The Yang-Yang anomaly in liquid-liquid criticality: Experimental evidence from adiabatic scanning calorimetry

► We detect the Yang-Yang anomaly in liquid-liquid criticality for the first time. ► Such anomaly as an impurity induced effect is ruled out. ► Results are in agreement with complete scaling predictions. ► Molecular size may not be the only microscopic parameter driving asymmetry. ► Exactly soluble models to account for the Yang-Yang anomaly are called for.