1886.] Conduction and Molecular Composition, fyc. 27 1 



it is surprising how little accurate knowledge we possess on this 

 subject. 



Composite Electrolytes. 



I assume it to be admitted that neither water nor liquid hydrogen 

 chloride, for example, is an electrolyte, although an aqueous solution 

 of hydrogen chloride conducts freely and is electrolysed by an 

 electromotive force of but little more than a volt. 



The theory put forward by Clausius in 1857 in explanation of 

 electrolysis is well stated in Clerk Maxwell's " Elementary Treatise 

 on Electricity" (p. 104), in the following words: — 



" According to the theory of molecular motion, every molecule of 

 the fluid is moving in an exceedingly irregular manner, being driven 

 first one way and then another by the impacts of other molecules 

 which are also in a state of agitation. The encounters of the 

 molecules take place with various degrees of violence, and it is 

 probable that even at low temperatures some of the encounters are so 

 violent that one or both of the compound molecules are split up into 

 their constituents. Each of these constituent molecules then knocks 

 about among the rest till it meets with another molecule of the 

 opposite kind, and unites with it to form a new molecule of the com- 

 pound. In every compound, therefore, a certain proportion of the 

 molecules at any instant are broken up into their constituent atoms. 

 Now, Clausius supposes that it is on the constituent molecules in 

 their intervals of freedom that the electromotive force acts, deflecting 

 them slightly from the paths they would otherwise have followed and 

 causing the positive constituents to travel, on the whole, more in the 

 positive than in the negative direction and the negative constituents 

 more in the negative direction than in the positive. The electro- 

 motive force, therefore, does not produce the disruptions and reunions 

 of the molecules, but finding these disruptions and reunions already 

 going on, it influences the motions of the constituents during their 

 intervals of freedom. The higher the temperature, the greater the 

 molecular agitation, and the more numerous are the free constituents : 

 hence the conductivity of electrolytes increases as the temperature 

 rises." 



This theory has been widely accepted by physicists ; but it appears 

 to me that, on careful consideration of the evidence, and especially of 

 recent exact observations on conditions of chemical change, it must 

 be admitted, as I have elsewhere contended (B. A. Address), that 

 proof is altogether wanting of the existence of a condition such as is 

 postulated by Clausius. Moreover, it has been shown by Hittorf that 

 cuprous and silver sulphides, and by F. Kohlrausch that silver iodide, 

 all undergo electrolysis in the solid state; the partisans of the dis- 

 sociation hypothesis would, I presume, scarcely contend that it is 



