368 



ABSORPTION. 



Fig. 101. 



The instrument which he employed in his experiments was 

 named an endosmometer. It may consist of a graduated 

 tube expanded into an open-mouthed bell 

 at one end, over which a portion of mem- 

 brane is tied (fig. 101). If now the bell be 

 filled with a solution of a salt say chloride 

 of sodium, and be immersed in water, the 

 water will pass into the solution, and part 

 of the salt will pass out into the water ; the 

 water will pass into the solution, much more 

 rapidly than the salt will pass out into the 

 water, and the diluted solution will rise in 

 the tube. To this passage of fluids through 

 membrane the term Osmosis is applied. 



The nature of the membrane used as a 

 septum, and its affinity for the fluids sub- 

 jected to experiment have an important 

 influence, as might be anticipated, on the 

 rapidity and duration of the osmotic current. 

 Thus, if a piece of ordinary bladder be used 

 as the septum between water and alcohol, the current is 

 almost solely from the water to the alcohol, on account of 

 the much greater affinity of water for ' this kind of mem- 

 brane ; while, on the other hand, in the case of a membrane 

 of caoutchouc, the alcohol, from its greater affinity for this 

 substance, would pass freely into the water. 



Various opinions have been advanced in regard to the 

 nature of the force by which fluids of different chemical 

 composition thus tend to mix through an intervening 

 membrane. According to some, this power is the result 

 of the different degrees of capillary attraction exerted by 

 the pores of the membrane upon the two fluids. Prof. 

 Graham, however, believes that the passage or osmose of 

 water through membrane may be explained by supposing 

 that it combines with the membranous septum, which thus 

 becomes hydrated, and that on reaching the other side it 

 partly leaves the membrane, which thus becomes to a 



