JACQUES LOEB 



223 



the two solutions. They were connected by a bent glass tube, filled 

 with a pure HNO3 solution, of the same pH as that in the 

 two beakers. Into each beaker was dipped a calomel electrode with 

 saturated KCl solution and the diffusion potential was ascertained 

 with the aid of a Compton electrometer. Fig. 7 gives the p.d. A 

 comparison between Figs. 5 and 7 shows that the curves represent- 

 ing the P.D. in the two cases are very similar. 



If we now return to a discussion of the curves in Figs. 1 and 2, repre- 

 senting the influence of the pH on the attraction of a m/256 solution 

 of a neutral salt for water through a collodion membrane impregnated 



I 

 I 





150 

 125 



100 r 

 75 



50 



Z5 





 pH 1.6 ZO 2.2 Z4 2.6 28 3.0 3.2 34 3.6 3B 4D 42 4.4 46 4B 5.0 5.2 



Fig. 6. Influence of m/128 cane sugar, m/256 NaCl, CaCU, CeCls, and Na2S0* 

 on the initial rate of diffusion of water through collodion membranes not treated 

 with gelatin. Otherwise the experiment is the same as in Fig: 2. Abscissae are 

 the pH; ordinates, rise of level of water in salt solution after 1 hour. Only 

 Na2S04 attracts water to a noticeable amount since the latter is positively charged 

 when diffusing through the membrane. 



with gelatin, we can say that these curves resemble the curves in 

 Fig. 3 for the p.d. on the opposite sides of the membrane. 



Figs. 4 and 7 show that the p.d. curves in Fig. 3 have a double 

 source. One is connected with the influence of the gelatin layer on 

 the unequal distribution of the acid on the opposite sides of the mem- 

 brane, which finds its explanation probably in the Donnan effect. 

 The other source of the p.d. seems to be the diffusion potentials as 

 shown in Fig. 7. 



These diffusion potentials which exist regardless of the presence or 

 absence of a membrane and regardless of the nature of the membrane 

 seem to be responsible for the fact that the ions with opposite sign 



