Kohlenberg—Osmosis and Osmotic Pressure. 257 
what higher. The explanation of this was, o?f course, per¬ 
fectly obvious at once. The pressure is produced by the en¬ 
trance of solvent into the omsotic cell, consequently right on 
the inner side of the membrane the solution becomes more di¬ 
lute than at other points in the interior of the cell. If the cell 
is left undisturbed the very slow processes of diffusion seek to 
equalize the strength of the solution in the cell, but clearly 
shaking the apparatus, or better yet, stirring the interior con¬ 
tent of the cell would at once accomplish what it would take 
diffusion processes a very long time to do, even though they be 
aided somewhat by gravity owing to the form of the osmotic 
cell. And it was, moreover, perfectly {evident, too, that [to 
shake the osmometer filled as it was with considerable pressure 
on, would not thoroughly mix the contents of the osmotic cell. 
It is clear that with a more dilute solution in immediate con¬ 
tact with the inner side of the membrane than is in the rest 
of the osmotic cell the maximum osmotic pressure can not be 
attained. Furthermore, as in cells slightly different in form 
when left perfectly at rest the dilute layer in contact with the 
inner side of the membrane would in general not disappear at 
the same rate by diffusion and disturbances due to gravity and 
difference of density of the layers, concordant results could not 
be expected in duplicate experiments, however carefully per¬ 
formed, without stirring the contents of the osmotic cell. In 
all direct measurements of osmotic pressures which have for 
their aim the determination of the maximum pressure attainable 
in a given case, it is consequently necessary to continually stir 
the interior contents of the osmotic cell while the measurement 
is being made, in order that the concentration of the contents 
of the cell may remain uniform and a layer of maximum con¬ 
centration be kept in immediate contact with the inner side of 
the septum. Again,, since there really is no such thing as a 
semi-permeable membrane in the strict sense of the word—which 
fact has already been emphasized above—it is evident that some 
of the inner content of the cell, be it ever so slight, is making 
its way through the membrane into the outer liquid. Thus right 
next to the membrane on the side bathed by the outer liquid, 
the septum is really not in contact with the pure solvent—the 
17 
