Summary. 351 



the existence of a simple approximate relation between the value of the 

 nn-ionized fraction and the product of the valences of the ions; the small 

 effect of temperature on the ionization of salts and a parallelism between 

 the magnitude of that effect and the effect upon the dielectric constant 

 of water; the validity of an exponential relation between ionization and 

 concentration, which differs from that required by the mass-action, and 

 which is approximately the same at all temperatures and for different 

 ionic types of salts ; and the fact that the optical properties and other 

 similar properties of dissolved salts (when referred to equal molal quan- 

 tities) is independent of this concentration and therefore of their ioniza- 

 tion, so long as the solution is even moderately dilute. 



The molecular explanation of these facts and the more general con- 

 clusions drawn from them would seem to be that primarily the ions are 

 united somewhat loosely in virtue of their electrical attraction to form 

 molecules, the constituents of which still retain their electric charges and 

 therefore to a great extent their characteristic power of producing optical 

 effects and such other effects as are not dependent on their existence as 

 separate aggregates. Secondly, the ions may unite in a more intimate 

 way to form ordinary uncharged molecules, whose constituents have com- 

 pletely lost their identity and original characteristics. These two kinds 

 of molecules may be designated electrical molecules and chemical mole- 

 cules, respectively, in correspondence with the character of the forces 

 which are assumed to give rise to them. Now in the case of salts and 

 most of the inorganic acids and bases, the tendency to form chemical 

 molecules is comparatively slight, so that the neutral electrical molecules 

 greatly predominate. On the other hand, in the case of most of the 

 organic acids, the tendency to form chemical molecules is very much 

 greater, so that as a rule these predominate. The facts, moreover, indi- 

 cate that chemical molecules are formed from the ions in accordance with 

 the principle of mass-action,* but that electrical molecules are formed in 

 accordance with an entirely distinct principle, whose theoretical basis is 

 not understood. 



It is to be expected that with neither class of substances will the pre- 

 dominating type of molecule be alone present; and that minor deviations 

 from the mass-action law in the case of moderately ionized substances, 



*The best evidence of this is that furnished by the change of the conductivity of 

 slightly ionized electrolytes with the concentration ; but distribution experiments also 

 indicate it. Thus it is probable that as a rule the chemical molecules alone distribute 

 into the gaseous phase or into organic solvents and that therefore the concentration 

 of the substance in such phases is a measure of the concentration of those molecules 

 in the aqueous solution ; and the few experiments thus far published indicate that 

 the latter is at least approximately proportional to the product of the concentrations 

 of the ions. (Compare the experiments on picric acid by Rothmund and Drucker, 

 Z. phys. Chem., 46, 826. 1903.) 



