Impurity effects on the critical behaviour of the electrical resistance of binary liquid mixtures

The electrical resistance of the binary liquid system cyclohexane + acetic anhydride is measured, in the critical region, both in the pure mixture and when the mixture is doped with small amounts (≈ 100 ppm) of H₂O/D₂O impurities.T _c was approached to aboutt=3×10⁻⁶ wheret=(T −T _c )/T _c . The critical exponentb ≈ 0.35 in the fit of the resistance data to the equationdR/dT ∼t ^−b does not seem to be affected appreciably by the impurities. There is a sign reversal ofdR/dt in the non-critical region. Binary liquid systems seem to violate the universality of the critical resistivity.