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The average relative rates of diffusion of the ziue in the two solutions 

 will (leiiend updn two couditions : (a) the relative permeability of the 

 membranes and (b) tlie relative concentrations of zinc salt. If the rela- 

 tive concentrations should undergo no change, through the more rapid 

 diffusion of one solution, the reversal of membranes should change the 

 rates of diffusion so that the value of m/p before reversal should exactly 

 equal the value of p/m after reversal. Au inspection of the table shows 

 that the membrane in which B. M. was enclosed before reversal was thin- 

 ner or less dense, or, from some other reason, more permeable than the 

 other, so that more rapid ditt'usion took place through this membrane and 

 the solution so enclosed was more rapidly diluted than the other. In order 

 to correct for the resultant change in concentrations the relative rates 

 of diffusion, m/p and p/m, were divided by the relative concentrations, 

 Cm/Cp and Cp/Cmtlie resultant corrected values being tabluated as ^'^^ 

 and "^^-^ Since the actual concentration of zinc was the same in the two 

 original solutions, the average corrected ratios should be equal unless 

 the zinc were partly in the colloidal, and hence non-dlffuslble, condition 

 and this to a different extent in the two solutions. Tbe table shows that 

 the average corrected ratio of diffusion of B. M. to B. P. before reversal 

 was 2.45 while the average corrected ratio of dift"usion of B. P. to B. M. 

 after reversal was 1.52. The actual concentration of diffusible zinc was 

 therefore greater in the B. M. solution. This actual concentration ol' 

 diff'usible, crystalloidal zinc will be called the "effective concentration." 

 Let Me = effective concentration of zinc in P.. ^I., 

 I*e = effective concentration of zinc in B. P., 

 T = thickness (or density) of membrane first containing B. M.. 

 T' = thickness of membrane first containing B. P.. 

 Dm =; average rate of dift'usion of B. ;m. before reversal, 

 Dp — average rate of diffusion of B. P. before reversal, 

 Dm' = aA'erage rate of diff'usinn of B. M. after reversal. 

 Dp' = average rate of diff"usion of B. P. after reversal, 

 k = a constant, depending upon the temperature ; 

 also let a = Dm/Dp = 2.45 and 

 b == Dp'/Dm' =. 1.52. 

 Using these symbols, 

 INIe = kDml' = kDm'T', 

 Pe = kDp'I^' = kDp'l' ; 



