Isoteniscope

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The isoteniscope is a glass device that is used to determine the vapor pressure of liquids .

Scheme of an isoteniscope

The difficulty of such a measurement is, on the one hand, not to let the pressure gauge come into contact with the potentially dangerous, possibly corrosive substance and, on the other hand, to keep the entire gas space filled with steam isothermal . The isoteniscope solves these problems elegantly.

The liquid to be examined is in a glass flask. This is connected to the pressure measurement via a U-tube, in the sink of which the substance to be examined is also located. This U-tube serves as a relative pressure gauge between the isothermal gas space and the outside space, in which there is a reflux condenser and the (absolute measuring) pressure gauge. A gas supply and a pump are also connected to the outside area.

If the vapor pressure of the liquid changes as a result of the temperature change in the isothermal gas space, the liquid level in the U-tube changes. It can be compensated for by adding or pumping off neutral gas in the outside space; the pressure outside then corresponds to the pressure inside. The gas pressure in the interior can therefore be determined by measuring the (identical) pressure in the exterior.