514 



SCIENCE. 



[N. S. Vol. IV. No. 93, 



solution of two layers the migration of the 

 ions could be directly measured, these re- 

 sults agree surprisingly well with Kohl- 

 rausch's, considering the widely different 

 conditions and the difficulty of measure- 

 ment. 



About 1887 electro-chemistry entered into 

 a new stage of progress ; the central figure 

 among those who were mainly active in 

 bringing about this development was Svante 

 Arrhenius, who, together with Ostwald and 

 others, advanced a theory of electrolytic 

 action, explaining very satisfactorily many 

 well-known phenomena. Arrhenius' theory 

 involves the general idea contained in the 

 theory of Clausius and Williamson, namely, 

 that the solution contains the electrolyte 

 dissociated into ions before the current is 

 forced through it. Arrhenius adds that this 

 dissociation is affected by solution or fusion, 

 and that the ions contain charges of posi- 

 tive and negative electricity dependent upon 

 their nature, but of equal quantity in every 

 ion. While in this state, that is, as ions, 

 they move in an irregular manner between 

 the molecules of the solvent and the undis- 

 sociated molecules of the electrolyte, now 

 attaching themselves to one another and 

 again separating, upon the whole maintain- 

 ing a condition of Kinetic equilibrium. As 

 soon as brought under the influence of the 

 electrodes of different potential, they are 

 impelled in definite directions, the anions 

 towards the anode, the kathions towards 

 the kathode. 



The first work done by the current is the 

 overcoming of the viscous resistances of the 

 medium, not an inconsiderable amount ; 

 thus a portion of the energy of the current 

 is fritted into heat. 



At the electrodes another kind of work 

 has to be done; either the charges have to 

 be removed from the ions, changing them 

 into the molecular condition, or new ions 

 must be produced from the material of the 

 electrode and the solvent, for kathions ar- 



riving the formation of anions or for 

 anions kathions. 



TJndissociated molecules of the electro- 

 lyte take no part directly in electrolysis, 

 except in so far as they may alter the vis- 

 cous resistance of the solution. 



The fact that molecular conductivity in- 

 creases with dilution means, that as infinite 

 dilution is approached complete dissocia- 

 tion or ionization of the electrolyte is ef- 

 fected. 



The ratio between molecular conductivity 

 at greater concentration and infinite dilu- 

 tion, expresses the degree of dissociation or 

 ionization. The conductivity can always 

 be expressed by the sum of the velocities 

 of the ions into a coefficient expressive of 

 the degree of dissociation: C=^A{u-\-v^. 

 In the limiting case J.=l and the conduc- 

 tivity is measured by the sum of the ionic 

 velocities, this in accord with Kohlrausch's 

 law. 



One of the important points in this 

 theory is that solution effects dissociation. 

 Chemically pure substances, such as HCl 

 in. the liquid state, should not be electro- 

 lyzed; such is found to be the case. The 

 curious fact that pure HCl and pure water 

 alone are non-conductors, but become elec- 

 trolytic conductors when mixed, is not 

 rationally explained, other than that disso- 

 ciation results. Why it takes place we do 

 not know; that some change in the asso- 

 ciated energy always takes place we do 

 know. In general, unless some chemical 

 change occurs, solution is accompanied by 

 refrigeration, except in the case of gases. 

 It is probable, then, that some of the heat 

 energy taken from the mixture is concerned 

 in this dissociation. 



In the case of fused substances heat may 

 be a considerable factor in dissociation. 



The question whence come the electric 

 charges upon the ions is not solved. 

 Whether they are inherent in the molecule 

 and become free by ionization or whether 



