( 732 ) 
on that wall from the inside and from the outside (of 1 atm.). This 
now is a perfectly unacceptable result, as immediately appears from 
What follows. Let us imagine the same solution as in the bell jar 
inclosed in a eylinder with a piston under the pressure of its satu- 
rated vapour p— Ap, where Ap is the decrease of vapourpressure. 
The cane sugar molecules contribute nothing to that pressure or hardly 
anything *), as appears from the fact that they cannot pass into the 
vapour (at least not in a measurable degree); all the pressure is 
furnished by the water molecules. Now we compress the liquid, till 
it has got a pressure P+ p, it is now in perfectly the same con- 
dition as the liquid in the bell jar, when we except the immediate 
neighbourhood of the membrane. On the supposition made just now 
the water molecules would exert a pressure p against the piston, the 
sugar molecules a pressure P, i.e. the pressure of the latter would 
have increased by an amount about 1000 times that of the former, 
whereas their initial pressure was at least a hundred thousand times 
smaller. And the result would be that the, let us say 2, sugar mole- 
cules, which are found to every 1000 water molecules would exert a 
pressure twice as great as the 1000 particles together. It is beyond 
doubt that the pressure P+ p on the piston or the glass wall of 
the bell jar is exclusively exerted by the watermolecules, and if he 
meant this, Lornar Meyer was certainly right when he asserted *), 
that the osmotic pressure was a result of the collisions of the solvent. 
Also in this respect the theory of the gaslike character of the dissolved 
substance falls short, as it leaves perfectly unexplained why in an 
isolated solution, e.g. a cane sugar solution, which in a glass vessel 
stands under atmospheric pressure, nothing is perceived of the gaslike 
character of the dissolved substance. For that in this case solvent 
and dissolved substance are less closely in contact than in the 
osmotic experiment, cannot seriously be asserted. 
§ 3. If therefore we must not seek the explanation of the 
laws of the osmotic pressure in a particular condition of matter, 
characteristic of dilute solutions, then the remarkable fact formulated 
by Van ’r Horr calls the more peremptorarily for an explanation. 
Nobody less than Lorentz and BOLTZMANN have made attemps to 
do this *), but even their endeavours do not seem to me to have solved 
the problem entirely. In saving this | agree with Prof. Lorenrz’s own 
opinion, at the beginning of his paper he terms it a “freilieh nur zum 
Teil gelungene Untersuchung”. As to the reasons of this partial failure, 
however, L shall most likely differ in opinion with Prof. Lorentz. 
1) Perhaps the pressure of these molecules would even prove to be negative, 
2) Zsch. Phys. Ch. 5, 23. 
