153 



The ;iver;ii,'e relative rates ot diffusion ol' tlie zinc in the two sohitions 

 will depend ii]pi:n two eouditions : (a) tlie relative permeability of the 

 nienihranes and (b) the relative conceutratioiis of zinc salt. If the rela- 

 tiv(,> foiicentrations should undergo no change, through the more rapitl 

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

 rates of diffusion si) that the value of m/p before reversal should exactlx' 

 equal the value of p/m after reversal. An insi)ecti(m of the table shows 

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

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

 other, so that more rapid diffusion took place through this membrane and 

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

 to correct for the I'esultant change in concentrations the relative rates 

 of diffusion, m/p and p/m, were diA'ided 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 



m. Cp- 



original solutions, the average corrected ratios sliould be equal unless 

 the zinc were partly in the colloidal, and hence uon-dift'usi))le, condition 

 and this to a different extent in the two solutions. The 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 diffusion of B. I', to B. M. 

 after reversal was l..")2. The actual concentration of diffusible zinc was 

 therefore greater in. the B. yi. solution. This actual concentration of 

 diffusible, crystalloidal zinc will be called the "effective concentration." 

 Let Me = effective concentration of zinc in 1'.. M., 

 I'e = effective concentration of zinc in 15. I'.. 



T = thickness (or density) of membrane Hrst rontaining B. -M.. 

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

 Dm = average rate of diff'usion of B. M. before reversal. 

 Dp =^ average rate of diff'usion of B. P. before reversal, 

 Dm' = average rate of dift'usinn of B. .M. after reversal. 

 Dp' == average rate of diff'usion of F>. P. after reversal, 

 k = a constant, depending upon the temperature ; 

 also let a = Dm/Dp = 2.4.5 and 

 b = Dp'/Dm' = 1.52. 

 I'sing these symbols. 

 Me = kDmT = kDm'T', 

 Pe = kDpT' = kDp'r ; 



