440 Proceedings of Royal Society of Edinburgh. [sess. 
siderably greater than that of phenol. It will he seen that the 
layer of phenol gradually rises in the cylinder. 
There is one point not explicitly referred to by Nernst, which is, 
however, of interest. It is the cause of the stoppage of the diffusion 
through the layer of B when the difference of pressure on the two 
sides becomes equal to the osmotic pressure. Increase of pressure 
increases the solubility of A in B, and when this increase of 
solubility just balances the diminution of solubility due to the 
presence of N, the layer of B will become homogeneous, and the 
gradient of concentration, the cause of the passage of A from the 
A side, having disappeared, there will be equilibrium. 
We may therefore say, if A is shaken up with B under pressure 
p, and a given solution of K in A is shaken up with B under 
pressure p, the solutions of A in B formed in the two cases will 
have the same concentration if p'—p is equal to the osmotic 
pressure. As it is possible, by optical means, to ascertain when 
the two solutions have the same concentration, a practical method 
of determining osmotic pressure might be founded on this relation. 
