158 REVISIONS OF THE THEORY OF ELECTROLYSIS. 



remaining molecules whose ions are firmly bound to each other, and 

 the ratio between the two he called " the activity coefficient.''' 

 The significant conclusions of Arrhenius are : 



1. " That Van't Hoflf's law holds not only for most^ but for all 

 suhstmices, even for those which have hitherto been regarded as 

 excejDtions (electrolytes in aqueous solution).-' 



2, "That every electrolyte (in aqueous solution) consists partly of 

 active (in electrical and chemical relation) and partly of inactive 

 molecules, the latter passing into active molecules on increasing the 

 dilution, so that in infinitely dilute solutions only active molecules 

 exist." 



The ratio of the active to the inactive molecules, or the activity 

 coefficient, is intimately connected with the electrical conductivity of 

 solutions. Molecules dissociated into ions are alone capable of con- 

 ducting or conveying electricity through a solution. The inactive 

 molecules are at best only inert and take no part in the electrical trans- 

 port. The activity coefficient increases with the dilution — that is, the 

 molecular conductivity, which expresses essentially the conductance 

 of a given number of molecules in solution, is greatest when the dilu- 

 tion is such that all molecules of the solute are dissociated. This is 

 the essential significance of the researches on electrolytic conductivity, 

 so far as they bear on the theory of electrolysis. 



The transition from the incidental and almost infinitesimal disso- 

 ciation assumed by Clausius to the ideal infinite dilution and com- 

 plete dissociation taught by the " Leipzig School " marks the essential 

 revision of the theor}- of electrolysis made in recent years. 



The theory of ionization has now passed beyond the bounds of 

 electrolytic solutions. As Van't Hoff imported the gas law into 

 solutions to explain osmotic pressure, so others, like J. J. Thomson, 

 have seized on electric convection by ions to explain electrical dis- 

 charges through gases. It is now conceded that the only tenable 

 explanation of electric currents through gases is tliat of convection 

 by ions. The ionization of gases is brought about by ultraviolet, 

 light, by Roentgen rays, and by the radiations from radio-active 

 substances. The electric charge conveyed by ions in gases appears 

 to be identical with the charge conveyed by ions in an electrolyte in 

 aqueous solution, but the masses conveying negative charges are only 

 about the one-thousandth part of the hydrogen ion. 



The passage of electricity through a gas, as well as through an 

 electrolyte, is accompanied by chemical changes; and chemical decom- 

 position, says J. J. Thomson, is not to be considered an accidental 

 attendant on the electrical discharge, but an essential feature without 

 which it could not occur. 



In reviewing the changes that have occurred in the theory of 



