92 



Chemistry. — ''On the behaviour of gels towards liquids and the 

 vapours thereof." II. By Dr. L. K. Wolff and Dr. E. H. 

 BüCHNER. (Communicated by Prof. A. F. Holleman). 



(Communicated in tlie meeting of April 24, 1914). 



In continuing the experiment» mentioned in our first communi- 

 cation about this subject ^), we hit upon two observations which 

 have given us the l<:ey to the solution of the problem. Firstly it 

 was found that, when leading saturated water vapour over gelatine 

 which at the same temperature had swollen in water, the weight 

 of the gelatine does not change ; secondly it appeared that the 

 amount of decrease with the experiments made in the previously 

 described way — in desiccators according to van Bemmelen — 

 depended upon the size of the desiccator, and besides that in this 

 way of experimenting pure water also lost in weight. These things 

 found, we came to the following conception of von Schroeder's 

 phenomenon : 



1. the state attained in water vapour is no equilibrium ; even 

 though the quantity of water absorbed does not visibly increase for 

 days and days, one must supi)Ose an extremely slow absorption still 

 to be taking place, at least if the experiment is made in the exact 

 way which will be [)resently described. However, it may be several 

 years, before the true equilibrium is reached, which in liquid water 

 appears within some days. So the so called vapourequilibrium is 

 only a "false equilibrium". 



2. the curve which indicates the connection between the water 

 content and the vapourtension, runs almost horizontally as soon as 

 the point which represents the vapour equilibrium, is passed ; the 

 tension being taken as ordinate, the concentration as abscissa. 



3. Tiie observation formerly advanced by von Schroeder, Bancroft, 

 and also by us against the hypothesis mentioned under 1, viz. that 

 the watercontent of gelatine swollen in the liquid, decreased again 

 in vapour, (from which was concluded that tlie "equilibrium" was 

 attained from two sides), is founded on an unsatisfactor}' way of 

 experimenting. This conception seems to give a satisfactory explana- 

 tion of the whole of the phenomena ; we can support it by a great 

 number of ex[)eriments. 



We shall now first of all treat tlie proof of the third thesis. As 



1) These Proc. 15, 1078 (1912/13). 



