" A classic experiment by
Dutrochet, effected about 1830, makes this phenomenon clear. Into pure
water is plunged the lower part of a vertical tube containing pure
alcohol, open at the top and closed at the bottom by a membrane, such
as a pig's bladder, without any visible perforation. In a very short
time it will be found, by means of an areometer for instance, that the
water outside contains alcohol, while the alcohol of the tube, pure at
first, is now diluted. Two currents have therefore passed through the
membrane, one of water from the outside to the inside, and one of
alcohol in the converse direction. It is also noted that a difference
in the levels has occurred, and that the liquid in the tube now rises
to a considerable height. It must therefore be admitted that the flow
of the water has been more rapid than that of the alcohol. At the
commencement, the water must have penetrated into the tube much more
rapidly than the alcohol left it. Hence the difference in the levels,
and, consequently, a difference of pressure on the two faces of the
membrane.
Pages:
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202