Manchester Memoirs, Vol. hi. (1908), No. 10. 37 



therefore, the essence of the change in the state of 

 chemical combination. 



The source of the energy required for the natural 

 degree of ionisation which occurs when, say, K.HO 

 is dissolved in water, has been a standing problem in 

 this department. The current mode of explanation 

 seems so far sound, that when a dilute base is neutralised 

 by an acid, say K.HO by H.Cl, the resulting heat 

 is derived from the free ions H and HO clashing 

 together at high speed generated by their strong electric 

 attraction, as H^O does not exist sensibly ionised — that 

 therefore the heat evolved is about the same per chemical 

 equivalent in all such cases. But when K.HO is added to 

 water, whence comes the supply of energy demanded for 

 the pulling apart of the K and the HO, into separated 

 ions, against their mutual attraction ? The concomitant 

 absorption of heat is far too slight to account for it* We 

 are tempted to conclude that internal potential energy is 

 released owing to the ions falling into relations of closer 

 affinity with the solvent, and that the process is nearly a 

 self-contained interchange of energy, reversible as regards 

 each molecule separately, being a steady static drawing 

 apart of the ions unaccompanied by the generation of 

 violent subsidiary electronic motions whose energy would 

 escape into the general store of heat. The fact above 

 alluded to, that in voltaic batteries so large a proportion 

 of the chemical energy is usually mechanically available, 

 also seems to point this way ; it shows, too, that the 

 fundamental interchanges of electrons at the electrodes, 

 which are the sources of the transformation of energy, are 

 intrinsically of the same not merely reversible but almost 



* Cf. G. F. FitzGerald : Helmholtz Memorial Lecture, Trans. Chem, 

 Soc, 1896: "Scientific Writings," p. 363 seq., also p. 521. 



