542 OSTERHOUT— DYNAMICAL THEORY OF ANTAGONISAl 



the formation of the salt compound which itself accounts for the 

 permeability). They also apply if Naoo^CaCUo is formed else- 

 where than at the surface and subsequently migrates into the surface 

 for, as the reaction is reversible, the equilibrium in the surface must 

 be determined by the amounts of X, NaCl, and CaCla, regardless of 

 whence they are derived. 



Let us consider what will happen if NaCl and CaCL do not 

 migrate equally into the surface. If for example CaCL accumu- 

 lates in the surface ten times as much" as NaCl we shall have in the 

 surface NaCl 2 -j- CaCL i when the body of the solution contains 

 NaCl 20 -f CaCL i (or NaCl 95.24 -f CaCL 4.76). 



Let us assume that this is the case and that the salt compound 

 formed is not NaooXCaCLo but NaoXCaCL. Its maximum amount 

 will be produced when the solution contains NaCl 20 + CaCl. i or 

 NaCl 95.24 -|- CaCL 4.76 and will be independent of the total con- 

 centration of salts so long as the surface is saturated. We may cal- 

 culate the amounts present in the surface according to the formula. ^- 



ConCNa^XCaCU 



A = 



(ConcNaci)HConccac]s)(Concjf) * 



When we have NaCl 95.24 4- CaCL 4.76 in the solution we have in 

 the surface NaCl 9.524 -|- CaCL 4.76 or NaCl 66.67 P^^" cent. -|- 

 CaCL 33-33 per cent. ; and since they are present in excess this will 



11 There is experimental evidence in favor of the view that CaCU accu- 

 mulates in the surface more than NaCl. 

 1- If we write 



2NaCl + CaCl. + U„X ^ Na.H.-.AXa + 4HCI 



we have at equilibrium 



-, _ (ConCNa^H„_ 4 XC.a) (ConCHCl)^ 



(ConcNaCi)^(ConccaCi2) (ConcH„x) 

 but 



ConCHCl=4(ConCNa2H„_4A'Ca) 



so that we may write 



(ConCNa2H„_4A'Ca)^ 



K 



(ConcNacOHConccaCia) (ConcH„x) 



In the present case this assumption does not fit the facts as well as the one 

 already made. 



