Chap. xxn. ] ENDOSMOTIC EQUIVALENT. 257 



beyond a certain limit, the increase in the quantity of 

 water does not nearly keep pace with the increase of 

 the salt in solution. Thus Graham found that "the 

 osmose absolutely greatest is obtained with small pro- 

 portions of salts in solution." He adds, "osmose 

 appeared, indeed, to be peculiarly the phenomenon of 

 dilute solutions." 



It may also be remarked that the nature of the 

 solutions employed will affect the osmosis by affecting 

 the membrane. Thus, a membrane capable of im- 

 bibing a certain quantity of water can imbibe a much 

 less quantity of alcohol, because of the contracting 

 effect the alcohol has upon the membrane. A con- 

 centrated saline solution has a similar effect. This 

 has been referred to already in discussing imbibition 

 (page 246). This is supposed to be due to the size of 

 the pores being affected. Thus, any substances which 

 would increase the density of the membranes would 

 also increase the endosniotic equivalent. The thick- 

 ness of the membrane, that is, the length of the pores, 

 similarly affects the result. 



If, instead of having pure water on one side of a 

 membrane and a saline solution on the other, a saline 

 solution be on each side, osmotic action will go 011 

 under certain circumstances. If a solution of the 

 same salt be on each side, osmosis will occur if there be 

 a difference of concentration between the two. The 

 increase of volume is on the side of the concentrated 

 solution, and salt passes from it to the more dilute. 

 The action will diminish as the difference between the 

 two becomes less ; but if the difference be maintained, 

 the action will remain constant. Thus, by maintaining 

 the concentration of the one solution, and by constantly 

 renewing the dilution of the other, the greatest effect 

 would be obtained. The concentration of the one 

 being maintained, a stream of the dilute solution 



O ' 



i lowing past the membrane would admirably fulfil the 



R 7 



