32 



DIFFUSION AND OSMOSIS 



taining any alkali in solution. As the alkali diffuses upward 

 through the gelatin, the phenolphthalein will take on the 

 characteristic crimson color (Fig. 8). 



III. Repeat this exercise, using gelatin colored with dilute 

 acidulated litmus and alkali in the beaker. Neutralization 

 is well illustrated by using a U-tube as in Figure 7 and 

 filling the arms with acid and alkali, while the bend is filled 

 with neutral litmus in gelatin. 



IV. If copper sulphate and potassium ferrocyanide are 

 used, they will meet and form a membrane in the midst of 

 the gelatin, 



19. OSMOSIS 



Object. To learn what is meant by osmosis and 

 dialysis. 



Apparatus. Several collodion bags (see Note) or pieces of thin 

 animal membrane (such as sheep gut or fish air bladder), starch, 

 sugar, egg albumin, etc. 



Method. Suspend the bags in cups of clear water as 

 follows : A containing starch paste, B containing sugar 



solution, and C a 

 mixture of starch 

 paste and sugar 

 solution (Fig. 9). 



After a half hour, 

 test some of the 

 water outside of 

 each bag for the substance which was put inside. Which 

 ones have diffused through the membrane? 

 Diffusion through a partition is called osmosis. 

 Query. Will starch, egg albumin, olive oil, sugar, or 

 salt diffuse through a partition? 



