OSMOSIS 



37 



is called osmosis. It is readily demonstrated by experiments 

 with thin animal or vegetable membranes. For instance, when 

 prunes, raisins, or other dried fruit, are put in water to soak, 

 water penetrates the outer skin and swells the seed or fruit, 

 while some of the material from within comes out through the 

 skin and flavors or discolors the water. If whole cranberries, 

 cherries, or plums are put in- 

 to boiling sirup, a similar ex- 

 change takes place, but in this 

 case the fruit is shriveled. 



A still better experiment is 

 that with an egg from which 

 a bit of the shell has been 

 chipped away at the bottom, 

 arranged as shown in Fig. 28. 

 The entrance of water is shown 

 by the rise of some of the con- 

 tents of the egg in the tube. 



49. Inequality of osmotic 

 exchange. The nature of the 

 two liquids separated by any 

 given membrane determines 

 in which direction the greater 



flow Shall take place unless The tube is cemented to the eggshell, into 



what would naturally be the 

 direction of flow is overruled 

 by the selective action of liv- 



FIG. 28. Egg on beaker of water, 

 to show osmosis 



which it opens. At the bottom a large 

 piece of the shell has been chipped 

 away, leaving the thin skin which lines 

 the egg in contact with the water in the 

 beaker 

 ing protoplasm. 



If one of the liquids is pure water and the other is water 

 containing solid substances dissolved in it, the greater flow of 

 liquid will be away from the pure water into the- solution, and 

 the stronger or denser the latter, the more unequal will be the 

 flow. This principle is well illustrated by the egg-osmosis 

 experiment. Another important principle is that substances 

 which readily crystallize and are easily soluble, like salt or 



