OF VITAL PHENOMENA 25 



this sort of phenomenon was found even before the law of mass 

 action was so widely applied, and is known as Ostwald's dilu- 

 tion law. 



If a represents the degree of dissociation of such an electrolyte, 

 of which one mol is dissolved in v liters, the concentration of 



a 

 the cations and of the anions is — , and of the undissociated 



v 

 1 — a 



molecules . Two reactions are going on at the same time, 



v 

 the dissociation of the molecules into ions and the recombina- 

 tion of the ions to form molecules. The rapidity of dissociation 



1 — a 

 depends on the concentration of the molecules, — — , and the re- 



v 

 combination on the product of the concentrations of the two 



a a a a 1 — a 



classes of ions, — X — , and at equilibrium, — X — = c , 



v v v v v 



a a 

 — X — 

 v v 

 where c is a constant, or = c 



v 



3 2 



by division we obtain = c. From this equation it is 



v(i— a)_ 

 seen that ionization increases with dilution. Expressed in words, 

 it means that the greater the dilution the farther removed the 

 ions are from one another and the less chance they have of 

 colliding with one another and recombining to form molecules, 

 or the chance of their meeting is equal to the product of the 

 concentration of the anions and the concentration of the cations. 

 This formula does not hold for the strong electrolytes, and 

 Rudolphi (1895) and van't Hoff have applied the empirical 



a 3 



formula, = c, to them. One reason that the strong 



v(i— a 2 ) 

 electrolytes do not seem to obey the law of mass action may be 

 that they form different hydrates at different dilutions. Some 

 of these hydrates have been crystallized and others detected in 

 other ways. Not only some molecules, but also all ions are sup- 



