CAUSES OF THE MOTION OF JUICES. 



355 



filled to the neck, and immersed the bladder in a vessel of 

 water. lie sa\v the liquid rise in the narro\v 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 T V that of the 

 membrane, and the narrow tube itself is 

 provided with a millimeter scale, we 

 have the Osmometer of Graham, fig. G7. 

 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 i; intended for the reception of w.v- 

 ter. The funnel-shaped interior vessel is closed below with membrane, 

 and stands upon a shelf of perforated zinc for support. The graduated 

 tube tits the neck of the funnel by a ground joint. 



Action Of the Membrane. \V~hen 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. 



Fiir. 07. 



