THROUGH MEMBRANES, OF TWO LIQUIDS. 19 



With reference to the porosity of the bladder, 

 the rapidity of the mixture of the two liquids is 

 directly proportional to the number of particles, 

 which, in a given time, come into contact ; it depends 

 also on the surface (the size of the membrane), and 

 on the specific gravity of the liquids. 



The influence of extent of surface on the time influence 

 required for mixture requires no particular elucida- equaf U 

 tion ; that of the unequal specific gravity is rendered the tSo 

 evident by the following experiments. qm ' 



R . 2 If the bent tube a b (Fig. 2), one end when the 



of which is tied over with bladder, liquid is 

 and the other open, be filled with brine membrane. 

 coloured blue,* and if pure water be 

 placed in the tube c, there is soon per- 

 ceived under the bladder a colourless 

 or nearly colourless stratum of liquid, 

 which continues for hours to float in 

 the same place. If the bent tube a b 

 be filled with colourless brine, while c 

 is filled with pure water coloured blue, there is found, 

 after a time, above the bladder, a colourless or 

 nearly colourless stratum of liquid. 



It appears from this, that an exchange of both 



* For this purpose it is best to take a solution of indigo in 

 sulphuric acid, diluted, and after adding subacetate of lead as 

 long as sulphoindigotate and sulphate of lead are precipitated, to 

 separate the precipitate by nitration and dry up the filtered liquid 

 in the water-bath. A mere trace of the blue residue suffices to 

 colour blue large masses of liquid. 



c2 



