DIFFUSION AND OSMOSIS 33 



DIALYSIS 



Test the liquid outside the bag C containing both starch 

 and sugar. Does only one or do both substances come 

 through the partition? In this way it is possible to separate 

 diffusible from non-diffusible substances by using a mem- 

 brane. This method of separation is called dialysis, and the 

 partition used is known as a dialyzer. 



Conclusion, State briefly the meaning of the terms 

 osmosis and dialysis. 



Note. A collodion bag is easily made by pouring collodion 

 into a perfectly clean, dry, cylindrical dish and then pouring off all 

 that will flow out. A thin film of collodion will thus be left lining 

 the vessel. It may be removed by carefully loosening the edge and 

 pulling it gently. To prevent tearing, a little water poured be- 

 tween the film and the glass will help to loosen it. Before trying to 

 remove the film, hold the dish in the hand to warm it. This will 

 hasten the evaporation of the ether contained in the collodion. 



20. OSMOSIS 

 Object. To prove that osmosis may produce pressure. 



Apparatus. An egg, a piece of glass tube, sealing wax, a 

 tumbler. 



Method. With the point of a knife blade, carefully pick 

 away the shell at the large end of an egg so as to expose the 

 delicate skin (membrana putaminis) which lines the shell. 

 But in no case let this membrane be ruptured. 



Then pierce a small hole through the opposite end so as to 

 expose the white of the egg. 



Place the glass tube (a) over the hole and fasten it with 

 sealing wax. Now arrange the egg in a glass of water so 

 that the membrane is in contact with the water (i) (Fig. 10). 



EXP. EOT. 3 



