22 Mr. S. U. Pickering on the Theory of 



inferred indirectly from the writings of dissociationists than 

 from any definite retraction which they have published ; nor 

 does it appear to have been followed by all the supporters of 

 the theory, for the explanation given by Arrhenius of the 

 constancy of the heat evolved on neutralizing acids with bases 

 is that it is in all cases due to the combination of the ions H 

 and OH to form H 2 0, and this explanation was quoted as 

 recently as September last (B. A. meeting) by Shaw as being 

 one of the strongest arguments in favour of the theory. It 

 may also be remarked that up to July 1889 Ostwald seems 

 to have held both views, and to have adopted either just as the 

 exigencies of the case suggested : he explains the normal 

 heat of neutralization as being due to the heat evolved in the 

 formation of a molecule from its ions (' Outlines of General 

 Chemistry,' 1890, p. 368), and the abnormal heat of neutraliza- 

 tion as being due to heat evolved in the formation of ions 

 from a molecule, though not, of course, the same molecule as 

 in the previous case (p. 369) . 



The first point, therefore, on which the dissociationists 

 should give us definite information is, whether the dissociation 

 of a molecule into ions is supposed to evolve or absorb heat. 



Presupposing that the answer will be that heat is evolved 

 (at any rate in cases similar to that of hydrochloric acid), 

 their theory cannot be said to be prima facie inconsistent with 

 the conservation of energy ; but other very serious difficulties 

 arise which call for explanation. 



The idea of heat being evolved by the combination of a 

 charge with an atom involves the conception that the charge 

 is originally independent of the atom : indeed the main idea 

 of the theory seems to lie in the distinction between an ion, or 

 charged atom, and an ordinary or uncharged atom*. We 

 may ask, therefore, whence come these charges ? All the 

 ordinary means by which bodies become charged seem to 

 be absent in the present case. No external energy has been 

 expended, no friction can be supposed to exist except such as 

 might result indirectly from an attraction between the water 

 and the acid ; but even if the existence of such an attraction 

 were admitted, it could never cause sufficient friction to over- 



* Cf. Ostwald, loc. cit., p. 275 : — " What actually exists in the solution 

 is single potassium atoms with enormous electrical charges. We do not 

 know what those charges are in reality, but this we do know, that the 

 chemical properties of substances are greatly altered by electrical charges. 

 ... As soon as the potassium atoms in solution lose their charge, as they 

 do, for example, when led b} T an electric current to a platinum wire, where 

 thej r can give up their electricity, potassium with its ordinary properties 

 is at once produced, as is seen in its ability to decompose water with 

 evolution of hydrogen." 



