48 ATTRACTION OF MEMBRANES 



If the cause of the change of volume in this 

 experiment were the unequal resistance which the 

 bladder opposes to the passage of the two liquids 

 with equal attraction (equal force) on both sides, 

 the phenomenon just described would be inexplica- 

 ble ; for a resistance can no doubt impede, but is 

 not capable of producing, motion. But we see, 

 that the water in this experiment is raised to a 

 higher level, and moreover, the tearing asunder of 

 the drop can only be the effect of a powerful attrac- 

 tion, residing in the substance of the bladder. 

 One liquid If the moistening of solid bodies by liquids be 

 another the effect of a chemical attraction, the force of 

 membrane, which is different in dissimilar liquids, it follows, 

 that when a porous body is saturated with a liquid, 

 and brought in contact with a second liquid, which 

 has a stronger attraction for its substance than the 

 first has, then the first liquid must be displaced 

 from the pores by the second, even in the absence 

 of hydrostatic pressure, and this, whether the two 

 liquids be miscible or not. 



We may suppose that the attraction of the 

 second liquid, of more powerful affinity, which dis- 

 places the other, is equal to the pressure of the 

 column of mercury required to force the latter 

 through the porous substance. 

 menTto ^ we *i e over one en( l ^ a cylindrical tube with 



prove this. 



then fill it with brine, and place it in pure water, the volume of 

 the liquid in the tube increases exactly as if the mercury were not 

 there. 



