206 



HYDROGEN ION CONCENTRATION 



ways use NaCl at the left end var5dng the salt at the right end, the 

 latter will be negative whenever the difference between the oil- 

 solubiUties of its two ions is less than that between the oil-solubiHties 

 of the two ions of the NaCl solution; and it will be positive when this 

 difference is greater. If we should vary only the cation on the right 

 side solution, the right end will become the more negative the more 

 oil-soluble is the cation in comparison with the Na+ ion. If only 

 the anion is varied, then the right end will become the more positive 

 with the increasing oil-solubiKty of this anion in comparison with 

 the Cl~ ion. In Beutner's experiments shown in table 32 0.1 N 

 NaCl solution was used uniformly on the left side (of the oil) and on 

 the right 0.1 iV solutions of the salts indicated in the first column of 



TABLE 32 



Salt 



(a) NaCl 



(b) Nal 



(c) NaSCN 



(d) Dimethylaniline-HCl 



(e) KCl 



(f) CaCU 



o-Toluidine 



IV 



millivolts 







+ 133 

 + 140 



- 25 







+ 10 



the table. In experiments a, b, c the anion was varied. It will be 

 seen that the positive effect increases in the series Cl~, I~, SCN~. 

 We must therefore conclude that this also represents the sequence 

 of the increasing oil-solubility of the ions. In fact, the ionic series 

 remains unaltered regardless of the oil used for the middle phase of the 

 chain. It is true that the quantitative differences between the ions 

 may not remain the same, but the sequence in the series is unchanged 

 These ionic series, which we encounter here for the first time and to 

 which we shall return later more extensively, are as follows: 



Decreasing negative effect, — decreasing oil solubility 

 Cations K Na Ba Ca Mg 



Increasing positive effect, — increasing oil-solubility 

 Anions SOi CI Br I SCN 



