Dissociation into Ions, and its Consequences. 21 



a conclusion I have already disputed (Phil. Mag. vol. xxix. 

 p. 490, and 'Nature,' xlii. p. 626) ; but theoretical objections of 

 a fundamental character can, I believe, be raised against this 

 dissociation theory, and, though I have already alluded to 

 these, they have not yet been fully discussed. Manv of the 

 'questions which are asked in the following pages can no doubt 

 be answered satisfactorily, but as far as I am aware this has not 

 yet been done, and it is certainly incumbent on the supporters 

 of the theory to give physicists and chemists a clear concep- 

 tion of what their theory involves. 



When hydrochloric-acid gas, for instance, is dissolved in 

 water, the molecules, which were intact to start with, become 

 resolved into their ions, so that each of these acts as if it were 

 a separate unit. This I believe is, according to the theory, the 

 total and only change which occurs : the water remains in the 

 same state in which it was to start with. The resolution of 

 HC1 into H and CI atoms has been held of necessity to involve 

 an absorption of heat, an absorption considerably in excess of 

 that which we know occurs when it is resolved into hydrogen 

 and chlorine molecules ; and, whether the ions are identical 

 with free atoms or not, we have the positive statement of 

 Arrhenius, the originator of the present dissociation theory, 

 that the resolution of a body such as hydrochloric acid into its 

 ions absorbs heat*. If then this, which is the only change, 

 absorbs heat, whence comes the 17,300 cal. which are, as a 

 matter of fact, evolved during dissolution ? 



In the communication to which reference has been made, 

 Arrhenius does not consider the thermal results of dissolution, 

 and a subsequent consideration of these seems to have led 

 some of the supporters of the theory to hold a view diametri- 

 cally opposed to that just quoted. They now hold, I believe 

 that the decomposition of molecules into their ions evolves 

 heat ; that that heat, which they still admit must be absorbed 

 by the decomposition of the molecules into ordinary atoms, is 

 more than counterbalanced by the combination of the atoms 

 with electric charges. This change of front must rather be 



* Arrhenius, Bitrag till Rongl. Svensha Vetenskaps-Akade?m'ens Hand- 

 lingar, Stockholm, 1883-4. Out of several sentences I may quote the 

 following italicised passage :— " La transformation de l'etat inactif en l'e'tat 

 actif d'un hydrate (faible) est accompagnee par une absorption de 

 chaleur;" and the heat absorbed in the transformation is named 

 "chaieur d'activite." The terms used in the above must be translated 

 into the more modern language of the dissociationists, thus : inactive = 

 undissociated ; active = dissociated into ions; hydrate=any hydrogen 

 compound, such as an acid or base ; feeble = not much dissociated. See 

 also Lodge's epitome of Arrhenius's paper, B. A. Report, 1886, pp. 361- 

 o84. 



