A new description regarding the approach to double criticality in quasi-binary liquid mixtures

Electrical resistance and phase diagram measurements are reported for reentrant liquid mixtures 3-methylpyridine + water + NaCI and 3-methylpyridine + water + heavy water respectively. The results are analyzed employing a new field variable — which allows for the description of the access to any point on the critical line — by the same universal exponent. This method is also in agreement with the doubling of the critical exponents near the double critical point, using the conventional field variable $|(T_c-T)/T_c|$