44 Mr. S. U. Pickering on the Heat of 



possible to deny the existence of dissociation on the score of 

 the energy changes evolved ; for whatever may be the thermal 

 changes actually accompanying dissolution, it is impossible to 

 say that they are inconsistent with the view that a decom- 

 position into atoms has taken place, since we may bring in 

 the heat of combination of these atoms with the solvent to 

 counterbalance the heat absorbed by the decomposition of 

 the dissolving molecules, and, however improbable such an 

 explanation may appear, we cannot say that is impossible so 

 long as all the quantities concerned are unknown. It is, as 

 van der Waals points out, only the difference between these 

 quantities, and not the real heat of dissociation of the mole- 

 cules, which Arrhenius measured in the work referred to by 

 Dr. Walker : in fact, Arrhenius at the time was basing his 

 results on the very grounds against which my criticism 

 was directed — the absence of action between the solvent and 

 dissolved substance. 



Dr. Walker then declares that I am misrepresenting the 

 views of the dissociationists when I state that, according to 

 them, the electric charges on the ions are the cause of decom- 

 position, and that the opposite charges on the different atoms 

 must be regarded as repelling each other. I did not pretend 

 to be quoting the actual words of the dissociationists, it is 

 true, but I do not see how the expressions which they use can 

 be interpreted in any other sense. Ordinary atoms are 

 represented by them as combining and pairing together to 

 form chemical compounds ; ions, on the contrary, are, as such, 

 incapable of chemical union *, and the only difference between 

 an ordinary atom and an ion, we are told, is that the latter 

 possesses " enormous electrical charges." Therefore, in the 

 absence of any other assigned cause, we can but conclude that 

 these charges are the supposed cause of the difference in the 

 behaviour of these ions and ordinary atoms, and that the 

 union which is possible when we are dealing with ordinary 

 atoms is rendered impossible when these atoms become 

 charged. 



Dr. Walker informs us that the positively and negatively 

 electrified ions in a solution of a dissociated substance " are no 

 longer paired off together," but there is " a complete com- 

 munism amongst " them. No doubt this is a very " elegant 

 theory," but any physicist, I believe, would tell us that a 

 number of + and — electrified particles of matter would not 

 be so accommodating as to remain in communism together. 



* Perhaps, according to van der Waals's deductions, it will now have 

 to be admitted that they are capable of union with solvents. 



