PRESIDENTIAL ADDRESS. Hi 



sociation of various electrolj^tes. Tliis field has been well 

 explored, and the dissociation constants of nearly all elec- 

 trolytes in water solution are known. Much attention is 

 now being given to solvents other than water, and to organic 

 substances, and, as in these papers, to matter in the solid state. 



The general acceptance of Arrhenius' theory of electrolytic 

 dissociation has led to our text books of inorganic chemistry 

 and analyses being re- written in ionic terms. According to 

 this, when a molecule of an electrolyte like NaCl is dissociated 

 in solution we have a positive Na ion and a negative CI ion. 

 A number of years ago Sir J. J. Thomson, in his hypothesis 

 of the electrical nature of matter, suggested that valency and 

 cause of chemical combination consisted in the transfer of 

 electrons between the reacting atoms. On this basis we have 

 as positive atom one which has lost one or more electrons, 

 and as negative atom one which has gained one or more 

 electrons, the valency of the atom depending on the number 

 of electrons transferred. The valency question is one of the 

 fundamental problems of chemistry and the electronic theory 

 has in many forms been applied as a solution. Electrolytic 

 dissociation tells us nothing of the solid state or the gaseous. 

 In dissociation we find H as a positive ion and CI as a negative. 

 What is the state of the atoms in the electrically neutral 

 molecule of CI ? In the majority of reactions there seems 

 to be no difference between the two halves of the molecule, 

 but some evidence has been found that the CI atom maj'' 

 act positively. On the assumption that the diatomic gas 

 molecule consists of one atom positive and the other negative, 

 we have theories of valency, one of which applied to the 

 formula of the benzene ring I shew on the blackboard. Any 

 conception of valency must pass the test of the benzene ring 

 and explain certain peculiarities in the formation of ortho, 

 meta, and para compounds. 



In general terms of the electronic theory, the loss of 

 electrons corresponds to oxidation, and a gain of electrons 



