MECHANICS. 45 
larity is nothing else than a mechanical molecular activity, which produces 
the drop and the bubble—the negative drop—and which is modified by the 
influence of the narrow space and of the adhesion. 
d. Endosmosis 
It is well known that a concentrated aqueous solution of any substance 
may be diluted with perfect uniformity throughout; if, however, there be 
no immediate contact between the water and the solution, but the two be 
separated by a porous partition with very fine pores, the liquid must pass 
through these pores to become mixed together. It may very often happen, 
however, that this partition admits of a more ready passage to one liquid 
than to the other, and the levels of the two, in their respective compartments, 
will then be different. Filling, for instance, a glass cylinder closed at the 
bottom by a bladder, with a concentrated solution of blue vitriol (sulphate 
of copper), and placing this in a vessel of water, the water will pass through 
to mix with the solution ; the elevation of the liquid in the inner cylinder 
consequently rises, that in the outer vessel falling. Ifthe inner cylinder be 
the one filled with water, the reverse will be the case, a depression here 
ensuing instead of an elevation. These phenomena investigated by 
Dutrochet, and by him named endosmosis and exosmosis, are exhibited 
sensibly in the apparatus figured in p/. 18, fig. 31, and by its inventor, 
Dutrochet, called endosmometer. The glass vessel, b is closed inferiorly 
by a piece of membrane or bladder, cd, and filled to a certain height with 
alcohol, the upper end stopped by a cork in which a glass tube, a, is fixed 
air-tight. This apparatus is placed in a larger vessel filled with water, and 
likewise closed by a cork, through which passes the tube, a. If the surface 
of water in the latter stand, say at n, equilibrium soon takes place, the 
surface of the alcohol standing perhaps at n’. Endosmosis now commences, ' 
the water penetrates the bladder against the resistance of the alcohol, and 
the alcohol column rises above v’, finally running out of the open end of 
the tube. If the experiment be reversed, so that the water shall occupy 
the place of the alcohol in the smaller vessel, the level will fall in the latter, 
owing to an ensuing exosmosis. Both operations continue until the liquids 
on each side of the membrane are homogeneous, and the difference of level 
is simply the result of the pores of the membrane being too minute to per- 
mit the action of hydrostatic pressure: for, if this membrane be moistened 
even on the side opposite to the liquid, no drops are found. Endosmosis 
and exosmosis play a great part in the organic world, since absorption and 
the distribution of the nutritious juices are almost entirely results of these 
operations. 
