166 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



tive temperature coefficient of the solution of metacresol in liquid hydro- 

 gen bromide at a dilution of 15 liters. Evidently, the temperature 

 coefficient in this case changes greatly with the concentration since at 

 normal concentration the coefficient is positive and equal to 1.16 per cent. 



It is difficult to account for the large value of the positive tempera- 

 ture coefficients of the very concentrated solutions, except on the assump- 

 tion that the ionization in the case of these solutions is relatively inde- 

 pendent of the temperature. While the concentration at which this con- 

 dition is fulfilled varies considerably with the nature of the dissolved 

 electrolyte, it varies but little with the nature of the solvent. While at 

 lower concentrations the ionization decreases throughout with the tem- 

 perature, at higher concentrations the ionization increases with the 

 temperature. 



It is probable that, at very low concentrations, the temperature 

 coefficient will always be found positive. The concentration at which 

 this holds, however, may be very low indeed in the case of solvents of 

 very low dielectric constant. It may be noted, in this connection, that 

 the conductance-temperature coefficient of nearly all solvents is positive. 

 It is true that, if no impurities were present, it might be expected that 

 the ionization of the solvent would increase with the temperature. How- 

 ever, in most cases, the final conductance of highly purified solvents is 

 due to impurities and not to the ionization of the pure solvent. What- 

 ever these impurities may be, it is evident that they must be sufficiently 

 ionized at these concentrations to yield a positive conductance-tempera- 

 ture coefficient. 



The ionization as a function of the concentration at different tem- 

 peratures is represented by a family of curves passing through two com- 

 mon points at a concentration zero, where the ionization is unity, and at 



a concentration corresponding to the ionization Y "i which for 



solutions of potassium iodide in sulphur dioxide is in the neighborhood 

 of 3.5 normal. At concentrations below this value the ionization de- 

 creases with the temperature. In very concentrated and very dilute 

 solutions, the decrease in the ionization is comparatively small, and the 

 conductance therefore increases with the temperature. At intermediate 

 concentrations, the conductance at higher temperatures decreases with 

 the temperature, while at low temperatures it increases with the tempera- 

 ture. If the A, T-curves are examined, it will be found that at inter- 

 mediate concentrations the conductance curves exhibit a maximum. As 

 the concentration decreases, however, this maximum is displaced toward 

 higher temperatures and presumably would ultimately disappear at suf- 



