150 



ISOELECTRIC POINTS OF PROTEINS 



be accounted for by differences in procedure. This variation was 

 no greater than the variation in the amount of tuberin in the juice, 

 but neither the amount of the precipitate nor its volume was depend- 

 ent merely upon the concentration of protein. More probably it 

 was related to differences in the content of electrolytes in the juice, 

 for the addition of sodium chloride had a great effect upon the behavior 

 both of the acid and of the alkaline precipitate. 



TABLE I. 



Measurements on Potato Juice. 



This is illustrated by the experiment recorded in Table II in which 

 different amounts of sodium chloride were added to juice to which 

 the same amount of hydrochloric acid had been added. The rates 

 of setthng and the volumes of the resulting precipitates were observed 



