Vapor Pressure Measurements in a Closed System.

VAPOR pressure; TEMPERATURE; VACUUM; PRESSURE; LIQUID nitrogen; WATER temperature; DRY ice; NITROGEN; LIQUEFIED gases

The article discusses an experiment that uses a simple apparatus to measure vapor pressure versus temperature in a closed system. The apparatus is filled with the liquid of interest, which is degassed by freeze-pump-thaw cycles. This technique is used to remove air so that the total pressure in the sample chamber is the vapor pressure of the liquid. The apparatus is then removed from the vacuum system and suspended in a water bath; pressure and temperature readings are noted down as the water temperature is increased. Then the liquid is again frozen and the pressure measured to verify that no leakage has occurred. The above procedure leaves the vacuum line free after sample preparation, it does not require a large ballast in the vacuum line, and no sample is volatilized into the vacuum line during the procedure. Even if liquid nitrogen is not available, one can degass the sample by briefly opening the valve to vacuum several times with the sample at room or dry ice temperature.