214 



HYDROGEN ION CONCENTRATION 



or, whether different oil phases were present in layers, as 



salt solution | oil I oil II | salt solution 

 such as, for example. 



Salt solution 



Nitrobenzene 

 + picric acid 



Nitrobenzene 

 without or with 

 less picric acid 



Salt solution 



corresponding to, in the case of the apple, 



Salt solution 



Outer layer 

 of apple peel 



Inner layer 

 of apple peel 



Free fluid of 

 apple pulp 



a- 



The following of Beutner's experiments answered 

 this question. Two places on the apple were con- 

 nected by means of iV/50 KCl solution (fig. 26). 

 In the case of the uninjured apple (I) the E.M.F. 

 was zero, of course. With a shght injury (II), a 

 current of 0.041 volt was produced. With further 

 injury (III) the effect remained unchanged. When 

 the injury or hollowing out was carried on until 

 but 0.25 cm. of pulp remained (IV), the E.M.F. 

 sank to 0.020 volt. And, finally, with the peel alone, 

 (V) an E.M.F. of but 0.01 volt remained. 



On the other hand, when the concentration of the 

 connecting fluid at the uninjured places was varied, 

 the concentration effect appeared exactly the same 

 as in the entirely uninjured apple. 



The interpretation of this observation is only pos- 

 sible when it is assumed that the apple peel does not 

 Fig. 26. (Taken represent a single oil-phase. Only the outermost 

 from Beutner) layer of the peel may represent such a single oil 

 phase, and hence, when placed between two salt solu- 

 tions of the same concentration, it produced no current. Experi- 

 ments II and IV above can only be explained by assuming a varying 

 composition of the peel in its various layers, and that the outer 

 laj^ers contain in their oil phases an organic acid, wliich is absent or 

 is present in a lesser concentration in the inner layers. 



b+ 



