188 J. W. Mallet— Constitutional formuloe of Urea, 



Products of substitution Tdv alcoholic radicals, in which the 

 urea type and character are 'preserved, are exemplified by e\hy\- 

 urea, CgH^N^O, in which one of the two similarly related 

 hydrogen atoms is replaced, and by normal di-ethyl-urea, 

 CjH, 2N3O, in which the replacement extends to both of these 

 atoms. One hydrogen atom of this pair and another (unlike) 

 atom at the same time are probably replaced in the isomeric 

 di-ethyl-urea, and tri-ethyl-urea, if this compound really exist, 

 will represent the replacement of both the similar and one un- 

 symmetric (probably imide) atom of hydrogen. 



Formulae for condensed ureas containing polyatomic radi- 

 cals, such as ethylene, follow easily enough from the above. 



In biuret, CaH.NjOg, we may suppose the residues of two 

 urea molecules united" with elimination of ammonia from 

 unlike (amidic and imidic) extremities of the chain of atoms — 



ic, uniting (by its amidic end probably) with one equivalent of 



HCl). 



Lo-H 



this giving a very obvious explanation of the formation of 

 biuret by heating urea, ammonia being at the same time 

 liberated. 



Conjugated compounds of urea residues and acid radicals 

 form a more numerous class. In these the type of the original 

 acid seems usually to predominate, but the urea residue modifies 

 the character of the substance in different ways according to the 

 mode of attachment This last point seems to have been the 

 chief one overlooked in the arrangement of most of the struc- 

 tural formulsB hitherto proposed. 



Thus, from carbonic acid, CHaO, (di-basic), we get allo- 

 phanicacid, C,H,J^,03, 



Carbonic acid (dibasic). Allophanic add (monobasic). 





