CAUSES OF THE MOTION OF JUICES. 



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 jiassage 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 tV 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 osmometer 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 iatended for the reception of wa- 

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

 and stands upon a shelf of perforated zinc 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 difi-usioi^m^ai^be |reatl^changed. 



Fig. 67. 



