26 GENERAL PROPERTIES OF LIVING TISSUES 



Dip the tension indicator into a soap solution. 



A thin layer of the solution will span the 

 frame on both sides of the dividing wire. The 

 tension of the membrane on one side of the di- 

 viding wire compensates that on the other and 

 the wire will not move. 



Hold the frame in a vertical position. The 

 cross wire will sink slightly, owing to the force 

 of gravity. Absorb the lower membrane with 

 filter paper. 



The cross wire will at once be lifted against 

 the force of gravity by the surface tension of the 

 remaining membrane. Destroy the remaining 

 membrane and the wire will fall again. 



2. Strew lycopodium 1 upon a water surface. 

 In the centre place a few drops of alcohol. 



The ; lycopodium will be driven in all direc- 

 tions. The surface tension of alcohol is less 

 than that of water. The water-air surface and 

 the alcohol-air surface are therefore not in 

 equilibrium. The water-air surface contracts 

 violently, and the alcohol-air surface expands, 

 producing the strong currents made visible by 

 the motion of the lycopodium. 



Electrolysis. 1. Connect two dry cells in 

 series (carbon of one cell connected with zinc of 

 other). Attach wires to the terminal zinc and 



1 Be careful not to briiig the lycopodium near a flame. 



