THE ELECTROLYTIC DISSOCIATION THEORY 393 



It must be borne in mind, in considering this question, that 

 the electrical conductivity method for determining the coefficient 

 of ionisation is not available with many non-aqueous solvents, 

 as it has not been found possible to estimate the limiting 

 molecular conductivity. 1 The coefficient of ionisation cannot 

 be estimated even approximately by comparison of the con- 

 ductivity of a salt in aqueous solution with that in another 

 solvent, as the conductivity depends on the mobility of the 

 ions, as well as on their number, and the former property 

 varies considerably in different solvents. 



There are certain cases, as Kahlenberg 2 more particularly 

 has pointed out, in which cryoscopic and ebullioscopic measure- 

 ments indicate polymerisation of the solute, notwithstanding 

 which the solution is a good conductor. Kahlenberg regards 

 such observations as incompatible with the electrolytic dissocia- 

 tion theory, while its supporters maintain that both ions and 

 polymerised molecules are present in the same solution. It is 

 clear that the experimental observations could be accounted 

 for in this way, as the decrease in the number of particles 

 owing to polymerisation might more than counterbalance the 

 increase owing to ionisation. It may be noted that solvents 

 of high ionising power have also, in general, a high capacity for 

 depolymerising associated molecules, and this probably explains 

 why complications of the kind just mentioned are very rare in 

 aqueous solution. 



Another problem, to which attention has been devoted in 

 recent years, is the conductivity of pure substances. The 

 classical example in this connexion, to which reference has 

 already been made (p. 383), is the conductivity of water. It is 

 interesting to note that the conductivity of most pure liquids 

 which have been so far investigated is of the same order as that 

 of water. This is true of liquid ammonia, according to Franklin 



1 Since the above was written, the results of a comprehensive series 

 of experiments on the electrical conductivity of halogen salts in twelve 

 inorganic and organic solvents have been communicated by Dutoit {Zeit. 

 Electrochemie, 1906, 12, 642). Solutions up to Brmnr — 7 0/000 molar have been 

 investigated, and in all cases a limiting value for the molecular con- 

 ductivity has been attained. Kohlrausch's law (p. 383) holds for the majority 

 of solvents, but Ostwald's dilution law does not in general apply. In very 

 dilute solution, the results are in excellent agreement with the electrolyte 

 dissociation theory. 



2 Jonrn. Physical Chem. 1901, 5, 339. 



