The changes in pH in the titration of carboxy methyl cellulose or pectin are much larger than those derived from the molecular dimensions on the basis of current theories. The possible causes of this discrepancy are discussed.

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Simultaneous measurements of osmotic pressure and permeation of solute have been made for a nonfractionated polystyrene with a number of membranes of widely different permeability. It is shown that, even after many days, no real equilibrium is reached in an osmometer with a membrane permeable to part of the polymer. The theory of equilibria in such osmometers is developed and shows that, in first approximation, the distribution of permeating solute over the two osmometer cells is not affected by the presence of nonpermeating solute. In second approximation, this distribution is affected indeed, but in this approximation the osmotic pressure is not affected by this unequal distribution. Some short‐time experiments also show that when the number of permeated molecules is negligible (t → 0) the contribution of a molecular species to the osmotic pressure is less than the value given by equilibrium thermodynamics if the membrane is not completely impermeable to that molecular species. This phenomenon is in accordance with the theory of permeability of membranes based upon nonequilibrium thermodynamics.

The osmotic pressure of solutions of sodium pectinate and three samples of sodium carboxy methyl cellulose in aqueous solutions of sodium chloride were measured in a Fuoss and Mead osmometer. The primary aim was to obtain the molecular weights of the samples. As a by‐product the change of osmotic pressure with polymer concentration and salt content was studied. The reduced osmotic pressure proves to be a linear functon of the polymer concentration. The slopes of the lines p/c versus c vary with the concentration of the sodium chloride in a manner which is in reasonable agreement with the predictions of the Donnan equilibrium. An accurate check is impossible because the activity coefficients are not known.