ioo A. P. MATHEWS 



In studying the action of any salt on an albumin solution, the real 

 question to be answered is: What will be the result upon the solu- 

 bility and state of the colloid of replacing the ion already in combina- 

 tion with the proteid by some other ion containing a different amount 

 of potential energy? We have to know, therefore, before we can 

 answer the question of the action of any salt on a colloid, what the ion 

 is which is already in combination with it. This is a very important 

 point, which is frequently overlooked in studying the action of salts. 



To get a clear idea of what happens when a salt is added to an 

 albumin solution, let us consider first, the condition of affairs in 

 the sodium albumin solution in which the proteid exists as Na -f albumi- 

 nate. As the colloid stands in a saturated solution, it is in a condition 

 of equilibrium. The sodium ion has separated a certain distance 

 from the albumin ion. The distance it moves depends, no doubt, on 

 several factors, but the most important will probably be its tendency 

 to go into solution i. e., its solution tension.* The positive ion of 

 sodium repels a negative charge with a power equal to 2.54 volts. 

 What the negative solution tension of the albumin ion is, unfortunately 

 is unknown. The effect of the positive charge on the sodium will 

 be, of course, to neutralize the negative charge on the albumin, 

 but, owing to the fact that the sodium repels the negative charge and 

 holds its positive charge so firmly, it is unable to neutralize it, and the 

 colloid remains in solution. We have, in other words, an equilibrium 

 between dissociated and undissociated sodium albuminate. 



The question, then, to be solved is this : What effect will it have on 

 the solubility of the colloid if we replace the sodium ion by another 

 ion containing a different quantity of potential energy, i. e., having a 

 different ionic potential? One of two results may be anticipated: 

 either the dissociation will increase and the colloid go more completely 

 into solution, or it will diminish and the colloid be more or less com- 

 pletely precipitated. 



If we introduce an ion of higher potential than sodium, evidently 

 the state of equilibrium can no longer be the same. Energy will 

 pass from the positive ion to the albumin, and will in some degree hold 

 or neutralize its negative charge. We may imagine that the new 



*Many facts indicate that one of the most important factors in determining the ionization of salts 

 is the ionic potential of its ions. For example, compare the ionization constants of the iodide, chloride, 

 and bromide of mercury or silver; or compare the ionization of silver and sodium nitrates. 



