CH. I.] AMPHOLYTES. 31 



conditions of a substance at its iso-electric point are of some 

 interest. They are : 



1 i ) The sum of the anions and kations is at a minimum. 



(2) The concentrations of the anions and kations are 

 equal. 



(3) If an ampholyte be added to a solution, whose [H] 

 is greater than its iso-electric point, it functions as a base, 

 and therefore decreases the [H] of the solution. If it be 

 added to a solution, whose [H] is less than its iso-electric 

 point, it functions as an acid. If the (H) of a solution is 

 no 1 " altered by addition of an ampholyte, then the (H) of 

 the solution must be equal to the iso-electric point of the 

 ampholyte. 



(4) The solubility of ah ampholyte is at a minimum at 

 its iso-electric point. If a colloid the ampholyte flocks most 

 readily at this point. (See Ex. 6.) 



(5) At its iso-electric point, a colloid is electrically 

 neutral. 



The significance of the iso-electric points of various 

 enzymes is discussed on p. 184. The iso-electric points of 

 certain substances of physiological interest are shewn in 

 Table II., p. 32. 



