102 A. P. MATHEWS 



lower than the albumin, it will have an opposite or precipitating 

 action, since then the colloid will tend to give up its charge to it. 



These conclusions are confirmed by my results on sodium albumi- 

 nate, and those of Osborne and Harris on edestin. 



From these general considerations the conclusion may be drawn that 

 the precipitating action oj the salt on the colloid will be proportional to 

 the difference between the ionic potential of the positive ion already com- 

 bined with the colloid and that substituted jor it; and that the dissolving 

 action oj the anion will be proportional to the difference in potential of 

 the anion of the colloid and that we introduce; or 



Precipitating action =E csait E c co]loid . 

 Dissolving action = E a sa i t E a c^oid- 



In this formula E c salt is the ionic potential of the cation of the salt 

 introduced, and E c colloid that of the cation of the colloid. E a salt 

 and E a colloid are the values for the anion? . 



Since these two actions are mutually antagonistic, the actual action 

 of the salt will be equal to the difference between them, or 

 Actual action = precipitating dissolving action 



= El salt E" colloid ~ - 



If the result is positive, the salt should precipitate ; if it is negative, 

 it should dissolve the colloid. If it is zero, the salt should not affect 

 the colloid except by mass action or by action on the water. In other 

 words, the actual action of any salt on a colloid in solution will be pro- 

 portional to the difference between the ionic potentials oj the ions oj the 

 salt y minus the difference in ionic potentials oj the ions oj the colloid. 



Let it be assumed that the logarithm of the dilution of the least 

 precipitating concentration, or the logarithms of the dilution of solu- 

 tions of equivalent dissolving power, are proportional to the actual 

 action of the salt. 1 This gives the following equation: 



log V=K[(&-E) - (E"-E iv )] + const. (2) 



Comparing two salts with the same sign of action, i. e., dissolving or 

 precipitating. 



log V^K^-Ef)- ("-")] +const. 

 log V 2 =K[(^ 2 -^) - ("-")] +const. 



log =tf (-E - (- (3) 



See Fig. I, p. 96. 



