1902.] on the Ions of Electrolysis. 29 



explained this, but after the proof of a cause of polarisation given by 

 Schonbein, and the accumulating evidence that Ohm's law applies to 

 electrolytic as well as to metallic conduction, no one could hold or 

 defend Grotthuss's theory, although it was retained as a sort of 

 makeshift until someone could think of something better. The 

 something better was produced by Clausius in 1857.* Clausius was 

 one of the eminent physicists to whom we owe the kinetic theory of 

 gases, and his theory of electrolysis is derived from an application to 

 solutions of the ideas involved in this kinetic theory. He supposes 

 that the molecules of the electrolyte move through the solution as 

 the molecules of a gas move, that they collide with one another as 

 the gas molecules do, and that it must happen that here and there 

 ions get separated, and remain separated for a time, cation again 

 uniting with anion when two of them meet under favourable con- 

 ditions. There will thus always be some detached ions moving 

 about just as molecules do. They will not always be the same ions 

 that are thus detached, and a very small proportion of such loose 

 ions will sufl&ce to explain the phenomena. These loose ions retain 

 in their separate condition the charges of electricity which they had 

 when united, the cations being positively and the anions negatively 

 charged. This is assumed to be the state of matters in any solution 

 of an electrolyte. If now into such a solution we place two electrodes 

 with any, however small, difference of potential, the cathode, being 

 negative, will exercise an attraction upon the positively charged 

 cations, and the positive anode will exercise a similar attraction on 

 the negatively charged anions, and thus the loose ions, which before 

 the introduction of the electrodes moved about in the liquid with no 

 definite preferred direction, will on the whole, now that the electrodes 

 have been introduced, move preferably, the cations towards the 

 cathode, and the anions towards the anode, and those which are near 

 the electrodes will be drawn to them and discharge their electric 

 charge. This theory seems therefore to explain the phenomena. 

 The essential difference between it and all previous theories is that 

 Clausius does not attribute the decomposition to the current or to the 

 attraction of the electrodes ; what the attraction of the electrodes does 

 is to separate the ions already disengaged from one another, and this 

 the smallest electromotive force can do. The theory is so far 

 adequate, but is it admissible ? Can we suppose that hydrogen and 

 chlorine atoms can move uncombined through the solution ? It is to 

 be noted that while Clausius does not give any opinion as to the 

 proportion of loose ions to the total ions in any case, he assumes that 

 this proportion increases as the temperature rises, on account of the 

 greater briskness of the movements of the particles, and points out 

 that this is in accordance with the fact that electrolytes conduct 

 better as the temi^eratura is higher. But he says, " to explain the 

 conduction of the electricity it is sufficient that in the encounters of 



* Clausius, Pogg. ci. p. 338 (1857). 



