390 Action of the Solvent in Electrolytic Conduction. 



The action of the solvents would seem to be twofold, 

 (a) Firstly, in certain cases to cause a decomposition of 

 the salt, the amount of such decomposition depending on, 



1. The temperature. 



2. The solvent. 



3. The state of dilution. 



(5) Secondly, there is the formation of molecular groups 

 in the solution ; there is definite experimental proof that 

 hydrates exist in concentrated solution ; and it follows that 

 such molecular groups, or more complex ones, exist in dilute 

 solution. 



The amount of water, or whatever the solvent may be, in 

 dilute solution will be far in excess of that required to form 

 these molecular groups, and consequently there will be a 

 continual dissociation and recombination going on, within the 

 solution, of these molecular groups ; beyond a certain dilution 

 further dilution will not affect the amount of such dissocia- 

 tion ; and hence the observed fact that in dilute solution the 

 conductivity is proportional to the amount of salt in solution. 

 When these molecular groups are dissociated or decomposed 

 by mutual collisions, it may be that the salt molecules being 

 brought together, there is an atomic interchange ; and that 

 at this moment the electromotive force asserts its directive 

 influence. But that there exist in the solution the " free " 

 atoms is untenable ; if free chlorine atoms are present in the 

 solution, the solution must have some of the properties of a 

 chlorine solution. 



It would be more satisfactory, I think, to consider the 

 whole of the decomposition as the result of the action of the 

 electromotive force, exerted at the moment of the decomposi- 

 tion of the molecular groups ; but all the experiments on the 

 application of Ohm's law to electrolytes would show that this 

 is not the case. 



But the influence of molecular groups in the conductivity 

 of saline solutions must be admitted, and the solvent must not 

 be regarded on the one hand as a suspending medium for the 

 salt molecules, or on the other as a dissociating agent. 



Note. — Bouty, in the January number for this year of the 

 Journal de Physique, states that the results obtained by the 

 method of alternate currents for dilute solution are quite 

 illusory, and he refers to the results that he and Foussereau 

 obtained when testing the method ; they employed a Wheat- 

 stone bridge, and placed in the fourth arm a resistance-coil 

 of considerable resistance, and used as indicator a telephone ; 

 when a coil of which the true resistance was 10,000 ohms 



