(190y) Spinodal Line Measurements of Water

   One of the experimental methods of critical point determination is darkening of scattering light through windows. For a pure substance, it is well known that a critical point satisfies   due to density fluctuation. The same mathematical condition should be applied to spinodal lines which are the stability limit of metastable region. At present, we have no information on spinodal line measurement. Indeed, through windows of a static cell, we cannot observe darken windows due to light scattering. However, when we used a continuous flow apparatus for vapor-liquid equilibrium measurement, we found that water showed two opaque points at a temperature ranging from 570 K to the critical temperature and higher temperature opaque points than the vapor pressure line down to 430K and 5 MPa. Several times experiments revealed excellent reproducibility. If our observation means spinodal points, the lower pressure spinodal line is just a little lower and the higher one is a few MPa higher than the vapor pressure line of water.  It suggests that a curve of an equation of state will be strongly asymmetric in the metastable region. We believe that our spinodal measurement will develop an equation of state.