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PRINCIPLES OF GENERAL PHYSIOLOGY 



acid are dissociated ; then, if V is the volume of the solution containing one 

 molecule of the electrolyte : 



a a 1 a 



(H') = ^, and also (A') = ^, since they are equal to each other, and (HA) = ^ . 



Therefore : 



o a . 



= y x V * 



l-a_ a 2 V 

 "IT ~ V( 1 - a) 



This result was worked out by Ostwald (1888), and is known as his "Dilution 

 Law." It is found experimentally to apply to weak acids and bases. To salts, 

 strong acids, and bases a different law applies, a law which is not dependent on 

 mass action, as described above (page 182). 



It will be seen that, when the dilution law applies, the constant K (known as 

 the "dissociation constant" or "affinity constant") is independent of dilution 

 and is valuable in comparing the strength of the electrolytes concerned. The 

 following series may be found useful. The basic constants, of course, indicate the 

 strength as bases, and are obtained from the concentration in OH' ions. The 

 substances with both acidic and basic properties are known as " amphoteric," and 

 will be discussed later. 



TABLE OF DISSOCIATION CONSTANTS 



Physiological Action of Hydrogen and Hydroxyl Ions. The great activity of 

 these ions in physiological processes will be seen in various phenomena to be 

 described in. later pages. This activity is undoubtedly in many cases connected 

 with their great rate of migration, as compared with other ions. It has been 

 suggested that this unusual rate is due to a special effect on the molecules of the 

 solvent. 



We have already had occasion to refer to the action of even very small 

 concentrations of H' or OH' ions on the sign of the electrical charge of colloidal 

 particles. Especial attention may also be called to the great sensitiveness of 

 enzymes in this respect, probably in great part due to the colloidal nature of 



