LIQUIDS THROUGH A MEMBRANE. 



21 



perceptible, although the mixture of the liquid pro- 

 ceeds, and the water in c becomes constantly more 

 charged with salt, while the brine in a b loses salt. 



If we reverse the positions of the two liquids in when the 

 the apparatus Fig. 2, or what is simpler, if we close 

 with bladder a tube 1 centimetre (-r^ths of an inch) 

 wide, fill it with brine, and immerse the end closed 

 with the bladder in a wider vessel filled with pure 

 water, giving to the tube an inclination of about 45, 

 we may observe (most distinctly when both liquids 

 contain some fine particles of indigo suspended) in 

 both liquids a continual motion. 

 We see in the tube (Fig. 3) a cur- 

 rent of liquid rising from the blad- 

 der in the direction of the arrow, 

 and flowing down again on the op- 

 posite side. A similar circulation 



is observable in the 



vessel of water. 



If the tube #, with brine, is about 

 2 centimetres (fths of an inch) wide, 

 and if we support it vertically in the 

 vessel b of water, the motion proceeds 

 from the middle, and in both the tube 

 and the vessel we perceive currents 

 in opposite directions. (Fig. 4.) 



These currents hardly require explanation. To 

 the brine in the tube a, pure water passes through 

 the bladder ; there is formed above the bladder a 

 mixture containing less salt, and therefore specifi- 





