A flow apparatus was developed to determine phase equilibria at elevated temperatures and pressures. The key component of the apparatus is a high-pressure view cell equipped with transparent sapphire windows for visual observation of the liquid level. The flow apparatus is used to the best advantage when the residence time of chemicals (or bic-materials) in the high-temperature zone has to be minimized to eliminate the possibility of thermal decomposition or polymerization reactions. Because the technique has the advantages of rapid attainment of equilibrium conditions and straightforward sampling procedures, it produces a fairly large quantity of data with a minimum amount of time. The sample system also offers the option of taking a desired size of sample by controlling the length of sampling time. This is important particularly for the asymmetric mixtures of a light gas in a very heavy compound of low volatility at some extreme conditions, for which a sufficiently large amount of samples are needed to determine the phase compositions with reasonable accuracy. The flow apparatus of different designs have been used for measurements of vapor-liquid and liquid-liquid equilibria for years. However, it is difficult for multiphase mixtures, and the liquid feed pump cannot handle solids of high-melting points.In operation of a flow apparatus, the liquid level in the equilibrium cell must be sensed and controlled at a certain range of elevation. Simnick et al. (1977) designed a blind cell in which an electric capacitor was installed to detect the liquid level. A similar cell was later fabricated by Inomata and coworkers (1986). However, the capacitor fails to function properly for the mixtures which are electrically conductive (Lin et al., 1985(Lin et al., , 1986. Lin and coworkers (1985) developed a visual cell in which a transparent sapphire window was equipped at each end of the cell body to permit observation of liquid level. A modification of this cell with a new design to improve its sealing of the sapphire windows for operation at higher pressures is Corrapondcna concerning thic pper ahould be addrtsscd to H. hi. Lin.

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