Chap. XXII.] OSMOSIS. 251 



leaving soda salts in a more concentrated form in the 

 cell. 



Salts can be even decomposed by diffusion. Thus 

 from a solution of bisulphate of potash placed in a 

 cell the sulphuric acid was found to diffuse to about 

 double the extent, in equivalents, of the sulphate of 

 potash, so that in the outer jar were found bisulphate 

 of potash and sulphuric acid, and a few crystals of the 

 neutral sulphate were seen to deposit in the cell. 

 Again, a solution of common potash-alum was de- 

 composed by diffusion into alum and sulphate of 

 potash. A simple way of effecting this diffusion 

 separation is to place in a cylindrical glass jar a 

 quantity of distilled water to make a liquid column 

 five or six inches high. Under this column, by means 

 of a fine pipette, introduce the mixed solution. 

 After several days the water may be siphoned off 

 in several layers, as it were. Less and less of the 

 least diffusive substance will be obtained, the higher 

 one goes in the liquid, the most diffusive substance 

 being able more completely to free itself from the 

 other as it ascends in the column of water above it. 

 Finally, it was observed that the diffusion of one salt 

 was not very sensibly affected if it was allowed to 

 diffuse into a solution of another salt instead of into 

 pure water, even though the two salts were isomor- 

 phous. That is to say, a solution of one salt will 

 diffuse almost as readily into a solution of another salt 

 as into water. The experiments were not made, 

 however, with any but dilute solutions of the other 

 salt in the outer jar. 



Osmosis. The laws of capillarity and of diffusion 

 have been applied to explain some very remarkable 

 phenomena first observed by Dutrochet, and described 

 by him in 1837. The elementary phenomena are 

 these : if a tube is closed at one end with bladder or 

 other animal membrane, and is, after being filled with 



