Values of the B coefficient of the viscosity of the Jones–Dole equation are reported for sodium iodide in the water–t-butyl alcohol system up to 90 mol % t-butyl alcohol at 26 °C. The calculation of the theoretical A coefficient of the Jones–Dole equation needs the ionic limiting conductivity data. The conductivity measurements of Bu₄NI and NaBPh₄ solutions in water–t-butyl alcohol mixtures at 26 °C were performed in order to divide the conductivity for NaI, known from our earlier investigations, into ionic contributions. The division is based on the assumption of Fuoss et al. that Λ₀(Bu₄N⁺)= 0.519Λ₀(Bu₄NBPh₄).

It was found that the Jones–Dole equation was obeyed by all solutions in the investigated range of NaI concentration, i.e. the D coefficient was equal to zero. The conductivity data showed that NaI was associated in solutions with more than 20 mol% of t-butyl alcohol. Thus, the ionic association was taken into consideration in calculating the values of B_i and B_p coefficients, referring to the ion–solvent and ion-pair–solvent interactions, respectively. The ion–solvent interactions (B_i) was higher than those resulting from B-coefficient values without correction.