DAVID I. HITCHCOCK 



609 



Since it had been noticed that the agreement between observed and 

 calculated p.d. was better when the solution had a higher concen- 

 tration of electrolyte, the experiment of Table VI was repeated with 

 all solutions m/512 with respect to NaCl. The results are given in 

 Table VII. 



The agreement with the theory is excellent up to pH 3, but again 

 becomes poor above pH 4. In comparing Tables VI and VII it 

 may be observed that the presence of m/512 NaCl had more effect in 

 decreasing the p.d. of those solutions which contained less HCl. This 



CO 



I 





ptl 1.0 1.5 2.0 2.5 aO 3.5 4.0 45 5.0 



Fig. 5. Effect of pH on p.d. observed and calculated for 1 per cent edestin 

 chloride. 



is in line with the experiments already described on the effect of salt 

 concentration on the p.d., indicating that the depression of the p.d. is 

 due to the anion. 



In order to obviate any error in the calculated p.d. which might be 

 due to difficulty in determining accurately the pH of the very dilute 

 acid in some of the outside solutions, an experiment was run in which 

 both inside and outside solutions were buffered by m/100 sodium ace- 

 tate and different concentrations of acetic acid. The results are 

 given in Table VIII and Fig. 6. 



