626 



SCIENCE 



[N. S. Vol. XXXIV. No. i 



(the ions and un-ionized molecules) as 

 deduced from the conductivities by the rule 

 of Arrhenius, we find that for a binary 

 substance a certain formula connecting 

 concentration and ionization should be fol- 

 lowed, a formula which we know by the 

 name of Ostwald's dilution law. This law 

 seems to be strictly applicable to solutions 

 of feeble electrolytes, but to solutions of 

 strong electrolytes it is altogether without 

 application. "Wherein lies the fundamental 

 difference between these two classes of 

 solutions? Two kinds of explanation may 

 be put forward. First, the ionized propor- 

 tion may not be given accurately for strong 

 electrolytes by the rule of Arrhenius; or 

 second, the strong electrolytes do not obey 

 the otherwise general law of active mass, 

 which states that the activity of a substance 

 is proportional to its concentration. The 

 first mode of explanation has been practi- 

 cally abandoned, for other methods of deter- 

 mining ionization give values for strong 

 electrolytes in sufficient agreement with the 

 values obtained by the method of Arrhenius. 

 The other explanation is that for some rea- 

 son the law of active mass is, apparently 

 or in reality, not obeyed by some or all of 

 the substances in a solution of a strong 

 electrolyte. An apparent disobedience to 

 the law of mass-action would, for example, 

 be caused by the formation of complexes 

 such as NajClo, or NasCl* or NaClj" in a 

 solution of sodium chloride. Mere hydra- 

 tion, e. g., the formation of a complex 

 NaCli 2 HgO, would not affect the mass- 

 action law in dilute solution, and the elec- 

 trolyte would obey the dilution law in solu- 

 tions of the concentration usually con- 

 sidered. A somewhat similar explanation, 

 which takes into account the properties of 

 the solvent, is that the ionizing power of 

 the solvent water undergoes a noticeable 

 change when the concentration of the ions 

 in it increases beyond a certain limit. 



I should wish now to draw attention to 

 a point of view which has not, so far as I 

 am aware, been fully considered. To begin 

 with we may put to ourselves the question : 

 Is it the ions in the solution which are 

 abnormal or is it the non-ionized substance ? 

 A simple consideration would point at 

 once to it being the non-ionized portion. 

 We have, for example, in acetic acid a sub- 

 stance which behaves normally, so that the 

 ions H+ and Ac" as well as the undisso- 

 ciated molecule HAe are normal. Simi- 

 larly in ammonium hydroxide the ions 

 NH^'^ and OH" as well as the non-ionized 

 NH3 and NH4OH all behave normally. 

 When we mix the two solutions there is 

 produced a substance, ammonium acetate, 

 which behaves abnormally. Now, on the 

 assumption that the equilibrium we are 

 now dealing with is 



NH.+ -1- Ac- ?± NH^Ac, 



which of these molecular species is ab- 

 normal in the relation between its concen- 

 tration and its activity? Probably not the 

 ions NH/ and Ac", because these were 

 found to act normally in the solutions of 

 acetic acid and ammonia. The presump- 

 tion is rather that the abnormal substance 

 is the undissociated ammonium acetate, for 

 this occurs only in the abnormal acetate 

 solution, and not in the normal acetic acid 

 and ammonia. This view, that it is the 

 non-ionized portion of the electrolyte which 

 exhibits abnormal behavior, and not the 

 ions, has been reached on other grounds 

 by Noyes and others, and I hope in what 

 follows to deduce reasons in its support. 



One is apt, because the ions are in gen- 

 eral the active constituents of an electro- 

 lyte, to lay too much stress on their behav- 

 ior in considering the equilibrium in an 

 electrolytic solution. We are justified in 

 attributing the fact that acetic acid is a 

 weak acid, whilst trichloracetic acid is a 

 powerful one, rather to the properties of 



