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CHAPTEE XI. 



CONDUCTION IN SOLUTIONS AND GASES, FROM FARADAY TO 

 J. J. THOMSON. 



THE hypothesis which Grothuss and Davy had advanced* to 

 explain the decomposition of electrolytes was open to serious 

 objection in more than one respect. Since the electric force 

 was supposed first to dissociate the molecules of the electrolyte 

 into ions, and afterwards to set them in motion toward the 

 electrodes, it would seem reasonable to expect that doubling 

 the electric force would double both the dissociation of the 

 molecules and the velocity of the ions, and would therefore 

 quadruple the electrolysis an inference which is not verified 

 by observation. Moreover it might be expected, on Grothuss' 

 theory, that some definite magnitude of electromotive force 

 would be requisite for the dissociation, and that no electrolysis 

 at all would take place when the electromotive force was below 

 this value, which again is contrary to experience. 



A way of escape from these difficulties was first indicated, in 

 1850, by Alex. Williamson,-)- who suggested that in compound 

 liquids decompositions and recombinations of the molecules are 

 continually taking place throughout the whole mass of the liquid, 

 quite independently of the application of an external electric 

 force. An atom of one element in the compound is thus paired 

 now with one and now with another atom of another element, 

 and in the intervals between these alliances the atom may be 

 regarded as entirely free. In 1857 this idea was made by 



* Cf. p. 78. 



f Phil. Mag. xxxvii (1850), p. 350 ; Liebig's Annulen d. Chem. u. Pharni. 

 Ixxvii (1851) p. 37. 



