid would be better represented by a chain of three 

 circles than by a trefoil, as contrasted in the diagram below ; 

 although, as I have said, the benzoic and ammoniacal residues 

 may be left in combination with one another by the excision, so 

 to speak, of the glycolic or oxiacetic residue. 



Hippuric Acid 



Be this as it may, I shall assume that hippuric acid consists of 

 a residue of benzoic acid and a residue of glycocine, which last 

 consists of a residue of glycolic or oxiacetic acid combined with a 

 residue of ammonia ; and similarly in the case of many other 



