ENDOSMOSIS.
100
through the capillary conduits of the plate, and
this flow would have become perceptible by
the sinking of the water in the tube, the inte¬
rior of which was only two millimeters in dia¬
meter.
The result of this experiment was that the
plate of marble, which was four centimeters in
diameter, did not lose by filtration, in one
day, more than the small quantity of water
capable, by its subtraction, of lowering its
level one millimeter and a half in the tube.
I next tried syrup in this endosmometer, the
reservoir being plunged into pure water ; but
no endosmosis was induced. I now reduced
the thickness of the plate of marble to one
millimeter and a half; in this state it lost by
filtration, in the course of a day, eleven mil¬
limeters of water measured by the tube. The
permeability of this plate was, as may be per¬
ceived, very sensibly increased : still the en¬
dosmometer which it closed when filled with
syrup showed no indications of endosmosis.
1 reduced the thickness of the plate of marble
to one millimeter. In this state it lost by fil¬
tration, in the space of a day, twenty-one milli¬
meters of water measured in the tube. I put
into the endosmometer, which this plate of
marble closed, the same syrup which had been
used in the preceding experiments, and the
density of which was 1.12, and I now ob¬
tained an endosmosis which manifested itself
by an ascension of seven millimeters in four-
and-twenty hours. This last experiment proved
to me that carbonate of lime was not, as I had
hitherto found it, totally without the power to
produce endosmosis. I wished to compare
this plate of marble with a piece of bladder of
the same surface under the double point of
view, of their permeability, and their respec¬
tive properties of producing endosmosis. Having
therefore taken off the plate of marble which
closed the endosmometer, I replaced it by a
piece of bladder whose permeability to water I
measured in the same manner as above. I found
this permeability very nearly equal to that of
the plate of marble of one millimeter in thick¬
ness. I then put into this endosmometer
some syrup similar in density to that which I
had used in the same endosmometer closed
with the plate of marble. The endosmosis
which I obtained raised the syrup seventy-three
millimeters in three hours. Thus the permea¬
bility to water being equal in the bladder and
in the plate of marble, the endosmosis pro¬
duced by the first was to the endosmosis pro¬
duced by the second as 584 is to 7, a most
extraordinary difference, and difficult to be
accounted for. These experiments prove that
carbonate of lime is but very little apt to pro¬
duce endosmosis, in which it differs singularly
from baked clay, thin laminae of which are
almost as apt to produce endosmosis as organic
membranes.
The varieties of sulphate of lime which may
be employed in endosmometrical experiments
are not sufficiently numerous or of sufficient
variety of permeability for it to be possible to
appreciate the properties of this substance in
relation to endosmosis. I found that the sul¬
phate of lime used in the manufacture of
plaster in the environs of Paris, employed in
thin plates to close an endosmometer, did not
produce endosmosis. But this mineral is per¬
haps too easily permeable. In fact it is found
impossible to obtain endosmosis when the in¬
terior fluid of the endosmometer flows easily
by filtration, in virtue of its weight, through
porous plates. I should say as much of plates
of freestone (grés) which I have employed
without success in these experiments, but that
I recollect to have obtained the phenomenon
in a very slight degree with a plate of freestone
very close-grained and very little permeable to
fluids.
I have tried a variety of experiments shew¬
ing that an increase of temperature increases
endosmosis. This result has been confirmed
by repeated experiments.
The quantity of the same fluid introduced
by endosmosis, and with the same sort of per¬
meable partition, is generally in proportion to
the extent of surface of this partition. The
following experiment demonstrated this fact.
I took two endosmometers, the membranes of
which, taken from the same bladder, were of
diameters in the relation of one to two ; I filled
the reservoirs of these two endosmometers with
syrup of equal density, and then plunged them
into pure water. I had taken care to weigh
them previously with great exactness. After
continuing the experiment for two hours, I
weighed the instruments afresh, and found in
the large endosmometer four times as great an
increase of weight as in the small one, which
proved that the first had introduced, by endos¬
mosis, four times as much water as the second.
This relation was exactly that of the extent of
surface of their respective membranes, the
diameters of which were as one is to two, and
their surfaces consequently as one is to four.
I have thus enumerated the effects ; let us
now endeavour to ascertain their causes.
The first idea which presented itself to my
mind to explain the phenomenon of endosmosis
was that it was owing to electricity. We know
that effects exactly similar to those of endos¬
mosis are produced by means of the electricity
of the voltaic pile in the experiment of M.
Porret, inserted in the Annules de Chimie,
vol. xi. p. 137. This naturalist having divided
a vessel into two compartments by a septum of
bladder, filled one of the compartments with
water, and put only a small quantity in the
other. Having placed the positive pole of the
pile in communication with the compartment
full of water, and the negative pole with the
compartment containing little water, the fluid
was forced through the bladder from the full
compartment into the almost empty one, and
there rose to a higher level than that to which
it was reduced in the original full compart¬
ment.
I varied this experiment by applying it to my
own apparatus. I put pure water into an
endosmometer, the membrane of which was
plunged into water. I made the interior water
of the endosmometer communicate with the
negative pole of the pile, and the exterior
