PASSAGE OF WATER AND DISSOLVED SUBSTANCES 153 



that the outer fluid, which is free from dye, contains a larger percentage 

 of sodium chloride than the inner solution of dye. This difference is 

 permanent and is more marked the greater the concentration of the 

 dye salt. In the following Table is given the concentrations of the 

 two fluids with different percentages of salt. The numbers indicate 



the litres to which each gramme molecule of the salt is diluted. Appa- 

 rently the difference depends on the fact that the non-dissociated salt 

 must be equal on the two sides of the membrane and that the dissocia- 

 tion is much impeded on the inner side on account of the presence 

 there of another salt of sodium. A sodium salt of any other indiffusible 

 substance, e.g. of a protein such as caseinogen, would behave in a 

 precisely similar fashion. 



