718 



Tlie |)rogi-essive change of the solubility is also characterised by 

 the fact that afler about 25 minutes, when the solubility ofphthalic 

 acid (35.2 millimol. per litre) has not yet been attained, the condition 

 is already such that the solution contains a preponderance of acid. 

 The idoa that phthalic anhydride should be readily soluble is, therefore, 

 without any foundation; the anhydride concentration can, moreover, 

 not be calculated bj simply deducting the solubility of the acid in 

 water from the total solubility. 



This last experimental series therefore also confirms our contention : 

 the anhydride passes into solution as such and then becomes hydrated 

 and this so rapidly in comparison with its solubility velocity that 

 the non-variant {p,t) equilibrium is not attained, or at least not 

 permanently so. The anhydride, if we will not credit it with an 

 ahnormaUy small solubility velocity (for which there exists no reason, 

 just the contrary), has a much smaller solubility than the acid. 



No measurements have as yet been carried out with succinic 

 anhydride, but looking at the parallel behaviour of the two acid 

 anhj'drides similar relations may be expected there also. 



Owing to the peculiar relations between the homogeneous and the 

 heterogeneous reaction velocities in this kind of systems, we are 

 here at the limitation wliere we may still speak of actual pseudo 

 ternary systems. In connection therewith and other correlated questions 

 the investigation of different systems is being continued. 



Utrecht, Dec. 1913. van 't UoFF-Lahoratori/. 



Chemistry. — "The mechanism of the acid formation of aliphatic 

 acid anhydrides in an excess of water". By Prof. J. Böeskkkn 

 and P. E. Verkade. (Communicated by Prof. Holleman). 



(Communicated in the meeting of December 27, 1913). 



The communication of Wii.sdon and Sidgwick ^) on the hydratation 

 of some acid anhydrides induces us to give a short résumé of the 

 results obtained by us when investigating the hydratation of the 

 aliphatic acid anhydrides. 



This investigation ") has already been announced by one of us 

 some time ago. He had found that the hydratation constant of the 

 cyclic acid anhydrides was connected with the dissociation constant 

 of the acids formed thereof. As it was his intention to get to know 



^) Soc. 103, 1959 (1913). 

 2) Recueil 31, 90 (1912). 



