September 2, 1909J 



NATURE 



28' 



anioni* us who are versed in the facts ; to speak of electrons 

 and use dots instead of dashes may serve to mislead the 

 unwary, vifho hang on the lips of authority, into a belief 

 that we have arrived at an explanation of the phenomena, 

 but those who know that we have reached only the Ict-it-be- 

 granted stage and who feel that the electron is possibly 

 but a figment of the imagination ' will remain satisfied 

 with a svmbolic system which has served us so long and so 

 well as a ineans of giving simple expression to facts which 

 wc do not pretftnd to explain. Not a few of us who listened 

 to the discussion of the nature of the atom at Leicester 

 could not but feel that the physicists knew nothing of its 

 structure and were wildly waving hands in the air in the 

 endeavour to grasp at an interpretation which would permit 

 ■of mathematical interpretation being given to the facts. 

 Until the credentials of the electron are placed on a higher 

 plane of practical politics, until they are placed on a prac- 

 tical plane, we may well rest content with our present 

 condition and admit frankly that our knowledge is in- 

 sufficient to enable us even to venture on an explanation 

 of valency. 



In 1SS5 and again in i888, I ventured to call in ques- 

 tion the interpretation of valency which Hclmholtz had 

 given in the Faraday lecture in iSSi. On the present 

 occasion, I would insist still more emphatically on the 

 insufficiency of the atomic charge hypothesis ; especially 

 that it affords no satisfactory explanation of variable 

 valency and of those fine shades of difference which are 

 manifest, especially in the case of nitrogen, when the 

 radicle attached to the dominant element is varied. In 

 1885 I discussed this question with reference to the nature 

 of electrolytes and questioned the conclusion Helmholtz 

 arrived at that electrolytes belong to the class of typical 

 compounds the constituents of which are united by atomic 

 aflfinities, not to the class of molecular aggregates. The 

 opinion I then ventured to give was as follows : — 



" The current belief among physicists would appear to 

 be that primarily the dissolved electrolyte — the acid or the 

 salt — is decomposed almost exclusively. We are commonly 

 told that sulphuric acid is added to water to mahe it con- 

 duct, 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 molecitlar aggregate, for it is an undoubted 

 fact that HCl and HjSO, dissolve in water, forming 

 'hydrates.' This production of an ' electrolytical sys- 

 tem ' 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 agree- 

 ment 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 been little but a conspiracy 

 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 observations has not 

 been sufficiently appreciated. Perhaps the most remarkable 



^ In my opinion the e-\perimental evidence is in no way satisfactory'. It 

 appears to me to be desirable that in studying the phenomena of electric dis- 

 charge in gases and especially in vapours of complex "substances, the horrible 

 pitfalls should be taken into account with which the field of work is studded ; 

 unless every precaution to secure purity — precautions such as Baker and 

 Dewar have taught us to use— be taken at every step, the conclusions based 

 on all such observations must be open to grave doubt. 



- Compare Chem. -Soc. Trans. i8q5, 1122 : Royal Soc. Proc. 1886, xl., 

 ^68; iqo2, Ixx.. go ; tqoi, Ixxii., 258 ; 1904, Ixxiii., 537; 1Q06, Ixxviii.. 264; 

 1907. Ixxix., 586 ; 1908, Ixxxi., 80 ; Science Pra^vss, April, igoQ, 



NO. 2079, VOL. 81] 



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 per- 

 sistently 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 momen- 

 tary displacement of the molecules wlien 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 adja- 

 cent electrode. .Apparently these considerations are applic- 

 able 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 change contemplated be one in- 

 volving development of energy. It is important to remem- 

 ber also that a change which could not otherwise take 

 place becomes possible when a suitable depolariser is 

 introduced into the circuit. 



The evidence that similar considerations apply to the 

 gaseous and the liquid states cannot well be gainsaid. 

 Before framing a theory of chemical change it is therefore 

 necessary to formulate a definition of an electrolyte. It is 

 doubtful if any single substance be an electrolyte ; the 

 conductivity of fused salts may well be and probably is 

 conditioned by some admi-xture. Aqueous solutions of 

 alkalies, acids and salts without exception are electrolytes. 

 Everything points to the fact that in such solutions the 

 solvent and solute act reciprocally ; the contention that the 

 solute alone is active cannot be justified. As water is 

 altogether peculiar in its activity as a solvent and is a 

 solvent which gives rise to conducting solutions, an 

 explanation of its efficiency must be sought in its own 

 special and peculiar properties. 



Since 1886 this conclusion has been impressed upon me 

 with indisputable force, and 1 have frequently ascribed the 

 effect produced by the one constituent upon the other in a 

 solution to the residual affinity of the negative elements in 

 the two compounds which act reciprocally. It was only 

 recently, however, that I saw my way to postulate a 

 complete theory which would serve to account for the 

 properties of solutions and generally that I realised how 

 the reciprocal effect might be produced. 



I would substitute for the misleading conception that 

 liquids are comparable in their behaviour with gases the 

 idea that the liquid state is one in which the residual 

 affinity of the negative elements in particular always comes 

 into play and causes the formation of molecular aggregates 

 of various degrees of complexity ; moreover, that the 

 alteration in the properties of anv given solvent by the 

 dissolution in it of another substance is largely, and, in some 

 cases, mainly due to a disturbance of the equilibrium 

 natural to the solvent by an alteration in the proportion 

 in which the several aggregates are present. The alteration 

 in some particular property produced in a given mass of 

 the solvent may, from this point of view, be taken as the 

 measure of the activity of a substance, just as the alteration 

 in the pressure of a particular volume is taken as the 

 measure of the alteration produced in a gas. In the case 



