New insight into 3-picoline—deuterium oxide (D(2)O) mixtures of limited miscibility with the lower critical consolute temperature

Coexistence curves in mixtures of limited miscibility with the lower critical consolute temperature (LCT), of 3-picoline with deuterium oxide (D(2)O), and D(2)O/H(2)O have been determined. They were tested with respect to the order parameter, the diameter of the binodal, and coordinates of the critical consolute point (critical temperature [Formula: see text] and critical concentration [Formula: see text] ). Studies were carried out using the innovative method based on the analysis of relative volumes occupied by coexisting phases, yielding high-resolution data. The clear violation of the Cailletet-Mathew law of rectilinear diameter for the LCT mixtures of limited miscibility is evidenced. For the order parameter, the new distortion-sensitive analysis method yielded the evidence for the model-value of the order parameter critical exponent [Formula: see text] , up to ca. 1 K from [Formula: see text] . Finally, the simple & easy method for determining the critical concentration by testing relative volumes of coexisting phases (or alternatively fractional meniscus heights, h) is presented. The significance of the invariant value [Formula: see text] is highlighted. The appearance of the milky & bluish critical opalescence is also shown. GRAPHICAL ABSTRACT: [Image: see text]