THEORIES OF ELECTROLYSIS. 



305 



By adding to these numbers for acids the heat of formation 

 of water from its ions, Arrhenius has calculated the total 

 heats of neutralisation of soda, and compared the results 

 with the observed values for many acids. 



The conductivity of a solution depends on two factors : 

 (1) the dissociation, and (2) the frictional resistance offered 

 by the solution to the passage of an ion through it. If we 

 call the reciprocal of this resistance the ionic fluidity of the 

 solution, the molecular conductivity will be proportional to 

 the dissociation and to the ionic fluidity. At infinite dilu- 

 tion the dissociation is complete, and the ions are so far 

 apart that no change in temperature can affect the state of 

 dissociation. Any alteration in conductivity with change 

 of temperature must then be due to an alteration in fluidity, 

 and, therefore, the temperature coefficient of fluidity can be 

 determined by measuring the temperature coefficient of 

 conductivity at a dilution so great that the molecular con- 

 ductivity has reached its limiting value. From the thermo- 

 dynamical investigation it follows that, if the heat of for- 

 mation is negative, that is, the heat of dissociation positive, 

 the temperature coefficient of dissociation must be negative, 

 so that the dissociation will decrease as the temperature 

 rises. The increase in conductivity, shown by electrolytic 

 solutions when they are heated, is, then, in general, due to 

 the increase in ionic fluidity being greater that the decrease 

 in dissociation. Now the table given above shows that 

 the heats of dissociation are greater at 35° than they are at 

 2 1 '5°, so that the negative temperature coefficient of dis- 

 sociation must grow numerically greater as the temperature 

 rises. If, at the same time, the positive temperature 

 coefficient of ionic fluidity keeps constant, gets less, or in- 



