MON-UKEIDE COMPOUNDS. 133 



effect the complete oxidation of the uric acid effecting also a 

 separation from one another of the resulting carbonic acid and 

 urea, which, however, may be obtained in combination by other 

 means. Allophanic acid, for instance, is a well known artifi- 

 cial mon-ureide of carbonic acid, but so far as I am aware no di- 

 ureide of the acid has hitherto been produced by any process 

 whatsoever. 



(140.) The mon-ureide of mesoxalic acid, of which I have 

 already spoken namely, alloxan, is formed from mesoxalate of 

 urea by an elimination of two atoms of water ; but there is another 

 ureide namely, alloxanic acid, which differs from the original 

 salt by the loss of only one atom of water. Similarly oxalic acid 

 forms two mon-ureides namely, parabanic acid or paraban ana- 

 logous to alloxan, and oxaluric analogous to alloxanic acid. 

 Carbonic acid, however, forms but a single ureide, which is pro- 

 duced by the elimination of only one atom of water, and accord- 

 ingly belongs to the same series as the oxaluric and alloxanic acids, 

 thus : 



Acids Ureides 



CH 2 3 Carbonic ^W> 3 Allophanic. 



n TT ~ n T (CJSTjHX), Oxaluric. 



C 2 H 4 4 Oxalic \ 3 3 4 4 



( C 3 N a H 4 3 Paraban. 



(C A N,ILOe Alloxanic. 

 C 3 HA Mesosahc ' 



Similarly among the di-ureides, some are formed from their 

 corresponding mon-ureides by an elimination of one atom, and 

 others by an elimination of two atoms of water. 



(141.) Now, mesoxalic acid is convertible by deoxidation or 

 hydrogenation into tartronic acid, as I have already observed ; 

 and by pushing the deoxidation a stage further we obtain 

 inalonic acid, both of them capable of forming mon-ureides 

 and di-ureides ; and, in a similar manner, the oxalic and carbonic 

 acids furnish a variety of similarly behaving deoxidation -products. 

 When we consider, then, the total number of carbonic or I -carbon, 



