18 THE THEORY OF IONS 



the ionic velocity or conductivity, for it has been 

 shown that henceforth the ionic velocity decreases 

 with the dilution.* Even when the conditions are 

 the same, ions travel at different rates ; but given 

 the same concentration and electrical conditions all 

 ions of one kind travel with a constant velocity, f 

 Thus, the cation H* travels with a velocity which 

 is twice as great as the anion OH', and five times as 

 great as that of the cation K\ The ionic velocity 

 is determined by conductivity experiments, and it 

 is found to vary with the condition ; by this method 

 the velocity of ions produced by X rays in air, 0, 

 C0 2 and H, has been determined. J It is even in- 

 fluenced by the solvent, e.g. the ionic velocity ot 

 CF in aqueous solution and in glycerol solution 

 was found by Cattaneo to be for sodium chloride 

 0-658 and 0-645 respectively, and for ammonium 

 chloride 0-510 and 0-568 respectively. Moisture also 

 diminishes the velocity of ions, especially negative 

 ions ; and, in general, the velocity of negative ions 

 is greater than that of positive ions.|| 



The degree of dissociation or ionisation of salts 

 in solution is usually determined by conductivity 

 experiments at a temperature of 18 to 25. The 

 temperature has considerable influence upon the 

 formation of ions. Dampier and Williams ^ have 

 shown that the degree of dissociation at 18 to 25 

 is not comparable with that at freezing-point. They 

 also showed that the degree of dissociation at 



* Hans Jahn : Zeit. fur Physik.-Chem., 1900, xxxv., 1-10. 



f Hittorf : cf. Newth's "Inorganic Chemistry." 



J Zeleny : Proc. Roy. Soc., 1900, Ixvi., 238-241. 



Real Acad.-Linc., 1896, v. and vi. 



|j Zeleny : loc. cit. IT Proc. Roy. Soe., 1900, Ixvi., 192. 



