708 Prof. I. Traube: Contribution to the Theories 
It is evident that osmotic velocity and surface-tension run 
parallel. Hence the difference of the surface-tensions (der 
Oberflichendruck *) és the motive force in osmotic phenomena; 
it is to this difference that osmotic pressure is due. 
The origin of osmotic pressure is thus at last brought to 
light, and proved to be of the nature which the author, in 
company with Lothar Meyer t, has maintained from the 
beginning of the discussion, in spite of much unfriendly 
criticism. The migration of water into sugar solutions, as 
also the pressure which is thereby set up, are accounted for 
py the difference between the surface-tensions, and by nothing 
else. It is now evident that the assumption, which regards 
the sugar-molecule as alone responsible for the osmotic 
pressure, was not justified{. Jt must, however, be emphasized 
that the difference between the surface-tensions cannot be 
considered as equal to the osmotic pressure, for this new 
pressure is quite different for isosmotic solutions ; it is in the 
first instance only the measure of the velocity with which 
the osmotic pressure rises, and this osmotic pressure is only a 
counterforce. 
From the foregoing it is evident that the idea of a “ semi- 
permeable membrane” is anything but an absolute one. A 
membrane which is semipermeable to aqueous solutions of 
salts, sugar, and at most such substances as urea, &e., will not 
be so to aqueous solutions of ethyl or amyl alcohol. And 
it may be assumed (but this must nevertheless be established 
by separate experiments) that a membrane impervious, for 
instance, to sodium chlorate from an aqueous solution, becomes 
pervious to the same, if a substance which lowers the surface- 
tension considerably is added to the water. This I intend 
to determine by experiment, and expect it to prove of the 
greatest importance, from both the physiological and the bio- 
logical point of view. 
The theory here stated is capable of wide generalization. 
It leads to a new conception of the phenomena of diffusion 
and dissolution. 
Thus let the membrane separating an aqueous salt solu- 
tion from pure water be eliminated; the phenomena of 
diffusion will then take place. According to the prevailing 
* Compare Pfliiger’s Archiv d. Physiol. Nov. or Dec. 1904. 
+ Lothar Meyer, Zeitschr. physik. Chem. v. p. 25 (1890), and I. Traube, 
Ann. Phys. u. Chem. |xii. p. 490 (1897). 
{ Perhaps a similar fate may be in store for certain other hypotheses 
concerning solutions, and the sceptics be justified in the end! Compare 
I. Traube, Grundriss Physik. Chem. Enke, Stuttgart, 1904, p. 194, and this 
Journal, viii. p. 158 (1904), 
