E. J. COHN, J. GROSS, AND O. C. JOHNSON 



155 



The flow of current during cataphoresis was measured, as has been 

 said, by a silver coulometer in series with the apparatus. Since the 

 juice of the potato contains both free electrolytes and electrolytes 

 combined with tuberin, deductions regarding the transference of cur- 

 rent by tuberin cannot readily be drawn from these data (Table III). 

 It would be reasonable to suppose, however, that as the acidity of 

 the solutions increased their specific conductivity would be increased 



TABLE III. 



Migration of Protein in Potato Juice during Cataphoresis. 



* Citrate mixture used. 



t m/60 phosphate mixture used. 



$ Cataphoresis continued for 17^ hours. 



because of the high mobility of hydrogen ions. None the less, the 

 flow of current during cataphoresis seems to pass through a maxi- 

 mum at a hydrogen ion concentration slightly less than 10~*N (Table 

 III). Presumably conductivity passes through a maximum in the 

 neighborhood of the isoelectric point. 



The hydrogen ion concentration which numerically represents the 

 isoelectric point of tuberin reveals the relatively stronger acid proper- 



