PHARMACODYNAMICS OF SALTS AND DRUGS 101 



ion no longer can move so far from the albumin, and in consequence 

 more nearly neutralizes its charge. The result is that the surface of 

 the colloidal particles will be reduced, the surface tension will be 

 increased and the colloid will be less stable. In another way of 

 putting it, the dissociation is somewhat reduced and consequently 

 some of the colloid tends to precipitate. If, in fact, the ion used to 

 supplant the sodium has a sufficiently high potential, it will practically 

 not leave the colloid at all, the dissociation will be greatly reduced, the 

 negative charges almost neutralized, and precipitation will occur. 

 If the ionic potential of the introduced ion is still higher, it may oxidize 

 the colloid; i. e., an actual exchange of charges will take place between 

 the albumin and the ion. 



If, however, an ion of lower potential is introduced in place of the 

 sodium, the reverse of these processes will take place. lonization 

 will be increased, the negative charge will be freer, and the solubility 

 of the colloid will be greater. This will be the case if potassium is 

 substituted for the sodium, provided that potassium has a lower ionic 

 potential than sodium, as is generally assumed, and that no other 

 factors come into play. 



It is, therefore, clear that the effect of any salt upon a saturated 

 colloidal solution of albumin in which the albumin is electronegative 

 will depend chiefly upon what ion is in combination with the colloid 

 when the salt is introduced. 



The quantitative differences in the effects of different salts must 

 depend upon the differences in the ionic potentials of the ion in com- 

 bination with the proteid and that substituted for it. 



So far, we have considered only the r61e of the positive ion. That 

 of the negative ion is also of importance, but somewhat more diffi- 

 cult to picture to ourselves. We may, however, look at it in this 

 way. The different negative ions introduced have different ten- 

 dencies to deposit on the colloid, and give up their negative charges 

 to it. This tendency is measured by the ionic potential of the ion. 

 If the negative ion does deposit, it will tend to increase the negative 

 charge on the colloid, and hence to dissolve it. The higher the ionic 

 potential of the anion introduced, the greater must be its dissolving 

 action on the colloid, since the greater will be its tendency to give its 

 negative charge to the albumin. If the ionic potential of this ion is 



