110 



Prof. H. E. Armstrong and Mr. E. Horton. [Jan. 26, 



account, a name which is significant of the origin of the substance rather 

 than of its functions is specially appropriate. 



Equilibration of Urea and Amnionic Cyanate in Solution. — Though the 

 conception that salts in solution must be pictured as in a state of constant 

 flux was advanced by A. Williamson, in 1850, in his celebrated memoir on 

 the Theory of Etherification, little notice was taken of the suggestion and the 

 phenomena of reversible change were not taken seriously into account until 

 Deville's work on dissociation at high temperatures attracted attention ; 

 since that time it has been realised gradually that the properties of solutions 

 are such as to necessitate the general application of Williamson's contention. 



Urea is a remarkably stable substance in solution and is but slowly 

 hydrolysed even by heating it with acids and alkalies.* At ordinary 

 temperatures no perceptible change takes place in the solution : that is to 

 say, it remains neutral and does not contain an appreciable amount of 

 ammonia ; on this account, probably, the alteration it undergoes was over- 

 looked until J. Walker and Y. J. Hamblyf drew attention to the fact that 

 urea and amnionic cyanate are related reversibly, thus : — 

 CON 2 H 4 . — NH 4 -CNO. 



Urea. Amnionic cyanate. 



The conversion into the cyanate is easily demonstrated. No precipitate is 

 noticeable on adding nitrate of silver to a cold solution of urea ; if, however, 

 the solution be heated to 80° — 100°, then quickly cooled and mixed with 

 the silver salt, cyanate of silver is at once thrown down; if equivalent 

 quantities of the two substances are heated together, a very large proportion 

 of urea is converted into cyanate, indeed the conversion may be rendered 

 almost complete by concentrating the solution. 



The silver precipitate contains only traces of carbonate when urea is used 

 initially, but when amnionic cyanate is transformed into urea, a considerable 

 proportion — as much as about 4 per cent. — is converted into carbonate. 



When equilibrium is established, a solution of urea which has been heated 

 at 80°— 100° appears to contain at most about 5 per cent, of the metameric 

 cyanate and at lower temperatures the proportion is much less. 



According to Walker and Hambly, the rate at which ammonic cyanate 

 undergoes conversion into urea is such that it cannot be supposed that only 

 a single changing substance is present in the solution, the inversion pro- 

 ceeding at a " bimolecular " rate : in other words, the single molecule of 

 cyanate is not changed directly into the single molecule of urea. According 

 to Fawsitt, the hydrolysis of urea follows the unimolecular law. 



* Comp. Fawsitt, ' Zeit. Phys. Chein.,' 1902, vol. 41, p. 601. 

 t ' Chem. Soc. Trans.,' 1895, p. 746. 



