DIFFUSION AND OSMOSIS 



31 



Now fill one arm of the U-tube with dilute hydrochloric 

 acid and the other arm with dilute caustic soda. As these 

 substances diffuse through the gelatin, they will color the 

 litmus blue or red as 

 the case may be, and 

 the progress of the 

 diffusion can be ob- 

 served. If the solu- 

 tion is kept in a cool 

 place, the potassium 

 bichromate need not 

 be added. FlG 7 



NaOH 



Ulmus'-fclue b 

 Diffused Nad 



HOI 



Litmus red by 

 diffused HCr 



..Gelatin colored 

 with neutral Litmus 



18. DIFFUSION 



Diffusion may be shown in several other ways. It is not 

 advisable to make much of this phenomenon since it does not 



enter very largely into elementary 

 study of plants. Some of these exer- 

 cises should therefore be optional. 



I. Arrange a U-tube as in Fig- 

 ure 7. Fill the bend with gelatin 

 which has been rendered insoluble 

 by addition of potassium bichro- 

 mate. After the gelatin has set, 

 fill one arm with strong copper 

 sulphate and the other with potas- 

 sium bichromate or any other 

 highly colored salt. These liquids 

 will diffuse and the advance can 

 be observed as it goes on. 

 II. Fill a glass tube with gelatin to which a little phenol- 

 phthalein has been added. Stand the tube in a beaker con- 



Phenolphthalein 



Caustic 

 Soda 



