In Investigations on the theory of Brownian movement, he says that osmosis holds for solute particles but not for Brownian ones, since they are too big to pass through a permeable membrane.

So what? Why should this prevent such Brownian particles to exercise pressure?

Later on, one reads

But a different conception is reached from the standpoint of the molecular-kinetic theory of heat. According to this theory a dissolved molecule is differentiated from a suspended body solely by its dimensions

In my view, this argument seems totally uncorrelated from the previous one, even though in the paper they are contiguous. I don't understand the reasoning.

  • 2
    $\begingroup$ If the Brownian particle can not go through the membrane, then the membrane is indistinguishable from a sheet of steel. It has no influence on the other side, it does not interact with the other side. Since this is associated with the size of the Brownian particle, it makes sense to contrast the second section using size as well. $\endgroup$
    – Jon Custer
    May 4 at 15:26
  • $\begingroup$ Ok, but... what happens concretely? I mean... If I put a membrane, do suspended particles exert pressure (even if they're too big for the membrane) or not? $\endgroup$
    – ric.san
    May 4 at 15:46


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