Abatraet-The conductance of NaNOB has heen measured between 9.0 and 1.0 mmolflitre in dioxanwater mixtures covering 7854 > D > 12.45 at 25°C. The data were analysed with Fuoss-Qnsager and Skinner (1965) equations on an IBM 7044 computer to get ho. KA and aa( &,v shows dependence on the solvent composition. The ion-size parameter so(L) increases with decrease in dielectric constant up to D = 36.05 and decreases thereafter. Log KA us l/D yields a straight line giving a value of aa = 8.63. The variation of so(L) with D is discussed. R&sum6-Mesure B 25°C de la conductance de NaNO, entre 9,0 et 1,0 mmole/l pour des melanges dloxane-eau dans le domaine 78,54 > D > 12,45. Les resultats sont analyses au moyen des equations de Fuoss-Onsager et Skinner (1965), sur ordinateur IBM 7044 pour obtcnir A,, & et a0 (I,). A,q d6pend de la composition du solvant. Le param&.re relatif a la dimension ionique o"(L) augmente quand la constante di&ctrique diminue jusqu'a D = 36,05, puis d&croft. La repr6sentation de Log KA en fonction de l/D eat rectiligne, ce qui conduit a u"(K) = 8,63 A. Discussion de la variation de a"(L) avec D. ZusammenfassunR-Die Leitfahigkeit von NaNOI (9,0-1,0 mMol/l) in verschiedenen Gem&hen von Wasser und Dioxan (Dielektrizitltskonstante D zwischen 78,54 und 12,45) bei 25'C gemessen. Die Ergebnisse wurden mlt den Gleichungen von Fuoss-Onsager und Skinner (1965) auf einer Rechenanlage IBM 7044 ausgewertet. A, hlngt von der Zusammensetzung des Lasungsmittels ab. Der lonengriisse-Parameter u"(L) nimmt mit kleiner werdender Dielektriziti&+konstante bis zu einem Wet-t von 36,OS zu, nachher nimmt er ab. Trlgt man log KA gegen l/D auf, so erhitlt man eine Gerade, welche fiir u"(L) den Wet-t 8,63 liefert. Die AbhZingigkeit von u"(L) von D wird diskutiert. EXPERIMENTAL TECHNIQUE Conductivity water was prepared by distillation of doubledistilled water with alkaline KMn04 in an all-Pyrex-glass set. The middle cut was collected and stored in a Pyrex-glass ground-stoppered bottle under nitrogen. Specific conductance was 2 x lO_' mholcm. Analar B.D.H. dioxan was refluxed over NaOH for 12 h and the distillate was refluxed again over metallic sodium followed by fresh additions of sodium metal from time to time for 20 h. It was finally distilled through a 60-cm column and stored under bubbling nitrogen. Analar B.D.H. NaNO, recrystallized three times from conductivity water and heated for 3 h at 150-18O"C was dried under vacuum for 12 h. An ac bridge similar in design to that of Jones and Josephsl with heavy shielding against external disturbances was employed to determine cell impedance. .A wide range R-C oscillator, Marconi TF 1370, was used for measurements of conductance