1902.] 



Conductivity of Electrolytic Solutions. 



51 



boiling point and experimental work is rendered very difficult, owing 

 to the ready solubility of glass in water at high temperatures ■ this 

 not only contaminates the solutions but greatly weakens the sealed 

 tubes in which they are contained. Hagenbach* has, however, made a 

 single observation which is of importance as showing that even the 

 salts of the alkali-metals may exhibit negative temperature coefficients 

 at high temperatures ; in the case of an aqueous solution of KC1, con- 

 taining dissolved glass, he actually observed on one occasion a maxi- 

 mum of conductivity before the explosion of the tube took place at 

 310°. 



Much more evidence is available for the existence of an upper con- 

 d activity zero in the case of non-aqueous solutions. Franklin and 

 Krausf have found that at high temperatures the conductivity of 

 solutions in liquid ammonia decreases as the temperature rises — an 

 effect directly opposite to that observed by Legrande at low tempera- 

 tures ; and Maltby^ has shown that even at atmospheric tempera- 

 tures the conductivity of an ethereal solution of hydrogen chloride 

 decreases as the temperature rises, and in the neighbourhood of the 

 critical temperature is only -.^ of the conductivity at 18°. Negative 

 temperature coefficients have also been observed by Cattaneo§ in solu- 

 tions in ether, alcohol and gtycerol. 



The most valuable experimental data, however, are those derived 

 from the study of solutions in liquid sulphur dioxide. Hagenbach,|j 

 in order to ascertain whether the limit of conductivity was reached 

 at the critical temperature, measured the conductivity of solutions 

 in sulphur dioxide at temperatures ranging from 20° to 160°, and 

 found that the temperature-coefficients between 100° and 140° of 

 KC1, KBr, KI, and Nal were all negative, and amounted to about 

 2 per cent, of the conductivity at 100° for each degree Centigrade. 

 The upper conductivity zero of these solutions, determined by extra- 

 polation from the measurements between 130° and 150°, would lie in 

 each case some 5° or 10° above the critical temperature of the solution, 

 but immediately below the critical temperature the conductivity falls 

 rapidly over a narrow range of temperature until it reaches the small 

 but measurable conductivity of the gas. It is to be noticed that the 

 substances examined by Hagenbach are all self-ionising — this would 

 retard the decay of ionisation, and would have the effect of raising the 

 upper temperature-limit of conductivity. High temperature measure- 

 ments have also been made by Walden and Centnerszwer^I in the case 



* ' Ann. d. Physik,' .1901 [5], toI. 2, p. 306. 



f ' Amer. Chem. Jour.,' 1900, vol. 24, p. 83. 



I ' Zeit. Phys. Chem.,' 1895, vol. 18, p. 133. 



§ ' Kend. Lincei' [5], vol. 2, I, p. 295, and II, p. 112, 1893. 



|| 'Ann. d. Physik,' 1901 [5], vol. 2, pp. 276—312. 



«f 'Zeit. Phys. Chem.,' 1902, vol. 39, p. 549. 



