Liquid - Gas Curve and Critical Point

If we are moving along the liquid - gas border line in increasing temperature and pressure, then the properties of the liquid and the gas are becoming increasingly similar. The gas becomes increasingly more dense than the hquid. Finally we arrive at the critical point. At the critical point there is no longer a difference the between liquid water and water vapor. The two phases will disappear. 

If we are adjusting temperature and pressure accordingly, to move along the border line, then two phases can be watched because of their optical properties. A meniscus can be observed. At the critical point the meniscus disappears. 

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