192 J. F. Mallet— Constitutional formulae of Urea, 



of nitrogen with two free bonds to the outside oxygen iu 

 oxatyl,* so that I represent one of the two such oxygen 

 atoms in oxalic acid as replaced by a urea residue connecting 

 itself by its amidic extremity, the hydrogen of the correspond- 

 ing hydroxyl of the acid retaining its basic character ; while 

 the second residue of urea, attached by the opposite end of its 

 chain of atoms, replaces hydroxyl instead of oxygen, and thus 

 changes a di-basic into a monobasic acid. Here we have an 

 instance of what seems to me the error arising in many of the 

 older formulas from considering merely the number of atoms, 

 with their additions or subtractions, without noticing the char- 

 acter of the compounds in question as an indication of molec- 

 ular structure. Odlingf says of mycomelic acid that it bears 

 "exactly the same relation to oxahc acid that uric has to 

 mesoxalic acid." So it does, in so far as the summation of the 

 atoms present is concerned, but the two last named acids are 

 both di-basic, while oxalic and mycomelic acids are di-basic 

 and^ mono-basic respectively. It will be seen presently that 

 the formulae I propose account fully for this, the two urea resi- 

 dues in uric acid being similarly connected with the residue 

 of the original acid, while in mycomelic acid they are con- 

 nected by what I have called the amidic and imidic ends 

 respectively. 



Passing to the 3-carbon acids, from malonic acid, CjH^O^, 

 No. 1, may be derived barbituric acid, C.H.NgOg, No. 2. 



1. Malonic acid (dibasic). 2. Barbituric acid (dibasic). 



La Li 



c-c— C C-C— c 



tJ. 



trifling misprint) i 



aquet* speaks of "Thydantdine, qui reprdsente de Tacide 

 "'""" - - jj^ atome d'oxyg^ne, et qui est, par conse- 



allanturiqu 

 (|uent, a \\ 



'acide allanturique ce que I'acide barbituriquc 



' ' " But of these two pairs of subst 



cyanic acid. Prof. Gibbs proposes 



(CN-OH)" cyanyl, as analogous to (COOH)', oxatyl. 

 f Lectures on Animal Chemistry, London, 1866, p. 



