22 PHENOMENA OF THE MIXTURE OF TWO 



cally lighter than the brine ; this mixture rises, and 

 the denser brine descends to occupy its place. 



On the other hand, the pure water receives 

 through the bladder salt, and becomes thereby spe- 

 cifically heavier ; while it sinks to the bottom of the 

 vessel, its place is supplied by water containing less 

 or no salt, and therefore specifically lighter, which 

 again comes in contact with the bladder. As long 

 as the motions just described are perceptible, we 

 observe a constant increase in the volume of the 

 brine in the tube a (Fig. 4), or a diminution in 

 the volume of the pure water in the vessel b. When 

 the motions cease, the rise of liquid in the tube is 

 arrested, and when this takes place, the two liquids 

 are found to possess almost exactly the same specific 

 gravity. 



When the two strata of liquid on either side of 

 the bladder are little different in composition (as 

 soon comes to pass in the experiment (Fig. 2) 

 where the saline contents of the liquid which fills 

 the pores of the bladder can hardly vary from that 

 of the next stratum), the mixture of the liquids 

 takes place, but without further change of volume. 

 But when an exchange of the mixtures on the 

 opposite sides of the bladder can occur in conse- 

 quence of their different specific gravity, and when 

 a continued difference between the strata on oppo- 

 site sides of the bladder is thus determined, then, so 

 long as (in the case of brine and water, for example) 

 one side of the bladder is in contact with a con- 



