Kohlenberg—Osmosis and Osmotic Pressure. 217 
the water in B and chloroform in A, nothing will take place, 1 
for these oils are not appreciably soluble in water, that is to 
say the attraction or affinity existing between them and water 
is insufficient to overcome their cohesions to the extent neces¬ 
sary to cause a fusion, a blending, an interpenetration of their 
masses. Again, if the water in B were replaced by a liquid in 
which neither ether nor chloroform are appreciably soluble, 
nothing would take place. Further if the chloroform A be re¬ 
placed by a liquid which does not dissolve water and has less 
attraction for ether than has water, nothing will take place. 
It is clear then that the process under consideration proceeds 
because of the specific nature of the septum B and also that of 
the two liquids that bathe it. It should also be emphasized in 
this connection that while it is essential, as stated above, that 
the layer B, the water, must be capable of dissolving C, the 
ether, it is further necessary that this solubility be restricted 
in character, as it is in fact, otherwise the layer B, would not 
be distinct from C and would become so rich in ether that the 
boundary lines between A and B would also disappear. 
Returning now to the original experiment Fig. 1 in which 
ether, water and chloroform are in A, B, and C respectively, let 
us imagine the aqueous layer B as quasi solid and also immov¬ 
able, i. e. attached firmly to the sides of the glass tube, never¬ 
theless otherwise retaining its original properties. This would 
make A a compartment whose volume remains fixed, and as the 
ether enters it from B, for reasons already detailed, a hydro¬ 
static pressure would be produced upon the sides, top and bot¬ 
tom of A; and as this pressure develops, it would become more 
and more difficult for additional ether to enter this compart¬ 
ment. Finally, if the walls of this compartment did not give 
way, a point of maximum pressure would be reached. At this 
point, at the temperature of the experiment, the affinity of the 
i If olive oil be dissolved in ether and this solution placed in C, 
whereas water and chloroform are retained in B and A respectively, 
the ether would pass through the water into the chloroform leaving 
the olive oil behind in C. We have here an illustration of what may 
be called selective action on part of the membrane (the aqueous sep¬ 
tum B) in which property biologists are particularly interested. The 
explanation is obvious. Water dissolves ether appreciably, but not 
olive oil, so the latter is left behind. 
