Vol. 6, 1920 
CHEMISTRY: J. LOEB 
213 
latter fact plays only a technical r61e in our experiments since it makes it 
easy to find a strictly semipermeable membrane. The writer has been 
able to show that the influence of ions on the osmotic pressure of gelatin 
solutions is connected with the existence of an electrical double layer at 
the boundary of watery phase and collodion membrane, whereby the 
water diff^uses into the solution in the form of electrified particles. 
III. When we separate a solution of a non-electrolyte like cane sugar 
from distilled water by a collodion membrane, water diffuses into the 
solution with an initial velocity which is (up to gram molecular concen- 
trations) a linear function of the concentration of the solute. When we 
separate a solution of an electrolyte from distilled water by a collodion 
membrane, water diffuses also into the solute but with an initial velocity 
which for lower concentrations of the solution is no longer a linear but a 
more complicated function of the concentration and the nature of the ions. 
The facts observed can be expressed in the following rules : 
(a) When pure water is separated from a solution of an electrol3rte by 
a collodion membrane, water diffuses into the solution as if its particles 
were positively charged and as if they were attracted by the anions and 
repelled by the cations of the solution with a force increasing with the 
valency and another constitutional quantity of the ion 
{h) When the collodion membrane has previously been dipped for a 
short time into a solution of a protein and if the protein solution is then 
removed Rule a holds also except that in the presence of hydrogen ions 
and of simple cations with a valency of 3 or above, in sufficient concen- 
tration, the particles of water diffuse into the solution as if they were nega- 
tively charged and as if they were attracted by the cation and repelled 
by the anion of the electrolyte with a force increasing with the valency and 
another property of the ion. 
{c) The relative influence of the oppositely charged ions of an electro- 
lyte is not the same for different concentrations of an electrolyte. At 
lower concentrations the influence of that ion prevails which has the op- 
posite sign of charge as the watery phase, while in higher concentrations 
(of many, but possibly not of all electrolytes), the effect of the other 
ion prevails. The turning point lies for a number of electrolytes at a 
molecular concentration of about M/256. Finally a concentration is 
reached where this ionic influence on diffusion ceases and the gas pressure 
effect prevails.^ 
These three rules apply also to solutions of gelatin salts. In the case 
of gelatin-acid salts water is negatively charged and is attracted by the 
gelatin ion (which is positively charged) and repelled by the acid anion. 
This repulsion is greater when the anion is bivalent (SO4) than when it is 
monovalent, e.g., CI. Hence the initial rate of diffusion of water into the 
gelatin-acid solution is greater in the case of gelatin chloride or gelatin 
nitrate, etc., than in the case of gelatin sulfate. 
