ENERGY AND FORCE 



51 



there would have been no change in the level of the liquids, but 

 osmosis would have taken place just the same, as indicated by the 

 color of the liquids. The same experi- 

 ment may be performed with a solution 

 of sugar with excellent results. By 

 tasting the water in the jar, the pres- 

 ence of sugar may be detected. 



The essential for an experi- 

 ment illustrating osmosis is to 

 have two solutions of different 

 densities separated by a semiper- 

 meable partition. Water will 

 pass through a membrane several 

 times as fast as a strong salt solu- 

 tion, and hydrogen will diffuse 

 four times as rapidly as air. 



Osmosis is important in the 

 distribution of food to the differ- FIG. 45. Osmosis, 

 ent parts of plants and animals. Note the h ^ t t ^ e the liquid in 

 That part of digestion known as 



absorption is largely osmotic action, the food passing 

 through the walls of the stomach and the intestines. 

 Since only substances known as crystalloids pass through 

 animal membranes, starch, which is an amorphous sub- 

 stance and a very important article of food, is changed 

 to sugar before it is absorbed. This particular kind of 

 osmosis is called dialysis. 



Plants get most of their nourishment from the' soil, 

 and osmosis seems to furnish a logical explanation of the 

 absorption of food by the roots of plants. By the pro- 

 cess of osmosis the roots take in food in the form of dilute 

 solutions which contain the plant food, while the denser 

 solution of cell sap inside the roots does not pass readily 



