CAUSES OF THE MOTION OF JUICES. 355 
filled to the neck, and immersed the bladder in a vessel of 
water. He saw the liquid rise in the narrow tube and fall 
in the outer vessel. He designated the passage of water 
into the funnel as endosmose, or inward propulsion. At 
the same time he found the water surrounding the funnel 
to acquire the taste of salt. The outward transfer of salt 
was his exosmose. The more general word, Osmose, ex- 
presses both phenomena; we may, however, employ Du- 
trochet’s terms to designate the direction of osmose. 
Osmometer.— When the apparatus employed by Du- 
trochet is so constructed that the size of 
the narrow tube has a known relation 
to, is, for example, exactly ;'; that of the 
membrane, and the narrow tube itself is 
provided with a millimeter scale, we 
have the Osmometer of Graham, fig. 67. 
The ascent or descent of the liquid in 
the tube gives a measure of the amount 
of osmose, provided the hydrostatic pres- 
sure is counterpoised by making the level 
of the liquid within and without equal, 
for which purpose water is poured into 
or removed from the outer vessel. 
Graham designates the increase of vol- 
ume in the csmometer as positive osmose, 
or simply osmose, and distinguishes the 
fall of liquid in the narrow tube as nega- 
tive osmose. 
In the figure, the external vessel is intended for the reception of wa- 
ter. The funnel-shaped interior vessel is closed below with membrane, 
and stands upon a shelf of perforated zine for support. The graduated 
tube fits the neck of the funnel by a ground joint. 
Action of the Membrane.—When the membrane itself 
has an attraction for one or more of the substances between 
which it is interposed, then the rate, amount, and even di- 
rection, of diffusion may be greatly changed. 
