PRESIDENTIAL ADDRESS. 433 
but the chemist desires to know why the solution becomes conducting. it may 
be that in all cases the ‘‘typical compound ”’ is the actual electrolyte—i.e., the 
body decomposed by the electric current—but the action only takes place when 
the typical compounds are conjoined and form the molecular aggregate, for it 
is an undoubted fact that HCl and H,SO, dissolve in water, forming ‘‘ hydrates.”’ 
This production of an “‘electrolytical system ’’ from dielectrics is, I venture to 
think, the important question for chemists to consider. I do not believe that 
we shall be able to state the exact conditions under which chemical change will 
take place until a satisfactory solution has been found.’ 
The position is not very different now. Although the propagation of 
the ionic dissociation cult has assumed the form of a fine art, we are 
still as far as ever from agreement as to the nature of chemical change; the 
speculation has not helped us in the least to clarify our ideas; at most we 
learn that interactions are between ions, and even these, as a rule, are 
supposed to remain apart until they enter into the solid state. Throughout 
all these years I have never varied my opinion that the dissociation hypo- 
thesis is incompatible with the facts. On more than one occasion I have 
stated definite reasons which induce me to deny its usefulness’ and these 
arguments have never been met; in fact, there has heen little but a con- 
spiracy of silence on the part of the upholders of the creed. 
A large amount of work bearing on the subject has been done, chiefly 
by H. Brereton Baker. Strangely enough, no proper notice of his results 
has been taken outside England, and even there the importance of the observa- 
tions have not been sufficiently appreciated. Perhaps the most remarkable 
feature in the situation is that Baker himself scarcely seems to be alive to 
the meaning of the evidence which he has supplied ; the attitude which he has 
displayed in his recent Wilde lecture can only be described as halting. Baker 
has shown, in case after case, that the occurrence of change is dependent on 
the presence of moisture, his greatest feat perhaps being the observation that 
it is possible not only to prepare nitrous anhydride in the solid and liquid 
states but to volatilise it unchanged if only water be excluded. 
I venture to think there is only one point of view from which the problem 
of chemical change can be approached, that, namely, which we owe to 
Faraday—to which hitherto justice has in no way been done—on which I 
dwelt persistently in my previous address: that the forces termed chemical 
affinity and electricity are one and the same. In every case of chemical 
change there is a coincident electrical change, an electric flux; on the 
other hand, every case of electrical change is accompanied by chemical 
change—some alteration in molecular configuration is effected; the force of 
chemical affinity is in some way disturbed by a momentary displacement of 
the molecules when a current passes through a conductor. Such being the 
case, the conditions determinative of chemical change can only be those 
which permit of an electric flux. Two substances in apposition do not 
give rise to a current; at least three are required to determine a slope of 
potential. Chemical change can only take place if one of the three be an 
electrolyte. In all cases apparently the chemical change supervenes upon 
the electrical, the electrolyte being resolved into its ions, one of which at 
least combines coincidently with the adjacent electrode. Apparently these 
considerations are applicable to changes generally. And it should be added 
that, according to this view, the catalyst actually determines the occurrence 
of change. 
The only other criterion which it is: necessary to apply in order to 
decide whether change be possible in any given case is to consider if the 
* Compare Chem. Soc. Trans., 1895, 1122; Roy. Soc. Proc., 1886, 40, 268; 1902, 
70, 99; 1903, 72, 58; 1904, 78, 537 ; 1906, 78, 261; 1907, 79, 586; 1908, 81, 80 ; Scienca 
Progress, April 1909, 
1909, Br 
