Division 1.5.2.2 Apparatus

The equipment consists of a constant-temperature bath (precision of ±0,2 K), a container for the sample connected to a vacuum line, a manometer and a system to regulate the pressure. The sample chamber (figure 3a) is connected to the vacuum line via a valve and a differential manometer (U-tube containing a suitable manometer fluid) which serves as zero indicator. Mercury, silicones and phthalates are suitable for use in the differential manometer, depending on the pressure range and the chemical behaviour of the test substance. However, based on environmental concerns, the use of mercury should be avoided, if possible. The test substance must not dissolve noticeably in, or react with, the U-tube fluid. A pressure gauge can be used instead of a U-tube (figure 3b). For the manometer, mercury can be used in the range from normal pressure down to 10² Pa, while silicone fluids and phthalates are suitable for use below 10² Pa down to 10 Pa. There are other pressure gauges which can be used below 10² Pa and heatable membrane capacity manometers can even be used at below 10^–1 Pa. The temperature is measured on the outside wall of the vessel containing the sample or in the vessel itself.