1902.] 



Conductivity of Electrolytic Solutions. 



49 



In no case is the temperature coefficient of viscosity so great as in 

 the case of water, and the conductivity zero for each of these liquids is 

 evidently very far below the conductivity zero for water. 



(2.) At great dilutions the influence of temperature on ionisation is 

 usually much reduced, and aqueous salt solutions of N/1000 strength 

 have temperature coefficients of conductivity which do not differ 

 appreciably from those calculated for solutions of indefinitely great 

 dilution. These coefficients can be used in determining the con- 

 ductivity zero of the solvent, and a rough estimation is possible from 

 measurements made in much less dilute solutions. The conductivity 

 of a number of salts dissolved in liquid ammonia has been determined 

 by Legrande* at temperatures ranging from - 32° to - 70° C, the 

 dilution in each case being greater than 100 litres per equivalent. The 

 mean temperature coefficient at - 60° C. for the five salts was + 0*012, 

 corresponding with a conductivity zero at - 140°. A similar examina- 

 tion of Walden and Centnerszwer's measurements of solutions in liquid 

 sulphur dioxide between 0° and - 70° C.f serves to place the con- 

 ductivity zero for this solvent at about - 160° C. The measurements 

 of Dutoit and FriedrichJ of the conductivity between 0° and 25° of 

 solutions of AmCNS and Nal in acetonitrile lead to a conductivity 

 zero for the nitrile at - 90° C. 



(3.) The temperature coefficient of conductivity of purified water 

 leads to a satisfactory value for the conductivity zero. By applying a 

 similar method to Fresnel's measurements of the conductivity between 

 -40° and -80° of purified ammonia § we have obtained for the con- 

 ductivity zero the value - 130°, a value which is substantially in 

 agreement with that deduced from the behaviour of Legrande's salt 

 solutions. 



Whilst at low temperatures the eftect of temperature on conductivity 

 is determined mainly by the changing mobility of the ions, at higher 

 temperatures the changing ionisation becomes the dominant factor. 

 And just as the increasing viscosity of the solution leads at low tem- 

 peratures towards a lower conductivity zero at which the viscosity of 

 the liquid would altogether prevent electrolysis, so at high temperatures 

 an upper limit may exist at which the conductivity would again 

 become zero owing to the complete disappearance of ionisation. 



In the case of aqueous solutions the indications of an upper conduc- 

 tivity zero are only slight. At 18° the temperature coefficients of 

 conductivity, are all positive, and only in very exceptional cases have 

 negative coefficients been observed, even at higher temperatures. 



* Thesis, Paris, 1900. 



f 'Zeit. Phys. Cliem.,' 1902, vol. 39, p. 542. 

 t 'Bui. Soc. Chira.,' 1898, vol. 19, pp. 321—337. 

 § ' Zeit. Electrochem.,' 1900, vol. 6, p. 485. 

 VOL. LXXI. E 



