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Updated: August 17, 2024
Such are the essential facts of osmosis. We may seek to interpret them and to thoroughly examine the mechanism of the phenomenon; but it must be acknowledged that as regards this point, physicists are not entirely in accord. In the opinion of Professor Nernst, the permeability of semi-permeable membranes is simply due to differences of solubility in one of the substances of the membrane itself.
Nevertheless, in the case of gases, there exists an excellent example of a semi-permeable wall, and a partition of platinum brought to a higher than red heat is, as shown by M. Villard in some ingenious experiments, completely impermeable to air, and very permeable, on the contrary, to hydrogen.
Only then will equilibrium be established; and, at that moment, an excess of pressure will naturally be produced in that recipient which, at the commencement, contained the gas with the smallest quantity of hydrogen. This experiment enables us to anticipate what will happen in a liquid medium with semi-permeable partitions.
Pfeffer, by producing these walls in the interstices of a porous porcelain, has succeeded in giving them sufficient rigidity to allow measurements to be made. It must be allowed that, unfortunately, no physicist or chemist has been as lucky as these two botanists; and the attempts to reproduce semi-permeable walls completely answering to the definition, have never given but mediocre results.
It was interesting to try to reproduce artificially semi-permeable walls analogous to those thus met with in nature; and Traube and Pfeffer seem to have succeeded in one particular case.
May it not therefore be supposed that there must exist dividing walls in which this difference of permeability becomes greater and greater, which would be permeable to the solvent and absolutely impermeable to the solute? If this be so, the phenomena of these semi-permeable walls, as they are termed, can be observed in particularly simple conditions.
Stevens disconnected all the lights save one, and so shielded that one before turning it on that it merely lightened the utter darkness into a semi-permeable gloom. He then stepped up to the lookout plate, and with his hand upon the control, pondered long the possible consequences of what he wished to do. "What harm would it do to take just a little peek?" "I don't know that's the dickens of it.
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