552 Professor Svante Arrhenius [June 3, 



WEEKLY EVENING MEETING, 



Friday, June 3, 1904. 



Hts Grace The Duke of Nobthumberland, E.G. D.C.L. F.R.S., 

 President, in the Chair. 



Professor Svante Arrhenius, of Stockholm, Ron. Mem. B.I. 



The Development of the Theory of Electrolytic Dissociation. 



At first sight nothing seems to be more evident than that everything 

 has a beginning and an end, and that it is possible to divide every- 

 thing. Nevertheless, the philosophers of antiquity, especially the 

 Stoicists, concluded on purely speculative grounds, that these opinions 

 are not at all necessary. The wonderful development of science has 

 reached the same conclusion as these philosophers, especially Empedo- 

 cles and Democritus, who lived about 500 years e.g., and for whom 

 the ancients had already a vivid admiration. 



Empedocles professed that nothing is made of nothing, and that 

 it is impossible to annihilate anything. All that happens in the 

 world depends upon a change of form, and upon the mixture or the 

 separation of bodies. Fire, air, water and earth are the four ele- 

 ments of which everything is composed. An everlasting circulation 

 is characteristic of Nature. 



The doctrine of Democritus still more nearly coincided with our 

 modem views. In his opinion bodies are built up of indefinitely 

 small indivisible particles, which he called atoms. These are dis- 

 tinguished by their form and magnitude, and also give different pro- 

 ducts by their different modes of aggregation. 



This atomic theory was revived by Gassendi about 1650, and 

 then accepted by Boyle and Newton. The theory received a 

 greatly increased importance by the discovery by Dalton of the 

 law of multiple proportions. For instance, the different combi- 

 nations of nitrogen with oxygen contain, for each unit weight of 

 nitrogen, * 57, 1 • 14, 1 • 72, 2*29 or 2 • 86 unit weights of oxygen.* 

 Between these combinations there is no intermediate proportion. 

 This peculiarity is characteristic of chemistry in contradistinction to 

 physics, where the more simple continuous and gradual transition 

 from one state to another prevails. This difference between the two 

 sister-sciences has often caused controversies in the domain of 

 physical chemistry. The occurrence of discontinuous changes and of 



* To explain this we suppose, in accordance with Dalton, that the molecules 

 of the different combinations of nitrogen with oxygen contain two atoms of nitrogen 

 and one, two, three, four or five atoms of oxygen. 



